# Quantum logic gate measurement?

1. Nov 13, 2008

### nfelddav

Do quantum logic gates perform measurements? (collapse the wavefunction)

For example:

If I apply a cNOT gate to a pair of cubits with wavefunction 1/$$\sqrt{2}$$ |10> + 1/$$\sqrt{2}$$ |00>
what would I expect as the result?

1/$$\sqrt{2}$$ |11> + 1/$$\sqrt{2}$$ |00>
?

or

1|11>
or
1|00>

or
are the states not entangled? This seems unlikely because it would be cloning...

2. Nov 13, 2008

### borgwal

A logic gate is unitary, a measurement (when described as including the collapse) is not unitary. So, the result of the cnot is 1/$$\sqrt{2}$$ |11> + 1/$$\sqrt{2}$$ |00>. And yes, this is an entangled state.

3. Nov 14, 2008

### nfelddav

Thank you,
That's what seemed the most reasonable, but I wasn't sure.