Speakers: Bedřich Velický (Department of Condensed Matter Theory, Institute of physics, ASCR, Prague; department of condensed matter physics, MFF UK Prague)
Place: Na Slovance, main lecture hall
Presented in English
Organisers:
Department of Condensed Matter Theory
Abstract:
The weak measurement as a theoretical concept was introduced into the quantum mechanics[1] in 1988-89. In this review I will first give an elementary theory of weak measurements. Then, I will recall the early disputes and the first experimental proofs of viability of weak measurements. In particular, I will discuss the meaning of weak values of an observable, which may be complex and may be "strange", beyond the spectral limits (negative kinetic energy, spin=100 h, superluminal velocities).
In the second part, I will describe two recent experimental papers, in which the quantum mechanical weak measurements are less just a subject and more an actual tool of an experimental investigation. The first paper [2] concerns the double slit experiment, in which the weak measurement is used to trace down the Bohm trajectories of photons. The second paper [3] is conceptually straightforward and describes a direct method of measuring the wave function of a single photon. I will add a comment on weak measurements on mesoscopic electron systems.
Finally, I will concentrate on the underlying general conceptions including the original time-symmetric formulation of quantum mechanics and some recent developments.
[1] Aharonov, Y., Albert, D.Z. , and Vaidman, L., How the result of the measurement of a component of the spin of a spin-½ particle can turn out to be 100 Phys Rev Lett 60, 1351-1354 (1988); DOI: 10.1103/PhysRevLett.60.1351
[2] Sacha Kocsis, et al., Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer Science 332, 1170 (2011); DOI: 10.1126/science.1202218
[3] Jeff S. Lundeen, et al., Direct measurement of the quantum wavefunction Nature 474, 188 (2011); doi:10.1038/nature10120
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