Asymptotic Vanishing of the Success Probability in Shor's Algorithm

Fuente: arXiv
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Autor principal: da Cruz, João P.
Formato: Preprint
Publicado: 2025
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author da Cruz, João P.
author_facet da Cruz, João P.
contents Shor's factoring algorithm guarantees a success probability of at least one half for any fixed modulus N = pq with distinct primes p and q. We show that this guarantee does not extend to the asymptotic regime. As N -> infinity, the multiplicative groups Omega_N = (Z/NZ)^x form a non-tight family of probability spaces, and the probability weight associated with successful bases, proportional to p(success | a', N) p(a' | N), decays as 1/phi(N). The ensemble of uniform measures {mu_N} therefore admits no weak limit, implying an asymptotic loss of ergodicity. Monte Carlo simulations up to N <= 10^6 confirm this decay and the absence of a stationary success probability. These results demonstrate that the "expected polynomial time" in order finding is only locally defined: no global expectation exists once the arithmetic domain expands. The asymptotic vanishing of success probability explains the empirical absence of large-N implementations of Shor's algorithm and sets a fundamental limit on the scalability of quantum factoring.
format Preprint
id arxiv_https___arxiv_org_abs_2510_06271
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Asymptotic Vanishing of the Success Probability in Shor's Algorithm
da Cruz, João P.
Quantum Physics
Mathematical Physics
Computational Physics
Shor's factoring algorithm guarantees a success probability of at least one half for any fixed modulus N = pq with distinct primes p and q. We show that this guarantee does not extend to the asymptotic regime. As N -> infinity, the multiplicative groups Omega_N = (Z/NZ)^x form a non-tight family of probability spaces, and the probability weight associated with successful bases, proportional to p(success | a', N) p(a' | N), decays as 1/phi(N). The ensemble of uniform measures {mu_N} therefore admits no weak limit, implying an asymptotic loss of ergodicity. Monte Carlo simulations up to N <= 10^6 confirm this decay and the absence of a stationary success probability. These results demonstrate that the "expected polynomial time" in order finding is only locally defined: no global expectation exists once the arithmetic domain expands. The asymptotic vanishing of success probability explains the empirical absence of large-N implementations of Shor's algorithm and sets a fundamental limit on the scalability of quantum factoring.
title Asymptotic Vanishing of the Success Probability in Shor's Algorithm
topic Quantum Physics
Mathematical Physics
Computational Physics
url https://arxiv.org/abs/2510.06271