Are Interaction-free Measurements Interaction Free?

In 1993 Elitzur and Vaidman introduced the concept of interaction-free measurements which allowed finding objects without ``touching'' them. In the proposed method, since the objects were not touched even by photons, thus, the interaction-free measurements can be called as ``seeing in the dark''. Since then several experiments have been successfully performed and various modifications were suggested. Recently, however, the validity of the term ``interaction-free'' has been questioned. The criticism of the name is briefly reviewed and the meaning of the interaction-free measurements is clarified.Comment: 11 pages, 3 eps figures. Contribution to the ICQO 2000, Raubichi, Belaru

High-efficiency quantum interrogation measurements via the quantum Zeno effect

The phenomenon of quantum interrogation allows one to optically detect the presence of an absorbing object, without the measuring light interacting with it. In an application of the quantum Zeno effect, the object inhibits the otherwise coherent evolution of the light, such that the probability that an interrogating photon is absorbed can in principle be arbitrarily small. We have implemented this technique, demonstrating efficiencies exceeding the 50% theoretical-maximum of the original ``interaction-free'' measurement proposal. We have also predicted and experimentally verified a previously unsuspected dependence on loss; efficiencies of up to 73% were observed and the feasibility of efficiencies up to 85% was demonstrated.Comment: 4 pages, 3 postscript figures. To appear in Phys. Rev. Lett; submitted June 11, 199

New facility for simultaneous implantation and evaporation

The Groningen isotope separator has been extended with a double uhv evaporation system. Implantation and evaporation can now be done at the same time under good vacuum conditions. Implanted systems with thicknesses up to 6.3 μm have been produced

Quantum-mechanical indirect measurements

So-called interaction-free measurements and “induced coherence without induced emission” experiments are analyzed from a macrorealistic point of view, that is up to the point of time that the whole wavefunction has developed into the macroscopic stage. From the measurement of the visibility of interference between light photons in a detector, conclusions can be drawn on the interaction properties of photons with solid matter at a remote spot; this matter does not need to be part of a real detector. This probably novel way of doing experiments might have practical applications. Certain recently presented quantum-mechanical phenomena can easily be understood by applying the macrorealistic approach, and new interpretations of the wavefunction are not nescessary

Coherent Bremsstrahlung and the Quantum Theory of Measurement

Coherent bremsstrahlung (CB) is the result of inelastic Bragg scattering of electrons of a few hundreds of keV, a collective effect of the whole crystal. In an electron microscope it is theoretically possible to determine the row of atoms where the electron was inelastically scattered. These statements are contradictory. Optical path calculations are made for 160 keV electrons inelastically scattered by a silicon [111] crystal and the results are compared with measured CB spectra, The results can be understood by application of Van Kampen's theory of quantum mechanical measurement. Experimental CB spectra turn out to be the result of coherent scattering of atoms within the same row, and incoherent summation of intensities from different rows, or, in other words, the electrons that cause CB are localised within atomic rows

Coherent Bremsstrahlung and the Quantum Theory of Measurement

Coherent bremsstrahlung (CB) is the result of inelastic Bragg scattering of electrons of a few hundreds of keV, a collective effect of the whole crystal. In an electron microscope it is theoretically possible to determine the row of atoms where the electron was inelastically scattered. These statements are contradictory. Optical path calculations are made for 160 keV electrons inelastically scattered by a silicon [111] crystal and the results are compared with measured CB spectra. The results can be understood by application of Van Kampen's theory of quantum mechanical measurement. Experimental CB spectra turn out to be the result of coherent scattering of atoms within the same row, and incoherent summation of intensities from different rows, or, in other words, the electrons that cause CB are localised within atomic rows

Theoretische beschouwingen over kiesrecht (art. 76 der grondwet)

Proefschrift--Utrecht.Mode of access: Internet