We study three-body recombination of fully spin-polarized ${}^6\mathrm{Li}$ atoms that are interacting resonantly in relative $p$ waves. Motivated by a recent experiment, we focus on negative scattering volumes where three atoms recombine into a deep dimer and another atom. We calculate the three-body recombination rate using a Faddeev equation derived from effective field theory. In particular, we study the magnetic field and temperature dependences of the loss rate and use the recombination data to determine the effective range of the $p$-wave atom-atom interaction. We also predict the existence of a shallow three-body resonance state that manifests itself as a prominent feature in the energy-dependent three-body recombination rate.

We introduce a method for the detection of chiral molecules using sequences of three pulses driving a closed-loop three-state quantum system. The left- and right-handed enantiomers have identical optical properties (transition frequencies and transition dipole moments) with the only difference being the sign of one of the couplings. We identify 12 different sequences of resonant pulses for which chiral resolution with perfect contrast occurs. In all of them, the first and third pulses are $\pi /2$ pulses and the middle pulse is a $\pi$ pulse. In addition, one of the three pulses must have a phase shift of $\pi /2$ with respect to the other two. The simplicity of the proposed chiral resolution technique allows for straightforward extensions to more efficient and more robust implementations by replacing the single $\pi /2$ and $\pi$ pulses by composite pulses. We present specific examples of chiral resolution by composite pulses which compensate errors in the pulse areas and the detuning of the driving fields.

We consider a bosonic $s$- and $p$-orbital system in a face-centered-cubic (fcc) optical lattice and predict a fluctuation-induced instability towards the orbital analog of the Palmer-Chalker state, which was originally proposed in an electronic spin system. For bosons loaded in the fcc optical lattice, the single-particle spectrum has four degenerate band minima with their crystal momenta forming a tetrahedron in the Brillouin zone. In the weakly interacting regime, the ensuing many-particle ground state, at the classical level, underlies a four-sublattice tetrahedral supercell of spontaneously generated $p$-orbital angular momenta through the Bravais-Bloch duality between real and momentum space and is macroscopically degenerate, originating from the geometric frustration. The fluctuations on top of the classical ground state lift its degeneracy and select the Palmer-Chalker ordering of $p$-orbital angular momenta as the quantum ground state through an order-by-disorder mechanism. These findings raise the exciting possibility of simulating the Palmer-Chalker state with its orbital counterpart in ultracold atomic gases.

We report on the production of a cold mixture of fermionic ${}^{53}\mathrm{Cr}$ and ${}^6\mathrm{Li}$ atoms delivered by two Zeeman-slowed atomic beams and collected within a magneto-optical trap (MOT). For lithium, we obtain clouds of up to $4\times {10}^8$ atoms at temperatures of about $500\mu \mathrm{K}$. A gray optical molasses stage allows us to decrease the gas temperature down to $45\left(5\right)\mu \mathrm{K}$. For chromium, we obtain MOTs of more than $1.1\times {10}^6$ atoms. The availability of magnetically trappable metastable $D$ states, from which $P$-state atoms can radiatively decay onto, enables to accumulate into the MOT quadrupole samples of almost ${10}^7$ ${}^{53}\mathrm{Cr}$ atoms. After repumping $D$-state atoms back into the cooling cycle, a final cooling stage decreases the chromium temperature down to $145\left(5\right)\mu \mathrm{K}$. While the presence of a lithium MOT decreases the lifetime of magnetically trapped ${}^{53}\mathrm{Cr}$ atoms, we obtain, within a 5-s duty cycle, samples of about $4\times {10}^6$ chromium and $3\times {10}^8$ lithium atoms. Our work provides a crucial step toward the production of degenerate Cr-Li Fermi mixtures.

We investigate the out-of-equilibrium physics of monodisperse bosonic ensembles on a square lattice. The effective Hamiltonian description of these systems is given in terms of an extended Hubbard model with cluster-forming interactions relevant to experimental realizations with cold Rydberg-dressed atoms. The ground state of the model, recently investigated in [Phys. Rev. Lett. 123, 045301 (2019)], features, aside from a superfluid and a stripe crystalline phase occurring at small and large interaction strength $V$, respectively, a rare first-order transition between an isotropic and an anisotropic stripe supersolid at intermediate $V$. By means of quantum Monte Carlo calculations we show that the equilibrium crystal may be turned into a glass by simulated temperature quenches and that out-of-equilibrium isotropic (super)solid states may emerge also when their equilibrium counterparts are anisotropic. These out-of-equilibrium states are of experimental interest, their excess energy with respect to the ground state being within the energy window typically accessed in cold atom experiments. We find, after quenching, no evidence of coexistence between superfluid and glassy behavior. Such an absence of superglassiness is qualitatively explained.

We compute the fluctuations of the number of bosons with a given momentum for the Tonks-Girardeau gas at zero temperature. We show that correlations between opposite momentum states, which are an important identifying characteristic of long-range order in weakly interacting Bose systems, are suppressed and that the full distribution of the number of bosons with nonzero momentum is exponential. The distribution of the quasicondensate is however quasi-Gaussian. The experimental relevance of our findings for recent cold-atom experiments is discussed.

