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New Journal of Physics

Independent telecom-fiber sources of quantum indistinguishable single photons

Monika Patel, Joseph B. Altepeter, Yu-Ping Huang, Neal N. Oza, Prem Kumar

Published Apr 23, 2014• 5 citations
Publisher

Abstract

Quantum-mechanically indistinguishable photons produced by independent (or equivalently, mutually phase incoherent) light sources are essential for distributed quantum information processing applications. We demonstrate heralded generation of such photons in two spatially separate telecom-fiber spools, each driven by pulsed pump waves that are measured to have no mutual phase coherence. Through Hong–Ou–Mandel experiments, we measure the quantum interference visibility of those photons to be . Our experimental results are well predicted by a quantum multimode theory we developed for such systems without the need for any fitting parameter.

DOI
10.1088/1367-2630/16/4/043019

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Quantum-mechanically indistinguishable photons produced by independent (or equivalently, mutually phase incoherent) light sources are essential for distributed quantum information processing applications. We demonstrate heralded generation of such photons in two spatially separate telecom-fiber spools, each driven by pulsed pump waves that are measured to have no mutual phase coherence. Through Hong–Ou–Mandel experiments, we measure the quantum interference visibility of those photons to be . Our experimental results are well predicted by a quantum multimode theory we developed for such systems without the need for any fitting parameter.
We experimentally demonstrate a bright pulsed source of correlated photon pairs at the 1550 nm telecom band by pumping 300 m dispersion-shifted fiber with a 4 ps pulse train. We investigate the coherence property of the source by measuring the second-order intensity correlation function g(2) of individual signal (idler) photons. A preliminary Hong-Ou-Mandel-type two-photon interference experiment with two such sources confirms the high temporal and spatial coherence of the source. The source is suitable for multiphoton quantum interference of independent sources, which is required in quantum information processing.
Abstract The interference between two independent photons stands as a crucial aspect of numerous quantum information protocols and technologies. In this work, we leverage fiber-coupled devices, which encompass fibered photon pair-sources and off-the-shelf optics, to demonstrate Hong-Ou-Mandel interference. We employ two distinct single photon sources, namely a heralded single-photon source and a weak coherent laser source, both operating asynchronously in continuous-wave regime. We record two-photon coincidences, showing a state-of-art visibility of 91.9(5)%. This work, compliant with telecom technology, provides realistic backbones for establishing long-range communication based on quantum teleportation in hybrid quantum networks.
Single photon sources (SPSs) play important roles in quantum communication and quantum information processing. Spontaneous four wave mixing (SFWM) in optical fibers provides a promising way to realize practical heralded single photon sources (HSPSs), since it is compatible with current techniques of optical communications. In this paper, two independent HSPSs at 1.5μm band are realized in one polarization maintaining dispersion shifted fiber (PM-DSF) utilizing its large birefringence. When pulsed pump light passes through an optical fiber, two kinds of SFWM will take place simultaneously. One is scalar processes, in which two annihilated pump photons and generated photon pair are all polarized along the same fiber polarization axis. The other is vector processes, in which two annihilated pump photons are polarized along different fiber polarization axes, either for the two photons of the generated pair. In the PM-DSF, the large birefringence generates obvious walk-off effect on the two pump polarization components, which leads to an effective suppression of the vector processes. Hence, by proper pump polarization, correlated photon pairs (CPPs) with different polarization directions can be generated independently by the two scalar processes, which can be used to realize two independent HSPSs. The indistinguishability of the heralded photons generated by the two independent sources is demonstrated by an experiment of Hong-Ou-Mandel (HOM) interference. Using a fiber coupler as the beam splitter, a visibility of HOM dip of 76% is achieved, showing their potential on quantum information.
The indistinguishable photon-pair sources are valuable in many quantum information applications, such as quantum microscopy, quantum synchronization, and quantum metrology. Based on cascaded sum-frequency generation (SFG) and spontaneous parametric downconversion (SPDC) processes, we propose and demonstrate a scheme for the generation of spatially separated broadband indistinguishable photon pairs in the telecom band by using only one piece of a fiber-pigtailed periodically poled lithium niobate waveguide in a modified Sagnac loop. The measured joint spectral intensity of the generated entangled photon pairs is 7.27 THz (57.6 nm) at the full width at half-maximum (FWHM). The Hong–Ou–Mandel (HOM) interference of the generated broadband photons is measured with bandwidths of 5.35 THz (∼42.8 nm) and 100 GHz (∼0.8 nm), respectively. Visibility of 94.0±1.4% is achieved with the bandwidth of 5.35 THz, demonstrating good indistinguishability of the generated two-photon states, which could benefit the development of quantum microscopy and quantum synchronization.
Interference between two completely independent photons lies at the heart of many photonic quantum information applications such as quantum repeaters, teleportation, and quantum key distribution. Here, we report the observation of Hong–Ou–Mandel (HOM) interference with two independent continuous-wave coherent light sources that are neither synchronized nor share any common reference. To prepare indistinguishable photons from two independent laser sources, we employ high-precision frequency-stabilization techniques using the 5 S 1 / 2 ( F = 3 ) − 5 P 1 / 2 ( F ′ = 3 ) transition line of Rb 85 atoms. We successfully observe an HOM interference fringe with two independent continuous-wave coherent photons originating from either the frequency-locked or the frequency-modulated lasers. An interference fringe involving two-photon beating is also observed when the frequency difference between the two interfering photons is beyond the spectral bandwidth of the individual coherent photons. We carry out further experiments to verify the robustness of the source preparation regardless of the separation distance between the two independent photon sources.