Observation of large Kerr nonlinearity at low light intensities

Interaction of a four-level atom with a quantized field in the presence of a nonlinear Kerr medium

Quantum entanglement and atomic coherence are examined for a system consisting of a four-level atom (FLA) interacted with a nonlinear quantum field. We assume that the FLA-field coupling, Kerr medium and quantified field are all [Formula: see text]-deformed with full nonlinear formalism. We consider N-configuration and cascade (C)-configuration of the FLA. We explore the impact of field deformation and Kerr medium on the dynamics of the quantumness measures when the quantized field is initially prepared in a deformed coherent state without and with Kerr medium effect. Moreover, we examine the statistical properties of the radiation field using the second order correlation function. The results indicate how the considered quantumness measures in the FLA-field system can be manipulated and controlled through the parameters of the quantum model.

Transfer and evolution of structured polarization in a double-V atomic system

We numerically investigate the transfer of optical information from a vector-vortex control beam to an unstructured probe beam, as mediated by an atomic vapour. The right and left circular components of these beams drive the atomic transitions of a double-V system, with the atoms acting as a spatially varying circular birefringent medium. Modeling the propagation of the light fields, we find that, for short distances, the vectorial light structure is transferred from the control field to the probe. However, for larger propagation lengths, diffraction causes the circular components of the probe field to spatially separate. We model this system for the D1 line of cold rubidium atoms and demonstrate that four wave mixing can lead to correlations between the optical polarization structure and the diffraction of light, generating coupled dynamics of the internal and external degrees of freedom.

Generation of quantum states with nonlinear squeezing by Kerr nonlinearity

In quantum optics, squeezing corresponds to the process in which fluctuations of a quadrature operator are reduced below the shot noise limit. In turn, nonlinear squeezing can be defined as reduction of fluctuations related to nonlinear combination of quadrature operators. Quantum states with nonlinear squeezing are a necessary resource for deterministic implementation of high-order quadrature phase gates that are, in turn, sufficient for advanced quantum information processing. We demonstrate that this class of states can be deterministically prepared by employing a single self-Kerr gate accompanied by suitable Gaussian processing. The required Kerr coupling depends on the energy of the initial system and can be made arbitrarily small. We also employ numerical simulations to analyze the effects of imperfections and to show to which extent can they be neglected.

Spatially dependent hyper-Raman scattering in five-level cold atoms

We demonstrate a scheme to control the spatially dependent hyper-Raman scattering based on electromagnetically induced transparency in a cold atomic system. By adjusting the different system parameters, one can effectively modulate the phase and intensity of the generated Raman field. Specifically, we show that electromagnetically induced transparency creates quantum interference, which results in greatly enhanced efficiency for the generated Raman field. Such improvement in Raman efficiency makes our scheme suitable for generation of short-wavelength coherent radiation, conversion of frequency, and nonlinear spectroscopy based on orbital angular momentum light.

Fluctuation-enhanced Kerr nonlinearity in an atom-assisted optomechanical system with atom-cavity interactions

We examine the effect of cavity field fluctuations on Kerr nonlinearity in an atom-assisted optomechanical system. It is found that a new self-Kerr (SK) nonlinearity term, which can greatly surpass that of a classical Λ type atomic system when the hybrid system has numerous atoms, is generated based on cavity field fluctuations by atom-cavity interactions. A strong photon-phonon cross-Kerr (CK) nonlinearity is also produced based on cavity field fluctuations. These nonlinearity features can be modified by atom-cavity and optomechanical interactions. This work may provide a new method to enhance the SK nonlinearity and generate the photon-phonon CK nonlinearity.

