Energy-time entanglement generation in optical fibers under CW pumping

Abstract

In this paper, the energy-time entangled photon-pairs at 1.5 μm are generated by the spontaneous four wave mixing (SFWM) in optical fibers under continuous wave (CW) pumping. The energy-time entanglement property is demonstrated experimentally through an experiment of Franson-type interference. Although the generation rates of the noise photons are one order of magnitude higher than that of the photon-pairs under CW pumping, the impact of noise photons can be highly suppressed in the measurement by a narrow time domain filter supported by superconducting nanowire single photon detectors with low timing jitters and time correlated single photon counting (TCSPC) module with high time resolution. The experiment results show that the SFWM in optical fibers under CW pumping provides a simple and practical way to generate energy-time entanglement at 1.5 μm, which has great potential for long-distance quantum information applications over optical fibers.

Observation of photon-pair generation in the normal group-velocity-dispersion regime with slight detuning from the pump wavelength

“…In addition, the fiber based photon-pair sources are able to be directly coupled to fiber systems with negligible coupling loss, but waveguide-to-fiber coupling efficiency of a periodically poled SPDC crystal is reported about 50% [8]. The SFWM process has been studied intensively for the fiber-based photon generation [6,[9][10][11][12][13][14][15][16][17][18][19][20] for quantum information applications including quantum key distribution.Photon-pair generation via SFWM is active near the zero group-velocity-dispersion (GVD) wavelength, λ ZGVD , in the anomalous GVD regime [6,[9][10][11][12][13][14][15] or normal GVD regime [16][17][18][19][20]. In the normal GVD regime, the wavelength of the generated photon pairs is significantly detuned from the pump wavelength.…”

“…In addition, the fiber based photon-pair sources are able to be directly coupled to fiber systems with negligible coupling loss, but waveguide-to-fiber coupling efficiency of a periodically poled SPDC crystal is reported about 50% [8]. The SFWM process has been studied intensively for the fiber-based photon generation [6,[9][10][11][12][13][14][15][16][17][18][19][20] for quantum information applications including quantum key distribution.…”

“…Photon-pair generation via SFWM is active near the zero group-velocity-dispersion (GVD) wavelength, λ ZGVD , in the anomalous GVD regime [6,[9][10][11][12][13][14][15] or normal GVD regime [16][17][18][19][20]. In the normal GVD regime, the wavelength of the generated photon pairs is significantly detuned from the pump wavelength.…”

“…Solution I and II are the fundamental solutions with k p =k s =k i , and solution III in the normal GVD regime is for signal/idler photons far from the pump wavelength (k p ≠ k s ≠ k i but 2k p =k s + k i + 2γP p ). With a non-zero pump power, the photon pairs can be generated for the regime II and III (red curves in figure 1(a)) [6,[9][10][11][12][13][14][15][16][17][18][19][20], but the nonlinear Kerr effects, 2γP p , in equation (2) cause difficulties in the generation of solution I for the normal GVD regime. Figure 1(b) shows the normalized probability density spectrum of photon pair emission against the pump wavelength.…”

“…A variable optical attenuator adjusts the input pump power. The pump beam travels through the band-pass filter and enters a 500 m DSF which is cooled down to the temperature of liquid nitrogen to reduce spontaneous Raman scattering (spRS) [10][11][12][13][14]. In addition, a fiber polarizer is placed after the DSF to remove the cross-polarized Raman-scattered photons [9][10][11].…”