Abstract
The modification of the effect of interactions of a particle as a function of its preselected and postselected states is analyzed theoretically and experimentally. The universality property of this modification in the case of local interactions of a spatially preselected and postselected particle has been found. It allowed us to define an operational approach for the characterization of the presence of a quantum particle in a particular place: the way it modifies the effect of local interactions. The experiment demonstrating this universality property provides an efficient interferometric alignment method, in which the position of the beam on a single detector throughout one phase scan yields all misalignment parameters.
Highlights
P reselected and postselected systems are ubiquitous in quantum mechanics
We find that there exists a general universality principle characterizing how the effects of the interactions in one location of a spatially preselected and postselected quantum system are modified as a function of preselection and postselection
Manifestation of the Trace as Shifts in Pointer States In the previous sections, we described the trace a particle leaves as the appearance of an orthogonal component in the quantum state of external systems
Summary
49, one arm of the interferometer is a Kerr medium, and the photon passing through this arm changes the quantum state of the pointer by introducing a shift in the relative phase between the wave packets of the pointer photons As it is done in most weak-measurement experiments, instead of coupling to external particles, we, rather, study interactions of the photons in an arm of the interferometer by observing the effect on other degrees of freedom of the photons itself. To evaluate the dependence of the weak value on the coherence between the two arms parametrized by η, we measured the effect of the displacement in x on the output beam For this run, we kept the phase fixed at φ = π and varied the amplitude ratio tan α covering another region of the parameter space from Fig. 2. The modification of the shift in the x direction presented in Fig. 5 follows nicely the weak value [12]
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