We study the dynamics of quantum systems interacting with a stream of entangled-qubit pairs in the weak coupling limit. For a large class of two-qubit bath states, we present a detailed framework describing conditional dynamical maps for the system, known as quantum trajectories, that arise when the qubits are measured. Depending on the measurement basis, these quantum trajectories can be jump-type or diffusive-type, and can successively transfer entanglement from the bath qubits other quantum systems. They also exhibit features not present in standard quantum optical trajectories due to the fact that collisional models are not confined by the standard white-noise limit for optical-mode baths. As an example of this formalism, we consider the case of two remote two-level systems, where jump-type quantum trajectories herald the birth and death of entanglement.

Uncertainty relations play a significant role in drawing a line between classical physics and quantum physics. Since the introduction by Heisenberg, these relations have been considerably explored. However, the effect of quantum entanglement on uncertainty relations was not probed. Berta et al. [Nat. Phys. 6, 659 (2010)] removed this gap by deriving a conditional-entropic uncertainty relation in the presence of quantum entanglement. In the same spirit, using inferred-variance, we formulate uncertainty relations in the presence of entanglement for general two-qubit systems and arbitrary observables. We derive lower bounds for the sum and product inferred-variance uncertainty relations. Strikingly, we can write the lower bounds of these inferred-variance uncertainty relations in terms of measures of entanglement of two-qubit states, as characterized by concurrence, or $G$ function. The presence of entanglement in the lower bound of inferred-variance uncertainty relation is quite distinctive. We also explore the violation of local uncertainty relations in this context and an interference experiment. Furthermore, we discuss possible applications of these uncertainty relations.

A unified theoretical framework is developed for measuring multimode Gaussian states of multiple point sources. The spatial and temporal mode functions are found analytically by aid of the circular symmetry of the object plane and aperture, as well as by the rectangular spectral density function of the background. They relate the modal operators and statistical moments to the locations of the point sources through the prolate spheroidal functions. An experimentally straightforward implementation is proposed, which consists of a nonabsorptive polarization- and phase-modulating spatial light modulator (SLM), three lenses, and a polarization beam splitter. Interestingly, it is found that the spatial modal annihilation operators are related to the modal field operators in the image plane by a simple complex-valued scale factor. The quantum Fisher information matrix and quantum Cramér-Rao bound (QCRB) are also discussed. The numerical calculation of QCRB is completed for the case where the spatially multimode aperture fields are prepared by the spatial propagation from temporally single-mode thermal states, coherent states, or quadrature squeezed states of the point sources in the object plane. The results show that the Rayleigh limit can always be surpassed by means of increasing the mean photon rate or the squeeze parameter.

In the quantum-computation scenario, the geometric phase gates are becoming increasingly attractive for their intrinsic fault tolerance to disturbance. With an adiabatic cyclic evolution, Berry phase appears to realize a geometric transformation. Performing the quantum gates as many as possible within the timescale of coherence, however, remains an inconvenient bottleneck due to the systematic errors. Here we propose an accelerated adiabatic quantum gate based on the Berry phase, the transitionless driving, and the dynamical decoupling. It reconciles a high fidelity with a high speed in the presence of control noise or imperfection. We optimize the dynamical-decoupling sequence in the time domain under a popular Gaussian noise spectrum following the inversely quadratic power law.

We use optical tweezers based on time-multiplexed acousto-optic deflectors to trap ultracold cesium atoms in one-dimensional arrays of atomic ensembles. For temperatures between $2.5\mu \mathrm{K}$ and $50\mathrm{nK}$ we study the maximal time between optical tweezer pulses that retains the number of atoms in a single trap. This time provides an estimate of the maximal number of sites in an array of time-multiplexed optical tweezers. We demonstrate evaporative cooling of atoms in arrays of up to 25 optical tweezer traps and the preparation of atoms in a box potential. Additionally, we demonstrate three different protocols for the preparation of atomic-ensemble arrays by transfer from an expanding ultracold atomic cloud. These result in the preparation of arrays of up to 74 atomic ensembles consisting of $\sim 100$ atoms on average.

We investigate theoretically resonant harmonic generation in $\text{H}{\text{e}}^{+}$ from an elliptically polarized laser field. The results show that there are two anomalous resonance-enhanced harmonics and the intensities of the anomalous resonance-enhanced harmonics remain unchanged for different laser ellipticities which are approximately two orders of magnitude stronger than those of nonresonant harmonics. We illustrate that the first resonance-enhanced harmonic is due to the transition between the ground state and the first excited state and the second one is due to the transition between the ground state and the second excited state. Our results also show that the enhancements of the harmonic intensities are related to the continuous collisions of the electron with the parent ion due to multiphoton resonance. The two resonance-enhanced harmonic intensities decrease gradually and orders do not change with an increase of the laser intensity, which can be illustrated through the Stark effect. The ellipticities of the two resonance-enhanced harmonics are approximately equal to the selected driving laser ellipticities regardless of the $\pm$ sign under different driving laser ellipticities, which might provide an accessible route toward characterizing the polarization properties of the laser. Our results offer a way for the generation of quasimonochromatic circularly polarized EUV radiation with high intensity.

