Periodic Reporting for period 1 - Q-AMP (quantum electro-optic amplifiers for the next generation quantum and supercomputers)
Reporting period: 2022-09-01 to 2025-02-28
In today's rapidly evolving technological landscape, quantum computers face significant challenges in scaling the number of qubits and enhancing computational power. A critical bottleneck for superconducting qubits lies in the radio frequency (RF) connections between the qubit processor inside the cryostat and the room temperature control and readout electronics.To overcome this, the project proposes replacing RF-links with optical fibers, creating a hybrid setup where RF-qubits handle computation and optical qubits manage remote communication. The elusive goal has been to develop electro-optical (EO) transducers that can parametrize RF-qubits directly to optical qubits with unity efficiency. Achieving this unity efficiency requires materials with low losses, strong nonlinearities, and the ability to confine the electromagnetic field within the smallest volumes.Q-Amp aims to revolutionize this field by introducing a new generation of EO-amplifiers, specifically designed to achieve the necessary unity efficiency and address current limitations. Traditional EO-architectures face a trade-off between EO interaction strength (g) and EO losses (Q-factors), as enhancing g often necessitates close proximity between the RF-superconducting circuit and the optical waveguide, thus increasing EO losses.The innovative technology from Q-Amp will enhance g without requiring superconductors and optical waveguides to be in close vicinity. This breakthrough is expected to significantly advance superconducting quantum computers, providing high-speed EO gateways essential for both classical superconducting supercomputers and next-generation quantum systems. By addressing current scaling limitations, the project will meet growing demands for computational power and efficiency.In summary, the Q-Amp project sets the stage for a transformative journey in quantum computing, with its innovative EO-amplifiers poised to tackle identified problems and needs, while also promising novel applications.
During the project, we performed DC to RF spectroscopy of thin-film strontium titanate (STO) across a range of temperatures from 4K to 293K to identify ferroelectric or quantum paraelectric phases. This was used in close collaboration with the material scientist to optimize the growth procedure on silicon substrates. For STO films we deemed most promising we performed 200mm wafer bonding on oxide to explore optical properties via PMMA-loaded waveguides and Mach-Zehnder interferometers, which were controlled by electrical signals via integrated electrodes.
Our main achievements included demonstrating the feasibility of STO as a high-k material with a large permittivity greater than 2000 and low RF losses with a tan delta of less than or equal to 10⁻³. We achieved optical losses of <10 dB/cm in STO, challenging its previous perception as a lossy optical material and identified STO as a cryogenic nonlinear material with electro-optical properties surpassing those of Lithium Niobate.
Our main achievements included demonstrating the feasibility of STO as a high-k material with a large permittivity greater than 2000 and low RF losses with a tan delta of less than or equal to 10⁻³. We achieved optical losses of <10 dB/cm in STO, challenging its previous perception as a lossy optical material and identified STO as a cryogenic nonlinear material with electro-optical properties surpassing those of Lithium Niobate.
The ERC project ventured into uncharted territory by re-discovering strontium titanate (STO) not only as a high-K material but also as an exceptional electro-optical material at cryogenic temperatures. Unlike prior research focusing on bulk crystals [Anderson et al., “Quantum Critical Electro-Optic Materials for Photonics.”], our work concentrated on thin-film STO. Notably, certain parameters of thin-film STO show nonlinear coefficients beyond LiNbO3, a leading thin-film material or any other nonlinear material at cryogenic temperatures. The unexpected discovery of STO's potential as a strong electro-optical material represents a significant breakthrough and might have implications for quantum technology, as it provides a novel electro-optical material that could drive future innovations in the field such as optical readout of superconducting quantum comptures.
[1] Ulrich, A. et al. Engineering high pockels coefficients in thin-film strontium titanate for cryogenic quantum electro-optic applications. arXiv preprint (2025).
https://doi.org/10.48550/arXiv.2502.14349(opens in new window)
[1] Ulrich, A. et al. Engineering high pockels coefficients in thin-film strontium titanate for cryogenic quantum electro-optic applications. arXiv preprint (2025).
https://doi.org/10.48550/arXiv.2502.14349(opens in new window)