Device-independent certification of tensor products of quantum states using single-copy self-testing protocols

TL;DR

This paper introduces a method to convert single-copy self-testing protocols into protocols that can certify tensor products of multiple quantum states simultaneously, without increasing measurement complexity, enabling potential unbounded randomness expansion.

Contribution

The authors present a novel procedure to parallelize self-testing protocols, allowing certification of multiple quantum states without increasing measurement settings or parties involved.

Findings

Transform single-copy protocols into tensor product certification methods

Prove that protocols certifying rank-one measurements can be parallelized

Suggests a pathway for device-independent unbounded randomness expansion

Abstract

Self-testing protocols are methods to determine the presence of shared entangled states in a device independent scenario, where no assumptions on the measurements involved in the protocol are made. A particular type of self-testing protocol, called parallel self-testing, can certify the presence of copies of a state, however such protocols typically suffer from the problem of requiring a number of measurements that increases with respect to the number of copies one aims to certify. Here we propose a procedure to transform single-copy self-testing protocols into a procedure that certifies the tensor product of an arbitrary number of (not necessarily equal) quantum states, without increasing the number of parties or measurement choices. Moreover, we prove that self-testing protocols that certify a state and rank-one measurements can always be parallelized to certify many copies of the state. Our results suggest a method to achieve device-independent unbounded randomness expansion with high-dimensional quantum states.