Coherence Time Extension by Large Scale Optical Spin Polarization in a Rare-Earth Doped Crystal

TL;DR

This paper demonstrates that optical pumping and spin diffusion can significantly polarize spins in a rare-earth doped crystal, leading to a substantial increase in optical coherence lifetime, which benefits quantum technologies.

Contribution

It introduces a novel spin polarization method in rare-earth doped crystals that enhances optical coherence times without requiring high magnetic fields or ultra-low temperatures.

Findings

Achieved over 90% spin polarization at 2 K and zero magnetic field.

Increased optical coherence lifetime from 0.3 ms to 0.8 ms.

Potential for improved quantum memory and sensing applications.

Abstract

Optically addressable spins are actively investigated in quantum communication, processing and sensing. Optical and spin coherence lifetimes, which determine quantum operation fidelity and storage time, are often limited by spin-spin interactions, which can be decreased by polarizing spins in their lower energy state using large magnetic fields and/or mK range temperatures. Here, we show that optical pumping of a small fraction of ions with a fixed frequency laser, coupled with spin-spin interactions and spin diffusion, leads to substantial spin polarization in a paramagnetic rare earth doped crystal, $^{171}$Yb$^{3+}$:YSO. Indeed, up to more than 90 % spin polarizations have been achieved at 2 K and zero magnetic field. Using this spin polarization mechanism, we furthermore demonstrate an increase in optical coherence lifetime from 0.3 ms to 0.8 ms, due to a strong decrease in spin-spin interactions. This effect opens the way to new schemes for obtaining long optical and spin coherence lifetimes in various solid-state systems such as ensembles of rare earth ions or color centers in diamond, which is of interest for a broad range of quantum technologies.