Phys.org December 19, 2024 For quantum computers the property called “magic” is critical. An international team of researchers (UK, Australia) considered the property of magic, which distinguished the quantum states leading to a genuine computational advantage over classical states when used in algorithms. They examined top-antitop pair production at the LHC produced magic tops, where the amount of magic varied with the kinematics of the final state. They compared results for individual partonic channels and at proton level. They showed that averaging over final states typically increased magic which contrasted with entanglement measures, such as the concurrence, which typically decreased. […]
Category Archives: Quantum science
Scientists observe ‘negative time’ in quantum experiments
Phys.org December 21, 2024 When a pulse of light traverses a material, it incurs group delay. Should the group delay experienced by photons be attributed to the time they spend as atomic excitations? However reasonable this connection may seem, it appears problematic when the frequency of the light is close to the atomic resonance, as the group delay becomes negative in this regime. An international team of researchers (Canada, Australia) used the cross-Kerr effect to probe the degree of atomic excitation caused by a resonant transmitted photon, by measuring the phase shift on a separate beam that was weak and […]
A connection between quantum theory and information theory proved
EurekAlert December 6, 2024 Wave-particle duality is one of the most notable and counterintuitive features of quantum mechanics, illustrating that two incompatible observables cannot be measured simultaneously with arbitrary precision. An international team of researchers (Sweden, Chile, Poland) experimentally demonstrated the equivalence of wave particle duality and entropic uncertainty relations using orbital angular momentum states of light. Their experiment used a reconfigurable platform composed of a few-mode optical results providing fundamental insights into the complementary principle from an informational perspective, with implications for the broader field of quantum technologies… read more. Open Access TECHNICAL ARTICLE
Particle that only has mass when moving in one direction observed for first time
Phys.org December 10, 2024 In two dimensions, a peculiar class of fermions that are massless in one direction and massive in the perpendicular direction was predicted 16 years ago. The semi-Dirac fermions remain undetected. An international team of researchers (USA – Columbia University, Pennsylvania State University, Florida State University, National High Magnetic Field Laboratory, Harvard University, Temple University, Princeton University, Flatiron Institute, the Netherlands, Spain) demonstrated the defining feature of semi-Dirac fermions in a prototypical nodal-line metal ZrSiS. Their nodal lines extended the band degeneracies from isolated points to lines, loops, or even chains in the momentum space. They pinpointed […]
Researchers demonstrate universal control of a quantum dot-based system with four singlet-triplet qubits
Phys.org November 13, 2024 The coherent control of interacting spins in semiconductor quantum dots is of interest for quantum information processing and studying quantum magnetism from the bottom up. Researchers in the Netherlands demonstrated a 2 × 4 germanium quantum dot array with full and controllable interactions between nearest-neighbour spins. As a demonstration of the level of control, they defined four singlet–triplet qubits in this system and showed two-axis single-qubit control of each qubit and SWAP-style two-qubit gates between all neighbouring qubit pairs, yielding average single-qubit gate and Bell state fidelities. Combining these operations, they implemented a circuit designed to generate and […]
Scientists capture images of a new quantum phase in electron molecular crystals
Phys.org November 17, 2024 Semiconductor Moiré superlattices provide a versatile platform to engineer quantum solids composed of artificial atoms on moiré sites. Previous studies have mostly focused on the simplest correlated quantum solid—the Fermi-Hubbard model—in which intra-atom interactions are simplified to a single onsite repulsion energy. An international team of researchers (USA – UC Berkeley, Lawrence Berkeley National Laboratory, MIT, University of Arizona, Japan) experimentally observed Wigner molecular crystals emerging from multielectron artificial atoms in twisted bilayer tungsten disulfide moiré superlattices. Using scanning tunneling microscopy, they demonstrated that Wigner molecules appeared in multielectron artificial atoms when Coulomb interactions dominated. The […]
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 […]