QASM support

Currently Supported Constructs

The qbraid_qir.qasm3.qasm3_to_qir() converter supports the following OpenQASM 3 constructs:

  1. Register Declarations : OpenQASM declarations of all forms qreg, qubit, bit and creg are supported.

  2. QuantumMeasurements : Openqasm measurements are supported which involve single qubit measurement and full register measurements. Range based measurements are not supported currently.

OPENQASM 3;

qubit[2] q1;
qubit[5] q2;
qubit q3;

bit[2] c1;
bit c2;

// supported
c1 = measure q1;
measure q1 -> c1;
c2[0] = measure q3[0];

//ERROR : not supported
c1[0:2] = measure q1[0:2];

  1. QuantumReset : Resets are supported on declared quantum registers in all forms.

  2. QuantumGates : pyqir._native gates are supported alongwith support for U3 and U2 gates. The U[x] gates are defined in the terms of existing rx and rz gates according to the decomposition present on the qiskit website - https://docs.quantum.ibm.com/api/qiskit/qiskit.circuit.library.UGate, https://docs.quantum.ibm.com/api/qiskit/qiskit.circuit.library.PhaseGate

  3. QuantumBarriers : Barriers are supported only if they are placed on ALL the qubits in the circuit. For example:

qubit q[2];

U(0.1, 0.2, 0.3) q[0];

// Barrier on all qubits
barrier q;

// ERROR : Barrier on a subset of qubits
barrier q[0];

  1. Custom Quantum Gates : Gates defined by users are supported as long as they are defined in terms of pyqir._native gate set. Identifier mapping in gate parameter expressions is not supported at the moment. Example -

OPENQASM 3.0;
include "stdgates.inc";

// Supported
gate custom2(g) s {
    h s;
    rz(g) s;
}

// Supported
gate custom(a,b,c) p, q{
    custom2(a) q;
    h p;
    cx p,q;
    rx(a) q;
    ry(0.5/0.1) q;
}
// ERROR : not supported
gate custom_error(a) p{
    rx(a + 5*2) p; // error
}

qubit[2] q;
custom(2 + 3 - 1/5, 0.1, 0.3) q[0], q[1];

  1. Simple Branching Statements (controlled on 1 bit) : Since QIR supports branching on a measurement result, single bit branching statements are supported at the moment. General boolean expressions and support for branching on full registers will be added in future. For example:

OPENQASM 3;
include "stdgates.inc";
qubit[4] q;
bit[4] c;
h q;
measure q -> c;
// supported
if(c[0]){
    x q[0];
    cx q[0], q[1];
}

if(c[1] == 1){
    cx q[1], q[2];
}

if(!c[2]){
    h q[2];
}

//ERROR : not supported
if(c == 8){
    x q[0];
}
// ERROR : not supported
int[4] element;
if(element > 5){
    y q[1];
}

  1. Expressions : General expression evaluation involving literals and constants is supported. For example:

OPENQASM 3;
qubit q;

// supported
rx(1.57) q;
rz(3-2*3) q;
rz(3-2*3*(8/2)) q;
rx(-1.57) q;
rx(4%2) q;

// ERROR : not supported
int[4] n = 8;
ry(2*pi / n) q;