Physical theories constrained with local quantum structure and satisfying the no-signaling principle can allow beyond-quantum global states. In a standard Bell experiment, correlations obtained from any such beyond-quantum bipartite state can always be reproduced by quantum states and measurements, suggesting the local quantum structure and no-signaling to be the axioms to isolate quantum correlations. In this Letter, however, we show that if the Bell experiment is generalized to allow local quantum inputs, then beyond-quantum correlations can be generated by every beyond-quantum state. This gives us a way to certify the beyond quantumness of locally quantum no-signaling theories and in turn suggests the requirement of additional information principles along with the local quantum structure and no-signaling principle to isolate quantum correlations. More importantly, our work establishes that the additional principle(s) must be sensitive to the quantum signature of local inputs. We also generalize our results to multipartite locally quantum no-signaling theories and further analyze some interesting implications.

While it is straightforward to count laser-cooled trapped ions by fluorescence imaging, detecting the number of dark ions embedded and sympathetically cooled in a mixed ion crystal is more challenging. We demonstrate a method to track the number of dark ions in real time with single-particle sensitivity. This is achieved by observing discrete steps in the amount of fluorescence emitted from the coolant ions while exciting secular motional resonances of dark ions. By counting the number of fluorescence steps, we can identify the number of dark ions without calibration and without relying on any physical model of the motional excitation. We demonstrate the scheme by detecting ${\mathrm{H}}_2^{+}$ and ${\mathrm{H}}_3^{+}$ ions embedded in a ${\mathrm{Be}}^{+}$ ion Coulomb crystal in a linear radio-frequency trap. Our method allows observing the generation and destruction of individual ions simultaneously for different types of ions. Besides high-resolution spectroscopy of dark ions, another application is the detection of chemical reactions in real time with single-particle sensitivity. This is demonstrated in this Letter.

We study theoretically driven quantum dynamics in periodic arrays of two-level qubits coupled to the waveguide. We demonstrate that strongly subradiant eigenstates of the master equation for the density matrix emerge under strong coherent driving for arrays with the anti-Bragg periods $d=\lambda /4,3\lambda /4...$. This happens even though are no such eigenstates at low driving powers and is directly manifested by long-living quantum correlations between the qubits.

We explore the potential of a spin-orbit-coupled Bose-Einstein condensate for thermodynamic cycles. For this purpose we propose a quantum heat engine based on a condensate with spin-orbit and Zeeman coupling as a working medium. The cooling and heating are simulated by contacts of the condensate with an external magnetized media and demagnetized media. We examine the condensate ground-state energy and its dependence on the strength of the synthetic spin-orbit and Zeeman couplings and interatomic interaction. Then we study the efficiency of the proposed engine. The cycle has a critical value of spin-orbit coupling related to the engine's maximum efficiency.

In this Research Letter it is shown how certain optical wave amplification phenomena, which do not obey standard phase-matching conditions and are generally classified as non-Hermitian phase matching or gain-through-loss(-filtering) processes, can be considered as particular cases of the more general phenomenon of converse symmetry breaking predicted and observed in various networks of coupled oscillators. It is shown that the abovementioned optical amplification processes are possible thanks to a phase-locking dynamics enabled by asymmetry or heterogeneity in the coupled-modes equations.

Experiments at the interface of quantum field theory and general relativity would greatly benefit theoretical research towards their unification. The gravitational aspects of quantum experiments performed so far can be explained either within Newtonian gravity or by Einstein's equivalence principle. Here, we describe a way to measure components of the Riemann curvature tensor with maximally path-entangled quantum states of light. We show that the entanglement-induced increase in sensitivity also holds for gravitationally induced phases in Mach-Zehnder interferometers. As a result, the height difference between the two interferometer arms necessary to rule out flat space-time by measuring gravity gradients can be significantly reduced.

Defects in wide-band-gap semiconductors are promising qubit candidates for quantum communication and computation. Epitaxially grown II-VI semiconductors are particularly promising host materials due to their direct band gap and potential for isotopic purification to a spin-zero nuclear background. Here, we show an alternative type of single photon emitter with potential electron spin qubits based on Cl impurities in ZnSe. We utilize a quantum well to increase the binding energies of donor emission and confirm single photon emission with short radiative lifetimes of 192 ps. Furthermore, we verify that the ground state of the Cl donor complex contains a single electron by observing two-electron-satellite emission, leaving the electron in higher orbital states. We also characterize the Zeeman splitting of the exciton transition by performing polarization-resolved magnetic spectroscopy on single emitters. Our results suggest single Cl impurities are suitable as a single photon source with a potential photonic interface.

We analyze the time-domain dynamics of resonators supporting exceptional points (EPs), at which both the eigenfrequencies and the eigenmodes associated with perfect capture of an input wave coalesce. We find that a time-domain signature of the EP is an expansion of the class of waveforms which can be perfectly captured. We show that such resonators have improved performance for storage or transduction of energy. They also can be used to convert between waveforms within this class. We analytically derive these features and demonstrate them for several examples of coupled optical resonator systems.

We propose a notion of the directional emission in microcavity lasers. First, the Shannon entropy of the far-field profiles in the polar coordinate can quantify the degree of unidirectionality of the emission, while previous notions about the unidirectionality cannot efficiently measure in the robust range against a variation of the deformation parameter. Second, a divergence angle of the directional emission is defined phenomenologically in terms of full width at half maximum, and it is only easily applicable to a simple peak structure. However, the Shannon entropy of semimarginal probability of the far-field profiles in the Cartesian coordinate can present equivalent results, and moreover it is applicable even to cases with a complicated peak structure of the emission.

