Transcript Prospectus of Course,6.10.03

Experimental Issues in
Quantum Measurement
Lectures: Tuesday, 10-11, Kleiner Hörsaal
Aephraim Steinberg
(auf Englisch, es tut mir leid)
• Why does one thing happen and not another?
• When is a quantum measurement?
• Does a measurement necessarily disturb the
system, and how?
• What can we say about an observable before we
measure it?
• Does a wave function describe a single particle,
or only an ensemble?
• Is a wave function a complete description of a
single particle?
• Can we predict the past?
Atoms falling out of a lattice trap
As the trap is lowered, each quantum state falls out
at a different time – we can see “by eye” how many
atoms were in each energy eigenstate.
The Wigner quasiprobability function
...combining many such measurements, we can completely
describe the quantum state of the atoms.
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
P(0,0) < 0 ?!
Some topics we’ll cover
• Must “collapse” really happen?
alternate pictures of measurements and correlations
• How much can we say about the past?
weak measurements and postselection...
• Can we measure the entire state of a particle?
density-matrix and Wigner function reconstruction
• Can we distinguish between indistinguishable things?
non-orthogonal state discrimination
• Are there different things we can never distinguish between?
different preparations of identical density matrices
• Can we measure something without interacting with it?
“Vaidman’s bomb” experiment
• Can we undo the disturbance introduced by a measurement?
The “quantum eraser”
• Can we use the measurement process to accomplish tasks?
Measurement-induced nonlinearity, LOQC
LECTURES: TUESDAYS 10-11, Kleiner Hörsaal