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

The article you provided presents research on engineering high Pockels coefficients in thin-film strontium titanate (SrTiO3) for cryogenic quantum electro-optic applications. The Pockels effect, which refers to a material's electro-optic response, is critical in technologies like quantum transduction. Traditional materials, like barium titanate (BaTiO3), suffer from reduced Pockels coefficients at cryogenic temperatures, limiting their use in quantum applications. However, this research shows that SrTiO3, typically not known for its Pockels effect, can be engineered to exhibit a substantial Pockels coefficient of 345 pm/V at 4K, the highest ever recorded for thin-film electro-optic materials.

The study demonstrates that adjusting SrTiO3's stoichiometry and applying strain can enhance its Curie temperature (TC), enabling the material to transition into a ferroelectric phase that supports a strong electro-optic effect. This transition occurs at cryogenic temperatures (≈100 K), avoiding quantum paraelectric behavior that would otherwise prevent the development of a non-zero Pockels coefficient.

Additionally, the material's optical losses are low (around 5.5 dB/cm), which is crucial for maintaining high-performance in quantum applications. The findings highlight the potential of SrTiO3 in quantum photonics, as it surpasses traditional Pockels materials, offering a route for further optimization through material engineering (stoichiometry, strain, doping).

In terms of electro-optic interaction strength, the study employs a Mach-Zehnder interferometer to measure SrTiO3's electro-optic properties, revealing high modulation efficiency and a voltage length product of approximately 1.04 Vcm at 4K. The research also identifies bandwidth measurements up to 1 MHz and discusses the challenges of reducing optical losses for integration into quantum photonic systems.

In conclusion, SrTiO3 is positioned as a promising material for future quantum electro-optic systems, combining high Pockels coefficients with low optical losses, and providing insights into material engineering strategies to further enhance its performance for cryogenic applications.