We study the quantum phases of mixtures of ultracold bosonic atoms held in an optical lattice that confines motion or hopping to one spatial dimension. The phases are found by using the Tomonaga-Luttinger liquid theory as well as the numerical method of time-evolving block decimation ͑TEBD͒. We consider a binary mixture of equal density with repulsive intraspecies interactions and either repulsive or attractive interspecies interaction. For a homogeneous system, we find paired and counterflow superfluid phases at different filling and hopping energies. We also predict parameter regions in which these types of superfluid order coexist with charge-density wave order. We show that the Tomonaga-Luttinger liquid theory and the TEBD qualitatively agree on the location of the phase boundary to superfluidity. We then describe how these phases are modified and can be detected when an additional harmonic trap is present. In particular, we show how experimentally measurable quantities, such as time-of-flight images and the structure factor, can be used to distinguish the quantum phases. Finally, we suggest applying a Feshbach ramp to detect the paired superfluid state and a / 2 pulse followed by Bragg spectroscopy to detect the counterflow superfluid phase.
We study a coupled array of coherently driven photonic cavities, which maps onto a drivendissipative XY spin-1 2 model with ferromagnetic couplings in the limit of strong optical nonlinearities. Using a site-decoupled mean-field approximation, we identify steady state phases with canted antiferromagnetic order, in addition to limit cycle phases, where oscillatory dynamics persist indefinitely. We also identify collective bistable phases, where the system supports two steady states among spatially uniform, antiferromagnetic, and limit cycle phases. We compare these mean-field results to exact quantum trajectories simulations for finite one-dimensional arrays. The exact results exhibit short-range antiferromagnetic order for parameters that have significant overlap with the mean-field phase diagram. In the mean-field bistable regime, the exact quantum dynamics exhibits real-time collective switching between macroscopically distinguishable states. We present a clear physical picture for this dynamics, and establish a simple relationship between the switching times and properties of the quantum Liouvillian.Despite numerous outstanding questions, the study of quantum many-body systems in thermal equilibrium is on relatively solid ground. In particular, very general guiding principles help to categorize the possible equilibrium phases of matter, and predict in what situations they can occur [1][2][3]. In comparison, quantum manybody systems that are far from equilibrium are less thoroughly understood, motivating a large scale effort to explore non-equilibrium dynamics experimentally, in particular using atoms, molecules, and photons [4][5][6][7][8][9]. At the same time, it has become clear that studying nonequilibrium physics in these systems is often more natural than studying equilibrium physics; they are, in general, intrinsically non-equilibrium. For example, thermal equilibrium is essentially never a reasonable assumption in photonic systems, where dissipation must be countered by active pumping [10]. Indeed, the inadequacy of equilibrium descriptions for photonic systems has long been recognized [11], even though close analogies to thermal systems sometimes exist [12][13][14][15][16].Until recently, photonic systems have been restricted to a weakly interacting regime. With notable progress towards generating strong optical nonlinearities at the few-photon level, for example with atoms coupled to small-mode-volume optical devices [17][18][19][20][21][22], Rydberg polaritons [23,24], and circuit-QED devices [25][26][27][28], this situation is rapidly changing. The production of strongly interacting, driven and dissipative gases of photons appears to be feasible [29,30], and affords exciting opportunities to explore the properties of open quantum systems in unique contexts, while studying the applicability of theoretical treatments designed with more weakly interacting systems in mind. For example, it is not fully understood how the steady states of these systems relate to the equilibrium states of their "closed" c...
Motivated by recent trapped-ion quantum simulation experiments, we carry out a comprehensive study of the phase diagram of a spin-1 chain with XXZ-type interactions that decay as $1/r^{\alpha}$, using a combination of finite and infinite-size DMRG calculations, spin-wave analysis, and field theory. In the absence of long-range interactions, varying the spin-coupling anisotropy leads to four distinct phases: a ferromagnetic Ising phase, a disordered XY phase, a topological Haldane phase, and an antiferromagnetic Ising phase. If long-range interactions are antiferromagnetic and thus frustrated, we find primarily a quantitative change of the phase boundaries. On the other hand, ferromagnetic (non-frustrated) long-range interactions qualitatively impact the entire phase diagram. Importantly, for $\alpha\lesssim3$, long-range interactions destroy the Haldane phase, break the conformal symmetry of the XY phase, give rise to a new phase that spontaneously breaks a $U(1)$ continuous symmetry, and introduce an exotic tricritical point with no direct parallel in short-range interacting spin chains. We show that the main signatures of all five phases found could be observed experimentally in the near future.Comment: 11 pages, 6 figure
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