There is currently significant interest in operating devices in the quantum regime, where their behaviour cannot be explained through classical mechanics. Quantum states, including entangled states, are fragile and easily disturbed by excessive thermal noise. Here we address the question of whether it is possible to create non-reciprocal devices that encourage the flow of thermal noise towards or away from a particular quantum device in a network. Our work makes use of the cascaded systems formalism to answer this question in the affirmative, showing how a three-port device can be used as an effective thermal transistor, and illustrates how this formalism maps onto an experimentally-realisable optomechanical system. Our results pave the way to more resilient quantum devices and to the use of thermal noise as a resource.
We present a scattering model which enables us to describe the mechanical force, including the velocity dependent
component, exerted by light on polarizable massive objects in a general one-dimensional optical system. We show
that the light field in an interferometer can be very sensitive to the velocity of a moving scatterer. We construct
a new efficient cooling scheme, 'external cavity cooling', in which the scatterer, that can be an atom or a moving
micromirror, is spatially separated from the cavity.