Abstract
Broadband light sources play essential roles in diverse fields, such as high-capacity optical communications, optical coherence tomography, optical spectroscopy, and spectrograph calibration. Although a nonclassical state from spontaneous parametric down-conversion may serve as a quantum counterpart, its detection and characterization have been a challenging task. Here we demonstrate the direct detection of photon numbers of an ultrabroadband (110 nm FWHM) squeezed state in the telecom band centred at 1535 nm wavelength, using a superconducting transition-edge sensor. The observed photon-number distributions violate Klyshko's criterion for the nonclassicality. From the observed photon-number distribution, we evaluate the second- and third-order correlation functions, and characterize a multimode structure, which implies that several tens of orthonormal modes of squeezing exist in the single optical pulse. Our results and techniques open up a new possibility to generate and characterize frequency-multiplexed nonclassical light sources for quantum info-communications technology.
Highlights
Broadband light sources play essential roles in diverse fields, such as high-capacity optical communications, optical coherence tomography, optical spectroscopy, and spectrograph calibration
We demonstrate the direct detection of photon numbers of an ultrabroadband (110 nm full-width at half maximum (FWHM)) squeezed state in the telecom band centred at 1535 nm wavelength, using a superconducting transition-edge sensor
The squeezed states are generated from a spontaneous parametric down-conversion (SPDC) source and their broadband multimode photon-number statistics is measured by a highly efficient Photon number resolving detection (PNRD) based on a titanium TES11,12
Summary
Broadband light sources play essential roles in diverse fields, such as high-capacity optical communications, optical coherence tomography, optical spectroscopy, and spectrograph calibration. CV entanglement over multiple transverse modes was generated from an OPO and characterized by homodyning[24,25] Besides these studies with CVs, discrete variable (DV) nature, i.e., photon-number statistics, of multimode quantum states have been investigated and characterized in this decade, by using PNRDs. The direct observation of nonclassical photon-number oscillation from a type-I SPDC source was demonstrated using a visible light photon counter (VLPC)[26,27]. The higher order photon-number correlations between the signal and idler beams of a twin beam from a type-II SPDC source were observed, and the influence of multimode structure to photonnumber statistics was analysed, using the APD-based time-multiplexing PNRD28,29 Extending this idea, reconstruction of the mode weight structure from the photon-number correlations was demonstrated for the states containing three modes[30]. The results and techniques pave a new simple way of characterizing ultrabroadband nonclassical states and we anticipate it will accelerate further research and development on quantum information technologies for the telecom fibre infrastructures
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