Abstract

OpenQASM3 is under development in https://github.com/Qiskit/openqasm. OpenQASM3 supports classical statements in addition to quantum statements. In this project, a OpenQASM3 file is generated by analyzing python code that uses qiskit.

Description

OpenQASM3 supports classical instructions which include loop, branch, and unary/binary operations. However, it is difficult to write large OpenQASM3 file without help of tools.

In this project, we define DSL (domain specific language) which is a subset of python 3 and generate a OpenQASM3 file from a function written in the DSL.

The DSL uses Qiskit to write quantum instructions and use python expressions to write classical instructions. For example, following qft function can be supported in the DSL.

def qft(circuit):
    n = 5
    qr = QuantumRegister(n)
    circuit.add_register(qr)
    cr = ClassicalRegister(n)
    circuit.add_register(cr)

    for i in range(n):
        circuit.h(qr[i])

    for i in range(n):
        for j in range(i):
            l = math.pi / float(2 ** (i - j))
            circuit.p(l / 2, qr[i])
            circuit.cx(qr[i], qr[j])
            circuit.p(-l / 2, qr[j])
            circuit.cx(qr[i], qr[j])
            circuit.p(l / 2, qr[j])
        circuit.h(qr[i])

    circuit.barrier(qr)
    circuit.measure(qr, cr)

This function will be converted to a OpenQASM3 file as follows:

OPENQASM 3;
include "stdgates.inc";

const n = 10;

qubit qr[n];
bit cr[n];

float[64] l;
int[64] i, j;

for i in [0:n-1:1]
    h(qr[i);

for i in [0:n-1:1] {
    for j in [0:i-1:1] {
        l = pi / 2.0 ** (i - j);
        p(l / 2, qr[i]);
        cx(qr[i], qr[j];
        p(-l / 2, qr[j]);
        cx(qr[i], qr[j]);
        p(l / 2, qr[j]);
    }
}
cr = measure(qr);

In this project, we parse a specific function of python (with many assumptions) and generate a OpenQASM3 file. In general, Python code is analyzed by using pytyon.ast. Python.ast tree can be generated with this code:

import ast
import astpretty

with open(filename, 'r') as f:
     source = f.read()

tree = ast.parse(source)

for stmt in tree.body:
    astpretty.pprint(stmt)

We can validate generated OpenQASM3 file with antlr g4 file of OpenQASM3.

Maybe work items will be

Study OpenQASM3 grammar (though the specification is under development, we can use the current master)
Define acceptable python expressions and Qiskit usages for the DSL
Develop a parser
Develop a QASM3 generator
Develop a validator to check generated files
etc

Because Qiskit and OpenQASM3 cover huge, we start a very limited scope of them. Maybe we can show strategy to implement remaining part of OpenQASM3.

One of example to use python ast is classicalfunction which generate oracle with an annotation @classical_function.

qiskit-community / qiskit-hackathon-korea-21

Generate OpenQASM3 from Qiskit code by parsing qiskit code with python ast #23

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