Two-qubit noise cross-correlation spectroscopy of electronic spins in diamond

Every quantum device is subject to noise due to entangling with its environment, which limits the lifetime and thus usefulness of the device. Characterizing the noise affecting quantum devices is thus of both practical interest (e.g., to find low-noise operating conditions) and fundamental interest (e.g., to probe the physical nature of the quantum environment). An established method based on dynamical decoupling control sequences has achieved single-qubit noise spectroscopy (1QNS) in many dephasing quantum systems. However, for a multi-qubit information processor, 1QNS alone is not sufficient to characterize the overall device noise, as it fails to capture the spatio-temporal correlations shared across the noise on each qubit. As the first step to address this, the theory of two-qubit noise spectroscopy (2QNS) was proposed to characterize such cross-correlations in the dephasing noise across spatially separated qubits. Here we demonstrate initial measurements of 1QNS and 2QNS of two weakly interacting electronic spins in diamond, which can yield a more complete understanding of the overall noise affecting the two-qubit register, and in turn inform practical considerations for improved operating conditions for the device.