We derive analytically the Lévy-like steady-state distribution with exponential tempering of emission intensities in random lasers. Our approach is based on the Langevin and associated Fokker-Planck equations describing the dynamics of the amplitudes of the resonance modes in a cavity with a disordered nonlinear dielectric medium. The reported results fully agree with the experimental characterization of the prelasing, Lévy-like, and self-averaged Gaussian lasing regimes in a random laser system as a function of the pump energy and disorder strength, as well as with the recent suggestion of the Lévy exponent $\alpha$ as a universal identifier of the random lasing threshold.

Atom- and site-resolved experiments with ultracold atoms in optical lattices provide a powerful platform for the simulation of strongly correlated materials. In this Rapid Communication, we present a toolbox for the preparation, control, and site-resolved detection of a tunnel-coupled bilayer degenerate quantum gas. Using a collisional blockade, we engineer occupation-dependent interplane transport which enables us to circumvent light-assisted pair loss during imaging and count $n=0$ to $n=3$ atoms per site. We obtain the first number- and site-resolved images of the Mott insulator “wedding cake” structure and observe the emergence of antiferromagnetic ordering across a magnetic quantum phase transition. We are further able to employ the bilayer system for spin-resolved readout of a mixture of two hyperfine states. This work opens the door to direct detection of entanglement and Kosterlitz-Thouless-type phase dynamics, as well as studies of coupled planar quantum materials.

We study the driven-dissipative dynamics of a network of spin-1/2 systems coupled to one or more chiral 1D bosonic waveguides within the framework of a Markovian master equation. We determine how the interplay between a coherent drive and collective decay processes can lead to the formation of pure multipartite entangled steady states. The key ingredient for the emergence of these many-body dark states is an asymmetric coupling of the spins to left and right propagating guided modes. Such systems are motivated by experimental possibilities with internal states of atoms coupled to optical fibers, or motional states of trapped atoms coupled to a spin-orbit coupled Bose-Einstein condensate. We discuss the characterization of the emerging multipartite entanglement in this system in terms of the Fisher information.

In leading fault-tolerant quantum-computing schemes, accurate transformations are obtained by a two-stage process. In a first stage, a discrete universal set of fault-tolerant operations is obtained by error-correcting noisy transformations and distilling resource states. In a second stage, arbitrary transformations are synthesized to desired accuracy by combining elements of this set into a circuit. Here we present a scheme that merges these two stages into a single one, directly distilling complex transformations. We find that our scheme can reduce the total overhead to realize certain gates by up to a few orders of magnitude. In contrast to other schemes, this efficient gate synthesis does not require computationally intensive compilation algorithms and a straightforward generalization of our scheme circumvents compilation and synthesis altogether.

BosonSampling is a restricted model of quantum computation proposed recently, where a nonadaptive linear-optical network is used to solve a sampling problem that seems to be hard for classical computers. Here we show that, even if the linear-optical network has a constant number (greater than four) of beam splitter layers, the exact version of the BosonSampling problem is still classically hard, unless the polynomial hierarchy collapses to its third level. This is based on a similar result known for constant-depth quantum circuits and circuits of 2-local commuting gates (IQP).

We introduce a class of light field that angularly accelerates during propagation. We show that the acceleration (deceleration) may be controlled by adjustment of a single parameter, and tuned continuously, down to no acceleration at all. As the angular acceleration takes place in a bounded space, the azimuthal degree of freedom, such fields accelerate periodically as they propagate. Notably, the amount of angular acceleration is not limited by paraxial considerations, may be tailored for large accelerations over arbitrarily long distances, and can be engineered independently of the beam's spatial extent. We discuss how such angularly accelerating light fields can maintain the conservation of angular momentum through an energy exchange mechanism across the field.

Magic wavelengths, for which there is no differential ac Stark shift for the ground and excited state of the atom, allow trapping of excited Rydberg atoms without broadening the optical transition. This is an important tool for implementing quantum gates and other quantum information protocols with Rydberg atoms, and reliable theoretical methods to find such magic wavelengths are thus extremely useful. We use a high-precision all-order method to calculate magic wavelengths for the $5s\text{−}18s$ transition of rubidium, and compare the calculation to experiment by measuring the light shift for atoms held in an optical dipole trap at a range of wavelengths near a calculated magic value.

