Quantum computers theoretically promise computational advantages in many tasks, but it is much less clear how such advantages can be maintained when using existing and near-term hardware that has limitations in the number and quality of its qubits. Layden et al. [Nature (London) 619, 282 (2023)] proposed a promising application by introducing a quantum-enhanced Markov chain Monte Carlo (QeMCMC) approach to reduce the thermalization time required when sampling from hard probability distributions. In QeMCMC, the size of the required quantum computer scales linearly with the problem, placing limitations on the sizes of systems that can be considered. In this paper we introduce a framework to coarse grain the algorithm in such a way that the quantum computation can be performed using considerably smaller quantum computers and we term the method the coarse grained quantum-enhanced Markov chain Monte Carlo (CGQeMCMC). Example strategies within this framework are put to the test, with the quantum speedup persisting while using only $\sqrt{n}$ simulated qubits where $n$ is the number of qubits required in the original QeMCMC—a quadratic reduction in resources. The coarse graining framework has the potential to be practically applicable in the near term as it requires very few qubits to approach classically intractable problem instances; in this case, only six simulated qubits suffice to gain an advantage compared with standard classical approaches when investigating the magnetization of a 36-spin system. Our method can be easily combined with other classical and quantum techniques and is adaptable to various quantum hardware specifications—in particular those with limited connectivity.

Novel targets were implemented in the beam-driven (in-target) proton-boron fusion with beneficial characteristics (chemical composition and density) compared to the commonly used boron nitride. A fusion-generated alpha particle flux of up to $\left(5\times {10}^7{\mathrm{sr}}^{-1}{\mathrm{J}}^{-1}\right)$ was generated via the proton-boron fusion reactions when irradiating the targets with a moderate laser system ($10\mathrm{J}, 800\mathrm{fs}, {10}^{19}\mathrm{W}{\mathrm{cm}}^{-2}$). Normalized by laser energy, the alpha particle flux generated in this experiment is comparable with the highest alpha particle yields reported in the literature. We present experimental results with supporting simulations and calculations of the expected alpha particle yield.

Predicting the fitness of viral proteins is fundamental to understanding viral evolution and developing antiviral strategies. This study introduces the Venus-EEM, an entropy-driven ensemble model, aimed at improving the performance of zero-shot predictions for protein fitness across diverse viral datasets. We demonstrate that entropy serves as an effective criterion for selecting optimal zero-shot models, enabling adaptive model selection for different prediction tasks. By incorporating entropy-weighted ensemble learning from multiple protein language models, Venus-EEM achieves superior performance compared to existing methods. We validate the model's effectiveness through comprehensive evaluation on multiple viral datasets and a detailed case study of T7 RNA polymerase (T7 RNAP) activity. Our findings provide an effective approach for predicting viral protein mutations based on entropy, bridging fundamental physics principles with practical biological challenges.

Many-body quantum chaos has immense potential as a tool to accelerate the preparation of entangled states and overcome challenges due to decoherence and technical noise. Here, we study how chaos in the paradigmatic Dicke model, which describes the uniform coupling of an ensemble of qubits to a common bosonic mode, can enable the rapid generation of non-Gaussian entangled spin-boson states without fine-tuning of system parameters or initial conditions. However, the complexity of these states means that unlocking their utility for quantum-enhanced sensing with standard protocols would require the measurement of complex or typically inaccessible observables. To address this challenge, we develop a sensing scheme based on interaction-based readout that enables us to implement near-optimal quantum-enhanced metrology of global spin rotations or bosonic displacements using only spin measurements. We show that our approach is robust to technical noise and imperfections and thus opens new opportunities to exploit complex entangled states generated by chaotic dynamics in current quantum science platforms such as trapped-ion and cavity-QED experiments.

The Kapitza-Dirac effect is the diffraction of quantum particles by a standing wave of light. We here report an analogous phenomenon in pilot-wave hydrodynamics, wherein droplets walking across the surface of a vibrating liquid bath are deflected by a standing Faraday wave. We show that, in certain parameter regimes, the statistical distribution of the droplet deflection angles reveals a diffraction pattern reminiscent of that observed in the Kapitza-Dirac effect. Through experiments and simulations, we show that the diffraction pattern results from the complex interactions of the droplets with the standing wave. Our study highlights nonresonant effects associated with the detuning of the droplet bouncing and the bath vibration, which are shown to lead to drop speed variations and droplet sorting according to the droplet's phase of impact. We discuss the similarities and differences between our hydrodynamic system and the discrete and continuum interpretations of the Kapitza-Dirac effect, and introduce the notion of ponderomotive effects in pilot-wave hydrodynamics.

