Catalyst

Development

Examples

API

  1. Docs
  2. PennyLane Python Frontend
  3. catalyst.measure

catalyst.measure

measure(wires, reset: bool | None = False, postselect: int | None = None) → DynamicJaxprTracer[source]

A qjit() compatible mid-circuit measurement on 1 qubit for PennyLane/Catalyst.

Important

The qp.measure() function is not QJIT compatible and catalyst.measure() from Catalyst should be used instead.

Parameters:

  • wires (int) – The wire the projective measurement applies to.

  • reset (Optional[bool]) – Whether to reset the wire to the \(|0\rangle\) state after measurement.

  • postselect (Optional[int]) – Which basis state to postselect after a mid-circuit measurement.

Returns:

A JAX tracer for the mid-circuit measurement.

Raises:

ValueError – Called outside the tape context.

Note

To configure the mid-circuit measurement simulation method and postselection mode, please see the relevant keyword arguments of the QNode().

For more details, check out our dynamic quantum circuit guide.

Example

import pennylane as qp
from catalyst import qjit, measure

dev = qp.device("lightning.qubit", wires=2)

@qjit
@qp.qnode(dev)
def circuit(x: float):
    qp.RX(x, wires=0)
    m1 = measure(wires=0)

    qp.RX(m1 * jnp.pi, wires=1)
    m2 = measure(wires=1)

    qp.RZ(m2 * jnp.pi / 2, wires=0)
    return qp.expval(qp.PauliZ(0)), m2

>>> circuit(0.43)
[Array(1., dtype=float64), Array(False, dtype=bool)]
>>> circuit(0.43)
[Array(-1., dtype=float64), Array(True, dtype=bool)]

Example with post-selection

dev = qp.device("lightning.qubit", wires=1)

@qjit
@qp.qnode(dev)
def circuit():
    qp.Hadamard(0)
    m = measure(0, postselect=1)
    return qp.expval(qp.PauliZ(0))

>>> circuit()
Array(-1., dtype=float64)

Example with reset

dev = qp.device("lightning.qubit", wires=1)

@qjit
@qp.qnode(dev)
def circuit():
    qp.Hadamard(0)
    m = measure(0, reset=True)
    return qp.expval(qp.PauliZ(0))

>>> circuit()
Array(1., dtype=float64)
Previous
Next