Frontiers of Physics最新文献

As an intrinsic magnetic topological insulator with magnetic order and non-trivial topological structure, MnBi₂Te₄ is an ideal material for studying exotic topological states such as quantum anomalous Hall effect and topological axion insulating states. Here, we carry out magnetic and electrical transport measurements on (Mn_1−xGe_x)Bi₂Te₄ (x = 0, 0.15, 0.30, 0.45, 0.60, and 0.75) single crystals. It is found that with increasing x, the dilution of magnetic moments gradually weakens the antiferromagnetic exchange interaction. Moreover, Ge doping reduces the critical field of ferromagnetic ordering, which may provide a possible way to implement the quantum anomalous Hall effect at lower magnetic field. Electrical transport measurements suggest that electrons are the dominant charge carriers, and the carrier density increases with the Ge doping ratio. Additionally, the Kondo effect is observed in the samples with x = 0.45, 0.60, and 0.75. Our results suggest that doping germanium is a viable way to tune the magnetic and electrical transport properties of MnBi₂Te₄, opening up the possibility of future applications in magnetic topological insulators.

Advancements in the experimental toolbox of cold atoms have enabled the meticulous control of atomic Bloch oscillation (BO) within optical lattices, thereby enhancing the capabilities of gravity interferometers. This work delves into the impact of thermal effects on Bloch oscillation in 1D accelerated optical lattices aligned with gravity by varying the system’s initial temperature. Through the application of Raman cooling, we effectively reduce the longitudinal thermal effect, stabilizing the longitudinal coherence length over the timescale of its lifetime. The atomic losses over multiple Bloch periods are measured, which are primarily attributed to transverse excitation. Furthermore, we identify two distinct inverse scaling behaviors in the oscillation lifetime scaled by the corresponding density with respect to temperatures, implying diverse equilibrium processes within or outside the Bose–Einstein condensate (BEC) regime. The competition between the system’s coherence and atomic density leads to a relatively smooth variation in the actual lifetime versus temperature. Our findings provide valuable insights into the interaction between thermal effects and BO, offering avenues for the refinement of quantum measurement technologies.

A unique feature of non-Hermitian systems is the extreme sensitivity of the eigenspectrum to boundary conditions with the emergence of the non-Hermitian skin effect (NHSE). A NHSE originates from the point-gap topology of complex eigenspectrum, where an extensive number of eigen-states are anomalously localized at the boundary driven by nonreciprocal dissipation. Two different approaches to create localization are disorder and flat-band spectrum, and their interplay can lead to the anomalous inverse Anderson localization, where the Bernoulli anti-symmetric disorder induces mobility in a full-flat band system in the presence of Aharonov–Bohm (AB) Cage. In this work, we study the localization–delocalization transitions due to the interplay of the point-gap topology, flat band and correlated disorder in the one-dimensional rhombic lattice, where both its Hermitian and non-Hermitian structures show AB cage in the presence of magnetic flux. Although it remains the coexistence of localization and delocalization for the Hermitian rhombic lattice in the presence of the random anti-symmetric disorder, it surprisingly becomes complete delocalization, accompanied by the emergence of NHSE. To further study the effects from the Bernoulli anti-symmetric disorder, we found the similar NHSE due to the interplay of the point-gap topology, correlated disorder and flat bands. Our anomalous localization–delocalization property can be experimentally tested in the classical physical platform, such as electrical circuit.

The van der Waals interface structures and behaviors are of great importance in determining the physical properties of two-dimensional atomic crystals and their heterostructures. The delicate interfacial properties are sensitively dependent on the mechanical behaviors of atomically thin films under external strain. Here, we investigated the strain-engineered rippling structures at the CVD-grown bilayer-MoS₂ interface with advanced atomic force microscopy (AFM). The in-plane compressive strain is sequentially introduced into the 1L-substrate and 2L-1L interface of bilayer-MoS₂ flakes via a fast-cooling process. The thermal strain-engineered rippling structures were directly visualized at the central 2H- and 3R-MoS₂ bilayer regions with friction force microscopy (FFM) and bimodal AFM techniques. These rippling structures can be further artificially manipulated into the beating-like rippling features and fully erased via the contact mode AFM scanning. Our results shed lights on the strain-engineered interfacial structures of two-dimensional materials and also inspire the further investigation on the interface engineering of their electronic and optical properties.

