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QASM Mapping

Bloch emits OpenQASM 2.0 for quantum operations performed by the interpreter and simulator. The CLI always writes <file>.qasm next to your source; use --emit-qasm to also print it to stdout.

Gate mappings​

Single-qubit gates:

BlochOpenQASM
h(q)h q[i];
x(q)x q[i];
y(q)y q[i];
z(q)z q[i];
rx(q, theta)rx(theta) q[i];
ry(q, theta)ry(theta) q[i];
rz(q, theta)rz(theta) q[i];

Two-qubit gate:

BlochOpenQASM
cx(ctrl, tgt)cx q[c], q[t];

Notes

  • q[i] refers to the underlying simulator qubit at index i. When using single qubit variables, the simulator assigns an index for that allocation; when using qubit[], q[k] maps directly to an index.
  • Rotation angles are emitted as-is (float values in radians).

Measurement and classical bits​

  • Statement form: measure q; becomes measure q[i] -> c[i]; in the log and collapses the qubit.
  • Expression form: bit b = measure q; also produces a measurement result and returns a bit value to the program.

The simulator maintains a classical register c[...] for recorded outcomes in the QASM log.

Example​

Bloch:

@quantum
function bell(qubit a, qubit b) -> void {
  h(a); cx(a, b);
}

function main() -> void {
  qubit q0; qubit q1;
  bell(q0, q1);
  measure q0; measure q1;
}

Emitted QASM:

OPENQASM 2.0;
include "qelib1.inc";
qreg q[2];
creg c[2];
h q[0];
cx q[0],q[1];
measure q[0] -> c[0];
measure q[1] -> c[1];

See also