Superpositions, of quantum states

Although it is possible with the adiabatic following of STIRAP to produce not only complete population transfer but also, through fractional STIRAP [16], any superposition of quantum states 1 and 3, so too is it possible to design a series of rotations that will produce an arbitrary change of polarization. However, in both cases, the full change of variables (quantum state or polarization) is more robust than a partial change. 

Only after the box is opened and the cat observed will the wavefunction collapse to a recognizable state of bliss or annoyance. In an extension of this experiment, an observer known as Wigner s friend is invited into a closed room with the apparatus. And until the door is opened. Wigner s friend himself will also become part of a quantum superposition, which is starting to become ridiculous We might be able to accept the concept of an atomic system being described as a superposition of quantum states. But a cat ... 

We note that also protocols using orthogonal states have been designed [164], Superpositions of quantum states are employed. A superposition is divided into parts, which are sent separately with a time delay larger than the time distance... 

Coherent superposition of quantum states and the concept of wave packets... 

Snider is best known for his paper reporting what is now referred to as the Waldmann-Snider equation.34 (L. Waldmann independently derived the same result via an alternative method.) The novelty of this equation is that it takes into account the consequences of the superposition of quantum wavefunctions. For example, while the usual Boltzmann equation describes the collisionally induced decay of the rotational state probability distribution of a spin system to equilibrium, the modifications allow the effects of magnetic field precession to be simultaneously taken into account. Snider has used this equation to explain a variety of effects including the Senftleben-Beenakker effect (i.e., is, the magnetic and electric field dependence of gas transport coefficients), gas phase NMR relaxation, and gas phase muon spin relaxation.35... 

The decay of the individual quasi-bound (metastable) resonance states follows an exponential law. The wave packet prepared by an ultrashort pulse can be represented as a (coherent) superposition of these states. The decay of the associated norm (i.e., population) follows a multi-exponential law with some superimposed oscillations due to quantum mechanical interference terms. The description given above is confirmed by experimental data. 

We end this section with a comparison of the basic concepts of laser control and traditional temperature control. This discussion includes an elementary explanation and definition of concepts such as incoherent superpositions of stationary states versus coherent superpositions of stationary states and quantum interference. 

This scenario opens up a wide range of possible experimental studies of control bimolecular collisions. Specifically, we need only prepare A and A in a control superposition of two states [e.g., by resonant laser excitation of A(1))] to produf superposition with r/>A(2)), direct them antiparallel in the laboratory, and vary t coefficients in the superposition to affect the reaction probabilities. Control -originates in quantum interference between two degenerate states associated wiili, r the contributions of 0A(1)) A<(2)> and I[Pg.154]

To understand any coherence other than SQC, we need a new and more general definition of coherence. Coherence arises from the quantum mechanical mixing or overlap of spin states ( superposition ). In the two spin system (I, S = ll, 13C) we have four spin states (aa, up, pa, and PP), which are all stable states of defined energy. Let s talk about a single - C pair (one molecule). It is possible for this pair to be in any one of the four energy states, but it is also possible for the pair to be in a mixture or overlap or superposition of two states. This is one of the fundamental tenets of quantum mechanics Sometimes you cannot be sure which energy state a particle is in. Let s say that this particular pair is in a mixture of states aa and pp ... 

As far as linear superpositions or quantum states are concerned, the view (1) asserts that a pure state provides a complete and exhaustive description of an individual system (e.g., an electron, molecule, and molecular objects) and the view exposed in case (2) asserts that a pure state provides a description of certain statistical properties of an ensemble of similarly prepared systems, but need not provide a complete description of an individual system. These statements correspond to those given in Refs. [7-9]. For details, the reader can go back to Refs. [1,9,10]. 

Classical physics categories are not sufficient to describe phenomena in the realm of quantum physics. Thus, objects wouldn t exist in a superposition of different states molecules as massive objects do not interfere in a quantum sense. But what about experiments described and discussed by Arndt et al. [26, 28] We comment the issue below. 

Einstein statistics and collective dynamics are represented with phonons totally decoupled from the lattice. The ground states can be represented as 2Ag + Bg + 2Au + Bu symmetry species [Lucazeau 1973], The g and u species correspond to collective oscillations of the singlet and triplet states, respectively. The ground state must be regarded as a superposition of coherent states of protons fully entangled with respect to spins and positions. This long-range quantum coherence can be probed with neutron diffraction. 

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