ESR at the quantum limit using high-Q superconducting resonators

Speaker: 
Dr Jarryd Pla
From: 
School of Electrical Engineering & Telecommunications UNSW
When: 
4 pm Thursday 13 October 2016
Where: 
CQC2T Conference Room Level 2, Newton Building, UNSW

The detection and characterization of paramagnetic species by electron spin resonance (ESR) spectroscopy has numerous applications in chemistry, biology, and materials science [1]. Most ESR spectrometers rely on the inductive detection of the small microwave signals emitted by the spins during their Larmor precession into a microwave resonator. Using the tools offered by circuit Quantum Electrodynamics (cQED), namely high quality factor superconducting micro-resonators and Josephson parametric amplifiers that operate at the quantum limit when cooled at 20mK [2], we report an increase of the sensitivity of inductively detected ESR by 4 orders of magnitude over the state-of-the-art, enabling the detection of 1700 bismuth donor spins in silicon with a signal-to-noise ratio of 1 in a single echo [3]. We also demonstrate that the energy relaxation time of the spins is limited by spontaneous emission of microwave photons into the measurement line via the resonator [4]. This constitutes the first observation of the Purcell effect for spins [5], an important step towards the coherent magnetic coupling of individual spins to microwave photons. Finally, we show that the presence of this high-sensitivity on-chip ESR spectrometer imparts a large strain-induced quadrupole interaction on the bismuth donors, of order 100 MHz [6]. Through finite-element strain simulations and effective mass theory calculations of the donor electron wavefunction, we are able to reconstruct key features of our experiments, including the electron spin resonance spectra.

[1] A. Schweiger and G. Jeschke, Principles of Pulse Electron Magnetic Resonance (Oxford University Press, 2001).
[2] X. Zhou et al., Physical Review B 89, 214517 (2014).
[3] A. Bienfait, et al., Nature Nanotechnology 11, 253 (2015).
[4] A. Bienfait, et al., Nature 531, 74 (2016).
[5] E. M. Purcell, Physical Review 69, 681 (1946).
[6] J. J. Pla, arXiv:1608.07346 (2016).