In this paper we study the propagation of optical vortices (OVs) through the loop resonator (LR) on a multimode fiber. Within the framework of a fully vectorial treatment that allows for the spin-orbit interaction (SOI) we demonstrate the existence in such LRs of a special topological resonance, which is in the inversion of the topological charge (TC) of the transmitted OV. We study the angular momentum (AM) of the transmitted field and show that near resonance points the orbital and spin AMs of the output field are sensitive to wavelength-scale variations of the LR's length parameters. The mechanism that underlies such supersensitivity is the multipass interference assisted by topological charge inversion in the coupling area. We show that this property can be used for superefficient control of the output field's OAM. We also demonstrate that such LRs are suitable for creation of combined wavelength and mode comb filters on their basis. The effect of losses is also discussed. We show the existence in LRs of an additional resonance: the spin-orbit resonance. This type of topological resonance arises due to the effect of the SOI enhancement, which nature we also unveil.

Ultrastrong optomechanical interaction is a significant element for the study of the fundamentals and applications of optomechanical physics, but its realization remains a big challenge in the field of optomechanics. In this work, we propose a reliable scheme to realize a generalized ultrastrong optomechanical-like coupling in a cross-Kerr-type coupled two-bosonic-mode system, in which one of the two bosonic modes is strongly driven. The generalized optomechanical-like interaction takes the form of a product of the excitation number operator of one mode and the rotated quadrature operator of the other mode. Here, both the coupling strength and the phase angle of the rotated quadrature operator are tunable via the driving field. The optomechanical-like coupling can be strongly enhanced to enter the ultrastrong-coupling regime, where the few-photon optomechanical effects such as photon blockade and macroscopic quantum superposition become accessible. The controllability of the quadrature phase angle provides a new degree of freedom for the manipulation of optomechanical systems and enables the implementation of geometric quantum operations. We also present some discussions on the experimental implementation of this scheme. This study will pave the way to the study of quantum physics and quantum technology at the few-photon level in optomechanical systems.

In any form of wave propagation, strong spatiotemporal coupling appears when nonelementary three-dimensional wave packets are composed by superimposing pure plane waves or spontaneously generated by light-matter interaction and nonlinear processes. Ultrashort pulses with orbital angular momentum (OAM), or ultrashort vortices, furnish a critical paradigm in which the analysis of the spatiotemporal coupling in the form of temporal-OAM coupling can be carried out accurately by analytical tools. By generalizing and unifying previously reported results, we show that universal and spatially heterogeneous space-time correlations occur in propagation-invariant temporal pulses carrying OAM. In regions with high intensity, the pulse duration has a lower bound fixed by the topological charge of the vortex and such that the duration must increase with the topological charge. In regions with low intensity in the vicinity of the vortex, a large blueshift of the carrier oscillations and an increase of the number of them are predicted for strongly twisted beams. We think that these very general findings highlight the existence of a structural coupling between space and time. These results have also applications in free-space communications, spectroscopy, and high-harmonic generation.

We propose to explore the quantum nature of gravity using the correlation of light between two optomechanical cavities, and the quantumness of the correlation is witnessed by squeezing. As long as the gravity between the end mirrors of two cavities is quantum in the Newtonian limit, we show that the squeezing is always nonzero and monotonically increases as the mechanical property of the mirrors is improved. The proposed scheme provides a new pathway for testing the quantum nature of gravity systematically with tabletop experiments.

Quantum simulators are engineered devices controllably designed to emulate complex and classically intractable quantum systems. A key challenge is to certify whether the simulator truly mimics the Hamiltonian of interest. This certification step requires the comparison of a simulator's output to a known answer, which is usually limited to small systems due to the exponential scaling of the Hilbert space. Here, in the context of Fermi-Hubbard spin-based analog simulators, we propose a modular many-body spin to charge conversion scheme that scales linearly with both the system size and the number of low-energy eigenstates to discriminate. Our protocol is based on the global charge state measurement of a 1D spin chain performed at different detuning potentials along the chain. In the context of semiconductor-based systems, we identify realistic conditions for detuning the chain adiabatically to avoid state mixing while preserving charge coherence. Large simulators with vanishing energy gaps, including 2D arrays, can be certified block-by-block with a number of measurements scaling only linearly with the system size.

We investigate optimal conditions for the quantum interface between a signal photon pulse and one-dimensional chain consisting of a varied number of atoms. The tested object is physically designed as an atomic array of tripod-type atoms confined with a nanoscale dielectric waveguide and experiencing its fundamental $\mathrm{HE}{}_{11}$ mode. The efficiency of interaction is mainly limited by achieved overlap and coupling of the waveguide evanescent field with the trapped atoms. We verify those physical conditions when the coupling within the main scattering channels would be sufficient for further providing various elementary interface protocols such as light storage, light-matter entanglement, preparation of a few photon states on demand.

