Engineering high Pockels coefficients in thin-film strontium titanate for cryogenic quantum electro-optic applications

TL;DR

This paper demonstrates that by engineering the stoichiometry of thin-film strontium titanate, it is possible to achieve record-high Pockels coefficients at cryogenic temperatures, surpassing traditional materials used in quantum photonics.

Contribution

The study shows that the Pockels effect in SrTiO3 can be enhanced at cryogenic temperatures through stoichiometric adjustments, creating a new pathway for quantum electro-optic devices.

Findings

Achieved an effective Pockels coefficient of 345 pm/V in engineered SrTiO3 at cryogenic temperatures.

Engineered SrTiO3 exhibits ferroelectric phase with high Pockels coefficient and low optical losses.

Demonstrated that Pockels coefficients can be increased at cryogenic temperatures, contrary to previous assumptions.

Abstract

Materials which exhibit the Pockels effect are notable for their strong electro-optic interaction and rapid response times and are therefore used extensively in classical electro-optic components for data and telecommunication applications. Yet many materials optimized for room-temperature operation see their Pockels coefficients at cryogenic temperatures significantly reduced - a major hurdle for emerging quantum technologies which have even more rigorous demands than their classical counterpart. A noted example is $\mathrm{BaTiO_3}$, which features the strongest effective Pockels coefficient at room temperature, only to see it reduced to a third (i.e. $\mathrm{r_{eff}} \approx$ 170 pm/V) at a few Kelvin. Here, we show that this behaviour is not inherent and can even be reversed: Strontium titanate ($\mathrm{SrTiO_3}$), a material normally not featuring a Pockels coefficient, can be engineered to exhibit an $\mathrm{r_{eff}}$ of 345 pm/V at cryogenic temperatures - a record value in any thin-film electro-optic material. By adjusting the stoichiometry, we can increase the Curie temperature and realise a ferroelectric phase that yields a high Pockels coefficient, yet with limited optical losses - on the order of decibels per centimetre. Our findings position $\mathrm{SrTiO_3}$ as one of the most promising materials for cryogenic quantum photonics applications.