Entanglement is a key phenomenon distinguishing quantum from classical physics, and is the paradigmatic resource enabling many applications of quantum information science. Generating and maintaining entanglement is therefore a central challenge. Decoherence caused by unavoidable interactions of a system with its environment generally degrades entanglement, and significant effort is invested in minimising the effect of such dissipation in experiments. However, dissipation can also be advantageous, and may indeed be exploited for the generation of entangled quantum states under the right conditions. Recently, several proposals have demonstrated that entanglement in the stationary regime can be generated using only incoherent couplings to thermal baths, in contrast to bath and/or coupling engineering. As such, these works have achieved important steps demonstrating that thermal machines using purely incoherent free-energy resource can achieve quantum tasks. However, the amount of entanglement generated with these simple machines is relatively weak. In particular, it is not high enough to violate Bell-type inequalities and therefore can not be useful for quantum information processing.
In this seminar, after reviewing these thermal machines, I will present you a new type of thermal machine elaborated with my colleagues in Geneva and Vienna. It achieves the generation of maximal entanglement in a heralded way. Our setup requires incoherent interactions with two thermal baths at different temperatures, but no source of work or control. A pair of (d + 1)-dimensional quantum systems is first driven to an entangled steady state by the temperature gradient, and maximal entanglement in dimension d can then be heralded via local filters.
I will also discuss possible experimental implementations, in particular with superconducting qubits. Based on these ideas, a novel collaboration with experimentalists has recently been established to realize such a thermal machine.
J. Bohr Brask, G, Haack, N. Brunner and M. Huber, NJP 17 (2015).
A. Tavakoli, G. Haack, M. Huber, N. Brunner and J. Bohr Brask, arXiv:1708.01428 (2017).