In ultracold atoms, achieving a period-3 structure poses a significant challenge. In this work, we propose a three-sublattice spin-flop transition mechanism, differing from the two-sublattice counterpart used to explain the emergence of ferrimagnetic orders in higher dimensions. Guided by this mechanism, we design a setup of alkaline-earth-metal atoms to create a spin-orbit-coupled optical lattice, where we identify a triplefold degenerate $YX\overline{Y}$ state with a period-3 coplanar spin ordering within the deep Mott-insulating phase region of the ground-state phase diagram. The $YX\overline{Y}$ state is protected by a finite gap, and its characteristic angle can be finely tuned by specific setup parameters. Moreover, we use the Rabi spectroscopy technique to detect the $YX\overline{Y}$ state. Our work not only shows the feasibility of achieving a period-3 structure via the new mechanism but also suggests its potential applications for exploring other periodic structures in optical lattices.

We investigate atom-photon entangling gates based on cavity quantum electrodynamics (QED) for a finite photon-pulse duration, where not only the photon loss but also the temporal mode-mismatch of the photon pulse becomes a severe source of error. We analytically derive relations between cavity parameters, including transmittance, length, and effective cross-sectional area of the cavity, that minimize both the photon loss probability and the error rate due to temporal mode-mismatch by taking it into account as state-dependent pulse delay. We also investigate the effects of pulse distortion using numerical simulations for the case of short pulse duration. We believe that these analyses are the first to suggest that a cavity has an optimal length for the atom-photon gate, providing a fundamental guideline for implementing quantum information processing.

Quantum heat engines (QHEs) employing Otto, Carnot, and Szilard cycles have already been demonstrated. Experimental demonstration of the quantum Stirling engine has been hindered due to the challenges in realizing a quantum isothermal process with qubits. Here, we experimentally execute a single-ion Stirling QHE and demonstrate that its efficiency is enhanced when dephasing is involved during the heat release strokes, which is contrary to the conventional viewpoint that dephasing deteriorates quantum features, resulting in reduced performance in QHEs. We also observe periodic oscillations in the heat absorption and the efficiency of the Stirling QHE, indicating the involvement of quantum coherence in the engine cycles. Our experiment is the first execution of Stirling QHE in a spin system, which may help better understand quantum thermodynamics and open new possibilities toward harnessing decoherence as a resource to improve the performance of QHEs.

The dynamical correlated properties of one-dimensional (1D) Bose gases provide profound understanding of novel physics emergent from collective excitations, for instance, the breakdown of off-diagonal long-range order, and the establishment of Tomonaga-Luttinger liquid theory. However, due to the nonperturbative nature of 1D many-body systems, the exact evaluation of correlation functions is notoriously difficult. Here, by means of a form factor approach based on an algebraic Bethe ansatz and numerics, we present a thorough study on the one-body dynamical correlation function (1BDCF) of the Lieb-Liniger model at finite temperature. The influence of thermal fluctuation and interaction on the behavior of 1BDCF has been demonstrated and analyzed from various perspectives, including the spectral distribution, the line shape at fixed momentum, and the corresponding static correlations.

We present an entanglement transition in an array of qubits, induced by the transfer of quantum information from a system to a quantum computer. This quantum-data collection is an essential protocol in quantum machine learning algorithms that promise exponential advantage over their classical counterparts. In this and an accompanying work [Phys. Rev. A 111, 012425 (2025)], we identify sufficient conditions for an entanglement transition to occur in the late-time state of the system and quantum computer. In this Letter, we present an example entanglement transition occurring in a system comprised of a one-dimensional (1D) chain of qubits evolving under a random brickwork circuit. After each layer, a fraction $p$ of sites undergo noisy quantum transduction in which quantum information is transferred to a quantum computer but at the cost of introducing noise from an environment. For an entanglement transition to occur, we argue that the environment must obtain the same amount of information as gained by the computer. Under this condition, the circuit shows a transition from volume law to area law entanglement as the rate $p$ is increased above a critical threshold. Our work delineates the prerequisites for quantum-data collection to induce entanglement transitions, thereby establishing a foundational framework for emergent entanglement phenomena in protocols relevant to quantum machine learning.