Localized gap modes of coherently trapped atoms in an optical lattice

We theoretically investigate one-dimensional localized gap modes in a coherent atomic gas where an optical lattice is formed by a pair of counterpropagating far-detuned Stark laser fields. The atomic ensembles under study emerge as Λ-type three-level configuration accompanying the effect of electromagnetically induced transparency (EIT). Based on Maxwell-Bloch equations and the multiple scales method, we derive a nonlinear equation governing the spatial-temporal evolution of the probe-field envelope. We then uncover the formation and properties of optical localized gap modes of two kinds, such as the fundamental gap solitons and dipole gap modes. Furthermore, we confirm the (in)stability regions of both localized gap modes in the respective band-gap spectrum with systematic numerical simulations relying on linear-stability analysis and direct perturbed propagation. The predicted results may enrich the nonlinear horizon to the realm of coherent atomic gases and open up a new door for optical communication and information processing.

Tunable and enhanced Goos-Hänchen shift via surface plasmon resonance assisted by a coherent medium

We present a scheme for enhancing Goos-Hänchen shift of light beam that is reflected from a coherent atomic medium in the Kretschmann-Raether configuration. The complex permittivity of the medium can be coherently controlled and has significant influence on the surface plasmon resonance (SPR) at the metal-medium interface. By tuning the atomic absorption, the internal damping of SPR system can be modulated effectively, thereby leading to giant positive and negative lateral displacements. The refractive index of medium determines the SPR angle. Thus the peak position of the beam shift becomes tunable. As the optical response of the coherent medium depends on the intensity and detuning of the controlling fields, we are able to conveniently manipulate the magnitude, the sign, and the angular position of Goos-Hänchen shift peaks.

Neuromorphic Functions of Light in Parity-Time-Symmetric Systems

As an elementary processor of neural networks, a neuron performs exotic dynamic functions, such as bifurcation, repetitive firing, and oscillation quenching. To achieve ultrafast neuromorphic signal processing, the realization of photonic equivalents to neuronal dynamic functions has attracted considerable attention. However, despite the nonconservative nature of neurons due to energy exchange between intra- and extra-cellular regions through ion channels, the critical role of non-Hermitian physics in the photonic analogy of a neuron has been neglected. Here, a neuromorphic non-Hermitian photonic system ruled by parity-time symmetry is presented. For a photonic platform that induces the competition between saturable gain and loss channels, dynamical phases are classified with respect to parity-time symmetry and stability. In each phase, unique oscillation quenching functions and nonreciprocal oscillations of light fields are revealed as photonic equivalents of neuronal dynamic functions. The proposed photonic system for neuronal functionalities will become a fundamental building block for light-based neural signal processing.

Enhancing Third- and Fifth-Order Nonlinearity via Tunneling in Multiple Quantum Dots

The nonlinearity of semiconductor quantum dots under the condition of low light levels has many important applications. In this study, linear absorption, self-Kerr nonlinearity, fifth-order nonlinearity and cross-Kerr nonlinearity of multiple quantum dots, which are coupled by multiple tunneling, are investigated by using the probability amplitude method. It is found that the linear and nonlinear properties of multiple quantum dots can be modified by the tunneling intensity and energy splitting of the system. Most importantly, it is possible to realize enhanced self-Kerr nonlinearity, fifth-order nonlinearity and cross-Kerr nonlinearity with low linear absorption by choosing suitable parameters for the multiple quantum dots. These results have many potential applications in nonlinear optics and quantum information devices using semiconductor quantum dots.

Parity-time symmetry in coherent asymmetric double quantum wells

A coherently prepared asymmetric double semiconductor quantum well (QW) is proposed to realize parity-time (PT) symmetry. By appropriately tuning the laser fields and the pertinent QW parameters, PT-symmetric optical potentials are obtained by three different methods. Such a coherent QW system is reconfigurable and controllable, and it can generate new approaches of theoretically and experimentally studying PT-symmetric phenomena.

