Ultrabroadband direct detection of nonclassical photon statistics at telecom wavelength

TL;DR

This paper demonstrates the direct detection and characterization of a highly multimode ultrabroadband nonclassical squeezed state at telecom wavelength, revealing complex multimode quantum structures using superconducting sensors.

Contribution

It introduces a method for directly observing and analyzing the multimode photon distribution of ultrabroadband nonclassical light at telecom wavelengths.

Findings

Direct observation of multimode photon distribution

Identification of multiple coexisting squeezers in the same mode

Potential for large-scale quantum networks in the frequency domain

Abstract

Broadband light sources play essential roles in diverse fields, such as high-capacity optical communications, optical coherence tomography, optical spectroscopy, and spectrograph calibration. Though an ultrabroadband nonclassical state from standard spontaneous parametric down-conversion may serve as a quantum counterpart, its detection and quantum characterization have been a challenging task. Here we demonstrate the quantitative characterization of a multimode structure in such an ultrabroadband (150 nm FWHM) squeezed state at telecom wavelength (1.5 \mu m). The nonclassical photon distribution of our highly multimode state is directly observed using a superconducting transition-edge sensor. From the observed photon correlation functions, we show that several tens of different squeezers are coexisting in the same spatial mode. We anticipate our results and technique open up a new possibility to generate and characterize nonclassical light sources for a large-scale optical quantum network in the frequency domain.