  We present an optical implementation of two programmable quantum measurement
devices. The first one serves for unambiguous discrimination of two
nonorthogonal states of a qubit. The particular pair of states to be
discriminated is specified by the quantum state of a program qubit. The second
device can perform von Neumann measurements on a single qubit in any basis
located on the equator of the Bloch sphere. Again, the basis is selected by the
state of a program qubit. In both cases the data and program qubits are
represented by polarization states of photons. The experimental apparatus
exploits the fact that two Bell states can be distinguished solely by means of
linear optics. The outcome corresponding to the remaining two Bell states
represents an inconclusive result.
