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Quantum Electronics

Coherence and lasers

Anatolii N Oraevsky

Published Dec 31, 2002• 1 citation
Publisher

Abstract

Recollections are reported about the attitude of N.G. Basov to the problem of coherence of stimulated transitions at the very beginning of studies devoted the creation of masers and lasers. It is shown that the problem of coherence of stimulated transitions can be solved in a multiparticle system. The role of stimulated transitions in a variety of processes proceeding in the nature is discussed. The contribution of N.G. Basov and his school to the development of quantum electronics and laser physics is briefly discussed.

DOI
10.1070/qe2002v032n12abeh002347

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Recollections are reported about the attitude of N.G. Basov to the problem of coherence of stimulated transitions at the very beginning of studies devoted the creation of masers and lasers. It is shown that the problem of coherence of stimulated transitions can be solved in a multiparticle system. The role of stimulated transitions in a variety of processes proceeding in the nature is discussed. The contribution of N.G. Basov and his school to the development of quantum electronics and laser physics is briefly discussed.
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Today, precise laser control of the quantum states of single ions cooled to low temperatures in traps ensures significant progress in the development of such physical areas as optical and microwave frequency standards, quantum computing, and accurate measurements of transition frequencies to confirm fundamental physical theories.Pioneering ideas about the possibility of using lasers in the development of frequency standards, expressed in the 1960s by the Nobel laureate N G Basov, have enjoyed rapid development: the relative accuracy of frequency standards has reached the 18th decimal place, and the experimentally demonstrated coherence time of narrow optical transitions amounts to tens of seconds.The paper presents a selective review, as well as the results of research at the Lebedev Physical Institute, in the area of using elements of quantum logic in the action of coherent laser pulses on single ions.Also discussed is the use of quantum logic methods in optical clocks based on the Al + ion and the multiply charged Al + ion, and also in quantum computers based on Ca + and Yb + ions.
The book embraces a wide spectrum of problems falling under the concepts of "Quantum optics" and "Laser experiments". These actively developing branches of physics are of great significance both for theoretical understanding of the quantum nature of optical phenomena and for practical applications. The book includes theoretical contributions devoted to such problems as providing a general approach to describe electromagnetic field states with correlation functions of different nature, nonclassical properties of some superpositions of field states in time-varying media, photon localization, mathematical apparatus that is necessary for field state reconstruction on the basis of restricted set of observables, and quantum electrodynamics processes in strong fields provided by pulsed laser beams. Experimental contributions are presented in chapters about some quantum optics processes in photonic crystals - media with spatially modulated dielectric properties - and chapters dealing with the formation of cloud of cold atoms in magneto optical trap. All chapters provide the necessary basic knowledge of the phenomena under discussion and well-explained mathematical calculations.
Radiative transitions When a system changes its energy as the result of the emission or the absorption of a photon, it is said to undergo radiative transition. There are three kinds of radiative transition. In the presence of an electromagnetic field the system can absorb a photon, so that its energy is raised to a higher level. If the system is initially in a state other than the ground state, it can emit a photon and so shed energy. This can happen without the presence of any external electromagnetic field, in which case a spontaneous emission is said to occur. On the other hand, if the excited system is placed in an electromagnetic field that varies in time with the appropriate frequency, the probability that it will emit a photon can be greatly enhanced. In this case the emission process is known as stimulated emission . Stimulated emission is the basis of maser and laser action, which we describe in this chapter. First, we construct a simple model that allows us to investigate how the internal structure of a quantum system changes as the result of a radiative transition. Although the model is very simple, it will allow us to understand the main features of the proper, more exact treatment. We shall deal mainly with absorption and stimulated emission, the two types of radiative transition where there is an external electromagnetic field.
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