Device independent witnessing of unknown quantum channels

TL;DR

This paper introduces a device-independent method to characterize unknown quantum channels solely based on input-output data, avoiding the circularity of traditional quantum process tomography, and provides explicit solutions for common channels.

Contribution

It presents a novel operational framework for device-independent quantum channel characterization, with explicit solutions for key quantum channels, advancing quantum information processing.

Findings

Successfully characterizes erasure, depolarizing, and amplitude-damping channels

Provides closed-form solutions for practical quantum channels

Eliminates the need for prior device calibration in quantum process analysis

Abstract

Quantum process tomography, the standard procedure to characterize any quantum channel in nature, is affected by a circular argument: in order to characterize the channel, the tomographic preparation and measurement need in turn to be already characterized. We break this loop by designing an operational framework able to optimally characterize any given unknown quantum channel in a device-independent fashion, namely, by only looking at its input-output statistics, under the sole assumption that quantum theory is valid. We provide explicit solutions, in closed form, for practically relevant cases such as the erasure, depolarizing, and amplitude-damping channels.