Temporal Quantum-State Tomography of Narrowband Biphotons

TL;DR

This paper introduces a quantum state tomography method for measuring the complex temporal waveform of narrowband biphotons, enabling detailed characterization of their time-frequency entanglement in the continuous-variable domain.

Contribution

It presents the first experimental application of this tomography technique to narrowband biphotons from cold atoms, confirming theoretical models of their temporal quantum states.

Findings

Successfully reconstructed the joint amplitude and phase functions of biphotons.

Confirmed theoretical predictions of temporal quantum states.

Demonstrated the technique's effectiveness for cold-atom generated biphotons.

Abstract

We describe and demonstrate a quantum state tomography for measuring the complex temporal waveform of narrowband biphotons. Through six sets of two-photon interference measurements projected in different polarization subspaces, we can construct the time-frequency entangled two-photon joint amplitude and phase functions in continuous-variable time domain. For the first time, we apply this technique to experimentally determine the temporal quantum states of narrowband biphotons generated from spontaneous four-wave mixing in cold atoms, and fully confirm the theoretical predictions.