The effects induced by the time-reversal ($\mathcal{T}$) and spatial parity ($\mathcal{P}$)-violating electron-nucleus and electron-electron interactions mediated by the axionlike particles (ALPs) in the BaF molecule were estimated. Molecular parameters characterizing these interactions were calculated across a wide range of ALP masses. In the case of the electron-nuclear interaction, the effect of the extended nucleus was studied and shown to be significant for heavy ALPs. Based on the calculated molecular parameters, we obtained a link between the $\mathcal{T},\mathcal{P}$-violating energy shift which can be measured in the ongoing experiment designed to search for the electron electric dipole moment using the BaF molecule (A. Boeschoten et al., arXiV:2303.06402) and the products of coupling constants of the ALP-electron or ALP-electron and ALP-nucleus interactions.

The ground ${\mathrm{X}}^1{\mathrm{\Sigma }}^{+}$ state potential energy curve (PEC) and dipole moment curve (DMC) of CO molecule have been revisited within the framework of the relativistic coupled-cluster approach, which incorporates nonperturbative single, double, and triple cluster amplitudes (CCSDT) in conjunction with a finite-field methodology. The generalized relativistic pseudopotential model was used for the effective introducing the relativity in all-electron correlation treatment and accounting the quantum-electrodynamics (QED) corrections within the model-QED-operator approach. The diagonal Born-Oppenheimer correction to PEC has been evaluated using the CCSD approach. The sensitivity of resulting PEC and DMC to variations in basis set parameters and regular intramolecular perturbations were considered as well. The present ab initio results are in a reasonable agreement with their most accurate semiempirical counterparts.

To take full advantage of the capabilities of grazing-incidence fast-atom diffraction (GIFAD) as an experimental technique for analyzing surfaces and phenomena that occur on them, versatile theoretical tools are needed that accurately describe the experiments while allowing a simple but meaningful interpretation at a reasonable computational cost. During the last years, the semiquantum method named surface initial value representation (SIVR) has been postulated to fill this room. However, to date, SIVR has not yet been validated using full quantum calculations as a reference. Here, we have contrasted GIFAD simulations performed with the SIVR approach with those obtained with the full quantum method known as multiconfiguration time-dependent Hartree (MCTDH), taking into account the influence of the size of the initial wave packet. Our comparative study, using GIFAD for the He-LiF(001) system as a benchmark, shows a very good agreement, both qualitative and quantitative, between SIVR and MCTDH simulated diffraction spectra, under different incidence conditions. These findings support the use of SIVR as a versatile theoretical tool to extract as much accurate information as possible from GIFAD experiments.

We present a modified saddle-point method and apply it to the high-order above-threshold ionization (HATI) and high-order harmonic generation (HHG) processes. When we use the Slater-type orbitals to describe the ground-state wave function of the valence electron in a noble gas atom, we cannot apply the ordinary saddle-point method (SPM) because the singular points of the ionization matrix element, as well as the recombination matrix element for HHG, are in the vicinity of the corresponding saddle points. Therefore, we present a modification of the SPM and show that the obtained results are in excellent agreement with the spectra calculated by numerical integration. Furthermore, we compare the results obtained by the modified SPM with those obtained by the ordinary SPM with the asymptotic ground-state wave function. We conclude that both methods work for HATI, but for HHG we show that it is necessary to use the modified SPM because the recombination happens close to the atomic core, where the electron ground state is well described only by the Slater-type orbitals.

We propose a temporal double-slit interferometric scheme to characterize the shaped intense femtosecond laser pulse directly, which can be applied to control electron tunneling wave packets with attosecond precision. By manipulating the spectral phase of the input femtosecond pulse in the frequency domain, one single pulse is split into two subpulses and their waveforms can be controlled by adjusting the spectral phase. In the interaction between the shaped pulse and atoms, the two subpulses are analogous to Young's double slit in the time domain. The interference pattern in the photoelectron momentum distribution can be used to retrieve the peak electric field and the time delay between two subpulses. Based on the characterization of the shaped pulse, we demonstrate that the subcycle dynamics of photoelectrons can be controlled with attosecond precision. The feasibility of this scheme is confirmed through quantum-trajectory Monte Carlo simulations and numerical solutions of the three-dimensional time-dependent Schrödinger equation.

The splitting instability of a doubly quantized vortex in the BEC-BCS crossover of a superfluid Fermi gas is investigated by means of a low-energy effective field theory. Our linear stability analysis and nonequilibrium numerical simulations reveal that the character of the instability drastically changes across the crossover. In the BEC limit, the splitting of the vortex into two singly quantized vortices occurs through the emission of phonons, while such an emission is completely absent in the BCS limit. In the crossover regime, the instability and phonon emission are enhanced and the lifetime of a doubly quantized vortex becomes minimal. The emitted phonon can be observed as a spiraling pattern amplified due to the rotational superradiance, known as a mechanism to carry away energy and angular momentum from a spinning black hole. We also investigate the influence of temperature, population imbalance, and three-dimensional effects.

