Does getting which-way info introduce a phase difference?

[San K]

does getting which-way info introduce a phase difference (or cause de-coherence) between both the "waves"?

and does erasure of which-way information restore coherence?

 

[genericusrnme]

a difference from what?

the 'which-way' information completely changes the state, like the slits be 1 and 2, then you have 1+2 without any information, then 1 OR 2 with information
you can't phase change your way between (1+2),(1),(2)

 

[San K]

a difference from what?

the 'which-way' information completely changes the state, like the slits be 1 and 2, then you have 1+2 without any information, then 1 OR 2 with information
you can't phase change your way between (1+2),(1),(2)

forgot to mention, sorry...

phase difference between two entangled photons (two-photon interference)

 

[genericusrnme]

Which way information usually referes to dual-slit type experiments, there's only one photon there at anyone time so there is no enganglement.