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Tag: Quantum Mechanics

  • Nobel Prize in physics goes to trio of researchers for discoveries in quantum mechanics

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    The 2025 Nobel Prize in physics has been awarded to a trio of scientists – a Briton, a Frenchman and an American – for their ground-breaking discoveries in the field of quantum mechanics.John Clarke, Michel Devoret and John Martinis will share the prize “for the discovery of macroscopic quantum mechanical tunnelling and energy quantization in an electric circuit,” the Nobel Committee announced Tuesday at a ceremony in Stockholm, Sweden.The committee praised the laureates for demonstrating that the “bizarre properties of the quantum world can be made concrete in a system big enough to be held in the hand.”Clarke, taking questions at a news conference, said he was “completely stunned” to learn he had won the award.“We had not realized in any way that this might be the basis of a Nobel Prize,” Clarke said of their research in the 1980s at the University of California, Berkeley.Quantum mechanics, which describes how matter and energy behaves at or below the scale of an atom, allows a particle to pass straight through a barrier, in a process called “tunnelling.”But when a larger number of particles are involved, these quantum mechanical effects usually become insignificant. What is true at the microscopic level was not thought to be true at the macroscopic level. For instance, while a single atom could pass through a barrier, a tennis ball – made up of a huge amount of particles – cannot.However, the trio of researchers conducted experiments to show that quantum tunnelling can also be observed on a macroscopic scale.In 1984 and 1985, the trio developed a superconducting electrical system that could pass from one physical state to another, as if a tennis ball could move straight through a barrier and not bounce back.Anthony Leggett, who won the Nobel Prize in physics in 2003, compared the laureates’ work on how quantum mechanics functions on a larger scale to the famous thought experiment of Erwin Schrödinger, another physics laureate.To show the paradoxical nature of quantum mechanics, Schrödinger imagined a cat in a sealed box with a device that releases poison when a radioactive source decays. Because there is no way to observe whether the cat is dead or alive, Schrödinger posited that the cat was both dead and alive simultaneously – just as, in quantum mechanics, a system can exist in multiple states at once until measured.Schrödinger’s thought experiment aimed to show the absurdity of this situation, because quantum mechanics doesn’t make sense on the scale of everyday objects, such as a cat.Leggett argued, however, that the experiments conducted by Clarke, Devoret and Martinis showed that there are phenomena on larger scales that behave just as quantum mechanics predicts.Clarke said their research had helped pave the way for technological advances, such as the creation of the cell phone.“There is no advanced technology used today that does not rely on quantum mechanics, including mobile phones, cameras… and fiber optic cables,” said the Nobel committee.Last year, the prize was awarded to Geoffrey Hinton – often called the “Godfather of AI” – and John Hopfield, for their fundamental discoveries in machine learning, which paved the way for how artificial intelligence is used today.In 2023, the prize went to a trio of European scientists who used lasers to understand the rapid movement of electrons, which were previously thought impossible to follow.The prize carries a cash award of 11 million Swedish kronor ($1 million).

    STOCKHOLM —

    The 2025 Nobel Prize in physics has been awarded to a trio of scientists – a Briton, a Frenchman and an American – for their ground-breaking discoveries in the field of quantum mechanics.

    John Clarke, Michel Devoret and John Martinis will share the prize “for the discovery of macroscopic quantum mechanical tunnelling and energy quantization in an electric circuit,” the Nobel Committee announced Tuesday at a ceremony in Stockholm, Sweden.

    The committee praised the laureates for demonstrating that the “bizarre properties of the quantum world can be made concrete in a system big enough to be held in the hand.”

    Clarke, taking questions at a news conference, said he was “completely stunned” to learn he had won the award.

    “We had not realized in any way that this might be the basis of a Nobel Prize,” Clarke said of their research in the 1980s at the University of California, Berkeley.

    Quantum mechanics, which describes how matter and energy behaves at or below the scale of an atom, allows a particle to pass straight through a barrier, in a process called “tunnelling.”

    But when a larger number of particles are involved, these quantum mechanical effects usually become insignificant. What is true at the microscopic level was not thought to be true at the macroscopic level. For instance, while a single atom could pass through a barrier, a tennis ball – made up of a huge amount of particles – cannot.

    However, the trio of researchers conducted experiments to show that quantum tunnelling can also be observed on a macroscopic scale.

    In 1984 and 1985, the trio developed a superconducting electrical system that could pass from one physical state to another, as if a tennis ball could move straight through a barrier and not bounce back.

    Anthony Leggett, who won the Nobel Prize in physics in 2003, compared the laureates’ work on how quantum mechanics functions on a larger scale to the famous thought experiment of Erwin Schrödinger, another physics laureate.

    To show the paradoxical nature of quantum mechanics, Schrödinger imagined a cat in a sealed box with a device that releases poison when a radioactive source decays. Because there is no way to observe whether the cat is dead or alive, Schrödinger posited that the cat was both dead and alive simultaneously – just as, in quantum mechanics, a system can exist in multiple states at once until measured.

    Schrödinger’s thought experiment aimed to show the absurdity of this situation, because quantum mechanics doesn’t make sense on the scale of everyday objects, such as a cat.

    Leggett argued, however, that the experiments conducted by Clarke, Devoret and Martinis showed that there are phenomena on larger scales that behave just as quantum mechanics predicts.

    Clarke said their research had helped pave the way for technological advances, such as the creation of the cell phone.

    “There is no advanced technology used today that does not rely on quantum mechanics, including mobile phones, cameras… and fiber optic cables,” said the Nobel committee.

    Last year, the prize was awarded to Geoffrey Hinton – often called the “Godfather of AI” – and John Hopfield, for their fundamental discoveries in machine learning, which paved the way for how artificial intelligence is used today.

    In 2023, the prize went to a trio of European scientists who used lasers to understand the rapid movement of electrons, which were previously thought impossible to follow.

    The prize carries a cash award of 11 million Swedish kronor ($1 million).

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  • C2QA, a Year in Review

    C2QA, a Year in Review

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    Newswise — The Co-design Center for Quantum Advantage (C2QA), led by the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, spans over 27 different partner and affiliate institutions ranging from research and academia to industry. C2QA’s primary focus is building the tools necessary to create scalable, distributed, and fault-tolerant quantum computer systems, and the center has been growing, building, and working hard every year to support that mission. 2023 has gone by quickly, with several memorable milestones to mark the way. Here are some highlights from the last year.

    Science and Technology

    Qubits, basic quantum systems that store information, are fussy things. The smallest fluctuations in their environment can cause them to break down. Heat, ambient radiation, magnetic fields, and even other surrounding qubits can cause the information stored in a qubit to leak into the environment and change its state, making it no longer viable. This is known as “decoherence,” and it’s one of the biggest challenges in making the quantum revolution a reality.

    The materials thrust has made significant progress in extending the lifetime of these finicky bits. Scientists from the Center for Functional Nanomaterials (CFN) and the National Synchrotron Light Source II (NSLS-II) at Brookhaven Lab and C2QA partner Princeton University investigated the fundamental reasons that tantalum qubits perform better by decoding this material’s chemical profile. The results of this work, which were recently published in the journal Advanced Science, will provide key knowledge for designing even better qubits in the future. CFN and NSLS-II are DOE Office of Science User Facilities at Brookhaven Lab.

    The Devoret Research Group at Yale University was also hard at work extending the lifetime and performance of qubits. Led by Michel Devoret, devices subthrust leader at C2QA, the team was able to double the life of a tantalum-based qubit through a process called error correction. Error correction is a special type of coding that will, theoretically, protect the information in a qubit. Researchers employed several methods that have built upon years of research to get to this groundbreaking result, which was published in Nature earlier this year.

    This year, Nathan Wiebe, leader of the Center’s software thrust, and his team worked on a quantum algorithm that simulated classical harmonic oscillators with significant advantage. While other simulations have achieved similar results, they have mostly investigated representations of systems that are already quantum mechanical in nature. This research demonstrated that, in the right conditions, a quantum computer could solve a classical problem in significantly less time.

    Community Outreach

    The quantum information science (QIS) community is growing as research accelerates, and C2QA is leaving no stone unturned to recruit outstanding talent and ensure that opportunities within the field are accessible to all communities and institutions. Some of this starts with reaching out to students as early as high school, introducing them to this budding field, and giving them a chance to connect with experts and learn more about it.

    This past summer, C2QA hosted QIS 101, a virtual quantum computing summer school. In its third year, QIS 101 built off its successes and learned from its challenges to optimize the course even more. The in-depth coursework, including 50 hands-on projects, was spread out over a six-week period this year. In its short three years, 12 alumni of the class obtained follow-on undergraduate or graduate internships at Brookhaven Lab, other DOE labs, or STEM-focused businesses; seven students were accepted into a master’s program in STEM fields; and two were accepted into Ph.D. programs in STEM fields. These accomplishments are a bright reflection of the talented pool of applicants that are accepted into QIS 101 and what they will bring to this growing field.

