Long-distance distribution of time-bin entangled photon pairs over 100 km using frequency up-conversion detectors

Abstract

We report an experimental demonstration of the distribution of time-bin entangled photon pairs over 100 km of optical fiber. In our experiment, 1.5-mum non-degenerated time-bin entangled photon pairs were generated with a periodically poled lithium niobate (PPLN) waveguide by using the parametric down conversion process. Combining this approach with ultra-low-loss filters to eliminate the pump light and separate signal and idler photons, we obtained an efficient entangled photon pair source. To detect the photons, we used single-photon detectors based on frequency up-conversion. These detectors operated in a non-gated mode so that we could use a pulse stream of time correlated entangled photon pairs at a high repetition frequency (1 GHz). Using these elements, we distributed time-bin entangled photon pairs over 100 km of dispersion shifted fiber and performed a two-photon interference experiment. We obtained a coincidence fringe of 81.6% visibility without subtracting any background noise, such as accidental coincidence or dark count, which was good enough to violate Bell's inequality. Thus, we successfully distributed time-bin entangled photon pairs over 100 km.

High-fidelity transmission of entanglement over a high-loss free-space channel

“…In the present experiment we demonstrate a fundamentally more interesting scenario by sending both photons of an entangled pair over this free-space channel. By violating a Clauser-HorneShimony-Holt (CHSH) Bell inequality [17] we find that entanglement is highly stable over these long time spans -the photon-pair flight time of ∼ 0.5 ms is the longest lifetime of photonic Bell states reported so far, almost twice as long as the previous high [4,5] of ∼ 250 µs.The achieved noise-limited fidelity paves the way for free-space implementations of quantum communication protocols that require the transmission of two photons, e.g. quantum dense coding [18], entanglement purification [19], quantum teleportation [20] and quantum key distribution without a shared reference frame [21].…”

“…Furthermore photons can be easily generated, manipulated and transmitted over large distances via optical fibres or free-space links. Since the maximal distance for the distribution of quantum entanglement in optical fibres is limited to the order [2,3,4,5] of ∼ 100 km, the most promising option for testing quantum entanglement on a global scale is currently free-space transmission, ultimately using satellites and ground stations [6].…”

Ultrashort Laser Pulses for Frequency Upconversion

“…Such a low background noise probability could remarkably improve the sensitivity of the frequency-upconversion PNRD. The remarkable decrease in background noise would optimize applications such as quantum entanglement and quantum teleportation [42] and improve the signal-to-noise ratio of widely used light detection and ranging system, since the background counts would randomly couple into the modes of the quantum states, which may significantly affect the original photon number distribution [38]. The approach may find promising applications in various quantum optical experiments using nonclassical light sources to demonstrate the features of quantum states around 1 μm [43].…”

Long-distance entanglement-based quantum key distribution over optical fiber

“…By repeating this sequence, Alice and Bob can generate a sifted key bit string. Figure 2 shows the setup we used for our QKD experiments [25]. A continuous lightwave emitted from an external-cavity semiconductor laser at a wavelength of 1551 nm was converted into a pulse stream by a LiNbO 3 intensity modulator.…”