  Measurement of the transmission phase through a quantum dot (QD) embedded in
an arm of a two-terminal Aharonov-Bohm (AB) interferometer is inhibited by
phase symmetry, i.e. the property that the linear response conductance of a
two-terminal device is an even function of magnetic field. It is demonstrated
that in a setup consisting of an interferometer with a QD in each of its arms,
with one of the QDs capacitively coupled to a nearby quantum point contact
(QPC), phase symmetry is broken when a finite voltage bias is applied to the
QPC. The transmission phase via the uncoupled QD can then be deduced from the
amplitude of the odd component of the AB oscillations.
