Device-independent (DI) quantum secret sharing (QSS) can relax the security assumptions about the devices' internal workings and provide QSS the highest level of security in theory. The original DI QSS protocol proved its correctness and completeness under a causal independence assumption regarding measurement devices. However, there has been a lack of DI QSS's performance characterization in practical communication situations, which impedes its experimental demonstration and application in the future. Here we propose a three-partite DI QSS protocol with noise preprocessing and postselection strategies and develop the numerical methods to implement its performance characterization in practical communication situations. The adoption of the noise preprocessing and postselection can reduce DI QSS's global detection efficiency threshold from 96.32% to 94.30% and increase the noise threshold from 7.148% to 8.072%. Our DI QSS protocol has two advantages. First, it is a DI QSS protocol with performance characterization in practical communication situations. Second, the adoption of noise preprocessing and postselection can effectively relax its experimental requirement and enhance the noise resistance. Our DI QSS protocol has potential for future experimental demonstration and application.

Digital-analog quantum computing (DAQC) combines digital gates with analog operations, offering an alternative paradigm for universal quantum computation. This approach leverages the higher fidelities of analog operations and the flexibility of local single-qubit gates. In this paper, we propose a quantum genetic algorithm within the DAQC framework using a Rydberg-atom emulator. The algorithm employs single-qubit operations in the digital domain and a global driving interaction based on the Rydberg Hamiltonian in the analog domain. We evaluate the algorithm performance by estimating the ground-state energy of Hamiltonians, with a focus on molecules such as ${\mathrm{H}}_2, \mathrm{LiH}$, and ${\mathrm{BeH}}_2$. Our results show energy estimations with less than 1% error and state overlaps nearing 1, with computation times ranging from a few minutes for ${\mathrm{H}}_2$ (two-qubit circuits) to one to two days for $\mathrm{LiH}$ and ${\mathrm{BeH}}_2$ (six-qubit circuits). The gate fidelities of global analog operations further underscore DAQC as a promising quantum computing strategy in the noisy intermediate-scale quantum era.

We theoretically study an artificial neuron circuit containing a quantum memristor in the presence of relaxation and dephasing. The charge transport in the quantum element is realized via tunneling of a charge through a quantum particle which shuttles between two terminals—a functionality reminiscent of classical diffusive memristors. We demonstrate that this physical principle enables hysteretic behavior in the current-voltage characteristics of the quantum device. In addition, being used in an artificial neural circuit, the quantum switcher is able to generate self-sustained current oscillations. Our analysis reveals that these self-oscillations are triggered only in quantum regimes with a moderate rate of relaxation, and cannot exist either in a purely coherent regime or at a very high decoherence. We investigate the hysteresis and instability leading to the onset of current self-oscillations and analyze their properties depending on the circuit parameters. Our results provide a generic approach to the use of quantum regimes for controlling hysteresis and generating self-oscillations.

Precision spectroscopic measurements in atoms and molecules play an increasingly important role in chemistry and physics, e.g., to characterize structure and dynamics at long timescales, to determine physical constants, or to search for physics beyond the standard model of particle physics. In this paper, we demonstrate the combination of Zeeman deceleration and transverse laser cooling to generate slow (mean velocity of 175 m/s) and transversely ultracold ($T_{\perp }\approx 135\mu \mathrm{K}$) supersonic beams of metastable $\left(1s\right)\left(2s\right){}^{3}S_1$ He (${\mathrm{He}}^{*}$) for precision spectroscopy. The curved-wavefront laser-cooling approach is used to achieve large capture velocities and high ${\mathrm{He}}^{*}$ number densities. The beam properties are characterized by imaging, time-of-flight, and high-resolution spectroscopic methods, and the factors limiting the Doppler widths in single-photon spectroscopic measurements of the $\left(1s\right)\left(40p\right){}^{3}P_J\leftarrow \left(1s\right)\left(2s\right){}^{3}S_1$ transition at UV frequencies around $1.15\times {10}^{15}$ Hz are analyzed. In particular, the use of skimmers to geometrically confine the beam in the transverse directions is examined and shown to not always lead to a reduction of the Doppler width. Linewidths as narrow as 5 MHz could be obtained, enabling the determination of line centers with a precision of $\mathrm{\Delta }\nu /\nu$ of $4\times {10}^{-11}$ limited by the signal-to-noise ratio. Numerical particle-trajectory simulations are used to interpret the experimental observations and validate the conclusions.

We extend the truncated three-wave theory used to describe degenerate four-wave mixing in optical fibers to take into account the impact of higher-order harmonic sidebands. Using second-order perturbation theory combined with adiabatic elimination, our extended theory preserves the initial framework of the three-wave description. This allows the subsequent discussion of the origin of the nonpreservation of the Fermi-Pasta-Ulam-Tsingou recurrence that is observed in optical fibers. Our analytical results are supported by numerical simulations and experimental observations.

