Quantum state tomography of qudits via Hong-Ou-Mandel interference

TL;DR

This paper introduces a passive, versatile quantum state tomography method for qudits using Hong-Ou-Mandel interference, enabling accurate state reconstruction with classical or quantum probes without active optical control.

Contribution

The proposed method simplifies quantum state tomography by eliminating active measurement controls and works with classical probe light, broadening practical applicability.

Findings

Successful experimental demonstration with polarization qubits.

Achieved accurate state reconstruction comparable to conventional QST.

Applicable to various degrees of freedom and probe light types.

Abstract

We propose a method to perform the quantum state tomography (QST) of an $\mathit{n}$-partite qudit state embedded in single photons using the Hong-Ou-Mandel (HOM) interference between the target state and probe state. This method requires only passive beam splitters for the HOM interference and removes all active optical devices in the target modes to control the measurement bases needed in conventional QST. Hence, it is applicable to various degree of freedom of the target state without altering the measurement setup. Moreover, a faithful estimation is realized even with classical probe light such as laser and thermal light. As a proof-of-principle, we performed the experimental demonstration using a polarization qubit. Regardless of the photon statistics of the probe light, the estimated results of state reconstruction are as accurate as those verified by conventional QST.