Dissipation is a ubiquitous phenomenon, and it is important to understand its role in non-equilibrium dynamics. In the quantum systems, dissipation often reduce the coherence of the quantum states. But sometimes, it induces completely different effects than the decoherence. For example, strong dissipation can be used to suppress the loss [1] and control the quantum state [2] and quantum phase transition [3].
Dissipation is a ubiquitous phenomenon, and it is important to understand its role in non-equilibrium dynamics. In the quantum systems, dissipation often reduce the coherence of the quantum states. But sometimes, it induces completely different effects than the decoherence. For example, strong dissipation can be used to suppress the loss [1] and control the quantum state [2] and quantum phase transition [3].
We investigate the many-body coherence and population dynamics of a two-component atomic Bose-Einstein condensate coupled with a continuum. We reveal that the combination of dissipation and nonlinearity may induce different steady states and modify the bifurcation of coherence. The steady states depend on the relative dissipation strengths. The coherence may be even enhanced by the dissipation effects. The combination of dissipation and nonlinearity allows one to control the switching between different self-trapped states or the switching between a self-trapped state and a non-self-trapped state. This opens an alternative route for manipulating coherence and population transition in an open many-body system via dissipation and nonlinearity.
We investigate the internal dynamics of the spinor Bose–Einstein condensates subject to dissipation by solving the Lindblad master equation. It is shown that for the condensates without dissipation its dynamics always evolve along a specific orbital in the phase space of ( n 0 , θ ) and display three kinds of dynamical properties including Josephson-like oscillation, self-trapping-like oscillation, and ‘running phase’. In contrast, the condensates subject to dissipation will not evolve along the specific dynamical orbital. If component-1 and component-(-1) dissipate at different rates, the magnetization m will not conserve and the system transits between different dynamical regions. The dynamical properties can be exhibited in the phase space of ( n 0 , θ , m ).
By using a weak imaginary random potential to simulate the random system dissipation and considering the quantum many-body effect, the role of random system dissipation in the quantum coherence establishment of Bose-Einstein condensates (BECs) is studied. It is found that even very weak random system dissipation may induce an obvious interference pattern between two initially independent BECs after the overlapping. Moreover, the random system dissipation has no effect on the spatial period of the interference fringes, which is identical to that observed in the current interference experiments. Under the assumption of weak dissipation, increasing the dissipation strength may accelerate the construction of the observable relative phase. Other behaviours of the interference are also investigated. The theoretical analysis and the numerical simulation show good consistency. This sort of interference has an observable effect, which significantly differs from other quantum interference mechanisms. The work may provide further theoretical basis for the future interference experiment of molecular BECs (Kohstall et al 2011 New J. Phys. 13 065027), considering the possible dissipation of the molecular BECs (e. g. the destruction of the weakly bound Feshbach molecules and the dissipation of the condensate fraction).
Quantum gases of light, such as photon or polariton condensates in optical microcavities, are collective quantum systems enabling a tailoring of dissipation from, for example, cavity loss. This characteristic makes them a tool to study dissipative phases, an emerging subject in quantum many-body physics. We experimentally demonstrate a non-Hermitian phase transition of a photon Bose-Einstein condensate to a dissipative phase characterized by a biexponential decay of the condensate's second-order coherence. The phase transition occurs because of the emergence of an exceptional point in the quantum gas. Although Bose-Einstein condensation is usually connected to lasing by a smooth crossover, the observed phase transition separates the biexponential phase from both lasing and an intermediate, oscillatory condensate regime. Our approach can be used to study a wide class of dissipative quantum phases in topological or lattice systems.
We review recent results on the coherence and superfluidity of driven dissipative condensates, i.e., systems of weakly interacting nonconserved bosons, such as polariton condensates. The presence of driving and dissipation has dramatically different effects depending on dimensionality and anisotropy. In three dimensions, equilibrium behaviour is recovered at large scales for static correlations, while the dynamical behaviour is altered by the microscopic driving. In two dimensions, for an isotropic system, drive and dissipation destroy the algebraic order that would otherwise exist; however, a sufficiently anisotropic system can still show algebraic phase correlations. We discuss the consequences of this behaviour for recent experiments measuring phase coherence and outline potential measurements that might directly probe superfluidity. Introduction This chapter is dedicated to superfluidity and its relation to Bose-Einstein condensation (BEC), a topic with a long history. Many reviews of the concepts of condensation and superfluidity in thermal equilibrium can be found; see for example Refs. [1, 2, 3, 4]. The focus of this chapter is on how these concepts apply (or fail to apply) to driven dissipative condensates – systems of bosons with a finite lifetime, in which loss is balanced by continuous pumping. We focus entirely on the steady state of such systems, neglecting transient, time-dependent behaviour. Experimentally, the most studied example of a driven dissipative condensate has been microcavity polaritons, an overview of which is given in Ref. [5] and Chapter 4. However, similar issues can arise in many other systems, most obviously photon condensates [6] (see also Chapter 19), magnon condensates [7] (see also Chapters 25–26), and potentially exciton condensates (although typical exciton lifetimes are much longer than for polaritons). Even experiments on cold atoms (see, e.g., Chapter 3) could be driven into a regime in which such physics occurs, when considering continuous loading of atoms balancing threebody losses [8] or atom laser setups [9, 10, 11]. Experiments on polaritons are two-dimensional, and in two dimensions it is particularly important to clearly distinguish three concepts often erroneously treated as equivalent: superfluidity, condensation, and phase coherence. This is because no true Bose-Einstein condensate exists in a homogeneous two-dimensional system.
Abstract We report the first experimental observation of dissipation-driven coherent quantum many-body oscillation, and this oscillation is manifested as the coherent exchange of atoms between the thermal and condensate components in a three-dimensional partially condensed Bose gas. Firstly, we observe that the dissipation leads to two different atom loss rates between the thermal and the condensate components, such that the thermal fraction increases as dissipation time increases. Therefore, this dissipation process serves as a tool to uniformly ramp up the system’s temperature without introducing extra density excitation. Subsequently, a coherent pair exchange of atoms between the thermal and the condensate components occurs, resulting in coherent oscillation of atom numbers in both components. This oscillation, permanently embedded in the atom loss process, is revealed clearly when we inset a duration of dissipation-free evolution into the entire dynamics, manifested as an oscillation of total atom number at the end. Finally, we also present a theoretical calculation to support this physical mechanism, which simultaneously includes dissipation, interaction, finite temperature, and harmonic trap effects. Our work introduces a highly controllable dissipation as a new tool to control quantum many-body dynamics.