Electron Spin Resonance with up to 20 Spin Sensitivity Measured using a Superconducting Flux Qubit

  1. Rangga P. Budoyo,
  2. Kosuke Kakuyanagi,
  3. Hiraku Toida,
  4. Yuichiro Matsuzaki,
  5. and Shiro Saito
We report on electron spin resonance spectroscopy measurements using a superconducting flux qubit with a sensing volume of 6 fl. The qubit is read out using a frequency-tunable Josephson bifurcation amplifier, which leads to an inferred measurement sensitivity of about 20 spins in a 1 s measurement. This sensitivity represents an order of magnitude improvement when compared with flux-qubit schemes using a dc-SQUID switching readout. Furthermore, noise spectroscopy reveals that the sensitivity is limited by flicker (1/f) flux noise.
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