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arXiv:1304.0304 · Physical Review A

Nonclassical two-photon interference between independent telecommunication light pulses converted by difference-frequency generation

Rikizo Ikuta, Toshiki Kobayashi, Hiroshi Kato, Shigehito Miki, Taro Yamashita, Hirotaka Terai, Mikio Fujiwara, Takashi Yamamoto, Masato Koashi, Masahide Sasaki, Zhen Wang, Nobuyuki Imoto

Published Oct 14, 2013• 17 citations
arXivHTMLPDF

Abstract

We experimentally demonstrated the Hong-Ou-Mandel (HOM) interference between two photons after visible-to-telecommunication wavelength conversion. In the experiment, we prepared a heralded single photon by using spontaneous parametric down conversion (SPDC) and the other photon from a weak laser source at 780 nm. We converted the wavelength of both photons to the telecommunication wavelength of 1522 nm by using difference-frequency generation in a periodically poled lithium niobate, and then observed the HOM interference between the photons. The observed visibility is $0.76\ifmmode\pm\else\textpm\fi{}0.12$ which clearly shows the nonclassical interference of the two photons. The high-visibility interference is an important step for fiber-based quantum communications of photons generated from visible-photon emitters.

DOI
10.1103/physreva.88.042317

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We experimentally demonstrated the Hong-Ou-Mandel (HOM) interference between two photons after visible-to-telecommunication wavelength conversion. In the experiment, we prepared a heralded single photon by using spontaneous parametric down conversion (SPDC) and the other photon from a weak laser source at 780 nm. We converted the wavelength of both photons to the telecommunication wavelength of 1522 nm by using difference-frequency generation in a periodically poled lithium niobate, and then observed the HOM interference between the photons. The observed visibility is 0.76\ifmmode±\else\textpm\fi0.120.76\ifmmode\pm\else\textpm\fi{}0.120.76\ifmmode±\else\textpm\fi0.12 which clearly shows the nonclassical interference of the two photons. The high-visibility interference is an important step for fiber-based quantum communications of photons generated from visible-photon emitters.
We demonstrate a Hong-Ou-Mandel interference between two independent, intrinsically pure, heralded single photons from spontaneous parametric down-conversion (SPDC) at telecommunication wavelength. A visibility of $85.5\ifmmode\pm\else\textpm\fi{}8.3%$ was achieved without using any bandpass filter. Thanks to the group-velocity-matched SPDC and superconducting nanowire single-photon detectors (SNSPDs), the fourfold coincidence counts are one order higher than that in the previous experiments. The combination of bright single-photon sources and SNSPDs is a crucial step for future practical quantum infocommunication systems at telecommunication wavelength.
A high visibility Hong-Ou-Mandel (HOM) interference between two independently prepared photons plays an important role in various photonic quantum information processing. In a standard HOM experiment using photons generated by pulse-pumped spontaneous parametric down conversion (SPDC), larger detection time windows than the coherence time of photons have been employed for measuring the HOM visibility and/or drawing the HOM dip. If large amounts of stray photons continuously exist within the detection time windows, employing small detection time windows is favorable for reducing the effect of background noises. Especially, such a setup is helpful for the HOM experiment using continuous wave (cw)-pumped SPDC and the time-resolved coincidence measurement. Here we argue that the method for determining the HOM visibility used in the previous cw experiments tends to suffer from distortion arising from biased contribution of the background noises. We then present a new method with unbiased treatment of the cw backgrounds. By using this method, we experimentally demonstrate a high visibility HOM interference of two heralded telecom photons independently generated by SPDC with employing cw pump light. An observed HOM visibility is 0.87 ± 0.04, which is as high as those observed by using pulse-pumped SPDC photons.
Heralded single photons with wavelength near 1550nm are expected to be an important resource for future quantum communications applications. Such applications often rely on non-classical Hong Ou Mandel interference (HOMI) that is observed between indistinguishable, pure photon states. While high visibility HOMI is routinely achieved for photons from identically prepared sources, here we observe interference between photons from two dissimilar systems. To generate synchronised indistinguishable photons, two photon sources were pumped with a single 1064nm, picosecond-pulsed fibre laser. In one source the laser pulses generated correlated pairs of photons at 810nm and 1550nm through four-wave mixing in photonic crystal fibre (PCF). In the other, the laser was used to generate second harmonic light at 532nm in a bulk crystal, before being launched into a periodically poled lithium niobate (PPLN) waveguide. This structure was designed to generate signal and idler photons through parametric down-conversion, matched in wavelength to the fibre based source. Idler photons from both sources were input into a fused-fibre coupler in order to measure the HOMI visibility. HOMI with a net visibility of 70% was demonstrated between photons from the two sources (after accounting for the background due to emission of multiple photons from a single source). A visibility of 80% is anticipated for the current sources after further improvement in the purity of the generated states. This result is the first step towards realising a quantum relay system, in which transmitted qubits produced by low loss, fibre-based photon sources interact with photons produced locally on a chip.
Quantum information protocols tend to involve more and more entangled photon pairs, for enabling advanced quantum tasks. To compensate for the low success efficiency of these protocols, one can increase the repetition rate of the emitted pairs, up to current telecom standard (40 GHz). In this context, we propose a realization of ultra-fast photon pair sources, intended for either heralded quantum state engineering or entanglement swapping at telecom wave- length. In this paper, we present preliminary results consisting of a two-photon interference experiment using four photons where the achieved raw visibility of the Hong-Ou-Mandel (HOM) dip exceeds 98.6 %. The interfering photons are generated through spontaneous parametric down conversion process (SPDC) in two independent, separate, periodically poled lithium niobate (PPLN) waveguides.
The frequency distinguishability of two single photons was successfully erased using single photon frequency up-conversion. A frequency nondegenerate photon pair generated via spontaneous four-wave mixing in a dispersion shifted fiber was used to emulate two telecom-band single photons that were in the same temporal mode but in different frequency modes. The frequencies of these photons were converted to the same frequency by using the sum-frequency generation process in periodically poled lithium niobate waveguides, while maintaining their temporal indistinguishability. As a result, the two converted photons exhibited a nonclassical dip in a Hong-Ou-Mandel quantum interference experiment. The present scheme will add flexibility to networking quantum information systems that use photons with various wavelengths.