We present, theoretically and experimentally, phase-matched noncritical off-axis second-harmonic generation which is easily tuned using a spatial light modulator. The phase-matching condition depends on both the spatial properties of the fundamental beam and the thermal properties of the medium. We show that a thermally induced phase mismatch can be compensated by choosing the pump beam spatial properties resulting in phase-matched noncollinear second-harmonic generation.

The ground-state entanglement entropy is studied in a many-body bipartite quantum system with either a single or multiple conserved quantities. It is shown that the entanglement entropy exhibits a universal power-law behavior at large $R$—the occupancy ratio between the two subsystems. Single and multiple conserved quantities lead to different power-law exponents, suggesting the entanglement entropy can serve to detect hidden conserved quantities. Moreover, occupancy measurements allow inference of the bipartite entanglement entropy. All the above results are generalized for the Rényi entropy.

It is common knowledge that atoms can form molecules if they attract each other. Here, we show that it is possible to create molecules where bound states of the atoms are not the result of attractive interactions but have the topological origin. That is, the bound states of the atoms correspond to the topologically protected edge states of a topological model. Such topological molecules can be realized if the interaction strength between ultracold atoms is properly modulated in time. A similar mechanism allows one to realize topologically protected localization of an electron on a classical orbit if a Rydberg atom is perturbed by a properly modulated microwave field.

Scattering of intense laser pulses on high-energy electron beams allows one to produce a large number of x and $\gamma$ rays. For temporally pulsed lasers, the resulting spectra are broadband which severely limits practical applications. One could use linearly chirped laser pulses to compensate for that broadening. We show for laser pulses chirped in the spectral domain that there is the optimal chirp parameter at which the spectra have the brightest peak. Additionally, we use catastrophe theory to analytically find this optimal chirp value.

We reveal universal connections between three important phenomena in classical wave physics: (i) the ponderomotive force acting on the medium particles in an oscillatory wave field, (ii) the Stokes drift of free medium particles in a wave field, and (iii) the canonical wave momentum in a medium. We analyze these phenomena for (a) longitudinal sound waves in a gas or fluid and (b) transverse electromagnetic waves interacting with electrons in a plasma or metal. In both cases, assuming quasimonochromatic yet arbitrarily inhomogeneous wave fields, the connections between the ponderomotive force, Stokes drift velocity, kinetic energy, and canonical wave momentum carried by the medium particles are given by the same simple expressions. This sheds light on the nature of these phenomena, their fine interplay, and can be useful for applications to dynamical transport phenomena in various types of waves.

A topological pump, a quantum pump protected by the bulk topology, enables the robust quantized transport of particles (or waves) when the system parameters are varied in a cyclic process. In previous studies, topological pumps were studied in undistorted systems. Here, we show topological pumps can happen between disclination states with different chiralities in a distorted lattice. Based on a generalized understanding of the charge pumping process, we explain the topological disclination pump by tracing the motion of Wannier centers in each unit cell. In addition, by constructing two disclination structures and introducing a symmetry-breaking perturbation, we achieve a topological pumping between different disclination cores. Furthermore, we expect to observe our predictions in femtosecond-laser-written waveguide arrays with a fine-tuned geometry and refractive index. Our result opens a route to study the topological pump in distorted systems and enables the quantized transport of photons between real-space topological defects.

We study the dynamical evolution of a two-dimensional Bose gas after a disorder potential quench. Depending on the initial conditions, the system evolves either to a thermal or a superfluid state. Using extensive quasiexact numerical simulations, we show that the two phases are separated by a Kosterliz-Thouless transition. The thermalization time is shown to be longer in the superfluid phase, but no critical slowing down is observed at the transition. The long-time phase diagram is well reproduced by a simple theoretical model. The spontaneous emergence of Kosterlitz-Thouless transitions following a quench is a generic phenomenon that should arise both in the context of nonequilibrium quantum gases and in the context of nonlinear classical wave systems.

We present quantum dynamics calculations showing that the electron-correlation-driven charge migration occurring in the correlation band of ionized molecules can lead to a redistribution of the charge which increases the stability of the system. These calculations offer an interpretation of recent experimental results obtained for adenine for which the stabilization induced by the electron-correlation-driven charge migration leads to a modification of the fragmentation pattern of the molecule after subsequent ionization. We argue that this charge-migration-induced stabilization is a general mechanism and discuss its implications for the development of attochemistry and how it can be understood in the context of the ultrafast, nonadiabatic relaxation taking place in highly excited molecular cations.

Rydberg atoms with dipole-dipole interactions provide intriguing platforms to explore exotic quantum many-body physics. Here we propose a mechanism dubbed laser-assisted dipole-dipole interactions to realize synthetic magnetic field for Rydberg atoms in a two-dimensional array configuration, which gives rise to the exotic bosonic topological states. In the presence of an external effective Zeeman splitting gradient, the dipole-dipole interaction between neighboring Rydberg atoms along the gradient direction is suppressed but can be assisted when Raman lights are applied to compensate the energy difference. With this scheme we generate a controllable uniform magnetic field for the complex spin-exchange coupling model, which can be mapped to hard-core bosons coupling to an external synthetic magnetic field. The highly tunable flat Chern bands of the hard-core bosons are then obtained and, moreover, the bosonic fractional quantum Hall states can be achieved with experimental feasibility. This Letter opens up an intriguing avenue for the realization of the highly sought-after bosonic topological orders using Rydberg atoms.