Exploiting Nonlocal Correlations for Dispersion-Resilient Quantum Communications

Encoding quantum information via time-bin entangled states has had a profound impact on the development of quantum communications. However, dispersive propagation limits their achievable transmission distances. Here we describe a regime for nonlocal dispersion cancellation where the sum of arrival times of photons undergoing identical dispersion remains highly correlated. We exploit this effect to mitigate dispersive effects in a quantum key distribution fiber link, allowing an increase in the secret key rate by over a factor of 5 after 80 km of optical fiber dispersion.

Read more at Physical Review Letters:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.134.220801

Photo caption:
Experimental quantum interference results. (a) Experimental Setup. MZI: Mach-Zehnder interferometer (delay of ∆τ=644 ps); PM: phase modulator; SW: spiral waveguide; DEMUX: demultiplexer. The same MZI is used for both the state preparation and analysis. Biphoton time-of-arrivals maps of (b) constructive and (c) destructive quantum interferences without introducing any dispersion, along with the histograms of their sum (t_s+t_i, green curves) and difference (t_s-t_i, orange curves) correlations. (d) Quantum interference patterns obtained by retrieving the post-selected sum (green circles) and difference (orange crosses) correlations within the blue dashed box, together with their corresponding fit shown by the dashed curves. Biphoton time-of-arrivals map of (e) constructive and (f) destructive quantum interferences after propagation through a total of 200 km SMF-equivalent dispersion with the histograms of their sum and difference correlations. (g) Resulting quantum interference patterns for the post-selected region in both cases. Error bars are omitted since they are smaller than the markers used for the data points.