This study aims at examination of the lower-order spectral moments in collision-induced absorption (CIA), taking the translational He-Ar band as an example. Quantum corrections for the zeroth and first spectral moments of the translational profile are derived on the basis of the Wigner expansion up to the order of ${\hslash }^8$ and ${\hslash }^{10}$, respectively. These corrections were then explored for numerical simulation of the He-Ar moments over the temperature range 50–500 K. The accuracy of the obtained temperature dependencies is validated through the comparison with direct quantum solution of the scattering and bound-state problems as well as with the results obtained using the path-integral (PI) approach. Close agreement was achieved as a result of the application of the two independent ways of approximate accounting for the quantum nature of absorption. The robustness of the Wigner expansion and PI corrections was thus demonstrated, both of which can be used to obviate direct quantum simulation of the CIA spectral moments. The approximate method is suggested for an accurate simulation of the CIA spectral profile on the basis of the obtained quantum-corrected moments and the classical trajectory-based formalism.

The aim of the Cold Molecule Nuclear Time-Reversal Experiment (CeNTREX) is to search for a time-reversal symmetry violation in the thallium nucleus by measuring the Schiff moment of ${}^{205}\mathrm{Tl}$ in the polar molecule thallium fluoride (TlF). CeNTREX uses a cryogenic beam of TlF with a rotational temperature of 6.3(2) K. This results in a population spread over dozens of rotational and hyperfine sublevels of TlF, although only a single level is useful for the Schiff-moment measurement. Here, we present a protocol for cooling the rotational and hyperfine degrees of freedom in the CeNTREX beam, transferring the majority of the Boltzmann distribution into a single rotational and hyperfine sublevel by using a single ultraviolet laser and a pair of microwave beams. We achieve a factor of 20.1(4) gain in the population of the $J=0, F=0$ hyperfine sublevel of the TlF ground state.

Shaped free electron vortices (SEVs) have recently been studied using atomic ($1+2$) resonance-enhanced multiphoton ionization (REMPI) by oppositely chirped counterrotating circularly polarized (OC-CRCP) femtosecond laser pulses. By transitioning from the perturbative to the nonperturbative REMPI regime, we identify an adiabatic excitation mechanism in a resonant V-type three-level system, termed V-RAP due to its similarities to rapid adiabatic passage (RAP). Experimentally, we observe a pronounced change in the shape of the measured three-dimensional (3D) photoelectron momentum distribution (PMD), which we trace back to this mechanism via analytical calculations and numerical simulations of the bound state and ionization dynamics. In V-RAP, the atom adiabatically follows the OC-CRCP field, with the two excited states driven in antiphase, leading to an adiabatic cancellation of specific ionization pathways and explaining the observed changes in the PMD. In the experiment, we combine supercontinuum polarization pulse shaping to generate OC-CRCP femtosecond laser pulses with velocity map imaging-based photoelectron tomography to reconstruct the 3D PMD. The reconstructed PMDs are decomposed by 3D Fourier analysis into SEVs of different rotational symmetry, revealing a significant enhancement of the $c_6$-symmetric contribution, which is the signature of the V-RAP.

We study nondipole effects in multiphoton ionization of a two-dimensional hydrogen-like atom by a flat-top laser pulse of varied intensity. For this purpose, we solve numerically a two-dimensional Schrödinger equation treating a propagating laser pulse exactly. The resulting distributions are then compared to those calculated in the dipole approximation. By investigating the energy-angular photoelectron distributions, we demonstrate that the multiphoton peaks shift toward either smaller or larger energies depending on the photoelectron emission angle. This is analytically interpreted based on the leading-order relativistic expansion of the electron Volkov state, showing a significant contribution of the electron recoil to that behavior. In contrast, the retardation correction originating from the space- and time dependence of the laser field leads to a tiny redshift of the photoelectron energy spectra. Other features of ionization distributions are also analyzed, including the sidelobes and the double-hump structures of multiphoton peaks, or their disappearance for intense propagating laser pulses.

