Towards coupling Bismuth Dopant Spins in Silicon to Superconducting Resonators at 'Clock Transitions’

Spins in nuclear-spin-free solid state systems such as purified 28Si have seen extensive research as candidates for quantum information storage and processing, thanks to their long spin coherence lifetimes [1]. Strongly coupling such spins to a high Q superconducting resonator provides a route to develop microwave quantum memories. Bismuth donor spins can be tuned to so-called ‘clock transitions’, which, due to their insensitivity to magnetic field noise, can have electron spin coherence times as long as 3 seconds [2]. Achieving coupling to such transitions requires resonators which are both magnetic-field resilient, and frequency tuneable.

We use a superconducting NbN microwave resonator which maintains a high Q-factor up to fields of 700mT. Resonators may be frequency-tuned by changing the orientation of the applied field, thereby changing the kinetic inductance of the superconducting film. In this way we can tune a resonator into resonance with the bismuth donor spins precisely at a clock transition.

[1] A. M. Tyryshkin et al., Nat. Mater. 11, 143 (2012).
[2] G.Wolfowicz et al., Nature Nanotechnology 8, 561, (2013)