Qian Xu [Caltech]

Talk Title: High-rate quantum processors: Rethinking fault-tolerant architectures

Abstract: Quantum error correction can make imperfect qubits reliable, but a useful quantum computer must also manipulate the protected information. Can we encode many logical qubits with little redundancy while retaining flexible control and fast computation? I will focus on our recent works on designing quantum processors with high-rate quantum low-density parity-check (qLDPC) codes. We introduce finite-size codes that combine high encoding rates of 20–30%, practical block sizes, and sufficient error protection. By constructing a structured logical basis and leveraging code symmetries, we can build a universal logical instruction set from a few gadgets with rigorously certified fault tolerance. For instance, as few as two reusable ancillary surgery gadgets, supplemented with magic-state input, enable universal logical processing. Using fast decoders compatible with real-time operation, direct simulations support logical computation involving more than ten billion operations. These processors further support highly parallel logic: some codes can perform hundreds of logical operations simultaneously, allowing logical parallelism to compensate for a slow physical clock. I will also discuss the compatibility of these designs with reconfigurable neutral-atom arrays and superconducting circuits. Together, these results point toward architectures that combine high encoding density, computational flexibility, and speed, opening new routes toward resource-efficient quantum computers capable of executing utility-scale algorithms.

Research interests: Quantum error correction; Fault-tolerant quantum computing

Notes:

• Main talk will begin @ 11:30 am in PAB 102/103
• Boxed lunch will available for attendees @ 12:30 pm in PAB 102/103
• Video Recordings once Speaker approved, will be available on our youtube channel
• On-site seminar attendance is limited to Stanford students, faculty, staff, and invited guests. Everyone is welcome to join via Zoom.