We investigate the replica symmetry breaking (RSB) phenomenon in random lasers (RLs) through Monte Carlo simulations employing photonic random walkers that diffuse and get randomly scattered in the active medium. The walkers interact not only with the population of excited atoms, but also among themselves, in a mean-field-type approach based on the Langevin equation for the stochastic dynamics of RL modes. We obtain the proper profile of the distribution $P\left(q\right)$ of the Parisi overlap parameter in the RSB glassy phase, with two pronounced side maxima at $q=\pm 1$ above the RL threshold, in contrast with some recent numerical studies. Remarkably, when the interactions among photonic walkers are not included, a replica-symmetric profile with a single maximum of $P\left(q\right)$ at $q=0$ is found for any excitation energy. We further study the Gaussian and Lévy emission regimes and statistical correlations of intensity fluctuations in distinct modes of the same spectrum, using a Pearson correlation coefficient recently applied to RLs. Our findings are consistent with experimental results for the intensity statistics and $P\left(q\right)$ distributions in RL materials.

We consider a computational model composed of ideal Gottesman-Kitaev-Preskill stabilizer states, Gaussian operations including all rational symplectic operations and all real displacements, and homodyne measurement. We prove that such architecture is classically efficiently simulatable by explicitly providing an algorithm to calculate the probability density function of the measurement outcomes of the computation. We also provide a method to sample when the circuits contain conditional operations. This result is based on an extension of the celebrated Gottesman-Knill theorem, via introducing proper stabilizer operators for the code at hand. We conclude that the resource enabling quantum advantage in the universal computational model considered by Baragiola et al. [Phys. Rev. Lett. 123, 200502 (2019)], composed of a subset of the elements given above augmented with a provision of vacuum states, is indeed the vacuum state.

Gaussian noise channels arise naturally in many physical situations and play an important role in information transmission involving continuous-variable quantum systems. In this work we employ Gaussian noise channels to probe and characterize correlations in two-mode bosonic fields. Based on the fact that local channels often cause more decoherence for global states than for local states due to correlations, we introduce a notion of conditional coherence relative to a local channel, which is defined as the difference between the global and local decoherence caused by the channel. We discuss its connections with quantum discord and relative quantum Fisher information and propose a class of correlation quantifiers for two-mode bosonic states in terms of conditional coherence relative to local Gaussian noise channels. We prove that any nonproduct state exhibits such correlations and show that these correlation quantifiers are measures of total correlations, which may include both classical and quantum parts. We further illustrate these correlation quantifiers through several typical two-mode bosonic states and make a comparative study between these correlation quantifiers and other known ones such as entanglement and discord.

We revisit the implementation of a two-qubit entangling gate, the Mølmer-Sørensen gate, using the adiabatic Rydberg dressing paradigm for neutral atoms as studied in [A. Mitra et al., Phys. Rev. A 101, 030301(R) (2020)]. We study the implementation of rapid adiabatic passage using a two-photon transition, which does not require the use of an ultraviolet laser, and can be implemented using only amplitude modulation of one field with all laser frequencies fixed. We find that entangling gate fidelities, comparable to the one-photon excitation, are achievable with the two-photon excitation. Moreover, we address how the adiabatic dressing protocol can be used to implement entangling gates outside the regime of a perfect Rydberg blockade. We show that, by using adiabatic dressing, we can achieve scaling of the gate fidelity set by the fundamental limits to entanglement generated by the Rydberg interactions while simultaneously retaining a limited population in the doubly excited Rydberg state. This allows for fast high-fidelity gates for atoms separated beyond the blockade radius.