High-efficiency backward four-wave mixing by quantum interference

Electromagnetically-induced-transparency-based four-wave mixing (FWM) in a resonant four-level double-Λ system has a maximum conversion efficiency (CE) of 25% due to spontaneous emission. Herein, we demonstrate that spontaneous emission can be considerably suppressed by arranging the applied laser beams in a backward configuration. With the backward double-Λ FWM scheme, we observe a CE of 63% in cold rubidium atoms with an optical depth (OD) of 48. To the best of our knowledge, this is the first observation of a CE exceeding the conversion limit in resonant FWM processes. Furthermore, we present a theoretical model that includes the phase-mismatch effect in the backward double-Λ FWM system. According to the theoretical model, the present scheme can achieve 96% CE using a medium with a large OD of 200 under ideal conditions. Such an efficient frequency conversion scheme has potential applications in optical quantum information technology.

Experimental proposal for performing nonlocal measurement of a product observable

Due to the restrictions on quantum measurement imposed by relativistic causality, it is not easy to perform a nonlocal measurement on spacelike separated systems instantaneously. Here we design an experiment in an optical system to perform the nonlocal measurement of a product observable on a two-qubit system, where a maximally-entangled two-qubit state, acting as an ancillary meter, and three identical Kerr media are used to couple the system under consideration and the target meter. It is shown that the nonlocal measurement of the product observable, σzA⊗σzB, which has two degenerate eigenvalues, could be implemented in a deterministic way without violating relativistic causality.

Nanoscale Kerr Nonlinearity Enhancement Using Spontaneously Generated Coherence in Plasmonic Nanocavity

The enhancement of the optical nonlinear effects at nanoscale is important in the on-chip optical information processing. We theoretically propose the mechanism of the great Kerr nonlinearity enhancement by using anisotropic Purcell factors in a double-Λ type four-level system, i.e., if the bisector of the two vertical dipole moments lies in the small/large Purcell factor axis in the space, the Kerr nonlinearity will be enhanced/decreased due to the spontaneously generated coherence accordingly. Besides, when the two dipole moments are parallel, the extremely large Kerr nonlinearity increase appears, which comes from the double population trapping. Using the custom-designed resonant plasmonic nanostructure which gives an anisotropic Purcell factor environment, we demonstrate the effective nanoscale control of the Kerr nonlinearity. Such controllable Kerr nonlinearity may be realized by the state-of-the-art nanotechnics and it may have potential applications in on-chip photonic nonlinear devices.

Condition for Doppler-free three-photon resonance in a ladder-type atomic system

We report the essential condition for three-photon electromagnetically induced absorption (TPEIA) in a Doppler-broadened ladder-type atomic system. When the two coupling lasers operate at different frequencies, we observed Doppler-free TPEIA resonance at a counterintuitive frequency, which is the almost half-frequency detuning of the frequency difference between the two coupling fields. Considering three-photon coherence in a Doppler-broadened ladder-type three-level atomic system, the TPEIA due to the atomic group of non-zero velocity was in good agreement with the calculated TPEIA spectrum under the one-photon resonance condition of all three optical fields. From the results, we found that an atomic group with a proper velocity for ladder-type TPEIA should satisfy the one-photon resonances of all three optical fields.

Quantum Process Tomography of an Optically-Controlled Kerr Non-linearity

Any optical quantum information processing machine would be comprised of fully-characterized constituent devices for both single state manipulations and tasks involving the interaction between multiple quantum optical states. Ideally for the latter, would be an apparatus capable of deterministic optical phase shifts that operate on input quantum states with the action mediated solely by auxiliary signal fields. Here we present the complete experimental characterization of a system designed for optically controlled phase shifts acting on single-photon level probe coherent states. Our setup is based on a warm vapor of rubidium atoms under the conditions of electromagnetically induced transparency with its dispersion properties modified through the use of an optically triggered N-type Kerr non-linearity. We fully characterize the performance of our device by sending in a set of input probe states and measuring the corresponding output via time-domain homodyne tomography and subsequently performing the technique of coherent state quantum process tomography. This method provides us with the precise knowledge of how our optical phase shift will modify any arbitrary input quantum state engineered in the mode of the reconstruction.

