Physical review letters最新文献

Nonstabilizerness, also known as "magic," quantifies the deviation of quantum states from stabilizer states, capturing the complexity necessary for quantum computational advantage. In this Letter, we investigate the dynamics of nonstabilizerness in disordered many-body localized (MBL) systems using the stabilizer Rényi entropy (SRE). Leveraging a phenomenological description based on the ℓ-bit model, we analytically and numerically demonstrate that interactions profoundly influence nonstabilizerness spreading, inducing a power-law growth of SRE that markedly contrasts with the rapid saturation observed in ergodic systems. We validate our theoretical predictions through numerical simulations of the disordered transverse-field Ising model, showing excellent agreement across various disorder strengths, system sizes, and initial states. Additionally, we uncover a universal relationship between SRE and entanglement entropy, revealing their common scaling in the MBL regime independent of disorder strength and system size. Our results offer critical insights into the interplay of disorder, interactions, and complexity in quantum many-body systems.

Edge states reflect the key physical properties yet are difficult to probe individually, particularly when several states are present at an edge. We present momentum resolved tunneling spectroscopy between a quantum well and a quantum wire to extract the dispersions of the quantum Hall edge states. Momentum and energy selective tunneling allows for separately addressing the different states even if they are spatially overlapping. This delivers the edge state velocities over broad ranges of magnetic field and density, in excellent agreement with a hard wall model. This technique provides a basis for future edge state selective spectroscopy on quantum materials.

We propose Josephson junction arrays as realistic platforms for observing nonequilibrium scaling laws characterizing the Kardar-Parisi-Zhang (KPZ) universality class, and space-time soliton proliferation. Focusing on a two-chain ladder geometry, we perform numerical simulations for the roughness function. Together with analytical arguments, our results predict KPZ scaling at intermediate time scales, extending over sufficiently long timescales to be observable, followed by a crossover to the asymptotic longtime regime governed by soliton proliferation.

High-resolution array detectors are widely used in single-particle tracking, but their performance is limited by excess noise from background light and dark current. As pixel resolution increases, the diminished signal per pixel exacerbates susceptibility to noise, degrading tracking accuracy. To overcome this limitation, we use spatial-mode demultiplexing (SPADE) as a noise-robust approach for estimating the motion characteristics of an optical pointlike source. We show that SPADE efficiently concentrate the information into a few key spatial modes, drastically reducing the number of detectors while maintaining high estimation precision. Furthermore, we enhance the robustness of the estimation against excess noise by elaborately designing the modes to be decomposed. We demonstrate, both theoretically and experimentally, that a SPADE with two specific modes outperforms direct imaging in estimating the microoscillation frequency of an optical point source in the presence of excess noise.

In this Letter, we experimentally and theoretically demonstrate an asymmetric elastic bound state in the continuum (BIC) induced by an exceptional point (EP) in an open elastic system. For positive incidence, the characteristic vanishing linewidth of a BIC is observed, whereas it is absent for negative incidence. Notably, the resulting nontrivial quasi-BIC (qBIC) exhibits perfect energy localization and extremely high quality factors (Q), while for the negative direction, most of the energy is radiated, yielding Q close to zero. By modulating the system's loss, this nontrivial qBIC mode can approximately evolve into a genuine BIC. Remarkably, the nontrivial mode can also coalesce into an EP BIC, where the energy is entirely localized within the non-Hermitian resonator system with asymmetric loss. Our Letter establishes a nontrivial connection between two seemingly unrelated concepts-BICs and EPs-and reveals a novel physical mechanism for achieving asymmetric high Q and strong energy localization, offering new opportunities for high-performance elastic-wave devices.

The energy spectrum of cosmic rays above 2.5 EeV has been measured across the declination range -90°≤δ≤+44.8° using ∼310 000 events accrued at the Pierre Auger Observatory from an exposure of (104 900±3 100)  km^{2} sr yr. No significant variations of energy spectra with declination are observed, after allowing or not for nonuniformities across the sky arising from the well-established dipolar anisotropies in the arrival directions of ultrahigh-energy cosmic rays. The instep feature in the spectrum at ≃10  EeV reported previously is now established at a significance above 5σ. Within the statistics, the energy spectra are indistinguishable across declinations so disfavoring an origin for the instep from a few distinctive sources.

