Quantum Algorithm for Fidelity Estimation

Publisher:
Institute of Electrical and Electronics Engineers (IEEE)
Publication Type:
Journal Article
Citation:
IEEE Transactions on Information Theory, 2023, 69, (1), pp. 273-282
Issue Date:
2023-01-01
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For two unknown mixed quantum states ρ and σ in an N-dimensional Hilbert space, computing their fidelity F (ρ, σ) is a basic problem with many important applications in quantum computing and quantum information, for example verification and characterization of the outputs of a quantum computer, and design and analysis of quantum algorithms. In this paper, we propose a quantum algorithm that solves this problem in poly(log(N), r, 1/ϵ) time, where r is the lower rank of ρ and σ, and ϵ is the desired precision, provided that the purifications of ρ and σ are prepared by quantum oracles. This algorithm exhibits an exponential speedup over the best known algorithm (based on quantum state tomography) which has time complexity polynomial in N.
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