Controlled breaking of phase symmetry in a 'Which-Path?' interferometer

Linear response conductance of a two terminal Aharonov-Bohm (AB) interferometer is an even function of magnetic field, as dictated by Onsager-Buettiker relations. We discuss an experimental setup in which this phase symmetry can be broken in a controlled way. To this end we consider a 'Which Path?' detector, which consists of an interferometer with quantum dots (QDs) in each of its arms, one of the QDs being capacitively coupled to a nearby quantum point contact (QPC). This coupling results in breaking of the phase symmetry of the AB oscillations, given that a finite voltage bias is applied to the QPC. Sweeping in the same time the level in the other QD across the Fermi level allows one to observe smooth change of the phase from 0 to π, rather than an abrupt jump observed in isolated AB interferometers. We explore the possibility of using this setup in order to measure the transmission phase through a QD.