We propose a multilevel scheme to coherently transfer the population of a diatomic molecule, either polar or nonpolar, from a rovibrational level to a target rovibrational level of the same electronic state or another. It involves a linear chain of $N$ rovibrational levels alternating between the initial electronic state and a second electronic state, conveniently selected according to the dipole couplings between consecutive levels. A set of $N-1$ simultaneous weak ($\approx {10}^4\mathrm{W}/{\mathrm{cm}}^2$) laser pulses, with simple analytical shapes, each in resonance between two neighbors of the chain, transfers the population from the initial rovibronic state gradually and consecutively through the chain, until at the end of the process it resides in the target rovibronic state, as in a kind of ping-pong game between the two electronic states. Using the partial-wave expansion of the molecular wave function, vibrational bases within the $J$ manifolds of each electronic state, and the rotating-wave approximation (RWA), we map the radial Hamiltonian to the one of a spin $s=(N-1)/2$ under a static magnetic field, providing an analytical formula for the populations of the linked states. As an illustration, we apply this pseudospin representation to the stabilization into the absolute ground state of a KRb molecule initially in the high-lying $\upsilon =75, J=6$ level of the ground electronic state $X^1{\mathrm{\Sigma }}^{+}$. With a chain of seven rovibronic states, three of them belonging to the excited $A^1{\mathrm{\Sigma }}^{+}$ electronic state, and pulses of 0.4 ns of duration, the population is fully transferred into the target state in about 1 ns. In addition, we perform a numerical simulation of the ping-pong process, taking into account the entire rovibrational space of both electronic states and without invoking the RWA, finding a good agreement with the results of the pseudospin model.

We investigate the phenomenon of Bose-Einstein condensation in ideal bosonic gases confined to axially symmetric surfaces of revolution. The single-particle Schrödinger equation is formulated on a general surface and then explicitly solved in the ellipsoidal and toroidal geometries to determine the one-body energy spectrum. We discuss how the curved geometry impacts the quantum statistical properties of ideal Bose gases confined on these surfaces. Specifically, we observe that Bose-Einstein condensation is suppressed when the surface aspect ratio is increased and, correspondingly, it becomes highly elongated and acquires a one-dimensional character. We also evaluate the Bogoliubov excitation spectrum, providing insights into the collective excitations of the condensate. Our results establish the conditions to achieve quantum degeneracy in curved manifolds, thus guiding forthcoming experiments with thin shells, and set the basis for solving the few-to-many body problem in general surfaces of revolution.

We investigate the control of two-body inelastic spin-exchange loss in ultracold atoms by applying an electric field to modulate magnetic Feshbach resonances. While conventional magnetic tuning can enhance or suppress two-body spin-exchange losses, the incorporation of an electric field introduces an additional degree of freedom, enabling more flexible control over resonances for different partial waves. Taking the ${}^6{\text{Li-}}^{40}\text{K}$ collision as an example, we demonstrate how this approach can be employed to control $s$- and $p$-wave inelastic loss processes and improve the suppression of the loss rate coefficient. This study may open a new possibility for the control of ultracold atomic inelastic collisions.

Far from equilibrium, universal dynamics prevails in many different situations, from pattern coarsening to turbulence. A central longstanding problem concerns the development of a theory of coarsening that rests on the microscopic properties of the system and allows identifying the interaction mechanisms underlying a possible overarching universality class of the associated scaling dynamics. In quantum systems, this is complicated by the existence of nonlinear and topological excitations due to the compact nature of phase degrees of freedom. We show that the double sine-Gordon model as a noncompact low-energy effective model of the spin-1 Bose gas accounts for subdiffusive coarsening dynamics, identifying field configurations spread over multiple wells of the sinusoidal potential as a precondition for the slow scaling. This is in contrast to diffusion-type scaling, which the model is known to exhibit as well, where field configurations are seen to not extend over more than two wells. Experimental observations of a spinor BEC support these characteristics, thus constituting a platform for the investigation of sine-Gordon dynamics. Our results point to a path towards a classification of pattern coarsening in many-body systems on the basis of microscopic models.

