Physical review letters最新文献

This Letter introduces a unified emulation framework for studying continuum physics in finite quantum systems. Using a reduced basis method, we construct powerful emulators for the inhomogeneous Schrödinger equation that operate in a combined parameter space of complex energy (E) and other inputs (θ). Within the space, the emulators simultaneously perform analytical continuation in E-extracting continuum physics from numerically simpler bound-state-like calculations-and interpolate this entire process across θ. This yields a small, non-Hermitian system whose properties (e.g., resonances and scattering observables) can be rapidly predicted for any θ. Crucially, the complex-E emulation provides a pathway to compute continuum observables for complex systems where advanced bound-state methods exist but direct continuum calculations are yet to be developed, while the θ emulation enables rapid parameter-space exploration and can be adapted to accelerate other existing continuum calculations. Demonstrations with two- and three-body systems highlight the method's effectiveness and suggest its connection to (near-)optimal rational approximation. This Letter presents the key results, with further details reserved for a companion paper.

Quantum technologies have been widely recognized as unprecedented opportunities for ultrahigh precision metrology. As a celebrated example in modern quantum optics, the Hong-Ou-Mandel (HOM) interferometer is well known for enabling temporal resolutions on the attosecond scale. However, the relatively low Fisher information per trial in ordinary HOM measurements typically necessitates tens of thousands of repetitions to achieve such precision. Here, we propose and demonstrate a sample-half-inserted HOM (SHOM) interferometer, which enhances the Fisher information by 5 orders of magnitude in a single interference event. By introducing an asymmetric photon-sample interaction, the SHOM configuration produces a distinctive dip-bump-dip interference structure, converting what was previously viewed as an artifact into a helpful metrological resource. Experimentally, we measured the optical path difference with an average precision of 4.09 nm (13.63 as) and an average accuracy of 1.22 nm (4.07 as) using O(10^{7}) photons. Our results establish SHOM interferometry as an efficient phase-insensitive approach, not only paving the way toward practical quantum-enhanced thickness measurement for transparent materials, but also serving as an elegant strategy to improve the performance of various quantum devices.

Electron quantum optics explores coherent single-electron charge pulse propagation in electronic nanoscale circuits akin to tabletop photon setups. While past experiments focused on normal-state conductors, incorporating superconductors holds promise for exploiting the electron-hole degree of freedom in quantum sensing applications and quantum information processing. Here, we propose and analyze an on-demand and tunable mechanism for converting single-electron pulses into holes through Andreev processes on a superconductor. We develop a Floquet-Nambu scattering formalism to demonstrate the dynamic conversion of charge pulses and the controllable generation of coherent electron-hole superpositions through interferometric magnetic flux control based on the chiral edge states of a quantum Hall sample. Our discussion covers optimal conditions in realistic scenarios, affirming the feasibility of our proposal with current technology.

Interlayer excitons in semiconducting bilayers separated by insulating hexagonal boron nitride (h-BN) layers constitute a promising platform for investigation of strongly correlated bosonic phases. Here, we report an optical method for the generation and characterization of long-lived interlayer excitons. We confirm the presence of tightly bound interlayer excitons by measuring 1s and 2s intralayer excitons in each layer concurrently. Using a pump-probe technique, we find interlayer exciton lifetimes up to 8.8  μs, increasing with the thickness of the h-BN. With optical access to long-lived interlayer excitons, our approach provides a new route to explore degenerate Bose-Fermi mixtures of excitons and itinerant electrons with high spatial and temporal resolution.

Bound states in the continuum (BICs), exotic resonances with infinite lifetimes embedded in radiation continua, have long been studied for their topological robustness. Meanwhile, nodal lines-degenerate momentum-space manifolds in photonic and electronic band structures-represent another cornerstone of topological physics. Here, we unveil a profound connection between these phenomena by demonstrating that BICs act as topological chain points pinning together nodal lines within scattering-matrix eigenvalue space. Through scattering-matrix eigenphase analysis, we show that BICs enforce robust nodal chain formation in frequency-momentum space, even when system symmetries are broken. Experimentally, we validate this mechanism using a metasurface platform, where angle-resolved phase measurements reveal nodal lines intersecting at a symmetry-protected BIC. Strikingly, breaking mirror symmetry preserves the BIC-pinned nodal chain, highlighting its origin in the intrinsic singular scattering nature of BICs rather than conventional symmetry protection. This Letter establishes scattering matrices as a natural framework to unify BICs and nodal topology, offering new pathways to engineer topologically robust photonic systems resilient to perturbations. Our findings bridge fundamental concepts in topological photonics and open avenues for applications in metasurfaces and light-matter interaction control.

