We investigate quantum thermometry using a single-qubit probe embedded in a non-Markovian environment, employing the numerically exact hierarchical equations of motion (HEOM) to overcome the limitations of Born-Markov approximations. Through a systematic analysis of the dynamical and steady-state behavior of the quantum signal-to-noise ratio (QSNR) for temperature estimation, we identify several key findings that challenge the conventional expectation that strong coupling necessarily enhances thermometric performance. In nonequilibrium dynamical thermometry, weak system-environment coupling generally yields the optimal QSNR, whereas in the steady-state regime, strong coupling enhances sensitivity only in the ultralow-temperature limit, while weak coupling significantly improves precision at moderately low temperatures. To optimize performance across coupling regimes, we develop a hybrid computational framework that integrates HEOM with quantum-enhanced particle swarm optimization, enabling precise quantum dynamical control under varying coupling strengths. Our results reveal fundamental constraints and opportunities in quantum thermometry, offering practical strategies for the design of high-performance quantum thermometers operating in realistic open quantum systems.

We apply reverse engineering to design laser pulse shapes for controlling the time evolution of strong-field transitions under environmental effects. Our effective two-state representation of the full quantum system involves dynamic Stark shifts and multiphoton Rabi frequency. Furthermore, the environment is modeled with dephasing and dissipative terms. Solving the master equation of the two-level density matrix inversely for the field, we obtain quasianalytic laser pulse shapes that simultaneously drive the populations and relative phase according to user-defined quantum pathways. The validity of the proposed scheme is demonstrated with the example of the $3s\to \to 4s$ two-photon transition of atomic sodium by solving the master equation of the multilevel system that incorporates effects beyond the adiabatic elimination and the rotating wave approximation. Due to the open character of the system, the proposed control is not always possible. We explore these situations and point out the conditions for creating steady states with large coherence.

We present a theoretical formalism to treat the ultracold dynamics of a pair of colliding polar molecules submitted to two laser fields. We express the dressed Hamiltonian including the dipole-dipole interaction of the colliding molecular pair, both in their ground and electronic excited states, as well as their interaction with the two laser fields. We apply adiabatic elimination of the electronic excited state to reduce the size of the dressed-state basis in which the dressed Hamiltonian is expressed. In an application, we investigate the feasibility of two-photon collisional shielding between two ${}^{23}\mathrm{Na}{}^{39}\mathrm{K}$ molecules, which could be favored by the Raman resonance condition suppressing unwanted spontaneous emission and photon scattering. We demonstrate the influence of laser Rabi frequencies on the dynamics through the computation of elastic, inelastic, and reactive collision rates, which is still insufficient to ensure noticeable shielding.

The ground-state properties of a spin-orbit-coupled rotating Bose-Einstein condensate with a gradient magnetic field in a toroidal trap are studied. When gradient magnetic fields are taken into account, the results are quite novel in that, in the spin-orbit-coupled nonrotating Bose-Einstein condensate with small gradient magnetic field intensity, the ferromagnetic system presents a plane-wave phase and satisfies the translational symmetry, and the antiferromagnetic system presents a stripe phase. With the increase of the magnetic field intensity, the translational symmetry of the ground state of the ferromagnetic system is broken, and the phase change tends to be similar in both ferromagnetic and antiferromagnetic systems. Considering the spin-orbit-coupled rotating Bose-Einstein condensate, the system gradually transforms from the nonsingle half-skyrmion chain to the single half-skyrmion chain with the increase of the gradient magnetic field, while the single half-skyrmion chain transforms to the nonsingle half-skyrmion chain with the increase of spin-orbit coupling. In addition, we obtain the phase diagram as a function of the gradient magnetic field and the spin-orbit-coupling intensity.

The partial polarization of the earth's radiation can be the source of radiometric errors for space instruments with polarization-sensitive components. It is therefore necessary to have a device capable of depolarizing the light before it enters the instrument, i.e., a polarization scrambler. Current scramblers used in optical payloads generally comprise combinations of prisms that enable spatial depolarization. However, polarization insensitivity comes at the cost of an inevitable degradation in imaging performance. Here we present a device based on an all-dielectric metasurface using anisotropic scatterers capable of generating multiple polarization states by varying their orientation angle. Our scrambling solution allows a massive reduction in the integrated degree of polarization and thus the spatial depolarization of any incident linear polarization, while reducing the impact on its image quality and allowing easier integration into the instrument design.

We demonstrate that statistical fluctuations in resonant radiation detectors operating in homodyne and heterodyne modes offer additional, complementary information to that obtained from their direct operation as click detectors. We use this to refine tests of the coherent-state hypothesis, which is of special interest for gravitational wave fields.