We investigate the superfluidity of a three-dimensional weakly interacting Bose gas with a one-dimensional Raman-type spin-orbit coupling at both zero and finite temperatures. Using the imaginary-time Green's function within the Bogoliubov approximation, we explicitly derive analytic expressions of the current-current response functions in the plane-wave and zero-momentum phases, from which we extract the superfluid density in the limits of long wavelength and zero frequency. At zero temperature, we check that the resultant superfluid density agrees exactly with our previous analytic prediction obtained from a phase-twist approach. Both results also satisfy a generalized Josephson relation in the presence of spin-orbit coupling. At finite temperature, we find a significant nonmonotonic temperature dependence of superfluid density near the transition from the plane-wave phase to the zero-momentum phase. We show that this nontrivial behavior might be understood from the sound velocity, which has a similar temperature dependence. The nonmonotonic temperature dependence is also shared by Landau critical velocity, above which the spin-orbit-coupled Bose gas loses its superfluidity. Our results would be useful for further theoretical and experimental studies of superfluidity in exotic spin-orbit-coupled quantum gases.

Librational motion, whereby a rigid body undergoes angular oscillation around a preferred direction, can be observed in optically trapped, silica microspheres. We demonstrate the cooling of 1 librational degree of freedom for $\sim 5-\mu \text{m-diameter}$ spheres that have been induced to rotate with an external electric field coupled to their electric dipole moment. Cooling is accomplished by adding a phase modulation to the rotating field. The degree of cooling is quantified by applying a $\pi /2$ shift to the phase of the electric field and fitting the resulting exponential decay of the librational motion to obtain a damping time, as well as estimating a mode temperature from the observed libration in equilibrium. The result is an important step in the study of the dynamics of trapped microspheres, crucial to cooling the mechanical motion to its ground state, as well as providing insights regarding the charge mobility in the material at microscopic scales.

Due to their highly coherent emission, tunability, and compactness, integrated single-frequency diamond Raman lasers are interesting tools for applications in integrated quantum technology, high-resolution spectroscopy, or coherent optical communications. While the fundamental emission linewidth of these lasers can be Fourier limited, their thermo-optic characteristics lead to drifts in their carrier frequency, posing important challenges for applications requiring ultrastable emission. We propose here a method for measuring accurately the temperature-dependent index of refraction of diamond by employing standing Stokes waves produced in a monolithic Fabry-Pérot diamond Raman resonator. Our approach takes into account the influence of temperature on the first-order phonon line and the average lattice phonon frequency under intense stimulated Raman scattering conditions. We further utilize this model to calculate the value of the average phonon frequency and then the temperature-dependent thermo-optic coefficient. The theory is accompanied by the demonstration of tunable Fourier-limited Stokes nanosecond pulses with a stabilized center frequency deviation of less than $4$ MHz.

We propose a method to adiabatically control an atomic ensemble using a decoherence-free subspace (DFS) within a dissipative cavity. We can engineer a specific eigenstate of the system's Lindblad jump operators by injecting a field into the cavity which deconstructively interferes with the emission amplitude of the ensemble. In contrast to previous adiabatic DFS proposals, our scheme creates a DFS in the presence of collective decoherence. We therefore have the ability to engineer states that have high multiparticle entanglements which may be exploited for quantum information science or metrology. We further demonstrate a more optimized driving scheme that utilizes the knowledge of possible diabatic evolution gained from the so-called adiabatic criteria. This allows us to evolve to a desired state with exceptionally high fidelity on a timescale that does not depend on the number of atoms in the ensemble. By engineering the DFS eigenstate adiabatically, our method allows for faster state preparation than previous schemes that rely on damping into a desired state solely using dissipation.

The antibunching effect generated in a cavity containing first a single two-level atomic system and then two identical atoms is explored for off-resonant interactions, in strong- and weak-coupling regimes. The cavity is driven by coherent and squeezed sources. Using the second-order correlation function analytically derived in the weak-excitation regime, we show that squeezed light achieves and improves strong antibunching, leading to a photon blockade. This enhancement is due to a destructive quantum interference mechanism induced by the nonclassical light, creating a supplementary transition pathway. The best effect is obtained for equal frequency detunings in the strong-coupling regime. More interestingly, our investigation reveals that the two-atom-cavity system can further improve the antibunching effect compared to the single-atom cavity. It turns out that the additional couplings appearing in the cavity due to the implementation of the two atoms, combined with the squeezed light, could substantially enhance the photon-blockade effect.

