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In this article, we investigate the optical response of a duplicated two-level atomic medium submitted to a strong stationnary control field and a weak co-propagating probe field, orthogonally polarized to each other. We show that both reflected and transmitted components of the probe may be absorbed and amplified. Moreover, for low optical depths, reflection and transmission factors are controlled by the relative phase between control and probe fields, which makes the configuration we present here promising for the development of optical devices, such as phase-controlled switches., Comment: 12 pages, 9 figures

An ideal experiment is designed to determine the past of a particle in the nested Mach-Zehnder interferometer (MZI) by using standard quantum mechanics with quantum non-demolition measurements. We find that when the photon reaches the detector, it only follows one arm of the outer interferometer and leaves no trace in the inner MZI; while when it goes through the inner MZI, it cannot reach the detector. Our result obtained from the standard quantum mechanics is contradict to the statement based on two state vector formulism, "the photon did not enter the (inner) interferometer, the photon never left the interferometer, but it was there". Therefore, the statement and also the overlap claim are incorrect.

We present the theory of a new method to slow a linearly polarized probe pulse as it propagates through a duplicated two-level system driven by an orthogonally polarized control field. The method makes use of Zeeman coherence oscillations (CZO) that arise in the atomic system because of the spatial and temporal modulation of the total polarization. This method exhibits properties similar to those that rely on the electromagnetically induced transparency (EIT) but without the existence of any trapping state. We demonstrated also the propagation of a dark polariton in the medium, Comment: Rapid communication in PRA, 4 pages, 3 figures. Phys Rev A, rapid com. accepted (2008)