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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Nonlinear coupler and qutrit-qubit entanglement

A. Kowalewska-Kudłaszyk

Published Dec 18, 2012• 1 citation
Publisher

Abstract

A nonlinear Kerr-coupler with nonlinear interaction between its parts is analyzed as a source of qutrit-qubit entanglement. Formation of maximal entanglement within 3⊗2 system is found and various types of entanglement decay (asymptotic and sudden entanglement death) in the amplitude damping reservoir are considered.
DOI
10.1117/12.2006767

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Decoherence effect on quantum entanglement of two optical qubits in a lossy cavity interacting with a nonlinear medium (Kerr nonlinearity) is analyzed. The qubits are assumed to be initially in the maximally entangled states (Bell or Bell-like states) or the maximally entangled mixed states, on the example of Werner and Werner-like states. Two kinds of measures of the entanglement are considered: the concurrence to describe a decay of the entanglement of formation of the qubits, and the negativity to determine a decay of an upper bound of the entanglement of distillation. It is observed that the Kerr nonlinearity does not affect the entanglement of the qubits initially in the Bell or Werner states, although the evolution of the qubits can depend on this nonlinearity explicitly. However, it is shown that for the initial Bell-like state and the corresponding Werner-like state, the loss of entanglement can be periodically reduced by inserting the Kerr nonlinearity in the lossy cavity.
We discuss a model of two nonlinear Kerr-like oscillators, mutually coupled and excited by parametric process. We show that the system’s evolution, starting from Werner-like states, remains closed within a small set of two-mode n-photon states and that a pure two-qubit entangled state can be generated. For some initial Werner-like states, delayed entanglement generation can be observed. We investigate the influence of two damping mechanisms on the system’s evolution. We show that, for both cases, entanglement can survive despite the presence of damping, and that the effects of sudden entanglement death and its rebirth can appear in the system.