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Currently Supported Constructs

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

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1. Register Declarations

OpenQASM declarations of all forms qreg, qubit, bit, and creg are supported.

OPENQASM 3;

// qubit declaration
qubit q1;
qubit[2] q2;
qreg q3[3];
qubit[1] q4;

// bit declaration
bit c1;
bit[2] c2;
creg c3[3];
bit[1] c4;

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2. Quantum Measurements

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];

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3. Quantum Reset

Resets are supported on declared quantum registers in all forms.

OPENQASM 3;

include "stdgates.inc";

// qubit declarations
qubit q1;
qubit[2] q2;
qreg q3[3];

// reset operations
reset q1;
reset q2[1];
reset q3[2];
reset q3[:2];

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4. Quantum Gates

  • pyqir._native gates are supported along with support for U3 and U2 gates. The U[x] gates are defined in terms of existing rx and rz gates according to the decomposition present on the Qiskit UGate documentation and PhaseGate documentation.
  • Full set of the openqasm3 “stdgates.inc” gates are supported. These gates are decomposed with the help of the pyqir._native gate set and subsequently converted to QIR.

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5. Quantum Barriers

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];

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6. 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;
}

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

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7. Simple Branching Statements

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];
}

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8. Expressions

  • General expression evaluation involving literals and constants is supported.
  • Expressions involving constants and variables are fully supported.
  • Expressions with arrays are also supported (in global scopes).
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;

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9. Variables and Types

  • Scalar types int, uint, float, bool and bit with arbitrary sizes are supported.
  • array type is supported for int, uint, float, bool and bit.
  • complex and angle types are not supported yet.
OPENQASM 3;
// declarations
int a;
uint b;
int[2] c = 1;
uint[13] d = 2;
float[32] my_pi = 3.14;

// assignments and expressions
a = 5 \* c;
b = 6 - d;

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10. Loops

Both for and while loops are supported at the moment. For example:

OPENQASM 3.0;
include "stdgates.inc";

qubit[2] q;
int[32] i;
for int[32] i in [0:2] {
h q[i];
}

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11. Aliasing

  • Aliasing quantum registers is supported and can be used to refer to the same quantum register with different names.
  • Aliases are currently supported in global scope of the qasm3 program, with support for function scopes coming soon.
OPENQASM 3.0;
include "stdgates.inc";

qubit[5] q;

let myqreg0 = q;
let myqreg1 = q[1];
let myqreg2 = q[1:];
let myqreg3 = q[:4];
let myqreg4 = q[1:4];
let myqreg5 = q[1:2:4];
let myqreg6 = q[{0, 1}];

x myqreg0[0];
h myqreg1;
cx myqreg2[0], myqreg2[1];
cx myqreg3[2], myqreg3[3];
ccx myqreg4;
swap myqreg5[0], myqreg5[1];
cz myqreg6;

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12. Subroutines

We support QASM3 subroutines in the QIR converter

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13. Switch

Switch statements in QASM3 are supported in the QIR converter. These are defined according to the OpenQASM3 spec and support all the features mentioned in the specification.

OPENQASM 3.0;
include "stdgates.inc";

const int i = 4;
const int j = 4;
qubit q;

switch(i) {
    case 6, j {
        x q;
    }
    default {
        z q;
    }
}