Photon-loss tolerance of the surface-GKP code with anti-photon-loss decoding

arXiv:2611.00694v1 Announce Type: new Abstract: Photon loss somewhat limits fault-tolerant photonic quantum computing. We investigate its effect on finite-energy Gottesman--Kitaev--Preskill (GKP) states by modeling the pure-loss channel directly. We obtain photon-loss threshold estimates for the surface-GKP code using nearest-lattice-point inner GKP decoding and minimum-weight perfect matching for the outer surface code. For GKP states with $\epsilon=0.01$ and $\epsilon=0.05$, corresponding to GKP squeezing of $20$ and $13\,\mathrm{dB}$, the estimated thresholds are $\gamma^\ast=5.5\%$ ($0.24\,\mathrm{dB}$) and $\gamma^\ast=5.9\%$ ($0.26\,\mathrm{dB}$), respectively. We then introduce an anti-photon-loss inner decoder that compensates for the contraction of the measured quadrature.