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Computer Optics

Qubit dynamics in an external laser field

D.M. Vasilev, Vitalii Semin

Published Aug 1, 2019• 1 citation
Publisher

Abstract

In this paper, dynamics of a qubit in an external laser field is investigated for the non-Markov environment described by an Ornstein-Uhlenbeck process. A non-linear non-Markovian stochastic Schrödinger equation is derived for the quantum system. The stochastic equation is preserved for a positive semi-definite of the density matrix and its trace. By the numerical solution of the equation, the probability of finding the system in the excited state and the influence of non-Markov noise parameters on this probability are studie.

DOI
10.18287/2412-6179-2019-43-4-562-566

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In this paper, dynamics of a qubit in an external laser field is investigated for the non-Markov environment described by an Ornstein-Uhlenbeck process. A non-linear non-Markovian stochastic Schrödinger equation is derived for the quantum system. The stochastic equation is preserved for a positive semi-definite of the density matrix and its trace. By the numerical solution of the equation, the probability of finding the system in the excited state and the influence of non-Markov noise parameters on this probability are studie.
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The unavoidable interaction of a quantum system with its environment usually degrades its coherence and quantumness. The environment and the decoherence process may be described as the interaction with a classical or quantized bath. As a matter of fact, the classical description becomes progressively more reliable as far as the environment has many degrees of freedom, i.e. it becomes complex, or when the interaction between a quantum system and a classical fluctuating field is taken into account. In this thesis, I consider a qubit system coupled to a stochastic classical field and address�the decoherence and non-Markovianity induced by the external noise as well as the spectral characterization of the classical field by quantum-limited measurement on the qubit. I thus analyze the dynamics of quantum correlations between two non-interacting, initially entangled qubits subject to a classical noise generated by a stochastic process. Two relevant classes of noise are taken into account: Gaussian noise, such as the Ornstein-Uhlenbeck process, and non-Gaussian noise, such as the random telgraph noise and the colored noise with 1/f spectrum. I also discuss the evaluation of non-Markovianity of the induced dynamical map and link the presence of revivals of quantum correlations with the information backflow to the system. The precise characterization of the stochastic process generating the classical noise, possibly using minimal resources, is a crucial ingredient for the design of high-precision measurements and reliable communication protocols. To this purpose, I also address the characterization of the spectral parameters of classical noise by quantum probes, e.g. a qubit coupled to the stochastic process generating the noise. By using the tools of quantum estimation theory, I explore the performances of quantum measurements on the qubit and show that it is possible to effectively extract information about the noise.