4 can be used as a means of measuring and reducing stray field effects, phase variation for the primary measure- ments can be implemented through continuous, external, optical means such as a simple delay cell filled with a non-absorbing variable-pressure gas (argon or nitrogen, for example). A delay cell is attractive in its simplicity and relative immunity from variations in polarization, amplitude, or beam alignment. The measurement deter- mines the magnitude and sign of Im ( E$_{PNC}$ ) relative to α , whose calculated value is more reliable than that of β . Precise calibration of the two-photon amplitude is not required, since we are only interested in the relative vari- ation in the modulation amplitude vs. E$_{z}$ . Our proposed measurements employ exclusively linear polarizations, a further simplification. Finally, this technique can allow reduction of magnetic dipole contributions without intro- ducing standing-wave optical fields. Experimental efforts leading toward these measurements are currently under- way in our laboratory. Useful conversations with C. E. Wieman, M. A. Safronova, A. V. Smith, Yong P. Chen, and A. M. Weiner are gratefully acknowledged. We conclude that two-pathway coherent control tech- niques can present a new means for determination of weak interaction amplitudes. While we focussed our at- tention on measurement of Im ( E$_{PNC}$ ), the coherent con- trol technique can also be used to measure the amplitude of the M1 transition moment using a different field ge- ometry. The primary advantage of the present technique is that the phase of the cross term interference signal can be varied by varying the optical phase difference be- tween the laser beams. While reversing the direction of dc electric fields, dc magnetic fields, or field polarizations tions that are in-phase with the PNC term in Eq. (6). There are also terms that contribute signal in phase with the α E$_{z}$ ε ω 1 z term. 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