We propose and demonstrate numerically a measurement scheme for complete reconstruction of the 2D quantum wave function of a Bose-Einstein condensate, amplitude and phase, from a time-of-flight measurement. We identify a fundamental ambiguity present in the measurement of phase structures of high-symmetry excitations (e.g., vortices) and show how to overcome it by allowing for different expansion durations in different directions. We demonstrate this approach with the reconstruction of matter-wave vortices and arrays of vortices.

Recently the role of the mobility edge in localization transitions has been extensively studied for one-dimensional tight-binding quasiperiodic models. In this work we study the mobility edge in a family of quasiperiodic systems evolving far from equilibrium, such as quench dynamics. We report numerical simulations of the Loschmidt echo based on a polynomial expansion-based technique with a moderate computational cost. Remarkably, we obtain an identical energy dependence on the equilibrium and dynamical quantum phase transitions of quasiperiodic models. The self-dual energy-independent localization model under quench dynamics exhibits energy-independent dynamical quantum phase transitions. On the other hand, self-dual energy-dependent localization models undergo energy-dependent dynamical quantum phase transitions. The results provide insights into energy-dependent dynamical localization transitions in quasiperiodic systems relevant to experiments.

This experimental study aims to investigate the convex combinations of Pauli semigroups with arbitrary mixing parameters to determine whether the resulting dynamical map exhibits Markovian or non-Markovian behavior. Specifically, we consider the cases of equal as well as unequal mixing of two Pauli semigroups, and demonstrate that the resulting map is always non-Markovian. Additionally, we study three cases of three-way mixing of the three Pauli semigroups and determine the Markovianity or non-Markovianity of the resulting maps by experimentally determining the decay rates. To simulate the nonunitary dynamics of a single-qubit system with different mixing combinations of Pauli semigroups on an NMR quantum processor, we use an algorithm involving two ancillary qubits. The experimental results align with the theoretical predictions.

We describe an experiment that strongly supports a two-path interferometric model in which the spin-up and spin-down components of each neutron propagate coherently along spatially separated parallel paths in a typical neutron spin-echo small-angle scattering (SESANS) experiment. Specifically, we show that the usual semi-classical, single-path treatment of Larmor precession of a polarized neutron in an external magnetic field predicts a damping as a function of the spin-echo length of the SESANS signal obtained with a periodic phase grating when the transverse width of the neutron wave packet is finite. However, no such damping is observed experimentally, implying either that the Larmor model is incorrect or that the transverse extent of the wave packet is very large. In contrast, we demonstrate theoretically that a quantum-mechanical interferometric model in which the two mode-entangled (i.e., intraparticle entangled) spin states of a single neutron are separated in space when they interact with the grating accurately predicts the measured SESANS signal, which is independent of the wave packet width.

Arrays of neutral atoms have emerged as promising platforms for quantum computing. The realization of high-fidelity two-qubit gates with robustness is currently a significantly important task for large-scale operations. In this paper, we present a convenient approach for implementing a two-qubit controlled-phase gate with Rydberg blockade. We achieve noncyclic and geometric control within a single modulated pulse. Compared with the control scheme by cyclic evolution determined by dynamical parameters, the robustness of our proposal against systematic errors will be remarkably improved due to its geometric characteristics. Importantly, the noncyclic geometric control reduces the gate time for small rotation angles and is more insensitive to decoherence effects. Furthermore, we accelerate the adiabatic control with the aid of shortcuts to adiabaticity to further shorten the operation time. We apply our protocol to the quantum Fourier transformation algorithm to demonstrate the actual acceleration. Therefore, the proposed scheme provides analytical wave forms for arbitrary two-qubit gates and may play an important role in experiments involving atomic arrays.

Coherent focusing of high-order harmonic generation (HHG) from optically curved relativistic plasma mirrors provides a promising route to achieve unprecedented high intensities, opening up prospects to study phenomena occurring in extremely strong fields, the region of which is however limited within extremely small spatial and temporal scales. Here through three-dimensional particle-in-cell simulations we demonstrate HHG driven by Bessel-Gaussian beams exhibiting the intriguing feature of self-healing up to the relativistic and extreme nonlinear regime. This allows a secondary intensification of reflected fields after the focus of curved plasma mirrors and thus extends the high-intensity region in both space and time, beneficial for extreme field applications.

