Multi-second Electron Spin Coherence in Ultra-pure Silicon

1. Multi-second Electron Spin Coherence in Ultra-pure Silicon NaiPhuanOng, Princeton University, DMR 0819860 A challenge facing the development of quantum computers is maintaining the phase coherence of the quantum states (qubits). Qubits based on manipulating the electron spin in silicon are a leading contender. However, the longest measured coherence was ~600 s. Recently, an international team, led by PCCM IRG-D researchers, with experts in silicon purification, enrichment, and crystal growth have pushed the measured electron spin coherence to about 10 seconds.1 At this level, the main source of decoherence is the weak magnetic interaction between the dilute impurities, which was suppressed by carefully distorting the external magnetic field (Fig. 2b). 1. A. Tyryshkin, et al., Nature Mater. 11, 143-147 (2012). Fig. 1 Photograph of the ~1 cm long ultra-high purity, isotopically enriched 28Si crystal. While natural Si contains about 4.7% ofthe isotope 29Si, this piece has less than 0.01%. The crystal intentionally contains about 1014/cm3 phosphorus atoms but less than a part per billion of other impurities. Fig. 2 (a) Plots of the decoherence rate (1/T2) as a function of the turning angle (pulse energy) of a spin echo refocusing pulse. The y-intercept gives the extrapolated T2 of an electron spin bound to an isolated phosphorus impurity. (b) Microwave absorption by the spins in a homogeneous (blue) and purposely inhomogeneous (red) magnetic field. Princeton Center for Complex Materials (PCCM)