HW 10 - Ex3

HW 10 - Ex3

by Emma Romanetti -
Number of replies: 1

Hello,

I can not make any sens of question d. of ex 3... 

First, Eve does a measurement, "the state of the pair is thus left in a product state gamma X delta" 

What are gamma and delta ? Two basis that Eve choses ? A notation to denote an (alpha,beta) combination ? If it is the first case, why would Eve measure both of the qubits, and why would we discuss the values that gamma and delta can take (they can take any values in [0, 2pi]? ) ?

Thank you.

In reply to Emma Romanetti

Re: HW 10 - Ex3

by Nicolas Macris -
Hi,
gamma and delta reporesent some combination of (alpha, beta)'s as you say. And for your question:

"If it is the first case, why would Eve measure both of the qubits, and why would we discuss the values that gamma and delta can take (they can take any values in [0, 2pi]? ) ?"

Well this is just one possible attack from Eve. But yes in general Eve could choose other angles in [0, 2\pi] and you are of course free to discuss a more general situation. In fact the basic result (checking the inequaality for the security test) is the same whatever angles Eve chooses.

Hope this clarifies. Best,

N.M