Permitting the transmission of unknown quantum states over long distances by using entanglement, quantum teleportation serves as an important building block for many quantum technologies. However, in the noisy intermediate-scale quantum era, the practical realization of quantum teleportation is inevitably challenged by the noise-induced decoherence. We here propose a noise-mitigation mechanism applicable in both the discrete- and continuous-variable quantum teleportation schemes. Via investigating the non-Markovian decoherence dynamics of the two types of quantum teleportation schemes, we find that, as long as a bound state is formed in the energy spectrum of the total system consisting of the involved subsystems and their respective reservoirs, the quantum superiority of the fidelity is persistently recovered. Supplying an insightful understanding of the noise-mitigation protocols, our result paves the way to the practical realization of noise-tolerant quantum teleportation.

The glory effect is one of the characteristic manifestations of the divergence of the classical scattering cross section, which occurs whenever the deflection function goes through zero for a nonzero impact parameter. This effect, companion of the more frequently discussed rainbow effect, occurs in particular in atomic photoionization in the presence of an external electric field, where it manifests itself by the appearance of an intense peak at the center of the photoelectron momentum distribution transversely to the field. Above the field-free ionization threshold where solely continuum Stark states exist (while quasibound ones are absent), the intensity of the glory signal, extracted from high-resolution momentum distribution images, oscillates as a function of energy. These oscillations exhibit a spectral frequency that increases with increasing energy, and Fourier analysis allows the extraction of time-dependent information from them. In this work we present a detailed analytical study of the dynamical aspects of classical electron trajectories in atomic Rydberg states in the presence of an external electric field. We demonstrate the strong connection between those classical properties and the spectral signatures of the glory signal. This close link provides a brilliant illustration of the correspondence principle in a complex situation where the quantum system is in the continuum and exhibits characteristic frequencies that vary with the excitation energy.

We consider ultralong-range polyatomic Rydberg molecules formed by combining a Rydberg cesium atom and a ground-state RbCs molecule. We explore the regime where the charge-dipole interaction due to the Rydberg electron with the diatomic polar molecule couples the quantum defect Rydberg states $\mathrm{Cs}\left(ns\right)$ to the nearest degenerate hydrogenic manifold. We consider polyatomic Rydberg molecules in states which are amenable to production in optical tweezers and study the influence of nonadiabatic coupling on the likelihood of their formation. The decay rates of the vibrational states reflect the interference signature of wave function spread in different coupled potential wells.

We present numerical simulations for a chiral soliton model with $N=2,3$ bosons in a ring, which is a few-particle version of our previous mean-field model for a quantum time crystal. Following Syrwid, Kosior, and Sacha (SKS), the notion is that a precise position measurement of one particle can lead to spontaneous formation of a bright soliton that in a time crystal should rotate intact for at least a few revolutions around the ring. In their work SKS found spontaneous formation of a soliton due to the position measurement, but quantum fluctuations cause the soliton to subsequently decay before it has a chance to perform even one revolution of the ring. Based on this, they concluded that time-crystal dynamics are impossible for Wilczek's model of a bright soliton in a ring. In contrast, for our few-boson chiral soliton model, allowing for imprecise (weak) measurements of the particle position, we show that time-crystal-like behavior is possible, allowing for several revolutions of the spontaneously formed soliton around the ring.

The nanosuspension is a stable solid-liquid hybrid fluid formed by suspending solid nanoparticles in a liquid. Based on nanosuspension, an optical-gradient-force–induced optical nonlinear characteristics in a coupled microcavities is theoretically investigated. Under high incident power, the nanoparticles that are in one of the cavities redistribute themselves leading to a significant change of the effective refractive index. The consequence of the redistribution is investigated by solving the nonlinear coupled mode theory equations. Both nonreciprocal transmission and bistability are observed due to disparate forward and backward incident field intensities in the coupled microcavities. Furthermore, the numerical simulation shows details of the mode interaction within the coupled microcavities, and agrees well with the theoretical modeling. This work demonstrates the viability of nanoparticle-mediated nonlinearity in microscale optical systems. The findings open more possibilities for light manipulation in sophisticated microfluidic systems and beyond.

