Experimental characterization of universal one-way quantum computing

TL;DR

This paper demonstrates the experimental realization and characterization of a universal set of quantum logic gates using a four-photon cluster state, advancing the development of scalable one-way quantum computing.

Contribution

It reports the first comprehensive characterization of multiple quantum gates on a single entangled resource in photonic one-way quantum computing.

Findings

Achieved a cluster state fidelity of 0.66 +/- 0.01.

Measured process fidelities of 0.64, 0.67, and 0.76 for CNOT, Hadamard, and T gates.

Simulated a Swap gate using three concatenated CNOT gates.

Abstract

We report the characterization of a universal set of logic gates for one-way quantum computing using a four-photon `star' cluster state generated by fusing photons from two independent photonic crystal fibre sources. We obtain a fidelity for the cluster state of 0.66 +/- 0.01 with respect to the ideal case. We perform quantum process tomography to completely characterize a controlled-NOT, Hadamard and T gate all on the same compact entangled resource. Together, these operations make up a universal set of gates such that arbitrary quantum logic can be efficiently constructed from combinations of them. We find process fidelities with respect to the ideal cases of 0.64 +/- 0.01 for the CNOT, 0.67 +/- 0.03 for the Hadamard and 0.76 +/- 0.04 for the T gate. The characterisation of these gates enables the simulation of larger protocols and algorithms. As a basic example, we simulate a Swap gate consisting of three concatenated CNOT gates. Our work provides some pragmatic insights into the prospects for building up to a fully scalable and fault-tolerant one-way quantum computer with photons in realistic conditions.