Relaxation process of a two-level system in a coherent superposition of two environments
- PDF / 1,439,228 Bytes
- 23 Pages / 439.37 x 666.142 pts Page_size
- 89 Downloads / 175 Views
Relaxation process of a two-level system in a coherent superposition of two environments Masashi Ban1 Received: 13 June 2020 / Accepted: 1 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Relaxation processes are studied for a two-level system which is placed under the influenced by a superposition of two environments. Two cases are treated: one is that the two-level system interacts with the environment via both linear dissipative coupling and pure dephasing coupling in the Markovian limit and the other uses an exactly solvable single-excitation spin-boson model. In both the cases, an ancillary two-level system determines which environment of the two actually interacts with the relevant two-level system. In the Markovian limit, the reduced time-evolution of the two-level system is characterized by the longitudinal relaxation time T1 and the transversal relaxation time T2 which satisfy the inequality 2T1 ≥ T2 . If the strict inequality 2T1 > T2 is fulfilled, the coherence of the two-level system can be definitely enhanced by the environmental superposition effect. If the equality 2T1 = T2 holds, it can be improved probabilistically. On the other hand, in the exactly solvable model, although the non-Markovian effect is observed in the reduced time-evolution, the coherence can be improved only probabilistically since the model does not include a pure dephasing coupling. Keywords Decoherence · Two-level system · Dissipative process · Dephasing process · Superposition of environments
1 Introduction A quantum system in the real world has an unavoidable coupling with its surrounding environment, however small it is. Such a coupling creates entanglement between a quantum system of interest and an environment, which causes irreversibility in the reduced time-evolution [1–4]. Since quantum mechanical properties such as quantum
B 1
Masashi Ban [email protected] Graduate School of Humanities and Sciences, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan 0123456789().: V,-vol
123
351
Page 2 of 23
M. Ban
coherence [5], entanglement [6] spatial and temporal non-local correlations [7–9] are very fragile in lossy and noisy processes; they are inevitably degraded during the irreversible time evolution. However, quantum coherence and quantum correlation are essential resources in quantum information processing [10] which includes the quantum cryptography [11,12], the quantum communication [13,14] and the quantum computation [15,16]. The quantum information processing makes it possible to perform novel information tasks which cannot be done by the traditional information technology [17,18] which uses devices obeying laws of the classical physics. Hence, it is very important to protect the quantum mechanical properties of an open quantum system from a surrounding environment. For this purpose, the dynamical decoupling [19–26], the quantum error correction [27,28] and the decoherence free subspace [29,30] have been investigated in detail. Furthermore, the w
Data Loading...