We report on double differential cross sections of cusp electrons obtained in MeV/u collisions of open-shell He-like oxygen ions with helium. We use zero-degree electron spectroscopy and our double measurement technique, involving ${\mathrm{O}}^{6+}\left(1s^2\right)$ ground-state and ${\mathrm{O}}^{6+}(1s^2,1s2s)$ mixed-state beams, to extract the cusp contribution from only the excited ${\mathrm{O}}^{6+}\left(1s2s\right)$ beam. Theoretical calculations based on the continuum distorted wave eikonal initial state are in very good agreement with the measurements. The roles of the processes of electron capture to the continuum, electron loss to the continuum, and electron loss to the continuum with simultaneous target ionization, which contribute to the cusp peak, are discussed in detail.

We unravel the existence and stability properties of dark soliton solutions as they extend from the regime of trapped quantum droplets towards the Thomas-Fermi limit in homonuclear symmetric Bose mixtures. Leveraging a phase-plane analysis, we identify the regimes of existence of different types of quantum droplets and subsequently examine the possibility of black and gray solitons and kink-type structures in this system. Moreover, we employ the Landau dynamics approach to extract an analytical estimate of the oscillation frequency of a single dark soliton in the relevant extended Gross–Pitaevskii model. Within this framework, we also find that the single soliton immersed in a droplet is stable, while multisoliton configurations exhibit parametric windows of oscillatory instabilities. Our results pave the way for studying dynamical features of nonlinear multisoliton excitations in a droplet environment in contemporary experimental settings.

We investigate the ground-state properties of an ultracold-atom system consisting of many-body polarons, quasiparticles formed by impurity atoms in optical lattices immersed in a Bose-Einstein condensate. We find the nearest-neighbor attractive interaction between polarons can give rise to rich physics that is peculiar to this system. In a relatively shallow optical lattice, the attractive interaction can drive the system to be in a self-bound superfluid phase, with its particle density distribution manifesting a self-concentrated structure. However, in a relatively deep optical lattice, the attractive interaction can drive the system, leading to the Mott-insulator phase even though the global filling factor is not an integer. Interestingly, in the Mott-insulator regime, the system can support a series of different Mott insulators, with their effective density manifesting a devil's-staircase structure with respect to the strength of the attractive interaction. A detailed estimation of the relevant experimental parameters shows that these rich physics can be readily observed in current experimental setups.

The ability to engineer the distribution of light with high precision is the key to improving the control accuracy and freedom of optical manipulation. Instead of traditional optical manipulation based on using the three-dimensional adjustable displacement platform, our report demonstrates that evolutions of light field distributions during propagation can be used to manipulate particles. By devising a hyperbolic-cosine-form inseparable phase, we theoretically endow the partially coherent light beam with the optional self-stretching or self-splitting ability. Importantly, we achieved the controllable separation of the particles in our experiment by using this self-splitting ability. Our results demonstrate the feasibility of manipulating particles by using light beam evolutions and further improve the control freedom and precision of traditional optical tweezers.

A neutral but polarizable particle at rest near a perfectly conducting plate feels a force normal to the surface of the plate, which tends to pull the particle towards the plate. This is the well-known Casimir-Polder force, which has long been theoretically proposed and experimentally observed. In this paper, we explore the transverse frictional force on an atom moving uniformly parallel to a perfectly conducting plate. Although many theoretical predictions can be found for the quantum friction on a particle moving above an imperfect surface, the extreme situation with a perfectly conducting plate seems to have been largely unaddressed by the theoretical community. We investigate this ideal case as a natural extension of our previous work on quantum vacuum friction, and conclude that there does exist a quantum frictional force on an atom moving above a perfectly conducting plate, which we will abbreviate by PCQF. Like quantum vacuum friction, PCQF arises from the interaction between the particle and the surrounding blackbody radiation. But, the behavior of PCQF differs from the quantum vacuum friction in that the vacuum fields are modified by the perfectly conducting plate. Very interestingly, the distance dependence, the temperature dependence, and even the sign of the frictional force can depend on the polarization state of the atom. For an isotropic atom with a static polarizability, the resultant frictional force is found to be negative definite and therefore remains a true drag. Just above the surface of the plate, the magnitude of the frictional force is twice that of the quantum vacuum friction in the absence of the plate.

