Observation of coherent optical information storage in an atomic medium using halted light pulses

Optical control of the refractive index of a single atom

We experimentally demonstrate the elementary case of electromagnetically induced transparency with a single atom inside an optical cavity probed by a weak field. We observe the modification of the dispersive and absorptive properties of the atom by changing the frequency of a control light field. Moreover, a strong cooling effect has been observed at two-photon resonance, increasing the storage time of our atoms twenty-fold to about 16 seconds. Our result points towards all-optical switching with single photons.

Tunable optical time delay of quantum signals using a prism pair

We describe a compact, tunable, optical time-delay module that functions by means of total internal reflection within two glass prisms. The delay is controlled by small mechanical motions of the prisms. The device is inherently extremely broad band, unlike time delay modules based on "slow light" methods. In the prototype device that we fabricated, we obtain time delays as large as 1.45 ns in a device of linear dimensions of the order of 3.6 cm. We have delayed pulses with a full width at half-maximum pulse duration of 25 fs, implying a delay bandwidth product (measured in delay time divided by the FWHM pulse width) of 5.8 x 10(4). We also show that the dispersion properties of this device are sufficiently small that quantum features of a light pulse are preserved upon delay.

Femtowatt-light-level phase measurement of slow light pulses via beat-note interferometer

We report on an experimental demonstration of applying the beat-note interferometer to simultaneously measure the phase and amplitude variations of light pulses after propagating through an electromagnetically induced transparency medium at femtowatt-light levels. Furthermore, we observe that the measured phase noise approaches the shot-noise level arising from the fluctuations of detected photons.

Electromagnetically induced transparency in metamaterials at near-infrared frequency

We employ a planar metamaterial structure composed of a split-ring-resonator (SRR) and paired nano-rods to experimentally realize a spectral response at near-infrared frequencies resembling that of electromagnetically induced transparency. A narrow transparency window associated with low loss is produced, and the magnetic field enhancement at the center of the SRR is dramatically changed, due to the interference between the resonances with significantly different linewidths. The variation of the spectral response in terms of relative position of the bright and dark elements is evaluated with numerical simulations.

Frequency downconversion for a quantum network

By using a parametric downconversion process with a strong signal field injection, we demonstrate coherent frequency downconversion from a pump photon to an idler photon. Contrary to a common misunderstanding, we show that the process can be free of quantum noise. With an interference experiment, we demonstrate that the coherence is preserved in the conversion process. This may lead to a high-fidelity quantum state transfer from a high-frequency photon to a low-frequency photon and connects a missing link in a quantum network. With this scheme of coherent frequency downconversion of photons, we propose a method of single-photon WDM.

Acoustic analog of electromagnetically induced transparency in periodic arrays of square rods

We theoretically demonstrate a classical analog of electromagnetically induced transparency (EIT) in an acoustic structure. Each unit in the proposed structure consists of two square polymethyl methacrylate (PMMA) rods with one rod rotating 45° relative to the other. Both square rods can support certain surface resonant modes respectively, which have almost identical resonant frequencies but highly different quality factors. Thus, the two resonant modes can act as radiative mode and dark mode in the analog, respectively, and the destructive interference of them results in EIT-like transmission effect in our structure.

Advanced and delayed images through an image resonator

We performed optical image propagation experiments in an image resonator consisting of a Fabry-Perot resonator in reflection geometry. Two-dimensional images encoded on optical pulses of 32ns were stored, and either advanced, -6.0ns, or delayed, 10.9ns, using the dispersion relation relevant to the image resonator, in the under- or over- coupling condition, respectively. The overall images are propagated through the resonator clearly, while the diffraction effects were analyzed both in real-space and in k-space.

