We present a rigorous study of momentum distribution and $p$-wave contacts of one-dimensional spinless Fermi gases with an attractive $p$-wave interaction. Using the Bethe ansatz wave function, we calculate analytically the high-momentum tail and show that the leading ($\sim 1/p^2$) and sub-leading terms ($\sim 1/p^4$) are determined by two contacts $C_2$ and $C_4$, which are related to the short-distance behavior of the two-body density matrix and its derivatives. As one increases the one-dimensional scattering length, the contact $C_2$ increases monotonically from zero while $C_4$ exhibits a peak at finite scattering length. In addition, we obtain analytic expressions for $p$-wave contacts at finite temperature from the thermodynamic Bethe ansatz equations for both weak and strong attractive interactions.

Quantum Hall (QH) states of two-dimensional (2D) single-layer optical lattices are examined using the Bose-Hubbard model (BHM) in the presence of an artificial gauge field. We study the QH states of both the homogeneous and inhomogeneous systems. For the homogeneous case, we use cluster Gutzwiller mean-field (CGMF) theory with cluster sizes ranging from $2\times 2$ to $5\times 5$. We then consider the inhomogeneous case, which is relevant to experimental realization. In this case, we use CGMF and exact diagonalization (ED). The ED studies are using lattice sizes ranging from $3\times 3$ to $4\times 12$. Our results show that the geometries of the QH states are sensitive to the magnetic flux $\alpha$ and cluster sizes. For homogeneous systems, among various combinations of $1/5\le \alpha \le 1/2$ and filling factor $\nu$, only the QH state of $\alpha =1/4$ with $\nu =1/2,1,3/2$, and 2 occur as ground states. For other combinations, the competing superfluid (SF) state is the ground state and QH state is metastable. For BHM with envelope potential, all the QH states observed in homogeneous systems exist for box potentials, but none exist for the harmonic potential. The QH states also persist for very shallow Gaussian envelope potential. As a possible experimental signature, we study the two-point correlations of the QH and SF states.

We study the criticality of a long-range quantum ferromagnetic Ising chain with algebraically decaying interactions $1/r^{\alpha }$ via the fidelity susceptibility based on the exact diagonalization and the density-matrix renormalization-group techniques. We find that critical exponents change monotonically from the mean-field universality class to the short-range Ising universality class for intermediate $\alpha$, which are consistent with recent results obtained from renormalization-group techniques. In addition, we determine the critical values for $1.8\le \alpha \le 3$ from the finite-size scaling of the fidelity susceptibility. Our work provides very nice numerical data from the fidelity susceptibility for the quantum long-range ferromagnetic Ising chain.

We determine the evolution of a cluster of quantum vortices initially placed at the center of a larger vortex-free region. We find that the cluster spreads out spatially. This spreading motion consists of two effects: the rapid evaporation of vortex dipoles from the cluster and the slow expansion of the cluster itself. The latter is akin to a diffusion process controlled by the quantum of circulation. Numerical simulations of the Gross-Pitaevskii equation show that this phenomenon is qualitatively unaffected by the presence of sound waves, vortex annihilations, and boundaries, and it should be possible to create it in the laboratory.

The reflectance of graphene is investigated in the framework of the Dirac model with account of its realistic properties, such as nonzero chemical potential and band gap, at any temperature. For this purpose, the exact reflection coefficients of the electromagnetic waves on a graphene sheet expressed via the polarization tensor and ultimately via the electrical conductivity of graphene have been used. The reflectance of graphene is computed as a function of frequency and chemical potential at different temperatures and values of the band-gap parameter. The minimum values of the reflectance are found which are reached in the infrared domain at the points of vanishing imaginary part of the conductivity of graphene. For a gapped graphene, the maximum reflectance equal to unity is reached at the points where the imaginary part of conductivity diverges. The computational results demonstrate an interesting interplay between the band gap and chemical potential in their combined effect on the reflectance. Specifically, there are wide frequency intervals where the reflectance of graphene increases with increasing chemical potential and decreasing band gap. The numerical computations are found to be in good agreement with the analytic asymptotic expressions in the regions of their applicability. Several technological areas, where the obtained results could be used, are listed.

