Experimental realization of universal quantum gates and six-qubit entangled state using photonic quantum walk

TL;DR

This paper demonstrates the experimental realization of universal quantum gates and a six-qubit entangled state using photonic quantum walks, advancing photonic quantum computing at room temperature.

Contribution

It introduces a method to implement deterministic quantum gates and generate multi-qubit entanglement using single-photon quantum walks with multiple degrees of freedom.

Findings

High-fidelity quantum gates achieved via quantum walk

Successful creation of six-qubit GHZ state

Framework for scalable photonic quantum computing

Abstract

For quantum computation using photons, performing deterministic quantum gate operations is a challenge due to the probabilistic nature of the photon-photon interaction. Encoding qubits in multiple degrees-of-freedom of photons and controlling operations between them is one of the promising ways to navigate the probabilistic behavior. Using single-photon discrete-time quantum walk in combination with polarization and path degrees-of-freedom, we experimentally demonstrate the realization of a universal set of quantum gates with high fidelity at room temperature. The deterministic realization of quantum gates through photonic quantum walk are characterized via quantum state tomography. For a three-qubit system using a single photon, the first qubit is encoded using polarization information, and the other two qubits are encoded using path information, closely resembling a Galton-board setup. To generate a six-qubit Greenberger-Horne-Zeilinger state, entangled photon pairs are used to entangle the two three-qubit modules on which gate operations are performed. We also provide insights into the mapping of photonic quantum walk operations to quantum circuits and propose methods to resourcefully scale. This demonstration marks a significant progress towards using quantum walks for quantum computing and provides a framework for using fewer photons in combination with different degrees-of-freedom of photon to scale the number of qubits.