Final Report Summary - CIRQUSS (Circuit Quantum Electrodynamics with Single Electronic and Nuclear Spins)
The detection and manipulation of electron and nuclear spins is the focus of magnetic resonance spectroscopy. The main method to achieve that goal is to couple the spins to a resonant circuit that detects the rf or microwave signals emitted during the spin Larmor precession. In usual conditions, the spin to microwave coupling is weak, implying that large numbers of spins are needed to detect a signal.
Since 15 years, research on superconducting quantum circuits has developed novel tools for the detection and manipulation of microwave and rf signals at millikelvin temperature, with a degree of control never achieved so far since the very quantum state of the field can be engineered more or less at will. These tools include superconducting micro-resonators at microwave frequency, that confine the field on micron- or sub-micron scale, and superconducting microwave amplifiers that are nearly noiseless. The CIRQUSS project (CIRcuit QUantum electrodynamics with Single Spins) aims at applying those novel techniques and concepts to revisit magnetic resonance spectroscopy, at millikelvin temperature and in a regime of stronger spin-microwave interaction. Reaching single-electron-spin sensitivity was the ultimate goal of the project.
As a model system to demonstrate these ideas, we chose NV centers in diamond and donors in silicon, which are model electron-spin systems with well-understood magnetic resonance spectrum and properties. We fabricated superconducting micro-resonators on top of samples containing these spins close to its surface. We developed a complete electron-spin-resonance spectrometer at millikelvin temperatures including a Josephson Parametric Amplifier. We performed pulse electron-spin-resonance measurements and demonstrated the detection of up to 70 electron spins of donors in silicon within 1 second of integration time. Such 5-orders-of-magnitude improvement over the state-of-the-art by is obtained thanks to the large spin-resonator coupling and the noiseless amplifier.
The enhanced spin-resonator coupling also enabled us to observe a novel physical effect: spontaneous emission of microwave photons becomes the dominant relaxation mechanism for the spins that are resonant with the cavity. This spin Purcell effect, which was predicted in 1946, is manifested by a 3-orders-of-magnitude decrease of the relaxation time when the spin-resonator detuning becomes smaller than the resonator linewidth.
As another highlighted outcome of the project, circuit QED techniques have also been harnessed to perform an experiment in which we demonstrate an enhancement of the sensitivity of magnetic resonance spectroscopy when the spectrometer is illuminated by a source of squeezed microwave photons.
Overall, CIRQUSS pioneered the study of magnetic resonance spectroscopy in the quantum regime, with demonstrations of unprecedented spin detection sensitivity and novel spin dynamics caused by quantum fluctuations of the microwave field used for drive and control.
Since 15 years, research on superconducting quantum circuits has developed novel tools for the detection and manipulation of microwave and rf signals at millikelvin temperature, with a degree of control never achieved so far since the very quantum state of the field can be engineered more or less at will. These tools include superconducting micro-resonators at microwave frequency, that confine the field on micron- or sub-micron scale, and superconducting microwave amplifiers that are nearly noiseless. The CIRQUSS project (CIRcuit QUantum electrodynamics with Single Spins) aims at applying those novel techniques and concepts to revisit magnetic resonance spectroscopy, at millikelvin temperature and in a regime of stronger spin-microwave interaction. Reaching single-electron-spin sensitivity was the ultimate goal of the project.
As a model system to demonstrate these ideas, we chose NV centers in diamond and donors in silicon, which are model electron-spin systems with well-understood magnetic resonance spectrum and properties. We fabricated superconducting micro-resonators on top of samples containing these spins close to its surface. We developed a complete electron-spin-resonance spectrometer at millikelvin temperatures including a Josephson Parametric Amplifier. We performed pulse electron-spin-resonance measurements and demonstrated the detection of up to 70 electron spins of donors in silicon within 1 second of integration time. Such 5-orders-of-magnitude improvement over the state-of-the-art by is obtained thanks to the large spin-resonator coupling and the noiseless amplifier.
The enhanced spin-resonator coupling also enabled us to observe a novel physical effect: spontaneous emission of microwave photons becomes the dominant relaxation mechanism for the spins that are resonant with the cavity. This spin Purcell effect, which was predicted in 1946, is manifested by a 3-orders-of-magnitude decrease of the relaxation time when the spin-resonator detuning becomes smaller than the resonator linewidth.
As another highlighted outcome of the project, circuit QED techniques have also been harnessed to perform an experiment in which we demonstrate an enhancement of the sensitivity of magnetic resonance spectroscopy when the spectrometer is illuminated by a source of squeezed microwave photons.
Overall, CIRQUSS pioneered the study of magnetic resonance spectroscopy in the quantum regime, with demonstrations of unprecedented spin detection sensitivity and novel spin dynamics caused by quantum fluctuations of the microwave field used for drive and control.