We demonstrate that reorientational spatial solitons can curve when propagating in a medium with engineered walk-off along the direction of propagation. In this regard, we employ nematic liquid crystals with molecular anchoring defined by electron-beam lithography and optic axis distribution modulated in the longitudinal direction only, keeping the transverse orientation constant. The experimental results are in remarkably good agreement with a simple modulation theory based on momentum conservation.

We explore the coherent dynamics of a three-level $\mathsf{V}$-type system interacting with a thermal bath in the regime where thermal excitation occurs much faster than spontaneous decay. We present analytic solutions of the Bloch-Redfield quantum master equations, which show that strong incoherent pumping can generate long-lived quantum coherences among the excited states of the $\mathsf{V}$-type system in the overdamped regime defined by the condition $\mathrm{\Delta }/\left(\overline{n}\gamma \right)<f\left(p\right)$, where $\mathrm{\Delta }$ is the excited-state level splitting, $\gamma$ is the spontaneous decay rate, $\overline{n}\gg 1$ is the effective photon occupation number proportional to the pumping intensity, and $f\left(p\right)$ is a universal function of the transition dipole alignment parameter $p$. In the limit of nearly parallel transition dipoles ($p\to 1$) the coherence lifetime ${\tau }_c=1.34(\overline{n}/\gamma ){(\mathrm{\Delta }/\gamma )}^{-2}$ scales linearly with $\overline{n}$ and is enhanced by the factor $0.67\overline{n}$ with respect to the weak-pumping limit [Phys. Rev. Lett. 113, 113601 (2014); J. Chem. Phys. 144, 244108 (2016)]. We also establish the existence of long-lived quasistationary states, which occur in the overdamped regime and affect the process of thermalization of the $\mathsf{V}$-type system with the bath, slowing down the approach to thermal equilibrium. In the case of nonparallel transition dipole moments ($p<1$), no quasistationary states are formed and the coherence lifetime decreases sharply. The sharp transition between the different regimes of coherent dynamics is due to an interplay between coherence-generating Fano interference and various coherence-destroying processes (such as stimulated decay). Using a newly developed effective decoherence rate model, we find that in the limit $p\to 1$ the rates of coherence generation and decay are almost exactly balanced and the effective decoherence rate is minimized, leading to long coherence lifetimes. Our results reveal new regimes of long-lived quantum coherent dynamics, which could be observed in thermally driven atomic and molecular systems.

Spatial coherence quantifies spatial field correlations and is one of the fundamental properties of light. Here we investigate the spatial coherence of highly multimode lasers in the regime of short timescales. Counterintuitively, we show that in this regime, the temporal (longitudinal) modes play a crucial role in spatial coherence reduction. To evaluate the spatial coherence we measured the temporal dynamics of speckle fields generated by a highly multimode laser with over ${10}^5$ lasing spatial (transverse) modes and examined the dependence of speckle contrast on the exposure time of the detecting device. We show that in the regime of short timescales, the spatial and temporal modes interact to form spatiotemporal supermodes, such that the spatial degrees of freedom are encoded onto the temporal modes. As a result, the speckle contrast is suppressed according to the number of temporal modes, and the degree of spatial coherence is reduced. Moreover, the functional form of the spatial coherence is shown to have a bimodal distribution. In the regime of long timescales, the supermodes are no longer a valid representation of the laser modal structure. Consequently, the spatial coherence is independent of the temporal modes, and the classical result, where the speckle contrast is suppressed according to the number of spatial modes, is obtained. Due to this spatiotemporal mechanism, highly multimode lasers can be used for speckle suppression in high-speed full-field imaging applications, as we demonstrate here for imaging of a fast moving object.

Hafnium is the last transition-metal element with an undetermined electron affinity. Using a slow-electron velocity-map imaging spectrometer equipped with a cold ion trap, the electron affinity of hafnium atoms is measured to be $1436\left(5\right)\mathrm{c}{\mathrm{m}}^{-1}$ or 0.1780(6) eV. The cold ion trap employed in the present measurement is found to be crucial for reducing the background noise from the hafnium hydride anions.

