# Fundamental limits on the capacities of bipartite quantum interactions

## TL;DR

This paper investigates the fundamental limits of bipartite quantum interactions, providing bounds on their capacities for entanglement and secret key generation, with applications in quantum cryptography and secure memory readout.

## Contribution

It introduces efficiently computable upper bounds on quantum and secret key capacities of bipartite interactions, advancing understanding of their fundamental limitations.

## Key findings

- Derived an upper bound on the positive-partial-transpose-assisted quantum capacity.
- Established an upper bound on secret-key-agreement capacity with LOCC assistance.
- Proposed a cryptographic protocol for secure digital memory readout.

## Abstract

Bipartite quantum interactions have applications in a number of different areas of quantum physics, reaching from fundamental areas such as quantum thermodynamics and the theory of quantum measurements to other applications such as quantum computers, quantum key distribution, and other information processing protocols. A particular aspect of the study of bipartite interactions is concerned with the entanglement that can be created from such interactions. In this Letter, we present our work on two basic building blocks of bipartite quantum protocols, namely, the generation of maximally entangled states and secret key via bipartite quantum interactions. In particular, we provide a nontrivial, efficiently computable upper bound on the positive-partial-transpose-assisted quantum capacity of a bipartite quantum interaction. In addition, we provide an upper bound on the secret-key-agreement capacity of a bipartite quantum interaction assisted by local operations and classical communication. As an application, we introduce a cryptographic protocol for the readout of a digital memory device that is secure against a passive eavesdropper.