We introduce a mechanism of stable spatiotemporal soliton formation in a multimode fiber laser. This is based on spatially graded dissipation, leading to distributed Kerr-lens mode locking. Our analysis involves solutions of a generalized dissipative Gross-Pitaevskii equation. This equation has a broad range of applications in nonlinear physics, including nonlinear optics, spatiotemporal pattern formation, plasma dynamics, and Bose-Einstein condensates. We demonstrate that the careful control of dissipative and nondissipative physical mechanisms results in the self-emergence of stable ($2+1$)-dimensional dissipative solitons. Achieving such a regime does not require the presence of any additional dissipative nonlinearities, such as a mode locker in a laser, or inelastic scattering in a Bose-Einstein condensate. Our method allows for stable energy (or “mass”) harvesting by coherent localized structures, such as ultrashort laser pulses or Bose-Einstein condensates.

Hybrid nanoparticles have gained intense attention in the field of optical trapping due to their potential wide-ranging applications, for example, in drug delivery. The utility of the optical Kerr effect in modulating trapping force and potential under high-repetition-rate ultrafast pulsed excitation has recently been realized for dielectric and metallic particles ranging from micron to nanometer. However, in the context of hybrid nanoparticles, the mechanism of trapping is yet to be fully explored. Here, we present a comparative study of trapping force and potential on conventional, hybrid, and hollow-core type nanoparticles using generalized Lorenz-Mie theory and dipole approximation incorporating third-order optical nonlinearity. We find an explicit advantage of using pulsed excitation over continous-wave excitation which can have potentially far-reaching practical applications.

We consider the reflection from a random medium of light with short coherence length. We found that the second-order correlation function of light can have a peak in a direction where the reflection angle is equal to the angle of incidence. This occurs when the size of the region, from which light is collected, is larger than the coherence length.

We show how one may test macroscopic local realism where, differently from conventional Bell tests, all relevant measurements that lead to a violation of a Bell inequality need only distinguish between two macroscopically distinct states of the system being measured. Here, measurements give macroscopically distinct outcomes for some property of the system and do not resolve microscopically (of order $\hslash$). To obtain a quantifiable test, we define $N$-scopic local realism where the outcomes are separated by an amount $\sim N$. We show for $N$ up to 20 that violations of $N$-scopic local realism are predicted for entangled systems of $N$ bosons at each of two sites. We further demonstrate for arbitrarily large $\alpha$ the violation of $\alpha$-scopic local realism, for entangled superpositions of coherent states with amplitudes $\sim \alpha$, infinitely separated in phase space, as $\alpha \to \infty$. To achieve the Bell violations, the two separated subsystems evolve dynamically according to a local nonlinear unitary interaction. The tests may be understood in two ways. First, they are macroscopic Bell tests involving spacelike separated measurement events, where the choice of measurement setting at each site corresponds to a choice between two different times of local interaction. The interaction may be seen as the unitary stage of a local measurement process. Second, the proposal is a strong version of a Leggett-Garg test of "macrorealism" that uses two trajectories, where the usual assumption of noninvasive measurability as applied to measurements at one site is replaced by that of macroscopic locality. For $N=1$, tests are feasible and give a way to demonstrate “no classical trajectories” without the assumption of noninvasive measurability, using instead that of locality.

In this paper, we propose a scheme to generate nonclassical states in a nonlinear oscillator system, such as Fock states, squeezed coherent states, Schrödinger-cat states, etc. These nonclassical states are achieved by directly applying the classical field to the nonlinear oscillator, where the amplitude of the field is customized through a state-based Lyapunov control. For generating Fock states, there is no need to precisely control the operation time. As for the generation of other nonclassical states, we resort to a unitary transformation to design the control field, resulting in the requirement of a specific time. The Wigner function of the generated states shows the nonclassical property and shape that matches well with the target. Numerical simulations suggest that the scheme is robust against the field fluctuations and immune to variations in the initial state. In addition, the time-varying control field can be replaced by a square pulse based on the characteristics of the Lyapunov control, which may reduce the difficulty of the experiment.

Key reconciliation of quantum key distribution is the process of correcting errors caused by channel noise and an eavesdropper. Reconciliation efficiency is the most important figure for judging the quality of a key reconciliation scheme. The single-matrix rate-compatible reconciliation (SRCR) scheme can access optimal reconciliation efficiency because of rate-compatible technologies, i.e., shortening and puncturing. In this paper, a technique called multimatrix reconciliation is introduced into SRCR, which is referred to as the multimatrix rate-compatible reconciliation (MRCR) scheme. Simulation results show that MRCR we proposed outperforms SRCR in reconciliation efficiency and throughput. In addition, it is observed that MRCR surpasses several non-low-density-parity-check-based reconciliation schemes in terms of comprehensive performance.

