Efficient tomography of microwave photonic cluster states

TL;DR

This paper introduces an efficient tomography method for large microwave photonic cluster states using matrix-product-operator formalism, enabling full state reconstruction of up to 35 qubits and facilitating performance benchmarking.

Contribution

It presents a novel, scalable tomography technique based on matrix-product-operators, allowing full characterization of large entangled photonic states.

Findings

Successfully reconstructed a 2^35 x 2^35 density matrix.

Detected performance degradation in photon source for large cluster states.

Method is applicable to various physical qubit systems.

Abstract

Entanglement among a large number of qubits is a crucial resource for many quantum algorithms. Such many-body states have been efficiently generated by entangling a chain of itinerant photonic qubits in the optical or microwave domain. However, it has remained challenging to fully characterize the generated many-body states by experimentally reconstructing their exponentially large density matrices. Here, we develop an efficient tomography method based on the matrix-product-operator formalism and demonstrate it on a cluster state of up to 35 microwave photonic qubits by reconstructing its $2^{35} \times 2^{35}$ density matrix. The full characterization enables us to detect the performance degradation of our photon source which occurs only when generating a large cluster state. This tomography method is generally applicable to various physical realizations of entangled qubits and provides an efficient benchmarking method for guiding the development of high-fidelity sources of entangled photons.