High dimensional frequency bin entanglement over 60 km

The use of high-dimensional entangled states is a key enabler for high-capacity quantum communications and key distribution, quantum computation, and information processing. For the success of these quantum photonic... [ view full abstract ]

The use of high-dimensional entangled states is a key enabler for high-capacity quantum communications and key distribution, quantum computation, and information processing. For the success of these quantum photonic applications, however, high visibility quantum interference and high integration is essential. Among the different degrees of freedom of photons, entangled photon pairs at telecommunication wavelengths allows the implementation of high visibility experiments and are especially well suited for integration with the current fiber optic infrastructure.

Although the initial approach to applying entanglement in quantum information processing exploited the concept of time bins, much recent work has focused on the concept of frequency bin entanglement because of its particular advantages: (i) the frequency domain is naturally of high dimensionality; (ii) building blocks such as frequency entangled sources, modulators and filters can be readily integrated on chip; (iii) systems based on the frequency domain are more naturally scalable than those using the time domain approach and exhibit robustness and reliability.

In this contribution, we will describe a frequency bin entanglement architecture in which high-dimensional quantum entanglement is preserved even after the photons have propagated in long-haul optical fiber. The frequency-entangled photon pairs are created by parametric down conversion in a periodically poled Lithium Niobate (PPLN) waveguide symmetrically around 1550 nm. A 3dB coupler separates the entangled photons and each photon is then launched in a distinct single mode fibre spool. A commercial tunable dispersion-compensation module is used at the output of one of the two spools which allows compensation of the relative dispersion effects (classical and non-local) experienced during propagation. Each output photon is then modulated by independent electro-optic phase modulators with the relative phase Dj between the modulation signals independently controlled by two phase shifters. After modulation, the photons are sent through narrowband fiber Bragg filter. Correlations are measured using commercial photon counter and Figure 1 shows the excellent recovery of the expected Bessel interference pattern after 60 km propagation in dispersive fiber. We expect such systems to play a major role in future quantum information networks, particularly for quantum-key distribution frequency-based systems or combined with resonator-based quantum frequency combs.