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OpenQASM 3 and Qiskit

Qiskit provides some tools for converting between OpenQASM representations of quantum programs, and the QuantumCircuit class. Note these tools are still in an exploratory phase of development and will continue to evolve as Qiskit’s support for dynamic circuit capabilities expressed by OpenQASM 3 increases.

Note

This function is still in the exploratory phase. Therefore, it is likely that the syntax and capabilities will evolve.

Import an OpenQASM 3 program into Qiskit

Currently two high-level functions are available for importing from OpenQASM 3 into Qiskit. These functions are load(), which takes a file name, and loads(), which takes the program itself as a string:

qiskit.qasm3.load(file_name)
qiskit.qasm3.loads(program-string)

You must install the package qiskit_qasm3_import to use this function. For example:

pip install qiskit-qasm3-import

In this example, we define a quantum program using OpenQASM 3, and use loads() to directly convert it into a QuantumCircuit:

import qiskit.qasm3
 
program = """
    OPENQASM 3.0;
    include "stdgates.inc";
 
    input float[64] a;
    qubit[3] q;
    bit[2] mid;
    bit[3] out;
 
    let aliased = q[0:1];
 
    gate my_gate(a) c, t {
      gphase(a / 2);
      ry(a) c;
      cx c, t;
    }
    gate my_phase(a) c {
      ctrl @ inv @ gphase(a) c;
    }
 
    my_gate(a * 2) aliased[0], q[{1, 2}][0];
    measure q[0] -> mid[0];
    measure q[1] -> mid[1];
 
    while (mid == "00") {
      reset q[0];
      reset q[1];
      my_gate(a) q[0], q[1];
      my_phase(a - pi/2) q[1];
      mid[0] = measure q[0];
      mid[1] = measure q[1];
    }
 
    if (mid[0]) {
      let inner_alias = q[{0, 1}];
      reset inner_alias;
    }
 
    out = measure q;
"""
circuit = qiskit.qasm3.loads(program)
circuit.draw("mpl")
output

Export to OpenQASM 3

You can export Qiskit code to OpenQASM 3 with dumps(), which exports to a string, or dump(), which exports to a file.

Example with dumps()

from qiskit import QuantumCircuit
from qiskit.qasm3 import dumps
 
qc = QuantumCircuit(2)
qc.h(0)
qc.cx(0,1)
qc.measure_all()
 
dumps(qc)

Output:

'OPENQASM 3;\ninclude "stdgates.inc";\nbit[2] meas;\nqubit[2] q;\nh q[0];\ncx q[0], q[1];\nbarrier q[0], q[1];\nmeas[0] = measure q[0];\nmeas[1] = measure q[1];\n'

Example with dump()

from qiskit import QuantumCircuit
from qiskit.qasm3 import dump
 
qc = QuantumCircuit(2)
qc.h(0)
qc.cx(0,1)
qc.measure_all()
 
f = open("my_file.txt", 'w')
dump(qc, f)
f.close()

See more information in the Exporting to OpenQASM 3 section of the API reference.

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