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Optics Express

Generation of highly stable WDM time-bin entanglement by cascaded sum-frequency generation and spontaneous parametric downconversion in a PPLN waveguide device

Shin Arahira, Hitoshi Murai, Hironori Sasaki

Published Aug 15, 2016• 14 citations
Publisher

Abstract

device. Visibilities of approximately 94% were clearly observed in two-photon interference experiments for all the wavelength-multiplexed channels under investigation (five pairs), with insensitivity to the polarization states of the photon pairs. We also evaluated the performances in terms of quantum-key-distribution (QKD) applications by using four single-photon detectors, which enables to evaluate the QKD performance properly. The results showed long-term stability over 70 hours, maintaining approximately 3% of the quantum error rate and 110 bit/s of the sifted key rate.

DOI
10.1364/oe.24.019581

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Entangled photon pairs based on silicon straight waveguides have been applied in the area of quantum information owing to the compactness of the devices and high nonlinearity of the silicon material. In order to fully take advantage of the broad emission spectrum of photon pairs for quantum-key-distribution, dense wavelength division multiplexer (DWDM) is often required. However, the relationship between the channel bandwidth of DWDM and the two-photon interference visibility remains unambiguous, in which the high visibility of quantum interference fundamentally reduces quantum bit error rate in quantum-key-distribution system. In this paper, time-bin entangled photon pairs with a raw visibility of 94.3% ± 3.3% are generated in a silicon chip with a channel bandwidth of 0.1 nm, showing a violation of Bell’s inequality by more than three standard deviations, and a fidelity of 0.942 ± 0.02 is obtained by quantum state tomography. Applying variable channel bandwidths, the corresponding two-photon interference visibilities are measured, fitting well with the theoretical model incorporating multiple parameters such as optical loss, dark count probability, and averaged photon-pair number in DWDM channel.

IEEE Journal of Quantum Electronics•Jun 14, 2023•3 citations
device. Visibilities of approximately 94% were clearly observed in two-photon interference experiments for all the wavelength-multiplexed channels under investigation (five pairs), with insensitivity to the polarization states of the photon pairs. We also evaluated the performances in terms of quantum-key-distribution (QKD) applications by using four single-photon detectors, which enables to evaluate the QKD performance properly. The results showed long-term stability over 70 hours, maintaining approximately 3% of the quantum error rate and 110 bit/s of the sifted key rate.
In this paper we report the generation of wavelength-multiplexed polarization-entangled photon pairs in the 1.5-μm communication wavelength band by using cascaded optical second nonlinearities (sum-frequency generation and subsequent spontaneous parametric down-conversion, c-SFG/SPDC) in a periodically poled LiNbO(3) ridge waveguide device. The c-SFG/SPDC method makes it possible to fully use the broad spectral bandwidth of SPDC in nearly frequency-degenerate conditions, and can provide more than 50 pairs of wavelength channels for the entangled photon pairs in the 1.5-μm wavelength band, using only standard optical resources in the telecom field. Visibilities higher than 98% were clearly observed in two-photon interference fringes for all the wavelength channels under investigation (eight pairs). We further performed a detailed experimental investigation of the cross-talk characteristics and the impact of detuning the pump wavelengths.
We report the generation of high-purity correlated photon-pairs and polarization entanglement in a 1.5 μm telecommunication wavelength-band using cascaded χ((2)):χ((2)) processes, second-harmonic generation (SHG) and the following spontaneous parametric down conversion (SPDC), in a periodically poled LiNbO(3) (PPLN) ridge-waveguide device. By using a PPLN module with 600%/W of the SHG efficiency, we have achieved a coincidence-to-accidental ratio (CAR) higher than 4000 at 7.45×10(-5) of the mean number of the photon-pair per pulse. We also demonstrated that the maximum reach of the CAR was truly dark-count-limited by the single-photon detectors used here. This indicates that the fake (noise) photons were negligibly small in this system, even though the photon-pairs, the Raman noise photons, and the pump photons were in the same wavelength band. Polarization entangled photon pairs were also generated by constructing a Sagnac-loop-type interferometer which included the PPLN module and an optical phase-difference compensator to observe maximum entanglement. We achieved two-photon interference visibilities of 99.6% in the H/V basis and 98.7% in the diagonal basis. The peak coincidence count rate was approximately 50 counts per second at 10(-3) of the mean number of the photon-pair per pulse.
Abstract In this paper, we demonstrate the generation of high-performance entangled photon-pairs in different degrees of freedom from a single piece of fiber pigtailed periodically poled LiNbO 3 (PPLN) waveguide. We utilize cascaded second-order nonlinear optical processes, i.e., second-harmonic generation (SHG) and spontaneous parametric downconversion (SPDC), to generate photon-pairs. Previously, the performance of the photon-pairs is contaminated by Raman noise photons. Here by fiber-integrating the PPLN waveguide with noise-rejecting filters, we obtain a coincidence-to-accidental ratio (CAR) higher than 52,600 with photon-pair generation and detection rate of 52.36 kHz and 3.51 kHz, respectively. Energy-time, frequency-bin, and time-bin entanglement is prepared by coherently superposing correlated two-photon states in these degrees of freedom, respectively. The energy-time entangled two-photon states achieve the maximum value of CHSH-Bell inequality of S = 2.71 ± 0.02 with two-photon interference visibility of 95.74 ± 0.86%. The frequency-bin entangled two-photon states achieve fidelity of 97.56 ± 1.79% with a spatial quantum beating visibility of 96.85 ± 2.46%. The time-bin entangled two-photon states achieve the maximum value of CHSH-Bell inequality of S = 2.60 ± 0.04 and quantum tomographic fidelity of 89.07 ± 4.35%. Our results provide a potential candidate for the quantum light source in quantum photonics.
In this paper we report experimental investigation in transmission performance over standard single-mode optical fibers (SMFs) of polarization-entangled photon-pairs in a 1.5-μm band generated by cascaded second-harmonic generation and spontaneous parametric down conversion (c-SHG/SPDC) from a periodically poled LiNbO(3) (PPLN) ridge-waveguide device. Clear two-photon interference fringes were observed even after the transmission over 140 km of the SMF spools, remaining small degradation in the visibilities of less than 3%. The performance was also investigated by using optical attenuators, instead of the SMF spools, to study the maximum reach of the distribution of the entanglement in terms of loss penalty. The results show that the quantum entanglement could be distributed even with 50 dB of the transmission loss with violation of Bell inequality by using the c-SHG/SPDC-based photon-pair source.
Entangled photon pairs based on silicon straight waveguides have been applied in the area of quantum information owing to the compactness of the devices and high nonlinearity of the silicon material. In order to fully take advantage of the broad emission spectrum of photon pairs for quantum-key-distribution, dense wavelength division multiplexer (DWDM) is often required. However, the relationship between the channel bandwidth of DWDM and the two-photon interference visibility remains unambiguous, in which the high visibility of quantum interference fundamentally reduces quantum bit error rate in quantum-key-distribution system. In this paper, time-bin entangled photon pairs with a raw visibility of 94.3% ± 3.3% are generated in a silicon chip with a channel bandwidth of 0.1 nm, showing a violation of Bell’s inequality by more than three standard deviations, and a fidelity of 0.942 ± 0.02 is obtained by quantum state tomography. Applying variable channel bandwidths, the corresponding two-photon interference visibilities are measured, fitting well with the theoretical model incorporating multiple parameters such as optical loss, dark count probability, and averaged photon-pair number in DWDM channel.