Hall 123

Control of Entanglement Longevity in Open Interacting Two Qubit System

Namitha C. V.

Dept. of Physics, Pondicherry University

Quantum information science involves transfer of information among spatially separated parties
using quantum entanglement as a resource. Due to inevitable interaction with the environment,
coherence and nonlocal correlations of shared entangled state decay in time. Such a loss of
correlations would hamper the success of quantum information processing protocols. We
consider a dipole coupled two qubit system in contact with vacuum/thermal reservoir and
investigated the entanglement dynamics under Markov approximation. It is observed that, in
most cases, initial entanglement is lost abruptly due to decoherence, which is called
entanglement sudden death (ESD). It has been shown in the studies that for a vacuum bath,
second and third rank mixed states do not exhibit ESD and all fourth rank mixed states exhibit
ESD. In applications like quantum teleportation, fourth rank mixed states give high success, it
has been shown that among fourth rank states, states with maximum amount of two photon
coherence is a better resource for which the time of disentanglement is least. We show that by
switching with local gate operations, it is possible to avoid ESD in case of vacuum bath and
delay ESD in case of thermal bath. Local gate operations and time windows of operations are
identified for avoiding ESD in a select but important class of entangled initial states two qubit
system in contact with a vacuum bath. It is found that other indicators of nonlocal correlations
such as teleportation fidelity more than 2/3 and violation of Bell CHSH inequality also register a
sudden loss during the evolution. Further, it is also observed that there is a hierarchy among
these nonlocal correlations. During the evolution, state fails to violate Bell CHSH inequality
first, followed by state fails to be a resource for teleportation and then loss of entanglement
occurs.

Based on: Phd. Thesis, Namitha C V, Department of Physics, Pondicherry University