English: Discussion about how quantum key distribution methods based on measuring the polarization of photons can be used to keep communications secure. In particular, the methods of Bennett and Brassard (BB84) and Ekert (E91) are explained.

Contents 00:00 - Introduction 00:25 - One-time pad 02:17 - Public key cryptography 03:22 - Photon polarization 04:46 - BB84 08:31 - No-cloning theorem 09:06 - Quantum networks 09:55 - E91 11:50 - Closing remarks

References [1] Black Marble 2016, NASA's Goddard Space Flight Center https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=30878 [2] IQM Quantum Computer in Espoo Finland by Ragsxl, File:IQM_Quantum_Computer_Espoo_Finland.jpg [3] C. H. Bennett and G. Brassard, “Quantum cryptography: Public key distribution and coin tossing”, Proceedings of the International Conference on Computers, Systems and Signal Processing 175 (1984). [4] C. H. Bennett and G. Brassard, “Quantum cryptography: Public key distribution and coin tossing”, Theoretical Computer Science 560, 7 (2014). [5] S.-K. Liao et al., “Satellite-Relayed Intercontinental Quantum Network”, Physical Review Letters 120, 030501 (2018). [6] A. K. Ekert, “Quantum Cryptography Based on Bell’s Theorem”, Physical Review Letters 67, 661 (1991). [7] R. Ursin et al., “Entanglement-based quantum communication over 144 km”, Nature Physics 3, 481 (2007). [8] 3D cut of the LHC dipole , CERN, OPEN-PHO-ACCEL-2014-003-8 https://home.cern/resources/image/accelerators/lhc-images-gallery [9] NASA's Laser Communications: To the Space Station and Beyond, NASA's Goddard Space Flight Center https://images.nasa.gov/details/NASAs_Laser_Communications_To_the_Space_Station_and_Beyond

[10] David J. Griffiths and Darrell F. Schroeter, “Introduction to Quantum Mechanics Third Edition”, (CUP 2018). ISBN: 978-1-107-18963-8