Exceptional points (EPs) have seen substantial advances in both experiment and theory. However, in quantum systems, higher-order EPs remain of great interest and possess numerous intriguing properties yet to be fully explored. Here we describe a parity-time symmetry-protected three-level non-Hermitian system with dissipative spin-orbit-coupled fermions in which a third-order exceptional point (EP3) emerges when both the eigenvalues and eigenstates of the system collapse into one. The band structure and its spin dynamics are explored for the ${}^{173}\mathrm{Yb}$ fermion. We highlight the enhanced sensitivity to the external perturbation of the EP3 with cubic-root energy dispersion. Additionally, we investigate the second-order EP (EP2) with square-root energy dispersion in a three-level quantum system in the absence of parity symmetry, which proves that the enhanced sensitivity closely relates to the symmetries of the non-Hermitian system. Furthermore, we analyze the encircling behavior of the EP3 in terms of the slowly evolving limit and the nonadiabatic dynamics beyond the slowly evolving limit and discover some results different from those of the EP2.

We derive the quantum master equation predicting how the translational and rotational dynamics of a nanoparticle is affected by the emission of surface adsorbates. This is motivated by recent experiments which prepared the motion of internally hot silica particles in the deep quantum regime. In the limit of a well localized nanoparticle the rotranslational dynamics can be characterized by diffusion rates in quantitative agreement with classical expectations. The theory is also suited to describe the decoherence effect of outgassing and sublimation.

A model of a nonstationary metamaterial is introduced and its electromagnetic properties are studied. The metamaterial is composed of two sublattices: a stationary one and an activated one. It is shown that an initial polariton excites not only the usual frequency-shifted polaritons but also a mode consisting of almost out-of-phase sublattice oscillations coupled to the electromagnetic field and possessing a small negative group velocity. The presented framework forms a basic description of the processes in time-varying media with spatial dispersion.

We present a framework for quantifying information flow within general quantum processes. For this purpose, we introduce the signaling power of quantum channels and discuss its relevant operational properties. This function supports extensions to higher-order maps, enabling the evaluation of information flow in general quantum causal networks and processes with indefinite causal order. Furthermore, our results offer a rigorous approach to information dynamics in open systems that applies also in the presence of initial system-environment correlations, and allows for the distinction between classical and quantum information backflow.

In this paper we investigate the thermal quantum correlations in a semiconductor double-quantum-dot system. The device comprises a single electron in a double quantum dot subjected to a longitudinal-magnetic-field and a transverse-magnetic-field gradient. The thermal entanglement of the single electron is driven by the charge and spin qubits. Employing the density-matrix formalism, we derive analytical expressions for thermal concurrence and correlated coherence, providing a comprehensive analysis of how temperature and various system parameters influence quantum coherence. Our results demonstrate that the transverse magnetic field serves as a tunable parameter for controlling thermal entanglement and quantum coherence. We also highlight the roles of thermal entanglement and correlated coherence in generating quantum correlations, noting that thermal correlated coherence is consistently more robust than thermal entanglement. This suggests that quantum algorithms based solely on correlated coherence might be more resilient than those relying on entanglement.

We introduce the qudit noisy stabilizer formalism, a framework for efficiently describing the evolution of stabilizer states in prime-power dimensions subject to generalized Pauli-diagonal noise under Clifford operations and generalized Pauli measurements. For arbitrary dimensions, the formalism remains applicable, though restricted to a subset of stabilizer states and operations. The computational complexity scales linearly with the number of qudits in the initial state and exponentially with the number of qudits in the final state. This ensures that when noisy qudit stabilizer states evolve via generalized Pauli measurements and Clifford operations to generate multipartite entangled states of a few qudits, their description remains efficient. We demonstrate this by analyzing the generation of a generalized Bell pair from a noisy linear cluster state subject to two distinct noise sources acting on each of the qudits.