Quantum coherence can be used to infer the presence of a detector without triggering it. Here we point out that, according to quantum mechanics, such interaction-free measurements cannot be perfect, i.e., in a single-shot experiment one has strictly positive probability to activate the detector. We formalize the extent to which such measurements are forbidden by deriving a trade-off relation between the probability of activation and the probability of an inconclusive interaction-free measurement. Our description of interaction-free measurements is theory independent and allows derivations of similar relations in models generalizing quantum mechanics. We provide the trade-off for the density cube formalism, which extends the quantum model by permitting coherence between more than two paths. The trade-off obtained hints at the possibility of perfect interaction-free measurements and indeed we construct their explicit examples. Such measurements open up a paradoxical possibility where we can learn by means of interference about the presence of an object in a given location without ever detecting a probing particle in that location. We therefore propose that absence of perfect interaction-free measurement is a natural postulate expected to hold in all physical theories. As shown, it holds in quantum mechanics and excludes the models with multipath coherence.

We experimentally and theoretically investigate the nonequilibrium phase structure of a well-controlled driven-dissipative quantum spin system governed by the interplay of coherent driving, spontaneous decay, and long-range spin-spin interactions. We discover that the rate of population loss provides a convenient macroscopic observable that exhibits power-law scaling with the driving strength over several orders of magnitude. The measured scaling exponents reflect the underlying nonequilibrium phase structure of the many-body system, which includes dissipation-dominated, paramagnetic, and critical regimes as well as an instability which drives the system towards states with high excitation density. This opens up a means to study and classify quantum systems out of equilibrium and extends the domain where scale-invariant behavior may be found in nature.

High-fidelity qubit measurements play a crucial role in quantum computation, communication, and metrology. In recent experiments, it has been shown that readout fidelity can be improved by performing repeated quantum nondemolition (QND) readouts of a qubit's state through an ancilla. For a qubit encoded in a two-level system, the fidelity of such schemes is limited by the fact that a single error can destroy the information in the qubit. On the other hand, if a bosonic system is used, this fundamental limit can be overcome by utilizing higher levels such that a single error still leaves states distinguishable. In this work, we present a robust readout scheme which leverages both repeated QND readouts and higher-level encodings to asymptotically suppress the effects of mode relaxation and individual measurement infidelity. We calculate the measurement fidelity in terms of general experimental parameters, provide an information-theoretic description of the scheme, and describe its application to several encodings, including cat and binomial codes.

Both coherence and entanglement stem from the superposition principle, capture quantumness of a physical system, and play a central role in quantum physics. In a multipartite quantum system, coherence and quantum correlations are closely connected. In particular, it has been established that quantum coherence of a bipartite state is an important resource for its conversion to entanglement [A. Streltsov et al., Phys. Rev. Lett. 115, 020403 (2015)] and to quantum discord [J. Ma et al., Phys. Rev. Lett. 116, 160407 (2016)]. We show here that there is a very close association between partial coherence introduced by Luo and Sun [S. Luo and Y. Sun, Phys. Rev. A 96, 022136 (2017)] and quantum correlations (quantified by quantum discord) in both directions. Furthermore, we propose families of coherence measures in terms of quantum correlations and quantum Fisher information.

The complex Kohn variational method is extended to compute light-driven electronic transitions between continuum wave functions in atomic and molecular systems. This development enables the study of multiphoton processes in the perturbative regime for arbitrary light polarization. As a proof of principle, we apply the method to compute the photoelectron spectrum arising from the pump–probe two-photon ionization of helium induced by a sequence of extreme ultraviolet and infrared light pulses. We compare several two-photon ionization pump–probe spectra, resonant with the ($2s2p){}^{1}P_1^o$ Feshbach resonance, with independent simulations based on the atomic B-spline close-coupling stock code, and find good agreement between the two approaches. This finite-pulse perturbative approach is a step towards the ab initio study of weak-field attosecond processes in polyelectronic molecules.

We provide a theoretical analysis for a recently demonstrated cooling method. Two-level particles undergo successive adiabatic transfers upon interaction with counterpropagating laser beams that are repeatedly swept over the transition frequency. We show that particles with narrow linewidth transitions can be cooled to near the recoil limit. This cooling mechanism has a reduced reliance on spontaneous emission compared to Doppler cooling, and hence shows promise for application to systems lacking closed cycling transitions, such as molecules.