    The C2QA-led Quantum Information Science Virtual Career Fair continues to grow in both attendees and offerings. This year, the number of exhibitors more than doubled, reaching 42 booths that represented research, academia, and industry. The event drew in over 1,300 registrants, 39% more than the previous year, and 780 attendees—an encouraging 59% more than the previous year. About three-quarters of the attendees were students (23% undergrads and 44% graduate students) and postdocs (13%). There were 2,100 clicks on the job website, where jobseekers could apply instantly, and over 10,000 booths visited!

    The virtual Quantum Thursdays lecture series is still going strong. C2QA hosted 13 Quantum Thursdays on a variety of topics this year. While undergraduate students are the target audience for these beginner sessions, approximately 40% of attendees identified as undergraduate or graduate students. The series was expanded to include speakers and involvement from all five of the DOE Office of Science National Quantum Information Science Research Centers, setting the stage for a bigger picture of the quantum landscape in the coming year. Previous lectures can be viewed in C2QA’s video archive.

    Another important facet of growing the center is to ensure there is a place for everyone in quantum. The diverse talent brought in through programs that highlight otherwise underrepresented people and institutions benefits the entire QIS landscape.2023 saw the launch of the Faculty Outreach for Quantum-Interested UniversitieS (FOQUS) program. This collective program leveraged the resources and expertise of Brookhaven Lab, including the Office of Diversity, Equity and Inclusion and the Office of Educational Programs, C2QA, the DOE Office of Science’s Office of Workforce Development for Teachers and Scientists, and the IBM-HBCU Quantum Center. This ambitious program encouraged university faculty to combine and expand their networks and leverage programs offered by DOE to engage students and teachers. By breaking down barriers and fostering networking, faculty can prepare and develop underrepresented students from all STEM disciplines to enter the world of QIS.

    Looking to the Future 

    “In 2023, we’ve seen so many promising developments across each thrust in the Center,” remarked C2QA director Andrew Houck. “We’re not just uncovering answers, we’re finding new questions to ask in the year ahead. I think we are at this cusp, and we are about to see—in the next five or 10 years—these machines start to do things that are useful and better than any other technology.”

    Teaming up with other NQISRCs in the future can help remove some of the limitations on rapidly growing programs. QIS 101, for example, received 424 applications when the program can only support up to 40 students due to budget limitations. Joining forces with the other centers could allow a larger number of participants to take advantage of these opportunities in the future.

    Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.

    Follow @BrookhavenLab on social media. Find us on Instagram, LinkedIn, X, and Facebook.

     

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  • Nobel Laureate Serge Haroche sheds light on research at CityU

    Nobel Laureate Serge Haroche sheds light on research at CityU

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    Newswise — A sharing session on 3 October, featuring Professor Serge Haroche, Chairman of Hong Kong Institute for Advanced Study (HKIAS) and Nobel Laureate in Physics (2012), sheds light on the inter-relationship between teaching and research.

    Professor Haroche emphasised that teaching is crucial when conducting research. It is not simply the transmission of knowledge to the next generation. The transmission is “essential for doing research as it clarifies your ideas when you explain them to the students.” He also highlighted the significance in providing support and patience to researchers, quoting the 2023 Nobel Prize winner Professor Katalin Karikó as an example.

    The sharing session at City University of Hong Kong (CityU) was organised for CityU students, faculty members as well as secondary school students which included winners of CityU Science Patent Challenge 2022, the CityU Science Video Competition 2023, and the Hong Kong Secondary School Cosmetic Formulation Competition 2023. It was facilitated by Professor lo Chun Hoi, Associate Professor of Department of Physics and Professor Andy Siu, Associate Professor of Department of Chemistry. During the sharing, Professor Haroche gave his insights on Quantum Physics and advised students on how to seize the opportunities to prepare for the future. He encouraged the youths to redirect their focus away from immediate gains or funding and emphasised instead the value of investing deeply in their work. Professor Haroche also underlined that researchers would eventually achieve the tangible outcome of their efforts as long as they maintain their patience and immerse themselves in their research endeavors.

    After the sharing session, Professor Serge Haroche, who is also Professor Emeritus at the Collège de France, Member of the French Academy of Sciences and Foreign Member of the US National Academy of Sciences, was taken on a guided visit, by Professor Xun-Li Wang, Executive Director of HKIAS, Professor Jeff Ou, Chair Professor of Physics and Professor Denver Li, Assistant Professor at Department of Physics, to the Quantum Optics Lab, the Laser MBE Lab, and the Centre for Neutron Scattering, to explore the facilities and advancement of the Physics laboratories at CityU.

    (View detailed profile of Professor Haroche at HKIAS website.)

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    Hong Kong Institute for Advanced Study, City University of Hong Kong

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  • Dance sparks magnetism’s birth

    Dance sparks magnetism’s birth

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    Newswise — Quantum materials hold the key to a future of lightning-speed, energy-efficient information systems. The problem with tapping their transformative potential is that, in solids, the vast number of atoms often drowns out the exotic quantum properties electrons carry.

    Rice University researchers in the lab of quantum materials scientist Hanyu Zhu found that when they move in circles, atoms can also work wonders: When the atomic lattice in a rare-earth crystal becomes animated with a corkscrew-shaped vibration known as a chiral phonon, the crystal is transformed into a magnet.

    According to a study published in Science, exposing cerium fluoride to ultrafast pulses of light sends its atoms into a dance that momentarily enlists the spins of electrons, causing them to align with the atomic rotation. This alignment would otherwise require a powerful magnetic field to activate, since cerium fluoride is naturally paramagnetic with randomly oriented spins even at zero temperature.

    “Each electron possesses a magnetic spin that acts like a tiny compass needle embedded in the material, reacting to the local magnetic field,” said Rice materials scientist and co-author Boris Yakobson. “Chirality ⎯ also called handedness because of the way in which left and right hands mirror each other without being superimposable ⎯ should not affect the energies of the electrons’ spin. But in this instance, the chiral movement of the atomic lattice polarizes the spins inside the material as if a large magnetic field were applied.”

    Though short-lived, the force that aligns the spins outlasts the duration of the light pulse by a significant margin. Since atoms only rotate in particular frequencies and move for a longer time at lower temperatures, additional frequency- and temperature-dependent measurements further confirm that magnetization occurs as a result of the atoms’ collective chiral dance.

    “The effect of atomic motion on electrons is surprising because electrons are so much lighter and faster than atoms,” said Zhu, Rice’s William Marsh Rice Chair and an assistant professor of materials science and nanoengineering. “Electrons can usually adapt to a new atomic position immediately, forgetting their prior trajectory. Material properties would remain unchanged if atoms went clockwise or counterclockwise, i.e., traveled forward or backward in time ⎯ a phenomenon that physicists refer to as time-reversal symmetry.”

    The idea that the collective motion of atoms breaks time-reversal symmetry is relatively recent. Chiral phonons have now been experimentally demonstrated in a few different materials, but exactly how they impact material properties is not well understood.

    “We wanted to quantitatively measure the effect of chiral phonons on a material’s electrical, optical and magnetic properties,” Zhu said. “Because spin refers to electrons’ rotation while phonons describe atomic rotation, there is a naive expectation that the two might talk with each other. So we decided to focus on a fascinating phenomenon called spin-phonon coupling.”

    Spin-phonon coupling plays an important part in real-world applications like writing data on a hard disk. Earlier this year, Zhu’s group demonstrated a new instance of spin-phonon coupling in single molecular layers with atoms moving linearly and shaking spins.

    In their new experiments, Zhu and the team members had to find a way to drive a lattice of atoms to move in a chiral fashion. This required both that they pick the right material and that they create light at the right frequency to send its atomic lattice aswirl with the help of theoretical computation from the collaborators.

    “There is no off-the-shelf light source for our phonon frequencies at about 10 terahertz,” explained Jiaming Luo, an applied physics graduate student and the lead author of the study. “We created our light pulses by mixing intense infrared lights and twisting the electric field to ‘talk’ to the chiral phonons. Furthermore, we took another two infrared light pulses to monitor the spin and atomic motion, respectively.”

    In addition to the insights into spin-phonon coupling derived from the research findings, the experimental design and setup will help inform future research on magnetic and quantum materials.

    “We hope that quantitatively measuring the magnetic field from chiral phonons can help us develop experiment protocols to study novel physics in dynamic materials,” Zhu said. “Our goal is to engineer materials that do not exist in nature through external fields ⎯ such as light or quantum fluctuations.”

    The research was supported by the National Science Foundation (2005096, 1842494, 2240106), the Welch Foundation (C-2128) and the Army Research Office (W911NF-16-1-0255).

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  • Quantum-classical partnership enhances performance in parallel hybrid network.

    Quantum-classical partnership enhances performance in parallel hybrid network.

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    Newswise — Building efficient quantum neural networks is a promising direction for research at the intersection of quantum computing and machine learning. A team at Terra Quantum AG designed a parallel hybrid quantum neural network and demonstrated that their model is “a powerful tool for quantum machine learning.” This research was published Oct. 9 in Intelligent Computing, a Science Partner Journal.