We present the design of an asymmetric metasurface made of germanium antimony tellurium nanowires that supports quasibound states in the continuum. A fully coupled optothermal model is used to show that, when exposed to brief and intense laser pulses, the metasurface undergoes a partial, geometrically controlled crystallization, thereby inducing an ultrafast dynamic wavelength shift of the quasibound state in the continuum of the order of 350 nm with pump intensities as low as $35{\mathrm{MW}/\mathrm{cm}}^2$. The proposed approach highlights the potential for controlling nanostructures' response through laser illumination, opening avenues for applications in dynamic optical modulation and beyond.

We propose a time-dependent perturbation theory to study a newly discovered pseudocoherent phase of the spin-boson model. Effectiveness of the method is confirmed by comparing its results with that calculated from the numerically exact quantum dynamics method, which exhibits good agreements. We then describe how an incoherent nature of the pseudocoherent phase emerges from explicit expressions of the proposed method, and properties of invariant time of extreme values and scaling of amplitudes resulting from a second-order approximation. Correction effects of higher-order terms are also discussed. In addition, we utilize trace distance to investigate non-Markovianity and influences of model parameters. We find propagations in the pseudocoherent phase are always non-Markovian because of bath-driving oscillations. The non-Markovianity shows different dependence on cutoff frequency of bosonic baths from coherent and incoherent phases, which can be applied for qualitative identifications of different dynamic phases in realistic detections.

We study the possibility of deterministic protocols for extracting work from quantum systems. Focusing on the two-point measurement work extraction scenario, we prove that, with enough copies of the system, such zero-fluctuation protocols always exist if the Hamiltonian has a rational spectrum. Leveraging this result, we show that for any Hamiltonian, it is possible to construct a unitary driving protocol on sufficiently many copies of the system with work fluctuations strictly bounded within an arbitrary interval $\pm \delta$, albeit requiring exponentially many copies in $1/\delta$.

We explore the information which proposed matterwave interferometry experiments with large test masses can provide about parameterizable extensions to quantum mechanics, such as have been proposed to explain the apparent quantum to classical transition. Specifically, we consider a matterwave near-field Talbot interferometer and Continuous Spontaneous Localization (CSL). Using Bayesian inference we compute the effect of decoherence mechanisms including pressure and blackbody radiation, find estimates for the number of measurements required, and provide a procedure for optimal choice of experimental control variables. We show that in a simulated space-based experiment it is possible to reach masses of $\sim {10}^9\text{u}$, and we quantify the bounds which can be placed on CSL. These specific results can be used to inform experimental design, and the general approach can be applied to other parameterizable models.

Matrix pencils provide a robust method for finding simultaneous eigensystems of mutually commuting degenerate operators. In this paper, we utilize these techniques to investigate the quantum logical structures of the Peres-Mermin square and the Greenberger-Horne-Zeilinger-Mermin configuration. Our analysis uncovers analogous complete contradictions between classical and quantum predictions in a four-dimensional system involving two spin-1/2 particles.

Time continues to be an intriguing physical property in the modern era. On the one hand, we have the classical and relativistic notion of time, where space and time have the same hierarchy, essential in describing events in spacetime. On the other hand, in quantum mechanics, time appears as a classical parameter, meaning that it does not have an uncertain relation with its canonical conjugate. In this work we use a recent spacetime-symmetric proposal [Phys. Rev. A 95, 032133 (2017)] that tries to solve the unbalance in nonrelativistic quantum mechanics by extending the usual Hilbert space: the time parameter $t$ and the position operator $\widehat{X}$ in one subspace, and the position parameter $x$ and time operator $\mathbb{T}$ in the other subspace. Time as an operator is better suited for describing tunneling processes. We then solve the $1/2$-fractional integrodifferential equation for a particle subjected to strong and weak potential limits and obtain an analytical expression for the tunneling time through a rectangular barrier. Using a Gaussian energy distribution, we demonstrate that for wave packets well resolved in time, the expectation value of the operator $\mathbb{T}$ is the energy average of the classical time $T_{\text{class}}=\partial S/\partial E$, where $S$ is the classical action, which can be real or imaginary. The imaginary classical time does not contribute to the traveling time. Furthermore, we apply our results to a Gaussian energy distribution and compare them to previous works. This work is a correction of a previous paper [Phys. Rev. A 107, 052220 (2023)].

