Photon-assisted electron transport across a quantum phase transition

Quantum-dot circuit quantum electrodynamics (QD-cQED) offers an important platform for achieving photon-to-electron conversion in the linear regime, but it has been challenging to efficiently control the photocurrent. Here, we propose a nonlinear QD-cQED setup of a double quantum dot system capacitively coupled to a microwave resonator containing Kerr nonlinearity. By means of the quantum master equation, we derive a general formulation to establish the connection between photon excitation and generated photocurrent. It is revealed that the excitation of photons undergoes a first-order quantum phase transition, which provides a mechanism to adjust the photon-assisted electron transport and leads to an increase in the photocurrent. In contrast to the linear QD-cQED setups, the enhancement in photocurrent benefits from the enhanced energy transfer from photon to electron systems near the phase transition. Our results establish the quantum phase transition as an invaluable tool for optimizing the photon-to-electron conversion in QD-cQED devices.