Generation and Preservation of Entanglement in Quantum Spin Models
November 28th, 2018 TITAS CHANDA Jagiellonias University

Quantum many-body systems, specifically spin models, are one of the natural candidates for the implementation of quantum information processing tasks, as these models possess highly entangled ground states. However, there exist zero-temperature states in such systems that are fully factorized, thereby possessing vanishing entanglement, and hence being of no use as resource in quantum information processing tasks. Such states can become useful for quantum protocols when the temperature of the system is increased, and when the system is allowed to evolve under either the influence of an external environment, or a closed unitary evolution driven by its own Hamiltonian due to a sudden change in the system parameters. Using the one-dimensional anisotropic XY model in a uniform and an alternating transverse magnetic field, we show that entanglement of the thermal states, corresponding to the factorization points in the space of the system parameters, revives once or twice with increasing temperature. We also study the evolution of the quantum spin chain driven out of equilibrium, and report that considerable entanglement is generated during the dynamics, when the initial state has vanishing entanglement. We also find that when the initial state is not factorized, bipartite entanglement in such spin models undergoing time-evolution under local Markovian environments can be frozen or preserved over time. We observe that the length of the freezing interval, for a chosen pair of nearest-neighbor spins, may remain independent of the length of the spin-chain indicating a scale-invariance.

Seminar, November 28, 2018, 12:00. ICFO’s Seminar Room

Hosted by Prof. Maciej Lewenstein