# Homework Help: Need help understanding question regarding Bell states

1. Apr 3, 2013

### Ocifer

1. The problem statement, all variables and given/known data
Basically, in a homework question, I'm presented with the definition of bell states and asked to show some elementary properties. I've been able to show they form an orthonormal basis, and express them in terms of the usual basis, |00>, |01> |10> |11>.

"Find a quantum circuit that performs the Bell measurement (measurement of two qubits
in the Bell basis) in terms of single qubit unitary gates, CNOT gates, and single qubit
measurements in the {|0> , |1> } basis."

2. Relevant equations

$| \psi_{xy} \rangle = CNOT_{12}H_1 | xy \rangle$

3. The attempt at a solution

I don't understand what is being asked of me. I can figure out a circuit which encodes any of the normal basis states |00>, |01> |10> |11> into its corresponding Bell basis, state. This is a circuit with only two wires (since it's a two qubit space), but do I simply then add a single qubit "M" (measurement) gate to each wire? Is that all that is being asked, or is there more I'm not understanding?

Last edited: Apr 3, 2013