Quantum machines have the potential to serve as groundbreaking tools for scientific discovery in the coming decades. As the complexity of these devices increases, it may be necessary to borrow ideas from complex classical systems, and build them in a modular fashion, with independently designed, optimized, and tested components, networked together into a functioning whole. To build a modular machine from superconducting circuits requires the ability to perform operations between quantum bits housed in separate modules. For this, we must be able to move qubits between modules, or generate entanglement across the network, conveying information in the form of photons. In all implementations to date, photon loss in the links between modules is a dominant source of error, which must be overcome in order to build a scalable modular machine. We demonstrate two approaches for rapid and faithful quantum communication and entanglement between modules in a superconducting quantum network. Encoding information in cavity resonators allows application of strategies for error mitigation in harmonic oscillators to detect photon loss in the communication path. Using a low-loss communication bus, we transfer a qubit in a multi-photon encoding and track loss events to improve the fidelity. Furthermore, generating entanglement with two-photon interference and post-selection against loss errors produces a Bell state with half the error obtained in the single photon case. We discuss several routes towards high-fidelity operations in superconducting quantum networks based off these tools.
Thesis Advisor: Prof. Rob Schoelkopf
Prof. Michel Devoret
Prof. Steven Girvin
Prof. Jack Harris