    Hybrid quantum neural networks typically consist of both a quantum layer — a variational quantum circuit — and a classical layer — a deep learning neural network called a multi-layered perceptron. This special architecture enables them to learn complicated patterns and relationships from data inputs more easily than traditional machine learning methods.

    In this paper, the authors focus on parallel hybrid quantum neural networks. In such networks, the quantum layer and the classical layer process the same input at the same time and then produce a joint output — a linear combination of the outputs from both layers. A parallel network could avoid the information bottleneck that often affects sequential networks, where the quantum layer and the classical layer feed data into each other and process data alternately.

    The training results demonstrate that the authors’ parallel hybrid network can outperform either its quantum layer or its classical layer. Trained on two periodic datasets with high-frequency noise added, the hybrid model shows lower training loss, produces better predictions, and is found to be more adaptable to complex problems and new datasets.

    The quantum and classical layers both contribute to this effective quantum-classical interplay. The quantum layer, specifically, a variational quantum circuit, maps the smooth periodical parts, while the classical multi-layered perceptron fills in the irregular additions of noise. Both variational quantum circuits and multi-layered perceptrons are considered “universal approximators.” To maximize output during training, variational quantum circuits adjust the parameters of quantum gates that control the status of qubits, and multi-layered perceptrons mainly tune the strength of the connections, or so-called weights, between neurons.

    At the same time, the success of a parallel hybrid network rides on the setting and tuning of the learning rate and other hyperparameters, such as the number of layers and number of neurons in each layer in the multi-layered perceptron.

    Given that the quantum and classical layers learn at different speeds, the authors discussed how the contribution ratio of each layer affects the performance of the hybrid model and found that adjusting the learning rate is important in keeping a balanced contribution ratio. Therefore, they point out that building a custom learning rate scheduler is a future research direction because such a scheduler could enhance the speed and performance of the hybrid model.

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    Intelligent Computing

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  • Scientists Amplify Superconducting Sensor Arrays Signals Near the Quantum Limit

    Scientists Amplify Superconducting Sensor Arrays Signals Near the Quantum Limit

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    The Science

    Newswise — Understanding how energy moves in materials is fundamental to the study of quantum phenomena, catalytic reactions, and complex proteins. Measuring how energy moves involves shining special X-ray light onto a sample to start a reaction. Detectors then collect the radiation the reaction emits. Conventional sensors usually lack the sensitivity needed for these studies. One solution is to use superconducting sensors. But amplifying the signals from these sensors is a major challenge. Building on advances from quantum computing, researchers added a special type of amplifiers, superconducting traveling-wave parametric amplifiers. While most amplifiers add noise to the measurement, these amplifiers are almost noiseless. In a major advance, researchers recently showed that the amplifiers can operate at 4 Kelvin, which is considered relatively high operating temperatures.

    The Impact

    Reducing the noise that is added during signal processing can improve a sensor’s performance. Amplification allows each sensor to operate faster and be more sensitive. Recent experiments have shown that parametric amplifiers can potentially analyze signals from many superconducting sensors at the same time. Superconducting sensors work at very low temperatures. At these temperatures, parametric amplifiers have very good noise performance, close to the limit of quantum mechanics. The advance paves the way to integrate such amplifiers with a variety of sensor technologies.

    Summary

    A superconducting sensor consists of a superconducting thermometer and an absorber. When X-rays are stopped in the absorber, they change the superconducting state of the sensor. This generates a small current in an electrical circuit. To make the detector more sensitive, many sensors are arranged into an array, like in a digital camera. Superconducting sensors operate at very cold temperatures (approximately 0.09 Kelvin), so they require specialized readout electronics and amplifiers. These amplifiers need to combine the signals from multiple sensors on a single readout line. Combining signals is known as multiplexing. One efficient way to do this is to couple each sensor in an array to a resonator. All of the resonators are coupled to a single output line. The current produced by an absorbed photon shifts the resonant frequency in a unique way for each sensor.

    Because these resonators work in microwave frequencies, the electronic chip that contains all the resonators as well as the output feedline is called the microwave multiplexer. Researchers are preparing to measure the signals from an array of sensors and a microwave multiplexer with a readout chain whose first amplifier is a kinetic-inductance traveling-wave parametric amplifier instead of a conventional semiconductor amplifier. Using the parametric amplifier will reduce readout noise and enable larger arrays of faster sensors.

     

    Funding

    This work was funded by the Department of Energy Office of Science, Basic Energy Sciences Accelerator and Detector Research Program, the National Institute of Standards and Technology’s Innovations in Measurement Science Program, and NASA.


    Journal Link: Physical Review Applied, Apr-2022

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    Department of Energy, Office of Science

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  • New Material Enables an Ultrafast Electron Diffraction Probe for Quantum Materials

    New Material Enables an Ultrafast Electron Diffraction Probe for Quantum Materials

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    Newswise — The Science

    Quantum materials have a host of exotic electronic, magnetic, and optical properties that make them prime candidates for use in future computing and energy technologies. Their properties arise from a complex interaction of their electrons and atomic nuclei. Researchers can observe these interactions as they happen using short pulses of X-rays or electron beams. These pulses last less than a trillionth of a second. Using new materials that emits a narrow electron probe, researchers have developed an ultrafast electron beam technique to probe small, thin pieces of quantum materials with very high resolution.

    The Impact

    Scientists so far cannot create many newly emerging quantum materials as large crystals. Instead, these materials form crystals only one-tenth as wide as a human hair. This poses a challenge for researchers probing these materials using ultrafast electron beam accelerators, as electron beam quality often limits how small an area these beams can focus on. In this study, researchers used a specialized source of electrons to produce a substantial improvement in electron beam quality. This enables crisp images of samples only a few microns wide and of processes that take place in less than a trillionth of a second. This work could lead to a clearer image and understanding of how quantum materials function at atomic space and time scales.

    Summary

    These accelerators typically generate ultrafast electron pulses via a process called photoemission, wherein laser light knocks electrons out of a material, usually a simple metal like copper. If the laser pulse is short in duration, the emitted electron beam will also be short. One challenge with typical photoemission sources is that the electrons emitted do not all travel in the same direction. This spread in emission angle can ultimately limit researchers’ ability to focus the electron beam on a small spot.

    In this work, researchers developed a photoemission-based electron accelerator with an advanced, in-house grown photoemission material that produces many electrons with a much smaller spread in emission angle. Using this source in conjunction with precise electron focusing optics, the researchers performed proof-of-principle ultrafast electron diffraction experiments which showed the ability to resolve subtle atomic details in samples as small as just a few microns in size.

    Funding

    This research was supported by the Department of Energy Office of Science, Basic Energy Sciences and by the National Science Foundation.


    Journal Link: Structural Dynamics, Mar-2022

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    Department of Energy, Office of Science

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  • Researchers Test Quantum Theory with Precision-Engineered Thin Films

    Researchers Test Quantum Theory with Precision-Engineered Thin Films

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    The Science

    Comparing experimental results and theoretical calculations can be difficult for quantum materials. These are materials that have special properties, such as superconductivity, that can only be understood using the rules of quantum mechanics. One way that scientists compare experiments and computations is to use sample materials that isolate and emphasize an atomic line with one dimensional (1D) properties. In this study, scientists grew thin films of layered copper-oxygen (cuprate) materials to isolate 1D copper chains. This allowed them to test theories of how electrons interact in quantum materials. They grew the films under conditions that allowed them to carefully modify the films’ chemistry and electronic structure. They then measured the electronic structure. The research was possible in part because of a specialized synchrotron X-ray beam line designed and built for this purpose.

    The Impact

    Describing how the properties of quantum materials interact and testing related theories are mathematically very complex and time consuming. This work enabled a direct comparison of computational results against experimental measurements. The study indicates that standard theory is not sufficient and requires a new term to fit the experimental data. The work will help scientists refine theories that are essential to describing and engineering new quantum materials and effects. This could eventually lead to new quantum electronic devices.

    Summary

    It is currently impossible to computationally solve the electronic structure of multi-dimensional quantum materials. 1D theory is computationally possible but difficult to test because most materials have 3D structures. The structure of inherently layered 2D cuprate materials can be rearranged, when synthesized in the ultra-thin limit, resulting in 1D copper-oxygen chains that run parallel to the material surface. However, to fully test theories of electron interactions and transport, researchers also need well characterized “doping” defects in the cuprate oxygen stoichiometry.

    In this research, scientists figured out a synthesis method, using ozone during molecular beam epitaxial growth, to add extra oxygen atoms that grab electrons from the copper atoms and create holes in the electronic structure. This was done at a thin film deposition station connected to a synchrotron X-ray beamline that was designed with a sensitive X-ray photoemission spectroscopy capability that can map out the resulting electronic structure. By comparing experimental results with theory, the researchers showed that the standard theory of electron interactions and transport could not predict the 1D doping effects without a modification used to show an unusually strong attraction between certain electrons at longer separations. This attraction is mediated by atomic vibrations. Understanding the coupling between chemistry, defects, vibrations, and the spin direction of electrons are a necessary part of engineering quantum materials for future devices. This work provides a needed direct connection between theory and experiment at the level of correlated electron theory.

