Physicists propose Bell test for probing quantum entanglement

Phys.org  November 4, 2024 Attosecond physics enables the study of ultrafast coherent electron dynamics in matter upon photoexcitation and photoionization where there has been a strong focus on probing the physical manifestations of internal quantum coherence within the individual parent ion and photoelectron systems. An international team of researchers (UK, Germany) designed theoretically and modelled numerically a direct probe of quantum entanglement in attosecond photoionization in the form of a Bell test and paved the way for the direct observation of entanglement in the context of ultrafast photoionization of many-electron systems. According to the researchers their work provides a novel […]

Quantum simulator could help uncover materials for high-performance electronics

Phys.org  October 30, 2024 Arrays of coupled superconducting qubits natively emulate the dynamics of interacting particles according to the Bose–Hubbard model. However, many interesting condensed-matter phenomena emerge only in the presence of electromagnetic fields. A team of researchers in the US (MIT, MIT Lincoln Laboratory) emulated the dynamics of charged particles in an electromagnetic field using a superconducting quantum simulator. They produced a broadly adjustable synthetic magnetic vector potential by applying continuous modulation tones to all qubits. The synthetic vector potential obeyed the required properties of electromagnetism… read more. TECHNICAL ARTICLE

Proof-of-concept design shrinks quantum rotation sensor to micron scale

Phys.org  October 1, 2024 A team of researchers in the US (University of Michigan, DEVCOM Army Research Laboratory) investigated the possible realization of an ultracold-atom rotation sensor that was based on recently proposed tractor atom interferometry (TAI). They described an experimental design that included the generation of a Laguerre–Gaussian-beam-based “pinwheel” optical lattice and multi-loop interferometric cycles. Numerical simulations of the proposed system demonstrated TAI rotation sensitivity comparable to that of contemporary matter-wave interferometers. They applied quantum optimal control to devise a methodology suitable to address nonadiabaticity which might hinder systems performance. According to the researchers their studies are of interest […]

Quantum researchers cause controlled ‘wobble’ in the nucleus of a single atom

Phys.org  September 12, 2024 The nuclear spin presents opportunities for quantum experiments with prolonged coherence times. Electron spin resonance (ESR) combined with scanning tunnelling microscopy (STM) provides a bottom-up platform to study the fundamental properties of nuclear spins of single atoms on a surface. However, access to the time evolution of nuclear spins remained a challenge. An international team of researchers (The Netherlands, Germany) developed an experiment resolving the nanosecond coherent dynamics of a hyperfine-driven flip-flop interaction between the spin of an individual nucleus and that of an orbiting electron. They used the unique local controllability of the magnetic field […]

Theoretical research holds promise for advancing modular quantum information processing

Phys.org  August 15, 2024 As quantum information processing systems are scaled to many qubits to reach their full potential, highly complex electronics are needed to control the complex circuitry. A team of researchers in the US (University of Rhode Island, University of Maryland, NIST, UCLA) considered a pair of quantum dot-based spin qubits that interact via microwave photons in a superconducting cavity and parametrically driven by separate external electric fields. For this system, they formulated a model for spin qubit entanglement in the presence of mutually off-resonant qubit and cavity frequencies. They showed that the sidebands generated via the driving […]

Study unveils limits on the extent to which quantum errors can be ‘undone’ in large systems

Phys.org  August 11, 2024 Recently quantum error mitigation has been successfully applied to reduce noise in near-term applications. However, an international team of researchers (Germany, USA – Harvard University, France) identified strong limitations to the degree to which quantum noise can be effectively ‘undone’ for larger system sizes. They developed a framework which rigorously captures large classes of error-mitigation schemes in use today. By relating error mitigation to a statistical inference problem, they showed that even at shallow circuit depths comparable to those of current experiments, a superpolynomial number of samples was needed in the worst case to estimate the […]

New method achieves tenfold increase in quantum coherence time via destructive interference of correlated noise

Phys.org  July 10, 2024 Decoherence and imperfect control are crucial challenges for quantum technologies. Common protection strategies rely on noise temporal autocorrelation, which is not optimal if other correlations are present. An international team of researchers (Israel, Germany, USA – Caltech, industry) developed and experimentally demonstrated a strategy that used the cross-correlation of two noise sources. Utilizing destructive interference of cross-correlated noise extended the coherence time tenfold, improved control fidelity, and surpassed the state-of-the-art sensitivity for high frequency quantum sensing, significantly expanding the applicability of noise protection strategies… read more. Open Access TECHNICAL ARTICLE

Novel 2D device for quantum cooling converts heat to voltage at ultra-low temperatures

Phys.org  July 5, 2024 Nernst effect has potential for energy conversion achieving high performance and versatility at low temperatures. However, achieving high performance and versatility at low temperatures remains elusive. An international team of researchers (Switzerland, Japan) demonstrated a large and electrically tunable Nernst effect by combining the electrical properties of graphene with the semiconducting characteristics of indium selenide in a field-effect geometry. Photovoltage measurements revealed a stronger photo-Nernst signal in the graphene/indium selenide heterostructure compared with individual components. They observed a record-high Nernst coefficient at ultralow temperatures and low magnetic fields, an important step towards applications in quantum information […]

An alternative way to manipulate quantum states

EurekAlert  July 2, 2024 Control over quantum systems is typically achieved by time-dependent electric or magnetic fields. Alternatively, electronic spins can be controlled by spin-polarized currents. Researchers in Switzerland demonstrated coherent driving of a single spin by a radiofrequency spin-polarized current injected from the tip of a scanning tunneling microscope into an organic molecule. With the excitation of electron paramagnetic resonance, they established dynamic control of single spins by spin torque using a local electric current. Their work highlighted the dissipative action of the spin-transfer torque, in contrast to the nondissipative action of the magnetic field, which allowed for the […]

Understanding quantum states: New research shows importance of precise topography in solid neon qubits

Phys.org  June 26, 2024 Single electrons trapped on solid-neon surfaces, which have long coherence times, are promising platform for charge qubits. The actual quantum states of the trapped electrons have not been understood. A team of researchers in the USA (National High Magnetic Field Laboratory (Florida), Florida State University, University of Florida, FAMU-FSU College of Engineering) examined the electron’s interactions with neon surface topography and by evaluating the surface charges induced by the electron, they demonstrated its strong perpendicular binding to the neon surface. They revealed that surface bumps could bind an electron, forming unique quantum ring states that aligned […]