Jan 29 2019
Although quantum key distribution (QKD) is the most sophisticated quantum technology, currently, the secure encryption of information units using this method is limited by the capacity of the channel to share or send secret bits.
In a study reported recently in EPJ D, Gan Wang, affiliated with Peking University, Bejing, China as well as the University of York, United Kingdom, and colleagues demonstrate ways for a better approach to the secret key capacity by enhancing the lower boundary of the channel.
While using the QKD method for secure encryption of information units, secret keys are distributed between two parties—namely, Alice, the sender, and Bob, the receiver—by using quantum systems as information carriers.
In a QKD transmission, the first stage is monitored by Eve, an eavesdropper, when a raw key is shared by Alice and Bob. However, due to quantum rules, Eve does not have access to a flawless copy of the signals sent by Alice. In the second stage, Bob and Alice follow classical protocols which involve the correction of errors and improvement of privacy levels. Thus, Bob and Alice share a full secret key that can be used afterward to convey confidential messages.
The focus of the researchers on a specific type of channel, known as the noisy thermal amplifier channel, in which the input signals are amplified along with noise produced by the thermal environment. The researchers evaluate the highest known amount of secret information units, or bits, that can be shared by Bob and Alice through such a channel. This is performed by injecting controlled noise—formed of well-defined thermal agitation—into the detection apparatuses. The lower boundary of the capacity in the amplifier channel can be improved by optimizing over this noise. The researchers also affirm that the secret key distribution over this channel may take place at higher rates compared to the transmission of quantum information itself.