Quantum computers promise to harness the principles of quantum mechanics to perform certain tasks extremely quickly. In the near future, they will enable us to solve problems that are intractable even for the largest supercomputers today, such as simulating the behavior of new drug molecules, predicting the properties of novel materials, and factoring large numbers for cryptography. In order to get the maximum performance out of these new computers, it will be useful to connect them into networks much like today’s internet. However, because quantum signals are extremely fragile, quantum computers must be connected using optical fibers rather than normal wires which are inherently noisy at room temperature. The goal of our project is to create a microchip that will convert the microwave frequency electrical signals from a quantum processor into light signals which can be sent via an optical fiber. This chip will function as a dual-purpose transmitter and receiver, allowing quantum computers to be linked into a quantum network.
One approach we are pursuing combines electrical circuits and optical waveguides together on a single microchip and using an electro-optic material to exchange energy between electricity and light. The electro-optic material changes its refractive index under an applied electric field, thus encoding the quantum information in the electric field from a quantum processor onto photons. Another promising approach integrates the piezoelectric effect and photoelastic effect to achieve a refractive index change under an electric field. The electric field mechanically deforms the piezoelectric material, which then causes the refractive index change via the photoelastic effect.
The electro-optic converters benefit from the single-step conversion, and are relatively easy to design and fabricate, while the piezo-optomechanical converters could potentially offer higher conversion bandwidth but suffer from the design and fabrication complexity. They are equally promising candidates of quantum frequency converters for different application scenarios. The research field of electro-optic and piezo-optomechanical quantum frequency converters has seen rapid development, exploring different material platforms including gallium arsenide, aluminum nitride, and lithium niobate, and the figure of merits such as conversion efficiency and added noise have been constantly improving over orders of magnitude in the last five years.
Achieving highly efficient conversion requires optimization and integration of ultra-high performance of every component in the conversion system, and many technical challenges remain.