We examine entanglement dynamical flow among all participants of a two-reservoir spin system. “Freezing” and “thawing” phenomena are identified. A set of novel entanglement constraint inequalities is discovered with tetrahedron representation.
Spin collective phenomena including superradiance are even today being intensively investigated with experimental tests performed based on state-of-the-art quantum technologies. Such attempts are not only for the simple experimental verification of predictions from the last century, but also as a motivation to explore new applications of spin collective phenomena and the coherent control of the coupling between spin ensembles and reservoirs. In this paper, we investigate the open quantum dynamics of two spin ensembles (double-spin domains) coupled to a common bosonic reservoir. We analyze in detail the dynamics of our collective state and its structure by focusing on both the symmetry and asymmetry of this coupled spin system. We find that when the spin size of one of the double domains is larger than that of the other domain, at the steady state this system exhibits two unusual collective behaviors: the negative-temperature-state relaxation in the smaller spin domain and the reservoir-assisted quantum entanglement between the two domains. These results are the consequence of the asymmetry of this system and the decoherence driven by the common reservoir.
In a system where two identical two-level atoms interact with their common one-mode cavity field, it is shown that entanglement can become abruptly frozen in time, remaining at a constant value for a period of time until it begins to thaw from this value from the entanglement sharing perspective [Ding et al., Phys. Rev. A 103, 032418 (2021)]. We generalize this exotic behavior of entanglement sharing dynamics to more general systems with arbitrary N qubits, instead of restricting to the atom-cavity mode interaction system. We also demonstrate methods to control the entanglement freezing time and freezing value, and we discover a nontrivial dynamics where entanglement is frozen permanently. In addition, we show that this phenomenon is not a coincidence but a universal feature in a variety of systems with a geometric explanation of the mechanisms.
We investigate the dynamics of different configurations of entanglement in a one-dimensional N -site optical lattice chain. Entanglement freezing has so far been primarily associated with noisy or decoherence-induced processes. Remarkably, we show that this phenomenon also occurs in a fully coherent and lossless many-body system. By deriving exact analytical results, we demonstrate the emergence of permanent entanglement freezing in the thermodynamic limit ( N → ∞). Even more surprisingly, for finite N , where purely unitary dynamics would normally be expected to destroy such stationary behavior, the system still exhibits robust entanglement freezing over a finite time interval. This frozen behavior is subsequently followed by a phenomenon of entanglement “thawing," manifested as revivals of quantum correlations. Furthermore, alternating regimes of entanglement freezing and thawing appear during the time evolution. Our results reveal that entanglement freezing can arise intrinsically from coherent many-body dynamics, even in finite lossless systems, and provide analytical guidance for entanglement control in optical-lattice-based quantum information processing and photonic quantum technologies.
We show how to freeze distributed entanglement that has been created from the natural dynamics of spin chain systems. The technique that we propose simply requires single-qubit operations and isolates the entanglement in specific qubits at the ends of branches. Such frozen entanglement provides a useful resource, for example for teleportation or distributed quantum processing. The scheme can be applied to a wide range of systems---including actual spin systems and alternative qubit embodiments in strings of quantum dots, molecules, or atoms.