Towards Fault-Tolerant Bosonic Quantum Computation
Abstract
This is a joint experiment/theory proposal to advance a novel hybrid circuit QED platform in which high coherence microwave resonators provide long-lived quantum states that can be controlled via ancilla qubits. The main goal of this proposal is to realize performance that is provably well beyond the threshold for extensible fault-tolerant computing with cluster state or biased-noise surface codes and lay the groundwork for a new and more practical scaling to large-scale quantum computing than the traditional surface code with simple transmons. Our collaboration is taking a Òfull-stackÓ approach, built out of four complementary thrusts: (I) Predictions for scalability that analyze the behavior of concatenated QEC based on experimental parameters and measurements, (II) Smart bosonic logic in which we construct and test robust and high-fidelity gates and logical operations on several types of bosonic logical qubits, (III) Quantum control where we will advance and improve the capabilities for primitive operations that are the building blocks for this work with bosonic systems, and (IV) Devices and coherence, which will develop novel devices and implementations of superconducting circuits, and increase their coherence times. We have demonstrated in previous work that our hybrid qubit/cavity architecture offers great advantages in terms of hardware efficiency, error correction and the ability to realize protocols that are tolerant of certain faults. We will improve fidelity in two ways, first by improving the performance of the primitive bosonic operations, and second by implementing fault-tolerant quantum error correction (distance 3) at the hardware level. We aim to achieve fidelity of these operations of 99.9% or better, by exploring a variety of strategies and bosonic encodings. Because the inherent robustness of these operations can offer first-order immunity to the dominant error processes, we will also show that their fidelity increases quadratically, rather than linearly, with qubit and cavity coherence times. This approach will therefore scale faster and reap greater benefits as basic devices and materials continue to improve. Progress towards the long-term goal of system-level fault tolerance requires not only fidelities that are much better than the QEC threshold, but an understanding and control of the types of errors. By realizing noise-biased qubits and noise-preserving operations, for instance, we intend to show that thresholds and hardware overheads for error-correction can be significantly reduced. Therefore, we will perform error metrology on our new family of operations and use the actual experimental behavior to predict the improvements in overhead and scaling that can be obtained. Finally, we will continue our efforts to better understand decoherence processes and design devices which improve the underlying coherence times of cavities, transmons, and other non-linear Josephson devices. These device improvements will be key enablers for our other goals, which together will demonstrate a faster path to fully fault-tolerant quantum computing with superconducting circuits.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 19, 2023
- Source ID
- W911NF2310051
Entities
People
- Robert J. Schoelkopf
Organizations
- Army Contracting Command
- United States Army
- Yale University