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Paper 1

State Decoding in Multi-Stage Cryptography Protocols

Sindhu Chitikela

Year

2013

Journal

arXiv preprint

DOI

arXiv:1306.5192

arXiv

1306.5192

This paper presents a practical method of quantum tomography for decoding the state of photons in a multistage cryptography protocol. This method works if the polarization angles are defined on a fixed plane, as is assumed in several quantum cryptography protocols. We show if there are 2m polarization angles in a fixed plane, we need m number of filters and m2 number of photons through each filter.

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Paper 2

Estimating and decoding coherent errors of QEC experiments with detector error models

Evangelia Takou, Kenneth R. Brown

Year

2025

Journal

arXiv preprint

DOI

arXiv:2510.23797

arXiv

2510.23797

Decoders of quantum error correction (QEC) experiments make decisions based on detected errors and the expected rates of error events, which together comprise a detector error model. Here we show that the syndrome history of QEC experiments is sufficient to detect and estimate coherent errors, removing the need for prior device benchmarking experiments. Importantly, our method shows that experimentally determined detector error models work equally well for both stochastic and coherent noise regimes. We model fully-coherent or fully-stochastic noise for repetition and surface codes and for various phenomenological and circuit-level noise scenarios, by employing Majorana and Monte Carlo simulators. We capture the interference of coherent errors, which appears as enhanced or suppressed physical error rates compared to the stochastic case, and also observe hyperedges that do not appear in the corresponding Pauli-twirled models. Finally, we decode the detector error models undergoing coherent noise and find different thresholds compared to detector error models built based on the stochastic noise assumption.

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