The study of topological effects in physics is a hot area of research, and only recently have researchers been able to address the important issues of topological properties of interacting quantum systems. But it is still a great challenge to describe multiparticle and interaction effects. Here, we introduce the multiparticle Wannier states for interacting systems with cotranslational symmetry, which provide an orthogonal basis for constructing effective Hamiltonians for the isolated bands. We reveal how the shift of multiparticle Wannier state relates to the Chern number of the multiparticle Bloch band and study the Thouless pumping of two interacting bosons in a one-dimensional superlattice. In addition to the Thouless pumping of bound states when two bosons move unidirectionally as a whole, we describe topologically resonant tunneling when two bosons move unidirectionally, one by the other, provided the neighboring-well potential bias matches the interaction energy. Our work creates a paradigm for multiparticle topological effects and provides a way to detect topological states in interacting multiparticle systems.

In quantum lattice systems with geometric frustration, particles cannot move coherently due to destructive interference between tunneling processes. Here we show that purely local, Markovian dissipation can induce mobility and long-range first-order coherence in frustrated lattice systems that is entirely generated by incoherent processes. Interactions reduce the coherences and mobility but do not destroy them. These effects are observable in experimental implementations of driven-dissipative lattices with a flat band and nonuniform dissipation.

We analyze the dynamics leading to radiative cooling of an atomic ensemble confined inside an optical cavity when the atomic dipolar transitions are incoherently pumped and can synchronize. Our study is performed in the semiclassical regime and assumes that cavity decay is the largest rate in the system dynamics. We identify three regimes characterizing the cooling. At first hot atoms are individually cooled by the cavity friction forces. After this stage, the atoms' center-of-mass motion is further cooled by the coupling to the internal degrees of freedom while the dipoles synchronize. In the latest stage dipole-dipole correlations are stationary and the center-of-mass motion is determined by the interplay between friction and dispersive forces due to the coupling with the collective dipole. We analyze this asymptotic regime by means of a mean-field model and show that the width of the momentum distribution can be of the order of the photon recoil. Furthermore, the internal excitations oscillate spatially with the cavity standing wave forming an antiferromagnetic-like order.

Recent progress towards realizing quantum emitters (QEs) suitable for integration in quantum information networks stimulates the demand for a self-consistent numerical approach to describe scattering of radiatively limited QEs in complex dielectric environments. As the QE response has to be characterized without the use of phenomenological damping parameters, the divergent nature of the pointlike emitter's in-phase self-field has to be carefully dealt with to avoid unphysical frequency shifts. Here we provide a solution to this problem and show two ways to obtain accurate results in the weak excitation limit using finite-difference time-domain algorithms. One of these approaches lays important groundwork needed for future simulations of nonlinear QE networks. The solution for dealing with the frequency shift reveals that dynamical contributions to the resonant depolarization field of arbitrarily small dielectric objects make crucial contributions to the net dipole moment induced by an external field when radiative scattering is the only source of damping.

A scheme is proposed for dissipative generation of maximally entanglement between two Rydberg atoms in the context of cavity QED. The spontaneous emission of atoms combined with quantum Zeno dynamics and the Rydberg antiblockade guarantees a unique steady solution of the master equation of the system, which just corresponds to the antisymmetric Bell state $|S\rangle$. The convergence rate can be accelerated by the ground-state blockade mechanism of Rydberg atoms. Meanwhile the effect of cavity decay is suppressed by the Zeno requirement, leading to a steady-state fidelity about $90\%$ as the single-atom cooperativity parameter $C\equiv g^2/\left(\kappa \gamma \right)=10$, and this restriction is further relaxed to $C=5.2$ once the quantum-jump-based feedback control is exploited.

Quantum discord has been studied extensively as a measure of nonclassical correlations which includes entanglement as a subset. Although it is well known that nonzero discord can exist without entanglement, the origin of quantum discord is not well understood as compared to entanglement, which manifests itself more simply as inseparable higher-dimensional quantum superposition. In this paper we establish the discordlike correlation of bipartite coherence and then compare it to quantum discord. Consequently, we show that the minimum of the discordlike correlation of coherence coincides with the original quantum discord. This demonstrates quantum discord as the irreducible correlated bipartite coherence. In addition, the discordlike correlated coherence is shown to admit the postulates of the quantum resource theory (QRT), although the original quantum discord is not a “good” candidate under the QRT. We also find that the relative entropy measure induced from the discordlike coherence is a well-defined coherence measure for bipartite states.

