We investigate a four-wave-mixing process in an N interaction scheme in Rb vapor placed inside a low-finesse ring cavity. We observe strong amplification and generation of a probe signal, circulating in the cavity, in the presence of two strong optical pump fields. We study the variations in probe field gain and dispersion as functions of experimental parameters with an eye on the potential application of such a system for enhanced rotation measurements. Density-matrix calculations are performed to model the system and are shown to provide good qualitative agreement with the experiment.
We investigate the propagation of a weak probe laser field in a medium of warm Rb atoms, controlled with two strong resonant pump fields tuned to the D1 and D2 optical transitions to form an N-scheme arrangement. We have shown theoretically that four-wave mixing has a profound effect on the probe-field group velocity and absorption, allowing the probe-field propagation to be continuously tuned from superluminal to slow-light regimes with amplification. We have also identified the experimental conditions for observation of such tunable slow-to-fast light regime (continuously through the point of zero group index) with positive probe-field gain, and demonstrated that the spectral range corresponding to the zero group index can be tuned by controlling the power of one of the pump laser.
We investigate weak optical probe pulse propagation in a resonant Lambda and N-interaction schemes, and investigate the role of the four-wave mixing on classical and quantum properties of the probe field. In particular, we focus our attention on two configurations. In the first case we take into account the off-resonant coupling of the strong field to the signal field ground state. Such configuration is relevant for EIT-based slow light and quantum memory. In the second configuration the additional control field is derived from an independent laser, and it is tuned to a different optical resonance from the ones forming an original Lambda system. Such interaction scheme allows realization of tunable slow and fast light, and was considered with regards to enhancement of optical gyroscopes performance.
We demonstrate that in both cases the four-wave mixing (FWM) has a profound effect on signal field group velocity and absorption profile, and may even lead to gain. We present both semi-classical and fully quantum treatments for propagation of both signal and newly generated Stokes fields that include accurate description of their quantum noise. In particular, we analyze the case of a quadrature-squeezed signal field, and demonstrate that vacuum fluctuations of the Stokes field couple into the signal field through the FWM process and degrades the squeezing. The severity of this degradation grows with optical depths of an atomic medium, setting an additional practical limits for the experiments.
In this manuscript we present calculations that consider the propagation of a squeezed vacuum signal field through
a resonant atomic medium under electromagnetically induced transparency (EIT). We show that squeezing is
degraded due to four-wave mixing processes at high optical depth of the atomic medium. We also present some
preliminary results for degenerate Zeeman EIT resonances.