Relaxation of a quantum dot electron spin coupled with a Fermi sea

Recent development of high-fidelity spin control and nuclear spin cooling in self-assembled quantum dots has enabled hundred folds of improvement on the electron or hole spin coherence, approaching the limit set by spin relaxation. Understanding spin relaxation in quantum dots is thus a requisite towards highly coherent quantum interfaces with quantum dot spins. Spin relaxation in quantum dots is complicated due to a variety of interactions with phonons, local charges, and the nearby Fermi sea. Under different experimental conditions, different mechanisms dominate and determine the spin relaxation behavior. Here, we study the relaxation of an electron spin in a quantum dot under different experimental conditions, including the bias voltage, temperature, and magnetic field. Bias voltage tunes the quantum dot levels relative to the Fermi level of a nearby Fermi sea, changing the co-tunneling rate. The relaxation rate increases by nearly 10 times when we lower the temperature from 4 K to 40 mK, and shows interesting dependence on the magnetic field. We model our observations by considering a Kondo-like exchange interaction between the quantum dot electron spin and the Fermi sea. Our results provide new insights into the optimal operating conditions of a coherent quantum interface with a quantum dot spin and may find applications in optical low-temperature thermometry of an electron gas.