Self-consistent tomography and measurement-device independent cryptography

TL;DR

This paper addresses the challenge of jointly estimating quantum states and measurements, extending tests for correlated errors to a cryptographic setting where parties trust their states but not the measurement device.

Contribution

It introduces a self-consistent tomography method that detects correlated SPAM errors in a cryptographic context where measurement devices are untrusted.

Findings

Extended tests for correlated errors to cryptographic scenarios

Demonstrated detection of measurement-device correlations

Applicable to quantum cryptography protocols

Abstract

A recurring problem in quantum mechanics is to estimate either the state of a quantum system or the measurement operator applied to it. If we wish to estimate both, then the difficulty is that the state and the measurement always appear together: to estimate the state, we must use a measurement; to estimate the measurement operator, we must use a state. The data of such quantum estimation experiments come in the form of measurement frequencies. Ideally, the measured average frequencies can be attributed to an average state and an average measurement operator. If this is not the case, we have correlated state-preparation-and-measurement (SPAM) errors. We extend some tests developed to detect such correlated errors to apply to a cryptographic scenario in which two parties trust their individual states but not the measurement performed on the joint state.