Solving for the many-body wave function represents a significant challenge on both classical and quantum devices because of the exponential scaling of the Hilbert space with system size. While the complexity of the wave function can be reduced through conventional Ansätze (e.g., the coupled-cluster Ansatz), it can still grow rapidly with system size even on quantum devices. An exact, universal two-body exponential Ansatz for the many-body wave function has been shown to be generated from the solution of the contracted Schrödinger equation (CSE), and recently this Ansatz has been implemented without classical approximation on quantum simulators and devices for the scalable simulation of many-body quantum systems. Here we combine the solution of the CSE with a form of artificial intelligence known as reinforcement learning to generate highly compact circuits that implement this Ansatz without sacrificing accuracy. As a natural extension of the CSE, we reformulate the wave-function update as a Markovian decision process and train the agent to select the optimal actions at each iteration based upon only the current CSE residual. Compact circuits with high accuracy are achieved for ${\mathrm{H}}_3$ and ${\mathrm{H}}_4$ molecules over a range of molecular geometries.

Parameterized quantum circuits (PQCs) play a crucial role in variational quantum algorithms. While it is commonly believed that the optimal PQC can be used to reproduce the target state, here we reveal that the optimal PQC can also provide valuable insights into the state's properties. We propose variational toolboxes to identify the $k$-separability of pure states, with or without preparation noise, by checking the structure within the optimal PQCs. Additionally, we introduce adaptive optimization strategies to detect the $k$-separability of mixed states. Compared to fixed PQCs, our approach controls fewer parameters for low-rank states. Finally, we validate our methods through numerical demonstrations for various states.

We study operator scrambling in quantum circuits built from “super-Clifford” gates. For such circuits it was established by Blake and Linden [Phys. Rev. Lett. 125, 030502 (2020)] that the time evolution of operator entanglement for a large class of many-body operators can be efficiently simulated on a classical computer, including for operators with volume-law entanglement. Here we extend the scope of this formalism in two key ways. First we provide evidence that these classically simulable circuits include examples of fast scramblers, by constructing a circuit for which operator entanglement is numerically found to saturate in a time $t_{*}\sim \ln \left(N\right)$ (with $N$ the number of qubits). Second we demonstrate that, in addition to operator entanglement, certain out-of-time-ordered correlation functions (OTOCs) can be classically simulated within the same formalism. As a consequence such OTOCs can be computed numerically in super-Clifford circuits with thousands of qubits and we study several explicit examples in the aforementioned fast scrambling circuits.

We demonstrate that, in the tripartite scenario with all parties' local events being space-like separated, Hardy-type nonlocality reveals a stronger nonlocal correlation than those captured by Mermin-type inequalities, an important distinction previously unrecognized. To substantiate this assertion, we develop a general framework for tripartite correlations by extending the notion of Settings Independence and Outcome Independence beyond their bipartite formulation. This framework highlights the pivotal role of Hardy-type reasoning in detecting genuine multipartite nonlocality. Furthermore, we show that the tripartite Hardy-nonlocality enables self-testing of a broad class of pure nonmaximally genuine entangled tripartite states, offering a key advantage over Bell inequality-based methods by allowing certification even under nonmaximal violations. Unlike Bell functionals, which typically self-test only a single extremal point, the Hardy relation self-tests a set of extremal correlations for any nonzero Hardy probability. This, in turn, facilitates the device-independent certification of randomness from Hardy-type correlations. We find that the maximum certifiable randomness is ${log}_{2}7\approx 2.8073$-bits, highlighting both the practical and foundational significance of Hardy-based techniques for quantum randomness generation.