     

    Funding

    This work was supported by the Department of Energy (DOE) Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. Film growth and X-ray ARPES experiments were performed at Beamline 5-2 of the Stanford Synchrotron Radiation Light Source, a DOE Office of Science user facility at SLAC National Accelerator Laboratory. Computational resources were provided by the National Energy Research Scientific Computing Center, a DOE Office of Science user facility.

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    Department of Energy, Office of Science

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  • Physicists Forge New Path to Uncover Exotic Superconductivity

    Physicists Forge New Path to Uncover Exotic Superconductivity

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    Newswise — Physicists have identified a mechanism for the formation of oscillating superconductivity known as pair-density waves. Physical Review Letters published the discovery, which provides new insight into an unconventional, high-temperature superconductive state seen in certain materials, including high-temperature superconductors.

    “We discovered that structures known as Van Hove singularities can produce modulating, oscillating states of superconductivity,” says Luiz Santos, assistant professor of physics at Emory University and senior author of the study. “Our work provides a new theoretical framework for understanding the emergence of this behavior, a phenomenon that is not well understood.”

    First author of the study is Pedro Castro, an Emory physics graduate student. Co-authors include Daniel Shaffer, a postdoctoral fellow in the Santos group, and Yi-Ming Wu from Stanford University.

    The work was funded by the U.S. Department of Energy’s Office of Basic Energy Sciences.

    Santos is a theorist who specializes in condensed matter physics. He studies the interactions of quantum materials — tiny things such as atoms, photons and electrons — that don’t behave according to the laws of classical physics.

    Superconductivity, or the ability of certain materials to conduct electricity without energy loss when cooled to a super-low temperature, is one example of intriguing quantum behavior. The phenomenon was discovered in 1911 when Dutch physicist Heike Kamerlingh Onnes showed that mercury lost its electrical resistance when cooled to 4 Kelvin or minus 371 degrees Fahrenheit. That’s about the temperature of Uranus, the coldest planet in the solar system.

    It took scientists until 1957 to come up with an explanation for how and why superconductivity occurs. At normal temperatures, electrons roam more or less independently. They bump into other particles, causing them to shift speed and direction and dissipate energy. At low temperatures, however, electrons can organize into a new state of matter.

    “They form pairs that are bound together into a collective state that behaves like a single entity,” Santos explains. “You can think of them like soldiers in an army. If they are moving in isolation they are easier to deflect. But when they are marching together in lockstep it’s much harder to destabilize them. This collective state carries current in a robust way.”

    Superconductivity holds huge potential. In theory, it could allow for electric current to move through wires without heating them up, or losing energy. These wires could then carry far more electricity, far more efficiently.

    “One of the holy grails of physics is room-temperature superconductivity that is practical enough for everyday-living applications,” Santos says. “That breakthrough could change the shape of civilization.”

    Many physicists and engineers are working on this frontline to revolutionize how electricity gets transferred.

    Meanwhile, superconductivity has already found applications. Superconducting coils power electromagnets used in magnetic resonance imaging (MRI) machines for medical diagnostics. A handful of magnetic levitation trains are now operating in the world, built on superconducting magnets that are 10 times stronger than ordinary electromagnets. The magnets repel each other when the matching poles face each other, generating a magnetic field capable of levitating and propelling a train.

    The Large Hadron Collider, a particle accelerator that scientists are using to research the fundamental structure of the universe, is another example of technology that runs through superconductivity.

    Superconductivity continues to be discovered in more materials, including many that are superconductive at higher temperatures.

    One focus of Santos’ research is how interactions between electrons can lead to forms of superconductivity that cannot be explained by the 1957 description of superconductivity. An example of this so-called exotic phenomenon is oscillating superconductivity, when the paired electrons dance in waves, changing amplitude.

    In an unrelated project, Santos asked Castro to investigate specific properties of Van Hove singularities, structures where many electronic states become close in energy. Castro’s project revealed that the singularities appeared to have the right kind of physics to seed oscillating superconductivity.

    That sparked Santos and his collaborators to delve deeper. They uncovered a mechanism that would allow these dancing-wave states of superconductivity to arise from Van Hove singularities.

    “As theoretical physicists, we want to be able to predict and classify behavior to understand how nature works,” Santos says. “Then we can start to ask questions with technological relevance.”

    Some high-temperature superconductors — which function at temperatures about three times as cold as a household freezer — have this dancing-wave behavior. The discovery of how this behavior can emerge from Van Hove singularities provides a foundation for experimentalists to explore the realm of possibilities it presents.

    “I doubt that Kamerlingh Onnes was thinking about levitation or particle accelerators when he discovered superconductivity,” Santos says. “But everything we learn about the world has potential applications.”

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    Emory University

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  • Texas Tech Physicist Lands NSF Grant

    Texas Tech Physicist Lands NSF Grant

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    BYLINE: Doug Hensley

    Newswise — Myoung-Hwan Kim, an assistant professor in the Department of Physics and Astronomy at Texas Tech University, has been awarded a National Science Foundation grant in the field of materials research (DMR) related to quantum information science (QIS).

    An emerging field of research, QIS involves studying the transmission of information through quantum mechanics principles. Kim’s research will examine the influence of magnetism and topology on quantum particles delivering information. Kin’s award is one of two Texas Tech recently received from the NSF for QIS research. The other was awarded to Lu Wei, an assistant professor in the Department of Computer Sciences.

    “When a magnetic field is applied, the particles’ spin aligns with the field’s direction. However, when both an electric and a magnetic field are present, charged particles move in a direction parallel to the electric field but perpendicular to the magnetic field. As a result, the spin direction of the particles remains perpendicular to their direction of motion,” Kim said.

    “But some quantum particles in a solid react differently. The spin direction determines where the particle moves so the quantum particles only move when both electric and magnetic fields are aligned in the same direction. This we call a quantum anomaly that could be the foundation for a new qubit.”

    The NSF award acknowledges the vital work Texas Tech researchers are doing in this area, said Joseph A. Heppert, vice president for research & innovation.

    “Congratulations to Dr. Kim for receiving this new award from the National Science Foundation,” he said. “Quantum science is a high-priority research area for the nation. Innovations in quantum technology are expected to lead to revolutions in many areas of technology, including computer science and telecommunications. Texas Tech is extremely proud of Dr. Kim for his contributions to this critical and rapidly developing research field.”

    Kim’s work is in response to one of the challenges facing current quantum computers, a concept known as quantum decoherence, which occurs when information is lost during a computational process or information transport. Current quantum computers attempt to resolve decoherence by keeping qubits (quantum bits) from their surroundings, but as the qubit numbers increase, this becomes more difficult.

    As a result, scientists are seeking “topological qubits” that protect against decoherence because of their unique makeup, which could ultimately resolve the information loss issue. Two promising avenues of research have developed to try and address the problem.

    The first involves particles known as Majorana fermions, which are their own antiparticles, but this possibility has not gained significant traction yet. The second, research path involves Weyl fermions, which have shown more promise and where Kim is focusing his work during the life of the two-year NSF grant.

    “I am very pleased that two early-career faculty members at Texas Tech have successfully obtained NSF grants in the area of quantum information science research,” said Sung-Won Lee, department chair. “QIS is a new cross-disciplinary field of research, and a variety of research in this area has taken place on the Texas Tech campus since 2019.”

    The NSF grant will support Kim’s research, which aims to gain a fundamental understanding of quantum anomalies as well as their relationship with topology and the magnetic environment surrounding Weyl fermions. Kim’s lab at Texas Tech includes an advanced magneto-optical setup that was developed on campus. The hope is Kim’s work will provide new insights into controlling the functionality of Weyl fermions through optical, electrical and magnetic means.

    “The quantum anomalies can be controlled,” Kim said. “I want to study how the topology and the magnetic field influence the quantum particles’ motion and see how we control the quantum information flow using polarized light.”

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    Texas Tech University

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  • Thanks to Trapped Electrons, a Material Expected to be a Conducting Metal Remains an Insulator

    Thanks to Trapped Electrons, a Material Expected to be a Conducting Metal Remains an Insulator

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    The Science

    New research sheds light on the mechanism behind how a special material changes from an electrically conducting metal to an electric insulator. The researchers studied lanthanum strontium nickel oxide (La1.67Sr0.33NiO4) derived from a quantum material La2NiO4. Quantum materials have unusual properties that result from how their electrons interact. Below a critical temperature, the strontium doped material is an insulator. This is due to the separation of introduced holes from the magnetic regions, forming “stripes.” As the temperature increases, these stripes fluctuate and melt at 240K. At this temperature, researchers expected the material to become a conducting metal. Instead, it remains an insulating material. Neutron scattering sheds light on this intriguing phenomenon. The results indicate that the material stays an insulator because of certain atomic vibrations that trap electrons and thus impede electrical conduction.

