Quantum information science promises fundamentally new and vastly more powerful paradigms of computation, sensing, and communications. It also necessitates new classes of devices that are capable of processing quantum signals. One promising approach to engineered quantum systems uses low-temperature superconducting circuits to perform quantum information processing. These quantum machines are now being developed actively in academic, government, and industrial labs around the world. However, there is no way to connect these systems to one another across more than a few inches while preserving their important quantum properties. Creating links that traverse longer distances and leave the low temperature environments of the qubits demands converting the quantum information from a form suited for processing to another form suited for transmission, and vice versa. In fact, all computation, sensing, and communication systems depend on devices that convert information from one form to another. The lack of this capability in the quantum domain impedes the emergence of truly compelling quantum technologies that promise to perform tasks beyond the means of today's technologies. The proposed research effort is focused on creating such a capability to address a basic and long-standing challenge in engineering science. The program will develop and demonstrate a device that can convert quantum information across the electromagnetic spectrum while preserving its important quantum properties. Such a device, a quantum electro-optic converter, will convert information between optical photons capable of travelling long distances, and microwave photons in low-temperature superconducting circuits being used to implement the first quantum computers. Much like the electro-optic modulators that enable the Internet, quantum electro-optic converters may someday enable the quantum Internet.
The objective of this research is to develop a device that can interconvert quantum information between optical and microwave frequencies. The approach is to fabricate high-Q optical cavities and microwave superconducting cavities on the same electro-optical substrate, heterogeneously integrated silicon on lithium niobate, and to generate interactions between excitations in the two cavities. To achieve this, recently developed techniques for creating high-Q electro-optic photonic crystal cavities, techniques for making high-Q superconducting inductors with very low stray capacitance, as well as theoretical insight on perfect quantum state conversion methods will be used. The PI's lab will develop the technology for quantum electro-optic converters by advancing and synthesizing techniques from photonics, heterogeneous integration, superconducting circuits, and cryogenic optical and microwave experiments to realize this vision. The quantum electro-optic converter being developed in this program promises to 1) connect these quantum machines to each other, 2) allow optical access to quantum nonlinearities at microwave frequencies, and 3) to simplify their scaling to larger numbers of superconducting qubits by allowing multiplexing of many microwave signals over an optical fiber. This will have a major impact on experimental quantum information science. Finally, the device will demonstrate for the first time quantum optical control of microwave circuits using laser light, which can enable new and unforeseen types of quantum sensing and communications capabilities at microwave frequencies.