~ Time ~
“I don’t understand you,” said Alice. “It’s dreadfully confusing!”
“That’s the effect of living backwards,” the Queen said kindly:
“it always makes one a little giddy at first—”
“Living backwards!” Alice repeated in great astonishment. “I
never heard of such a thing!”
“–but there’s one great advantage in it, that one’s memory
works both ways.”
“I’m sure mine only works one way,” Alice remarked. “I can’t
remember things before they happen.”
“It’s a poor sort of memory that only works backwards,” the
Queen remarked.
~ Tell 'em a hookah smoking caterpillar Has given you the call ~
~
All right,’ said the Cat; and this time it vanished quite slowly,
beginning with the end of the
tail, and ending with the grin, which remained
some time after the rest of it had gone.
‘Well! I've often seen a cat without a grin,’
thought Alice, ’but a grin without a cat! It’s the
most curious thing I ever saw in my life!’
http://i42.tinypic.com/2ebu26o.jpg
No wonder Alice is surprised. In real life, assuming
that cats do indeed smile, then the smile is a property of
the cat – it makes no sense to think of a smile without a
cat. And this goes for almost all physical properties. The
polarization is a property of a photon, it makes no sense
to have a polarization without a photon. Yet, as we will
show here, in the interesting way of quantum mechanics, a photon polarization may exist where there is no
photon at all. At least this is the story that quantum mechanics tells via pre- and post-selected measurements.
http://arxiv.org/pdf/1202.0631.pdf
We have shown that Cheshire cats have a place in
quantum mechanics – physical properties can be
disembodied from the objects they belong to in a pre- and
post-selected experiment. Although here we have only
presented one example where a photon is disembodied
from its polarization, it should be clear that this effect is
completely general – we can separate, for example the
spin from the charge of an electron, or internal energy
of an atom from the atom itself. Furthermore it is important
to realize that is not just that pointers of well prepared
measuring devices indicate that the properties
are disembodied – any external system which interacts
weakly with the pre- and post-selected system will react
accordingly.
This therefore opens many intriguing questions, both
conceptual and applied ones. First of all, how will
an electron with charge and mass disembodied effect
A nearby electron? In an atom with the internal energy disembodied from the mass, what will the resulting
gravitational field look like? What sort of thermal equilibrium will achieved by a system whose two degrees
of freedom are separated? Furthermore, when considering more than two degrees of freedom, can we separate
them all from each other? Can photons impart angular
momentum to one object while their radiation pressure
is felt by another object?
On the applied side, we may ask whether Cheshire
cats are useful in precision measurements, just as weak
measurements themselves have now shown to be useful
as a powerful amplification technique .
Suppose
for example that we wish to perform a measurement
in which the magnetic moment plays the central role,
whilst the charge causes unwanted disturbances. Using
this scheme it would appear possible to remove this disturbance, in a post-selected manner (i.e. heralded), by
producing a Cheshire cat where the charge is confined
to a region of the experiment far from the magnetic moment.
https://www.youtube.com/watch?t=205&v=ooLby5mluRo