We assess the theoretical performance of a mode-locked silicon-rich-nitride ring laser, which is partly overlayed with a ${\mathrm{MoS}}_2/{\mathrm{WSe}}_2$ bilayer and partly with a graphene monolayer. Through an external vertical optical pump at 740 nm, the transition-metal dichalcogenide (TMD) bilayer can be inverted and provide gain at 1128 nm while the graphene monolayer acts as the fast broadband saturable absorber. We show that under modest pumping conditions, we can reach a stable mode-locked regime that can deliver on-chip pulsed output with milliwatt peak power and down to 400 fs in duration. The ring laser is studied by rigorously modeling the TMD bilayer as a semiclassical three-level system and incorporating the resulting resonant polarization to the nonlinear Schrödinger equation (NLSE). Within the NLSE formalism we are able to also incorporate material and waveguide dispersion as well as the significant Kerr-type nonlinearity of the silicon-rich-nitride waveguide. Furthermore, we discuss all the necessary physical and mathematical approximations needed to numerically solve the propagation problem, based on an implementation of the split-step Fourier method with the atomic polarization term. Our mathematical treatment is very general and can be adapted to any two-dimensional-material-enhanced traveling wave source. Finally, this work shows the feasibility and potential of TMD bilayers as well as graphene for the development of efficient integrated pulsed on-chip sources.

We propose to achieve and enhance the magnon blockade effect in an optomechanical-magnetic system based on a quantum destructive interference mechanism between three indirect transition pathways. By introducing a degenerate parametric amplifier, we analytically obtain the optimal parametric gain and phase for achieving the magnon blockade. Under the optimized parameter conditions, the driving detunings of cavity and magnon modes can be flexibly controlled to achieve the smallest second-order magnon correlation function. Moreover, the magnon blockade can exhibit fascinating features by proper driving detuning and weaker driving strength. Our scheme combines the benefits of destructive interference-induced magnon blockade and energy-level anharmonicity-induced magnon blockade, which results in a reduction of equal-time second-order magnon correlation while simultaneously avoiding time-delay second-order magnon correlation with rapid oscillation. Our work provides an alternative and experimentally feasible platform for manipulating few-magnon states and generating single-magnon sources.

The [[7,1,3]] Steane code and [[23,1,7]] quantum Golay code have been identified as good candidates for fault-tolerant quantum computing via code concatenation. These two codes have transversal implementations of all Clifford gates but require some other scheme for fault-tolerant $T$ gates. Using magic states, Clifford operations, and measurements is one common scheme, but magic-state distillation can have a large overhead. Code conversion is one avenue for implementing a universal gate set fault tolerantly without the use of magic-state distillation. Analogously to how the [[7,1,3]] Steane code can be fault tolerantly converted to and from the [[15,1,3]] Reed-Muller code which has a transversal $T$ gate, the [[23,1,7]] Golay code can be converted to a [[95,1,7]] triorthogonal code with a transversal $T$ gate. A crucial ingredient of this procedure is the [[49,1,5]] triorthogonal code, which can itself be seen as being related to the self-dual [[17,1,5]] two-dimensional color code. Additionally, a method for code conversion based on a transversal cnot between the codes, rather than stabilizer measurements, is described.

We present a quantum thermometry method utilizing a probe-meter system and leveraging reinforcement learning (RL) to enhance sensitivity at low temperatures. Temperature information is exclusively obtained by coupling the probe qubit with the bath, facilitating efficient information extraction by measuring the meter system. Our evaluations, considering both dephasing and dissipative probe-bath couplings, demonstrate a significant enhancement in temperature sensitivity through meter-assisted thermometry, excluding the ultralow-temperature range. To further optimize performance, RL is employed to adjust both the interaction strength between the probe-meter system and the frequency of the meter system. Results showcase that RL effectively enhances temperature sensitivity across a broad low-temperature spectrum by improving average sensitivity within the specified temperature range. This optimization successfully expands the operational range of quantum thermometers. These findings highlight the promising potential of the RL approach for high-resolution, low-temperature quantum thermometry applications.

Hamiltonian simulation represents an important module in a large class of quantum algorithms and simulations such as quantum machine learning, quantum linear algebra methods, and modeling for physics, material science, and chemistry. One of the most prominent methods for realizing the time-evolution unitary is via the Trotter-Suzuki decomposition. However, there is a large class of possible decompositions for the infinitesimal time-evolution operator as the order in which the Hamiltonian terms are implemented is arbitrary. We introduce a perspective for generating a low-depth Trotter-Suzuki decomposition assuming the standard $\mathrm{Clifford}+$rz gate set by adapting ideas from quantum error correction. We map a given Trotter-Suzuki decomposition to a constrained path on a graph which we deem the Pauli frame graph (PFG). Each node of the PFG represents the set of possible Hamiltonian terms currently available to be applied, Clifford operations represent a move from one node to another, and so the graph distance represents the gate cost of implementing the decomposition. The problem of finding the optimal decomposition is then equivalent to solving a problem similar to the traveling salesman. Although this is an NP-hard problem, we demonstrate the simplest heuristic, greedy search, and compare the resulting two-qubit gate count and circuit depth to more standard methods for a large class of scientifically relevant Hamiltonians, both fermionic and bosonic, found in chemical, vibrational, and condensed-matter problems which naturally scale. We find, in nearly every case we study, the resulting depth and two-qubit gate counts are less than those provided by standard methods, by as much as an order of magnitude. We also find the method is efficient and amenable to parallelization, making it scalable for problems of real interest.