Thirty millisecond electron-spin coherence in an erbium doped crystal

Rare-earth-ion doped solids are interesting physical systems because they have long lived states and record coherence times for both the optical and nuclear transitions [1]. Rare-earths with an odd number of electrons are also paramagnetic, with an electron-spin transition at GHz frequencies in magnetic fields less than 1 Tesla. Recently erbium doped calcium-tungstate (Er:CaWO4) has demonstrated 23ms electron-spin coherence at 10mK [2]. Measured using a superconducting micro-resonator and parametric amplifier [3], this is the longest electron-spin coherence observed on a magnetically-sensitive transition in a crystal with a natural abundance of nuclear spins. Here we demonstrate that the coherence can be extended up to 30ms by choosing a magnetic field orientation that minimizes the magnetic dipole-dipole interaction between the Er ions and W nuclei.

[1] Zhong, M. et al., Nature 517, 177-180 (2015)

[2] M. Le Dantec. et al., arXiv:2106.14974 (2021)

[3] A. Bienfait et al., Nature nanotechnology, vol. 11, no 3, p. 253, (2016)

We acknowledge Lincoln Labs for providing a Parametric Amplifier. We thank the Chaire Industrielle NASNIQ (grant ANR-17-CHIN-0001) supported by Atos, the project QIPSE (grant ACUHK403/15), the project MIRESPIN, SIRTEQ grant REIMIC and EU grant SMERC (792727)