Identification of Decoherence-Free Subspaces Without Quantum Process Tomography

TL;DR

This paper introduces an efficient protocol to identify decoherence-free subspaces in quantum processes without full process tomography, significantly reducing measurement requirements and demonstrating practical experimental application.

Contribution

The paper presents a novel protocol that directly identifies decoherence-free subspaces with fewer measurements, avoiding full quantum process reconstruction.

Findings

Achieved identification of DFS with 32 measurements instead of 256

Demonstrated quadratic speedup over standard tomography

Extended protocol applicability to higher-dimensional systems

Abstract

Characterizing a quantum process is the critical first step towards applying such a process in a quantum information protocol. Full process characterization is known to be extremely resource-intensive, motivating the search for more efficient ways to extract salient information about the process. An example is the identification of "decoherence-free subspaces", in which computation or communications may be carried out, immune to the principal sources of decoherence in the system. Here we propose and demonstrate a protocol which enables one to directly identify a DFS without carrying out a full reconstruction. Our protocol offers an up-to-quadratic speedup over standard process tomography. In this paper, we experimentally identify the DFS of a two-qubit process with 32 measurements rather than the usual 256, characterize the robustness and efficiency of the protocol, and discuss its extension to higher-dimensional systems.