While the common practice of decomposing general quantum algorithms into a collection of single- and two-qubit gates is conceptually simple, in many cases it is possible to have more efficient solutions where quantum gates engaging multiple qubits are used. In the noisy intermediate-scale quantum (NISQ) era where a universal error correction is still unavailable, this strategy is particularly appealing since it can significantly reduce the computational resources required for executing quantum algorithms. In this work, we experimentally investigate a three-qubit Controlled-CPHASE-SWAP (CCZS) gate on superconducting quantum circuits. By exploiting the higher energy levels of superconducting qubits, we are able to realize a Fredkin-like CCZS gate with a duration of 40 ns, which is comparable to typical single- and two-qubit gates realized on the same platform. By performing quantum process tomography for the two target qubits, we obtain a process fidelity of 86.0% and 81.1% for the control qubit being prepared in ∣0〉 and ∣1〉, respectively. We also show that our scheme can be readily extended to realize a general CCZS gate with an arbitrary swap angle. The results reported here provide valuable additions to the toolbox for achieving large-scale hardware-efficient quantum circuits.

Based on the AdS/CFT correspondence, this study employs an oscillating Gaussian source to numerically study the holographic images of an AdS black hole under f(R) gravity using wave optics. Due to the diffraction of scalar wave, it turns out that one can clearly observed the interference patten of the absolute amplitude of response function on the AdS boundary. Furthermore, it is observed that its peak increases with the f(R) parameter α but decreases with the global monopole η, frequency ω, and horizon r_h. More importantly, the results reveal that the holographic Einstein ring is a series of concentric striped patterns for an observer at the North Pole and that their center is analogous to a Poisson–Arago spot. This ring can evolve into a luminosity-deformed ring or two light spots when the observer is at a different position. According to geometrical optics, it is true that the size of the brightest holographic ring is approximately equal to that of the photon sphere, and the two light spots correspond to clockwise and anticlockwise light rays. In addition, holographic images for different values of black holes and optical system parameters were obtained, and different features emerged. Finally, we conclude that the holographic rings of the AdS black hole in modified gravities are more suitable and helpful for testing the existence of a gravity dual for a given material.

Some aspects of atom-field interactions in curved spacetime are reviewed. Of great interest are quantum radiative and entanglement processes arising out of Rindler and black hole spacetimes, which involve the role of Hawking–Unruh and dynamical Casimir effects. Most of the discussion surrounds the radiative part of interactions. For this, we specifically reassess the conventional understandings of atomic radiative transitions and energy level shifts in curved spacetime. We also briefly outline the status quo of entanglement dynamics study in curved spacetime, and highlight literature related to some novel insights, like entanglement harvesting. On one hand, the study of the role played by spacetime curvature in quantum radiative and informational phenomena has implications for fundamental physics, notably the gravity-quantum interface. In particular, one examines the viability of the Equivalence Principle, which is at the heart of Einstein’s general theory of relativity. On the other hand, it can be instructive for manipulating quantum information and light propagation in arbitrary geometries. Some issues related to nonthermal effects of acceleration are also discussed.

The spectral form factor (SFF) can probe the eigenvalue statistic at different energy scales as its time variable varies. In closed quantum chaotic systems, the SFF exhibits a universal dip-ramp-plateau behavior, which reflects the spectrum rigidity of the Hamiltonian. In this work, we explore the general properties of SFF in open quantum systems. We find that in open systems the SFF first decays exponentially, followed by a linear increase at some intermediate time scale, and finally decreases to a saturated plateau value. We derive general relations between (i) the early-time decay exponent and Lindblad operators; (ii) the long-time plateau value and the number of steady states. We also explain the effective field theory perspective of general behaviors. We verify our theoretical predictions by numerically simulating the Sachdev–Ye–Kitaev (SYK) model, random matrix theory (RMT), and the Bose–Hubbard model.