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Europhysics Letters (EPL)

The presence of a distant detector does not seem to influence spontaneous emission

Luiz Carlos Ryff

Published Jul 15, 1997• 4 citations
Publisher

Abstract

It is shown that a recent claim, according to which the spontaneous-emission process could be altered by continuously monitoring the emitting system by means of a spherical counter of quantum efficiency η < 1 placed at a finite distance L , is unfounded. The error arises from an incorrect reasoning.
DOI
10.1209/epl/i1997-00339-6

Related papers

Can spontaneous emission be influenced by the presence of a distant detector?

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We show that the spontaneous-emission process could be altered by continuously monitoring the emitting system by means of a spherical counter of quantum efficiency η < 1, placed at a finite distance L . This surprising result is related neither to Zeno's effect nor to any cavity effect, but is of intrinsically quantum-mechanical non-local nature.

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Reply to the paper “The presence of a distant detector does not seem to influence spontaneous emission” by L. C. Ryff

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We confute the criticism contained in a paper appearing in this issue of Europhys. Lett. , in which the author claims that the main result of a series of our papers concerning the influence of a distant detector on spontaneous emission is unfounded.

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Comment on “Spontaneous emission: vacuum fluctuations or radiation reaction” by R R Puri

Peter W. Milonni

It has recently been claimed that the vacuum field does not contribute explicitly, in any operator ordering, to spontaneous emission. This claim is based on a trivial observation that misses the point of a whole series of independent investigations.

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Introduction Ever since 1916/17 when Einstein argued [45] [46] that spontaneous emission must occur if matter and radiation are to achieve thermal equilibrium, physicists have believed that spontaneous emission is an inherent quantum mechanical property of atoms and that excited atoms inevitably radiate. This view, however, overlooks the fact that spontaneous emission is a consequence of the coupling of quantized energy states of atoms with the quantized radiation field, and is a manifestation of quantum noise or of emission ‘stimulated’ by ‘vacuum fluctuations’. An infinity of vacuum states is available to the photon radiated by an excited atom placed in free space, leading to the effective irreversibility of such emissions. If these vacuum states are modified, as for example by placing an excited atom between closely spaced mirrors or in a small cavity (essentially the Casimir effect), spontaneous emission can be greatly inhibited or enhanced or even made reversible. Recent advances in atomic and optical techniques have made it possible to control and manipulate spontaneous emission. A whole new branch of quantum optics called ‘cavity QED’ has developed since 1987 utilizing these dramatic changes in spontaneous emission rates in cavities to construct new kinds of microscopic masers or micromasers that operate with a single atom and a few photons or with photons emitted in pairs in a two-photon transition.
Particle properties of radiation One of the most important properties of macroscopic material systems is their ability to emit radiation spontaneously. According to quantum mechanics, the emission process is realized in the following way: an atom (or a molecule) makes a transition from a higher lying energy level (to which it was brought, for example, by an electron collision) to a lower lying energy level without any noticeable external influence (in the form of an existing electromagnetic field), and the released energy is emitted in the form of electromagnetic radiation. The discrete energy structure of the atom dictated by the laws of quantum mechanics is imprinted also on the emission process (quantization of the emission energy), since the energy conservation law is also valid for single (individual) transitions. Hence, a single photon, in the sense of a well defined energy quantum, is always emitted. The emitted quanta can be directly detected by a photodetector. (Strictly speaking, identifying a registered photon with an emitted one is possible only when it is guaranteed that the observed volume contains only a single atom. (For details see Sections 6.8 and 8.1.) Under realistic conditions, the experiment can be performed in the following way. First, a beam of ionized atoms is sent through a thin foil; the emerging beam then consists of excited atoms. (This procedure is known as the beam–foil technique.) A detector is placed at a distance d from the foil to detect light emitted sideways by the atomic beam (Fig. 6.1).