Constructing and manipulating quantum states in fast-rotating Bose-Einstein condensates (BECs) has long stood as a significant challenge as the rotating speed approached a critical velocity. Although a recent experiment [R. J. Fletcher et al., Science 372, 1318 (2021)] has realized the geometrically squeezed state of the guiding-center mode, the remaining degree of freedom, the cyclotron mode, remains unsqueezed due to the large energy gap of the Landau levels. To overcome this limitation, in this Letter, we propose a Floquet-based state-preparation protocol by periodically driving an anisotropic potential. This protocol not only facilitates single-cyclotron-mode squeezing, but also enables two-mode squeezing. Such two-mode squeezing offers a richer set of dynamics compared to single-mode squeezing and can achieve a wave-packet width well below the lowest-Landau-level limit. Our work provides a highly controllable knob for realizing diverse geometrically squeezed states in ultracold quantum gases within the quantum Hall regime.

The superfluid fraction $f$ of a quantum fluid is defined in terms of the response of the system to a weak and constant drag. Notably, Leggett long ago derived two simple expressions providing a rigorous upper bound and a heuristic lower bound for $f$. Here we study the superfluid fraction of bosonic gases in various two-dimensional potentials, such as regular optical lattices and disordered speckles, by solving the Gross-Pitaevskii equation and performing diffusion Monte Carlo simulations. We show that under conditions relevant for most ultracold experiments the bounds proposed by Leggett provide a surprisingly narrow bracketing of the exact value of the superfluid fraction.

We study a mixture of a repulsive dipolar condensate and a degenerate Fermi gas in a quasi-one-dimensional geometry. We demonstrate that the presence of fermions, which attract bosons, drastically changes the behavior of the dipolar condensate. For a strong enough boson-fermion attraction, a dipolar Bose-Fermi droplet appears in the mixture, and as the attraction becomes stronger, a roton excitation develops in the Bogoliubov spectrum, leading to the formation of a supersolid, and eventually a crystal of isolated droplets. We describe the system by coupled extended Gross-Pitaevskii (bosons) and Hartree-Fock (fermions) equations. We study the excitation spectrum of the system and identify a number of Goldstone and Higgs modes in the supersolid regime.

Open systems that are weakly coupled to a thermal environment and driven by fast, periodically oscillating fields are commonly assumed to approach an equilibriumlike steady state with respect to a truncated Floquet-Magnus Hamiltonian. Using a general argument based on Fermi's golden rule, we show that such Floquet-Gibbs states emerge naturally in periodically modulated Rydberg atomic systems, whose laboratory-frame Hamiltonian is a quasiperiodic function of time. Our approach applies as long as the inherent Bohr frequencies of the system, the modulation frequency, and the frequency of the driving laser, which is necessary to uphold high-lying Rydberg excitations, are well separated. To corroborate our analytical results, we analyze a realistic model of up to five interacting Rydberg atoms with periodically changing detuning. We demonstrate numerically that the second-order Floquet-Gibbs state of this system is essentially indistinguishable from the steady state of the corresponding Redfield equation if the modulation and driving frequencies are sufficiently large.

We derive a model for a single-mode laser that includes all two-particle quantum correlations between photons and electrons. In contrast to the predictions of semiclassical models, we find that lasing takes place in the presence of quantum bistability between a nonlasing and a nonclassical coherent state. The coherent state is characterized by a central frequency and a finite linewidth and emerges with finite amplitude from a saddle-node bifurcation together with an unstable coherent state. Hence coherent emission in nanolasers originates through a mixing of lasing and nonlasing states. In the limit of a macrolaser with a large number of emitters and nonresonant modes, the laser threshold approaches the prediction of the semiclassical theory, but with the important difference that lasing can be achieved only in the presence of finite-size perturbations.