The Jaynes-Cummings quantum optics model allows us to understand the dialogue between light and matter at its most fundamental level, which is crucial for advancements in quantum science and technology. Several generalizations of the model have been proposed, emphasizing their dynamic behavior but paying less attention to their spectroscopy. Here we obtain analytical expressions of the time-dependent spectral response of a nonlinear Jaynes-Cummings model based on deformed field operators. We show that the long-time response of the resulting nonlinear cavity field resembles the one experimentally obtained in the strong-dispersive regime of circuit quantum electrodynamics. The spectrum is intrinsically asymmetric with the nonlinear coupling, a signature of the impossibility of getting resonant conditions for finite field excitations.

We investigate the nonreciprocal quantum phase transition in a cavity magnonic system driven by a parametric field, where an yttrium iron garnet (YIG) sphere is placed in a spinning microwave resonator. The system exhibits a rich phase diagram due to both magnon Kerr nonlinearity in YIG and parametric drive on the resonator. Especially, Sagnac-Fizeau shift caused by the spinning of the resonator brings about a significant modification in the critical driving strengths for second- and first-order quantum phase transitions, which means that the highly controllable quantum phase can be realized by the spinning speed of the resonator. More importantly, based on the difference in the detunings of the counterclockwise and clockwise modes induced by spinning direction of the resonator, we show that the phase transition in this system is nonreciprocal, that is, the quantum phase transition occurs when the cavity is driven in one direction but not the other. Our work offers an alternative path to engineer and design nonreciprocal magnonic devices.

Trapped ions are an ideal platform to implement quantum simulation. Previously, the parity-time ($\mathcal{PT}$)-reversal symmetry-breaking transition in the paradigmatic non-Hermitian Hamiltonian $h_{\mathcal{PT}}=J{\sigma }_x-i\mathrm{\Gamma }{\sigma }_z$ was observed in a single-ion experiment in a passive way. In this work we propose to study the interaction effects on the $\mathcal{PT}$-symmetry-breaking transition in a chain of $N$ trapped interacting ions. We consider an effective Ising interaction $H_{\text{int}}^{\text{Ising}x}={\sum }_{j<k}{U}_{jk}{\sigma }_x^j{\sigma }_x^k$ between the ions on top of $h_{\mathcal{PT}}$. We find that sufficiently strong interaction strength can enhance the $\mathcal{PT}$-symmetric phase for even $N$, while the phase is suppressed in all the other cases. In particular, the suppression can be so strong that even infinitesimal dissipation, quantified by $\mathrm{\Gamma }$, can turn the system into the $\mathcal{PT}$-symmetry-breaking phase. In addition, we assess the convolved effects due to the coupling and the spin phase shifts. Our findings can be readily tested in ion chain experiments.

The system of a charged impurity in an interacting Bose gas has gained significant attention due to the long-range ion-atom interactions and the study of transport properties. Here, the ground-state energy of a charged Bose polaron is calculated within the Bogoliubov approximation using a generalized Feynman variational path-integral approach, which obtained accurate results for other polaron problems. We find that compared to other existing approaches, our approach gives similar and improved results while being numerically less intensive. Optical absorption, which is a standard tool to study the solid-state polaron, is introduced here as a probing method for the Bose polaron. It is calculated within the Bogoliubov approximation for weak ion-atom interactions, and the effect of finite temperature is studied. We show that the coupling of the ion to an oscillating external electric field offers a straightforward experimental probe for the charged polaron in a Bose gas, different from but complementary to existing spectroscopic techniques.

This paper proposes a class of tight upper and lower bounds for the optimal probability of correctly discriminating $K$ quantum signals. The tightness of these bounds is shown analytically and numerically. These bounds are optimal for a binary quantum signal. The proposed upper bounds are based on a generalized trace distance measure between more than two quantum states. Also, we propose projector measurements that are good candidates for the near-optimal projector measurement. Also, an equivalent expression for the bounds is given based on the Gram matrix, which is more appropriate for numerical calculations, especially for digital quantum communication purposes, such as investigating the error probability of classical communication by using high-dimension quantum pulse position modulation signals.

We introduce a strategy to develop optimally designed fields for continuous dynamical decoupling. Using our methodology, we obtain the optimal continuous field configuration to maximize the fidelity of a general one-qubit quantum gate. To achieve this, considering dephasing-noise perturbations, we employ an auxiliary qubit instead of the boson bath to implement a purification scheme, which results in unitary dynamics. Employing the sub-Riemannian geometry framework for the two-qubit unitary group, we derive and numerically solve the geodesic equations, obtaining the optimal time-dependent control Hamiltonian. Also, due to the extended time required to find solutions to the geodesic equations, we train a neural network on a subset of geodesic solutions, enabling us to promptly generate the time-dependent control Hamiltonian for any desired gate, which is crucial in circuit optimization.