    The Impact

    Quantum materials have properties that aren’t predicted by the parts that make up those materials. For example, they can transition from metals to insulators or act as superconductors. They hold tremendous promise for applications in science and technology. This research describes the tunability of electron-phonon interaction on the metal-insulator transition in one quantum material. The results will help validate theoretical models of materials that have strongly interacting electrons. These theories will help scientists design new quantum materials for future technologies.

    Summary

    In metals, electrons can be considered as free particles flying along trajectories enforced by the crystal structure. In recent decades, scientists discovered new materials where electrons strongly repel each other and bounce off atomic vibrations in the host crystal. These materials exhibit unusual and technologically useful properties. These properties can include dramatic electrical resistance drop in magnetic fields, electron conduction only on the surface, and high temperature superconductivity. Understanding these properties in different materials remains a grand challenge for the scientific community.

    This work used high intensity neutron beams at the Spallation Neutron Source, a Department of Energy user facility at Oak Ridge National Laboratory (ORNL), to look deep inside an archetype quantum material La2NiO4 in which one sixth of the lanthanum (La) atoms are replaced with strontium (Sr) atoms (La1.67Sr0.33NiO4). The team included researchers from the University of Colorado Boulder, ORNL, Brookhaven National Laboratory, and the RIKEN Center for Emergent Matter Science in Japan. These materials are insulating at low temperatures due to the so-called “stripe” order that results from the complex interplay between electronic spins and the holes introduced due to strontium doping. The doped material is expected to become metallic above 240K when the stripes melt. However, the material remains insulating. The collaboration uncovered strong friction between the holes and certain vibrations of oxygen ions and found evidence for this interaction in other materials of similar structure. The microscopic mechanism could pave way for the design of new materials with unusual properties useful for various quantum technologies.

     

    Funding

    Work at the University of Colorado Boulder was supported by the Department of Energy Office of Science, Basic Energy Sciences program. One of the researchers was supported by a Japan Science and Technology Agency CREST Grant. Work at Brookhaven National Laboratory was supported by the Department of Energy Office of Science, Basic Energy Sciences program.


    Journal Link: Scientific Reports, Jul-2020

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    Department of Energy, Office of Science

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  • Quantum physics secures digital payments

    Quantum physics secures digital payments

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    Newswise — Have you ever been compelled to enter sensitive payment data on the website of an unknown merchant? Would you be willing to consign your credit card data or passwords to untrustworthy hands? Scientists from the University of Vienna have now designed an unconditionally secure system for shopping in such settings, combining modern cryptographic techniques with the fundamental properties of quantum light. The demonstration of such “quantum-digital payments” in a realistic environment has just been published in Nature Communications.

    Digital payments have replaced physical banknotes in many aspects of our daily lives. Similar to banknotes, they should be easy to use, unique, tamper-resistant and untraceable, but additionally withstand digital attackers and data breaches. In today’s payment ecosystem, customers’ sensitive data is substituted by sequences of random numbers, and the uniqueness of each transaction is secured by a classical cryptographic method or code. However, adversaries and merchants with powerful computational resources can crack these codes and recover the customers’ private data, and for example, make payments in their name.

    A research team led by Prof. Philip Walther from the University of Vienna has shown how the quantum properties of light particles or photons can ensure unconditional security for digital payments. In an experiment the researchers have demonstrated that each transaction cannot be duplicated or diverted by malicious parties, and that the user’s sensitive data stays private. “I am really impressed how the quantum properties of light can be used for protecting new applications such as digital payments that are relevant in our every day’s life”, says Tobias Guggemos.

    For enabling absolute secure digital payments, the scientists replaced classical cryptographic techniques with a quantum protocol exploiting single photons. During the course of a classical digital payment transaction the client shares a classical code – called cryptogram – with his payment provider (e.g. a bank or credit card company). This cryptogram is then passed on between customer, merchant and payment provider. In the demonstrated quantum protocol this cryptogram is generated by having the payment provider sending particularly prepared single photons to the client. For the payment procedure, the client measures these photons whereby the measurement settings depend on the transaction parameters. Since quantum states of light cannot be copied, the transaction can only be executed once. This, together with the fact that any deviation of the intendent payment alters the measurement outcomes, which are verified by the payment provider, makes this digital payment unconditionally secure.

    The researchers successfully implemented quantum-digital payments over an urban optical fiber link of 641m, connecting two university buildings in down-town Vienna. Digital payments currently operate within a few seconds. “At present, our protocol takes a few minutes of quantum communication to complete a transaction. This is to guarantee security in the presence of noise and losses” says Peter Schiansky, first author of the paper. “However, these time limitations are only of technological nature” adds Matthieu Bozzio, who is convinced that “we will witness that quantum-digital payments reach practical performance in the very near future”.

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    University of Vienna

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  • IBM’s Jason Orcutt moves the world toward an interconnected quantum future

    IBM’s Jason Orcutt moves the world toward an interconnected quantum future

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    Newswise — Jason Orcutt of IBM provides an industry perspective on quantum simulation research at the Q-NEXT quantum research center and works to connect quantum information systems around the globe.

    Glance around Jason Orcutt’s office at IBM Quantum, and you’ll see circuit boards, hiking trail maps, qubit probes and his kids’ artwork. Part office, part lab, part gallery: It’s a cross section of a life of rigorous research and vigorous recreation.

    The scene also captures the kind of activity balancing that characterizes his work as a quantum information researcher, switching between hands-on investigation and high-level research strategy. He uses these wide-ranging skills in his role as a co-design engineer for Q-NEXT, the National Quantum Information Science Research Center led by the U.S. Department of Energy’s (DOE) Argonne National Laboratory.

    A principal research scientist at IBM Quantum, Orcutt provides an industry perspective on one of the pillars of Q-NEXT research: developing simulations to better design quantum information systems.

    “IBM brings a future-looking perspective on the problems we need to solve to develop a really useful quantum computer. And Q-NEXT really aligns with our vision on creating new types of quantum interconnects to scale quantum computers into the future.” — Jason Orcutt, IBM

    Q-NEXT collaborators use quantum computers and classical supercomputers to simulate the behaviors of materials used for quantum applications, which are expected to be revolutionary. In the decades ahead, scientists will deploy quantum sensors that can detect an earthquake from space and run powerful quantum computers that can rapidly suss out solutions to intractable problems.

    “We’re using simulations to better design materials and adapting those simulations to an interconnected quantum system,” Orcutt said. ​“IBM brings a future-looking perspective on the problems we need to solve to develop a really useful quantum computer. And Q-NEXT really aligns with our vision on creating new types of quantum interconnects to scale quantum computers into the future.”

    “Quantum interconnect” is a fancy way of referring to the components that link quantum devices. It could be the instruments connecting a sensor to a computer, or it could be a line on a printed circuit board. Without interconnects, quantum devices can’t talk to each other, and quantum information can’t be shared.

    At IBM Quantum, Orcutt coordinates the development of long-range quantum interconnects, which link devices separated by meters to kilometers, such as the nodes in a future quantum data center.

    “How do we extend quantum information or connect quantum systems over physical distance?” he said. ​“Right now, our IBM quantum systems are really restricted to a single chip. I and the people I work with, as well as the academic researchers such as those at Q-NEXT, are looking to develop connections between qubits that will extend beyond more than one chip.”

    Sending quantum information over longer distances is an obstacle course of physics challenges. For starters, quantum information is fragile. Qubits — the fundamental units of quantum information — fall apart at the smallest disturbance. Distance complicates matters. How do you provide qubits with safe, noise-free passage over a kilometer or more? The proposition is like asking a soap bubble not to pop as it travels down a galley of knives.

    “You can’t use the same tools to pattern a centimeter size chip as you would a meter-scale cable,” Orcutt said.

    Qubits must also be continually converted and reconverted to the right frequencies to be read by the devices they encounter on their journey. The most fundamental frequency conversion requirements arise from the different levels of thermal noise at different frequencies. For example: IBM Quantum focuses on a type of qubit that lives in the microwave frequency range. In this range, the quantum information must be cooled to a few hundredths of a degree from absolute zero to be protected from thermal noise. To be transported in room temperature materials — a requirement for long distance communication — the quantum information must be converted to the optical-wave range, a whopping 10,000 times the frequency of microwaves.

    The way that materials respond to the two frequency ranges is massively different. How do you engineer materials to successfully conduct information that starts as a murmur and ends in a trill?

    Such challenges are part of the growing pains of the field of quantum information science, which is working to tap the potential of information that, until recently, was kept cozily inside tiny instruments such as microchips.

    “We’re taking quantum information into places it traditionally doesn’t live,” Orcutt said. Instead of moving through chips built in clean rooms, qubits are having to find their way through ​“the messy world of macroscopic objects,” he said, such as meter-long coaxial cables or fiber optic cables that connect nodes that are miles apart.

    The scientific community is working to build quantum systems that will eventually connect the globe. Simulating them from soup to nuts is key to ensuring that the interconnected systems of the future will be successful. Orcutt draws on his experience at IBM to inform Q-NEXT’s quantum simulations work.