The realization of advanced materials with strong, low-loss, and pure magnetic responses to radiation fields both in linear and nonlinear regimes is an important and long-standing goal for fundamental physics and practical applications. Here, we propose a physical scheme for obtaining such responses by using a metamaterial constructed by an array of unit cells consisting of two coupled varactor-loaded split-ring resonators working under the condition of plasmon-induced transparency (PIT). We show that the PIT in such metamaterial not only significantly suppresses radiation absorption but also greatly enhances magnetic Kerr nonlinearity, which may be many orders of magnitude larger than that obtained by conventional magnetic materials reported up to now. Based on such a nonlinear metamaterial, we further show that stable magnetic solitons with ultraslow propagation velocity and very low generation power can be created. Our research opens a route for designing novel metamaterial devices with strong, low-loss, pure, and actively tunable magnetic responses and for obtaining stable and low-power nonlinear magnetic pulses, which are promising for applications in information processing and transmission.

We present a generalized understanding of the induced-coherence (IC) effect, aiming to find new strategies for engineering and optimizing the IC response of nonlinear systems. We establish that sensing the cross density of states (CDOS) of the field lies at the core of IC and that it is the spatial profile of the nonlinearity that determines how this CDOS information is sampled. Based on our findings, we identify integrated nonlinear waveguides as a versatile and suitable platform for spectroscopy based on IC and show that our generalized treatment allows us to optimize the sensing performance. Our results open the way for the design of compact IC-based spectroscopic devices with customized responses.

We study how the non-Markovian dynamics of an open quantum system is affected by the properties and parameters of its environment using a solvable model consisting of a single spin coupled to an Ising chain of spins with a transverse field playing the role of the environment. By solving the model's evolution exactly, we are able to calculate the memory kernel for the Nakajima-Zwanzig master equation and examine how its characteristics change with the temperature, field strength, and size of the environment. We discover that the thermal fluctuation enhances system-environment correlation in our model, leading to increased memory effect that is more prominent in larger environment and becomes dominant at higher temperatures to give rise to non-Markovian dynamics. Near the critical point of the environment, we find Fisher zeros in the Loschmidt echo exist for finite-environment sizes satisfying certain conditions, which results in exotic memory effects that can have a major impact on the system dynamics.

We propose a scheme to restore spatial symmetry of Hamiltonian in the variational-quantum-eigensolver (VQE) algorithm for which the quantum circuit structures used usually break the Hamiltonian symmetry. The symmetry-adapted VQE scheme introduced here simply applies the projection operator, which is Hermitian but not unitary, to restore the spatial symmetry in a desired irreducible representation of the spatial group. The entanglement of a quantum state is still represented in a quantum circuit but the nonunitarity of the projection operator is treated classically as postprocessing in the VQE framework. By numerical simulations for a spin-$1/2$ Heisenberg model on a one-dimensional ring, we demonstrate that the symmetry-adapted VQE scheme with a shallower quantum circuit can achieve significant improvement in terms of the fidelity of the ground state and has a great advantage in terms of the ground-state energy with decent accuracy, as compared to the non-symmetry-adapted VQE scheme. We also demonstrate that the present scheme can approximate low-lying excited states that can be specified by symmetry sectors, using the same circuit structure for the ground-state calculation.

Quantum walks of interacting particles may display nontrivial features due to the interplay between the statistical nature and the many-body interactions associated with them. We analyze the quantum walk of interacting defects on top of a uniform bosonic Mott insulator at unit filling in a one-dimensional graph. While the quantum walk of a single-particle defect shows trivial features, the case of two particles exhibits the interesting phenomenon of quantum walk reversal as a function of additional on-site three-body attractive interactions. In the absence of a three-body interaction a quantum walk of pairs of particles is obtained, and as the strength of the three-body interaction becomes more and more attractive, independent-particle behavior appears in the quantum walk. Interestingly, further increase in the three-body interaction leads to the reappearance of the quantum walk associated with a pair of particles. This quantum walk reversal phenomenon is studied using the real-space density evolution, Bloch oscillation, and two-particle correlation functions.

Quantum technologies such as quantum sensing, quantum imaging, quantum communications, and quantum computing rely on the ability to actively manipulate the quantum state of light and matter. Quantum emitters, such as color centers trapped in solids, are a useful platform for the realization of elementary building blocks (qubits) of quantum information systems. In particular, the modular nature of such solid-state devices opens up the possibility to connect them into quantum networks and create nonclassical states of light shared among many qubits. The function of a quantum network relies on efficient and controllable interactions among individual qubits. In this context, we present a scheme where optically active qubits of differing excitation energies are mutually coupled via a dispersive interaction with a shared mode of an optical cavity. This generally off-resonant interaction is prohibitive of direct exchange of information among the qubits. However, we propose a scheme in which by acoustically modulating the qubit excitation energies it is, in fact, possible to tune to resonance a preselected pair of qubits and thus open a communication channel between them. This method potentially enables fast (approximately nanoseconds) and parallelizable on-demand control of a large number of physical qubits. We develop an analytical and a numerical theoretical model demonstrating this principle and suggest feasible experimental scenarios to test the theoretical predictions.