Abstract
Vacuum fluctuations of the electromagnetic field set a fundamental limit to the sensitivity of a variety of measurements, including magnetic resonance spectroscopy. We report the use of squeezed microwave fields, which are engineered quantum states of light for which fluctuations in one field quadrature are reduced below the vacuum level, to enhance the detection sensitivity of an ensemble of electronic spins at millikelvin temperatures.} By shining a squeezed vacuum state on the input port of a microwave resonator containing the spins, we obtain a $1.2$\,dB noise reduction at the spectrometer output compared to the case of a vacuum input. This result constitutes a proof of principle of the application of quantum metrology to magnetic resonance spectroscopy.
Highlights
The detection and characterization of electron spins in a sample by magnetic resonance spectroscopy [1] has numerous applications in materials science, chemistry, and quantum information processing
Squeezing and noiseless amplification are achieved by the same type of device: a flux-pumped Josephson parametric amplifier (JPA) operated in the degenerate mode, denoted SQZ for the squeezer and AMP for the amplifier
The first one is the nonlinearity of both the SQZ and the AMP parametric amplifiers, which puts a lower bound on ηS and limits the maximum spin signal that can be amplified and detected
Summary
The detection and characterization of electron spins in a sample by magnetic resonance spectroscopy [1] has numerous applications in materials science, chemistry, and quantum information processing. Pulsed magnetic resonance detection proceeds by detecting weak microwave signals emitted by spins resonant with a cavity in which the sample is embedded. The thermal contribution to these fluctuations can be removed by lowering the temperature T of the sample and cavity such that kBT ≪ ħωs, where ωs is the spin resonance frequency and kB is Boltzmann’s constant [2]. Even at these cryogenic temperatures, quantum fluctuations of the electromagnetic field remain and pose a fundamental limitation to the achievable sensitivity
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