We theoretically investigate the collective dipole-dipole interactions in atoms coupled to a nanophotonic microring resonator. The atoms can interact with each other through light-induced dipole-dipole interactions mediated by free space and through the resonator whispering-gallery modes. The differing characteristics and mismatched wave numbers of these modes give rise to complex dynamics and provide new opportunities for controlling light-matter interactions. We explore these phenomena in the context of an experimentally realized atom cloud and study the potential of the proposed subwavelength atom arrays.

As a novel platform for exploring exotic quantum phenomena, the moiré lattice has garnered significant interest in solid-state physics, photonics, and cold-atom physics. While moiré lattices in two- and three-dimensional systems have been proposed for neutral cold atoms, the simpler one-dimensional moiré effect remains largely unexplored. We present a scheme demonstrating moiré effects in a one-dimensional cold-atom–cavity coupling system, which resembles a generalized open Dicke model exhibiting superradiant phase transitions. We reveal a strong link between the phase transition critical point and the one-dimensional moiré parameter. Evidence of the one-dimensional moiré effect is explicitly explored, including the cavity field spectrum, phase transition dynamics, and anomalous atomic diffusion. This work provides a new route for testing one-dimensional moiré effects with cold atoms and opens new possibilities in moiré metrology.

Distributing robust and long-distance entanglement between repeater nodes is a critical task for both foundational tests of quantum physics and the development of scalable quantum networks. In this paper, we propose a scheme for entangling two spatially separated exciton modes located in two exciton-optomechanical cavities. Each cavity, consisting of a semiconductor optomechanical cavity integrated with a quantum well, is simultaneously driven by a red-detuned laser and a squeezed vacuum light. Under realistic experimental conditions, we show that steady-state entanglement can be established between the two exciton modes by transferring quantum correlations from the squeezed light to them. Maximum entanglement is achieved when the exciton modes are tuned to resonance with the anti-Stokes sidebands of the driving lasers. With a high mechanical quality factor, the resulting entanglement exhibits robust behavior against thermal noise and remains significantly nonzero even at room temperature. Furthermore, we discuss a method to access and detect the excitonic entanglement. Our scheme provides a promising platform for practical long-distance entanglement distribution, which is of fundamental importance for quantum information processing and network architectures.

We revisit the generation and evolution of Bell nonlocality in hybrid scenarios of which the dynamics is determined by the Jaynes-Cummings Hamiltonian, a relevant example of which is the atom-cavity system. Previous approaches evaluate the nonlocality through the well-known qubit-qubit Clauser-Horne-Shimony-Holt (CHSH) formulas, using combinations of pseudospin operators for the electromagnetic (EM) field observables. While such an approach is sensible, it is far from optimal. In the present work we have used recent results on optimal Bell violation in qubit-qudit systems, showing that the nonlocality is much greater than previously estimated, both with and without noise. In addition, we provide an optimal treatment of noise, ensuring that our results are the best possible within this framework. We illustrate the results using different initial states for the EM field, including squeezed and coherent states. In addition, we study the asymptotic behavior of the entanglement. Remarkably, starting with a generic separable pure coherent state, the asymptotic mixed state is entangled, though it does not violate CHSH inequalities.

The diode-pumped Nd:vanadate laser is one of the most widely used lasers in the near-infrared range. Using passive Q-switching with a Cr:YAG saturable absorber, it generates nanosecond pulses at tens of kilohertz. It is well known to display either regular pulsing or low-dimensional deterministic chaos, depending on the absorber's position within the cavity. However, to our knowledge, a strange nonchaotic attractor (SNA) has never been reported in this system. Our experiments provide evidence that, for a specific absorber position, the laser dynamics correspond to a strange nonchaotic attractor. SNAs exhibit complex dynamical behavior that is neither periodic nor chaotic, positioning them as a valuable resource for applications requiring high spectral diversity while preserving predictable dynamics. By experimentally obtaining time series of two laser variables, we reconstruct the underlying attractor. For a certain position of the SA, we find that all Lyapunov exponents are negative and that the energy spectra exhibit a broad frequency range, indicating that the attractor is nonchaotic and lacks periodicity. Using Higuchi's method, we estimate the fractal dimension $\left(d_f\right)$ and find that $13\%$ of the nonchaotic time series exhibit a well-defined $d_f$, confirming the presence of an SNA.

Pulsed optical self-injection markedly affects the emission characteristics of semiconductor lasers. In this work, we analyze its influence on the statistical properties of laser-pulse interference. We experimentally demonstrate that varying the arrival time of reflected optical pulses back into the laser cavity influences the phase diffusion and induces an effect that, by analogy with external optical injection, we call phase locking. A comprehensive theoretical analysis of this phenomenon is also presented.