We investigate theoretically the dynamics of a spin-orbit-coupled soliton formed by a self-interacting Bose-Einstein condensate immersed in a random potential, in the presence of an artificial magnetic field. We find that, due to the anomalous spin-dependent velocity, the synthetic Zeeman coupling can play a critical role in the soliton dynamics by causing its localization or delocalization, depending on the coupling strength and on the parameters of the random potential. The observed effects of the Zeeman coupling qualitatively depend on the type of self-interaction in the condensate, since the spin state and the self-interaction energy of the condensate are mutually related if the invariance of the latter with respect to the spin rotation is lifted.

We studied numerically the effect of disorder on the propagation of the channel plasmon polaritons (CPP) in arrays of evanescently coupled rectangular grooves cut into the planar surface of metal in contact with vacuum or a dielectric medium. The grooves are assumed to be of the same width and depth while an off-diagonal disorder is introduced by randomly varying the distance between the grooves. To explore conditions under which transverse Anderson localization can be observed we employ a numerical technique based on the coupled mode theory. The distribution of the electric field of the CPP beam evaluated for a random system exhibits a transition from ballistic spreading of the CPP wave packets to transverse localization with an increasing disorder. We found that the interplay between the Ohmic losses and the coupling coefficients between the neighboring grooves plays a central role in realization of the transverse Anderson localization. We suggest two strategies, which are beneficial for its observation and discuss a potential impact of randomness on beam steering in the plasmonic nanodevices.

We investigate the dynamics of an optomechanical system where a cavity with a movable mirror involves a degenerate optical parametric amplifier and is driven by a periodically modulated laser field. Our results show that the cooperation between the parametric driving and periodically modulated cavity driving results in a twofold squeezing on the movable cavity mirror that acts as a mechanical oscillator. This allows the fluctuation of the mechanical oscillator in one quadrature (momentum or position) to be reduced to a level that cannot be reached by solely applying either of these two drivings. In addition to the fundamental interests, e.g., study of quantum effects at the macroscopic level and exploration of the quantum-to-classical transition, our results have potential applications in ultrasensitive sensing of force and motion.

We study the topological optical states in one-dimensional dimerized ultracold atomic chains, as an extension of the Su-Schrieffer-Heeger (SSH) model. By taking the fully retarded near-field and far-field dipole-dipole interactions into account, we describe the system by an effective non-Hermitian Hamiltonian, vastly different from the Hermitian Hamiltonian of the conventional SSH model. We analytically calculate the complex band structures for infinitely long chains, and show that the topological invariant, i.e., the complex Zak phase, is still quantized and becomes nontrivial when the dimerization parameter $\beta >0.5$, despite the broken chiral symmetry and non-Hermiticity. We have verified the validity of the bulk-boundary correspondence for this non-Hermitian system by further analyzing the eigenstate distributions along with their inverse participation ratios for finite chains, where topologically protected edge states are unambiguously identified. We also reveal that such topological edge states are robust under symmetry-breaking disorders. For transverse eigenstates, we further discover the increase of localization length of topological edge states with the increase of lattice period due to the presence of strong far-field dipole-dipole interactions. Moreover, the ultrastrong scattering cross section and ultranarrow linewidth of a single cold atom allow us to observe in more detail about topological states than in conventional systems, such as the frequency shift with respect to the single-atom resonance and the largely tunable band gap. We envisage these topological photonic states can provide an efficient interface between light and matter.

In this study, circularly polarized high-order harmonic generation (CP-HHG) from a chiral molecule, limonene, by a CP counter-rotating two-color laser field was found to possess circular dichroism. A high-order harmonic spectrum from a limonene enantiomer depends on the combination of the chirality of the enantiomer and the rotation direction of the superimposed two-color laser field in comparison with that of an achiral atom, helium. From the $R$ enantiomer, the harmonic orders with clockwise polarization were generated more efficiently than those with counterclockwise polarization and vice versa. CP-HHG can be a sensitive probe of the chirality of biomolecules on the femtosecond and attosecond timescales.