Wisconsin Alumni Research Foundation

Information Technology
Information Technology
Qubit Measurement System Is Efficient, Scalable
WARF: P140246US01

Inventors: Robert McDermott, Frank Wilhelm-Mauch, Britton Plourde, Maxim Vavilov, Luke Govia, Emily Pritchett

The Wisconsin Alumni Research Foundation (WARF) is seeking commercial partners interested in developing new hardware for the scalable measurement of quantum bits.
In the field of quantum computing, the performance of quantum bits (‘qubits’) has advanced rapidly in recent years. A truly scalable system requires the ability to rapidly and accurately measure qubits while minimizing costly resources. Conventional measurement methods rely on superconducting amplifiers and heterodyne detectors.

While this approach works well for a small number of readout channels, the various components entail significant overhead. Needed is a new approach that achieves high performance with fewer components and reduced overhead.
The Invention
UW–Madison researchers have developed a novel qubit measurement system based on counting microwave photons. The new system replaces currently used amplification and heterodyne detection techniques.

The measurement proceeds in three stages. First, the state of the qubit is mapped to the microwave photon occupation of a readout cavity. The occupation of the cavity is subsequently detected using the Josephson photomultiplier (JPM), a microwave-frequency photon counter. The measurement leads to a binary digital output: ‘click’ or ‘no click.’ The output may be transmitted to a single flux quantum (SFQ) circuit for classical processing.

SFQ circuits, like qubit circuits, are based on superconducting thin films. Therefore, the SFQ processor could be operated on the same cryogenic stage as the quantum circuit to make the system more compact and to reduce measurement latency. Other methods rely on wiring and electrical connections to take measurements and feed them to a room-temperature device for processing, resulting in losses and inefficiencies.
  • Quantum computing hardware
Key Benefits
  • Achieves high-fidelity qubit measurement
  • Method is efficient, scalable and amenable to further processing.
  • Measurement result is amenable to further processing by SFQ digital logic.
  • JPM circuit detectors have many advantages
    • Utilize relatively low-bandwidth DC wiring
    • More compact
    • Interface naturally with SFQ logic circuits
    • Help mitigate heat load/footprint caused by system connections
    • Support high-fidelity parity measurement for error detection
Stage of Development
The researchers have performed promising simulations and preliminary experiments
Additional Information
For More Information About the Inventors
  • Govia L.C.G., Pritchett E.J., Xu C., Plourde B.L.T., Vavilov M.G., Wilhelm F.K. and McDermott R. 2014. High-fidelity Qubit Measurement with a Microwave-photon Counter. Phys. Rev. A.
For current licensing status, please contact Emily Bauer at [javascript protected email address] or 608-960-9842