  We present the first quantum controlled-NOT (CNOT) gate realized using a
fiber-based indistinguishable photon-pair source in the 1.55 $\mu$m
telecommunications band. Using this free-space CNOT gate, all four Bell states
are produced and fully characterized by performing quantum state tomography,
demonstrating the gate's unambiguous entangling capability and high fidelity.
Telecom-band operation makes this CNOT gate particularly suitable for quantum
information processing tasks that are at the interface of quantum communication
and linear optical quantum computing.
