When reformulated as a resource theory, thermodynamics can analyze system behaviors in the single-shot regime. In this, the work required to implement state transitions is bounded by $\alpha$-Rényi divergences and so differs in identifying efficient operations compared to stochastic thermodynamics. Thus, a detailed understanding of the difference between stochastic and resource-theoretic thermodynamics is needed. To this end, we explore reversibility in the single-shot regime, generalizing the two-level work reservoirs used there to multilevel work reservoirs. This achieves reversibility in any transition in the single-shot regime. Building on this, we systematically develop multilevel work reservoirs in the nondissipation regime with and without catalysts. The resource-theoretic results show that two-level work reservoirs undershoot Landauer's bound, misleadingly implying energy dissipation during computation. In contrast, we demonstrate that multilevel work reservoirs achieve Landauer's bound while producing arbitrarily low entropy.

Despite multipartite entanglement being a global property of a quantum state, a number of recent works have made it clear that it can be quantified using only local measurements. This is appealing because local measurements are the easiest to implement on current quantum hardware. However, it remains an open question what protocol one should use in order to minimize the resources required to estimate multipartite entanglement from local measurements alone. In this work, we construct and compare several estimators of multipartite entanglement based solely on the data from local measurements. We first construct statistical estimators for a broad family of entanglement measures using local randomized measurement (LRM) data before providing a general criterion for the construction of such estimators in terms of projective 2-designs. Importantly, this allows us to derandomize the multipartite estimation protocol based on LRMs. In particular, we show how local symmetric, informationally complete positive operator-valued measures enable multipartite entanglement quantification with only a single measurement setting. For all estimators, we provide both the classical postprocessing cost and rigorous performance guarantees in the form of analytical upper bounds on the number of measurements needed to estimate the measures to any desired precision.

We present several improvements to the recently developed ground-state preparation algorithm based on the quantum eigenvalue transformation for unitary matrices (QETU), apply this algorithm to a lattice formulation of U(1) gauge theory in $(2+1)$ dimensions, as well as propose an alternative application of QETU, a highly efficient preparation of Gaussian distributions. The QETU technique was originally proposed as an algorithm for nearly optimal ground-state preparation and ground-state energy estimation on early fault-tolerant devices. It uses the time-evolution input model, which can potentially overcome the large overall prefactor in the asymptotic gate cost arising in similar algorithms based on the Hamiltonian input model. We present modifications to the original QETU algorithm that significantly reduce the cost for the cases of both exact and Trotterized implementation of the time evolution circuit. We use QETU to prepare the ground state of a U(1) lattice gauge theory in two spatial dimensions, explore the dependence of computational resources on the desired precision and system parameters, and discuss the applicability of our results to general lattice gauge theories. We also demonstrate how the QETU technique can be utilized for preparing Gaussian distributions and wave packets in a way which outperforms existing algorithms for as little as $n_q\gtrsim 2–5$ qubits.

We develop qutrit circuit models for discrete-time three-state quantum walks on Cayley graphs corresponding to dihedral groups $D_N$ and the additive groups of integers modulo any positive integer $N$. The proposed circuits comprise of elementary qutrit gates such as qutrit rotation gates, qutrit-$X$ gates and two-qutrit controlled-$X$ gates. First, we propose qutrit circuit representation of special unitary matrices of order three, and the block diagonal special unitary matrices with $3\times 3$ diagonal blocks, which correspond to multicontrolled $X$ gates and permutations of qutrit Toffoli gates. We show that one-layer qutrit circuit model needs $O\left(3nN\right)$ two-qutrit control gates and $O\left(3N\right)$ one-qutrit rotation gates for these quantum walks when $N=3^n$. Finally we numerically simulate these circuits to mimic its performance such as time-averaged probability of finding the walker at any vertex on noisy quantum computers. The simulated results for the time-averaged probability distributions for noisy and noiseless walks are further compared using KL divergence and total variation distance. These results show that noise in gates in the circuits significantly impacts the distributions than amplitude damping or phase damping errors.

