The Purcell effect describes the modification of the spontaneous decay rate in the presence of electromagnetic media and bodies. In this work, we shed light on the dependencies and magnitude of this effect for chiral materials. Using the framework of macroscopic quantum electrodynamics and Fermi's Golden Rule, we study a chiral bulk medium with and without local-field corrections, an idealized chiral mirror and a chiral surface. The results imply that the chiral effect is greatest for large transition frequencies, molecules with large optical rotatory strength and media with a strong cross-susceptibility. In the case of a half space, short distances from the molecule to the interface additionally enhance the effect.

Quantum state engineering of light is of great interest for quantum technologies, particularly for generating nonclassical states of light, and is often studied through conditioning approaches. Recently, we demonstrated that state engineering approaches can be applied in intense laser-atom interactions to obtain measurement statistics which resemble optical “cat” states by using intensity measurements and classical postselection of the measurement data. Postprocessing of a finite-size sampled data set allows one to select specific events, here the processes that are energy conserving, corresponding to measurement statistics of nonclassical states of light. However, to fully realize the potential of this method for quantum state engineering, it is crucial to thoroughly investigate the role of the involved measurements and the finite-size nature of the postselection scheme. We illustrate this by analyzing the postselection approach recently developed for high harmonic generation, which enables the generation of optical cat states bright enough to induce nonlinear phenomena. These findings provide significant guidance for quantum light engineering and the generation of intense optical cat states with potential applications in nonlinear optics and quantum science.

We investigate correlated three-electron escape in Ne when driven by an intense, infrared laser field. We do so by employing a reduced-dimensionality quantum-mechanical model and two three-dimensional semiclassical models. One semiclassical model is a recently developed one that accounts with effective Coulomb potentials for the interaction between two bound electrons (ECBB) while it fully accounts for all other interactions. The other semiclassical model is the Heisenberg one, which effectively accounts for the interaction of each electron with the core via a soft-core potential. We identify and compare the signatures of correlated three-electron escape for both quantum and semiclassical models on Dalitz plots and find a better agreement between the quantum and the ECBB model. We also show that a central “spot” on the Dalitz plots is reproduced by all models. Using the ECBB model we associate this spot with the direct triple ionization pathway and argue this to be the case also for the quantum model. Devising a simple classical model that accounts for the direct pathway of triple ionization, we show that the width of this spot in the Dalitz plots solely depends on the time of tunnel ionization.

Room-temperature quantum entanglement not only is significant for the advancement of quantum physics but also has broad application prospects in quantum technology. Here we investigate the generation of room-temperature quantum entanglement in a polariton optomechanical system consisting of an optical mode, a molecular vibrational mode, and $N$ excitonic modes. The excitons and vibration are coupled via conditional displacement interactions, while the photon-exciton couplings occur via electric dipole interactions. We find that, mediated by exciton-vibration interaction, strong entanglement is established between the photon and the exciton, as well as between the photon and the vibration. Notably, the photon-vibration entanglement exhibits an astonishing enhancement with an increasing number of excitons, even far surpassing the entanglement generated from direct coupling between the exciton and vibration. Moreover, we demonstrate that these entanglements not only can be generated in a room-temperature environment ($T=300$ K) but also exhibit considerable robustness against thermal noise. Furthermore, we achieve tripartite entanglement in this system under both room- and ultrahigh-temperature conditions. The increase in the number of excitons can significantly improve the tolerance of tripartite entanglement to thermal noise and optical dissipation. Our results indicate that polariton optomechanical systems could provide a promising platform for generating room-temperature and high-temperature-resistant entangled quantum resources, which are crucial for practical quantum technologies.

Nonlinear effects may play a crucial role in addressing optical nonreciprocal behaviors in scattering media. Such behaviors are however typically observed within a single transmission channel and predominantly in media with fixed optical structures, which inherently restrict the tunability of a nonreciprocal response. We suggest to combine the (intrinsic) nonlinearities of a coherent multilevel medium with a tailored driving geometry that relies on two phase-mismatched standing-wave (SW) beams. This combination is essential for creating extra scattering channels over which, in addition, fully tunable optical nonreciprocal reflection can be attained. Our general approach is adapted here to four-level double-$\mathrm{\Lambda }$ atoms that are found to exhibit distinct forms of nonreciprocal multichannel scattering and to be quite sensitive to easily tunable parameters of two SW driving beams. The numerical results we present offer valuable insights into the field of non-Hermitian optical scattering and arise indeed from the interplay of interference among scattering processes and Bragg reflection.

