Characterization of individual charge fluctuators in Si/SiGe quantum dots

Electron spins in silicon quantum dots are excellent qubits due to their long coherence times, scalability, and compatibility with advanced semiconductor technology. Although high gate fidelities can be achieved with spin qubits, charge noise in the semiconductor environment still hinders further improvements. Despite the importance of charge noise, key questions about the specific nature of the fluctuators that cause charge noise remain unanswered. Here, we probe individual two-level fluctuators (TLFs) in Si/SiGe quantum dots through simple quantum-dot transport measurements and analyses based on the Allan variance and factorial hidden Markov modeling. We find that the TLF switching times depend sensitively on gate voltages, decrease with temperature, and depend on the current through a nearby quantum dot. A model for the data of the primary TLF we study indicates that it may be a bistable charge dipole near the plunger gate electrode, heated by current through the sensor dot, and experiencing state transitions driven not by direct electron-phonon coupling but through some other mechanism such as coupling to electrons passing through the sensor dot.