Quantum Optics 2 - Two photons and more

Go to Course: https://www.coursera.org/learn/quantum-optics-two-photons

Introduction

## Course Review: Quantum Optics 2 - Two Photons and More ### Overview "Quantum Optics 2 - Two Photons and More," available on Coursera, is an engaging and highly informative course designed for anyone looking to deepen their understanding of quantum optics, particularly the fascinating realm of entangled photons. Building upon the foundation laid in "Quantum Optics 1 - Single Photons," this course takes learners on an intricate journey through the quantum world, emphasizing the revolutionary implications of entangled states and their applications in emerging quantum technologies. ### Course Structure and Syllabus Breakdown The course is organized into five meticulously crafted lessons, each designed to facilitate a progressive understanding of complex concepts in quantum optics: 1. **Quasi-Classical States of Radiation: Single Mode Case** In this lesson, learners explore the formalism of quasi-classical states of radiation. This foundational concept introduced by Roy Glauber bridges the gap between quantum and classical understandings of light. Participants will gain insights into shot noise and the Standard Quantum Limit (SQL), preparing them for advanced discussions regarding the limits of optical measurements. 2. **Multimode Quasi-Classical States of Radiation** Expanding upon the single-mode cases, this lesson delves into multimode quasi-classical states, essential for understanding real classical light. Through examples like beam-splitters and beatnotes from multiple lasers, learners uncover intricate behaviors that highlight crucial differences between classical and quantum optics. The exploration of incoherent versus coherent states equips them with the necessary context for appreciating squeezed light. 3. **Squeezed Light: Beating the Standard Quantum Limit** This lesson introduces non-classical squeezed states of light, elucidating how they enable measurements with uncertainties below the SQL. The historical context surrounding squeezed light’s development, particularly its applications in detecting gravitational waves, showcases its significance and relevance in contemporary quantum technology. 4. **Entanglement: A Revolutionary Concept** Dive into the captivating world of entanglement, a phenomenon often regarded as one of the most perplexing aspects of quantum mechanics. This lesson discusses the pivotal debates surrounding entanglement, encapsulated by Einstein and Bohr, and features John Bell’s test of Bell’s inequalities. Participants will focus on the implications of photon polarization entanglement, enriching their comprehension of quantum phenomena. 5. **Entanglement Based Quantum Technologies** The culmination of the course is dedicated to the innovative technologies birthed from our understanding of entanglement. Learners will explore quantum cryptography, teleportation, and the fundamental challenges in building a quantum internet. Insights into quantum simulators illuminate the ongoing evolution of quantum computing, providing a glimpse into future possibilities. ### Recommendation "Quantum Optics 2 - Two Photons and More" comes highly recommended for those who have completed the first course in the series or possess a foundational understanding of quantum mechanics and optics. The instructional design encourages not only comprehension but also critical thinking and real-world application of quantum optical principles. #### Who Should Enroll? This course is ideal for: - Physics students and professionals eager to enhance their expertise in quantum optics. - Researchers interested in the latest developments in quantum technology and its applications. - Anyone with a curious mind and a desire to understand the pivotal role of entanglement in modern science. ### Conclusion In a rapidly evolving field that forms the backbone of many futuristic technologies, "Quantum Optics 2 - Two Photons and More" serves as an essential resource for both academic and practical knowledge. By marrying theoretical concepts with practical applications, this course not only enriches participants' understanding of quantum optics but also empowers them to contribute to the second quantum revolution. With its engaging content and thorough exploration of pivotal topics, it is a must-take course for aspiring quantum physicists and technology enthusiasts alike.

Syllabus

QUASI-CLASSICAL STATES OF RADIATION: SINGLE MODE CASE

In this lesson you will discover the formalism of quasi-classical states of radiation. Introduced by Roy Glauber in the early 1960's, it has allowed one to fill the gap between the notion of photon, at the heart of quantum optics, and the fundamental property of light considered as a classical field, its coherence. You will understand why the classical model of light is so successful. You will also understand what is the shot noise, and the associated Standard Quantum Limit (SQL). It will allow you to better appreciate, in future lessons, the possibility to pass that Standard Quantum Limit, which was considered for a long time an ultimate limit.

In this lesson you will learn how to use multimode quasi-classical states of light to describe real classical light, with several components. You will find the demonstration of the behaviour of a quasi-classical wave packet on a beam-splitter, a property used in quantum optics 1 to show the dramatic difference between a classical and a single photon wave packet. You will also learn how to describe in quantum optics the observation of a beatnote between two lasers. This is an interesting subject in itself, which raised many discussions in the years following the invention of lasers, and which is crystal clear when discussed as in this lesson. It is also a much used technique in AMO laboratories, known a heterodyne detection, of which you will learn the interest and the limits. You will also encounter some fundamental ideas about incoherent vs coherent muitimode radiation, and about similarities and differences between a classical statistical average and a quantum average. With these notions, you will be armed to better appreciate specific quantum properties of squeezed light, presented in the next lesson.

In this lesson, you will learn about non-classcal states of light, squeezed states, which allow one to "beat the Standard Quantum Limit", ie, to realize measurements with an uncertainty smaller than what was considered the ultimate limit, which in fact applies to a perfectly controlled classical beam of light, either a laser beam or a beam from a standard source. The notion of squeezed states of light was discovered in 1980, in the hope to succeed in detecting gravitational waves with giant optical interferometers. Almost 40 years later, Squeezed States of Light are effectively used with these giant interferometers, and they promise to increase significantly the volume of the universe explored by these interferometers. This is an example of a quantum technology based on a multi-photons quantum state, without any classical equivalent.

Entanglement is a quantum mechanical feature which was ignored or underestimated for a long time, in spite of the debate between Einstein and Bohr about it. It is only with John Bell's discovery, in the mid 1960's, that one could experimentally settle the debate, that some physicists realized the possibility to use entanglement for new ways of processing and transmitting information. In this lesson, you will learn about entanglement and Bell's inequalities tests, about the case of a pair of photons entangled in polarization, which is the system that has lead to the first convincing experiments. consequences about our understanding of the quantum world will be addressed, leaving to the next lesson the description of some quantum technologies based on entanglement.

The second quantum revolution is not only conceptual, with the understanding of the extraordinary character of entanglemnt, but it also promises to be technological, with applications impossible to conceive before realizing the potential of entanglement. Entanglement based quantum cryptography and the fascinating concept of quantum teleportation are the quantum technologies at the root of quantum networks, the so-called quantum internet, and in this lesson you will understand in detail their principles. In order to build a long distance quantum network, one needs good quantum memories, a very important challenge at the moment. You will also find in this lesson, with less details, the basic idea of quantum simulators, which was introduced by Feynman in 1982, but which came of age only in the recent years. It offers, in 2019, the fascinating perspective not only to elucidate physics phenomena too hard to be solved on a classical computer, such as High Critical Temperature Superconduction, but also to solve hard practical optimization problems, thanks to the concept of NISQ (Noisy Intermediate Scale Quantum) simulators, which do not need to be perfect.