Hybrid Induced Transparency And Fast/Slow Light Manipulation In Atom-assisted Optomechanical Cavity

With the continuous development of optomechanics, people not only haveobserved many interesting phenomena in quantum world, but also have found themethods for quantum control of mechanical motion and for mechanical control oflight, for the reason that there could be wide applications of this in many fields likehigh-precision measurement, quantum information processing and fundamentaltheorem verification of quantum mechanics, and so on. In recent years, benefited fromthe rapid development of nano science and advanced semiconductor technology,people are able to observe more significant quantum optomechanical effects whenoptomechanical system is getting smaller in size. Optomechanical inducedtransparency, fast and slow light, optical storage as well as other quantum optical andnonlinear optical effects have become the focus of research. On the other hand,optomechanical systems coupled to other small subsystems (such as atoms, quantumdots, single electron transistors, etc.) also attract great attention in research. This isbecause the coupling system has not only provided more degrees of freedom forquantum manipulation, but also opened up more channels for classical and quantuminformation transfer. In this paper, we study hybrid induced transparency and fast/slow light control in atom-assisted optomechanical systems.First, we have studied the spectral features of the hybrid EIT and OMIT in atripartite optomechanical system in analog to four-level atomic inverted-Yconfiguration. We find that the EIT and OMIT may simultaneously exist owing tocavity-atom coupling and cavity-oscillator coupling, respectively. Such a tripartitesystem can be considered as being composed of two three-level sub-systems, i.e. Λand ladder configurations. Also, we can suppress single features of the hybrid EIT andOMIT due to one of the sub-systems by changing atomic number or driving fieldpower as desired. Therefore the hybrid EIT and OMIT windows’s width and heightare controlled by appropriately selecting the magnitude of the driving field power and the atomic number. Furthermore, by changing the system’s detuning it is possible tomake the OMIT dip appear at the EIT absorption peak, or at the bottom of the EITwindow, or occur in other locations, thus changing the entire shape of the hybrid EITand OMIT. On the other hand, it is possible to switch the shape of the hybrid EIT andOMIT from symmetry to asymmetry, as well as for the profile to change from anabsorption dip-like EIT to dispersion-like EIT in both real and imaginary parts of theoutput probe field. At the meantime, by manipulating system’s detuning we can alsocontrol the distribution of the output energy, something difficult to achieve with onlyone of the sub-systems alone. This kind of system is certainly useful in any opticalswitching devices based on the phenomenon of the hybrid EIT and OMIT. Also,dispersion control can find important applications in manipulating group velocity oflight pulses.Secondly, we theoretically investigate the slow and fast light effects of a probelaser in an optomechanical double-ended cavity filled with a bunch of identicaltwo-level cold atoms. With the absence of the atoms, the generic OMIT window canbe obtained; with the presence of the atoms, we obtain the steeper Fano shapes andthe broader normal mode splitting shapes than OMIT window by changing thedetuning between the atomic transition and the driving field. We find that thetransmission parts of output probe field have slow light. The group delay relating tothe Fano resonance is much greater than those relating to the OMIT and normal-modesplitting at the resonance. Meanwhile, the slow light of the transmitted probe field canbe controlled by modulating the power of the driving field and atomic number. Thereflection parts of output probe field have both slow light and fast light. With theabsent of atoms, the reflection part of output probe field has obviously slow light;when the atoms are resonant with frequency of mechanical resonator, the OMITwindow transfers to the normal-mode splitting shapes, where the slow light of thereflection probe field almost disappear; when the atoms are resonant with negativefrequency of mechanical resonator, the OMIT window transfers from symmetricshapes to asymmetric Fano shapes, where the slow light of the reflection probe fieldturns into fast light. It is worth noting that by adjusting the atomic number and detuning, we can not only change the magnitudes of the group delay and advance, butalso can make the slow light into fast light.Lastly, we study optomechanical induced transparency (OMIT) and fast/slowlight phase control in atom-assisted optomechanical cavity. Unlike the previoussystems, in this model the mechanical resonator is directly driven by an weakauxiliary driving field. We therefore find that, along with the change of amplituderatio and phase difference of auxiliary driving field and the probe field, the absorptionand dispersion properties of the whole system and the group delay time are changing.At the absence of auxiliary field, we observed the spectral features of the hybrid EITand OMIT in an atom-cavity-oscillator tripartite optomechanical system. When theauxiliary field and the probe field have no phase difference, we find that themembrane resonance absorption will enhance with the increasing of auxiliary fieldstrength at resonance, causing the optomechanical induced transparency suppression.Therefore we can modify the amplitude of auxiliary field to control the depth of theOMIT window. When keeping amplitude ratio of the auxiliary field and probe fieldunchanged, only modifying the phase difference between the auxiliary field and theprobe field, we see that the value of phase difference is directly affecting theoptomechanical coupling effect of the system. Therefore, via changing the phases ofauxiliary field and probe field, we can not only realize the manipulation of OMITwindow depth, but also get the control of tunable optical switch from "absorption" to"transparent" or "gain". In the meantime, we find that the system’s group delay timevaries periodically with the change of phase difference. It is worth noting that byadjusting the phase difference and amplitude ratio of auxiliary field and probe field,we can not only change the magnitudes of the group delay and advance, but alsorealize the conversion between slow light or fast light effects.