Vortex-based all-optical manipulation of stored light at low light levels

We exploit the giant cross-Kerr nonlinearity of electromagnetically induced transparency (EIT) system in ultracold atoms to implement vortex-based multimode manipulation of stored light at low light levels. Using image-bearing signal light fields with angular intensity profiles, sinusoidal grating structures with phase-only modulation can be azimuthally imprinted on the stored probe light field, where the nonlinear absorption loss can be ignored. Upon retrieval of the probe light, collinearly superimposed vortex modes can be generated in the far field. Considering the finite size of atomic gas, the Fraunhofer diffraction patterns of the retrieved probe fields and their spiral spectra are numerically investigated, where the diffracted vortex modes can be efficiently controlled by tuning the weak signal fields. Our studies not only exhibit a fundamental diffraction phenomenon with angular grating structures in EIT system, but also provide a fascinating opportunity to realize multidimensional quantum information processing for stored light in an all-optical manner.

Versatile, dynamically balanced low-noise optical-field manipulator using a coherently prepared atomic medium

We propose a versatile dynamic optical-field manipulator using a coherently prepared atomic medium. We show that by locking the pump power change with the two-photon detuning, a π-phase shifting can be realized with unit probe fidelity in a broad two-photon detuning range. The two-photon-insensitive π-phase-shift mode with significantly reduced fluctuation makes this scheme an attractive system for low-noise phase-gate operations.

Plasmon-Induced Transparency by Hybridizing Concentric-Twisted Double Split Ring Resonators

As a classical analogue of electromagnetically induced transparency, plasmon induced transparency (PIT) has attracted great attention by mitigating otherwise cumbersome experimental implementation constraints. Here, through theoretical design, simulation and experimental validation, we present a novel approach to achieve and control PIT by hybridizing two double split ring resonators (DSRRs) on flexible polyimide substrates. In the design, the large rings in the DSRRs are stationary and mirror images of each other, while the small SRRs rotate about their center axes. Counter-directional rotation (twisting) of the small SRRs is shown to lead to resonance shifts, while co-directional rotation results in splitting of the lower frequency resonance and emergence of a PIT window. We develop an equivalent circuit model and introduce a mutual inductance parameter M whose sign is shown to characterize the existence or absence of PIT response from the structure. This model attempts to provide a quantitative measure of the physical mechanisms underlying the observed PIT phenomenon. As such, our findings can support the design of several applications such as optical buffers, delay lines, and ultra-sensitive sensors.

Zero to π Continuously Controllable Cross Phase Modulation in Doppler Broadened N-Type Electromagnetically Induced Transparency Medium

We demonstrate an observation of zero to π continuously controllable cross-phase-modulation based on N-type electromagnetically induced transparency scheme in a room-temperature ⁸⁷Rb vapor. We theoretically and experimentally show that the signal field acquires a π phase shift compared with the reference light in the presence of the phase-control field. Using the method of the optical Mach-Zehnder interferometer, we demonstrate that a zero to π continuously controllable phase gate can be built by modulating the phase-control field. In addition, our theoretical calculation agrees well with the experimental observation, and the results presented in this work hold the potential applications for the orthogonal polarization/vector gate in the quantum information processing.

Impact of Substrate and Bright Resonances on Group Velocity in Metamaterial without Dark Resonator

Manipulating the speed of light has never been more exciting since electromagnetic induced transparency and its classical analogs led to slow light. Here, we report the manipulation of light group velocity in a terahertz metamaterial without needing a dark resonator, but utilizing instead two concentric split-ring bright resonators (meta-atoms) exhibiting a bright Fano resonance in close vicinity of a bright Lorentzian resonance to create a narrowband transmittance. Unlike earlier reports, the bright Fano resonance does not stem from an asymmetry of meta-atoms or an interaction between them. Additionally, we develop a method to determine the metamaterial “effective thickness”, which quantifies the influence of the substrate on the metamaterial response and has remained challenging to estimate so far. By doing so, very good agreement between simulated and measured group delays and velocities is accomplished. The proposed structure and method will be useful in designing optical buffers, delay lines, and ultra-sensitive sensors.

