The existence and stability of domain walls (DWs) and bubble-droplet (BD) states in binary mixtures of quasi-one-dimensional ultracold Bose gases with inter- and intraspecies repulsive interactions is considered. Previously, DWs were studied by means of coupled systems of Gross-Pitaevskii equations (GPEs) with cubic terms, which model immiscible binary Bose-Einstein condensates (BECs). We address immiscible BECs with two- and three-body repulsive interactions, as well as binary Tonks–Girardeau (TG) gases, using systems of GPEs with cubic and quintic nonlinearities for the binary BEC, and coupled nonlinear Schrödinger equations with quintic terms for the TG gases. Exact DW solutions are found for the symmetric BEC mixture, with equal intraspecies scattering lengths. Stable asymmetric DWs in the BEC mixtures with dissimilar interactions in the two components, as well as of symmetric and asymmetric DWs in the binary TG gas, are found by means of numerical and approximate analytical methods. In the BEC system, DWs can be easily put in motion by phase imprinting. Combining a DW and anti-DW on a ring, we construct BD states for both the BEC and TG models. These consist of a dark soliton in one component (the “bubble”), and a bright soliton (the “droplet”) in the other. In the BEC system, these composite states are mobile, too.

We study the cooling performance of a realistic mechanical resonator containing defects. The normal cooling method through an optomechanical system does not work efficiently due to those defects. We show that, by employing periodical ${\sigma }_z$ pulses, we can eliminate the interaction between defects and their surrounding heat baths up to the first order of time. Compared with the cooling performance of the no ${\sigma }_z$ pulses case, much better cooling results are obtained. Moreover, this pulse sequence has the ability to improve the cooling performance of the resonator with different defect energy gaps and different defect damping rates.

We study the dynamics of a spin ensemble strongly coupled to a single-mode resonator driven by external pulses. When the mean frequency of the spin ensemble is in resonance with the cavity mode, damped Rabi oscillations are found between the spin ensemble and the cavity mode which we describe very accurately, including the dephasing effect of the inhomogeneous spin broadening. We demonstrate that a precise knowledge of this broadening is crucial both for a qualitative and a quantitative understanding of the temporal spin-cavity dynamics. On this basis we show that coherent oscillations between the spin ensemble and the cavity can be enhanced by a few orders of magnitude, when driving the system with pulses that match special resonance conditions. Our theoretical approach is tested successfully with an experiment based on an ensemble of negatively charged nitrogen-vacancy centers in diamond strongly coupled to a superconducting coplanar single-mode waveguide resonator.

We consider a microcavity made by a graded-index glass, doped with dye molecules, placed within two planar mirrors and study Bose-Einstein condensation of photons. The presence of the mirrors leads to an effective photon mass, and the index grading provides an effective trapping frequency; the photon gas becomes formally equivalent to a two-dimensional Bose gas trapped in an isotropic harmonic potential. The inclusion of nonlinear effects provides an effective interaction between photons. We discuss, in particular, thermal lensing effects and nonlocal nonlinearity, and quantitatively compare our results with the reported experimental data.

We propose a conditional generation of quantum squeezing from realistic single-photon states. The proposed method does not require any coherent measurement projecting on a superposition of internal levels inside single-photon emitters. Interestingly, the squeezing can be generated despite a low single-photon efficiency of the emitters. The method can therefore substantially enlarge the set of existing sources of the squeezed states of electromagnetic radiation. For example, it can be used to produce squeezed ultraviolet radiation based on already available ultraviolet single-photon emitters.

We propose an ultrasensitive mass spectrometer based on a coupled quantum-bit-oscillator system. Under dynamical decoupling control of the quantum bit (qubit), the qubit coherence exhibits a comb structure in the time domain. The time-comb structure enables high-precision measurements of oscillator frequency, which can be used as an ultrasensitive mass spectrometer. We show that, in the ideal case, the sensitivity $\eta$ of the proposed mass spectrometer has better performance at higher temperature and scales with the temperature $T$ as $\eta \sim T^{-1/2}$. While taking into account qubit and oscillator decay, the optimal sensitivity reaches a universal value independent of environmental temperature $T$. The measurement sensitivity $\eta$ also shows an improved dependence on the control-pulse number $N$ as $\eta \sim N^{-3/2}$, in comparison with the $N^{-1/2}$ scaling in previous magnetometry studies. With the present technology on solid-state spin qubit and high-quality optomechanical system, our proposal is feasible to realize an ultrasensitive room-temperature mass spectrometer.

