2019/10/24 by Bartolo Albanese, B. Albanese, S. Probst +19 · 25 citations
Chemistry · Physics and Astronomy · #Advanced NMR Techniques and Applications #Atomic and Subatomic Physics Research #Coupling (piping) #Electron #Microwave #Microwave cavity #Phonon #Photon #Quantum and electron transport phenomena #Spin (aerodynamics) #Spin engineering #Spin polarization #Spins #cond-mat.mes-hall #quant-ph
paper · pdf · doi:10.1038/s41567-020-0872-2
published in Nature Physics 16(7), 751-755 (Nature Portfolio)
arxiv created 2019/10/24 · openalex created_date 2019/11/01 · openalex publication_date 2020/04/20 · arxiv updated 2020/08/26 · openalex updated_date 2026/08/05
Physical systems reach thermal equilibrium through energy exchange with their environment, and for spins in solids the relevant environment is almost always their host lattice. However, recent studies1 motivated by observations by Purcell2 have shown how radiative emission into a microwave cavity can become the dominant relaxation path for spins if the spin–cavity coupling is sufficiently large (such as for small-mode-volume cavities). In this regime, the cavity electromagnetic field overrides the lattice as the dominant environment, inviting the prospect of controlling the spin temperature independently from that of the lattice, by engineering a suitable cavity field. Here, we report on precisely such control over spin temperature, illustrating a novel and universal method to increase the electron spin polarization above its thermal equilibrium value (termed hyperpolarization). By switching the cavity input between resistive loads at different temperatures we can control the electron spin polarization, cooling it below the lattice temperature. Our demonstration uses donor spins in silicon coupled to a superconducting microresonator and we observe more than a twofold increase in spin polarization. This approach provides a general route to signal enhancement in electron spin resonance, or nuclear magnetic resonance through dynamical nuclear spin polarization3,4. Electron spins in solid usually relax their energy through the coupling with phonons in the host lattice. By using the coupling to microwave photons in a cavity as an alternative relaxation path, it is demonstrated that spins can be cooled below the lattice temperature.