We present an architecture for remotely connecting cavity-coupled trapped ions via a quantum repeater based on rare-earth-doped crystals. The main challenge for its realization lies in interfacing these two physical platforms, which produce photons with a typical temporal mismatch of one or two orders of magnitude. To address this, we propose an efficient protocol that enables custom temporal reshaping of single-photon pulses while preserving purity. Our approach is to modify a commonly used memory protocol, called atomic frequency comb, for systems exhibiting inhomogeneous broadening like rare-earth-doped crystals. Pertaining to a growing interest in hybrid quantum information systems designed to exploit the distinct advantages of diverse physical components, our results offer a viable solution for uniting quantum processing nodes with a quantum repeater backbone.

The quantum Hall effect is one of the most fundamental quantum phenomena in condensed matter physics, and via tuning the quantum Hall states (QHSs), the evolution of band topologies and electron correlations can be investigated and revealed therein. However, for the vast majority of QHS systems, even- and odd-integer quantized plateaus coexist and cannot be effectively regulated. Here, we demonstrate field-effect-tunable even-odd transition of QHSs in a fixed two-unit-cell-thick (2-uc-thick) Bi_{2}O_{2}Se film, which is unlike irreversible thickness-controlled approaches [J. Wang et al., Even-integer quantum Hall effect in an oxide caused by a hidden Rashba effect, Nat. Nanotechnol. 19, 1452 (2024)NNAABX1748-338710.1038/s41565-024-01732-z]. Only even-integer quantized plateaus are observed in the 2-uc-thick epitaxial film on SrTiO_{3} when the quantum oscillations show degenerated spin splitting under positive gate voltages. In contrast, the simultaneous emergence of even- and odd-integer QHSs is achieved under negative gate voltages, accompanied with significant spin splitting. Theoretical calculations reveal that this reversible switching stems from gate-controlled inversion symmetry breaking that modulates the splitting of Landau levels. This Letter demonstrates the significant tunability of electrostatic gating in altering inversion symmetry and modulating electron correlations in Rashba-type 2-uc-thick Bi_{2}O_{2}Se, enabling dynamic control of QHSs parity without structural changes, thereby extending the potential applications to fractional statistics and spintronics.

Quantum error correction (QEC) requires the execution of deep quantum circuits with large numbers of physical qubits to protect information against errors. Designing protocols that can reduce gate and space-time overheads of QEC is therefore crucial to enable more efficient QEC in near-term experiments. Multiqubit gates offer a natural path toward fast and low-depth stabilizer measurement circuits. However, they typically introduce high-weight correlated errors that can degrade the circuit-level distance, leading to slower scalings of the logical error probabilities. In this Letter, we show how to realize fast and efficient surface code stabilizer readout using only two singly controlled z gates acting simultaneously on two target qubits, i.e., two CZ_{2} gates-instead of four cz. We show that this scheme is fault tolerant and provide a blueprint for implementation in Rydberg atom arrays. We derive the time-optimal pulses implementing the gates and perform extensive QEC numerical simulations with Rydberg decay errors. Compared to the standard protocol using four cz gates, our scheme is faster, uses fewer gates, and crucially maintains fault tolerance with comparable logical error probabilities. Fault-tolerant generalizations of this scheme to biased and erasure-dominant noise models, as well as to other QEC codes such as quantum Low-Density Parity-Check codes, are also discussed.

We investigate the intercalation of epoxy resin into a Weyl semimetal, WTe_{2}, by using a scanning tunneling microscopy. We show that intercalant molecules have self-similar height variations with the silver-mean quasiperiodicity and also that they create phason and soliton defects to yield a mean coherence length of 15 sequential order. In addition, we unravel that weak quasiperiodic potentials imposed by the intercalation layer drive a WTe_{2} surface to have an enhanced conductance near the Fermi level while keeping its semimetal phase, providing a direct verification of theoretical prediction.