Superconducting quantum systems

Quantum systems that use the phenomenon of superconductivity are at the forefront of quantum computing, quantum sensing and various planned fundamental physics experiments.

These systems rely on the superposition of quantum states, which eventually collapse into a single state. The effectiveness of quantum systems depends a great deal on the length of time the superposition state survives, a quantity called coherence time. The longer the coherence time, the more time is available for the quantum system to perform operations.

For quantum computing, 3-D circuit architecture of qubits — units of quantum information — currently holds the highest coherence times among all superconductivity-based qubits.

A key enabling part of this architecture is 3-D-microwave resonators, structures that store and allow manipulation of electromagnetic fields. The resonators’ ability to retain energy can be measured by something called the quality factor, or Q, which directly affects the achievable coherence times. Fermilab is the world leader in both the underlying science and building and operating the full-scale particle accelerators based on ultrahigh-Q superconducting radio-frequency (SRF) resonators. We are working to apply this expertise to the field of quantum systems.

The current state-of-the-art Q value for quantum computing systems is roughly 1×108, corresponding to coherence times of about 1 millisecond. Fermilab-designed and surface engineered SRF resonators, built for accelerators, routinely achieve a Q value of more than 3×1010 in the broad range of microwave fields, with record cavities possessing a Q of more than 2×1011. This is more than 1,000 times better than best resonators currently employed in quantum computing. If such Q factors could be directly translated to the quantum regime, the potential coherence times of such SRF/3-D qubits could be more than 1 second, enabling a range of qualitatively different capabilities of quantum computing.

One of the main goals of Fermilab’s Superconducting Quantum Systems program is to demonstrate such ultrahigh-Q SRF/3-D qubits with the record long coherence times, and ultimately to put a number of them together in a multiqubit “quantum computer” type system.

University of Wisconsin-Madison and the National Institute of Standards and Technology are collaborators on this initiative.