Reduce, reuse, recycle, for robust cluster state generation

TL;DR

This paper presents a method for efficient, scalable generation of cluster states in measurement-based quantum computing by reusing ancilla buses, significantly reducing operations and decoherence effects.

Contribution

It introduces a bus reuse strategy that halves the required operations and doubles the feasible computational workspace in cluster state generation.

Findings

Fewer than half the operations needed with bus reuse

Bus reuse more than doubles the size of usable workspace

Parallel buses enable scalable cluster state generation with minimal gates

Abstract

Efficient generation of cluster states is crucial for engineering large-scale measurement-based quantum computers. Hybrid matter-optical systems offer a robust, scalable path to this goal. Such systems have an ancilla which acts as a bus connecting the qubits. We show that by generating smaller cluster "Lego bricks", reusing one ancilla per brick, the cluster can be produced with maximal efficiency, requiring fewer than half the operations compared with no bus reuse. By reducing the time required to prepare sections of the cluster, bus reuse more than doubles the size of the computational workspace that can be used before decoherence effects dominate. A row of buses in parallel provides fully scalable cluster state generation requiring only 20 CPhase gates per bus use.