Double photonic bandgaps dynamically induced in a tripod system of cold atoms

A tripod atomic system driven by two standing-wave fields (a coupling and a driving) is explored to generate tunable double photonic bandgaps in the regime of electromagnetically induced transparency. Both photonic bandgaps depend critically on frequency detunings, spatial periodicities, and initial phases of the two standing-wave fields. When the coupling and driving detunings are very close, a small fluctuation of one standing-wave field may demolish both photonic bandgaps. If the two detunings are greatly different, however, each standing-wave field determines only one photonic bandgap in a less sensitive way. Dynamic generation and elimination of a pair of photonic bandgaps shown here may be exploited toward the end of simultaneous manipulation of two weak light signals even at the single-photon level.

Controllable optical black hole in left-handed materials

Halting and storing light by infinitely decelerating its speed, in the absence of any form of external control, is extremely di+/-cult to imagine. Here we present a theoretical prediction of a controllable optical black hole composed of a planar left-handed material slab. We reveal a criterion that the effective round-trip propagation length in one zigzag path is zero, which brings light to a complete standstill. Both theory and ab initio simulation demonstrate that this optical black hole has degrees flexible controllability for the speed of light. Surprisingly, the ab initio simulations reveal that our scheme has degrees flexible controllability for swallowing, holding, and releasing light.

Band splitting and modal dispersion induced by symmetry braking in coupled-resonator slowlight waveguide structures

We study the dispersion relations in slow-light waveguide structures consisting of coupled microdisk resonators. A group theoretical analysis of the symmetry properties of the propagating modes reveals a fundamental phenomenon: The degeneracy of the CW and CCW rotating modes is removed, giving rise to two distinct transmission bands. This effect induces symmetry-based dispersion which may limit the usable bandwidth of such structures. The properties of this band splitting and its impact on CROW performance for optical communications are studied in detail.

Broadband frequency conversion and shaping of single photons emitted from a nonlinear cavity

Much recent effort has focused on coupling individual quantum emitters to optical microcavities in order to produce single photons on demand, enable single-photon optical switching, and implement functional nodes of a quantum network. Techniques to control the bandwidth and frequency of the outgoing single photons are of practical importance, allowing direct emission into telecommunications wavelengths and "hybrid" quantum networks incorporating different emitters. Here, we describe an integrated approach involving a quantum emitter coupled to a nonlinear optical resonator, in which the emission wavelength and pulse shape are controlled using the intra-cavity nonlinearity. Our scheme is general in nature, and demonstrates how the photonic environment of a quantum emitter can be tailored to determine the emission properties. As specific examples, we discuss a high Q-factor, TE-TM double-mode photonic crystal cavity design that allows for direct generation of single photons at telecom wavelengths (1425 nm) starting from an InAs/GaAs quantum dot with a 950 nm transition wavelength, and a scheme for direct optical coupling between such a quantum dot and a diamond nitrogen-vacancy center at 637 nm.

Creation of long-term coherent optical memory via controlled nonlinear interactions in Bose-Einstein condensates

A Bose-Einstein condensate confined in an optical dipole trap is used to generate long-term coherent memory for light, and storage times of more than 1 s are observed. Phase coherence of the condensate as well as controlled manipulations of elastic and inelastic atomic scattering processes are utilized to increase the storage fidelity by several orders of magnitude over previous schemes. The results have important applications for creation of long-distance quantum networks and for generation of entangled states of light and matter.

Observation of electromagnetically induced transparency and slow light in the dark state--bright state basis

The quantum coherence phenomenon of electromagnetically induced transparency (EIT) is observed in a three-level system composed of an excited state and two coherent superpositions of the two ground-state levels. This peculiar ground state basis is composed of the so-called bright and dark states of the same atomic system in a standard coherent population trapping configuration. The characteristics of EIT, namely, width of the transmission window and reduced group velocity of light, in this unusual basis, are theoretically and experimentally investigated and are shown to be essentially identical to those of standard EIT in the same system.

