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Relativistic and Quantum Cryptography

2. Light, Polarisation, and Measurement

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In this mini-lecture, we discuss how the polarisation of light can be affected by measurement. In particular, we consider: (i) the polarisation of light as the axis in space along which the light wave oscillates; (ii) horizontal and vertical polarisation; (iii) light polarisation in quantum theory; (iv) how measuring the polarisation of light causes it to ‘choose’ between one of two orthogonal polarisation states; (iv) an example of these quantum measurement rules as applied to polarised light; and (v) a demonstration of polarised light using a laser pointer and polarising filters.


In this course, Professor Adrian Kent (University of Cambridge) explores relativistic and quantum cryptography. In the first mini-lecture, we introduce the key principles in the Special Theory of Relativity and in Quantum Theory that are needed to understand the cryptographic schemes used in subsequent videos. In the second mini-lecture, we discuss the polarisation of light and how it can be affected by measurement. In the third mini-lecture, we introduce the No-Cloning Theorem and the Relativistic No-Summoning Theorem. In the fourth mini-lecture, we explore the concept of bit commitment. In the fifth mini-lecture, we discuss how to use one-time pads to encrypt messages and prevent eavesdropping. In the sixth mini-lecture, we introduce the BB84 (Bennett-Brassard, 1984) quantum key distribution protocol, which utilises polarisation states to encrypt messages.


Adrian Kent is Professor of Quantum Physics in the Department of Applied Mathematics and Theoretical Physics (DAMTP) at the University of Cambridge. He is also a member of the Cambridge Centre for Quantum Information and Foundations and a Distinguished Visiting Research Chair at the Perimeter Institute for Theoretical Physics. His principal research interests are in quantum foundations, quantum information theory, and quantum cryptography. He is a pioneer in the field of relativistic quantum cryptography, having provided the first relativistic cryptography protocols for bit commitment and ideal coin tossing that achieve unconditional security in 1999. He has published papers extensively on this topic as well as other topics such as quantum key distribution. Professor Kent is a co-editor of the book Many Worlds?: Everett, Quantum Theory, and Reality (2010).

Cite this Lecture

APA style

Kent, A. (2022, January 13). Relativistic and Quantum Cryptography - Light, Polarisation, and Measurement [Video]. MASSOLIT.

MLA style

Kent, A. "Relativistic and Quantum Cryptography – Light, Polarisation, and Measurement." MASSOLIT, uploaded by MASSOLIT, 13 Jan 2022,

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