Elucidating the kinetics of surface reconstruction is fundamentally important yet inherently challenging due to the complex collective atomic motions occurring across high-dimensional potential-energy landscapes. Here, we combine machine-learning-based molecular dynamics simulations enhanced by well-tempered metadynamics with in situ environmental transmission electron microscopy to directly uncover the critical role of surface titanium diffusion in driving the structural evolution of the TiO_{2}(110)-(1×2) reconstruction. Under oxygen-deficient conditions, the TiO_{2}(110)-(1×2) reconstruction remains thermodynamically stable, and surface Ti migration is largely suppressed. In contrast, under oxygen-rich conditions, the surface Ti atomic rows exhibit pronounced splitting and migration, facilitated by the incorporation of additional oxygen atoms that enhance Ti mobility. Our simulations demonstrate that these oxygen-promoted processes can induce structural transformations of the TiO_{2}(110)-(1×2) reconstruction, resulting in transitions from double-row to single-row or triple-row configurations. These predictions are further validated by experimental observations. This Letter establishes a microscopic mechanism for rutile surface reconstruction kinetics and provides valuable insights for the controlled manipulation of surface structures under varying chemical environments.

We derive an exact master equation that captures the dynamics of a quadratic quantum system linearly coupled to a Gaussian environment of the same statistics: the Gaussian master equation (GME). Unlike previous approaches, our formulation applies universally to both bosonic and fermionic setups, and remains valid even in the presence of initial system-environment correlations, allowing for the exact computation of the system's reduced density matrix across all parameter regimes. Remarkably, the GME shares the same operatorial structure as the Redfield equation and depends on a single kernel: a dressed environment correlation function accounting for all virtual interactions between the system and the environment. This simple structure grants a clear physical interpretation and makes the GME easy to simulate numerically, as we show by applying it to an open system based on two fermions coupled via superconductive pairing.

Stabilizer quantum error correction (QEC) codes, in particular topological surface codes, are prime candidates to enable practical quantum computing. While it is widely believed that strictly fault-tolerant protocols can only be implemented using single- and two-qubit gates, several quantum computing platforms, including trapped ions, neutral atoms, and superconducting qubits, support native multi-qubit operations. In this Letter, we show that stabilizer measurement circuits for unrotated surface codes can be fault tolerant using single auxiliary qubits and three-qubit gates. These gates enable lower-depth circuits with fewer fault locations and potentially shorter QEC cycle times. We find that in an optimistic parameter regime where fidelities of three-qubit gates are the same as those of two-qubit gates, the logical error rate can be up to one order of magnitude lower and the threshold significantly higher, increasing from ≈0.63% to ≈0.83%. Our results, applicable to a wide range of platforms, motivate further investigation into multi-qubit gates for fault-tolerant QEC as they can offer substantial time and physical qubit resource advantages to reach a given target logical error rate.

Kinetic equilibration at late times is physically required for heavy particles in a finite temperature medium. In Fokker-Planck dynamics, it is ensured by the Einstein relation between the drag and longitudinal momentum diffusion coefficients. However, in certain gauge field theories, this relation is violated at any nonzero heavy quark velocity. Recent work in strongly coupled N=4 SYM gauge theory shows that the Kolmogorov equation for the heavy quark phase space distribution (that reduces to Fokker-Planck form upon truncating the momentum transfer probability distribution to second moments) does equilibrate even though the Fokker-Planck equation does not. Going beyond these (to date theory-specific) insights, we derive a universal equilibration condition for the kernel of the Kolmogorov equation and, consequently, for the momentum transfer probability distribution that holds in any quantum field theory with any coupling strength. This condition, which is the generalization of the Einstein relation to quantum field theories which feature non-Gaussian fluctuations, reveals that the asymmetry between energy loss and energy gain in the momentum transfer probability distribution takes a simple, theory-independent, form.

Recent advances in materials informatics have expanded the number of synthesizable materials. However, screening promising candidates, such as semiconductors, based on defect properties remains challenging. This is primarily due to the lack of a general framework for predicting defect formation energies in multiple charge states from structural data. In this Letter, we present a protocol, namely data normalization, Fermi level alignment, and treatment of perturbed host states, and validate it by accurately predicting oxygen vacancy formation energies in three charge states using a single model. We also introduce a joint machine-learning model that integrates defect formation energies and band-edge predictions for virtual screening. Using this framework, we identify 89 hole-dopable oxides, including BaGaSbO, a potential ambipolar photovoltaic material. Our protocol is expected to become a standard approach for machine-learning studies on point defect formation energies.