Nonclassical states of bosonic modes are important resources for quantum-enhanced technologies. However, quantifying nonclassicality of these states, in particular mixed states, can be a challenge. Here we present results of quantifying the nonclassicality of a bosonic mode in a mixed Fock state via the operational resource theory measure [Phys. Rev. Res. 2, 023400 (2020)], which relates nonclassicality to metrological advantage. Generally speaking, evaluating a resource-theoretic measure for mixed states is challenging, since it involves finding a convex roof. However, we show that our problem can be reduced to a linear programming problem. By analyzing the results of numerical optimization, we are able to extract analytical results for the case where three or four neighboring Fock states have nonzero population. Interestingly, we find that such a mode can be in distinct phases, depending on the populations. Finally, we demonstrate how our method is generalizable to density matrices of higher ranks. Our findings suggest a viable method for evaluating nonclassicality of arbitrary mixed bosonic states and potentially for solving other convex roof optimization problems.

The ionization and fragmentation of small water clusters induced by electron impact (80 eV) is investigated. Using a multiparticle coincidence spectrometer (reaction microscope), all three charged final state particles—two outgoing electrons and one fragment ion—are detected. Nonprotonated ${\left({\mathrm{H}}_2\mathrm{O}\right)}_2^{+}$ and protonated water clusters ${\mathrm{H}}_3{\mathrm{O}}^{+}, {\left[{\mathrm{H}}_2\mathrm{O}\right]}_2{\mathrm{H}}^{+}, {\left[{\mathrm{H}}_2\mathrm{O}\right]}_4{\mathrm{H}}^{+}$, and ${\left[{\mathrm{H}}_2\mathrm{O}\right]}_5{\mathrm{H}}^{+}$ are identified in the measured ion spectrum. The ionization channels for formation of these species are investigated by measuring the kinetic energy distributions and the electronic states of the ions. Only a single state can lead to (${\mathrm{H}}_2{\mathrm{O})}_2^{+}$, which is identified as ionization of water dimer with a $1{\mathrm{b}}_1$ hole at the hydrogen bonding donor molecule, while for the protonated water species three major electronic states corresponding to the ionization of $1{\mathrm{b}}_1, 3{\mathrm{a}}_1$, and $1{\mathrm{b}}_2$ type orbitals are observed.

During recent years, interest has been rising for applications of vector light beams toward magnetic field sensing. A series of experiments were performed to extract information about properties of static magnetic fields from absorption profiles of light passing through an atomic gas target. In this paper, we propose an extension to this method for oscillating magnetic fields. To investigate this scenario, we carried out theoretical analysis based on the time-dependent density matrix theory. We found that absorption profiles, even when averaged over typical observation times, are indeed sensitive to both strength and frequency of the time-dependent field, thus opening the prospect for a powerful diagnostic technique. To illustrate this sensitivity, we performed detailed calculations for the $5s{}^2{S}_{1/2}(F=1)-5p{}^2{P}_{3/2}(F=0)$ transition in rubidium atoms, subject to a superposition of an oscillating (test) and a static (reference) magnetic field.

We present the results of stroboscopic microwave spectroscopy of a radio-frequency-dressed optically pumped magnetometer. The interaction between radio-frequency-dressed atoms and a synchronously pulsed microwave field followed by Voigt-effect-based optical probing allows us to perform a proper ground-state interrogation for dressed state and assess the efficiency of the state preparation process. This work shows that through the stroboscopic technique the microwave spectrum is simplified when compared to the continuous counterpart. This is a necessary step towards investigating vector magnetometers in unshielded environments, where the influence of the nonlinear Zeeman effect, a source of heading errors, would otherwise be spectrally unresolved in dressed states. To theoretically describe the system, we solve the dynamical equation of the density matrix employing Floquet expansion. Our theoretical results are in good agreement with experimental measurements over a wide range of parameters and pumping conditions.

The Airy gas, which is the simplest edge electron gas, became an important model system for the exchange-correlation and kinetic energy functional development of the ground-state density functional theory. In this work, we compute the random phase approximation (RPA) and the adiabatic local density approximation (ALDA) Airy-gas density response functions, using the exact one-particle orbitals and eigenvalues. From the dynamical response function, we study several properties of the Airy-gas model, such as the Airy loss-function, the induced density, the Airy-plasmon full width at half maximum, the screened interaction, and the stopping power, providing a systematic study of these properties with respect to the slope of the effective linear potential $F$ that can be considered the main variable of any metal surface. For instance, using the peaks of the loss function, we extract the Airy-gas plasmon energy dispersion, and we perform a careful analysis of the Airy-gas plasmons at various slopes of the effective linear potential. We find similar features with the real metal surfaces, such as the long-wavelength Airy-plasmon coefficient is negative and very sensitive to the slope value $F$, while the short-wavelength Airy-plasmon coefficient is almost independent on $F$. Overall, we show that the slope $F$ plays a crucial role for the surface plasmons and their related properties.