Quantum nonlocality is a significant feature in quantum information theory, prompting recent investigations into the potential reuse of postmeasurement states to uncover nonlocality among sequentially measuring observers. While prior studies primarily focused on bipartite or tripartite systems and observers with one chain, such as multiple Bobs with a single Alice or multiple Charlies with a single Alice and Bob, our work extends beyond this framework. We explore sequential nonlocality in systems comprising more parties and observer chains. Our findings reveal that in $n$-partite systems, regardless of whether it is a single-chain or double-chain scenario, there exist unbounded sequential observers capable of detecting nonlocality through violations of the Mermin inequality. In contrast to the conjecture that sequential Bell nonlocality cannot manifest with multiple Alices and Bobs in bipartite systems [i.e., the double-chain setting, see S. M. Cheng et al., Phys. Rev. A 104, L060201 (2021)], our results suggest that increasing the number of subsystems may enable more observer chains to detect nonlocality alongside single observers. Our study advances research on sequential nonlocality, providing valuable insights into its detection across diverse scenarios.

Bayesian networks are powerful tools for probabilistic analysis and have been widely used in machine learning and data science. Unlike the time-consuming parameter training process of neural networks, Bayes classifiers constructed on Bayesian networks can make decisions based solely on statistical data from samples. In this paper we focus on constructing quantum Bayes classifiers (QBCs). We design both a naïve QBC and three seminaïve QBCs (SN-QBCs). These QBCs are then applied to image classification tasks. To reduce computational complexity, we design a local feature sampling method to extract a limited number of feature attributes from an image. These attributes serve as nodes of the Bayesian networks to generate the QBCs. We simulate these QBCs on the MindQuantum platform and evaluate their performance on the MNIST and Fashion-MNIST data sets. Our results demonstrate that these QBCs achieve good classification accuracies even with a limited number of attributes. The classification accuracies of QBCs on the MNIST data set surpass those of classical Bayesian networks and quantum neural networks that utilize all available feature attributes. Additionally, we simulate these QBCs in a quantum noise environment.

This paper presents a hybrid classical-quantum approach to solve mixed-integer linear programming (MILP) using neutral-atom quantum computations. We apply Benders decomposition (BD) to segment MILPs into a master problem (MP) and a subproblem, where the MP is addressed using a neutral-atom device, after being transformed into a quadratic unconstrained binary optimization (QUBO) model, with an automatized procedure. Our MILP to QUBO conversion tightens the upper bounds of the continuous variables involved, positively impacting the required qubit count, and the convergence of the algorithm. To solve the QUBO, we develop a heuristic for atom register embedding and apply a variational algorithm for pulse shaping. In addition, we implement a proof of concept that outperforms existing solutions. We also conduct preliminary numerical results: In a series of small MILP instances our algorithm identifies over 95% of feasible solutions of high quality, outperforming classical BD approaches where the MP is solved using simulated annealing.

We provide a rigorous proof of the approximate convergence of sliding-window quantum belief-propagation as outlined heuristically in the work of Bilgin and Poulin [Phys. Rev. B 81, 054106 (2010)], in the absence of the quantum Markov property. In particular, we confirm the hypothesis outlined in this work that the approximation error of each step in the belief-propagation algorithm decreases exponentially with the sliding-window size, under the assumption that the underlying state on which belief-propagation is being performed possesses a so-called thermal boundedness property: a relaxation of the Markov property required for exact convergence.

The generation of a logical qubit called the Gottesman-Kitaev-Preskill (GKP) qubit in an optical traveling wave is a major challenge for realizing large-scale universal fault-tolerant optical quantum computers. Recently, probabilistic generation of elementary GKP qubits has been demonstrated using photon number measurements and homodyne measurements. However, the generation rate is only a few Hz, and it will be difficult to generate fault-tolerant GKP qubits at a practical rate unless success probability is significantly improved. Here, we propose a method to efficiently synthesize GKP qubits from several quantum states by adaptive Gaussian operations. In the initial-state preparation that utilizes photon number measurements, an adaptive operation allows any measurement outcome above a certain threshold to be considered as a success. This threshold is lowered by utilizing the generalized photon subtraction method. The initial states are synthesized into a GKP qubit by homodyne measurements and a subsequent adaptive operation. As a result, the single-shot success probability of generating fault-tolerant GKP qubits in a realistic scale system exceeds $10\%$, which is $1\times {10}^6$ times better than previous methods. This proposal will become a powerful tool for advancing optical quantum computers from the proof-of-principle stage to practical application.

