qml.to_openqasm

to_openqasm(qnode, wires=None, rotations=True, measure_all=True, precision=None)

Convert a circuit to an OpenQASM 2.0 program.

Note

Terminal measurements are assumed to be performed on all qubits in the computational basis. An optional rotations argument can be provided so that the output of the OpenQASM circuit is diagonal in the eigenbasis of the quantum circuit’s observables. The measurement outputs can be restricted to only those specified in the circuit by setting measure_all=False.

Parameters:

• wires (Wires or None) – the wires to use when serializing the circuit. Default is None, such that all device wires from the QNode are used for serialization.

• rotations (bool) – if True, add gates that diagonalize the measured wires to the eigenbasis of the circuit’s observables. Default is True.

• measure_all (bool) – if True, add a computational basis measurement on all the qubits. Default is True.

• precision (int or None) – number of decimal digits to display for the parameters.

Returns:

OpenQASM 2.0 program corresponding to the circuit.

Return type:

str

Example

The following QNode can be serialized to an OpenQASM 2.0 program:

from functools import partial
dev = qml.device("default.qubit", wires=2)

@partial(qml.set_shots, shots=100)
@qml.qnode(dev)
def circuit(theta, phi):
    qml.RX(theta, wires=0)
    qml.CNOT(wires=[0,1])
    qml.RZ(phi, wires=1)
    return qml.sample()

>>> print(qml.to_openqasm(circuit)(1.2, 0.9))
OPENQASM 2.0;
include "qelib1.inc";
qreg q[2];
creg c[2];
rx(1.2) q[0];
cx q[0],q[1];
rz(0.9) q[1];
measure q[0] -> c[0];
measure q[1] -> c[1];

Usage Details

By default, the resulting OpenQASM code will have terminal measurements on all qubits, where all the measurements are performed in the computational basis. However, if terminal measurements in the QNode act only on a subset of the qubits and measure_all=False, the OpenQASM code will include measurements on those specific qubits only.

from functools import partial
dev = qml.device("default.qubit", wires=2)

@partial(qml.set_shots, shots=100)
@qml.qnode(dev)
def circuit():
    qml.Hadamard(0)
    qml.CNOT(wires=[0,1])
    return qml.sample(wires=1)

>>> print(qml.to_openqasm(circuit, measure_all=False)())
OPENQASM 2.0;
include "qelib1.inc";
qreg q[2];
creg c[2];
h q[0];
cx q[0],q[1];
measure q[1] -> c[1];

If the QNode returns an expectation value of a given observable and rotations=True, the OpenQASM 2.0 program will also include the gates that diagonalize the measured wires such that they are in the eigenbasis of the measured observable.

from functools import partial
dev = qml.device("default.qubit", wires=2)

@partial(qml.set_shots, shots=100)
@qml.qnode(dev)
def circuit():
    qml.Hadamard(0)
    qml.CNOT(wires=[0,1])
    return qml.expval(qml.PauliX(0) @ qml.PauliY(1))

>>> print(qml.to_openqasm(circuit, rotations=True)())
OPENQASM 2.0;
include "qelib1.inc";
qreg q[2];
creg c[2];
h q[0];
cx q[0],q[1];
h q[0];
z q[1];
s q[1];
h q[1];
measure q[0] -> c[0];
measure q[1] -> c[1];

code/api/pennylane.to_openqasm

 

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