Characterizing spin-bath parameters using conventional and time-asymmetric Hahn-echo sequences

Spin-bath noise characterization, which is typically performed by multi-pulse control sequences, is essential for understanding most spin dynamics in the solid-state. Here, we theoretically propose a method for extracting the characteristic parameters of a noise source with a known spectrum, using a single modified Hahn-echo sequence. By varying the application time of the pulse, measuring the coherence curves of an addressable spin, and fitting the decay coefficients to a theoretical function derived by us, we extract parameters characterizing the physical nature of the noise. Assuming a Lorentzian noise spectrum, we illustrate this method for extracting the correlation time of a bath of nitrogen paramagnetic impurities in diamond, and its coupling strength to the addressable spin of a nitrogen-vacancy center. Considering a realistic experimental scenario with $5\%$ measurement error, the parameters can be extracted with an accuracy of $\sim 10 \%$. The scheme is effective for samples having a natural homogeneous coherence time ($T_2$) up to two orders of magnitude greater than the inhomogeneous coherence time ($T_2^*$), and mitigates technical noise when further averaging is irrelevant. Beyond its potential for reducing experiment times by an order-of-magnitude, such single-pulse noise characterization could minimize the effects of long time-scale drifts and accumulating pulse imperfections and numerical errors.

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