The vibrational branching ratios of SrOH for radiative decay to the ground electronic state, $X{}^2{\mathrm{\Sigma }}^{+}$, from the first two electronically excited states, $A{}^2\mathrm{\Pi }$ and $B{}^2{\mathrm{\Sigma }}^{+}$, are determined experimentally at the $\sim {10}^{-5}$ level. The observed small branching ratios enable the design of a full, practical laser-cooling scheme, including magnetooptical trapping and sub-Doppler laser cooling, with $>{10}^4$ photon scatters per molecule. Ab initio calculations sensitive to weak vibronic transitions are performed to facilitate the experimental measurement and analysis, and show good agreement with the experiment.

Wave tunneling is an intriguing phenomenon spanning different branches of physics, from quantum mechanics to classical electrodynamics and optics. The Wigner (or phase) time is proved to be an adequate measure to describe wave transit through a potential barrier or material layer in the tunneling regime. Here we analytically and numerically calculate the Wigner time for electromagnetic-radiation propagation through the layer of both lossless and lossy plasmas. It is shown that the plasma frequency is the key parameter governing the value of Wigner time, allowing us to interpret tunneling as due to the reaction of plasma as a whole. We analyze the Wigner time for obliquely incident waves of transverse electric (TE) and transverse magnetic (TM) polarizations and discuss the meaning of negative Wigner times appearing in the lossy case in the low-frequency range and close to the plasma frequency. The results show that plasma deserves attention as a perspective object for tunneling studies.

We study the optical properties of a hybrid device composed by a quantum dot (QD) resonantly coupled to a photonic mode of an optical microcavity and a Majorana nanowire: a topological superconducting segment hosting Majorana bound states (MBSs) at the opposite ends. In the regime of strong light-matter coupling, it is demonstrated that the leakage of the Majorana mode into the QD opens new optical transitions between polaritonic states formed due to hybridization of material excitation with cavity photons, which leads to the reshaping of the Jaynes-Cummings ladder and can lead to the formation of a robust single peak at cavity eigenfrequency in the emission spectrum. Moreover, weak satellite peaks in the low- and high-frequency regions are revealed for the distinct cases of highly isolated MBSs, overlapped MBSs, and MBSs not well localized at the nanowire ends.

Quantum dissipation arises from the unavoidable coupling between a quantum system and its surrounding environment, which is known as a major obstacle in the quantum processing of information. Apart from its existence, examining how to trace dissipation from observational data is important and may stimulate ways to suppress the dissipation. In this paper, we propose to learn about quantum dissipation from dynamical observations using the neural ordinary differential equation, and then demonstrate this method concretely on two open quantum-spin systems: A large spin system and a spin-1/2 chain. We also investigate the learning efficiency of the dataset, which provides useful guidance for data acquisition in experiments. Our work helps to facilitate effective modeling and decoherence suppression in open quantum systems.

Artificial neural networks are at the heart of modern deep learning algorithms. We describe how to embed and train a general neural network in a quantum annealer without introducing any classical element in training. To implement the network on a state-of-the-art quantum annealer, we develop three crucial ingredients: binary encoding the free parameters of the network; polynomial approximation of the activation function; and reduction of binary higher-order polynomials into quadratic ones. Together, these ideas allow encoding the loss function as an Ising model Hamiltonian. The quantum annealer then trains the network by finding the ground state. We implement this for an elementary network and illustrate the advantages of quantum training: its consistency in finding the global minimum of the loss function and the fact that the network training converges in a single annealing step, which leads to short training times while maintaining a high classification performance. After training the network using a quantum annealer, one can then use the quantum network weights in a classical network algorithm of identical design for inference. Our approach opens an avenue for the quantum training of general machine learning models.

We report on further investigation of nuclear hyperpolarization of ${}^3\mathrm{He}$ in magnetized plasma at a magnetic field of 3.66 T and at different experimental conditions in a dual cell of relatively large volume, compared to those reported in the original polarization of atoms in a magnetized plasma (PAMP) paper by Maul et al. [Phys. Rev. A 98, 063405 (2018)]. It was found that steady-state nuclear polarizations obtained by this method strongly increase with temperature and rf gas discharge power. We managed to reach almost 8% at the highest possible temperature in our setup which is to date the highest polarization obtained by this method at 10 mbar. It was also shown that atomic oxygen in plasma, considered as an impurity, could be a good probe of plasma parameters relevant for the PAMP process, either in the temperature or the metastable ${}^3\mathrm{He}$ density. The polarization buildup rates with the cell temperature stabilized near room temperature are found to be of the order of 1 ${\mathrm{s}}^{-1}$, which is by two orders of magnitude faster than was reported in the original PAMP paper for the same filling pressure. These observations promise a further optimization of experimental conditions towards strong and fast hyperpolarization by this method.

We calculate the intensity-field correlations in the light scattered by $N$ cold atoms driven by a quasiresonant laser field. Fundamental differences occur if the atomic state is an entangled single-excitation state or a coherent factorized state. We provide analytic expressions for the two-time field and intensity correlation functions for the timed Dicke state and the quasi-Bloch state. The comparison with multiatom simulations shows good agreement between numerical and analytic solutions.