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Quantum Optics – Quantum cryptography the BB84 QKD scheme

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One-photon based quantum technologies In this lesson, you will discover two quantum technologies based on one photon sources. Quantum technologies allow one to achieve a goal in a way qualitatively different from a classical technology aiming at the same goal. For instance, quantum cryptography is immune to progress in computers power, while many classical cryptography methods can in principle be broken when we have more powerful computers. Similarly, quantum random number generators yield true random numbers, while classical random number generators only produce pseudo-random numbers, which might be guessed by somebody else than the user. This lesson is also an opportunity to learn two important concepts in quantum information: (i) qubits based on photon polarization; (ii) the celebrated no-cloning theorem, at the root of the security of quantum cryptography. Learning Objectives • Apply your knowledge about the behavior of a single photon on a beam splitter to quantum random number generators. • Understand the no-cloning theorem • Understand and remember the properties of q qubit This course gives you access to basic tools and concepts to understand research articles and books on modern quantum optics. You will learn about quantization of light, formalism to describe quantum states of light without any classical analogue, and observables allowing one to demonstrate typical quantum properties of these states. These tools will be applied to the emblematic case of a one-photon wave packet, which behaves both as a particle and a wave. Wave-particle duality is a great quantum mystery in the words of Richard Feynman. You will be able to fully appreciate real experiments demonstrating wave-particle duality for a single photon, and applications to quantum technologies based on single photon sources, which are now commercially available. The tools presented in this course will be widely used in our second quantum optics course, which will present more advanced topics such as entanglement, interaction of quantized light with matter, squeezed light, etc... So if you have a good knowledge in basic quantum mechanics and classical electromagnetism, but always wanted to know: • how to go from classical electromagnetism to quantized radiation, • how the concept of photon emerges, • how a unified formalism is able to describe apparently contradictory behaviors observed in quantum optics labs, • how creative physicists and engineers have invented totally new technologies based on quantum properties of light, then this course is for you. Subscribe at: https://www.coursera.org
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Text Comments (4)
Muhammad Zeeshan (4 months ago)
Question: I have a confusion that, Why can't Eve measure the Polarization when he is getting the original photons? Does it require some speicific method or equipment that is not accessable by Eve or there is some other simple explanation. OR What if Eve got the Photons coming for Alice and he changes those and send ahead to Bob and FORTUNATELY he also put the 60% or 80% of photons in the same polarization sequence as original photons, What in that case? Can no one detect that the data is lost?
zef wolffs (1 month ago)
Eve can measure the Polarization when he is getting the original photons, it's just that this information is useless as Alice won't tell Eve which ones he measured correctly.
via prenestina (7 months ago)
do you have also a version in English?
Ayoub Merzak (1 year ago)
Thank you for the amazing presentation. One thing though you Sir did not talk about is how the sequence HHRLRVV.. both Alice and Bob have agreed on is actually converted into classical bits (0s and 1s)? And how do Alice and Bob agree on which encoding to use (I mean by that which beam spliter (HV, RL) corresponds to which bit (0, 1) )?

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