Yttrium orthosilicate as an alternative substrates for the fabrication of super-conducting devices

Yttrium orthosilicate (Y2SiO5, or YSO) has proved to be a convenient host for rare-earth ions used in demonstrations of microwave quantum memories and optical memories with microwave interfaces and shows promise for coherent microwave-optical conversion owing to its favorable optical and spin properties. The strong coupling required by such microwave applications could be achieved using superconducting resonators patterned directly on Y2SiO5 and hence we investigate here the use of Y2SiO5 as an alternative to sapphire or silicon substrates for superconducting-hybrid-device fabrication. A NbN resonator with frequency 6.008 GHz and low-power quality factor Q ≈ 400 000 is fabricated on a Y2 SiO5 substrate doped with isotopically enriched 145Nd. Measurements of dielectric loss yield a loss tangent tan δ = 4 × 10−6 , comparable to that of sapphire. Electron spin resonance (ESR) measurements performed using the resonator show the characteristic angular dependence expected from the anisotropic 145Nd spin and the coupling strength between the resonator and the electron spins is in the high-cooperativity regime (C = 30). These results demonstrate that Y2SiO5 is an excellent substrate for low-loss, high-Q microwave resonators, especially in applications for coupling to optically accessible rare-earth spins. It may also prove interesting to study the suitability as a substrate of other crystalline hosts for REIs, such as yttrium aluminium garnet (YAG), yttrium lithium fluoride (YLF), yttrium orthovana-date (YVO4), and calcium tungstate (CaWO4). The fabrication of superconducting devices on crystals doped with REIs as demonstrated here shows promise for integrating these optical elements alongside the fast information processing available from superconducting qubits. This is an important step toward making a microwave-optical transducer capable of connecting such quantum processors within a quantum network. By exploiting the long coherence times available from REIs, this is also a route to integrating fast quantum electronics with a spin ensemble acting as a quantum memory. (Fig. The onset of an avoided crossing when sweeping the B field through resonance, detail). 

You can read the paper at https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.11.054082