This work explores the possibility of using atomic cluster beams as a probe for neutral-atom microscopy (NAM) measurements. Using a beam of Kr clusters with mean size $\sim {10}^4$ atoms/cluster we demonstrate that topographical contrast can be obtained, similar to that in the case of monoatomic beams. Further, using atomically thin films of ${\mathrm{MoS}}_2$ grown on ${\mathrm{SiO}}_2\text{/}\mathrm{Si}$ substrate we show that NAM imaging using Kr clusters is also possible in domains where topographical contrast is not expected. Surprisingly, these images show an inverted contrast pattern when compared to the case of monoatomic beams. We attempt to understand these observations on the basis of angular distributions resulting from cluster-surface scattering. Finally, we discuss the implications of these results toward achieving a high lateral resolution neutral-atom microscope using atomic cluster beams as probe, with an estimated ultimate achievable lateral resolution up to 20 nm.

The current constraint on the electron electric dipole moment ($e\mathrm{EDM}$), $|d_{\mathrm{e}}|<4.1\times {10}^{-30} e\mathrm{cm}$ (90% confidence), was recently established using the trapped ${}^{180}\mathrm{Hf}{}^{19}\mathrm{F}^{+}$ molecular ions in the $J=1$ rotational level of its ${}^3\mathrm{\Delta }_1$ electronic state [T. S. Roussy, L. Caldwell, T. Wright et al., arXiv:2212.11841]. The extensive experimental study of the ${\mathrm{HfF}}^{+}$ cation provides detailed spectroscopy of the $\mathrm{\Omega }$-doublet levels in the external rotating electric and magnetic fields. We showed that previously developed theoretical approaches can fully reproduce the latest experimental data. Their justification from the first principles is very important for the examination of both modern molecular theory and possible systematic uncertainties in the interpretation of the experimental data obtained with high accuracy.

Polar lattice gases are usually assumed to have an intersite interaction that decays with the interparticle distance $r$ as $1/r^3$. However, a loose-enough transversal confinement may strongly modify the dipolar decay in one-dimensional lattices. We show that this modification alters significantly the ground-state properties of hard-core dipolar bosons. For repulsive intersite interactions, the corrected decay alters the conditions for devil's staircase insulators, affecting significantly the particle distribution in the presence of an overall harmonic confinement. For attractive interactions, it results in a reduction of the critical dipole interaction for the formation of self-bound clusters, and for a marked enhancement of the region of liquefied lattice droplets.

Dissipative Kerr solitons generated in high-$Q$ optical microresonators provide unique opportunities for different up-to-date applications. Increasing the generation efficiency of such signals is a problem of paramount importance. We perform a comprehensive analytical and numerical analysis using a simple single-cavity scheme. It is revealed that in order to obtain high pump-to-comb conversion efficiency such parameters as coupling rate, pump amplitude, detuning, and microresonator second-order dispersion should not be considered individually, only in the aggregate. The dependence of the optimal coupling rate on the pump power is shown, in addition to the trade-off relations balancing the efficiency versus the number of comb lines. Combining analytical predictions and numerical simulations, we find optimal conditions for the maximal pump-to-comb conversion efficiency (up to 100%) in the cases of free-running and self-injection-locked pump lasers. The discrepancy between numerical and analytical solutions and methods to increase the total comb power are also discussed.

We propose an integral formulation of macroscopic quantum electrodynamics in the Heisenberg picture for linear dispersive dielectric objects of finite size, utilizing the Hopfield-type approach. By expressing the electromagnetic field operators as a function of the polarization density field operator via the retarded Green function for the vacuum, we obtain an integral equation that governs the evolution of the polarization density field operator. This formulation offers significant advantages, as it allows for the direct application of well-established computational techniques from classical electrodynamics to perform quantum electrodynamics computations in open, dispersive, and absorbing environments.

