exam 2021. Problem 3, question c

exam 2021. Problem 3, question c

by Selim Jerad -
Number of replies: 1

Hello,

I am really struggling with the correction of this exercise. For instance, if Alice obtains B_11 (B_4 in exam), the state is alpha|00> - beta|11>. I thought Bob and Charlie would need to apply Z(sigma_z) to get the correct sign, but the correction says nothing has to be done (and the actual state is alpha|00> + beta|11>, without a minus).

In reply to Selim Jerad

Re: exam 2021. Problem 3, question c

by Guifré Sánchez i Serra -
I think they should do nothing because the asked protocol requires that the state the Bob and Charlie have jointly after Alice's measurement can be either alpha 00 + beta 11 or alpha 00 - beta 11. Since in the case Alice measures B4 the state in B&C lab is just alpha 00 - beta 11, nothing has to be done.