Recoil superpositional

Figure 5 Schematic representation of neutron Compton scattering on an entangled pair of identical particles. The state is a superposition corresponding to particles a and (3 receiving the recoil during the scattering process.

One example of an application is the measurement of the gravitational acceleration g on earth with an accuracy of 3 x 10 g with a light-pulse atomic interferometer [1291]. Laser-cooled wave packets of sodium atoms in an atomic fountain (Sect. 9.1.9) are irradiated by a sequence of three light pulses with properly chosen intensities. The first pulse is chosen as 7r/2-pulse, which creates a superposition of two atomic states 1) and 2) and results in a splitting of the atomic fountain beam at position 1 in Fig. 9.71 into two beams because of photon recoil. The second pulse is a tt-pulse, which deflects the two partial beams into opposite directions the third pulse finally is again a tt/2-pulse, which recombines the two partial beams and causes the wave packets to interfere. This interference can, for example, be detected by the fluorescence of atoms in the upper state 2). 

Emission processes always lead to a photon-related recoil velocity for an atom. Thus, in the quest for stiU lower temperatures it is necessaury to ascertain that an atom, which for some reason is brought to a standstill, can be exempt from further interaction with the fight. This is possible if the atom is placed in a so-called dark state [9.440]. If the atom is in a coherent superposition of two ground-state sublevels, from which the transition amplitudes exhibit a total destructive interference, a dark state is achieved (See also Sect. 9.5.3). It can be shown that for counter-propagating beams with circular polariza-... 

This section considers the behavior of polymeric liquids in steady, simple shear flows - the shear-rate dependence of viscosity and the development of differences in normal stress. Also considered in this section is an elastic-recoil phenomenon, called die swell, that is important in melt processing. These properties belong to the realm of nonlinear viscoelastic behavior. In contrast to linear viscoelasticity, neither strain nor strain rate is always small, Boltzmann superposition no longer applies, and, as illustrated in Fig. 3.16, the chains are displaced significantly from their equilibrium conformations. The large-scale organization of the chains (i.e. the physical structure of the liquid, so to speak) is altered by the flow. The effects of finite strain appear, much as they do when a polymer network is deformed appreciably. 

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