Multiparticle interference is a fundamental phenomenon in the study of quantum mechanics. It was discovered in a recent experiment [Y.-S. Ra et al., Proc. Natl. Acad. Sci. USA 110, 1227 (2013)] that spectrally uncorrelated biphotons exhibited a nonmonotonic quantum-to-classical transition in a four-photon Hong-Ou-Mandel (HOM) interference. In this work, we consider the same scheme with spectrally correlated photons. By theoretical calculation and numerical simulation, we found the transition not only can be nonmonotonic with negatively correlated or uncorrelated biphotons, but also can be monotonic with positively correlated biphotons. The fundamental reason for this difference is that the HOM-type multiphoton interference is a differential-frequency interference. Our study may shed new light on understanding the role of frequency entanglement in multiphoton behavior.

A well-studied scenario in quantum parameter estimation theory arises when the parameter to be estimated is imprinted on the initial state by a Hamiltonian of the form $\theta G$. For such “phase-shift Hamiltonians” it has been shown that one cannot improve the channel quantum Fisher information by adding ancillas and letting the system interact with them. Here we investigate the general case, where the Hamiltonian is not necessarily a phase shift, and show that in this case in general it $\mathit{is}$ possible to increase the quantum channel information and to reach an upper bound. This can be done by adding a term proportional to the derivative of the Hamiltonian, or by subtracting a term from the original Hamiltonian. Neither method makes use of any ancillas, which shows that, for quantum channel estimation with an arbitrary parameter-dependent Hamiltonian, entanglement with an ancillary system is not necessary to reach the best possible sensitivity. By adding an operator to the Hamiltonian we can also modify the time scaling of the channel quantum Fisher information. We illustrate our techniques with nitrogen vacancy center magnetometry and the estimation of the direction of a magnetic field in a given plane using a single spin-1 as probe.

The parity and time-reversal violating electric dipole moment (EDM) of ${}^{171}\mathrm{Yb}$ is calculated accounting for the electron-correlation effects over the Dirac-Hartree-Fock method in the relativistic Rayleigh-Schrödinger many-body perturbation theory, with the second- [MBPT(2) method] and third-order [MBPT(3) method] approximations, and two variants of all-order relativistic many-body approaches, in the random phase approximation (RPA) and coupled-cluster (CC) method with singles and doubles (CCSD method) framework. We consider electron-nucleus tensor-pseudotensor (T-PT) and nuclear Schiff moment (NSM) interactions as the predominant sources that induce EDM in a diamagnetic atomic system. Our results from the CCSD method to EDM ($d_a$) of ${}^{171}\mathrm{Yb}$ due to the T-PT and NSM interactions are found to be $d_a=4.85\left(6\right)\times {10}^{-20}\langle \sigma \rangle C_T\left|e\right|\text{cm}$ and $d_a=2.89\left(4\right)\times {10}^{-17}S/\left(\right|e\left|{\text{fm}}^3\right)$, respectively, where $C_T$ is the T-PT coupling constant and $S$ is the NSM. These values differ significantly from the earlier calculations. The reason for the same has been attributed to large correlation effects arising through non-RPA type of interactions among the electrons in this atom that are observed by analyzing the differences in the RPA and CCSD results. This has been further scrutinized from the MBPT(2) and MBPT(3) results and their roles have been demonstrated explicitly.

We experimentally and theoretically study the effect of the intraspecies scattering length onto the heteronuclear Efimov scenario, following up on our earlier observation of Efimov resonances in an ultracold Cs-Li mixture for negative [Pires et al., Phys. Rev. Lett. 112, 250404 (2014)] and positive Cs-Cs scattering length [Ulmanis et al., Phys. Rev. Lett. 117, 153201 (2016)]. Three theoretical models of increasing complexity are employed to quantify its influence on the scaling factor and the three-body parameter: a simple Born-Oppenheimer picture, a zero-range theory, and a spinless van der Waals model. These models are compared to Efimov resonances observed in an ultracold mixture of bosonic ${}^{133}\mathrm{Cs}$ and fermionic ${}^6\mathrm{Li}$ atoms close to two Cs-Li Feshbach resonances located at 843 G and 889 G, characterized by different sign and magnitude of the Cs-Cs interaction. By changing the sign and magnitude of the intraspecies scattering length different scaling behaviors of the three-body loss rate are identified, in qualitative agreement with theoretical predictions. The three-body loss rate is strongly influenced by the intraspecies scattering length.

