Hyperpolarizing the bismuth nuclear spin with superconducting microresonators.

Bismuth donors in silicon provide an ideal platform for a quantum memory, allowing random access state retrieval [1] and up to 3s coherence times [2]. Superconducting microresonators patterned on top of donor spins allow high sensitivity readout, efficient control of the spin system and provide an ideal pathway to couple the memory to a quantum processor [3]. We show how a nearby waveguide can be used as an RF antenna to drive nuclear spins in the donor system. We present ENDOR measurements on both the bismuth and silicon 29 nuclear spins, operating close to a ZEro-First-Order-Zeeman (ZEFOZ) point within the system. Here nuclear inversion is achieved much faster than the electron T1, allowing many nuclear gates before electron relaxation. This technique can be broadly applied to many designs and devices due to its minimal impact on the resonator. Nuclear spin control can be used to hyperpolarize the donor nuclear spins or to increase the quantum state storage capacity of the memory.

[1] O’Sullivan, J. et al. Physical Review X 12, (2022)

[2] Wolfowicz, G. et al. Nature Nanotechnology 8, 561–564 (2013)

[3] Kubo, Y. et al. Physical Review Letters 107, (2011)