Microwave-Induced Cooling in Double Quantum Dots: Achieving Millikelvin Temperatures to Reduce Thermal Noise around Spin Qubits

Spin qubits in gate-defined quantum dots are emerging as a leading technology due to their scalability and long coherence times. However, maintaining these qubits at ultra-low temperatures typically requires complex cryogenic systems. This paper proposes a novel gate-defined double quantum dot (DQD) cooling system using microwave-induced state depopulation and phonon filtering to achieve local temperatures below 10 mK at a bath temperature of 1 K. The system utilizes microwave-induced state depopulation and phonon filtering, combined with fast cyclic detuning of the quantum dot on-site energies and Rabi oscillations, to efficiently transfer thermal populations to the ground state, thereby surpassing natural thermal transition rates. The cooling cycle involves adjusting gate potentials to drive the system through adiabatic and diabatic transitions, complemented by microwave pulses resonant with specific energy level differences. This mechanism continuously pumps the population from excited states into the ground state, effectively reducing the system's temperature. Numerical calculations demonstrate the feasibility of achieving these low local temperatures, with detailed analysis showing the sensitivity of cooling performance to detuning energy, magnetic field strength, and diabatic return time.