# Device-independent characterization of quantum instruments

## TL;DR

This paper extends device-independent certification techniques based on Bell inequality violations to characterize quantum instruments, including post-measurement states, providing robust methods without assumptions on Hilbert space dimension or calibration accuracy.

## Contribution

It introduces a novel approach to device-independent characterization of quantum instruments, accounting for input-dependent post-measurement states, with practical certification recipes.

## Key findings

- Extended Bell-based certification to quantum instruments.
- Provided noise-robust certification protocols.
- Validated methods for input-dependent post-measurement states.

## Abstract

Among certification techniques, those based on the violation of Bell inequalities are appealing because they do not require assumptions on the underlying Hilbert space dimension and on the accuracy of calibration methods. Such device-independent techniques have been proposed to certify the quality of entangled states, unitary operations, projective measurements following von Neumann's model and rank-one positive-operator-valued measures (POVM). Here, we show that they can be extended to the characterization of quantum instruments with post-measurement states that are not fully determined by the Kraus operators but also depend on input states. We provide concrete certification recipes that are robust to noise.