Non-Hermitian systems have shown promising potential for realizing quantum information tasks that lack counterparts in the Hermitian realm. Understanding the dynamical characteristics of non-Hermitian systems as reflected in information-theoretic quantities is essential for advancing their applications. Here we investigate the dynamics of the trace distance and concurrence, which quantify information flow and entanglement, respectively, in non-Hermitian qubit systems exhibiting either parity-time or anti-parity-time symmetry. We identify dynamical fingerprints from the system density matrix which provide a unified explanation to the common oscillation and relaxation dynamics shared by the trace distance and concurrence observed in existing studies. We further investigate the fate of dynamical fingerprints under the impact of pure dephasing. Surprisingly, we find that pure dephasing can slow down the inherent relaxation of information flow and entanglement in non-Hermitian systems with unbroken anti-parity-time symmetry, suggesting a passive environment-assisted information protection in this class of non-Hermitian systems. Our findings enhance our understanding of dynamical non-Hermitian systems and have specific relevance to their information-oriented applications.

Quantum batteries represent one of the most promising applications of quantum thermodynamics, whose goal is not only to store energy inside small quantum systems but also to potentially leverage genuine quantum effects to outperform classical counterparts. In this context, however, energy fluctuations become extremely relevant and have a significant impact on the charging efficiency. In our work, we consider a simple yet paradigmatic model in which a flying qubit (the battery) coherently interacts with a single-mode optical cavity (the charger) through a number conserving Jaynes-Cummings interaction. By making use of full-counting statistics techniques, we fully characterize the average charging power, its fluctuations, and the associated charging efficiency for several different choices of initial states of the optical cavity, demonstrating that preparing the latter in a genuinely quantum non-Gaussian Fock state (rather than a classical or even nonclassical Gaussian state) leads to a definite and in principle measurable advantage in all these figures of merit.

As quantum computing advances towards practical applications, reducing errors remains a crucial frontier for developing near-term devices. Errors in the quantum gates and quantum state readout result in noisy circuits, which would prevent the acquisition of the exact expectation values of the observables. Although ultimate robustness to errors is known to be achievable by quantum error correction-based fault-tolerant quantum computing, its successful implementation demands large-scale quantum processors with low average error rates that are not yet widely available. In contrast, quantum error mitigation offers more immediate and practical techniques, which do not require extensive resources and can be readily applied to existing quantum devices to improve the accuracy of the expectation values. Here, we report the implementation of a zero-noise extrapolation-based error mitigation technique on a silicon spin qubit platform. This technique has recently been successfully demonstrated for other platforms such as superconducting qubits, trapped-ion qubits, and photonic processors. We first explore three methods for amplifying noise on a silicon spin qubit: global folding, local folding, and pulse stretching, using a standard randomized benchmarking protocol. We then apply global folding-based zero-noise extrapolation to the state tomography and achieve a state fidelity of 99.96% (98.52%), compared to the unmitigated fidelity of 75.82% (82.16%) for different preparation states. These results show that the zero-noise extrapolation technique is a versatile approach that is generally adaptable to quantum computing platforms with different noise characteristics through appropriate noise amplification methods.

Supersinglets are states of spin zero of $d\ge 3$ particles of $d$ levels. They are invariant under unitary transformations of the form $U^{\otimes d}$ and have applications in metrology, error protection, and communication. They also violate some specific Bell inequalities. However, none any of these applications require supersinglets nor do any of these Bell inequality violations capture the unique properties of the supersinglets. This leads to two questions. Question 1 is whether there exists a task that can be solved only with supersinglets. Question 2 is whether supersinglets can produce a unique $d$-partite, $d$-dimensional nonlocal signature. We answer both questions affirmatively by presenting a protocol that self-test all supersinglets by producing $d$-partite, $d$-dimensional perfect quantum strategies for any $d\ge 3$.

