Spatial noise correlations in a Si/SiGe two-qubit device from Bell state coherences
Jelmer M. Boter (TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/Vandersypen Lab, Kavli institute of nanoscience Delft)
Xiao Xue (TU Delft - QCD/Vandersypen Lab, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
Tobias Krähenmann (Kavli institute of nanoscience Delft, TU Delft - QCD/Vandersypen Lab, TU Delft - QuTech Advanced Research Centre)
Thomas F. Watson (TU Delft - QCD/Vandersypen Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Vickram N. Premakumar (University of Wisconsin-Madison)
Daniel R. Ward (University of Wisconsin-Madison)
Donald E. Savage (University of Wisconsin-Madison)
Mark A. Eriksson (University of Wisconsin-Madison)
Lieven M.K. Vandersypen (TU Delft - QCD/Vandersypen Lab, TU Delft - QuTech Advanced Research Centre, TU Delft - QN/Vandersypen Lab, Kavli institute of nanoscience Delft, Components Research)
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Abstract
We study spatial noise correlations in a Si/SiGe two-qubit device with integrated micromagnets. Our method relies on the concept of decoherence-free subspaces, whereby we measure the coherence time for two different Bell states, designed to be sensitive only to either correlated or anticorrelated noise, respectively. From these measurements we find weak correlations in low-frequency noise acting on the two qubits, while no correlations could be detected in high-frequency noise. We expect nuclear spin noise to have an uncorrelated nature. A theoretical model and numerical simulations give further insight into the additive effect of multiple independent (anti)correlated noise sources with an asymmetric effect on the two qubits as can result from charge noise. Such a scenario in combination with nuclear spins is plausible given the data and the known decoherence mechanisms. This work is highly relevant for the design of optimized quantum error correction codes for spin qubits in quantum dot arrays, as well as for optimizing the design of future quantum dot arrays.