Quantum Optical Experiments

Quantum optical experiments, by which we mean the investigation of the interaction between simple quantum systems and coherent light, have proven to be a successful tool to test basic concepts in quantum mechanics. Most of the experiments to date were performed with atoms or ions in vapors, beams or traps. An attractive feature of atoms relates to their relatively simple structure which is theoretically fairly well understood. 

In optical experiments that can be also done on ensembles of molecules (e.g. external perturbations by electric fields [19, 20]) the importance of single molecule investigations results from the fact that a single absorber is exquisitely sensitive to its 

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The virtually unlimited possibilities offered by organic chemistry in tailoring specific properties of PFs will give access to new polymeric systems which show remarkable and unexpected properties. As demonstrated in this chapter, SMS will be a valuable tool in answering scientific questions and will no doubt provide the experimental demonstration of many new phenomena. Ultimately, conjugated polymers may even prove versatile systems for sophisticated quantum optical experiments, due to the strong control over polarisation enabled by their anisotropic structure. 

The vast majority of single-molecule optical experiments employ one-photon excited spontaneous fluorescence as the spectroscopic observable because of its relative simplicity and inlierently high sensitivity. Many molecules fluoresce with quantum yields near unity, and spontaneous fluorescence lifetimes for chromophores with large oscillator strengths are a few nanoseconds, implying that with a sufficiently intense excitation source a single... 

Finally, tlie ability to optically address single molecules is enabling some beautiful experiments in quantum optics. The non-Poissonian photon arrival time distributions expected tlieoretically for single molecules have been observed directly, botli antibunching at short times [112] and bunching on longer time scales [6, 112 and 113]. The fluorescence excitation spectra of single molecules bound to spherical microcavities have been examined as a probe... 

The discovery of the 25 — 2P Lamb shift has led to the development of the theory of quantum electrodynamics. Today, radio frequency measurements of this splitting have reached the uncertainty limits imposed by the 100 MHz natural linewidth of the 2P state. The considerably sharper optical two-photon resonances used in optical experiments leave significant room for future improvements. 

Other contributions in this volume give detailed accounts of the work at Yale, Paris, and Oxford. This article will therefore focus on the past experiments of our laboratory at Stanford and on our current and future program at the Max-Planck-Institute for Quantum Optics in Garching. 

The introductory aspects related to these experiments are examined in Section 5.1 where a simplified base state model is presented. Here quantum optical test proposals are discussed. For details, view Figure 5 of Ref. [15] there, emphasis is provided on the location and construction of quantum states. 

It is possible to approach shot-noise-limited performance in many optical experiments. When light levels are low, photomultipliers serve as noise-free quantum amplifiers with a gain of 10 . For absorption measurements, detectors with the highest quantum efficiency and uniformity of response, such as end-on semitransparent photocathode styles, are better than the high gain, opaque photocathode, low dark count types that are used for luminescence measurements. If one needs to measure absorption with a precision of AA 10, then 10 photons need to be accumulated at each data point. At these light levels, the dark count usually may not contribute greatly to the S/N. However, in absorption... 

The research on quantum entanglement (QE) and decoherence, usually focuses on experiments and theory of quantum optics and optical traps involving single or just a few atoms. It is heavily dominated by the potential applica-... 

In brief, we propose the TOT electro-optical setup in which electrical measurements have a high quality factor combined with the coherence of an all optical experiment. The TOT can be easily incorporated in electrical circuits as a nonlinear element ensuring a scalability of the architecture. The quantum dot isolation in the TOT will protect entanglement of quantum states thus permitting field programmable gates arrays. 

J. Perina, Z. Hradil, and B. Jurco, Quantum Optics and Fundamentals of Physics, Kluwer, Dordrecht, 1994, Chap. 8.5 H. A. Bachor, A Guide to Experiments in Quantum Optics, Wiley, Weinheim, 1998, Chap. 9. 

In this review we have described some of the advances in the quantum electrodynamical formulation of theory for molecular photonics. We have shown how the framework described in an earlier review has now been extended to new areas of application, and reformulated for application to real dispersive media—as reflected in the new treatment of refractive, dissipative, and resonance properties. With all its conceptual splendor, conventional quantum optics has not generally been pursued at this level of detail on its dielectric host, and it is our hope that this work will help match its precepts with quantitative accuracy. Applications of the new theory have revealed new quantum optical features in two quite different aspects of the familiar process of second harmonic generation, one operating through local coherence within small particles and the other, a coherence between the quantum amplitudes for fundamental and harmonic excitation. Where the salient experiments have been performed, they exactly match the theoretical predictions. The theoretical foundation we have discussed therefore shows promise for the delivery of accurate insights into other optical processes yet to be characterized, and it should be well placed to facilitate the determination of meaningful data from the associated experiments. 

Until recently, the puzzling foundations of quantum mechanics could not be verified directly by experimentation. As a result of enormous technological advances in quantum electronics and quantum optics, it became possible to carry out experiments on single atoms, molecules, photons, etc. In 2004 a group of researchers has teleported for the first time an atomic state, while another group has successfully performed teleportation of a [dioton state across the Danube river (at a distance of 600 m). Even molecules such as fuUerene were subjected to successful interfenHice experiments. Quantum computer science is Just beginning to prove that its principles ate correct. 

For many years molecular beams were mainly employed for scattering experiments. The combination of new spectroscopic methods with molecular beam techniques has brought about a wealth of new information on the structure of atoms and molecules, on details of collision processes, and on fundamentals of quantum optics and the interaction of light with matter. 

Other fascinating future experiments may be contemplated based on the principles and methods presented here. Detailed study of the spectral diffusion process in crystals and polymers will help to eventually identify the actual microscopic nature of the two-level systems. The door is open to true photochemical experiments on single absorbers, quantum optics, and even the possibility of optical storage using single molecules [7]. Future efforts to increase the number of probe-host couples which allow SMS will lead to an even larger array of novel observations. 

I hope to have shown in this brief review that Rydberg atom radiation experiments are of central interest in a variety of studies not only in fundamental Quantum Optics, but also in the technology of new radiation sources and detectors and in metrology. 

H.A. Bachor A Guide to Experiments in Quantum Optics (Wiley VCH, Wein-heim 1998)... 

Phase-dependent coherence and interference can be induced in a multi-level atomic system coupled by multiple laser fields. Two simple examples are presented here, a three-level A-type system coupled by four laser fields and a four-level double A-type system coupled also by four laser fields. The four laser fields induce the coherent nonlinear optical processes and open multiple transitions channels. The quantum interference among the multiple channels depends on the relative phase difference of the laser fields. Simple experiments show that constructive or destructive interference associated with multiple two-photon Raman channels in the two coherently coupled systems can be controlled by the relative phase of the laser fields. Rich spectral features exhibiting multiple transparency windows and absorption peaks are observed. The multicolor EIT-type system may be useful for a variety of application in coherent nonlinear optics and quantum optics such as manipulation of group velocities of multicolor, multiple light pulses, for optical switching at ultra-low light intensities, for precision spectroscopic measurements, and for phase control of the quantum state manipulation and quantum memory. 

A more far-reaching phenomenon is the possibility of generating radiation in "squeezed" states [4.19]. Such radiation exhibits reduced noise below the quantum limit and could have important applications for optical communication and precision interferometric measurements of small displacements, e.g. in gravity-wave detection experiments. A considerable degree of "squeezing" has recently been experimentally demonstrated [4.20, 21]. Various aspects of modern quantum optics have been discussed in [4. 22-25]. 

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