    “We have to reengineer our systems, and to do that, we have to simulate them,” he said. ​“But how do we reengineer our systems around quantum interconnects instead of a monolithic computing device? Systems where there are different levels of connectivity? We have to rethink not just how we build the systems, but also how we adapt our algorithms to best use them.”

    Orcutt began his journey into quantum information science at Columbia University, planning initially to be a patent lawyer, combining interests in debate and technology.

    “What I quickly realized was that there are many other ways to pursue science and have a fulfilling career that was closer to creating new technical ideas,” he said.

    He pivoted to a bachelor’s in electrical engineering, with no intention of attending graduate school. But, again, he changed his mind after a couple of happy lab experiences working on electronics and photonics. For his Ph.D. research at MIT, Orcutt built the first optical interconnects in the commercial manufacturing processes used for microprocessor and memory chips.

    “This was a wonderful project because it wasn’t just about the devices — it was connected to the systems, which is something that has always been a key draw for me throughout my life,” he said.

    In 2013, Orcutt joined IBM. It was a major shift for someone who started his career as ​“the one soldering the circuit, the one simulating the physics or coding the program,” he said. And while he continues to work directly with the technology, 10 years later, he’s also the one asking how quantum computers should be wired, what components are required to connect the qubits and what direction IBM should take to tackle these strategic and technology questions.

    Orcutt’s experience both at the bench and at the center of operations made him a valuable contributor to Q-NEXT’s 2022 quantum technology report ​“A Roadmap for Quantum Interconnects,” which outlines the discoveries needed to build practical quantum information technologies in one or two decades.

    “It was a useful exercise to define the important challenges and potential solutions that are emerging within the community and define it so it could be addressed by the center on a 10-year scale,” he said.

    Producing the roadmap is just one example of IBM’s collaborative effort with Q-NEXT.

    “The next phase of quantum information science will involve creating new materials and refined products that have superior quantum information performance. And to address that, we need a whole bunch of forces coming together, which is another reason why the shared infrastructure at centers like Q-NEXT are critical,” Orcutt said. ​“Trying to tackle these really hard problems is one of the main reasons we like to work with other industrial players, national labs and a broad consortium of academic groups. To us — to me and to IBM in general — that is a paramount reason to get involved in Q-NEXT: to be able to tackle the really hard problems together with the best people in the field.”

    Building the quantum workforce through education and outreach is another goal for IBM Quantum. IBM creates connections to the students, postdocs and other early-career scientists conducting research at centers like Q-NEXT, widening opportunities to grow its own quantum workforce.

    For those thinking of entering the field, Orcutt notes the excitement of quantum research.

    “When I have a new task or project, I initially have absolutely no idea how we’re going to solve it. The wonderful thing is, we’ve been able to make significant progress against our goals,” he said. ​“It’s been a wonderful journey of figuring out ways to contribute to the quantum effort and trying to solve problems along the way.”

    This work was supported by the DOE Office of Science National Quantum Information Science Research Centers as part of the Q-NEXT center.

    About Q-NEXT

    Q-NEXT is a U.S. Department of Energy National Quantum Information Science Research Center led by Argonne National Laboratory. Q-NEXT brings together world-class researchers from national laboratories, universities and U.S. technology companies with the goal of developing the science and technology to control and distribute quantum information. Q-NEXT collaborators and institutions will create two national foundries for quantum materials and devices, develop networks of sensors and secure communications systems, establish simulation and network test beds, and train the next-generation quantum-ready workforce to ensure continued U.S. scientific and economic leadership in this rapidly advancing field. For more information, visit https://​q​-next​.org/.

    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.

    The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://​ener​gy​.gov/​s​c​ience.

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  • Quantum computers guess better, study finds

    Quantum computers guess better, study finds

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    Newswise — Daniel Lidar, the Viterbi Professor of Engineering at USC and Director of the USC Center for Quantum Information Science & Technology, and first author Dr. Bibek Pokharel, a Research Scientist at IBM Quantum, achieved this quantum speedup advantage in the context of a “bitstring guessing game.”  They managed strings up to 26 bits long, significantly larger than previously possible, by effectively suppressing errors typically seen at this scale. (A bit is a binary number that is either zero or one).

    Quantum computers promise to solve certain problems with an advantage that increases as the problems increase in complexity. However, they are also highly prone to errors, or noise. The challenge, says Lidar, is “to obtain an advantage in the real world where today’s quantum computers are still ‘noisy.’” This noise-prone condition of current quantum computing is termed the “NISQ” (Noisy Intermediate-Scale Quantum) era, a term adapted from the RISC architecture used to describe classical computing devices. Thus, any present demonstration of quantum speed advantage necessitates noise reduction.

    The more unknown variables a problem has, the harder it usually is for a computer to solve. Scholars can evaluate a computer’s performance by playing a type of game with it to see how quickly an algorithm can guess hidden information. For instance, imagine a version of the TV game Jeopardy, where contestants take turns guessing a secret word of known length, one whole word at a time. The host reveals only one correct letter for each guessed word before changing the secret word randomly.

    In their study, the researchers replaced words with bitstrings. A classical computer would, on average, require approximately 33 million guesses to correctly identify a 26-bit string. In contrast, a perfectly functioning quantum computer, presenting guesses in quantum superposition, could identify the correct answer in just one guess. This efficiency comes from running a quantum algorithm developed more than 25 years ago by computer scientists Ethan Bernstein and Umesh Vazirani. However, noise can significantly hamper this exponential quantum advantage.

    Lidar and Pokharel achieved their quantum speedup by adapting a noise suppression technique called dynamical decoupling. They spent a year experimenting, with Pokharel working as a doctoral candidate under Lidar at USC. Initially, applying dynamical decoupling seemed to degrade performance. However, after numerous refinements, the quantum algorithm functioned as intended. The time to solve problems then grew more slowly than with any classical computer, with the quantum advantage becoming increasingly evident as the problems became more complex.

    Lidar notes that “currently, classical computers can still solve the problem faster in absolute terms.” In other words, the reported advantage is measured in terms of the time-scaling it takes to find the solution, not the absolute time. This means that for sufficiently long bitstrings, the quantum solution will eventually be quicker.

    The study conclusively demonstrates that with proper error control, quantum computers can execute complete algorithms with better scaling of the time it takes to find the solution than conventional computers, even in the NISQ era.

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    University of Southern California (USC)

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  • X-rays show how nature’s strongest bond breaks

    X-rays show how nature’s strongest bond breaks

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    Newswise — The use of short flashes of X-ray light brings scientists one big step closer toward developing better catalysts to transform the greenhouse gas methane into a less harmful chemical. The result, published in the journal Science, reveals for the first time how carbon-hydrogen bonds of alkanes break and how the catalyst works in this reaction.

    Methane, one of the most potent greenhouse gases, is being released into the atmosphere at an increasing rate by livestock farming as well as the continuing unfreezing of permafrost. Transforming methane and longer-chain alkanes into less harmful and in fact useful chemicals would remove the associated threats, and in turn make a huge feedstock for the chemical industry available. However, transforming methane necessitates as a first step the breaking of a C-H bond, one of the strongest chemical linkages in nature.

    Forty years ago, molecular metal catalysts were discovered that can easily split C-H bonds. The only thing found to be necessary was a short flash of visible light to “switch on” the catalyst and, as by magic, the strong C-H bonds of alkanes passing nearby are easily broken almost without using any energy. Despite the importance of this so-called C-H activation reaction, it remained unknown over the decades how that catalyst performs this function.

    The research was led by scientists from Uppsala University in collaboration with the Paul Scherrer Institute in Switzerland, Stockholm University, Hamburg University and the European XFEL in Germany. For the first time, the scientists were able to directly watch the catalyst at work and reveal how it breaks those C-H bonds.

    In two experiments conducted at the Paul Scherrer Institute in Switzerland, the researchers were able to follow the delicate exchange of electrons between a rhodium catalyst and an octane C-H group as it gets broken. Using two of the most powerful sources of X-ray flashes in the world, the X-ray laser SwissFEL and the X-ray synchrotron Swiss Light Source, the reaction could be followed all the way from the beginning to the end. The measurements revealed the initial light-induced activation of the catalyst within 400 femtoseconds (0.0000000000004 seconds) to the final C-H bond breaking after 14 nanoseconds (0.000000014 seconds).

    “The time-resolved X-ray absorption experiments we performed are only possible at large-scale facilities like SwissFEL and the Swiss Light Source, which provide extremely bright and short X-ray pulses. The catalyst is immersed in a dense octane solution, but by taking the perspective of the metal, we could specifically pick the one C-H bond out of hundreds of thousands which is made to break,” explains Raphael Jay, Researcher at Uppsala University and lead experimentalist of the study.

    To interpret the complex experimental data, theoreticians from Uppsala University and Stockholm University teamed up and performed advanced quantum-chemical calculations.