Interference effects in the ejected electron spectrum for the ionization of ${\mathrm{H}}_2$ by fast ions are theoretically analyzed. The previous model, which used plane waves for the description of the final electronic state, is improved. The present results for the ${\mathrm{H}}_2\text{and}2\mathrm{H}$ differential cross-section ratios are compared to the experimental data for $\mathrm{Kr}^{34+}, \mathrm{Kr}^{33+}$, and $\mathrm{F}^{9+}$ projectiles, continuum-distorted-wave–Eikonal-initial-state (CDW-EIS) theory, and other more simple models. The obtained oscillations as a function of ejected electron velocity are in very good agreement with the CDW-EIS results and the experimental data for forward and partly backward angles. The main result of the present approach is observable for perpendicular ejection. Here the secondary oscillations observed in the experimental data are reproduced, while the other models predict a constant or monotonically increasing cross-section ratio.

A concrete mechanism of angular-momentum transfer in photoionization process is proposed for electron photoemission from deep inner atomic shells. It is demonstrated that the leading contribution to angular-momentum transfer is provided by postcollision interaction of the photoelectrons and Auger electrons. The standard theoretical approach to postcollision interaction has been considerably improved by taking into account angular-momentum transfer. The theory developed is applied to the photoionization of $1s^2$ shell in Ar. Calculations show the noticeable influence of angular-momentum transfer on the photoelectron angular distribution.

We propose an efficient stepwise adiabatic merging (SAM) method to generate many-body singlet states in antiferromagnetic spin-1 bosons in concatenated optical superlattices with isolated double-well arrays, by adiabatically ramping up the double-well bias. With an appropriate choice of bias sweeping rate and magnetic field, the SAM protocol predicts a fidelity as high as 90% for a 16-body singlet state and even higher fidelities for smaller even-body singlet states. During their evolution, the spin-1 bosons exhibit interesting squeezing dynamics, manifested by an odd-even oscillation of the experimentally observable squeezing parameter. The generated many-body singlet states may find practical applications in precision measurement of magnetic field gradient and in quantum information processing.

We present a platform for the bottom-up construction of itinerant many-body systems: ultracold atoms transferred from a Bose-Einstein condensate into freely configurable arrays of microlens generated focused-beam dipole traps. This complements traditional optical lattices and provides a different access to the field of two-dimensional quantum simulators. The ultimate control of topology, well depth, atom number, and interaction strength is matched by sufficient tunneling. We characterize the required light fields, derive the Bose-Hubbard parameters for several alkali-metal species, and investigate the loading procedures and heating mechanisms. To demonstrate the potential of this approach, we analyze coupled annular Josephson contacts exhibiting many-body resonances.

Within the renormalization-group framework we study the stability of superfluid density wave states, known as Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases, with respect to thermal order-parameter fluctuations in two- and three-dimensional ($d\in \{2,3\}$) systems. We analyze the renormalization-group flow of the relevant ordering wave vector $\overrightarrow{Q_0}$. The calculation indicates an instability of the FFLO-type states towards either a uniform superfluid or the normal state in $d\in \{2,3\}$ and $T>0$. In $d=2$ this is signaled by $\overrightarrow{Q_0}$ being renormalized towards zero, corresponding to the flow being attracted either to the usual Kosterlitz-Thouless fixed point or to the normal phase. We supplement a solution of the RG flow equations by a simple scaling argument, supporting the generality of the result. The tendency to reduce the magnitude of $\overrightarrow{Q_0}$ by thermal fluctuations persists in $d=3$, where the very presence of long-range order is immune to thermal fluctuations, but the effect of attracting $\overrightarrow{Q_0}$ towards zero by the flow remains observed at $T>0$.

We consider two-dimensional imperfect attractive Fermi and repulsive Bose gases consisting of spinless point particles whose total interparticle interaction energy is represented by $a{N}^2/2V$ with $a=-a_F\le 0$ for fermions and $a=a_B\ge 0$ for bosons. We show that, in spite of the attraction, the thermodynamics of a $d=2$ imperfect Fermi gas remains well defined for $0\le a_F\le a_0=h^2/2\pi m$, and is exactly the same as the one of the repulsive imperfect Bose gas with $a_B=a_0-a_F$. In particular, for $a_F=a_0$ one observes the thermodynamic equivalence of the attractive imperfect Fermi gas and the ideal Bose gas.

An optical ray equation is derived for a trajectory in a medium with directional birefringence. The birefringence is described as an artificial gauge field for light that gives an effective magnetic field and a Lorentz force on light. The gauge invariance is also confirmed. This paper opens a door to realize an artificial gauge field for a light ray in a nonreciprocal medium.