ESR at the quantum limit using high-Q superconducting resonators
October 13, 2016 @ 4:00 pm
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The detection and characterization of paramagnetic species by electron spin resonance (ESR) spectroscopy has numerous applications in chemistry, biology, and materials science . 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 , 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 . 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 . This constitutes the first observation of the Purcell effect for spins , 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 . 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.
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