Applying a projector to a qubit in a qiskit circuit

Question

I'd like to be able to apply $|0 rangle langle 0|$ to project a qubit to the state $|0 rangle$ in the middle of qiskit circuit (see, for example, the attached circuit).

I wonder if, in general, one can customize those orange boxes in some way and if that works in the real hardware.

KAJ226 · Accepted Answer

I hope this is what you are looking for.

Within IBM hardware, there is a new option called "reset" that allows you to reset a certain qubit back to the state $|0rangle$. For instance,
from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit
qreg_q = QuantumRegister(3, 'q')
creg_c = ClassicalRegister(3, 'c')
circuit = QuantumCircuit(qreg_q, creg_c)
circuit.x(qreg_q[0])
circuit.h(qreg_q[2])
circuit.cswap(qreg_q[2], qreg_q[0], qreg_q[1])
circuit.h(qreg_q[2])
circuit.reset(qreg_q[1])

Within the circuit composer, you can find the reset method as well with the $|0rangle$ symbol:

Applying a projector to a qubit in a qiskit circuit

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