    “Our calculations allow us to clearly identify how electronic charge flows between the metal catalyst and the C-H group in just the right proportion. We can see how charge flowing from the metal onto the C-H bond glues the two chemical groups together. Charge flowing in the opposite direction instead acts as a scissor that eventually breaks the C and the H atom apart,” explains Ambar Banerjee, Postdoctoral researcher at Uppsala University and lead theoretician of the study.

    The study solves a forty-year-old mystery about how an activated catalyst can actually break strong C-H bonds by carefully exchanging fractions of electrons and without the need for huge temperatures or pressures. With their new tool to hand, the researchers next want to learn how to direct the flow of electrons to help develop better catalysts for the chemical industry in order to make something useful out of methane and other alkanes.

    Facts

    The study builds on the pioneering work of grandfather, father and son Manne, Kai, and Per Siegbahn.

    Manne Siegbahn (Uppsala University), who received the Nobel Prize in Physics in 1924, pioneered how different elements can be distinguished by X-rays.

    Kai Siegbahn (Uppsala University), who received the Nobel Prize in Physics in 1981, pioneered how different chemical environments of the same element can be distinguished by X-rays.

    Per Siegbahn (Stockholm University) theoretically predicted the concerted exchange of electronic charge required for breaking a C-H bond.

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    Uppsala University

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  • Semiconductor quantum dots create dream material

    Semiconductor quantum dots create dream material

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    Newswise — Researchers from the RIKEN Center for Emergent Matter Science and collaborators have succeeded in creating a “superlattice” of semiconductor quantum dots that can behave like a metal, potentially imparting exciting new properties to this popular class of materials.

    Semiconducting colloidal quantum dots have garnered tremendous research interest due to their special optical properties, which arise from the quantum confinement effect. They are used in solar cells, where they can improve the efficiency of energy conversion, biological imaging, where they can be used as fluorescent probes, electronic displays, and even quantum computing, where their ability to trap and manipulate individual electrons can be exploited.

    However, getting semiconductor quantum dots to efficiently conduct electricity has been a major challenge, impeding their full use. This is primarily due to their lack of orientational order in assemblies. According to Satria Zulkarnaen Bisri, lead researcher on the project, who carried out the research at RIKEN and is now at the Tokyo University of Agriculture and Technology, “making them metallic would enable, for example, quantum dot displays that are brighter yet use less energy than current devices.”

    Now, the group has published a study in Nature Communications that could make a major contribution to reaching that goal. The group, led by Bisri and Yoshihiro Iwasa of RIKEN CEMS, has created a superlattice of lead sulfide semiconducting colloidal quantum dots that displays the electrical conducting properties of a metal.

    The key to achieving this was to get the individual quantum dots in the lattice to attach to one another directly, “epitaxially,” without ligands, and to do this with their facets oriented in a precise way.

    The researchers tested the conductivity of the material they created, and as they increased the carrier density using a electric-double-layer transistor, they found that at a certain point it became one million times more conductive than what is currently available from quantum dot displays. Importantly, the quantum confinement of the individual quantum dots was still maintained, meaning that they don’t lose their functionality despite the high conductivity.

    “Semiconductor quantum dots have always shown promise for their optical properties, but their electronic mobility has been a challenge,” says Iwasa. “Our research has demonstrated that precise orientation control of the quantum dots in the assembly can lead to high electronic mobility and metallic behavior. This breakthrough could open up new avenues for using semiconductor quantum dots in emerging technologies.”

    According to Bisri, “We plan to carry out further studies with this class of materials, and believe it could lead to vast improvements in the capabilities of quantum dot superlattices. In addition to improving current devices, it could lead to new applications such as true all-QD direct electroluminescence devices, electrically driven lasers, thermoelectric devices, and highly sensitive detectors and sensors, which previously were beyond the scope of quantum dot materials.”

    In addition to RIKEN, the team included researchers from Tokyo Institute of Technology, the University of Tokyo, SPring-8, and the Tokyo University of Agriculture and Technology.

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  • Quantum-Enhanced Microscope Doubles Resolution

    Quantum-Enhanced Microscope Doubles Resolution

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    Newswise — Using a “spooky” phenomenon of quantum physics, Caltech researchers have discovered a way to double the resolution of light microscopes.

    In a paper appearing in the journal Nature Communications, a team led by Lihong Wang, Bren Professor of Medical Engineering and Electrical Engineering, shows the achievement of a leap forward in microscopy through what is known as quantum entanglement. Quantum entanglement is a phenomenon in which two particles are linked such that the state of one particle is tied to the state of the other particle regardless of whether the particles are anywhere near each other. Albert Einstein famously referred to quantum entanglement as “spooky action at a distance” because it could not be explained by his relativity theory.

    According to quantum theory, any type of particle can be entangled. In the case of Wang’s new microscopy technique, dubbed quantum microscopy by coincidence (QMC), the entangled particles are photons. Collectively, two entangled photons are known as a biphoton, and, importantly for Wang’s microscopy, they behave in some ways as a single particle that has double the momentum of a single photon.

    Since quantum mechanics says that all particles are also waves, and that the wavelength of a wave is inversely related to the momentum of the particle, particles with larger momenta have smaller wavelengths. So, because a biphoton has double the momentum of a photon, its wavelength is half that of the individual photons.

    This is key to how QMC works. A microscope can only image the features of an object whose minimum size is half the wavelength of light used by the microscope. Reducing the wavelength of that light means the microscope can see even smaller things, which results in increased resolution.

    Quantum entanglement is not the only way to reduce the wavelength of light being used in a microscope. Green light has a shorter wavelength than red light, for example, and purple light has a shorter wavelength than green light. But due to another quirk of quantum physics, light with shorter wavelengths carries more energy. So, once you get down to light with a wavelength small enough to image tiny things, the light carries so much energy that it will damage the items being imaged, especially living things such as cells. This is why ultraviolet (UV) light, which has a very short wavelength, gives you a sunburn.

    QMC gets around this limit by using biphotons that carry the lower energy of longer-wavelength photons while having the shorter wavelength of higher-energy photons.

    “Cells don’t like UV light,” Wang says. “But if we can use 400-nanometer light to image the cell and achieve the effect of 200-nm light, which is UV, the cells will be happy, and we’re getting the resolution of UV.”

    To achieve that, Wang’s team built an optical apparatus that shines laser light into a special kind of crystal that converts some of the photons passing through it into biphotons. Even using this special crystal, the conversion is very rare and occurs in about one in a million photons. Using a series of mirrors, lenses, and prisms, each biphoton—which actually consists of two discrete photons—is split up and shuttled along two paths, so that one of the paired photons passes through the object being imaged and the other does not. The photon passing through the object is called the signal photon, and the one that does not is called the idler photon. These photons then continue along through more optics until they reach a detector connected to a computer that builds an image of the cell based on the information carried by the signal photon. Amazingly, the paired photons remain entangled as a biphoton behaving at half the wavelength despite the presence of the object and their separate pathways.

    Wang’s lab was not the first to work on this kind of biphoton imaging, but it was the first to create a viable system using the concept. “We developed what we believe a rigorous theory as well as a faster and more accurate entanglement-measurement method.  We reached microscopic resolution and imaged cells.”

    While there is no theoretical limit to the number of photons that can be entangled with each other, each additional photon would further increase the momentum of the resulting multiphoton while further decreasing its wavelength.

    Wang says future research could enable entanglement of even more photons, although he notes that each extra photon further reduces the probability of a successful entanglement, which, as mentioned above, is already as low as a one-in-a-million chance.

    The paper describing the work, “Quantum Microscopy of Cells at the Heisenberg Limit,” appears in the April 28 issue of Nature Communications. Co-authors are Zhe He and Yide Zhang, both postdoctoral scholar research associates in medical engineering; medical engineering graduate student Xin Tong (MS ’21); and Lei Li (PhD ’19), formerly a medical engineering postdoctoral scholar and now an assistant professor of electrical and computer engineering at Rice University.

    Funding for the research was provided by the Chan Zuckerberg Initiative and the National Institutes of Health.

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    California Institute of Technology

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  • First-ever measurement of a quantum paradoxical phenomenon

    First-ever measurement of a quantum paradoxical phenomenon

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    Newswise — Some things are related, others are not. Suppose you randomly select a person from a crowd who is significantly taller than the average. In that case, there is a good chance that they will also weigh more than the average. Statistically, one quantity also contains some information about the other.

    Quantum physics allows for even stronger links between different quantities: different particles or parts of an extensive quantum system can “share” a certain amount of information. There are curious theoretical predictions about this: surprisingly, the measure of this “mutual information” does not depend on the size of the system but only on its surface. This surprising result has been confirmed experimentally at the TU Wien and published in Nature Physics. Theoretical input to the experiment and its interpretation came from the Max-Planck-Institut für Quantenoptik in Garching, FU Berlin, ETH Zürich and  New York University.

    Quantum information: More strongly connected than classical physics allows

    “Let’s imagine a gas container in which small particles fly around and behave in a very classical way like small spheres,” says Mohammadamin Tajik of the Vienna Center for Quantum Science and Technology (VCQ) – Atominstitut of TU Wien, first author of the current publication. “If the system is in equilibrium, then particles in different areas of the container know nothing about each other. One can consider them completely independent of each other. Therefore, one can say that the mutual information these two particles share is zero.”

