Composing teleportation circuit in Qiskit Circuit Composer

Question

I'm trying to create the teleportation circuit in IBM Qiskit Circuit Composer.

OPENQASM 2.0;
include "qelib1.inc";

qreg q[3];
creg a[3];   // should be crz
creg b[4];   // should be crx

h q[1];
cx q[1],q[2];
barrier q; //[0];

cx q[0],q[1];
h q[0];
barrier q;

measure q[0] -> a[0];
measure q[1] -> b[0];
barrier q;

This gives me the following circuit till the 3rd measurement barrier. How do I add CRX and CRZ gates - to obtain the circuit as shown in the picture? Also, how to change the names of the classical registers from a3, b4 to crz and crx?

Answer 1

crx and crz are classical register. The gates CRX or CRZ mean that you apply the X gate on qubit 2 if the measurement on the classical register crx is a 1, that is if qubit 1 (q1) is in the $|1\rangle$ state; and you will apply the Z gate on qubit 2 if the classical register crz is 1.

This can be done in qiskit with c_if operation. You can see example of the teleportation code in Qiskit here: https://qiskit.org/textbook/ch-algorithms/teleportation.html

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Anyway, if you want to use OPENQASM, then you can do it as follow:

OPENQASM 2.0;
include "qelib1.inc";

qreg q[3];
creg crzz[3];   // since crz is already taken I use crzz instead
creg crxx[4];   // Again I use crxx instead of crx

h q[1];
cx q[1],q[2];
barrier q; //[0];

cx q[0],q[1];
h q[0];
barrier q;

measure q[0] -> crzz[0];
measure q[1] -> crxx[0];
barrier q;

if(crzz==1) z q[2];
if(crxx==1) x q[2]; 

Here is the image of the circuit when using Circuit_Composer option within IBMQ Experience environment.