We investigate the stability of persistent currents in superfluid fermionic gases confined to a ring geometry. Our study, conducted at zero temperature using time-dependent density functional theory, cover interaction regimes from strong (unitary Fermi gas) to weak (Bardeen-Cooper-Schrieffer regime) couplings. Stability is tested against the presence of an external defect within the ring. The dissipation mechanism associated with vortex generation is present in all interaction regimes. Vortex emission is accompanied by Cooper pair breaking, which occurs even beyond the vortex core in the weakly interacting regime. The pair-breaking mechanism prevents the imprinting of a persistent current with a winding number above a threshold, which decreases as the system approach the BCS regime. Our study reveals the existence of two types of critical winding numbers above which currents cease to be persistent in Fermi superfluids: one related to the proliferation of quantum vortices and the other to the onset of the pair-breaking mechanism.

The existence of a quantum critical point (QCP) and fluctuations around it are believed to be important for understanding the phase diagram in unconventional superconductors such as cuprates, iron pnictides, and heavy fermion superconductors. However, the QCP is usually buried deep within the superconducting dome and is difficult to investigate. The connection between quantum critical fluctuations and superconductivity remains an outstanding problem in condensed matter. Here combining both electrical transport and Nernst experiments, we explicitly demonstrate the onset of superconductivity at an unconventional QCP in gate-tuned monolayer tungsten ditelluride $\left({\mathrm{WTe}}_2\right)$, with features incompatible with the conventional Bardeen-Cooper-Schrieffer scenario. The results lead to a superconducting phase diagram that is distinguished from other known superconductors. Two distinct gate-tuned quantum phase transitions are observed at the ends of the superconducting dome. We find that quantum fluctuations around the QCP of the underdoped regime are essential for understanding how the monolayer superconductivity is established. The unconventional phase diagram we report here illustrates a previously unknown relation between superconductivity and QCP.

Exceptional points are spectral degeneracies in open systems, which have attracted considerable attention in recent years. One reason for the attention is that physical systems with an exceptional point exhibit a strong spectral response to perturbations. This response can be quantified by a single quantity known as the spectral response strength. Up to now, the theory for the spectral response strength is restricted to effective non-Hermitian Hamiltonians acting on a finite-dimensional Hilbert space, which often appear naturally within coupled-mode theory. We introduce here a scheme for the computation of the spectral response strength directly from numerical results of wave simulations, which correspond to an infinite Hilbert-space dimension. Our approach is based on the relation of the spectral response strength to the Petermann factors of eigenstates in a system near the exceptional point. To illustrate our theory, we consider three different photonic systems: a microring dimer, waveguide-coupled microrings, and a weakly deformed microdisk. A comparison to results provided by effective Hamiltonians based on coupled-mode theory and perturbation theory demonstrates very good agreement.

Traditional spin noise spectroscopy generally does not address spatial spin correlations, which are in fact crucial for an in-depth understanding of spin relaxation. In semiconductors, one requires spin noise measurements at substantial angles from the incident beam to study spatial correlations on the relevant submicron scale. Recording electron spin noise over a wide range of angles via goniometric homodyne detection enables us to recover the spatiotemporal spectra of electron spin fluctuations with virtually no losses in spin noise power in reciprocal space. Applied to a series of insulating $n$-doped CdTe samples, the technique permits the separation of various spin motion mechanisms in reciprocal space. We show that cross correlations between localized and delocalized spins are crucial in explaining the observed long-distance spin jumps between neutral donors, and they have a profound impact on the spin relaxation of localized electrons even at temperatures that are low compared to the activation energy. We develop a theoretical two-state model based on Bloch equations that take these cross correlations into account via a release-and-trapping spin transport mechanism. The model is in quantitative agreement with the entire body of our experimental data, where spatiotemporal electron spin noise spectra are measured as functions of temperature, donor density, and magnetic field.

