title: Direct fidelity estimation from few Pauli measurements.
abstract: We describe a simple method for certifying that an experimental device prepares a desired quantum state ρ. Our method is applicable to any pure state ρ, and it provides an estimate of the fidelity between ρ and the actual (arbitrary) state in the lab, up to a constant additive error. The method requires measuring only a constant number of Pauli expectation values, selected at random according to an importance-weighting rule. Our method is faster than full tomography by a factor of d, the dimension of the state space, and extends easily and naturally to quantum channels.
authors.affiliation: Institute for Quantum Information, California Institute of Technology, Pasadena, California, USA.
authors.forename: Steven T
authors.initials: ST
authors.lastname: Flammia
authors.forename: Yi-Kai
authors.initials: YK
authors.lastname: Liu