We have built and investigated an electronic interferometer based on a
2D electron gas in a AlGaAs/GaAs heterojunction. This is the smallest
interferometer that has ever been built. We established that at T < 0
. 1 K the amplitude of the Aharonov-Bohm oscillations of the interfero
meter reaches 35% of the resistance of the interferometer in the absen
ce of a magnetic field; this is almost twice the amplitude previously
achieved.