Verifying the quantumness of a channel with an untrusted device

TL;DR

This paper introduces a method to verify the non-entanglement-breaking nature of quantum channels using a trusted input device and an untrusted measurement device, linking concepts like EPR-steering and joint measurability.

Contribution

It establishes a novel framework connecting channel verification, EPR-steering, and joint measurability, with implications for quantum resource theories and secure quantum communication.

Findings

Identifies the trusted-input, untrusted-output scenario as particularly interesting.

Connects EPR-steering to joint measurability in the context of channel verification.

Provides insights into the security of BB84 protocol with untrusted measurement devices.

Abstract

Suppose one wants to certify that a quantum channel is not entanglement-breaking. I consider all four combinations of trusted and untrusted devices at the input and output of the channel, finding that the most interesting is a trusted preparation device at the input and an untrusted measurement device at the output. This provides a time-like analogue of EPR-steering, which turns out to reduce to the problem of joint measurability, connecting these concepts in a different way to other recent work. I suggest a few applications of this connection, such as a resource theory of incompatibility. This perspective also sheds light on why the BB84 key distribution protocol can be secure even with an untrusted measuring device, leading to an uncertainty relation for arbitrary pairs of ensembles.