We present an experiment with numerical simulations for the state-selective single-electron-capture process in low-energy 1–8-keV/u ${\mathrm{Ar}}^{8+}$-He collisions. The relative cross sections for the state-selective transitions are obtained from the measured $Q$-value spectra. Subshell-resolved differential scattering angle distributions (DSADs) for the dominant ($n=4$) $1s$ to $4s, 4p, 4d$, and $4f$ transitions and weak ($n=5$) $1s$ to $5s$ and $5p$ transitions at 1 keV/u and some mixed state transitions for 5- and 8-keV/u collision energy are measured. The experimentally obtained state-selective DSADs are compared with the two-center atomic orbital close-coupling calculations and qualitatively reproduced the oscillatory structures, which are quantum in nature. Undulations in the small scattering angles for $1s$ to $4s$ and $4p_0$ transitions are found to be arising from quantum matter-wave scattering, further satisfied by the simple mathematical model based on the optical Fraunhofer diffraction theory of light. The double differential $Q$-value versus scattering angle distributions give insight into the double-electron-capture mechanisms measured at 5- and 8-keV/u collision energies. Our findings shed light on the excited-state electronic dynamics to characterize the highly charged ion-atom collisions in the highly perturbative regime.

Attosecond time delays in molecular photoionization at low energies are dominated by the contribution of the Coulomb phase, which diverges as the energy of the photoelectron decreases towards zero. With calculations on core-electron ejection from ${\mathrm{CN}}^{-}$ and ${\mathrm{C}}_2^{-}$ we demonstrate that in photodetachment of molecular anions the absence of the long-range Coulomb interaction in the final state can reveal the delays of narrow low-energy shape resonances that do not generally occur in photoionization. Delays of several femtoseconds can be associated with such resonances. The angular dependence of photodetachment time delays in the body frame is highly sensitive to short-range anisotropies in the electron-molecule interaction as well as to the initial state.

We investigate the properties of the mobility edge in an Aubry-André-Harper model with nonreciprocal long-range hopping. The results reveal that there can be a type of mobility edge featuring both strength-dependent and scale-free properties. By calculating the fractal dimension, we find that the positions of mobility edges are robust to the strength of nonreciprocal long-range hopping. Furthermore, through scale analysis of the observables such as fractal dimension, eigenenergy, eigenstate, etc., we show that four different specific mobility edges can be observed in the system. This paper extends the family tree of mobility edges and hopefully it will shed more light on the related theory and experiment.

We investigate the violation of the Leggett-Garg inequalities for a harmonic oscillator in various quantum states and with various choices of a projection operator for a dichotomic variable. We focus on the two-time quasiprobability distribution function with a dichotomic variable constructed with the position or momentum operator of a harmonic oscillator. Our results are the generalization of the previous work by Mawby and Halliwell [Phys. Rev. A 107, 032216 (2023)], but the new points are the following. We first obtain the explicit expression for the two-time quasiprobability distribution function for the (thermal) squeezed coherent state. Second, we find the two-time quasiprobability distribution function with the dichotomic variable and the projection operator constructed in terms of the momentum operator. Third, we demonstrate that the violation of the Leggett-Garg inequalities can be boosted by adopting the dichotomic variable and the projection operator defined by a finite range of the position/momentum, in which a larger violation appears for the ground state and the squeezed state. We give an intuitive interpretation when the violation of the Leggett-Garg inequalities appears. We also present a mathematical formula to compute the quasiprobability distribution function by using the integral representation of the Heaviside function, which is useful to generalize it to a quantum field theory.

An electron tunneling across a junction integrated into an electric circuit can generate an excitation in the photonic field (electromagnetic environment) and lose energy in the process. Such inelastic tunneling of particles is commonly described using the $P\left(E\right)$ theory. In the conventional approach to this theory, the tunneling rate and the electric current through the junction are derived using Fermi's golden rule and by averaging over the environmental photonic degrees of freedom. In this work, we address the same problem of inelastic tunneling due to photonic environment in Lindbladian formalism and we present how the photonic degrees of freedom are traced out in the quantum master equation approach. The resulting quantum master equation is parametrized by the same $P\left(E\right)$ function and enables us to obtain not only the electric current but various other quantities, for instance, the heat current, in a systematic and convenient way. We also demonstrate that the Lindbladian formalism provides a comprehensive description of Bogoliubov quasiparticle tunneling through superconducting junctions and that it properly accounts for the coherence factors. The coherence factors become important if the normal-state density of states is particle-hole asymmetric.

The efficiency of quantum measurements in distinguishing neighboring quantum states is a central topic in quantum information sciences. We study the efficiency of vertex measurement in two-parameter estimation from the information geometry perspective, where the vertex measurement is a rare typical measurement recognized as optimal for both single-parameter estimation and multiparameter estimation of states in manifolds with vanishing Berry curvature. This article focuses explicitly on scenarios with nonzero Berry curvature. We quantify the precision of an estimation scheme with the density of distinguishable states and measure the efficiency of a given vertex measurement by comparing its precision to the maximum value. Exemplified by the three-level system with two parameters, we show that the efficiency is highly anisotropic concerning the direction of a small mismatch vector between the applied measurement and the estimated parameter. It may even vanish in some specific directions. Furthermore, the direction is hardly acknowledged prior, hindering the practical application of vertex measurement in multiparameter estimations. To remove this obstacle, we further introduce a scheme that can adaptively approach the optimal vertex measurements.