    In the quantum world, however, things are different: If particles behave quantumly, then it may happen that you can no longer consider them independently of each other. They are mathematically connected – you can’t meaningfully describe one particle without saying something about the other.

    “For such cases, there has long been a prediction about the mutual information shared between different subsystems of a many-body quantum system,” explains Mohammadamin Tajik. “In such a quantum gas, the shared mutual information is larger than zero, and it does not depend on the size of the subsystems – but only on the outer bounding surface of the subsystem.”

    This prediction seems intuitively strange: In the classical world, it is different. For example, the information contained in a book depends on its volume – not merely on the area of the book’s cover. In the quantum world, however, information is often closely linked to surface area.

    Measurements with ultracold atoms

    An international research team led by Prof. Jörg Schmiedmayer has now confirmed for the first time that the mutual information in a many body quantum system scales with the surface area rather than with the volume. For this purpose, they studied a cloud of ultracold atoms. The particles were cooled to just above absolute zero temperature and held in place by an atom chip. At extremely low temperatures, the quantum properties of the particles become increasingly important. The information spreads out more and more in the system, and the connection between the individual parts of the overall system becomes more and more significant. In this case, the system can be described with a quantum field theory. 

    “The experiment is very challenging,” says Jörg Schmiedmayer. “We need complete information about our quantum system, as best as quantum physics allows. For this, we have developed a special tomography technique. We get the information we need by perturbing the atoms just a bit and then observing the resulting dynamics. It’s like throwing a rock into a pond and then getting information about the state of the liquid and the pond from the consequent waves.”

    As long as the system’s temperature does not reach absolute zero (which is impossible), this “shared information” has a limited range. In quantum physics, this is related to the  “coherence length” – it indicates the distance to which particles quantumly behave similar, and thereby know from each other. “This also explains why shared information doesn’t matter in a classical gas,” says Mohammadamin Tajik. “In a classical many-body system, coherence disappears; you can say the particles no longer know anything about their neighboring particles.” The effect of temperature and coherence length on mutual information was also confirmed in the experiment.

    Quantum information plays an essential role in many technical applications of quantum physics today. Thus, the experiment results are relevant to various research areas – from solid-state physics to the quantum physical study of gravity.

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    Vienna University of Technology

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  • Signs of Gluon Saturation Emerge from Particle Collisions

    Signs of Gluon Saturation Emerge from Particle Collisions

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    The Science

    Nuclear physicists collide protons with heavier ions (atomic nuclei) to explore the fundamental constituents that make up those ions. By tracking particles that stream out of the collisions, they can zoom in beyond the ions’ protons and neutrons to study those particles’ innermost building blocks—quarks and gluons. Recent results revealed a suppression of certain back-to-back pairs of particles that emerge from interactions of single quarks from the proton with single gluons in the heavier ion. The suppression was greatest in collisions with the heaviest nuclei. The results suggest that gluons in heavy nuclei recombine, as predicted by the theory of the strong force, quantum chromodynamics.

    The Impact

    Previous experiments have shown that when ions are accelerated to high energies, gluons split to multiply to very high numbers. But scientists suspect that gluon multiplication can’t go on forever. Instead, in nuclei moving close to the speed of light, where relativistic motion flattens the nuclei into speeding gluon “pancakes,” overlapping gluons should start to recombine. Seeing evidence of recombination would be a step toward proving that gluons reach a postulated steady state called saturation, where gluon splitting and recombination balance out. The new results match with theoretical models postulating this saturated state.

    Summary

    To search for signs of gluon recombination, scientists with the STAR Collaboration used the STAR detector at the Relativistic Heavy Ion Collider, a Department of Energy Office of Science user facility. They were looking for a telltale signal produced in collisions of protons with a range of ions when a single quark from the proton interacts with an individual gluon in the ion. That signal is a pair of neutral pions striking a forward detector at back-to-back angles. If gluons in the nuclei recombine, scientists would expect to see a suppression in this back-to-back signal because fewer gluons would be available for the quark-gluon interactions. They looked for the signal in collisions of protons with different sized ions.

    Theorists had predicted that gluon recombination would be more prominent the larger the ion. That’s because heavy ions (nuclei) have more quark-and-gluon-containing protons and neutrons. When accelerated to near the speed of light, these ions flatten out, making the abundant gluons overlap and more likely to merge. Bigger nuclei with more gluons, should mean more merging and more suppression in the signal. That’s exactly what the scientists found. The results provide evidence that gluons recombine—and a strong suggestion that gluon splitting and recombination could produce the predicted saturated state.

     

    Funding

    This research was funded by the Department of Energy Office of Science, Nuclear Physics program, the National Science Foundation, and a range of international agencies listed in the published paper.

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    Department of Energy, Office of Science

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  • “Y-Ball” Compound Yields Quantum Secrets

    “Y-Ball” Compound Yields Quantum Secrets

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    BYLINE: Kitta MacPherson

    Newswise — Scientists investigating a compound called “Y-ball” – which belongs to a mysterious class of “strange metals” viewed as centrally important to next-generation quantum materials – have found new ways to probe and understand its behavior.

    The results of the experiments, aided by the insights of theoretical physicists at Rutgers, could play a role in the development of revolutionary technologies and devices.

    “It’s likely that that quantum materials will drive the next generation of technology and that strange metals will be part of that story,” said Piers Coleman, a Distinguished Professor at the Rutgers Center for Materials Theory in the Department of Physics and Astronomy at the Rutgers School of Arts and Sciences and one of the theoreticians involved in the study. “We know that strange metals like Y-ball exhibit properties that need to be understood to develop these future applications. We’re pretty sure that understanding this strange metal will give us new ideas and will help us design and discover new materials.”

    Reporting in the journal Science, an international team of researchers from Rutgers, the University of Hyogo and the University of Tokyo in Japan, the University of Cincinnati and Johns Hopkins University described details of electron motion that provide new insight into the unusual electrical properties of Y-ball. The material, technically known as the compound YbAlB4, contains the elements ytterbium, aluminum and boron. It was nicknamed “Y-ball” by the late Elihu Abrahams, founding director of the Rutgers Center for Materials Theory.

    The experiment revealed unusual fluctuations in the strange metal’s electrical charge. The work is groundbreaking, the researchers said, because of the novel way the experimenters examined Y-ball, firing gamma rays at it using a synchrotron, a type of particle accelerator.

    The Rutgers team – including Coleman, fellow physics professor Premala Chandra and former postdoctoral fellow Yashar Komijani (now an assistant professor at the University of Cincinnati) – have spent years exploring the mysteries of strange metals. They do so through the framework of quantum mechanics, the physical laws governing the realm of the ultra-small, home of the building blocks of nature such as electrons.

    Analyzing the material using a technique known as Mossbauer spectroscopy, the scientists probed Y-ball with gamma rays, measuring the rate at which the strange metal’s electrical charge fluctuates. In a conventional metal, as they move, electrons hop in and out of the atoms, causing their electrical charge to fluctuate, but at a rate that is thousands of times too fast to be seen by Mossbauer spectroscopy. In this case, the change happened in a nanosecond, a billionth of a second.

    “In the quantum world, a nanosecond is an eternity,” said Komijani. “For a long time, we have been wondering why these fluctuations are actually so slow.” “We reasoned,” continued Chandra, “that each time an electron hops into an ytterbium atom, it stays there long enough to attract the surrounding atoms, causing them to move in and out. This synchronized dance of the electrons and atoms slows the whole process so that it can be seen by the Mossbauer.”

    They moved to the next step. “We asked the experimentalists to look for these vibrations,” said Komijani, “and to our delight, they detected them.”

    Coleman explained that when an electrical current flows through conventional metals, such as copper, random atomic motion scatters the electrons causing friction called resistance. As the temperature is raised, the resistance increases in a complex fashion and at some point it reaches a plateau.

    In strange metals such as Y-ball, however, resistance increases linearly with temperature, a much simpler behavior. In addition, further contributing to their “strangeness,” when Y-ball and other strange metals are cooled to low temperatures, they often become superconductors, exhibiting no resistance at all.

    The materials with the highest superconducting temperatures fall into this strange family. These metals are thus very important because they provide the canvas for new forms of electronic matter – especially exotic and high temperature superconductivity. 

    Superconducting materials are expected to be central to the next generation of quantum technologies because, in eliminating all electrical resistance, they allow an electric current to flow in a quantum mechanically synchronized fashion.  The researchers see their work as opening a door to future, perhaps unimaginable possibilities.

     “In the 19th century, when people were trying to figure out electricity and magnetism, they couldn’t have imagined the next century, which was entirely driven by that understanding,” Coleman said. “And so, it’s also true today, that when we use the vague phrase ‘quantum materials,’ we can’t really envisage how it will transform the lives of our grandchildren.”

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    Rutgers University-New Brunswick

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