  We report the implementation of a perceptron quantum gate in an ion-trap
quantum computer. In this scheme, a perceptron's target qubit changes its state
depending on the interactions with several qubits. The target qubit displays a
tunable sigmoid switching behaviour becoming a universal approximator when
nested with other percetrons. The procedure consists on the adiabatic ramp-down
of a dressing-field applied to the target qubit. We also use two successive
perceptron quantum gates to implement a XNOR-gate, where the perceptron qubit
changes its state only when the parity of two input qubits is even. The
applicability can be generalized to higher-dimensional gates as well as the
reconstruction of arbitrary bounded continuous functions of the perceptron
observables.