The objective of this work is to derive approximate rovibrational selection rules for the interaction-induced molecular absorption in dipole-less polyatomic molecules. Taking a combination ${\nu }_2+{\nu }_3$ band in the ${\mathrm{CO}}_2$ molecule as an example, we show that selection rules $\mathrm{\Delta }J=\pm 1$ are allowed in collision-induced absorption (CIA) along with conventional selection rules $\mathrm{\Delta }J=0,\pm 2$ characteristic for CIA in homonuclear diatomics. The basis of that condition relates to the combined effect of the anisotropy of an external electric perturbation and the anharmonicity of the vibrations.

We investigate the effects of quantum correlations on dipolar quantum droplets. To this end, we derive self-consistent time-dependent Hartree-Fock-Bogoliubov equations that fairly describe the dynamics of the order parameter, the normal quantum correlations, and anomalous quantum correlations of the droplet. We analyze the density profiles, the critical number of particles, the condensate depletion, and the pair correlation function. Our predictions are compared with very recent experimental and quantum Monte Carlo simulations results and excellent agreement is found.

We present a theory of radio-frequency spectroscopy of impurities interacting with a quantum gas at finite temperature. By working in the canonical ensemble of a single impurity, we show that the impurity spectral response is directly connected to the finite-temperature equation of state (free energy) of the impurity. We consider two different response protocols: injection, where the impurity is introduced into the medium from an initially noninteracting state, and ejection, where the impurity is ejected from an initially interacting state with the medium. We show that there is a simple mapping between injection and ejection spectra, which is connected to the detailed balance condition in thermal equilibrium. To illustrate the power of our approach, we specialize to the case of the Fermi polaron, corresponding to an impurity atom that is immersed in a noninteracting Fermi gas. For a mobile impurity with a mass equal to the fermion mass, we employ a finite-temperature variational approach to obtain the impurity spectral response. We find a striking nonmonotonic dependence on temperature in the impurity free energy, the contact, and the radio-frequency spectra. For the case of an infinitely heavy Fermi polaron, we derive exact results for the finite-temperature free energy, thus generalizing Fumi's theorem to arbitrary temperature. We also determine the exact dynamics of the contact after a quench of the impurity-fermion interactions. Finally, we show that the injection and ejection spectra obtained from the variational approach compare well with the exact spectra, thus demonstrating the accuracy of our approximation method.

We explore a few-body mixture of two bosonic species confined in quasi-one-dimensional parabolic traps of different length scales. The ground-state phase diagrams in the three-dimensional parameter space spanned by the harmonic length scale ratio, interspecies coupling strength, and particle-number ratio are investigated. As a first case study we use the mean-field ansatz (MF) to perform a detailed analysis of the separation mechanism. It allows us to derive a simple and intuitive rule predicting which of the immiscible phases is energetically more favorable at the miscible-immiscible phase boundary. We estimate the critical coupling strength for the miscible-immiscible transition and perform a comparison to correlated many-body results obtained by means of the multilayer multiconfiguration time-dependent Hartree method for bosonic mixtures (ML-X). At a critical ratio of the trap frequencies, determined solely by the particle-number ratio, the deviations between MF and ML-X are very pronounced and can be attributed to a high degree of entanglement between the components. As a result, we evidence the breakdown of the effective one-body picture. Additionally, when many-body correlations play a substantial role, the one-body density is in general not sufficient for deciding upon the phase at hand which we demonstrate exemplarily.

The sensitivity of future gravitational wave interferometers is expected to be limited throughout the detection band by quantum vacuum fluctuations, which can be reduced by applying quantum optics techniques such as squeezed vacuum injection. However, decoherence caused by optical losses in the readout chain will severely limit the effectiveness of such schemes. It was proposed that effect of losses in the final stage of detection can be mitigated by a phase-sensitive amplifier placed in between the output port of the interferometer and the photodetector. In this paper we propose to implement such amplification using an optomechanical device, study some of its practical limitations, and discuss its applicability to next-generation gravitational-wave detectors.

We consider the problem of quantitative wave-particle duality from the perspective of quantum state discrimination. Specifically, we obtain quantifiers of both the particle aspect and the wave aspect from state discrimination. We show that the familiar one-bet duality relation coincides with the relation obtained from considerations of ambiguous discrimination, and the quantifiers suggested by unambiguous discrimination provide us with additional duality relations. In contrast to earlier similar works, the path asymmetry of the interferometer provides the ensemble to be discriminated, and therefore there is no need to introduce which-path detectors.

We prove bounds on operator growth and infinite temperature out-of-time-ordered correlators in many-body systems with $N$ spin-$\frac{1}{2}$ degrees of freedom which interact via two-body all-to-all interactions. Our results parametrically improve previous bounds and sharply constrain when and how quantum simulators, including trapped-ion crystals and cavity quantum electrodynamics, can study quantum gravity.