In recent years, the rapid development of quantum networks and distributed quantum clusters has created new opportunities to implement large-scale quantum algorithms. However, this advancement also presents a significant challenge: efficiently executing quantum programs based on entanglement distribution protocols within quantum clusters. This paper analyzes existing entanglement distribution protocols in the context of distributed quantum circuit execution, focusing on the on-demand distribution of entanglement (on-demand protocols) and the continuous distribution of entanglement (CD protocols). We define the min-depth qubit mapping and scheduling problem within the CD protocols, and we propose a systematic solution that encompasses protocol analysis, circuit partitioning and mapping, and remote operation scheduling. Furthermore, we introduce a connectivity-first swapping (CFS) scheme that outperforms the single random swap (SRS) scheme in the execution of distributed quantum circuits in most cases. Extensive evaluations demonstrate the effectiveness of our algorithms, achieving significant reductions in circuit execution times of 52.4%, 49.9%, and 53.1% in clusters with average bandwidths of 1, 3, and 5, respectively. The CFS protocol further enhances performance, reducing execution time by 24.5%, 19.7%, and 17.8% compared to the SRS protocol. Our method also reduces entanglement costs, decreasing consumption by an average of 20.3% compared to the baseline method at an average bandwidth of 3, while the CFS protocol further reduces costs by 11.5% compared to the SRS protocol.

We study the ${}^3\mathrm{He}^{2+}+\mathrm{He}$ differential ionization problem using the two-electron wave-packet convergent close-coupling (WP-CCC) method. We present the results for doubly differential cross sections for ionization in terms of the angle and energy of the emitted electrons at intermediate collision energies. In this energy region, coupling between all reaction channels and electron-electron correlation effects are of considerable importance. These are fully accounted for in the WP-CCC approach. Overall, our results are in good agreement with the available experimental data and other theoretical calculations. We also discuss the saddle-point ionization mechanism for this collision system. It is concluded that this mechanism is not justified in the intermediate-energy region.

We report a comprehensive study of charge-exchange dynamics in collisions of $\mathrm{H}{\mathrm{e}}^{+}$ and $\mathrm{H}{\mathrm{e}}^{2+}$ ions with Ne and Ar targets at velocities ranging from 0.63 to 1.41 a.u. (atomic units). Using a high-voltage cylindrical mirror analyzer, we analyzed scattered ions at a fixed large scattering angle of 14°, achieving sub-$K$-shell penetration where projectile-target separations fall below the $K$-shell radius of the target atoms. This work bridges the gap between low-velocity quasimolecular-orbital models and high-velocity perturbative approaches. The measured $\mathrm{H}{\mathrm{e}}^{2+}/\mathrm{H}{\mathrm{e}}^{+}$ ratios exhibit a strong dependence on both velocity and target species, which are quantitatively reproduced by a modified classical overbarrier model incorporating empirical corrections for screening effects. Our analysis reveals that $K$-shell electrons dominate charge exchange at intermediate velocities due to their ultrashort orbital periods, particularly in heavy targets like Ar. Our study advances the understanding of electron dynamics in deeply penetrating ion-atom collisions and provides a valuable reference for modeling charge transfer in asymmetric systems.

We study the nonlinear optical response of argon to a four-wave-mixing pulse sequence consisting of an extreme-ultraviolet pulse, a collinear IR dressing pulse, and a delayed noncollinear IR probe pulse. Sequential absorption of an extreme ultraviolet photon and an IR photon from the collinear beams excites the $3s^{-1}4p$ bright state and the $3s^{-1}3d/5s$ dark states. The subsequent absorption of an IR photon from the noncollinear beam then leads to an angled extreme ultraviolet emission, whose variation with delay encodes the coupling between autoionizing states, the lifetimes of dark states, and nonperturbative effects. Both our measurements and ab initio simulations of the angled four-wave-mixing signal reveal a double-peak structure in the delay dependence, in good agreement with each other. We attribute the central minimum between the two peaks to rapid Rabi cycling, driven by the collinear IR dressing pulse, between the dark states and the $3s^{-1}4p$ resonance, which leads to destructive interference in the final transition amplitude.

