# Efficient verification of bipartite pure states

## TL;DR

This paper introduces practical, efficient protocols for verifying bipartite pure states using adaptive local measurements, outperforming tomography-based methods and applicable even in adversarial scenarios.

## Contribution

The authors develop new local measurement protocols for bipartite state verification that are both practical and optimal, leveraging MUBs and complex projective 2-designs.

## Key findings

- Protocols are more efficient than tomography-based methods.
- Applicable to adversarial scenarios with optimal local measurement protocol.
- Highlight the importance of MUBs and 2-designs in quantum verification.

## Abstract

We propose practical and efficient protocols for verifying bipartite pure states for any finite dimension, which can also be applied to fidelity estimation. Our protocols are based on adaptive local projective measurements with either one-way or two-way communications, which are very easy to implement in practice. They can extract the key information much more efficiently than known protocols based on tomography or direct fidelity estimation, and their efficiencies are comparable to the best protocols based on entangling measurements. These protocols highlight the significance of mutually unbiased bases (MUBs) and complex projective 2-designs in quantum state verification and fidelity estimation. Moreover, our protocols can be applied to the adversarial scenario, in which states are controlled by a malicious adversary. In this case, surprisingly, one of our protocols based on local measurements is even optimal among protocols without locality restriction.