Self-consistent noise characterization of quantum devices.

Characterizing and understanding the environment of quantum systems is critical to engineering more robust quantum devices as well as probing many-body quantum environments of interest.

Here we present a practical protocol for quantum device noise characterization which, by reducing the quantum environment to an effective classical noise spectrum model, is also predictive.

Inspired by quantum noise spectroscopy (QNS), our approach is to model the environment affecting the qubit with a classical noise spectrum that is `self-consistent’ , i.e., predictive of all observed decoherence under various qubit dynamics.

Crucially, by reconciling existing techniques of QNS, our method is strictly more accurate and robust: even when the existing methods fail our method succeeds.

We experimentally demonstrate our approach by characterizing the noise affecting a nanoscale quantum device composed of two nearby interacting electronic spins in diamond, which surprisingly reveals a complex, non-uniform and quantum spin environment.

Our work enables quantum sensing of complex many-body environments with up to nanoscale spatial resolution, and characterization of correlated noise between qubits which has implications for practical realizability of quantum error correction.