Twin-field (TF) quantum key distribution (QKD) has been extensively researched because of its long transmission distance. The phase-encoding TF-QKD can realize both a high key rate and a long transmission distance, so it has attracted a lot of attention. In this article, we are inspired by the sending-or-not-sending TF-QKD, in which the information leakages of correct rounds and erroneous rounds are calculated separately. And, we notice that this kind of method has been used in many QKD protocols—for example, the six-state QKD. We apply a similar method to the phase-matching TF-QKD and find some improvement in it. With the new analysis, the transmission distance can be improved without any changes in experiments. We also apply the new analysis in the four-phase partial-phase-postselection protocol, and a similar improvement can be achieved.

We obtain a Gorini-Kossakowski-Sudarshan-Lindblad-like master equation for two or more quantum systems connected locally to a combination of Markovian and non-Markovian heat baths. The master equation was originally formulated for multiparty systems with either exclusively Markovian or non-Markovian environments. We extend it to encompass the case of multiple quantum systems connected to a mixture of Markovian and non-Markovian heat baths. The coexistence of both non-Markovian and Markovian environments is a plausible scenario, particularly when studying hybrid physical systems such as atom-photon arrangements. We analyze the thermodynamic quantities for such a set of local environments, and derive a modified form of the Spohn's theorem for the setup. The modification of the theorem naturally leads to a witness as well as an easily computable quantifier of non-Markovianity. Expectedly, we find that for multiparty situations, where a combination of Markovian and non-Markovian heat baths are active, the response in thermodynamic system characteristics due to non-Markovian baths is prominent at times close to the initial time of evolution, whereas the long-time behavior is predominantly controlled by the Markovian ones.

Determining whether a subspace spanned by certain quantum states is entangled and its entanglement dimensionality remains a fundamental challenge in quantum information science. This paper introduces a geometric measure of $r$-bounded rank, $E_r\left(\mathcal{S}\right)$, for a given subspace $\mathcal{S}$. Derived from the established geometric measure of entanglement, this measure is specifically designed to assess the entanglement within $\mathcal{S}$. It not only serves as a tool for determining the entanglement dimensionality but also illuminates the subspace's capacity to preserve such entanglement. By employing developed nonconvex optimization techniques utilized in machine learning area, we can accurately calculate $E_r\left(\mathcal{S}\right)$ within the manifold optimization framework. Our approach demonstrates notable advantages over existing hierarchical methods, PPT relaxation techniques, and the seesaw strategy, particularly by combining computational efficiency with broad applicability. More importantly, it paves the way for high-dimensional entanglement certification, which is crucial for numerous quantum information tasks. We showcase its effectiveness in validating high-dimensional entangled subspaces in bipartite systems, determining the border rank of multipartite pure states, and identifying genuinely or completely entangled subspaces.

Quantum error correction (QEC) with single-shot decoding enables the reduction of errors after every single round of noisy stabilizer measurement, easing the time-overhead requirements for fault tolerance. Notably, several classes of quantum low-density parity check (qLDPC) codes are known which facilitate single-shot decoding, potentially giving them an additional overhead advantage. However, the perceived advantage of single-shot decoding is limited because it can significantly degrade the effective code distance. This degradation may be compensated for by using a much larger code size to achieve the desired target logical error rate, at the cost of increasing the amount of syndrome information to be processed, as well as increasing complexity of logical operations. Alternatively, in this paper we study sliding-window decoding, which corrects errors from previous syndrome measurement rounds while leaving the most recent errors for future correction. We observe that sliding-window decoding significantly improves the logical memory lifetime and hence the effective distance compared to single-shot decoding on hypergraph-product codes and lifted-product codes. Remarkably, we find that this improvement may not cost a larger decoding complexity. Thus, the sliding-window strategy can be more desirable for fast and accurate decoding for fault-tolerant quantum computing with qLDPC codes.

