On the possibility of classical client blind quantum computing

TL;DR

This paper introduces a method enabling classical clients to delegate quantum computations securely without quantum communication, using a new pseudo-secret random qubit generator functionality and a protocol based on quantum-safe cryptography.

Contribution

It defines the PSRQG functionality, proposes the QFactory protocol, and demonstrates secure delegated blind quantum computing with classical clients without quantum communication.

Findings

PSRQG enables classical clients to generate secret quantum states.

QFactory protocol securely implements PSRQG using quantum-safe cryptography.

Allows verifiable blind quantum computing with only classical communication.

Abstract

We define the functionality of delegated pseudo-secret random qubit generator (PSRQG), where a classical client can instruct the preparation of a sequence of random qubits at some distant party. Their classical description is (computationally) unknown to any other party (including the distant party preparing them) but known to the client. We emphasize the unique feature that no quantum communication is required to implement PSRQG. This enables classical clients to perform a class of quantum communication protocols with only a public classical channel with a quantum server. A key such example is the delegated universal blind quantum computing. Using our functionality one could achieve a purely classical-client computational secure verifiable delegated universal quantum computing (also referred to as verifiable blind quantum computation). We give a concrete protocol (QFactory) implementing PSRQG, using the Learning-With-Errors problem to construct a trapdoor one-way function with certain desired properties (quantum-safe, two-regular, collision-resistant). We then prove the security in the Quantum-Honest-But-Curious setting and briefly discuss the extension to the malicious case.