@article{discovery1474850,
           title = {Classical nature of nuclear spin noise near clock transitions of Bi donors in silicon},
            year = {2015},
            note = {{\copyright}2015 American Physical Society},
         journal = {PHYSICAL REVIEW B},
           month = {October},
          volume = {92},
          author = {Ma, W-L and Wolfowicz, G and Li, S-S and Morton, JJL and Liu, R-B},
            issn = {1098-0121},
             url = {http://dx.doi.org/10.1103/PhysRevB.92.161403},
        abstract = {Whether a quantum bath can be approximated as classical Gaussian noise is a fundamental issue in central spin decoherence and also of practical importance in designing noise-resilient quantum control. Spin qubits based on bismuth donors in silicon have tunable interactions with nuclear spin baths and are first-order insensitive to magnetic noise at so-called clock transitions (CTs). This system is therefore ideal for studying the quantum/classical Gaussian nature of nuclear spin baths since the qubit-bath interaction strength determines the back-action on the baths and hence the adequacy of a Gaussian noise model. We develop a Gaussian noise model with noise correlations determined by quantum calculations and compare the classical noise approximation to the full quantum bath theory. We experimentally test our model through a dynamical decoupling sequence of up to 128 pulses, finding good agreement with simulations and measuring electron spin coherence times approaching 1 s-notably using natural silicon. Our theoretical and experimental study demonstrates that the noise from a nuclear spin bath is analogous to classical Gaussian noise if the back-action of the qubit on the bath is small compared to the internal bath dynamics, as is the case close to CTs. However, far from the CTs, the back-action of the central spin on the bath is such that the quantum model is required to accurately model spin decoherence.}
}