Correlated offset charge jumps in Si/SiGe quantum dots

Here we report correlated jumps in the offset charge between very closely spaced SiGe quantum dots. To observe correlations, we utilize a fiber in a 3K cryogenic refrigerator to deposit energy from multiple 1.6 eV photon impacts on the back side of the host silicon substrate. These bursts simulate the effects of environmental radiation depositing energy in the substrate, which have recently been found to cause correlated errors in superconducting qubits on silicon substrates [1,2]. It is of great interest to know if Si/SiGe quantum dot qubits, which are also fabricated on silicon substrates, are similarly sensitive to radiation.

One key difference between these qubits is that Si/SiGe heterostructures have additional interfaces between the substrate and the qubit region. These interfaces are of interest for two reasons: first, they are locations at which charge can be trapped, which can induce errors.  Second, in principle, they can block charge migration. We show here that such interfaces do not preclude charge migration to the qubit region.

We track multiple offset charge jumps from a series of photon bursts by using active feedback [3] to sit on the sides of Coulomb blockade peaks for two dots simultaneously. We find that photon bursts can result in discrete jumps in the offset charge, indicating that excess charge has become trapped at a nearby interface, with some of these trapping events resulting in correlated jumps on both dots. A Poisson solver is used to find a vertical location of the newly trapped charge that is consistent with experimentally observed jumps.

[1] Nature 584, 551–556 (2020).

[2] Nature 594, 369–373 (2021).

[3] Phys. Rev. Appl., 15, L031003 (2021)