Trond Hjerpekjøn Haug, Quantum Technology

Abstract: Quantum computers are entering the era of fault tolerance, demonstrated by error-correction beyond break-even in platforms such as trapped ions, neutral atoms, and superconducting circuits in the last couple of years. With performance below the fault-tolerance threshold, the next big challenge is to scale up processors to achieve exponential error suppression. However, processors today are constrained to a single refrigeration unit which limits their size. A possible solution is to engineer optical interfaces to quantum processors so that they may be networked together into a larger, modular processor. In this seminar, I will present a protocol for building modular quantum processors from superconducting circuits equipped with noisy piezo-optomechanical quantum transducers. The transducers act as sources of heralded microwave-optical Bell pairs—a fundamental resource from which we can deterministically entangle optical photons in cluster states. I show how imperfections in the transducers translate to errors on the microwave-optical Bell pairs and discuss the severity of these errors for fault tolerance. Finally, I will give examples of how microwave-optical Bell pairs can be used to implement surface codes where Bell measurements are natural operations, such as in fusion-based quantum computation.

Discussion leader:  Anja Metelmann, Professor, Karlsruher Institut für Technologie

Main supervisor: Raphaël Van Laer, Assistant Professor, Quantum Technology Lab

Examiner: Per Delsing, Full Professor, Quantum Technology Lab

Assistant supervisor: Anton Frisk Kockum, Associate Professor, Applied Quantum Physics