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Why Quantum of Quasars?

C. Foellmi

Published Jul 5, 2010• 0 citations
Publisher

Abstract

Why the Quantum of Quasars Workshop?Or more precisely: why reopening the questions of second-order photon correlations in astrophysics?The answer lies in the combination of three things.First, quantum optics made fantastic progresses since the original experiment by Hanbury Brown & Twiss; progresses ignored so far in astrophysics.Second, the astrophysics community plans to built giant telescopes and telescope arrays.Third, there have been important technological breakthroughs in the field of ultra-fast low-light detectors.More importantly, light carries much more information that its instantaneous frequency, intensity and polarization.For a scientific field aiming at exploring the Universe, and whose exploration tools are mostly based on light, it is stunning to realize that so far, astrophysics mostly remained at the first order of photon correlations, and furthermore extremely exciting to explore the possible links or applications of quantum light studies in astrophysics.The slides of all talks are available at http://quantumofquasars.org.

DOI
10.22323/1.101.0001

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Physica Scripta•Feb 17, 2012•1 citation
Why the Quantum of Quasars Workshop?Or more precisely: why reopening the questions of second-order photon correlations in astrophysics?The answer lies in the combination of three things.First, quantum optics made fantastic progresses since the original experiment by Hanbury Brown & Twiss; progresses ignored so far in astrophysics.Second, the astrophysics community plans to built giant telescopes and telescope arrays.Third, there have been important technological breakthroughs in the field of ultra-fast low-light detectors.More importantly, light carries much more information that its instantaneous frequency, intensity and polarization.For a scientific field aiming at exploring the Universe, and whose exploration tools are mostly based on light, it is stunning to realize that so far, astrophysics mostly remained at the first order of photon correlations, and furthermore extremely exciting to explore the possible links or applications of quantum light studies in astrophysics.The slides of all talks are available at http://quantumofquasars.org.
Why the Quantum of Quasars Workshop? Or more precisely: why reopening the questions of second-order photon correlations in astrophysics? The answer lies in the combination of three things. First, quantum optics made fantastic progresses since the original experiment by Hanbury Brown & Twiss; progresses ignored so far in astrophysics. Second, the astrophysics community plans to built giant telescopes and telescope arrays. Third, there have been important technological breakthroughs in the field of ultra-fast low-light detectors. More importantly, light carries much more information that its instantaneous frequency, intensity and polarization. For a scientific field aiming at exploring the Universe, and whose exploration tools are mostly based on light, it is stunning to realize that so far, astrophysics mostly remained at the first order of photon correlations, and furthermore extremely exciting to explore the possible links or applications of quantum light studies in astrophysics. The slides of all talks are available at http://quantumofquasars.org.
The idea of exploiting quantum features of light to perform more precise astrophysical measurements is a long-desired goal of both the optics and astrophysics communities, but only recently have theoretical proposals started to be experimentally implemented. One important goal is to increase the baseline distance between telescopes in interferometry, and thus improve the angular resolution of the celestial object. Some of the earlier proposals rely on the use of quantum repeaters to connect the two baseline stations. However, another proposal employs other quantum optical approaches to circumvent the need for quantum repeaters, while still providing a quantum advantage. I will discuss the on-going project for building quantum-enhanced telescopes for precision astrometry, i.e., measurements of position and velocity of celestial objects. I will present a proof-of-principle experimental demonstration of a two-photon interferometer for such goal. Moreover, I will present a single-photon-sensitive spectrometer, based on a linear array of 512 single-photon avalanche diode detectors, with 0.04 nm spectral and 40 ps temporal resolutions. This device enables us to implement a spectral binning technique, essentially allowing us to perform multiple measurements together, because each frequency can be treated as an independent measurement. Such device could also be used in other applications. Lastly, I will report on our frequency-resolved Hanbury Brown-Twiss experiments. Our work represents an important step towards quantum telescopes.
Quantum technologies have been introduced widely in different scientific fields and some industry application have been developed. In this work we outline the history and development of a new field of Astronomy which is based on the concept of quantum mechanics and takes advantage from the technological instruments developed recently for quantum information in order to investigate new properties of the light coming from the sky. The development of this Quantum Astronomy instruments is still very active (e.g. Adaptive Optics integration) and the scientific target is pushed to new exiting limits: for example, periodic optical monitor of pulsars, lunar occultation; transit-occultations and application of the Hanbury Brown Twiss Intensity Interferometry.
I briefly review second order or two-photon correlations starting from the Hanbury Brown-Twiss correlations to its modern versions in quantum optics studies. With this background, I address some foundational issues in the physics of quantum correlations and quantum entanglement and argue in favour of the validity of Einstein locality, to settle a long-standing debate. Understanding entanglement from this perspective has applications in quantum information theory, especially in gaining intuition about the relation between different measures of entanglement and its time evolution. Some examples are highlighted. I discuss how ideas on photon correlations applied to squeezing fluctuations in coherent light have become important in metrology, and perhaps crucial, in the successful operation of high sensitivity gravitational wave detectors.
