Writing a basic quantum program

In this notebook, you will learn how to write a quantum program in Python on the Quantum Learning Machine.

In the QLM python framework, a quantum program is contained in a Program class. It comes with methods to allocate quantum and classical registers, apply gates, measures and resets. A given instance of a Program can then be converted to a quantum Circuit, which is the object that can be fed to a quantum processor.

Initializaton of a Quantum Program

In the following snippet, we instantiate a quantum program object called prog:

from qat.lang.AQASM import Program

prog = Program()

Quantum bit allocation

The allocation of quantum bits is done via the qalloc method. It returns a register, which will then be used to refer to the qubits.

In the following snippet, we allocated an 8-qubit register:

qbits = prog.qalloc(8)

Applying quantum gates

The application of quantum gates is carried out through the apply method.

Here, we apply standard Hadamard gate on qbit 0, a Pauli X gate on qubit 1, a CNOT gate on qubits 1 and 5, and a phase gate with angle $\pi/6$ to qubit 5.

from qat.lang.AQASM import H, X, CNOT, PH
from math import pi

prog.apply(H, qbits[0])
prog.apply(X, qbits[1])
prog.apply(CNOT, qbits[1], qbits[5])
prog.apply(PH(pi/6), qbits[5])

Generation of a quantum circuit

Before we describe other common operations such as measurements, let us introduce the final step that allows to generate a quantum-simulation-ready quantum circuit out of the quantum program.

This generation is done via the to_circ method:

circ = prog.to_circ()

Circuit display

The .display method outputs a graphical representation of the quantum circuit:

circ.display()

For a more comprehensive reference on the Python AQASM library, including measures, classical control, custom gates, etc., check out this tutorial. You will find a list of all available gates here.