[15p-K309-1~12] 3.9 Optical quantum physics and technologies

2:45 PM - 3:00 PM JST(5:45 AM - 6:00 AM UTC)English Presentation

[15p-K309-6] SPDC photon pairs generation using different pump pulse widths

〇HsinPin Lo¹, Kai Asaoka^1,2, Hiroki Takesue¹ (1.NTTBRL, 2.UBC)

Keywords:

joint spectrum intensity,spontaneous parametric down-conversion (SPDC) photon pairs

Quantum interference between independent photon sources is an important element for realizing quantum communication based on multi-partite entanglement. Recently, we have reported the first GHZ state generation based on time-bin qubits using quantum interference between an SPDC photon pair source and a weak coherent light. In that experiment, the fidelity of the generated GHZ state to the pure state was limited to 70%, presumably caused by the insufficient purity of the SPDC photons. So in this work, we investigate the effect of the bandwidth of the pump pulse for the SPDC on the purity of the generated photon pairs.Figure 1 (a) shows the experimental setup. Here, we placed a bandwidth-tunable filter after a mode-locked laser so that we can change the bandwidth of the 1.5-um pulses. The pulses are then amplified by an EDFA and are launched into a PPLN waveguide to generate 780-nm pulses through the SHG process. Then the SHG pulses are input into another PPLN waveguide to generate entangled photon pairs through the SPDC process. The photons are then input into a WDM filter with which the signal and idler photons are separated with a 20-GHz bandwidth. The signal/idler photons are then input into FBG filters with 4-GHz bandwidths and then received by SSPDs for coincidence measurement using a time-interval analyzer. By sweeping the center wavelength of the 4-GHz filters, we can obtain Joint spectrum intensity. The JSI results, shown in Figure 1 (b), indicate that the SPDC photon becomes more symmetric and purer as the pump bandwidth increases. On the other hand, the SPDC photon pair generation rate decreases when we maintain a constant coincidence-to-accidental ratio (CAR) value of 100 across all pump bandwidth measurements by adjusting the pump power, as depicted in Figure 1(c).