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Variational Quantum Fidelity Estimation

Journal Article · · Quantum
Computing quantum state fidelity will be important to verify and characterize states prepared on a quantum computer. In this work, we propose novel lower and upper bounds for the fidelity F(ρ,σ) based on the ``truncated fidelity'' F( ρm ,σ) , which is evaluated for a state ρm obtained by projecting ρ onto its m -largest eigenvalues. Our bounds can be refined, i.e., they tighten monotonically with m . To compute our bounds, we introduce a hybrid quantum-classical algorithm, called Variational Quantum Fidelity Estimation, that involves three steps: (1) variationally diagonalize ρ , (2) compute matrix elements of σ in the eigenbasis of ρ , and (3) combine these matrix elements to compute our bounds. Our algorithm is aimed at the case where σ is arbitrary and ρ is low rank, which we call low-rank fidelity estimation, and we prove that no classical algorithm can efficiently solve this problem under reasonable assumptions. Finally, we demonstrate that our bounds can detect quantum phase transitions and are often tighter than previously known computable bounds for realistic situations.
Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
National Science Foundation (NSF); US Air Force Office of Scientific Research (AFOSR); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
Grant/Contract Number:
89233218CNA000001
OSTI ID:
1659189
Report Number(s):
LA-UR--19-25585
Journal Information:
Quantum, Journal Name: Quantum Vol. 4; ISSN 2521-327X
Publisher:
Quantum Science Open CommunityCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (5)

Variational quantum algorithms journal August 2021
Variational quantum algorithm for estimating the quantum Fisher information journal February 2022
Variational quantum Gibbs state preparation with a truncated Taylor series text January 2020
Reformulation of the No-Free-Lunch Theorem for Entangled Data Sets text January 2020
Quantum Algorithm for Fidelity Estimation text January 2021

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