Propagation And Manipulation Of Optical Pulses In Ultracold Rydberg Atomic Gases And Metamaterials

In recent years,due to the proposal of electromagnetically induced trans-parency(EIT),many efforts has been paid to the investigation on nonlinear optics in coherent medium at at weak-light level.By the quantum interference effect induced by an additional control field,the optical absorption can be largely suppressed.Simultaneously,due to drastic change of dispersion,EIT can achieve a large reduction of group velocity,which can be used to realize optical buffers and quantum memory.Light propagation in EIT media can also obtain a en-hancement of Kerr nonlinearity,which can be used to design all-optical quantum phase gates and realize quantum information and computation.However,the largest Kerr nonlinearity,obtained in conventional EIT media,is still too small for nonlinear optics at single-photon level.The coherent optical detection of highly excited Rydberg states using electro-magnetically induced transparency(EIT)was reported by C.S.Admas research group,providing a direct nondestructive probe of the fine structure splitting of Rydberg energy levels.Since then,considerable achievements have been made on the EIT in cold Rydberg gases.Experimental and theoretical works showed that EIT can be used to realize quantum logic gates,measure high-resolution Ry-dberg spectrum,and especially for obtaining giant Kerr nonlinearity.Different from conventional EIT media,the giant Kerr nonlinearity in Rydberg-EIT sys-tems comes from the strong Rydberg-Rydberg interaction between atoms,which can be arrived at 7×10-2 V-2m2 and can be five orders of magnitude larger than that obtained in traditional EIT systems.Rydberg atoms are atoms in highly excited electronic states with a large principal quantum number n.Due to their long lifetime,large electric dipole moment(atomic scales,electric polarizability),and especially for the strong atom-atom interaction in Rydberg gases.Due to the fragile nature of highly excited Rydberg atoms,systematic studies of such large interactions only be-came possible with the availability of laser-cooled gases that permitted spectro-scopic interrogations of effectively "frozen Rydberg gases".The most prominent phenomenon relevant to such a scenario is the so-called Rydberg blockade effect.Those exaggerated properties brings many intriguing aspects that can be used not only for precision spectroscopy,precision measurement,but also for simulat-ing strongly correlated quantum many-body systems,including Rydberg dressed BEC,supersolid formation,and ultracold plasma.In addition,such striking fea-tures also have advantages on realizing quantum information and computation,etc.These important studies opened a new and important avenue for nonlinear and quantum optics in the ultracold Rydberg gases.In the dissertation,we shall investigate nonlinear effect and quantum in-terference in the ultracold Rydberg atomic gases,which include:(i)Develop a theoretical method beyong mean-field approach to study the quantum dynam-ics of interacting Rydberg atomic system and calculate every-order correlation,functions of atomic transition operators in a systematic way,so as to obtain every-order optical susceptibilities contributed by atom-atom and photon-atom inter-actions;(ii)Study the formation and propagation of weak-light spatial-temporal solitons in the ultracold Rydberg atomic system based on the giant enhancemen-t of nonlinear response resulted from electromagnetically induced transparency effect;(iii)Explore the possibility of storage and retrieval of optical solitons by using ultracold Rydberg atoms.The main work contains the following aspects:1.Study on giant optical Kerr effect in a cold Rydberg atomic system via EIT.By using an approach beyond mean-field theory on the cor-relators of one-body,two-body,and three-body based on a second-order ladder approximation,we show that the system possesses not only an enhanced third-order nonlinear optical susceptibility,but also a giant fifth-order nonlinear optical susceptibility,which has a cubic dependence on atomic density and can.be ar-rived at the order of magnitude 10-11 m4V-4.Our results demonstrate that both the third-order and the fifth-order nonlinear optical susceptibilities consist of t-wo parts.One part is contributed by photon-atom interaction and another part comes from the Rydberg-Rydberg interaction.The Kerr nonlinearity induced by the Rydberg-Rydberg interaction plays a leading role at high atomic density.We find that the fifth-order nonlinear optical susceptibility in the Rydberg-EIT system may be five orders of magnitude larger than that obtained in tradition-al EIT systems,which may have promising applications in light and quantum information processing and transmission at weak-light level.2.Study on(3+1)-dimensional ultraslow weak-light spatiotempo-ral solitons in a cold Rydberg atomic gas.Starting from the Maxwell-Bloch equations and using a standard method of multiple scales,we derive a modified nonlocal nonlinear Schrodinger(NNLS)equation governing the spatiotemporal evolution of the probe-field envelope that describes effects of linear absorption,diffraction,dispersion,and two types of(synergetic)optical nonlinearities.We demonstrate that the system allows various optical bullet solutions,which can be stabilized by the balance between the dispersion,diffraction,and the syner-getic Kerr nonlinearities.We also demonstrate that the light bullets obtained have very slow propagation velocity,extremely low generation power,and can be stored and retrieved with high efficiency and fidelity through switching on and off of a control field.In addition,we shall also investigate the classical analogue of EIT in the metamaterials systems,which is so called plasmon induced transparency(PIT).EIT in atomic systems often requires special and often cumbersome experimental conditions,such as large device size and ultracold temperature,which hampers compact chip-integrated applications working at room temperature;Compared with EIT in atomic system,PIT raises the possibility for compact chip-integrated applications for EIT effect based on room-temperature metamaterials.our works includes the following aspects:3.Study on giant Kerr nonlinearity and low-power plasmonic solitons(dromions)via plasmon-induced transparency.We suggest a new type of metamaterial,which is constructed by an array of unit cell consisting of a cut-wire and a pair of varactor-loaded split-ring resonators.The dynamics of the PIT unit cell can be described by the coupled Lorentz oscillator model.and show that the system can not only mimic the EIT of three-level atomic systems,but also display a crossover to Autler-Townes splitting(ATS)(i.e.PIT-ATS crossover)when the bright and dark modes of the system is changed from weak to strong coupling regions.We also show that,due to PIT effect and the nonlinearity contributed by the varactor,the system may possess very large second-order and third-order nonlinear susceptibilities.We further show that the system supports a resonant interaction between longwave and shortwave and hence effective third-order nonlinear susceptibility can be further enhanced one order of magnitude,which may be used to create plasmon solitons and dromions with extremely low power.Our work raises the possibility for obtaining strong nonlinear effect for gigahertz radiation at very low intensity based on room-temperature metamaterials.4.Study on storage and retrieval of electromagnetic waves with orbital angular momentum via Plasmon-Induced Transparency.The system we consider is a plasmonic metamaterial,which consists of an array of meta-atoms constructed by a metallic structure loaded with two varactors.The PIT in such meta-atoms can be used to actively manipulate the PIT transparency window using a control wave.We find that,based on the PIT effect,shape-preserving(3+1)D "dark-mode plasmonic polaritons" carrying various OAMs can be generated,which are mixture of(3+1)-dimensional EM-wave modes and dark oscillatory modes of the meta-atoms combined with spatial Laguerre-Gaussian(LG)beams.We show that the(3+1)D multi-mode EM waves with OAMs can have very slow group velocity,and may be stored and retrieved through the switching-off and switching-on of a control field.We also suggest a method to increase the memory efficiency of the high-dimensional EM waves by using a gain to compensate for the Ohmic loss of the metamaterial.Our work raises the possibility for realizing PIT-based spatial multi-mode memory of electromagnetic waves and is promising for practical application of information processing with large capacity by using room-temperature metamaterials.