Large phase-by-phase modulations in atomic interfaces

Phase-resonant closed-loop optical transitions can be engineered to achieve broadly tunable light phase shifts. Such a novel phase-by-phase control mechanism does not require a cavity and is illustrated here for an atomic interface where a classical light pulse undergoes radian level phase modulations all-optically controllable over a few micron scale. It works even at low intensities and hence may be relevant to new applications of all-optical weak-light signal processing.

Nonlinear interaction between single photons

Harnessing nonlinearities strong enough to allow single photons to interact with one another is not only a fascinating challenge but also central to numerous advanced applications in quantum information science. Here we report the nonlinear interaction between two single photons. Each photon is generated in independent parametric down-conversion sources. They are subsequently combined in a nonlinear waveguide where they are converted into a single photon of higher energy by the process of sum-frequency generation. Our approach results in the direct generation of photon triplets. More generally, it highlights the potential for quantum nonlinear optics with integrated devices and, as the photons are at telecom wavelengths, it opens the way towards novel applications in quantum communication such as device-independent quantum key distribution.

Polarized linewidth-controllable double-trapping electromagnetically induced transparency spectra in a resonant plasmon nanocavity

Surface plasmons with ultrasmall optical mode volume and strong near field enhancement can be used to realize nanoscale light-matter interaction. Combining surface plasmons with the quantum system provides the possibility of nanoscale realization of important quantum optical phenomena, including the electromagnetically induced transparency (EIT), which has many applications in nonlinear quantum optics and quantum information processing. Here, using a custom-designed resonant plasmon nanocavity, we demonstrate polarized position-dependent linewidth-controllable EIT spectra at the nanoscale. We analytically obtain the double coherent population trapping conditions in a double-Λ quantum system with crossing damping, which give two transparent points in the EIT spectra. The linewidths of the three peaks are extremely sensitive to the level spacing of the excited states, the Rabi frequencies and detunings of pump fields, and the Purcell factors. In particular the linewidth of the central peak is exceptionally narrow. The hybrid system may have potential applications in ultra-compact plasmon-quantum devices.

All-optical image switching in a double-Λ system

The coherent control of optical images has garnered attention because all information embedded in optical images is expected to be controlled in a parallel way. One of the most important control processes is switch for information delivery. We experimentally demonstrated phase-controlled optical image switching in a double-Λ system where the transmission of the image through a medium was switched. Two independent laser sources were adopted for a double-Λ system such that images inscribed in two weak probe light beams were incoherent with each other. Arbitrary phase was added to the optical images to show that switching could be accomplished just with the relative phase difference between the probe pixels.

Fast, optically controlled Kerr phase shifter for digital signal processing

We demonstrate an optically controlled Kerr phase shifter using a room-temperature 85Rb vapor operating in a Raman gain scheme. Phase shifts from zero to π relative to an unshifted reference wave are observed, and gated operations are demonstrated. We further demonstrate the versatile digital manipulation of encoded signal light with an encoded phase-control light field using an unbalanced Mach-Zehnder interferometer. Generalizations of this scheme should be capable of full manipulation of a digitized signal field at high speed, opening the door to future applications.

Fast, all-optical, zero to π continuously controllable Kerr phase gate

We demonstrate a fast Kerr phase gate in a room-temperature (85)Rb vapor using a Raman gain method where the probe wave travels "superluminally". Continuously variable, zero to π radian nonlinear Kerr phase shifts of the probe wave relative to a reference wave have been observed at 333 K. We show rapid manipulation of digitally encoded probe waves using a digitally encoded phase-control light field, demonstrating the capability of the system in information science and telecommunication applications.