We study the dynamics of genuine multipartite entanglement for a system of four qubits. Using a computable entanglement monotone for multipartite systems, we investigate the as yet unexplored aspects of a cavity-reservoir system of qubits. For one specific initial state, we observe a sudden transition in the dynamics of genuine entanglement for the four qubits. This sudden change occurs only during a time window where neither cavity-cavity qubits nor reservoir-reservoir qubits are entangled. We show that the sudden change in dynamics of this specific state is extremely sensitive to white noise.

We derive the analytical expressions for the thermal Casimir-Polder energy and force between a spheroidal nanoparticle above a semi-infinite material and a graphene covered interface. We analyze in detail the Casimir-Polder force between a gold nanoparticle and a single sheet of pristine graphene focusing on the impact of anisotropy. We show that the effect of anisotropy, i.e., the shape and orientation of the spheroidal nanoparticle, has a much larger influence on the force than the tunability of graphene. The effect of tuning and anisotropy both add up such that we observe a force between the particle and the sheet of graphene which is between 20% and 50% of that between the same particle and an ideal metal plate. Hence the observed force is much larger than the results found for the Casimir force between a metal half-space and a layer of graphene.

Ejection of core electrons as a result of recollision in a laser-driven carbon atom is theoretically investigated with a quasiclassical model. The model, called “fermionic molecular dynamics,” gives rise to a ground-state carbon atom where the six electrons are paired in shells, with different binding energies. This feature renders possible, on a classical level, the discussion of the ejection of electrons from different shells. By analyzing a large number of trajectories of a carbon atom exposed to an intense, few-cycle laser pulse, we reveal a class of recollision trajectories where the recolliding electron is recaptured into the atomic core after ejecting a core electron. We also discuss the difference between quadruple ionization trajectories leading to a final ${\mathrm{C}}^{4+}$ ion where the two bound electrons have opposite spin, and the trajectories where the bound electrons have equal spin.

In this work we study the applicability of the local generalized Gibbs ensemble (GGE) to integrable one-dimensional systems with bound states. We find that the GGE, when defined using only local conserved quantities, fails to describe the long-time dynamics for most initial states, including eigenstates. We present our calculations by studying the attractive Lieb-Liniger gas and the $XXZ$ magnet, although similar results may be obtained for other models.

In this work we study a quench between a Mott insulator and a repulsive Lieb-Liniger liquid. We explicitly find the stationary state when a long time has passed after the quench. It is given by a generalized Gibbs ensemble (GGE) density matrix, which we completely characterize, calculating the quasiparticle density that describes the system after the quench. In the long-time limit we find an explicit form for the local three-body density-density-density correlation function and the asymptotic long-distance limit of the two-point density-density correlation function. The latter is shown to have Gaussian decay at large distances.

We study phase diffusion in a Bose–Einstein condensate of light in a dye-filled optical microcavity, i.e., the spreading of the probability distribution for the condensate phase. To observe this phenomenon, we propose an interference experiment between the condensed photons and an external laser. We determine the average interference patterns, considering quantum and thermal fluctuations as well as dissipative effects due to the dye. Moreover, we show that a representative outcome of individual measurements can be obtained from a stochastic equation for the global phase of the condensate.

We consider bosons in a Hubbard lattice with an $\text{SU}\left(\mathcal{N}\right)$ pseudospin degree of freedom which is made dynamical via a coherent transfer term. It is shown that, in the basis which diagonalizes the pseudospin coupling, a generic hopping process affects the spin state, similarly to a spin-orbit coupling. This results, for the system in the Mott phase, in a ferromagnetic phase with a variable quantization axis. In extreme cases, it can even give rise to antiferromagnetic order.

