Zhi-Yuan Wei

Super-Logarithmic Entanglement Scaling in a Monitored Superconducting Chain

  1. Rui-Jing Guo,
  2. and Zhi-Yuan Wei
We develop a Keldysh-replica non-linear sigma model (NLSM) for the entanglement dynamics of a monitored one-dimensional spinful s-wave BCS chain in the rare-measurement regime, γ≪J,Δ.
Although the clean spinful s-wave BCS Hamiltonian belongs to symmetry class CI, spin-resolved measurements and projection to a conserved f-sector reduce the effective problem to class C. Starting from the corresponding parent symplectic saddle, we show that measurement backaction and the pairing amplitude impose complementary mass constraints that gap out different fluctuation channels. Their interplay dynamically projects the surviving massless modes onto an SO(R) target manifold in replica space. A one-loop renormalization group analysis of this SO(R) NLSM shows that, in the replica limit R→1, the beta function becomes negative, producing a weak-anti-localization flow. This flow yields a super-logarithmic steady-state entanglement scaling S(L)∼ln2L in the rare-measurement regime. Our field-theoretic result explains the numerical evidence reported in the companion Letter [arXiv:2604.04375] and shows that a topologically trivial monitored s-wave superconductor can realize an SO(R) weak-anti-localizing critical phase without relying on a Wess-Zumino-Witten term.
arxiv pdf

Generation of photonic tensor network states with Circuit QED

  1. Zhi-Yuan Wei,
  2. J. Ignacio Cirac,
  3. and Daniel Malz
We propose a circuit QED platform and protocol to deterministically generate microwave photonic tensor network states. We first show that using a microwave cavity as ancilla and a transmon
qubit as emitter is a favorable platform to produce photonic matrix-product states. The ancilla cavity combines a large controllable Hilbert space with a long coherence time, which we predict translates into a high number of entangled photons and states with a high bond dimension. Going beyond this paradigm, we then consider a natural generalization of this platform, in which several cavity–qubit pairs are coupled to form a chain. The photonic states thus produced feature a two-dimensional entanglement structure and are readily interpreted as radial plaquette projected entangled pair states, which include many paradigmatic states, such as the broad class of isometric tensor network states, graph states, string-net states.
arxiv pdf