Methods for Producing Decoherence-Free States and Noiseless Subsystems Using Photonic Qutrits

TL;DR

This paper proposes a method to create decoherence-free logical qubits and maximally entangled states using three-photon qutrit systems and linear optics, enhancing robustness against certain noise types.

Contribution

It introduces a novel approach to generate and verify decoherence-free states and noiseless subsystems with photonic qutrits using linear optical elements and spontaneous parametric down conversion.

Findings

Successful preparation of decoherence-free logical qubits.

Method to select maximally entangled two-qutrit states.

Conditions identified for decoherence-free states beyond collective errors.

Abstract

We outline a proposal for a method of preparing an encoded two-state system (logical qubit) that is immune to collective noise acting on the Hilbert space of the states supporting it. The logical qubit is comprised of three photonic three-state systems (qutrits) and is generated by the process of spontaneous parametric down conversion. The states are constructed using linear optical elements along with three down-conversion sources, and are deemed successful by the simultaneous detection of six events. We also show how to select a maximally entangled state of two qutrits by similar methods. For this maximally entangled state we describe conditions for the state to be decoherence-free which do not correspond to collective errors.