The contribution to the ionization cross section of ionization-excitation processes by electron impact is usually negligibly small for low- and medium-$Z$ elements. We demonstrate here, however, that for heavy atomic ions with the outermost shell being $nd$ $\left(n=4,5\right)$ the ionization-excitation processes play an evident role in the ionization cross section. For the $4s^{2}4p^{6}4d^{10}$ ground level of ${\mathrm{Gd}}^{18+}$, the ionization-excitation cross section due to the excitation of levels in the $4s^{2}4p^{6}4d^{8}4f$ configuration is comparable to the direct $4p$ and $4s$ ionization cross sections of ${\left(4s^{2}4p^{5}4d^{10}\right)}_{1/2}$ and ${\left(4s4p^{6}4d^{10}\right)}_{1/2}$. The total ionization cross section will be underestimated by 15% without including the contribution from ionization-excitation processes. This is a general conclusion for heavy atomic ions, which is verified by taking Pd-like ions of ${\mathrm{Sn}}^{4+},{\mathrm{Ba}}^{10+},{\mathrm{Nd}}^{14+},{\mathrm{Tb}}^{19+},{\mathrm{Yb}}^{24+}$, and ${\mathrm{W}}^{28+}$ as examples. The role of ionization-excitation processes can be understood from the overlapping of the wave functions between the $4d$ and $4f$ orbitals.

We present an ab initio investigation of the below-threshold harmonic generation of helium (He) atoms in few-cycle infrared laser fields by accurately solving the time-dependent Schrödinger equation and Maxwell's equation simultaneously. We find that the enhancement of the below-threshold harmonic generation only occurs to near the resonance structure of He, for which this mechanism is in agreement with the recent experimental study [M. Chini et al., Nat. Photonics 8, 437 (2014)]. Moreover, we perform the quantum and semiclassical trajectories analysis, including both the atomic potential and the laser field, as well as the synchrosqueezed transform of the harmonic spectra. Our results reveal that several multirescattering trajectories contribute to the resonance-enhanced below-threshold harmonic generation.

This paper introduces a theoretical framework for understanding the accumulation of non-Abelian geometric phases in rotating nitrogen-vacancy centers in diamond. Specifically, we consider how degenerate states can be achieved and demonstrate that the resulting geometric phase for multiple paths is non-Abelian. We find that the non-Abelian nature of the phase is robust to fluctuations in the path and magnetic field. In contrast to previous studies of the accumulation of Abelian geometric phases for nitrogen-vacancy centers under rotation we find that the limiting time scale is $T_1$. As such a non-Abelian geometric phase accumulation in nitrogen-vacancy centers has potential advantages for applications as gyroscopes.

We derive the Pauli equation for a charged spin particle confined to move on a spatially curved surface $\mathcal{S}$ in an electromagnetic field. Using the thin-layer quantization scheme to constrain the particle on $\mathcal{S}$, and in the transformed spinor representations, we obtain the well-known geometric potential $V_g$ and the presence of $e^{-i\phi }$, which can generate additive spin connection geometric potentials by the curvilinear coordinates derivatives, and we find that the two fundamental evidences in the literature [Giulio Ferrari and Giampaolo Cuoghi, Phys. Rev. Lett. 100, 230403 (2008)] are still valid in the present system without source current perpendicular to $\mathcal{S}$. Finally, we apply the surface Pauli equation to spherical, cylindrical, and toroidal surfaces, in which we obtain expectantly the geometric potentials and new spin connection geometric potentials, and find that only the normal Pauli matrix appears in these equations.

The existing distributed quantum gates required physical particles to be transmitted between two distant nodes in the quantum network. We here demonstrate the possibility to implement distributed quantum computation without transmitting any particles. We propose a scheme for a distributed controlled-phase gate between two distant quantum-dot electron-spin qubits in optical microcavities. The two quantum-dot-microcavity systems are linked by a nested Michelson-type interferometer. A single photon acting as ancillary resource is sent in the interferometer to complete the distributed controlled-phase gate, but it never enters the transmission channel between the two nodes. Moreover, we numerically analyze the effect of experimental imperfections and show that the present scheme can be implemented with high fidelity in the ideal asymptotic limit. The scheme provides further evidence of quantum counterfactuality and opens promising possibilities for distributed quantum computation.