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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

The quantum smooth label cover problem is undecidable

Eric Culf, Kieran Mastel, Connor Paddock, Taro Spirig

Year

2025

Journal

arXiv preprint

DOI

arXiv:2510.03477

arXiv

2510.03477

We show that the quantum smooth label cover problem is undecidable and RE-hard. This sharply contrasts the quantum unique label cover problem, which can be decided efficiently by a result of Kempe, Regev, and Toner (FOCS'08). On the other hand, our result aligns with the RE-hardness of the quantum label cover problem, which follows from the celebrated MIP* = RE result of Ji, Natarajan, Vidick, Wright, and Yuen (ACM'21). Additionally, we show that the quantum oracularized smooth label cover problem is RE-hard. Our second result fits with the alternative quantum unique games conjecture recently proposed by Mousavi and Spirig (ITCS'25) on the RE-hardness of the quantum oracularized unique label cover problem. Our proof techniques include a quantum version of Feige's reduction from 3SAT to 3SAT5 (STOC'96) for BCSMIP*-protocols, which may be of independent interest.

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