Light-induced offset charge tracking in Si/SiGe quantum devices

Recently, it has been shown that gamma ray radiation impacts induce correlated errors in superconducting qubits fabricated on silicon substrates, which is particularly detrimental for error correcting codes [1]. Here, we imitate such radiation impacts in Si/SiGe quantum devices using a fiber optic connection in a 3K cryogenic refrigerator to deposit energy from multiple 1.6 eV photon-impacts on the back side of the host silicon substrate. We show that such photon impacts shift the Coulomb blockade behavior of gate-defined quantum dots. In some cases, these shifts are small enough that conventional, open-loop charge sensing can track the offset charge as a function of time. In order to enlarge the dynamic range of the measurement, we apply active feedback [2]. We demonstrate the effectiveness of this method for tracking light-induced background charge trapping by feeding back on the current through a sub-micron field-effect channel in the two-dimensional electron gas. Measurement of the gate voltage required to maintain a steady current correlates with light-induced charge trapping in the device, demonstrating that electron-hole pair generation deep in the substrate of Si/SiGe quantum devices can shift the offset charge for gate-defined devices on the other side of the wafer.



[1] Wilen, C.D., Abdullah, S., Kurinsky, N.A. et al. Correlated charge noise and relaxation errors in superconducting qubits. Nature 594, 369–373 (2021).

[2] Nakajima, Takashi, Kojima, Yohei et al. Real-Time Feedback Control of Charge Sensing for Quantum Dot Qubits, Phys. Rev. Appl., 15, L031003 (2021)