Magnetless superconducting microwave isolators and circulators for quantum applications
Abstract
Magnetless superconducting microwave isolators and circulators for quantum applications Circulators and isolators are simultaneously one of the most important enabling technologies for superconducting-qubit devices and one of the primary bottlenecks to scalability. Every single high- fidelity readout system for superconducting qubits needs an isolator or a circulator. In particular, quantum-limited Josephson-junction-based amplifiers require circulators/isolators to route signals and prevent unwanted pump tones and amplifier tones from returning to the readout resonator and the qubit. Currently, off-the-shelf circulator/isolator devices are exclusively ferrite based and require magnetic biasing, which in turn necessitates bulky shielding and separate isolated packaging to protect the delicate qubits. As a result, when compared to the planar microfabricated superconducting quantum devices that they support, ferrite circulators/isolators occupy orders of magnitude greater volume and present a major scaling challenge. Moreover, these devices exhibit unavoidable insertion loss, and a concomitant loss in amplifier performance is suffered, meaning that in practice these devices are used extremely sparingly. Every additional circulator/isolator stage represents a significant cost both in space inside the cryogenic environment and in terms of signal-to-noise in the detection chain. We propose a novel architecture for magnetless circulators and isolators that can overcome all of the above challenges and offer a clear path to scalability. The proposed devices will exhibit ultra-low insertion loss, will be electrically driven, and can be co-fabricated on the same chip as the qubit systems that they support, and are therefore highly suitable for use in conjunction with Josephson-junction quantum amplifiers. Our device architecture leverages a ring-resonator design that has previously been implemented in the optical-frequency domain, and produced record-setting isolation. We expect that a microwave implementation of this innovative design could approach ideal circulator/isolator behavior in which the device is essentially invisible to any forward-propagating signal within the feedline, and simultaneously produces strong absorption for signals propagating in the opposite direction. In order to achieve these goals, we adopt a two-pronged strategy which makes use of parallel development and characterization of room temperature (RT) and superconducting (SC) implementations. This project will lead to the development of magnetless circulators and isolators for the microwave domain that operate in the single/few-photon regime required for superconducting qubit readout, exhibit ultralow insertion loss, and that do not require separate packaging and shielding. These devices will constitute a significant advance in the state of the art of on-chip magnetless microwave isolators and circulators and will be the springboard for future work to implement optimized designs capable of outperforming current ferrite devices for narrowband isolation tasks such as quantum-limited amplification of qubit readout signals, simultaneously improving the effective noise performance of Josephson amplifiers, thereby enabling faster high-fidelity readout, and increasing the number of output channels possible per unit cryogenic volume.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 24, 2023
- Source ID
- W911NF2310219
Entities
People
- Alicia Kollar
Organizations
- Army Contracting Command
- United States Army
- University of Maryland