The network scenario offers interesting new perspectives on the phenomenon of quantum nonlocality. Notably, when considering networks with independent sources, it is possible to demonstrate quantum nonlocality without the need for measurement inputs, i.e., with all parties performing a fixed quantum measurement. Here we aim to find minimal examples of this effect. Focusing on the minimal case of the triangle network, we present examples involving output cardinalities of $3\text{−}3\text{−}3$ and $3\text{−}3\text{−}2$. A key element is a rigidity result for the parity token counting distribution, which represents a minimal example of rigidity for a classical distribution. Finally, we discuss the prospects of finding an example of quantum nonlocality in the triangle network with binary outputs and point out a connection to the Lovasz local lemma.

We perform a calculation of the nuclear recoil ionization efficiency in silicon using an improved version of Lindhard's theory, in which atomic bond breaking is modeled as a function of the initial ionic energy, the interatomic potential, and the average energy for ion-vacancy pair production. Better descriptions of the effects due to electronic stopping and straggling, charge screening, and Coulomb repulsion between ions are also incorporated. Our model provides a good description of the available data over nearly four orders of magnitude of nuclear recoil energy.

Continuously measured interacting quantum systems almost invariably heat, causing loss of quantum coherence. Here, we study Bose-Einstein condensates (BECs) subject to repeated weak measurement of the atomic density and describe several protocols for generating a feedback signal designed to remove excitations created by measurement back-action. We use a stochastic Gross-Pitaevskii equation to model the system dynamics and find that a feedback protocol utilizing momentum-dependent gain and filtering can effectively cool both one-dimensional (1D) and two-dimensional systems. The performance of these protocols is quantified in terms of the steady-state energy, entropy, and condensed fraction. These are the first feedback cooling protocols demonstrated in two dimensions, and in one dimension our optimal protocol reduces the equilibrium energy by more than a factor of 100 as compared with a previous cooling protocol developed using the same methodology. We also use this protocol to quench-cool 1D BECs from noncondensed highly excited states and find that they rapidly condense into a far-from-equilibrium state with energy orders of magnitude higher than the equilibrium ground-state energy for that condensate fraction. We explain this in terms of the near integrability of our 1D system, whereby efficiently cooled low-momentum modes are effectively decoupled from the energetic “reservoir” of the higher-momentum modes. We observe that the quench-cooled condensed states can have nonzero integer winding numbers described by quantized supercurrents.

We study higher-order modulation instability phenomena in the frame of Manakov equations. Evolution that starts with a single pair of sidebands expands over several higher harmonics. The choice of initial pair of sidebands influences the structure of unstable frequency components and changes drastically the wave evolution, leading, in some cases, to jumps across spectral components within the discrete spectrum. This complex dynamics includes several growth-decay cycles of evolution. We show this using numerical simulations of the modulation instability process and confirm the results using the exact multi-Akhmediev breather solutions. Detailed explanations of the observed phenomena are given.

We study chiral and nonreciprocal single-photon scattering in a chiral-giant-molecule waveguide-QED system. Here, the giant molecule consists of two coupled giant atoms, which interact with two linear waveguides, forming a four-port quantum device. We obtain the exact analytical expressions of the four scattering amplitudes using a real-space method. Under the Markovian limit, we find that the single-photon scattering behavior is determined by the coupling strength between the giant atoms and the waveguides, the coupling strength between the two giant atoms, and the nondipole effect caused by the phase accumulation of photons traveling between the coupling points. It is also found that chiral and nonreciprocal single-photon scattering can be realized by introducing the chiral coupling to break the symmetry in the coupling configuration between the giant molecule and the waveguides. In addition, an ideal chiral emitter-waveguide coupling enables a directional single-photon routing. In the non-Markovian regime, the scattering spectra are characterized by more abundant structures with multiple peaks and dips. In particular, we demonstrate that the non-Markovian retarded effect can induce the nonreciprocal single-photon scattering. Our results have potential applications in the design of optical quantum devices involving giant atoms, which can provide an efficient platform for studying chiral quantum optics.