In situ amplification of spin echoes within a kinetic inductance parametric amplifier

The use of superconducting microresonators together with quantum-limited Josephson parametric amplifiers has enhanced the sensitivity of pulsed electron spin resonance (ESR) measurements by more than four orders of magnitude. So far, the microwave resonators and amplifiers have been designed as separate components due to the incompatibility of Josephson junction-based devices with magnetic fields. This has produced complex spectrometers and raised technical barriers toward adoption of the technique. Here, we circumvent this issue by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field-resilient superconducting microwave resonator. We perform pulsed ESR measurements with a 1-pL mode volume containing 6 x 10(7) spins and amplify the resulting signals within the device. When considering only those spins that contribute to the detected signals, we find a sensitivity of 2.8 x10(3)spins/root Hz for a Hahn echo sequence at a temperature of 400 mK. In situ amplification is demonstrated at fields up to 254 mT, highlighting the technique's potential for application under conventional ESR operating conditions.

Automated summary

The sensitivity of pulsed electron spin resonance (ESR) measurements has been greatly enhanced by using superconducting microresonators and quantum-limited Josephson parametric amplifiers, achieving an improvement of more than four orders of magnitude. Incompatibility between Josephson junction-based devices and magnetic fields has resulted in the design of separate microwave resonators and amplifiers, leading to complex spectrometers and technical barriers. However, by coupling an ensemble of spins directly to a weakly nonlinear and magnetic field-resilient superconducting microwave resonator, this issue is circumvented. Pulsed ESR measurements with amplification within the device are successfully performed, demonstrating a high sensitivity and potential for application under conventional ESR operating conditions.