Davide Bacco
DTU - Technical University of Denmark
Davide Bacco was born in Italy in 1986. He received his M.Sc degree on Telecommunication Engineering in 2011 at the University of Padova, Italy. In 2015 he accomplished the Ph.D. degree on Science Technology and Spatial Measures at the University of Padova. During 2015 he worked as a postdoctoral fellow at the Institute for Photonic and Nanotechnology of the National Research Center, Padova. Now he is currently a MSCA H.C. Ørsted Postdoc at the Department of Photonics Engineering of the Technical University of Denmark (DTU). His research interests regard quantum optical communications, secure communications and silicon photonics for optical communications.
IntroductionQuantum key distribution (QKD), a branch of Quantum Communications (QCs), provides ultimate security based on quantum mechanics laws. The main problems are related to the relatively short propagation distances and... [ view full abstract ]
Introduction
Quantum key distribution (QKD), a branch of Quantum Communications (QCs), provides ultimate security based on quantum mechanics laws. The main problems are related to the relatively short propagation distances and the low transmittable bit rates. A fundamental way to overcome these issues is represented by high-dimensional (HiD) quantum states, which allow increased information capacity and higher robustness against channel noise. Multicore fibers (MCF) open a new scenario for quantum communications allowing HiD QCs encoded in spatial modes. Photonic integrated circuits (PIC) are particularly suitable for the generation and manipulation of HiD quantum states. Based on silicon PIC, we use a MCF for proving decoy-state HiD QKD.
Method
In Figure 1 we report the chip design of the HiD decoy-state protocol. By tuning cascaded Mach-Zehnder interferometers (MZIs), we prepare HiD quantum states in different mutually unbiased basis (MUBs). A train of weak coherent pulses (WCPs) is injected into Alice chip, where multiple variable optical attenuators (VOAs) are used to decrease the number of photons per pulse. Alice randomly chooses one of the bases and one of the four states to transmit to Bob. After the transmission, the quantum states are coupled into Bob’s chip and randomly measured in one of the bases.
Results
The three mutually unbiased bases (figure 2a)) are prepared and measured with states tomographies in figures 2b/c). A real-time QKD experiment with a 5kHz repetition rate is proved over 3m link. Fig 3 a) shows the comparison between experimental data and theoretical simulation. In Fig. 3b) we present the QBER (13% below coherent and individual attacks limit) as a function of time for 10 minutes.
Discussion
In fiber transmission, phase and polarization of coherent light randomly change, mostly due to environmental perturbations. In MCF, each core acts independently from the other. This effect was mitigated by the short link distance, but a phase stabilization system can be implemented for a longer transmission. The repetition rate of 5kHz represents the main limitation for a long link deployment. Different kinds of material for the active modulators can be investigated to overcome this problem.