Hagedorn wave packets have been used to compute single vibronic level (SVL) spectra efficiently in model harmonic potentials. To make the Hagedorn approach practical for realistic polyatomic molecules with anharmonicity, here we combine local harmonic Hagedorn wave-packet dynamics with on-the-fly ab initio dynamics. We then test this method by computing the SVL fluorescence spectra of difluorocarbene, a small, floppy molecule with a very anharmonic potential energy surface. Our time-dependent approach obtains the emission spectra of all initial vibrational levels from a single anharmonic semiclassical wave-packet trajectory without the need to fit individual anharmonic vibrational wave functions and to calculate the Franck-Condon factors for all vibronic transitions. We show that, whereas global harmonic models are inadequate for ${\mathrm{CF}}_2$, the spectra computed with the on-the-fly local harmonic Hagedorn wave-packet dynamics agree well with experimental data, especially for low initial excitations.

Quantum simulation with adiabatic annealing can provide insight into difficult problems that are impossible to study with classical computers. However, it deteriorates when the systems scale up due to the shrinkage of the excitation gap and thus places an annealing rate bottleneck for high success probability. Here, we accelerate quantum simulation using digital multiqubit gates that entangle primary system qubits with ancillary qubits. The practical benefits originate from tuning the ancillary gauge degrees of freedom to enhance the quantum algorithm's original functionality in the system registry. For simple but nontrivial short-ranged, infinite long-ranged transverse-field Ising models, and the hydrogen molecule model after qubit encoding, we show improvement in the time to solution by one hundred percent but with higher accuracy through exact state-vector numerical simulation in a digital-analog setting. The findings are further supported by time-averaged Hamiltonian theory.

Random number generators play an essential role in cryptography and key distribution. It is thus important to verify whether the random numbers generated from these devices are genuine and unpredictable by any adversary. Recently, quantum nonlocality has been identified as a resource that can be utilized to certify randomness. Although these schemes are device independent and thus highly secure, the observation of quantum nonlocality is extremely difficult from a practical perspective. In this work, we provide a scheme to certify unbounded randomness in a semi-device-independent way based on the maximal violation of Leggett-Garg inequalities. Interestingly, the scheme is independent of the choice of the quantum state and consequently even classical noise like a thermal state or even microwave background radiation could be utilized to self-test quantum measurements and generate unbounded randomness, making the scheme highly efficient for practical purposes.

We present a theoretical study on photonic topological crystals whose symmetry is governed by quantum valley-Hall topological insulators and whose propagating edge modes are strongly confined due to bowtie geometries. Dielectric bowtie structures exploit the field discontinuities at the boundaries between materials with different refractive indices, and here bowties emerge at the topological interface due to the close proximity of two triangular features in the underlying crystal. The topological bowtie mode features a unit-cell mode volume down to $8\times {10}^{-4}$ cubic wavelengths at the center of the bowtie bridge of width $10\mathrm{nm}$. Valley-Hall photonic topological insulators have often been assumed to be immune to backscattering, but we show that perturbed versions of the topological unit cells can form highly reflective mirrors. This enables us, in turn, to design topological heterostructure bowtie cavities with quality factors exceeding ${10}^7$ and a Purcell factor of $3\times {10}^6$, implying that unprecedented regimes of light-matter interaction may be in reach with topological bowtie modes.

Dissipative many-body quantum dynamics can feature strong symmetries which give rise to conserved quantities. We discuss here how a strong symmetry in conjunction with a nonequilibrium phase transition allows to devise a protocol for measuring collective many-body observables. To demonstrate this idea we consider a collective spin system whose constituents are governed by a dissipative dynamics that conserves the total angular momentum. We show that by continuously monitoring the system output, the value of the total angular momentum can be inferred directly from the time-integrated emission signal, without the need of repeated projective measurements or reinitializations of the spins. This may offer a route towards the measurement of collective properties in qubit ensembles, with applications in quantum tomography, quantum computation, and quantum metrology.

