Symmetry-Protected Qubits and Non-Reciprocal Devices: Building Blocks for Superconducting Quantum Hardware, Dr. Chen-How Huang, University of Jyväskylä

Thursday 30 Jul 2026, 14:00 → 16:00 Asia/Taipei

Physics/019 (NTHU)

Scalable quantum computing requires two distinct ingredients: qubits that store information
robustly, and devices that route and control quantum signals between them. This seminar
presents two results, one for each ingredient, unified by a common design principle: symmetry
protection can be engineered rather than merely observed. On the qubit side, we propose a
spin-singlet qubit realized in triangulene spin-1 chains coupled to a superconducting substrate.
Using the numerical renormalization group (NRG), we identify a pair of low-lying singlet states,
isolated from opposite-parity doublets by an avoided crossing, that is intrinsically protected
against random Zeeman and spin-orbit noise. On the device side, we address non-reciprocal
multi-terminal microwave components such as circulators, which are central to next-generation
scalable circuit quantum electrodynamics (cQED). The standard criterion, that both time-reversal
and spatial inversion must be broken, states only whether non-reciprocity can exist. It does not
predict which of the many inequivalent multi-terminal responses are allowed, nor how the device
geometry selects among them. We close this gap with a group-theoretical classification that
partitions all possible response configurations into symmetry orbits and yields explicit selection
rules linking device geometry to admissible circulator-type responses, validated on a minimal
quantum-dot model. Together, these results outline a research programme in which symmetry
principles guide the design of both the information-storage and the signal-routing components of
superconducting quantum hardware for quantum computers.