Abstract
We report the generation of frequency-uncorrelated photon pairs from counter-propagating spontaneous parametric down-conversion in a periodically-poled KTP waveguide. The joint spectral intensity of photon pairs is characterized by measuring the corresponding stimulated process, namely, the difference frequency generation process. The experimental result shows a clear uncorrelated joint spectrum, where the backward-propagating photon has a narrow bandwidth of 7.46 GHz and the forward-propagating one has a bandwidth of 0.23 THz like the pump light. The heralded single-photon purity estimated through Schmidt decomposition is as high as 0.996, showing a perspective for ultra-purity and narrow-band single-photon generation. Such unique feature results from the backward-wave quasi-phase-matching condition and does not has a strict limitation on the material and working wavelength, thus fascinating its application in photonic quantum technologies.
Highlights
We report the generation of frequency-uncorrelated photon pairs from counter-propagating spontaneous parametric down-conversion in a periodically-poled KTP waveguide
We demonstrate an observation of the frequency-uncorrelated photon pairs using the thirdorder QPM counter-propagating Spontaneous parametric down-conversion (SPDC) process in a periodically-poled KTP (PPKTP) waveguide
We demonstrate the generation of a frequency-uncorrelated photon pairs using counter-propagating SPDC in a PPKTP waveguide with a poling period on the order of interaction wavelength
Summary
We set the pump pulse duration τp = 2 ps to satisfy the condition of τi ≫ τp ≫ τs for frequency-uncorrelated photon pairs generation. The forward-propagating signal photon is coupled into a superconducting nanowire single photon detector (SNSPD1) through port a with a long-pass filter (LPF) filtering the pump light. When the pump power coupled into the waveguide is 11.3 mw, a coincidence counting rate of 870 Hz is measured. A traditional and direct way to measure the JSI is spectrally resolved single photon coincidence measurements. This method is time consuming and has a low resolution, due to the low generation rate of photon pairs. To further evaluate the spectral uncorrelation, we perform the Schmidt d ecomposition[30] on the JSI, from which we can estimate the heralded single-photon purity to be 0.996
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