The simultaneous quantum estimation of multiple parameters has recently become an essential aspect of quantum metrology. Although the ultimate sensitivity of a multiparameter quantum estimation in a noiseless environment can overcome the standard quantum limit that every classical sensor is bounded by, it is unclear whether a quantum sensor has an advantage over a classical sensor under a realistic level of noise. In this study, we present the framework of a simultaneous estimation of multiple parameters using quantum sensors under a specific noisy environment. Three components of an external magnetic field are estimated, and we consider the dephasing noise. We show that there is an optimal sensing time in a time-inhomogeneous noisy environment and that its sensitivity can overcome the standard quantum limit.

The process of dissociative electron attachment (DEA) to molecules with several vibrational degrees of freedom is usually treated in the approximation of the local potential for the description of the nuclear motion. We develop the nonlocal complex potential theory to treat the dissociation dynamics when there is more than one vibrational mode in the neutral molecule. We demonstrate the application of the multimode nonlocal theory to a generic molecule of the type $\mathrm{C}{Y}_{3}X$, where Y denotes the H or F atom and X denotes the halogen atom, with the inclusion of symmetric C–X stretch and $\mathrm{C}{Y}_3$ deform (“umbrella”) vibrational modes. We present results for the dependence of DEA cross sections on the electron energy and vibrational energy for the ${\mathrm{CF}}_3\mathrm{Cl}$ molecule in the two-mode approximation. The 1.5 eV peak in the DEA cross section is well described in the one-mode approximation. However, inclusion of additional modes is required to explain the experimentally observed low-energy peak in the DEA cross section at the vibrational temperature $T_v=800$ K.

An explicitly correlated functional form for expanding the wave function of an $N$-particle system with arbitrary angular momentum and parity is presented. We develop the projection-based approach, numerically exploited in our previous work [J. Muolo, E. Mátyus, and M. Reiher, J. Chem. Phys. 149, 184105 (2018)], to explicitly correlated Gaussian functions with one-axis-shifted centers and derive the matrix elements for the Hamiltonian and the angular momentum operators by analytically solving the integral projection operator. Variational few-body calculations without assuming the Born-Oppenheimer approximation are presented for several rotationally excited states of three- and four-particle systems. We show how the formalism can be used as a unified framework for high-accuracy calculations of properties of small atoms and molecules.

A complete effective Hamiltonian for relativistic corrections at orders $m{\alpha }^6$ and $m{\alpha }^6(m/M)$ in a one-electron molecular system is derived from the nonrelativistic QED Lagrangian. It includes spin-independent corrections to the energy levels and spin-spin scalar interactions contributing to the hyperfine splitting, both of which had been studied previously. In addition, corrections to electron spin-orbit and spin-spin tensor interactions are obtained. This allows the improvement of the hyperfine structure theory in hydrogen molecular ions. Improved values of the spin-orbit hyperfine coefficient are calculated for a few transitions of current experimental interest.

State changing in thermal-energy collisions between strontium atoms in very-high-$n$, $n\approx 300$, $n{}^1{F}_3$ Rydberg states is studied. In collisions between Rydberg atoms, the dipole-dipole interaction generates an effective electric field at each atom, which triggers Stark precession and the evolution of their angular momenta, $L$. Such $L$-changing collisions are examined using both quantum and classical theory. The theoretical predictions are experimentally verified by monitoring the damping of quantum beats induced by the sudden application of a DC “pump” field. The present work shows that, due to the long-range nature of the interactions, the cross sections, $\sigma$, for $L$ changing are considerably larger than the geometric collision cross section. For thermal collisions the cross section $\sigma$ for $n{}^1{F}_3$ Rydberg states with $n\simeq 300$ is $\approx 8\times {10}^{-5}{\mathrm{cm}}^2$. Scaling rules derived in this paper predict that for cold collisions $\sigma$ may increase by a further factor of 4.

Using a three-dimensional semiclassical method, we theoretically investigate frustrated double ionization (FDI) of Ar atoms subjected to strong laser fields. The double-hump photoelectron momentum distribution generated from FDI observed in a recent experiment [S. Larimian et al., Phys. Rev. Research 2, 013021 (2020)] is reproduced by our simulation. We confirm that the observed spectrum is due to recollision. The laser intensity dependence of FDI is investigated. We reveal that the doubly excited states of Ar atoms and excited states of ${\mathrm{Ar}}^{+}$ are the dominant pathways for producing FDI at relatively low and high intensities, respectively. The information of which pathway leads to FDI is encoded in the electron momentum distributions. Our work demonstrates that FDI is a general strong-field physical process accompanied with nonsequential double ionization and it can be well understood within the context of recollision scenario.