Noise correlations in a two-qubit Si/SiGe quantum dot device*

Qubits are affected by noise in their environment, but conversely can also be used to probe this noise and study properties such as spectral density and correlations. We use a two-qubit device in a Si/SiGe hetrostructure [1] to investigate noise correlations by studying the decay of two Bell states. These Bell states are insensitive to either correlated or anti-correlated noise, resembling the concept of decoherence-free subspaces, which allows us to extract the uncorrelated, correlated and anti-correlated contributions to the noise affecting the qubits from the decay times for the different initial states. Knowledge about the noise properties makes it possible to design operations that are less sensitive to this noise, and yields information on the noise source, which potentially makes it possible to reduce the noise. We demonstrate this method by artificially adding (anti-) correlated noise and use it characterize the noise in our system.

[1] T.F. Watson et al., Nature 555, 633 (2018)