Abstract
We propose and experimentally demonstrate a plug-and-play, practical, and enabling method allowing to synchronise the building blocks of a quantum network in an all-optical way. Our scheme relies on mature and reliable classical telecommunication and non-linear optical technologies, and can be implemented in a universal way with off-the-shelf components. Compared to already reported solutions, it allows achieving high-quality synchronisation compatible with high network-operation rate and is free from opto-electronic jitters affecting servo-loop-based configurations. We test our scheme with a genuine quantum optical method in terms of the interference between two photons coming from two remotely synchronised sources spaced by distances of up to 100 km. Measured visibilities well above 90% confirm the validity of our approach. Due its simplicity and high-quality performance, our scheme paves the way for the synchronisation of long-distance quantum networks based on fibre, free-space, as well as hybrid solutions.
Highlights
In the context of digital society, quantum networks promise to combine highly efficient data processing with ultra-secure data exchanges.[1,2,3]. This vision has motivated the development of crucial constituents including quantum memories,[4,5] coherent interfaces between different systems,[6,7,8,9] and optical quantum communication links based on quantum teleportation over long fibre connections.[10,11,12,13]
We have presented and experimentally demonstrated a novel protocol that solely and relies on an alloptical master clock laser, the timing precision of which guarantees the synchronisation of a network blocks over long distance
The synchronisation approach proposed here is extremely versatile and allows in principle to add to a quantum network as many nodes as necessary and this whatever their nature is
Summary
In the context of digital society, quantum networks promise to combine highly efficient data processing with ultra-secure data exchanges.[1,2,3] This vision has motivated the development of crucial constituents including quantum memories,[4,5] coherent interfaces between different systems,[6,7,8,9] and optical quantum communication links based on quantum teleportation over long fibre connections.[10,11,12,13] the development of operational quantum networks remains hindered by the lack of practical synchronisation methods that allow the different building blocks to work together under high timing accuracy. We emphasise that random timing-jitters are responsible for the main limitation in timing precision for most of the reported synchronisation configurations They represent an intrinsic limit to maximum achievable clock rates as they cause signals from different clock cycles to superpose.[22] In our scheme, the timing accuracy is in principle only defined by the stability of the master clock repetition rate, whose uncertainty is well below 100 fs for off-the-shelf ultra-fast lasers and can go down to a fraction of a femtosecond in research-grade systems.[27] our method guarantees high precision and is straightforwardly compatible with ultra-fast operation driven by master clock lasers paced at GHz repetition rates.[24] Eventually, in the particular case of quantum network configurations requiring an interferometric phase stabilisation,[28] our method is fully compliant with the addition of an optical frequency reference, as achieved in large infrastructures for time–frequency dissemination.[29]. Without changing the pumping conditions, and, as a consequence, the photon-pair emission statistics, this can be done by using a clock with a higher repetition rate of 10 GHz and state-of-the-art superconducting detector with ultra-low detection jitters and quantum efficiency close to 90%.30 This would increase the overall count by a factor 40 and lead to a measured jitter ~0.5 ps
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