Classically Replaceable Operations

TL;DR

This paper establishes rigorous criteria for when quantum operations can be replaced by classical processing, aiming to reduce resource demands in quantum computing by identifying and characterizing classically replaceable operations.

Contribution

It defines the concept of classically replaceable operations in four scenarios and provides necessary and sufficient criteria for their identification.

Findings

Criteria for classical replaceability in four scenarios

Deterministic classical processing for unitary operations

Relating irreplaceability to quantum resource and non-local game performance

Abstract

Quantum information science provides powerful technologies beyond the scope of classical physics. In practice, accurate control of quantum operations is a challenging task with current quantum devices. The implementation of high fidelity and multi-qubit quantum operations consumes massive resources and requires complicated hardware design to fight against noise. An approach to alleviating this problem is to replace quantum operations with classical processing. Despite the common practice of this approach, rigorous criteria to determine whether a given quantum operation is replaceable classically are still missing. In this work, we define the classically replaceable operations in four general scenarios. In each scenario, we provide their necessary and sufficient criteria and point out the corresponding classical processing. For a practically favorable case of unitary classically replaceable operations, we show that the replaced classical processing is deterministic. Beyond that, we regard the irreplaceability of quantum operations by classical processing as a quantum resource and relate it to the performance of a channel in a non-local game, as manifested in a robustness measure.