Breakdown of the cross-Kerr scheme for photon counting

We show, in the context of single-photon detection, that an atomic three-level model for a transmon in a transmission line does not support the predictions of the nonlinear polarizability model known as the cross-Kerr effect. We show that the induced displacement of a probe in the presence or absence of a single photon in the signal field, cannot be resolved above the quantum noise in the probe. This strongly suggests that cross-Kerr media are not suitable for photon counting or related single-photon applications. Our results are presented in the context of a transmon in a one-dimensional microwave waveguide, but the conclusions also apply to optical systems.

Manipulating stored images with phase imprinting at low light levels

Coherent manipulation of stored images is performed at low light levels based on enhanced cross-Kerr nonlinearity in a four-level N-type electromagnetically induced transparency (EIT) system. Using intensity masks in the signal pulse, quadratic phase shifts with low nonlinear absorption can be efficiently imprinted on the Fraunhofer diffraction patterns already stored in the EIT system. Fast-Fourier-transform-based numerical simulations clearly demonstrate that the far-field images of the retrieved probe light can be flexibly modulated by applying different signal fields. Our studies could help advance the goals of nonlinear all-optical processing for spatial information coherently stored in EIT systems.

EIT-based all-optical switching and cross-phase modulation under the influence of four-wave mixing

All-optical switching (AOS) or cross-phase modulation (XPM) based on the effect of electromagnetically induced transparency (EIT) makes one photon switched or phase-modulated by another possible. The existence of four-wave mixing (FWM) process greatly diminishes the switching or phase-modulation efficiency and hinders the single-photon operation. We proposed and experimentally demonstrated an idea that with an optimum detuning the EIT-based AOS can be completely intact even under the influence of FWM. The results of the work can be directly applied to the EIT-based XPM. Our work makes the AOS and XPM schemes more flexible and the single-photon operation possible in FWM-allowed systems.

Intensity-dependent effects on four-wave mixing based on electromagnetically induced transparency

We extend the study on a four-wave mixing (FWM) scheme of contiuous-wave lasers in a hot rubidium vapor when the probe and coupling fields work in the electromagnetically induced transparency (EIT) regime while the pump and signal fields work in the two-photon Raman regime. Our experimental results show that the generated signal field is well contained in an EIT dip of the incident probe field as a result of efficient FWM. We find, in particular, that an optimal FWM process can only be attained when the coupling and pump fields are well matched in intensity. If the probe intensity is far beyond the EIT condition, however, the nonlinear efficiency of energy transfer from the probe field to the signal field will be greatly reduced.

All-optical switching in an N-type foul-level atom-cavity system

We report an experimental observation of all-optical switching in an N-type atom-cavity system with a rubidium atomic vapor cell inside an optical ring cavity. Both absorptive and dispersive switching can be realized on dark- or bright-polariton peaks by a weak switching laser beam (with the extinction ratio better than 20:1). The switching mechanism can be explained as the combination of quantum interference and intracavity dispersion properties.

Dynamic generation of robust and controlled beating signals in an asymmetric procedure of light storage and retrieval

We propose an efficient scheme for the robust and controlled generation of beating signals in a sample of stationary atoms driven into the tripod configuration. This scheme relies on an asymmetric procedure of light storage and retrieval where the two classical coupling fields have equal detunings in the storage stage but opposite detunings in the retrieval stage. A quantum probe field, incident upon such an atomic sample, is first transformed into two spin coherence wave-packets and then retrieved with two optical components characterized by different time-dependent phases. Therefore the retrieved quantum probe field exhibits a series of maxima and minima (beating signals) in intensity due to the alternative constructive and destructive interference. This interesting phenomenon involves in fact the coherent manipulation of two dark-state polaritons and may be explored to achieve the fast quantum limited measurement.

Low-light-level cross-phase modulation with double slow light pulses

We report on the first experimental demonstration of low-light-level cross-phase modulation (XPM) with double slow light pulses based on the double electromagnetically induced transparency (EIT) in cold cesium atoms. The double EIT is implemented with two control fields and two weak fields that drive populations prepared in the two doubly spin-polarized states. Group velocity matching can be obtained by tuning the intensity of either of the control fields. The XPM is based on the asymmetric M-type five-level system formed by the two sets of EIT. Enhancement in the XPM by group velocity matching is observed. Our work advances studies of low-light-level nonlinear optics based on double slow light pulses.

