Skip to Content

A thermal bath: more friend than foe?


Traditionally, the interaction of quantum systems with a thermal bath is viewed as detrimental to their quantumness. Yet this is not always the case, as the bath may actually promote quantumness, particularly when system-bath interactions are subject to control. I will review our recent results concerning different types of control capable of generating or enhancing quantum processes via the bath:
1. Control by modulation: By periodically modulating the energy of two-level or multilevel systems we may purify the state of the systems or the bath they couple to, upon tailoring the modulation to the bath spectrum. An intriguing consequence of such purification is the possibility to cool a bath consisting of coupled spins down to absolute zero, in apparent violation of Nernst's third law of thermodynamics. The thermal bath may also mediate the transfer of quantum information between distant systems, at a rate and fidelity controllable by the modulation.
2. Control by state preparation: The quantum state of an oscillator coupled to a thermalized qubit determines the amount and efficiency of work extractable from the thermal bath, thereby retaining its quantum features over surprisingly long time scales. Remarkably, certain quantum states yield higher efficiency than allowed by the Carnot bound, yet in full compliance with the second law of thermodynamics. In N-level systems, appropriate state preparation allows for N-fold enhancement of work extractable from the bath at steady state.
3. Control by bath engineering: The ability to control the coupling of quantum systems to appropriately designed, axially-guided modes of the bath, may drastically enhance the range of entanglement mediated by the bath, or lead to giant enhancement of bath-induced dispersion forces, colloquially known as van der Waals and Casimir forces.