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New protocols related to internet-of-things applications may introduce previously unnoticed measurement effects due to the narrowband nature of these protocols. Such technologies also require less loading to meet the coherence bandwidth conditions, which may lead to higher variations accross the channel. This can cause a need to take additional components into account in the assessment of uncertainty. In this work, we present a preliminary study on uncertainties of NB-IoT measurements in reverberation chambers. We show a need to account for both the number of mode-stirring samples and the lack of spatial uniformity in the uncertainty analysis, where the latter generally dominates for wireless testing. We provide preliminary results for the uncertainty including both effects. We introduce a hypothesis for the effects of loading on the uncertainty, introducing that there may be an optimal loading point to minimize uncertainty, where we describe that this decision may not depend only on coherence bandwidth, but also on the number of significant modes.

Quantum key distribution (QKD) enables participants to exchange secret information over long distances with unconditional security. However, the performance of today's QKD systems is subject to hardware limitations, such as those of available nonclassical-light sources and single-photon detectors. By encoding photons in high-dimensional states, the rate of generating secure information under these technical constraints can be maximized. Here, we demonstrate a complete time-energy entanglement-based QKD system with proven security against the broad class of arbitrary collective attacks. The security of the system is based on nonlocal dispersion cancellation between two time-energy entangled photons. This resource-efficient QKD system is implemented at telecommunications wavelength, is suitable for optical fiber and free-space links, and is compatible with wavelength-division multiplexing., United States. Army Research Office (Defense Advanced Research Projects Agency. Information in a Photon (InPho) Program (Grant W911NF-10-1-0416)), National Science Foundation (U.S.). Integrative Graduate Education and Research Traineeship (Grant DGE-1069420)

Conventional quantum key distribution (QKD) typically uses binary encoding based on photon polarization or time-bin degrees of freedom and achieves a key capacity of at most one bit per photon. Under photon-starved conditions the rate of detection events is much lower than the photon generation rate, because of losses in long distance propagation and the relatively long recovery times of available single-photon detectors. Multi-bit encoding in the photon arrival times can be beneficial in such photon-starved situations. Recent security proofs indicate high-dimensional encoding in the photon arrival times is robust and can be implemented to yield high secure throughput. In this work we demonstrate entanglement-based QKD with high-dimensional encoding whose security against collective Gaussian attacks is provided by a high-visibility Franson interferometer. We achieve unprecedented key capacity and throughput for an entanglement-based QKD system because of four principal factors: Franson interferometry that does not degrade with loss; error correction coding that can tolerate high error rates; optimized time–energy entanglement generation; and highly efficient WSi superconducting nanowire single-photon detectors. The secure key capacity yields as much as 8.7 bits per coincidence. When optimized for throughput we observe a secure key rate of 2.7 Mbit s[superscript −1] after 20 km fiber transmission with a key capacity of 6.9 bits per photon coincidence. Our results demonstrate a viable approach to high-rate QKD using practical photonic entanglement and single-photon detection technologies., United States. Army Research Office (Defense Advanced Research Projects Agency. Information in a Photon (InPho) Program Grant W911NF-10-1-0416)