Lattice models display bound states for repulsive interactions that smoothly connect to high-energy two-particle states of doubly occupied sites, namely doublons, for strong on-site interactions. In this work, we show that a distinct type of repulsively bound states, namely vortex bound states of two bosons, appear in dimerized square lattices pierced by a uniform $\pi$ flux for moderate interactions. By focusing on a ladder geometry as an illustrative example, we characterize their properties, including chirality-changing decay channels induced by flux detuning, and we develop protocols to perform state preparation in optical lattices via adiabatic sequences or recently developed current imprinting methods. Finally, we show how to measure currents and thus chirality by quenching the system onto isolated pairs of nearest-neighbor sites and then sampling the corresponding dynamics. These results can also provide an experimentally realistic strategy for state preparation and probing of chiral gapped many-body phases in optical lattices.

We utilize a method using frequency combs to construct waves that feature superoscillations—local regions of the wave that exhibit a change in phase that the bandlimits of the wave should not otherwise allow. This method has been shown to create superoscillating regions that mimic any analytic function—even ones well outside the bandlimits—to an arbitrary degree of accuracy. We experimentally demonstrate that these waves are extremely robust against noise, allowing for accurate reconstruction of a superoscillating target function thoroughly buried in noise. We additionally show that such a construction can be easily used to range-resolve a signal well below the commonly accepted fundamental limit.

Measurements in quantum theory can fail to be jointly measurable. Like entanglement, this incompatibility of measurements is necessary but not sufficient for violating Bell inequalities. The (in)compatibility relations among a set of measurements can be represented by a joint measurability structure, i.e., a hypergraph whose vertices denote measurements and hyperedges denote all and only compatible sets of measurements. Since incompatibility is necessary for a Bell violation, the joint measurability structure on each wing of a Bell experiment must necessarily be nontrivial, i.e., it must admit a subset of incompatible vertices. Here we show that, for any nontrivial joint measurability structure with a finite set of vertices, there exists a quantum realization with a set of measurements that enables a Bell violation, i.e., given that Alice has access to this incompatible set of measurements, there exists a set of measurements for Bob and an entangled state shared between them such that they can jointly violate a Bell inequality. Hence, a nontrivial joint measurability structure is not only necessary for a Bell violation, but also sufficient.

Attosecond ionization delays in molecules are novel probes of electron correlations in the molecular environment. Relativistic effects in molecules due to spin-orbit coupling are known to figure in structural chemistry and can affect chemical reactions, but the anisotropic potential and congested spectra make it difficult to disentangle contributions from neighboring spin-orbit states. Here, we measure the energy-dependent relative delays between the photoelectron wave packets from two valence spin-orbit states of methyl iodide. We observe substantial modulations in the time-delay photoelectron spectrum from 5–20 eV, a region that includes both spin-orbit and two-electron states. Our calculations show this complex delay spectrum is connected to the interplay between relativistic spin-orbit activated interchannel coupling and spin-flip transitions, as well as the high density of two-electron transitions. This work establishes spin-orbit resolved time delay measurements as a viable tool to probe electronic correlations in molecules and highlights the significant role of relativistic effects on molecular time delay measurements.

Theoretical descriptions of excited states of molecular systems in high-energy regimes are crucial for supporting and driving many experimental efforts at light source facilities. However, capturing their complicated correlation effects requires formalisms that provide a hierarchical infrastructure of approximations. These approximations lead to an increased overhead in classical computing methods and, therefore, decisions regarding the ranking of approximations and the quality of results must be made on purely numerical grounds. The emergence of quantum computing methods has the potential to change this situation. In this study, we demonstrate the efficiency of the quantum phase estimator (QPE) in identifying core-level states relevant to x-ray photoelectron spectroscopy. We compare and validate the QPE predictions with exact diagonalization and real-time equation-of-motion coupled-cluster formulations, which are some of the most accurate methods for states dominated by collective correlation effects.