A well-known empirical rule for the demand of wireless communication systems is that of Edholm's law of bandwidth. It states that the demand for bandwidth in wireless short-range communications doubles every 18 months. With the growing demand for bandwidth and the decreasing cell size of wireless systems, terahertz (THz) communication systems are expected to become increasingly important in modern day applications. With this expectation comes the need for protecting users' privacy and security in the best way possible. With that in mind, we show that quantum key distribution can operate in the THz regime and we derive the relevant secret key rates against realistic collective attacks. In the extended THz range (from 0.1 to 50 THz), we find that below 1 THz, the main detrimental factor is thermal noise, while at higher frequencies it is atmospheric absorption. Our results show that high-rate THz quantum cryptography is possible over distances varying from a few meters using direct reconciliation, to about 220m via reverse reconciliation. We also give a specific example of the physical hardware and architecture that could be used to realize our THz quantum key distribution scheme.

The transmission of one-hundred-femtosecond-long pulses by following an ON-OFF keying modulation spread in time has been proposed as a way to enable Terahertz (THz)-band (0.1-10 THz) communications over short distances. Such modulation minimizes the probability of collisions due to the very small time that the channel is occupied by a user. However, given that many of the envisioned applications involve very large node densities, multi-user interference becomes unavoidable. In this paper, a stochastic model of multi-user interference is developed and experimentally validated. The model takes into account the fact that the interference power at the receiver is not a combination of the received powers from the individual nodes, but the power of the combination of the received signal amplitudes. For this, first, a mathematical framework is developed to compute the probability density function (PDF) of the interference generated by one interfering node at the receiver, starting from the PDFs of the pulse received energy and the PDF of the pulse shape. Then, the model is extended to account for multiple nodes which can constructively or destructively interfere. The developed model is experimentally validated by means of an innovative setup and the extensive numerical results are provided to analyze the trends of multi-user interference in pulse-based THz communications.