measuring the first q-bit on the computational basis

measuring the first q-bit on the computational basis

by Quentin Marguet -
Number of replies: 1

Good evening,

I was wondering how we could measure the first q-bit on the computational basis |0>, |1> (2 entries vector) since we have a 2^n vectors after the second Hadammard gate ?

Should we use the projection on the n tensor product of the |0> state to have matching dimensions ?


In reply to Quentin Marguet

Re: measuring the first q-bit on the computational basis

by Nicolas Macris -
Hi,
When you meadure only the first qubit this means you must project the state with P_0=
|0><0|xId and P_1= |1><1|xId
Where the Id is the identity matrix over other qubits (since they are not measured/touched). The prob of finding 0 is then and similar for 1.
This should help.
NM