Optical investigation of nuclear spin coherence in Tm:YAG

With all-optical means, the nuclear spin coherence lifetime is measured for the first time in a crystal doped with low-concentration thulium. A novel Raman echo scheme is demonstrated. The hyperfine splitting is varied over a 15 MHz-wide range with the help of an external magnetic field. Over this range the spin coherence lifetime remains close to 350 μs in the electronic ground state. Thulium-doped materials are proved to be interesting substitutes to other rare earth ion-doped crystals as quantum memory candidates, thanks to their convenient wavelength, their adjustable three-level system and their stable and long spin coherence lifetime.