Quantum-well subband-degeneracy refrigeration with cascaded cryogenic solid-state heat pumps

Design for a solid-state heat pump to eventually replace dilution refrigerators is introduced based on the cyclic adiabatic expansion and compression of 2D electron gas subbands to achieve sub-Kelvin temperatures. With the one-shot version proposed by Rego & Kirczenow (APL, 1999), the proposed device cools by a factor of T_C/T_H = g₁/g₂ by decreasing the electric field in the quantum well via gates to increase the subband occupancy from g₁ to g₂. Narrow “throttle” gates to the left and right of the compression/expansion gates can selectively deplete a narrow strip of electrons, which electrically and thermally isolate the central electron reservoir alternately from the heat sink and from the cold load. Optimal materials selection and device design is supported by an analytical model of device function. A 1 cm² single-stage device is predicted to cool to 0.85 K with a 1 K heat sink and 1 MHz cycle frequency. Moreover, temperatures below 0.10 K can be achieved by a multi-stage cascaded device. Future generations of this device are intended to eventually supplant dilution refrigerators for cooling of solid-state quantum computers.