Phase-controlled switching by interference between incoherent fields in a double-Λ system

We showed experimentally interference could be occurred between incoherent lights in a double-Λ lambda transition implemented with rubidium atomic vapor. Switching of probe transmission was controlled by the phases of two` independent probe lasers with low light intensity. More than 70% of the probe transmission could be switched by ultra-weak incoherent field. We suggested optically cryptic information could be delivered by the phase-controlled switching with incoherent fields in a double-Λ system.

Electromagnetically-induced phase grating: a coupled-wave theory analysis

We use a coupled-wave theory analysis to describe an atomic phase grating based on the giant Kerr nonlinearity of an atomic medium under electromagnetically induced transparency. An analytical expression is found for the diffraction efficiency of the grating. Efficiencies greater than 70% are predicted for incidence at the Bragg angle.

Electromagnetically induced transparency in cesium vapor with probe pulses on the single-photon level

We perform electromagnetically induced transparency (EIT) experiments in cesium vapor with pulses on the single-photon level for the first time. This was made possible by an extremely large total suppression of the EIT coupling beam by 118 dB mainly due to a newly developed triple-pass planar Fabry-Pérot etalon filter. Slowing and shaping of single-photon light pulses as well as the generation of pulses suitable for quantum key distribution applications and testing of approaches for single photon storage is demonstrated. Our results extend single-photon EIT to the particularly interesting wavelength of the Cs D1 line.

All-optical modulation of four-wave mixing in an Rb-filled photonic bandgap fiber

We demonstrate efficient all-optical modulation using Rb vapor confined to a hollow-core photonic bandgap fiber. The intensity of a signal field participating in the four-wave-mixing process is modulated using a weak switching field. We observe 3 dB of attenuation in the signal field with only 3600 photons of switching energy, corresponding to 23 photons per atomic cross section lambda(2)/(2pi). Modulation bandwidths as high as 300 MHz are observed.

Electromagnetically induced phase grating

I propose an electromagnetically induced phase grating based on the giant Kerr nonlinearity of an atomic medium under electromagnetically induced transparency. The atomic phase grating behaves similarly to an ideal sinusoidal phase grating, and it is capable of producing a pi phase excursion across a weak probe beam along with high transmissivity. The grating is created with arbitrarily weak fields, and diffraction efficiencies as high as 30% are predicted.

Large Kerr nonlinearities on cavity-atom polaritons

I analyze a scheme that is capable of producing large Kerr nonlinearities on cavity-atom polaritons in a cavity quantum electrodynamics system consisting of multiple three-level atoms confined in a cavity mode. A weak control laser coupled to the atoms from free space induces destructive quantum interference in the polariton excitation of the coupled cavity-atom system and creates large Kerr nonlinearities on the intra-cavity light field. The scheme can be used for optical switching or cross-phase modulation of the cavity-atom polariton at ultralow light levels.

Giant Kerr nonlinearities in circuit quantum electrodynamics

The very small size of optical nonlinearities places strict restrictions on the types of novel physics one can explore. This work describes how a single artificial multilevel Cooper pair box molecule, interacting with a superconducting microwave coplanar resonator, when suitably driven, can generate extremely large optical nonlinearities at microwave frequencies, with no associated absorption. We describe how the giant self-Kerr effect can be detected by measuring the second-order correlation function and quadrature squeezing spectrum.

Realization of an all-optical zero to pi cross-phase modulation jump

We report on the experimental demonstration of an all-optical pi cross-phase modulation jump. By performing a preselection, an optically induced unitary transformation, and then a postselection on the polarization degree of freedom, the phase of the output beam acquires either a zero or pi phase shift (with no other possible values). The postselection results in optical loss in the output beam. An input state may be chosen near the resulting phase singularity, yielding a pi phase shift even for weak interaction strengths. The scheme is experimentally demonstrated using a coherently prepared dark state in a warm atomic cesium vapor.

