From three-photon GHZ states to ballistic universal quantum computation

TL;DR

This paper introduces a resource-efficient, loss-tolerant scheme for linear optical quantum computing that constructs universal cluster states using only 3-GHZ states and passive linear optics, avoiding complex adaptive operations.

Contribution

It presents a novel, scalable scheme for linear optical quantum computing that eliminates adaptive switching and large memories, enhancing robustness and resource efficiency.

Findings

Scheme tolerates ~1.6% photon loss without active encoding

Uses only 3-GHZ states and passive linear optics

Fully models cluster generation with loss and failure

Abstract

Single photons, manipulated using integrated linear optics, constitute a promising platform for universal quantum computation. A series of increasingly efficient proposals have shown linear-optical quantum computing to be formally scalable. However, existing schemes typically require extensive adaptive switching, which is experimentally challenging and noisy, thousands of photon sources per renormalized qubit, and/or large quantum memories for repeat-until-success strategies. Our work overcomes all these problems. We present a scheme to construct a cluster state universal for quantum computation, which uses no adaptive switching, no large memories, and which is at least an order of magnitude more resource-efficient than previous passive schemes. Unlike previous proposals, it is constructed entirely from loss-detecting gates and offers a robustness to photon loss. Even without the use of an active loss-tolerant encoding, our scheme naturally tolerates a total loss rate of $\sim 1.6\%$ in the photons detected in the gates. This scheme uses only 3-GHZ states as a resource, together with a passive linear-optical network. We fully describe and model the iterative process of cluster generation, including photon loss and gate failure. This demonstrates that building a linear optical quantum computer need be less challenging than previously thought.