Enhancing Cryogenic Electro-Optic and Piezo-Electric Performance by Tuning Quantum Criticality

The Stanford team has dramatically enhanced materials properties crucial for low-temperature quantum photonic and phononic applications. By manipulating the oxygen isotope ratio in strontium titanate, they have demonstrated proof-of-concept devices with record-breaking performance at cryogenic temperatures. This establishes an flexible tuning mechanism for nonlinear materials.

Electro-optic tunability—a change in the refractive index upon the application of an electrical voltage—is a key requirement for tunable photonic elements and quantum technologies. However, at the cryogenic temperatures where many devices operate, there is a fundamental limitation: when cooled, leading electro-optic and piezo-electric materials lose their strong nonlinearity, becoming less efficient and preventing applications ranging from photonic quantum computing to microwave-to-optical transduction that could scale quantum computers.

The team discovered that SrTiO₃ (STO) is the most tunable electro-optic and piezoelectric material at cryogenic temperatures below 10 K. By approaching a quantum critical point through changing the ratio of Oxygen-16 to Oxygen-18 isotopes in strontium titanate, the electro-optic and piezoelectric nonlinearities are enhanced even further at cryogenic temperatures. This breakthrough will enable devices such as transducers, cryogenic piezoelectric positioners, and modular quantum computers.

Stage of Development: Proof of Concept