  The electronic structure of atomic quantum systems and their dynamical
interaction with light is reflected in transition dipole matrix elements
coupling the system's energy eigenstates. In this work, we measure phase shifts
of the time-dependent ultrafast absorption to determine the relative signs of.
the transition-dipole matrix elements. The measurement relies on precise
absolute calibration of the relative timing between the used light pulses,
which is achieved by combining attosecond transient absorption and attosecond
streaking spectroscopy to simultaneously measure the resonant photoabsorption
spectra of laser-coupled doubly excited states in helium, together with the
attosecond streaked photoelectron spectra. The streaking measurement reveals
the absolute timing and the full temporal profile of the interacting electric
fields which is then used to quantify the state-specific dynamics of the
measured photoabsorption spectra. By comparing the 1-fs time-scale modulation
across the absorption lines corresponding to the 2s2p (1P) and sp2,3+ (1P)
doubly excited states between simulation and measurement, we quantify the signs
of the transition dipole matrix elements for the laser-coupled autoionizing
states 2s2p-2p2 and 2p2-sp2,3+ to be opposite of each other.
