Post on 22-Dec-2015
transcript
Quantum Cheshire Cats
Y. Aharonov, S. Popescu, D. Rohrlich,P. Skrzypczyk (2012)
Quantum weak values
A pre- and post-selected ensemble:
The initial state is
The final state is
in
fin
Quantum weak values
A pre- and post-selected ensemble:
The initial state is
The final state is
in
fin
measure A “weakly”
Quantum weak values
If we measure A “weakly” on an ensemble of systems pre-selected in and post-selected in
, the result is the “weak value” :
Y. Aharonov, D. Albert and L. Vaidman, PRL 60 (1988) 1351
infin
wA
infin
infin
w
AA
Quantum Cheshire Cats
“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 all my life!”
Quantum Cheshire Cat
The Cat in the Left box, and the Cat is grinning. Hence it is obvious, dear Alice, that the Cat is grinning in the Left box!
Quantum Cheshire Cat
The Cat in the Left box, and the Cat is grinning. Hence it is obvious, dear Alice, that the Cat is grinning in the Left box!
Obvious but false: the weak value of
vanishes!
SLL
Quantum Cheshire Cat
The Cheshire Cat is in the Left box, but there is no net grin in the Left box. On the contrary, the only net grin is in the Right box.