Optical coherence of¹⁶⁶Er:⁷LiYF₄crystal below 1 K

Abstract

We explore optical coherence and spin dynamics of an isotopically purified 166 Er: 7 LiYF 4 crystal below 1 K and at weak magnetic fields < 0.3T. Crystals were grown in our lab and demonstrate narrow inhomogeneous optical broadening down to 16MHz. Solid-state atomic ensembles with such narrow linewidths are very attractive for implementing of off-resonant Raman quantum memory and for the interfacing of superconducting quantum circuits and telecom C-band optical photons. Both applications require a low magnetic field of ∼10mT. However, at conventional experimental temperatures T>1.5K, optical coherence of Er:LYF crystal attains m 10 s time scale only at strong magnetic fields above 1.5 T. In the present work, we demonstrate that the deep freezing of Er:LYF crystal below 1 K results in the increase of optical coherence time to m 100 s at weak fields.

All-Optical Control of the Silicon-Vacancy Spin in Diamond at Millikelvin Temperatures

“…This is the same emitter used in [9] and the spectroscopic characterization of this emitter at zero magnetic field can be found therein. The diamond sample is cooled down to millikelvin temperatures in a dilution refrigerator with free-space optical access using a home-built confocal setup [17]. The setup is capable of operating at millikelvin temperatures and consists of a copper cage carrying a titanium slip-stick positioner stack with a copper sample holder containing a SmCo permanent magnet and a numerical aperture of 0.9 achromatic microscope objective [18].…”

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

“…(2) On the contrary, if an optical transition has no overlap with those originating from other groundstate spin levels, DEOP and LSOP can strongly polarize spin ensembles. Materials with very narrow optical inhomogeneous linewidths, and/or large g factors, such as Er 3þ ∶LiYF 4 [14], Yb 3þ ∶YVO 4 [34], or Er 3þ ∶Y 2 SiO 5 [50], can show such properties. LSOP, which does not rely on spin diffusion, may be advantageous over DEOP in this case, in terms of, e.g., polarization rate.…”

“…This investigation was motivated by several studies that have shown that flipping ground-state spins of paramagnetic RE can be a major source of magnetic noise and therefore cause dephasing to RE optical and spin transitions [8,33]. This dephasing can be reduced by inducing strong spin polarization under large magnetic field and/or ultralow temperatures, by broadband optical pumping, or by using excited-state spins [13,14,30,42,43]. As shown in the previous section, DEOP also induces large-scale spin polarization and could therefore achieve similar effects.…”

“…This work includes isotope purification to eliminate elements with nonzero spins [10,11] and spin polarization. The latter can be obtained by application of high magnetic fields [12,13], very low temperatures [14], or optical pumping [15]. Another approach is to decouple the optically addressable spins from the bath by using clock transitions that are insensitive to magnetic-field fluctuations at first order [16][17][18] or by filtering out bath fluctuations by dynamical techniques [19,20].…”

Electromagnetically induced transparency in an isotopically purified Nd3+:YLiF4 crystal

“…The same material was used in [33,36] for implementing quantum memory protocols based on atomic frequency combs. The crystal was grown by using Bridgman-Stockbarger method in an argon atmosphere of high purity (see [33,35] for details). We started by measuring the absorption spectrum (σ polarization) of the sample on the 4 I 9/2 (1)-4 F 3/2 (1) transition (867.5 nm) at 2 K as a function of dc magnetic field directed along the crystal c axis.…”