  Accurate values for atomic dipole matrix elements are useful in many areas of
physics, and in particular for interpreting experiments such as atomic parity
violation. Obtaining accurate matrix element values is a challenge for both
experiment and theory. A new technique that can be applied to this problem is
tune-out spectroscopy, which is the measurement of light wavelengths where the
electric polarizability of an atom has a zero. Using atom interferometry
methods, tune-out wavelengths can be measured very accurately. Their values
depend on the ratios of various dipole matrix elements and are thus useful for
constraining theory and broadening the application of experimental values.
Tune-out wavelength measurements to date have focused on zeros of the scalar
polarizability, but in general the vector polarizability also contributes. We
show here that combined measurements of the vector and scalar polarizabilities
can provide more detailed information about the matrix element ratios, and in
particular can distinguish small contributions from the atomic core and the
valence tail states. These small contributions are the leading error sources in
current parity violation calculations for cesium.
