Commercial Production of Low-Loss Quantum Frequency Conversion and Electro-Optical Modulation Devices Enabled by Wafer-Level Processing of Reverse-Proton-Exchange Lithium Niobate Waveguides

Fiber-based quantum networks can utilize existing infrastructure and heavily optimized fiber optic-based systems in the telecommunications band; however, the quantum information to be transported across the quantum network is often generated or manipulated outside of the telecom range. Quantum frequency conversion, or tailoring the wavelength of a photonic qubit, can be utilized to transfer information to or from the quantum network while maintaining the qubits’ quantum information. Additionally, electro-optic phase and amplitude modulators find a range of applications in quantum networking including quantum information and quantum communications. The work proposed herein will expand the range of commercially available quantum frequency conversion and modulator devices while achieving low device insertion loss and low noise which is critical for quantum network applications, as requested in the United States Department of Energy Small Business Innovation Research Program, fiscal year 2021, Topic 6a: Transparent Optical Quantum Network Devices. The overall goal of this program is to fabricate highly efficient, extremely low loss, low noise, fiber-coupled, lithium niobate waveguide-based quantum network devices for quantum frequency conversion and phase and amplitude modulation. The key innovation of this project is using wafer-level processing to enable commercial production of low-loss (<1.5 dB fiber-to-fiber) reverse-proton-exchanged waveguides in lithium niobate with optimized parameters for quantum frequency conversion and electro-optic modulation. Because the applications of reverse-proton-exchange lithium niobate are diverse and include quantum frequency conversion and modulation among others, the effort proposed herein enables the use of the same technology for these differing functions. The specific goal of this Phase I effort is to establish the feasibility of fabricating low loss wafer-level reverse- proton-exchange waveguides in lithium niobate. The reverse-proton-exchange processing steps will first be modified to allow for wafer-level processing of lithium niobate waveguides by introducing a temperature ramping process and utilizing a platinum mesh basket for placing the lithium niobate wafers in the high-temperature reverse-proton-exchange bath. Then, chips intended for both quantum frequency conversion and modulation that are fully processed at the wafer level will be tested to verify high efficiency and low propagation loss. Successful demonstration of high conversion efficiency and low propagation loss in wafer-level reverse-proton-exchange is the first step in increasing the commercial availability of quantum frequency conversion and modulation devices while moving toward amplified production capability and decreased device cost, thereby making these technologies more accessible to researchers in quantum network devices. Quantum frequency conversion and modulation devices find a range of applications including single photon detection at telecommunication wavelengths, entangled photon pair generation, connection of disparate matter qubit-based nodes, quantum cloning, quantum teleportation, and modulation of heralded single photons and entangled photon pairs. Common to all of these diverse applications, is the need for low-loss waveguides, low- loss coupling, high conversion efficiency, and low-noise operation. All of these topics will be investigated as part of this multi-phase project.