Electromagnetically induced transparency (EIT) in multilevel atomic systems exhibits complex dependencies on optical depth (OD) and polarization configurations, yet their combined effects remain underexplored. Here, we introduce a dissipation factor $\kappa$ which quantifies polarization-dependent absorption resulting from the emergence of dissipative channels. Starting from a semiclassical framework, we derive the transmission of a resonant probe as $T_{\text{res}}=exp(-\kappa ·d)$, where $d$ denotes the optical depth, demonstrating that $\kappa$ and OD jointly govern the transparency. And broadly, $\kappa$ is universally applicable across any multilevel system when its value spans a range $\kappa \in [0,1]$, where $\kappa =0$ corresponds to ideal transparency and $\kappa =1$ represents pure absorption. Our experimental results in cold ${}^{87}\mathrm{Rb}$ atomic ensemble across low and high OD regimes confirm the completeness of the theoretical model, with EIT line shapes showing close agreement with simulations. By elucidating the joint effects of OD and polarization-dependent dissipation in EIT, this work is conducive to systemic optimization in multilevel EIT systems such as quantum memory, optical switching, and precision metrology applications.

We investigate dynamical quantum phase transitions (DQPTs) in both pure and mixed states within the extended Su-Schrieffer-Heeger (SSH) model framework, focusing on the SSH-3 and SSH-4 models, which differ in symmetry properties. The SSH-3 model, characterized by a chiral-like point symmetry rather than true chiral symmetry, supports robust localized edge states tied to its topological nature. Our results show that for pure states, DQPTs occur after quenches crossing the topological transition, even when the energy band gap remains open. For mixed states, DQPT behavior aligns with pure states at low temperatures but undergoes significant changes at higher temperatures, including the emergence of multiple critical times. In contrast, the SSH-4 model, which possesses chiral symmetry, features four distinct energy-spectrum configurations. We find that pure-state DQPTs arise only when the quench starts from the initial state, chosen from a band that becomes gapless with another band at a certain critical point, and crosses the critical point. At finite temperature, mixed-state DQPTs persist at low temperatures only if the corresponding pure-state quench induces DQPTs, but they disappear at elevated temperatures. These findings elucidate the interplay between symmetry, band structures, and temperature in governing DQPTs within generalized SSH models.

Quantum process tomography (QPT) is a fundamental tool for fully characterizing quantum systems. It relies on querying a set of quantum states as input to the quantum process. Previous QPT methods typically employ a straightforward strategy for randomly selecting quantum states, overlooking differences in informativeness among them. In this work we propose a general active learning (AL) framework that adaptively selects the most informative subset of quantum states for reconstruction. We design and evaluate various AL algorithms and provide practical guidelines for selecting suitable methods in different scenarios. In particular, we introduce a learning framework that leverages the widely used variational quantum circuits to perform the QPT task and integrate our AL algorithms into the query step. We demonstrate our algorithms by reconstructing the unitary quantum processes resulting from random quantum circuits with up to seven qubits. Numerical results show that our AL algorithms achieve significantly improved reconstruction and the improvement increases with the size of the underlying quantum system. Our work opens new avenues for further advancing existing QPT methods.

The atomic hydrogen anion ${\mathrm{H}}^{-}$ is the lightest stable anion and its bound states and resonances are well studied in the literature. Due to the planned comparison of the bare antiproton to ${\mathrm{H}}^{-}$ in a Penning trap, we study the magnetic shielding of ${\mathrm{H}}^{-}$ using the nonrelativistic quantum electrodynamics theory, by accurately calculating the nonrelativistic shielding, as well as finite nuclear mass, relativistic, and partially QED corrections. We find that the finite nuclear mass correction is quite significant in ${\mathrm{H}}^{-}$ contributing about $0.1\%$ of the total shielding, which is more than twice as much as the relativistic correction. Our final result for the shielding constant has a nine-parts-per-trillion accuracy and paves the way for direct comparison of the antiproton-to-proton magnetic moments.

Coherent exciton transport is investigated in the presence of several different forms of disorder. We consider linear dye assemblies capable of functioning as exciton transmission lines and focus on the degrading effects of static disorder on exciton coherence in several scenarios, whether introduced through lattice imperfections or in the optical response of the constituent dyes. Impurities are ascribed to sections of consecutive dyes in the line in which incident ballistic excitons can propagate in and scatter, reflecting and transmitting as conditions permit. Single- and few-site impurities are first considered, and then static disorder is introduced in the scattering sections in two ways: as random transition energies or as altered transfer couplings between dyes. These cases are compared, and some intriguing dynamics result: reflection (attenuation) is more significant with disorder in the transfer couplings, some conditions have an even-odd pattern in reflections, and midband exciton encounters with this type of disorder acquire no phase alteration. Lastly, these two cases of static disorder are compared with the dynamic noise arising from molecular vibrations, and both are found to be comparably modest. With applications in mind, several phenomenological and quantitative relations for coherent exciton transport are obtained as simple functions of the introduced disorder.