arXiv:2610.38704
Gravitational anomaly spectroscopy of a Kitaev spin liquid
Kumar Ghosh
Abstract
The chiral central charge $c$ measures the gravitational anomaly of a two-dimensional topological phase. It fixes the heat current carried along the edge. So far, it has been accessed through thermal transport, where phonons complicate the signal, or through wave-function probes that need a pure ground state. Here we show that $c$ is a spectroscopic quantity of the edge. A weak modulation of the edge couplings that travel along the edge is absorbed according to the Virasoro algebra. Normalized by the response to a static change of the same couplings, the absorbed weights obey $D_n=2n\langle L_0\rangle+\frac{c}{12}(n^3-n)$, so that $\mathcal{C}\equiv2D_2-4D_1=c$ in any state of the ideal edge theory, thermal or not. The central charge thus appears in transition weights, although it cancels from excitation gaps. The ratio of line weights with and without a vison in the bulk, $Λ=4h_σ/c$, needs no calibration and fixes the conformal spin $h_σ$ of the non-Abelian Ising anyon. For the Kitaev honeycomb spin liquid we find $\mathcal{C}=0.49999$ and $h_σ=0.06250$ on 7168 spins. Calibrating with the shift of the measured line itself gives $c$ within about $1\%$ on 96 spins and within $1\%$ under $20\%$ random coupling errors. Interacting edge Majoranas in a fixed flux sector, treated with DMRG, keep $\mathcal{C}$ within $1.5\%$ while the edge velocity changes by $\pm13\%$. An exact simulation of a quantum-processor protocol, including the native Floquet circuit, returns $c$ within $3.5\%$ on 96 to 600 spins.
AI Summary
Can the chiral central charge of a two-dimensional topological phase be extracted from edge spectroscopy without thermal transport or pure-state tomography? This paper proposes a traveling modulation of edge couplings that projects onto stress-tensor modes. Normalizing directional absorption weights by the edge-level-spacing response to a static modulation gives $D_n=2n\langle L_0\rangle+c(n^3-n)/12$. Consequently, $2D_2-4D_1=c$ independently of the ideal edge-CFT state. A ground-state line-weight ratio between sectors with and without a bulk vison gives $4h_\sigma/c$, providing access to the Ising anyon’s conformal spin. Exact free-Majorana calculations for the Kitaev honeycomb model yield $c=0.49999$ and $h_\sigma=0.06250$ on 7,168 spins. Calibration using the measured absorption line’s own frequency shift reduces finite-size errors: a 96-spin flake gives $|c|=0.5055$. Tests include thermal and nonstationary edge states, static visons and random couplings; suitable flakes remain within about $1\%$ under $20\%$ coupling errors. Fixed-flux-sector DMRG with four-Majorana interactions finds variation within $1.5\%$ while edge velocities change by approximately $\pm13\%$. Processor readouts and a native Floquet circuit are simulated separately. Echo simulations recover $c$ within $3.5\%$ on 96–600 spins, but assume pure initial states; correlator readout supports mixed states. Proposed measurements require roughly $25/J$ coherent evolution and $10^5$–$10^6$ shots per setting. Limitations include bulk-quasiparticle contamination, dispersion curvature, boundary-mode control and decoherence-induced spectral leakage. Interactions are tested only with fixed gauge flux; the full Kitaev–Heisenberg/field problem and multibranch edges remain open.
Error found: The abstract omits that the calibration-free identity Λ = 4h_σ/c is established for the two sector ground states, rather than arbitrary edge states. The abstract describes the processor-protocol accuracy as including the native Floquet circuit, although the reported echo-protocol and Floquet-Hamiltonian spectroscopy simulations are separate tests.
Written by gpt-6.1-sol from the paper's full text. Automated: it can be wrong.
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- 10 pages 5 figures