  Quantum computation has attracted much attention, among other things, due to
its potentialities to solve classical NP problems in polynomial time. For this
reason, there has been a growing interest to build a quantum computer. One of
the basic steps is to implement the quantum circuit able to realize a given
unitary operation. This task has been solved using decomposition of unitary
matrices in simpler ones till reach quantum circuits having only single-qubits
and CNOTs gates. Usually the goal is to find the minimal quantum circuit able
to solve a given problem. In this paper we go in a different direction. We
propose a general quantum circuit able to implement any specific quantum
circuit by just setting correctly the parameters. In other words, we propose a
programmable quantum circuit. This opens the possibility to construct a real
quantum computer where several different quantum operations can be realized in
the same hardware. The configuration is proposed and its optical implementation
is discussed.