We study nonlinear interactions in a strongly driven optomechanical cavity, in regimes where the interactions give rise to resonant scattering between optomechanical polaritons and are thus strongly enhanced. We use a Keldysh formulation and self-consistent perturbation theory, allowing us to include self-energy diagrams at all orders in the interaction. Our main focus is understanding how nonequilibrium effects are modified by the polariton interactions, in particular the generation of nonzero effective polariton temperatures from vacuum fluctuations (both in the incident cavity drive and in the mechanical dissipation). We discuss how these effects could be observed in the output spectrum of the cavity. Our work also provides a technical toolkit that will be useful for studies of more complex optomechanical systems.

Detection of entanglement in bipartite states is a fundamental task in quantum information. The first method to verify entanglement in mixed states was the partial-transpose criterion. Subsequently, numerous quantifiers for bipartite entanglement were introduced, among them concurrence and negativity. Surprisingly, these quantities are often treated as distinct or independent of each other. The aim of this contribution is to highlight the close relations between these concepts, to show the connections between seemingly independent results, and to present various estimates for the mixed-state concurrence within the same framework.

We propose a Raman quantum memory scheme that uses several atomic ensembles to store and retrieve the multimode highly entangled state of an optical quantum frequency comb, such as the one produced by parametric down-conversion of a pump frequency comb. We analyze the efficiency and the fidelity of such a quantum memory. Results show that our proposal may be helpful to multimode information processing using the different frequency bands of an optical frequency comb.

We present a horizontal gravity gradiometer atom interferometer for precision gravitational tests. The horizontal configuration is superior for maximizing the inertial signal in the atom interferometer from a nearby proof mass. In our device, we have suppressed spurious noise associated with the horizonal configuration to achieve a differential acceleration sensitivity of $4.2\times {10}^{-9}g/\sqrt{\mathrm{Hz}}$ over a 70-cm baseline or $3.0\times {10}^{-9}g/\sqrt{\mathrm{Hz}}$ inferred per accelerometer. Using the performance of this instrument, we characterize the results of possible future gravitational tests. We demonstrate a statistical uncertainty of $3\times {10}^{-4}$ for a proof-of-concept measurement of the gravitational constant that is competitive with the present limit of $1.2\times {10}^{-4}$ using other techniques. From this measurement, we provide a statistical constraint on a Yukawa-type fifth force at $8\times {10}^{-3}$ near the poorly known length scale of 10 cm. Limits approaching ${10}^{-5}$ appear feasible. We discuss improvements that can enable uncertainties falling well below ${10}^{-5}$ for both experiments.

Low-energy $(E_0=65\mathrm{eV})$ electron-impact single ionization of Ne $(2p)$ has been investigated to thoroughly test state-of-the-art theoretical approaches. The experimental data were measured using a reaction microscope, which can cover nearly the entire $4\pi$ solid angle for the secondary electron emission energies ranging from 2 to 8 eV, and projectile scattering angles ranging from $8.5^{\circ }$ to $20.0^{\circ }$. The experimental triple-differential cross sections are internormalized across all measured scattering angles and ejected energies. The experimental data are compared to predictions from a hybrid second-order distorted-wave Born plus $R$-matrix approach, the distorted-wave Born approximation with the inclusion of postcollision interaction (PCI), a three-body distorted-wave approach (3DW), and a $B$-spline $R$-matrix (BSR) with pseudostates approach. Excellent agreement is found between the experiment and predictions from the 3DW and BSR models, for both the angular dependence and the relative magnitude of the cross sections in the full three-dimensional parameter space. The importance of PCI effects is clearly visible in this low-energy electron-impact ionization process.

The cavity-optomechanical radiation pressure interaction provides the means to create entanglement between a mechanical oscillator and an electromagnetic field interacting with it. Here we show how we can utilize this entanglement within the framework of time-continuous quantum control, in order to engineer the quantum state of the mechanical system. Specifically, we analyze how to prepare a low-entropy mechanical state by (measurement-based) feedback cooling operated in the blue-detuned regime, the creation of bipartite mechanical entanglement via time-continuous entanglement swapping, and preparation of a squeezed mechanical state by time-continuous teleportation. The protocols presented here are feasible in optomechanical systems exhibiting a cooperativity larger than 1.

