Center for Relativistic Laser Science

OPC 2018

Abstract― The characterization of single photon frequency comb was confirmed by the properties of generated signal photons and the second order correlation function of them depended on injection of pump and seed laser.

I. Introduction

Recently, we demonstrated  the frequency comb single-photon interferometry, which provided an attractive platform for quantum technological development. In this work, the properties of generated signal photons and the second order correlation functions of the signal photons obtained by nonlinear crystals were estimated by measuring the RF spectrum and the time-tagged data of TCSPC. The generated signal photons with unique properties were investigated by measuring the optical bandwidth and the linewidth of individual comb tooth. Also, because there was continuous wave ultra-narrow seed laser for stimulated parametric down conversion (StPDC), the g⁽²⁾ functions were obtained as a function of pump and seed beam power without detecting heralded single photon.

II. Result and Discussion

To confirm the comb structure of signal photon generated by StPDC in frequency domain, the optical bandwidth and the linewidth of individual comb tooth of the signal single-photon frequency comb from PPLN crystal were directly measured by RF spectrum analyzer. The measured optical linewidth was measured to be 1 Hz, which was five orders of magnitude narrower than that of the pump frequency comb (~200 kHz). It is induced by the stimulated emission process in the StPDC crystal with our exceptionally narrow (1Hz) CW seed laser.

Furthermore, the second order correlation functions (g⁽²⁾(τ)) were measured by the Hanbury Brown and Twiss experiment. Although our single photon source could not be detected by heralded configuration, because of the injection of CW seed laser, the two detectors measurement of signal photons was applied to estimate the second order correlation function. As observing the g⁽²⁾(0) of signal photons dependence on the injection of seed laser, we investigated the properties of single party of two mode squeezed coherent state. The time-tagged data were measured as a function of the power of pump and seed laser. In this respect, the estimated values of g⁽²⁾(0) were shown the dependence on the power of seed laser, which suggested that the properties of detected photons could be changed by seed laser from coherent state to squeezed vacuum state.