© PAVIOT_Tristan
The colloquium will be streamed online.
Prof. Patrice Bertet, CEA Saclay
Invited by Prof. Dmitri Efetov
We have developed a novel EPR detection method at millikelvin temperatures [1]. It is based on the energy relaxation of paramagnetic centers by spontaneous emission of a microwave photon at their Larmor frequency, enhanced by resonant coupling to a superconducting resonator with a micron- or sub-micron-scale constriction [2]. The spins in the vicinity of the constriction are excited by a π pulse, and the photons subsequently emitted are detected by a specially designed microwave photon counter based on a superconducting qubit [3]. Thanks to the high sensitivity of the counter, the method can reach single spin sensitivity, as recently demonstrated with individual Er3+ ions in a scheelite crystal of CaWO4 [4].
We then use individual Er3+ spins as nano-antenna to dynamically polarize and measure the spectrum of individual nuclear spins surrounding them [5]. We will focus on one ion that has a 93Nb impurity in its immediate vicinity. We determine all 10 NMR transition frequencies of this spin-9/2 with Hertz spectral resolution, enabling to fully determine its quadrupolar tensor and to assess its insertion site in the crystal. We harness the high spectral resolution to investigate higher-order terms in the spin Hamiltonian, and we find evidence of a small coupling term between the electron spin and the nuclear quadrupole [6]. Its physical origin and implications are discussed.
[1] E. Albertinale et al., Nature, 2021, 600, 434
[2] A. Bienfait et al., Nature, 2016, 531, 74
[3] R. Lescanne et al., Physical Review X, 2020, 10, 021038
[4] Z. Wang et al., Nature, 2023, 619, 276
[5] J Travesedo et al., Science Advances 11 (10), eadu0581
[6] J. Travesedo et al., in preparation (2025)