Method logical_observable

python/cudaq/kernel/kernel_builder.py:1279–1306

Define a logical observable over one or more measurement results. ``observable_index`` selects which logical qubit observable this call defines; codes with a single logical qubit can omit it. Any combination of scalar handles and handle vectors is accepted.

(self, *measurements, observable_index=0)

            qec.DetectorOp(values)

    def logical_observable(self, *measurements, observable_index=0):
        """Define a logical observable over one or more measurement results.

        ``observable_index`` selects which logical qubit observable this
        call defines; codes with a single logical qubit can omit it. Any
        combination of scalar handles and handle vectors is accepted.
        """
        if not measurements:
            emitFatalError("kernel.logical_observable requires at least one "
                           "cudaq.measure_handle argument")
        if not isinstance(observable_index, int) or isinstance(
                observable_index, bool):
            emitFatalError(
                "kernel.logical_observable requires observable_index "
                "to be an integer literal")
        if observable_index < 0 or observable_index > (1 << 63) - 1:
            emitFatalError(
                "kernel.logical_observable observable_index must be in "
                "the range [0, 2^63 - 1]")
        with self.ctx, self.insertPoint, self.loc:
            values = [
                self.__qecOperandValue(m, "logical_observable")
                for m in measurements
            ]
            # Skip the attribute at the default 0 so the printed IR omits
            # the optional `index 0` literal at the spec shape.
            idxAttr = None if observable_index == 0 else observable_index
            qec.ObservableOp(values, observableIndex=idxAttr)

    def detectors(self, prev, curr):
        """Define N detectors by pairing two measurement vectors