Improvement of continuous-variable quantum key distribution systems by using optical preamplifiers

Abstract

Continuous-variable quantum key distribution protocols have been implemented recently, based on Gaussian modulation of the quadratures of coherent states. A present limitation of such systems is the finite efficiency of the detectors, that can in principle be compensated for by the use of classical optical preamplifiers. Here we study this possibility in detail, by deriving the modified secret key generation rates when an optical parametric amplifier is placed at the output of the quantum channel. After presenting a general set of security proofs, we show that the use of preamplifiers does compensate all the imperfections of the detectors when the amplifier is optimal in terms of gain and noise. Imperfect amplifiers can also enhance the system performance, under conditions which are generally satisfied in practice.

Improving the maximum transmission distance of continuous-variable quantum key distribution using a noiseless amplifier

“…First, it should be noted that while amplifiers can effectively recover classical signals, they only offer limited advantages when working on quantum signals, as amplification is bound to preserve the original signal to noise ratio (SNR) [19,24,25]. This implies that ordinary linear amplifiers, as those realized by optical parametric processes [26], can only find limited applications in the context of QKD [27].…”

Heralded photon amplification for quantum communication

“…This is an attractive proposal from a practical point of view, and it has already triggered a couple of proof-of-principle experiments [9,10]. These experiments focus on the applications of the amplifiers in continuous-variable-based quantum information science, e.g., distilling continuous-variable entanglement [9] or improving continuous-variable quantum key distribution [10,11].…”

Continuous-variable measurement-device-independent quantum key distribution using squeezed states

“…Compared with the performance of using perfect and imperfect detectors, we find that the inefficiency and electronic noise of the practical homodyne detector have a significant influence on the transmission distance. It is possible that these imperfections can be compensated by optical phase-sensitive-amplifiers [45,46].…”