Observation of the Fano-Kondo Anti-Resonance in a Quantum Wire with a Side-Coupled Quantum Dot

We have observed the Fano-Kondo anti-resonance in a quantum wire with a side-coupled quantum dot. In a weak coupling regime, dips due to the Fano effect appeared. As the coupling strength increased, conductance in the regions between the dips decreased alternately. From the temperature dependence and the response to the magnetic field, we conclude that the conductance reduction is due to the Fano-Kondo anti-resonance. At a Kondo valley with the Fano parameter $q\approx 0$, the phase shift is locked to $\pi/2$ against the gate voltage when the system is close to the unitary limit in agreement with theoretical predictions by Gerland {\it et al.} [Phys. Rev. Lett. {\bf 84}, 3710 (2000)].