Quantum random access memory (QRAM) is an essential ingredient for many quantum algorithms, such as quantum machine learning models. The quantum resources (qubit counts and circuit depths) required to load classical data into a circuit severely prohibit many reasonably sophisticated demonstrations in the near term. To this end, we propose a method to construct a compact QRAM circuit, leveraging classical preprocessing to design as shallow a circuit with as few auxiliary qubits as possible. The underlying idea is to map data-encoded quantum states into an orthogonal set of quantum states (characterized by a family of parametrized circuits); then one can straightforwardly entangle the data qubits with the address qubits using cnot gates to realize a data-loading QRAM circuit. The nonunitary transformation to convert the orthogonalized quantum states back to the original data-encoded quantum states can be easily achieved with the help of a small set of auxiliary qubits and postselections. Numerical simulations on handwritten digits and Iris data sets are performed to assess the effectiveness of the proposed method, and we also highlight how noise influences quantum circuit performance across diverse configurations using random data sets. The proposed method for constructing a QRAM circuit can potentially facilitate the development and testing of many quantum machine learning methods in the near term.

Strong-field ionization can induce electron motion in both the continuum and valence shell of the parent ion. Here we report on a joint theoretical and experimental investigation of laser-induced electron diffraction in xenon. We explore the interplay of electron recollision with spin-orbit dynamics in the valence shell of the xenon cation. On the theory side, the electron-hole potentials for two different states are constructed, and the quantitative rescattering model is used to calculate the photoelectron momentum distributions (PMDs) for high-order above-threshold ionization of xenon. Measurements were carried out using 40-fs laser pulses with a central wavelength of 3100 nm and a peak laser intensity of $6\times {10}^{13}{\text{W/cm}}^2$. The simulated PMDs describe well the features of the measured angular distributions of photoelectrons. Our study reveals a theoretical distinction between the electron signals resulting from rescattering off the $m=0$ and $\left|m\right|=1$ hole states, particularly noting a distinct change along the backward scattering angles. However, to fully identify the contributions of the hole states, a more accurate agreement between theory and experiment will be needed.

We implement an all-particle multireference Fock-space relativistic coupled-cluster theory to probe the $6s^2{}^1{S}_0\text{–}6s6p{}^3{P}_0^o$ clock transition in an even isotope of ${\mathrm{Pb}}^{2+}$. We compute the excitation energy for several low-lying states, $E1$ and $M1$ transition amplitudes, and the lifetime of the clock state. Moreover, we also calculate the ground-state dipole polarizability using perturbed relativistic coupled-cluster theory. To improve the accuracy of results, we incorporate the corrections from the relativistic and QED effects in all our calculations. The contributions from triple excitations are accounted perturbatively. Our computed excitation energies are in excellent agreement with the experimental values for all the states. Our result for lifetime, $9.76\times {10}^6$ s, of clock state is approximately 8.5% larger than the previous value using a combined method of configuration-interaction and many-body perturbation theory [Phys. Rev. Lett. 127, 013201 (2021)]. Based on our analysis, we find that the contributions from the valence-valence correlations arising from higher-energy configurations and the corrections from the perturbative triples and QED effects are essential to get accurate clock transition properties in ${\mathrm{Pb}}^{2+}$. Our computed value of dipole polarizability is in good agreement with the available theoretical and experimental data.

We consider the comparative dynamics of one- and two-photon ionization in atoms through semianalytical representations of the continuum wave functions, in order to model the probe-induced anisotropy in interferometric measurements of photoemission delays. We find an approximate expression of the long-range half-scattering phase based on an asymptotic expansion of the continuum eigenfunctions within the Wentzel-Kramers-Brillouin approximation, which encompasses and expands commonly used lower-order derivations. Combined with a perturbative approach, the resulting analytic formalism can treat, at the same time, the two-photon propensity rules, the anisotropy in the continuum-continuum photoionization time delay, and the soft-photon regime.

In this study, a viable platform for atom traps using a dielectric-loaded surface-plasmon-polariton waveguide is proposed. A trap depth of 0.239 mK can be achieved above a ${\mathrm{SiO}}_2$ waveguide on an Au-${\mathrm{SiO}}_2$ substrate, with mode powers of $0.5\mathrm{mW}$ for the blue-detuned ${\mathrm{TM}}_0$ mode, $0.1\mathrm{mW}$ for the ${\mathrm{TM}}_1$ mode, and $0.55\mathrm{mW}$ for the red-detuned ${\mathrm{TM}}_0$ mode. The trap center is about 180 nm above the waveguide surface, and the corresponding cooperativity parameter for coupling the ${}^{87}\mathrm{Rb}$ atom with a guided photon is about 0.137. By controlling the phase difference between counterpropagating red-detuned ${\mathrm{TM}}_0$ modes, atoms can be delivered along the waveguide by an optical conveyor belt. Compared to the dielectric waveguide without the enhancement of surface plasmon polaritons, our scheme has the advantage of forming a trap depth with low-power requirements and stronger atom-photon interactions, which makes it highly suitable for applications in photonic-atomic chips.