In the two decades since the beginning of the field, dramatic progress has been made towards realizing solid-state systems for quantum information processing with superconducting circuits. Superconducting qubits have improved their coherence by more than a million-fold, and they have also proven to be a wonderful platform for exploring the concepts of entanglement, quantum information, and quantum measurement.
The next challenge for the field is demonstrating quantum error correction (QEC) that actually improves the lifetimes of superpositions and entangled states and makes these systems robust by increasing the fidelity of gates. Today this topic is entering an exciting new stage, where experiment and theory begin to productively overlap, and one can begin to “co-design” the quantum hardware and QEC codes to other’s strengths.
At Yale, our team has been pursuing a novel, “hardware-efficient” approach for quantum error correction, based on encoding information in the multiple energy levels of a harmonic oscillator such as a microwave cavity. By allowing for redundancy without necessarily introducing more error channels, the “cat code” and other such bosonic error correction codes allow us to experimentally explore the concepts and the practice of QEC today, with smaller and less complex systems. Recent experimental breakthroughs (https://arxiv.org/abs/2212.11929) on this type of quantum hardware and has dramatically improved our ability to perform high-fidelity operations.
I will present a new architecture for bosonic error correction (https://arxiv.org/abs/2212.12077) which adapts and extends the well known “dual-rail” encoding, where a single photon can be superposed between two distinguishable microwave cavity modes. When the techniques of circuit QED are applied to this system, we can develop a full family of universal gates (https://arxiv.org/abs/2212.11196) in which all of the known decoherence errors can be efficiently detected, allowing postselected gate fidelities higher than any other solid-state platform. I will show recent experimental results confirming that this scheme can reach remarkably high levels of performance on several metrics. Finally, if these qubits are implemented in a higher-level scheme such as a surface code, the dominant errors can be converted to erasures, easing the required performance levels by orders of magnitude. This approach therefore opens a new and dramatically faster path to fault-tolerant computing.
Robert Schoelkopf is the Sterling Professor of Applied Physics and Physics at Yale University, and the Founding Director of the Yale Quantum Institute. His research focuses on the development of superconducting devices for quantum information processing, which are leading to revolutionary advances in computing. He and his collaborators founded the field of circuit quantum electrodynamics and have produced many firsts in the field of solid-state quantum computing, including the development of the transmon qubit, a “quantum bus” for information, and the first demonstrations of quantum algorithms and quantum error correction with integrated circuits.
Schoelkopf, who came to Yale as a postdoctoral researcher in 1995, joined the faculty in 1998, becoming a full professor in 2003. In 2015, he and his colleagues founded Quantum Circuits, Inc., a venture-backed startup in New Haven working to build the world’s first useful quantum computers.
Professor Schoelkopf’s work has been recognized with several honors and awards, including the Joseph F. Keithley Award of the American Physical Society (2009), the John Stewart Bell Prize (2013, with Michel Devoret )for fundamental and pioneering experimental advances in superconducting qubits, the Fritz London Memorial Prize for Low Temperature Physics (2014, with Devoret and John Martinis), the Max Planck Forschungspreis (2014), and the CT Medal of Science (2017). In 2015, Professor Schoelkopf was elected to the National Academy of Science.
This seminar is supported with funds from the Korhammer Lecture Series.