We present a momentum-resolved study of strong field multiple ionization of ionic targets. Using a deconvolution method we are able to reconstruct the electron momenta from the ion momentum distributions after multiple ionization up to four sequential ionization steps. This technique allows an accurate determination of the saturation intensity as well as of the electron release times during the laser pulse. The measured results are discussed in comparison to typically used models of over-the-barrier ionization and tunnel ionization.

A two-dimensional topologically ordered quantum memory is well protected against error if the energy gap is large compared to the temperature, but this protection does not improve as the system size increases. We review and critique some recent proposals for improving the memory time by introducing long-range interactions among anyons, noting that instability with respect to small local perturbations of the Hamiltonian is a generic problem for such proposals. We also discuss some broader issues regarding the prospects for scalable quantum memory in two-dimensional systems.

We study the quantum dynamics of interacting bosons in a three-dimensional disordered lattice. We show that the superfluid current induced by an adiabatic acceleration of the disordered lattice undergoes a dynamical instability signaling the onset of the Bose-glass phase. The dynamical superfluid–Bose-glass phase diagram is found in very good agreement with static superfluid fraction calculation. A different boundary is obtained when the disorder is suddenly quenched in a moving periodic lattice. In this case we do not observe a dynamical instability but rather a depletion of the superfluid density. Our analysis is based on a dynamical Gutzwiller approach which we show to reproduce the quantum Monte Carlo static phase diagram in the strong interaction limit.

In this work we consider the dynamics of two tunnel-coupled chains after a quench in the tunneling strength is performed and the two systems are allowed to evolve independently. We describe the form of the initial state, comparing with previous results concerning the dynamics after the splitting of a one-dimensional gas of bosons into two phase-coherent systems. We compute different correlation functions, among which are those that are relevant for interference measurements, and discuss the emergence of effective temperatures also in connection with previous works.

We experimentally and theoretically study the peak fraction of a Bose-Einstein condensate loaded into a cubic optical lattice as the lattice potential depth and entropy per particle are varied. This system is well described by the superfluid regime of the Bose-Hubbard model, which allows for comparison with mean-field theories and exact quantum Monte Carlo (QMC) simulations. By correcting for systematic discrepancies between condensate and peak fraction, we find that the QMC simulations and measured peak fraction agree at low entropies per particle. At high entropy, however, we discover that the experiment consistently shows the presence of a condensate at temperatures higher than the critical temperature predicted by QMC simulations. This metastability suggests that turning on the lattice potential is nonadiabatic. To confirm this behavior, we compute the time scales for relaxation in this system, and find that equilibration times are comparable with the known heating rates. The similarity of these time scales implies that turning on the lattice potential adiabatically may be impossible. Our results point to the urgent need for a better theoretical and experimental understanding of the time scales for relaxation and adiabaticity in strongly interacting quantum gases, and the importance of model-independent probes of thermometry in optical lattices.

The collective interference of partially distinguishable bosons in multimode networks is studied via double-sided Feynman diagrams. The probability for many-body scattering events becomes a multidimensional tensor permanent, which interpolates between distinguishable particles and identical bosons and easily extends to mixed initial states. The permanent of the distinguishability matrix, composed of all mutual scalar products of the single-particle mode functions, emerges as a natural measure for the degree of interference: It yields a bound on the difference between event probabilities for partially distinguishable bosons and the idealized species and exactly quantifies the degree of bosonic bunching.

We explore the possible regimes of decaying two-dimensional quantum turbulence, and elucidate the nature of spectral energy transport by introducing a dissipative point-vortex model with phenomenological vortex-sound interactions. The model is valid for a large system with weak dissipation, and also for systems with strong dissipation, and allows us to extract a meaningful and unambiguous spectral energy flux associated with quantum vortex motion. For weak dissipation and large system size we find a regime of hydrodynamic vortex turbulence in which energy is transported to large spatial scales, resembling the phenomenology of the transient inverse cascade observed in decaying turbulence in classical incompressible fluids. For strong dissipation the vortex dynamics are dominated by dipole recombination and exhibit no appreciable spectral transport of energy.