Coherent control of the effective susceptibility through wave mixing in a duplicated two-level system

We theoretically demonstrate the coherent control of the effective susceptibility of a duplicated two-level system. The control is obtained for a linearly polarized weak field in the presence of a much stronger orthogonally polarized field. For small optical depths, the effective susceptibility chi(eff) behaves as chilin(e 2iphi) (chilin) is the linear susceptibility, phi the phase shift) allowing coherent control of the optical response. For large optical depths, chi(eff) approximately chi(lin), turning an absorber into an amplifier without affecting the dispersion.

Refractive index enhancement with vanishing absorption in an atomic vapor

We report a proof-of-principle experiment where the refractive index of an atomic vapor is enhanced while maintaining vanishing absorption of the beam. The key idea is to drive alkali atoms in a vapor with appropriate control lasers and induce a gain resonance and an absorption resonance for a probe beam in a two-photon Raman configuration. The strength and the position of these two resonances can be manipulated by changing the parameters of the control lasers. By using the interference between these two resonances, we obtain an enhanced refractive index without an increase in the absorption.

Electromagnetically induced transparency on GaAs quantum well to observe hole spin dephasing

Electromagnetically induced transparency (EIT) was observed with transient optical response of exciton correlation in GaAs/AlGaAs quantum well structure. Decoherence of EIT was increased with temperature (12-60 K), which could be simulated by increasing non-radiation decay rate between coherently coupled ground states in Bloch equation for Lambda type three level. The non-radiation decay was mainly due to hole spin dephasing in the system for EIT via coulomb correlation. The hole spin dephasing rate was found with increasing lattice temperature and well accorded to the past results of time resolving method with n-doping material.

Enhanced cross-phase modulation based on a double electromagnetically induced transparency in a four-level tripod atomic system

We report experimental observations on the simultaneous electromagnetically induced transparency (EIT) effects for probe and trigger fields (double EIT) as well as the enhanced cross-phase modulation (XPM) between the two fields in a four-level tripod EIT system of the D1 line of 87Rb atoms. The XPM coefficients (larger than 2 x 10(-5) cm2/W) and the accompanying transmissions (higher than 60%) are measured at a slight detuning of the probe field from the exact EIT-resonance condition. The system and enhanced cross-Kerr nonlinearities presented here can be applied to quantum information processes.

Bootstrapping approach for generating maximally path-entangled photon states

We propose a bootstrapping approach to the generation of maximally path-entangled states of photons, so-called "NOON states." The strong atom-light interaction of cavity QED can be employed to generate NOON states with about 100 photons. These can then be used to boost the existing experimental Kerr nonlinearities based on quantum coherence effects, to facilitate NOON generation with an arbitrarily large number of photons. We also offer an alternative scheme that uses an atom-cavity dispersive interaction to obtain a sufficiently high Kerr nonlinearity necessary for arbitrary NOON generation.

Stable high-dimensional spatial weak-light solitons in a resonant three-state atomic system

We study the formation of a nonlinear localized high-dimensional optical beam in a lifetime-broadened three-state atomic system. We show that stable high-dimensional spatial optical solitons with extremely weak-light intensity can occur in such a highly resonant medium through a mechanism of electromagnetically induced transparency. We demonstrate that the interaction between two high-dimensional spatial optical solitons displays interesting properties and these solitons can be easily controlled by manipulating the coupling optical field of the system.

Large cross-phase modulation between slow copropagating weak pulses in 87Rb

We propose a scheme to generate double electromagnetically induced transparency and optimal cross-phase modulation for two slow, copropagating pulses with matched group velocities in a single species of atom, namely 87Rb. A single pump laser is employed and a homogeneous magnetic field is utilized to avoid cancellation effects through the nonlinear Zeeman effect. We suggest a feasible preparational procedure for the atomic initial state to achieve matched group velocities for both signal fields.