Reliable quantum certification for photonic quantum technologies

TL;DR

This paper presents a practical, mathematically rigorous certification method for complex photonic quantum states, enabling reliable validation of large-scale photonic quantum devices with minimal assumptions.

Contribution

It introduces a new certification protocol for both Gaussian and certain non-Gaussian states using simple measurements, applicable to large-scale photonic quantum systems.

Findings

Efficient certification protocol for Gaussian states.

Extension to non-Gaussian states generated by linear optics.

No assumptions on noise or prover capabilities.

Abstract

A major roadblock for large-scale photonic quantum technologies is the lack of practical reliable certification tools. We introduce an experimentally friendly - yet mathematically rigorous - certification test for experimental preparations of arbitrary m-mode pure Gaussian states, pure non-Gaussian states generated by linear-optical circuits with n-boson Fock-basis states as inputs, and states of these two classes subsequently post-selected with local measurements on ancillary modes. The protocol is efficient in m and the inverse post-selection success probability for all Gaussian states and all mentioned non-Gaussian states with constant n. We follow the mindset of an untrusted prover, who prepares the state, and a skeptic certifier, with classical computing and single-mode homodyne-detection capabilities only. No assumptions are made on the type of noise or capabilities of the prover. Our technique exploits an extremality-based fidelity bound whose estimation relies on non-Gaussian state nullifiers, which we introduce on the way as a byproduct result. The certification of many-mode photonic networks, as those used for photonic quantum simulations, boson samplers, and quantum metrology, is now within reach.