We develop a pulse-driven jump protocol to achieve all-optical Raman control of ultracold atomic hyperfine states. By establishing general conditions for adiabatic evolution between quantum states in parameter space, we derive the essential pulse area and phase conditions necessary for quantum state transfer in a resonant single-$\mathrm{\Lambda }$ three-level system. We extend this approach to a double-$\mathrm{\Lambda }$ four-level system by incorporating a neighboring intermediate state, which leads to a single-photon detuned $\mathrm{\Lambda }$ three-level system. Through numerical simulations of the ultracold ${}^{87}\mathrm{Rb}$ atomic system, we demonstrate that high-fidelity and robust control of quantum state transfer can be achieved in the single-$\mathrm{\Lambda }$ three-level system using stimulated Raman adiabatic passage and the pulsed jump protocol. Furthermore, we show that the destructive quantum interference effects between resonant and detuned Raman pathways in the double-$\mathrm{\Lambda }$ four-level system can be mitigated by optimizing the pulse area and two-photon detuning parameters within the pulsed jump protocol. This work presents a promising approach for achieving all-optical Raman control of quantum state transfer in ultracold atomic hyperfine states.

Using a specially constructed set of hard 2-satisfiability problems with four satisfying assignments, we study the scaling and sampling performance of numerical simulation of quantum annealing as well as that of the physical quantum annealers offered by D-Wave. To this end, we use both the standard quantum annealing and reverse annealing protocols in both our simulations and on the D-Wave quantum annealer. In the case of ideal quantum annealing the sampling behavior can be explained by perturbation theory and the scaling behavior of the time to solution depends on the scaling behavior of the minimum energy gap between the ground state and the first-excited state of the annealing Hamiltonian. The corresponding results from the D-Wave quantum annealers do not fit to this ideal picture, but suggest that the scaling of the time to solution from the quantum annealers matches those calculated from the equilibrium probability distribution.

Quantum error mitigation (QEM), an error suppression strategy without the need for additional ancilla qubits for noisy intermediate-scale quantum (NISQ) devices, presents a promising avenue for realizing quantum speedups of quantum computing algorithms on current quantum devices. However, prior investigations have predominantly been focused on Markovian noise, which only occurs when the separation between the system and environment is sufficiently large. In this paper, we propose a non-Markovian noise mitigation (NMNM) method by extending the probabilistic error cancellation (PEC) method in the QEM framework to treat non-Markovian noise. We present the derivation of a time-local quantum master equation where the incoherent coefficients are directly obtained from bath correlation functions (BCFs), key properties of a non-Markovian environment that will make the error mitigation algorithms environment aware. We further establish a direct connection between the overall approximation error and sampling overhead of QEM and the spectral property of the environment. Numerical simulations performed on a spin-boson model further validate the efficacy of our approach.

A quantum algorithm for computing the determinant of a unitary matrix $U\in U\left(N\right)$ is given. The algorithm requires no preparation of eigenstates of $U$ and estimates the phase of the determinant to $t$-binary digits accuracy with $O(N{log}^{2}N+t^2)$ operations and $tN$ controlled applications of $U^{2^m}$ with $m=0,...,t-1$. For an orthogonal matrix $O\in O\left(N\right)$ the algorithm can determine with certainty the sign of the determinant using $O\left(N{log}^{2}N\right)$ operations and $N$ controlled applications of $O$. An extension of the algorithm to contractions is discussed.

We investigate the measurement-induced entanglement transition (MIET) in a free-fermion chain under continuous measurements, using fluctuation as a scalable and accessible probe. The bipartite fluctuation of particle number within the subsystem is demonstrated to exhibit behaviors analogous to that of entanglement entropy. It effectively captures the nonequilibrium entanglement dynamics, as well as the transition in steady states from the critical phase with subextensive growth law to the area-law phase. By performing finite-size scaling analysis, we identify the critical measurement strength and demonstrate that the fluctuation can serve as a reliable indicator of the MIET. The results are consistent with previous entanglement entropy studies and reveal that the MIET belongs to the Berezinskii-Kosterlitz-Thouless universality class. Even when there are long-range hoppings or disorders, the fluctuation still acts as a reliable probe for the MIET. This approach offers a practical alternative to directly measuring entanglement entropy in monitored free-fermion chains, particularly for larger systems.