Optical control of Berry phase in a diamond spin qubit*

Geometric phase, a fascinating quantum mechanical phenomenon that arises from cyclic state evolution, is a promising avenue to realize fault-tolerant quantum information processing. Here, we demonstrate an all-optical approach to accumulate a geometric phase, or Berry phase, within a solid-state spin qubit, the nitrogen-vacancy center in diamond \footnote{C. G. Yale*, F. J. Heremans*, B. B. Zhou,* A. Auer, G. Burkard, D. D. Awschalom, arXiv:1507.08993 (2015).}. With stimulated Raman adiabatic passage (STIRAP), we evolve two light fields to cycle the resulting dark state of a low temperature lambda system in a `tangerine slice' trajectory that we examine through time-resolved state tomography. This type of trajectory acquires a Berry phase which we then measure through phase comparison to a reference state. We then probe the limits of this control as a result of adiabatic breakdown for short timescales and unintended excitation driven by far-detuned optical fields that accumulate for long timescales. We also investigate the intrinsic resilience of this Berry phase to noise introduced into the system, which is the focus of the following talk. As an all-optical approach, this geometric control represents a pathway to the development of optical geometric gates in the solid state.