dorsal/arxiv
View SchemaNon-Markovian qubit dynamics in a thermal field bath: Relaxation, decoherence and entanglement
| Authors | S. Shresta, C. Anastopoulos, A. Dragulescu, B. L. Hu |
|---|---|
| Categories | |
| ArXiv ID | quant-ph/0408084 |
| URL | https://arxiv.org/abs/quant-ph/0408084 |
| DOI | 10.1103/PhysRevA.71.022109 |
| Journal | Phys. Rev. A 71, 022109 (2005) |
Abstract
We study the non-Markovian dynamics of a qubit made up of a two-level atom interacting with an electromagnetic field (EMF) initially at finite temperature. Unlike most earlier studies where the bath is assumed to be fixed, we study the coherent evolution of the combined qubit-EMF system, thus allowing for the back-action from the bath on the qubit and the qubit on the bath in a self-consistent manner. In this way we can see the development of quantum correlations and entanglement between the system and its environment, and how that affects the decoherence and relaxation of the system. We find non-exponential decay for both the diagonal and non-diagonal matrix elements of the qubit's reduced density matrix in the pointer basis. From the diagonal elements we see the qubit relaxes to thermal equilibrium with the bath. From the non-diagonal elements, we see the decoherence rate beginning at the usually predicted thermal rate, but changing to the zero temperature decoherence rate as the qubit and bath become entangled. These two rates are comparable, as was shown before in the zero temperature case [C. Anastopoulos and B. L. Hu, Phys. Rev. A {\bf 62} (2000) 033821]. On the entanglement of a qubit with the EMF under this type of resonant coupling we calculated, for the qubit reduced density matrix, the fidelity and the von Neumann entropy, which is a measure of the purity of the density matrix. The present more accurate non-Markovian calculations predict lower loss of fidelity and purity as compared with the Markovian results. Generally speaking, with the inclusion of quantum correlations between the qubit and its environment, the non-Markovian processes tend to slow down the drive of the system to equilibrium, prolonging the decoherence and better preserving the fidelity and purity of the system.
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"abstract": "We study the non-Markovian dynamics of a qubit made up of a two-level atom\ninteracting with an electromagnetic field (EMF) initially at finite\ntemperature. Unlike most earlier studies where the bath is assumed to be fixed,\nwe study the coherent evolution of the combined qubit-EMF system, thus allowing\nfor the back-action from the bath on the qubit and the qubit on the bath in a\nself-consistent manner. In this way we can see the development of quantum\ncorrelations and entanglement between the system and its environment, and how\nthat affects the decoherence and relaxation of the system. We find\nnon-exponential decay for both the diagonal and non-diagonal matrix elements of\nthe qubit\u0027s reduced density matrix in the pointer basis. From the diagonal\nelements we see the qubit relaxes to thermal equilibrium with the bath. From\nthe non-diagonal elements, we see the decoherence rate beginning at the usually\npredicted thermal rate, but changing to the zero temperature decoherence rate\nas the qubit and bath become entangled. These two rates are comparable, as was\nshown before in the zero temperature case [C. Anastopoulos and B. L. Hu, Phys.\nRev. A {\\bf 62} (2000) 033821]. On the entanglement of a qubit with the EMF\nunder this type of resonant coupling we calculated, for the qubit reduced\ndensity matrix, the fidelity and the von Neumann entropy, which is a measure of\nthe purity of the density matrix. The present more accurate non-Markovian\ncalculations predict lower loss of fidelity and purity as compared with the\nMarkovian results. Generally speaking, with the inclusion of quantum\ncorrelations between the qubit and its environment, the non-Markovian processes\ntend to slow down the drive of the system to equilibrium, prolonging the\ndecoherence and better preserving the fidelity and purity of the system.",
"arxiv_id": "quant-ph/0408084",
"authors": [
"S. Shresta",
"C. Anastopoulos",
"A. Dragulescu",
"B. L. Hu"
],
"categories": [
"quant-ph"
],
"doi": "10.1103/PhysRevA.71.022109",
"journal_ref": "Phys. Rev. A 71, 022109 (2005)",
"title": "Non-Markovian qubit dynamics in a thermal field bath: Relaxation, decoherence and entanglement",
"url": "https://arxiv.org/abs/quant-ph/0408084"
},
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