The classical-quantum interface for loading classical data into quantum systems is an indispensable component of quantum information processing, and the parameterized quantum circuit (PQC) represents significant methodology in this area. However, a challenge in designing parameterized quantum circuits that can fully utilize limited qubit resources while accurately representing classical data remains. To address this issue, we propose the enhanced natural parameterized quantum circuit (ENPQC), which achieves the maximum parameter capacity of quantum systems and preserves the local structure of the original dataset. To make the encoding circuits more experiment friendly, we further provide two near-optimal circuits that achieve near-maximum capacity and are comparable in complexity to the existing PQCs. We numerically show that the ENPQC overwhelms other encoding methods for multiple datasets, demonstrating its potential for machine learning tasks. Furthermore, we experimentally validate our scheme by demonstrating a three-class classification task on an NMR platform, which achieves over $97\%$ accuracy. This work provides a powerful tool for the classical-quantum interface, paving the way for quantum big data processing during the noisy intermediate-scale quantum era.

We propose a natural, parameter-free, discrete-variable formulation of Feynman path integrals. We show that for discrete-variable quantum systems, Feynman path integrals take the form of walks on the graph whose weighted adjacency matrix is the Hamiltonian. By working out expressions for the partition function and transition amplitudes of discretized versions of continuous-variable quantum systems, and then taking the continuum limit, we explicitly recover Feynman's continuous-variable path integrals. We also discuss the implications of our result.

We study the collective oscillations of spin-orbit-coupled Bose-Einstein condensates in the presence of position-dependent detuning. Specifically, we explore the quadrupole modes of the system using both numerical and analytical approaches based on the Gross-Pitaevskii equation and hydrodynamic theory. Due to spin-orbit coupling and the synthetic magnetic field, the $xy$ scissors mode couples with a superposition of the three diagonal quadrupole modes ($x^2,y^2$, and $z^2$), resulting in the characteristic beating effect. The remaining two scissors modes, $xz$ and $yz$, are coupled, giving rise to a Lissajous-like pattern that is highly sensitive to the excitation method and orientation of the synthetic magnetic field. Furthermore, we find that anisotropic interactions as well as the direction of the synthetic magnetic field, can significantly influence the oscillation amplitude and frequency of the quadrupole modes. These findings highlight the potential of Bose-Einstein condensates under synthetic magnetic fields for quantum sensing applications, such as magnetic field gradient measurements, and provide a promising foundation for future experimental research and technological development.

In two spatial dimensions, vortex-vortex interactions approximately vary with the logarithm of the inter-vortex distance, making it possible to describe an ensemble of vortices as a Coulomb gas. We introduce a duality between vortices in a quasi-two-dimensional (quasi-2D) scalar Bose-Einstein condensates (BEC) and effective Maxwell's electrodynamics. Specifically, we address the general scenario of inhomogeneous, time-dependent BEC number density with dissipation or rotation. Starting from the Gross-Pitaevskii equation (GPE), which describes the mean-field dynamics of a quasi-2D scalar BEC without dissipation, we show how to map vortices in a quasi-2D scalar BEC to 2D electrodynamics beyond the point-vortex approximation, even when dissipation is present or in a rotating system. The physical meaning of this duality is discussed.

A train of intense attosecond pulses can be obtained through relativistic high harmonic generation when an intense laser field is reflected on a plasma surface. Separating a single isolated attosecond pulse from the train is critical not only for applications such as time-resolved pump-probe experiments but also for studying laser-plasma interactions with attosecond temporal resolution. Various methods have been developed for an isolated attosecond pulse generation in gas. However, they require ultrashort laser pulses, which are difficult to apply with high-power lasers typically employed in relativistic high harmonic generation. Here, we demonstrate that an isolated attosecond pulse can be obtained through relativistic high harmonic generation using noncollinear temporal gating. Our approach also provides direct access to each attosecond pulse in the train, allowing us to diagnose the laser-plasma interaction, such as plasma denting and reflection positions, in a time-resolved manner. Thus, it offers breakthroughs in attosecond pulse generation at relativistic laser intensities.