Abstract
Quantum key distribution (QKD) relies on quantum communication to allow distant parties to share a secure cryptographic key. Widespread adoption of QKD in current telecommunication networks will require the development of simple, low-cost, and stable systems. However, current QKD implementations usually include additional hardware that perform auxiliary tasks such as temporal synchronization and polarization basis tracking. Here we present a polarization-based QKD system operating at 1550 nm that performs synchronization and polarization compensation by exploiting only the hardware already needed for the quantum communication task. Polarization encoding is performed by a self-compensating Sagnac loop modulator that exhibits high temporal stability and the lowest intrinsic quantum bit error rate reported so far. The QKD system was tested over a fiber-optic link, demonstrating tolerance up to about 40 dB of channel losses. Due to its reduced hardware requirements and the quality of the source, this work represents an important step towards technologically mature QKD systems.
Highlights
A major challenge for today’s communication networks is to ensure safe exchange of sensitive data between distant parties
This measurement was performed by sending a pseudo-random qubit sequence of {|0, |1, |+ } states and measuring the quantum bit error rate (QBER) of the sifted string recovered by Bob
The QBER was estimated for both the Z key-generation basis and the X control basis
Summary
A major challenge for today’s communication networks is to ensure safe exchange of sensitive data between distant parties. Global navigation satellite systems (GNSSs) can be used to synchronize Alice and Bob, since these systems can give precise temporal references [14,36,37] All these approaches, require additional hardware with respect to what is already needed for the quantum communication task. The QKD source here presented exhibits several hours of stability and an intrinsic quantum bit error rate (QBER) on the order of 0.05%, which is, to the best of our knowledge, the lowest reported so far This source exploits the scheme for polarization encoding based on a Sagnac loop ( the name POGNAC) we introduced in Ref. A low dark count rate allows the QBER to stay low even for strong levels of channel attenuation (i.e., long fiber links)
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