Key preparation improves the efficiency of cryptic key transmissions
Key preparation improves the efficiency of cryptic key transmissions lead image
Quantum key distribution (QKD) is a secure communication method for sharing an informatic key with which a communication can be decrypted. Each qubit key is selected randomly and encoded in the states of photons. Any eavesdropping on the qubit transfer is picked up as a measurement in the detection statistics. Physicists have altered key preparation to improve speed and efficiency and report their new experimental protocol in Applied Physics Letters.
Intensity modulators are important in encoding the key as they randomly apply a different intensity to each photon generated by a pulsed diode laser. Most types of QKD protocols use four different quantum states and three intensities as a decoy, and this requires two modulators. However, in this protocol the researchers were able to use only three states and two intensities, and therefore required only one intensity modulator, increasing the speed and simplicity of qubit preparation.
The researchers encoded time-bin properties of photons at 2.5 gigahertz. Over a 200-kilometer fiber, this increased the secret key rate by an order of magnitude. When tested continuously for 24 hours over a standard 200-kilometer fiber, the signal automatically stabilized and suffered no interruptions. The authors carried out a security analysis taking into account finite-key effects and so proved the security of the protocol against the most general class of attacks.
The record for long-distance QKD transmission is 300 kilometers along a standard optical fiber, but co-author of the study Alberto Boaron is now using the new transmitter setup with other detectors to push the transmission distance to the limits and break the record.
Source: “Simple 2.5 GHz time-bin quantum key distribution,” by Alberto Boaron, Boris Korzh, Raphael Houlmann, Gianluca Boso, Davide Rusca, Stuart Gray, Ming-Jun Li, Daniel Nolan, Anthony Martin, and Hugo Zbinden, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5027030 .
