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qml.from_qasm3

from_qasm3(quantum_circuit, wire_map=None)[source]

Converts an OpenQASM 3.0 circuit into a quantum function that can be used within a QNode.

Note

The standard library gates, qubit registers, built-in mathematical functions and constants, subroutines, variables, control flow, measurements, inputs, outputs, custom gates and end statements are all supported. Pulses are not yet supported.

In order to use this function, openqasm3 and 'openqasm3[parser]' must be installed in the user’s environment. Please consult the OpenQASM installation instructions for directions.

Parameters:

  • quantum_circuit (str) – a QASM 3.0 string containing a simple quantum circuit.

  • wire_map (Optional[dict]) – the mapping from OpenQASM 3.0 qubit names to PennyLane wires.

Returns:

A quantum function that will execute the program.

Return type:

Callable

Examples

First, we define a QASM 3.0 circuit as a string. In this example, we define three qubits, a few parameterized gates, a subroutine with a measurement, and a control flow statement.

qasm_string = '''
        qubit q0;
        qubit q1;
        qubit q2;

        float theta = 0.2;
        int power = 2;

        ry(theta / 2) q0;
        rx(theta) q1;
        pow(power) @ x q0;

        def random(qubit q) -> bit
        {
            bit b = "0";
            h q;
            measure q -> b;
            return b;
        }

        bit m = random(q2);

        if (m) {
            int i = 0;
            while (i < 5) {
                i = i + 1;
                rz(i) q1;
                break;
            }
        }
'''

We can convert this circuit into a PennyLane quantum function using:

@qml.qnode(qml.device("default.qubit", wires=[0, 1, 2]))
def my_circuit():
    qml.from_qasm3(
        qasm_string,
        {'q0': 0, 'q1': 1, 'q2': 2}
    )()
    return qml.expval(qml.Z(0))

Inspecting the circuit, we can see that the operations and measurements have been correctly interpreted.

>>> print(qml.draw(my_circuit)())
0: ──RY(0.10)──X²────────────┤  <Z>
1: ──RX(0.20)───────RZ(1.00)─┤
2: ──H─────────┤↗├──║────────┤
                ╚═══╝
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