Quantum Refrigeration with Indefinite Causal Order

Understand

We propose a thermodynamic refrigeration cycle which uses Indefinite Causal Orders to achieve non-classical cooling.

• The cycle cools a cold reservoir while consuming purity in a control qubit.
• We first show that the application to an input state of two identical thermalizing channels of temperature $T$ in an indefinite causal order can result in an output state with a temperature not equal to $T$.
• We investigate the properties of the refrigeration cycle and show that thermodynamically, the result is compatible with unitary quantum mechanics in the circuit model but could not be achieved classically.