An account is given of optical coherence theory as it existed in the 1950's when, essentially, only thermal sources and slow detectors were available and it sufficed to characterize the coherence and polarization properties of an electromagnetic field by second-order correlation functions. The necessity for a more sophisticated specification of the coherence properties of fields, involving the use of higher-order correlation functions, first hinted at by the Hanbury-Brown-Twiss experiments and emphasized by the advent of the laser, is then introduced. Both classical and quantum mechanical treatments are discussed, each leading, in almost all cases of practical interest, to similar results. It is seen that the development of fast detectors enabled the higher-order correlation functions to be measured using photon counting techniques and an account of experimental work verifying the complete theory using such techniques is given. The review concludes with a discussion of some developments in associated areas whose origin lies in the resurgence of interest in coherence theory during the last decade.
Much of our present understanding of the microscopic world is based on quantum mechanics. The field owes much of its existence to the venerable science of optics, since the fundamental ideas on the nature of the interaction between light and matter lie at the roots of its origin. We have now reached one century of quantum mechanics. In contrast, the splendid blossoming of quantum optics began only after the comparatively recent invention of the laser. Since then, it has become an exciting and always expanding area at the cutting-edge of research, in part because theory and experiment are more closely connected in this field than any other. Moreover, the technological distance between fundamental studies and practical applications has always been very short in quantum optics. As a result, modern engineering is increasingly based on quantum rather than classical physics; we are facing a transition similar to the one society confronted 200 years ago, at the start of the Industrial Revolution. In parallel with this, the physics community is witnessing the recent and vigorous emergence of quantum information. It aims at exploring the physical foundations of information and at developing efficient methods for processing quantum information. The questions driving this field reveal a profound change in attitude towards fundamental aspects of quantum theory. The photon turns out to be a tool extremely well suited to exploring theoretical quantum information schemes and their experimental implementations. Mirroring this continued progress has been the growth and development of the series of annual Central European Workshops on Quantum Optics (CEWQO). The series started at the beginning of the 1990s, as rather small meetings of physicists from a few countries in central-eastern Europe. In two decades, the workshops have transformed into important events that reach well beyond the original rather restricted geographical limits. The history of CEWQOs can be found in the preface to the proceedings of the 15th CEWQO ( Physica Scripta 2009 T135 011005 ). The 18th edition of CEWQO (CEWQO11) was held in Madrid in 2011. There were about 250 participants, from practically every European country. Many colleagues from other continents also joined the event, including well-established researchers in the field. This is a clear demonstration that these meetings provide an excellent chance to hear about the latest results and new directions of research. The organization of CEWQO11 was carried out by a committee consisting of members active in this topic in Madrid. From Universidad Complutense, Alberto Galindo and Luis L Sánchez-Soto; from Universidad Autónoma, Jose Calleja and Carlos Tejedor; from Universidad Politécnica, Enrique Calleja; from Universidad Carlos III, Alberto Ibort; and from the National Research Council (CSIC), Juan León and Juan J García-Ripoll. Special thanks go to the Spanish Ministry for Science and Innovation, Universidad Complutense and the Quitemad Consortium for financial support. The proceedings of the 16th CEWQO held at the University of Turku, Finland and the 17th CEWQO held at the University of St Andrews, Scotland, UK are also available ( Physica Scripta 2010 T140 and Physica Scripta 2011 T143 ). The present Topical Issue is a collection of papers presented in Madrid; they represent an illustrative sample of the major achievements and trends in this area. In turn, they reflect the wide range of interests in this rapidly evolving field. Some collaborators from different scientific centres who could not, due to different reasons, come to Madrid, but participated in previous CEWQOs and plan to participate in future CEWQOs, also contributed to this issue. The papers are arranged alphabetically by the name of the first author. Special thanks goes to Roger Wäppling, the Managing Editor of Physica Scripta , and Graeme Watt, the Publisher, for the opportunity to publish CEWQO11. From a Physica Scripta Editorial Board meeting it was decided that Physica Scripta could offer a poster prize (200 euros + certificate) for young scientists (less than 30 years old) at the annual CEWQO conference. A panel of experts was formed to judge the posters which included Apostol Vourdas, University of Bradford, UK (Chairman), Alberto Ibort, University Carlos III of Madrid, Spain, Andrei Klimov, University of Guadalajara, Mexico, Margarita A Man'ko, P N Lebedev Physical Institute, Moscow, Russia and Antonino Messina, University of Palermo, Italy. The poster ''How can we check the uncertainty relation?'' by Vladimir Chernega, PhD student of the P N Lebedev Physical Institute, won the prize. The 19th Central European Workshop on Quantum Optics will be held in Sinaia, Romania on 2–6 July 2012. It will be chaired by Professor Aurelian Isar from the Horia Hulubei National Institute for Research and Development in Physics and Nuclear Engineering, Bucharest.