Elementary quantum systems out of thermal equilibrium: From quantum thermalization to entanglement
Résumé
We study the internal dynamics, the quantum thermalization and the entanglement
of elementary quantum systems (one or two atoms) placed close to a body held at a
temperature different from that of the surrounding radiation.
Concerning the single atom dynamics [1,2], we derive general expressions for lifetime
and density matrix valid for bodies of arbitrary geometry and dielectric permittivity.
Out of equilibrium, the thermalization process and steady states become both qualitatively
and quantitatively significantly different from the case of radiation at thermal
equilibrium. For the case of a three-level atom close to a slab of finite thickness, we
predict the occurrence of population inversion and an efficient cooling mechanism for
the quantum system, whose effective internal temperature can be driven to values much
lower than both involved temperatures. Our results show that non-equilibrium configurations
provide new promising ways to control the state of an atomic system.
We also consider two two-level atomic quantum systems (qubits) [3]. While at thermal
equilibrium the two-qubit dynamics is characterized by not entangled steady thermal
states, we show that absence of thermal equilibrium may bring to the generation
of entangled steady states. Remarkably, this entanglement emerges from the two-qubit
dissipative dynamic itself, without any further external action on the two qubits, suggesting
a new protocol to produce and protect entanglement which is intrinsically robust
to environmental effects.
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[1] Bruno Bellomo, Riccardo Messina, and Mauro Antezza, Europhys. Lett. 100, 20006
(2012).
[2] Bruno Bellomo, Riccardo Messina, Didier Felbacq, and Mauro Antezza, Phys. Rev.
A 87, 012101 (2013).
[3] Bruno Bellomo, and Mauro Antezza, arXiv:1304.2864 (2013).