Cryogenic piezoelectric effects in thin film strontium titanate devices

TL;DR

This paper demonstrates that strain-engineered thin-film strontium titanate exhibits exceptional cryogenic piezoelectric and electro-optic properties, enabling high-performance quantum photonic devices at low temperatures.

Contribution

It reports the first measurement of large cryogenic piezoelectric coefficients in strained SrTiO3 thin films and their application in a high-performance acousto-optic modulator.

Findings

Piezoelectric tensor elements of d15=151.8 pm/V and d33=54.8 pm/V at 5 K

Effective photoelastic coefficient p_eff=0.56 at 5 K

Achieved low-voltage acousto-optic modulation with V_pi*L of 0.874 V cm

Abstract

Next generation quantum technologies will need to rely on efficient transduction between electrical, optical, and mechanical quantum degrees of freedom to generate large-scale entanglement over large distances. The performance of such transducers is fundamentally limited by the cryogenic properties of the underlying materials. Here, we demonstrate that engineering strain in ferroelectric thin-film strontium titanate ($\mathrm{SrTiO_3}$) not only results in an exceptionally large Pockels coefficient, but also in a robust linear piezoelectric response at cryogenic temperatures, surpassing previous thin-film benchmarks. We measure piezoelectric tensor elements of $d_{15} = 151.8 \pm 1.5$ pm/V and $d_{33} = 54.8 \pm 4$ pm/V, and an effective photoelastic coefficient of $p_{\mathrm{eff}}$ = 0.56 at 5~K. Utilizing these enhanced properties, we demonstrate the first $\mathrm{SrTiO_3}$-on-oxide acousto-optic modulator with a voltage-length product ($V_{\pi}L$) of $0.874 \pm 0.084$ V cm, outperforming state-of-the-art unreleased modulators that typically feature a $V_{\pi}L$ of a few V cm. Our results establish thin-film $\mathrm{SrTiO_3}$ as a promising material system for integrated quantum photonics operating at cryogenic temperatures.