Photonic heat amplifiers based on a disordered semiconductor

Abstract: A photonic heat amplifier (PHA) designed for cryogenic operations is introduced and analyzed. This device comprises two variable-range-hopping reservoirs connected by lossless lines, which allow them to exchange heat through photonic modes. This configuration enables negative differential thermal conductance (NDTC), which can be harnessed to amplify thermal signals. To achieve this, one reservoir is maintained at a high temperature, serving as the source terminal of a thermal transistor. Concurrently, in the other one, we establish tunnel contacts to metallic reservoirs, which function as the gate and drain terminals. With this arrangement, it is possible to control the heat flux exchange between the source and drain by adjusting the gate temperature. We present two different parameter choices that yield different performances: the first emphasizes modulating the source-drain heat current, while the second focuses on the modulation of the colder temperature variable range hopping reservoir. Lastly, we present a potential design variation in which all electronic reservoirs are thermally connected through only photonic modes, allowing interactions between distant elements. The proposal of the PHA addresses the lack of thermal transistors and amplifiers in the mK range while being compatible with the rich toolbox of circuit quantum electrodynamics. It can be adapted to various applications, including sensing and developing thermal circuits and control devices at sub-Kelvin temperatures, which are relevant to quantum technologies.