We give an explicit construction to perform any $n$-qubit computational-basis-state transposition using $\mathrm{\Theta }\left(n\right)$ gates. This nearly coincides with the lower bound $\mathrm{\Omega }[n/log(nd\left)\right]$ on worst-case and average-case gate complexities to perform transpositions using a $d$-element gate set, which we also prove.

A fault-tolerant way to prepare logical code states of ${\mathcal{Q}}_1$ codes, i.e., quantum polar codes encoding one qubit, was recently proposed. The fault tolerance therein is guaranteed by an error detection gadget, where, if an error is detected during the preparation, one entirely discards the preparation. Due to error detection, the preparation is probabilistic and its success rate, referred to as the preparation rate, decreases rapidly with the code length, preventing the preparation of code states of large code- lengths. In this paper, to improve the preparation rate, we consider a factory preparation of ${\mathcal{Q}}_1$ code states, where one attempts to prepare several copies of ${\mathcal{Q}}_1$ code states in parallel. Using an extra scheduling step, we can avoid discarding the preparation entirely every time an error is detected, hence, achieving an increased preparation rate in turn. We further provide a theoretical method to estimate preparation and logical error rates of ${\mathcal{Q}}_1$ codes, prepared using factory preparation, which is shown to tightly fit the Monte Carlo simulation-based numerical results. Therefore, our theoretical method is useful for providing estimates for large code lengths, where Monte Carlo simulations are practically not feasible. Our numerical results, for a circuit-level depolarizing noise model, indicate that the preparation rate increases significantly, especially for large code-length $N$. For example, for $N=256$, it increases from $0.02\%$ to $27\%$ for a practically interesting physical error rate $p={10}^{-3}$. Remarkably, a ${\mathcal{Q}}_1$ code with $N=256$ achieves logical error rates around ${10}^{-11}$ and ${10}^{-15}$ for $p={10}^{-3}$ and $p=3\times {10}^{-4}$, respectively. This corresponds to an improvement of about three orders of magnitude compared to a surface code with similar code length and minimum distance, thus showing the promise of the proposed scheme for large-scale fault-tolerant quantum computing.

Fast nuclear-spin entangling gates of divalent atoms can be realized with one global laser pulse when ${\mathrm{\Delta }}_{\text{Z}}<\mathrm{\Omega }$, where ${\mathrm{\Delta }}_{\text{Z}}$ is the Zeeman-splitting-dominated frequency difference between the two clock-Rydberg transitions of the two qubit states and $\mathrm{\Omega }$ is the maximal Rabi frequency. The condition ${\mathrm{\Delta }}_{\text{Z}}<\mathrm{\Omega }$ and the sensitivity of Rydberg-state energy to magnetic fluctuation demand the magnetic field to be weak, making the gate compatible with large-scale atomic arrays because weaker magnetic fields can be smoother in a large qubit array. The gate can have a high fidelity for the decoherence of Rydberg states, which limits the gate fidelity and grows with $1/\mathrm{\Omega }$, can be mitigated with easily attainable large $\mathrm{\Omega }$.

The correspondence between long-range interacting quantum spin glasses and combinatorial optimization problems underpins the physical motivation for adiabatic quantum computing. On one hand, in disordered (quantum) spin systems, the focus is on exact methods such as the replica trick that allow the calculation of system quantities in the limit of infinite system and ensemble size. On the other hand, when solving a given instance of an optimization problem, disorder-averaged quantities are of no relevance, as one is solely interested in instance-specific, finite-size properties, in particular the optimal solution. Here, we apply the nonequilibrium Green's function formalism to the spin coherent-state path integral to obtain the statistical fluctuations and the collective-excitation spectrum along the annealing path. For the example of the quantum Sherrington-Kirkpatrick spin glass, by comparing to extensive numerically exact results, we show that this method provides access to the instance-specific bottlenecks of the annealing protocol.