Highly selective terahertz bandpass filters based on trapped mode excitation

We present two types of metamaterial-based spectral bandpass filters for the terahertz (THz) frequency range. The metamaterials are specifically designed to operate for waves at normal incidence and to be independent of the field polarization. The functional structures are embedded in films of benzocyclobutene (BCB) resulting in large-area, free-standing and flexible membranes with low intrinsic loss. The proposed filters are investigated by THz time-domain spectroscopy and show a pronounced transmission peak with over 80% amplitude transmission in the passband and a transmission rejection down to the noise level in the stopbands. The measurements are supported by numerical simulations which evidence that the high transmission response is related to the excitation of trapped modes.

Active chromatic control on the group velocity of light at arbitrary wavelength in benzocyclobutene polymer

A novel method is proposed to generate slow and fast lights at arbitrary signal wavelength in benzocyclobutene (BCB) polymer, which eliminates the requirement on the optical nonlinearity or the resonant effect at the signal wavelength with the help of the thermo-optic nonlinear effect induced by a control beam at a different but fixed wavelength. The signal group velocity can be precisely tuned simply by scanning the position of the BCB sample along the light propagation direction. Another advantage is the ability to control chromatically the group velocity of the signal beam by adjusting the control beam in the BCB sample, which, in essence, is to control the refractive index change experienced by the signal beam. This method provides an active chromatic control on the group velocity of light at arbitrary signal wavelength and therefore may have important potential applications in optical communication network and optical information processing.

All-optical light confinement in dynamic cavities in cold atoms

We show how to realize in a cold atomic sample a dynamic magneto-optically controlled cavity in which a slow-light pulse can be confined and released on demand. The probe optical pulse is retrieved from the atomic spin coherence initially stored within the cavity and is subsequently confined there subject to a slow-light regime with little loss and diffusion for time intervals as long as a few hundred microseconds before being extracted from either side of the cavity. Our proof-of-principle scheme illustrates the underlying physics of this new mechanism for coherent light confinement and manipulation in cold atoms. This may ease the realization of nonlinear interactions between weak light pulses where strong atom-photon interactions are required for quantum information processing.

Slowing and storage of double light pulses in a Pr3+:Y2SiO5 crystal

We experimentally demonstrate the slowing and storage of double light pulses in a Pr(3+):Y(2)SiO(5) crystal using a multilevel-tripod scheme. Owing to double dark-state polaritons of the tripod-type system, two signal pulses can be simultaneously slowed. Also, we realize the simultaneous storage (and retrieval) of double light pulses by switching off (and back on) the control field. Slowing and storage of double light pulses in solids may have practical applications in quantum information and quantum networks.

Plasmonic analogue of electromagnetically induced transparency at the Drude damping limit

In atomic physics, the coherent coupling of a broad and a narrow resonance leads to quantum interference and provides the general recipe for electromagnetically induced transparency (EIT). A sharp resonance of nearly perfect transmission can arise within a broad absorption profile. These features show remarkable potential for slow light, novel sensors and low-loss metamaterials. In nanophotonics, plasmonic structures enable large field strengths within small mode volumes. Therefore, combining EIT with nanoplasmonics would pave the way towards ultracompact sensors with extremely high sensitivity. Here, we experimentally demonstrate a nanoplasmonic analogue of EIT using a stacked optical metamaterial. A dipole antenna with a large radiatively broadened linewidth is coupled to an underlying quadrupole antenna, of which the narrow linewidth is solely limited by the fundamental non-radiative Drude damping. In accordance with EIT theory, we achieve a very narrow transparency window with high modulation depth owing to nearly complete suppression of radiative losses.

Frequency matching in light-storage spectroscopy of atomic Raman transitions

We investigate the storage of light in an atomic sample with a Lambda-type coupling scheme driven by optical fields at variable two-photon detuning. In the presence of electromagnetically induced transparency (EIT), light is stored and retrieved from the sample by dynamically varying the group velocity. It is found that for any two-photon detuning of the input light pulse within the EIT transparency window, the carrier frequency of the retrieved light pulse matches the two-photon resonance frequency with the atomic ground state transition and the control field. This effect which is not based on spectral filtering is investigated both theoretically and experimentally. It can be used for high-speed precision measurements of the two-photon resonance as employed, e.g., in optical magnetometry.

Plasmonic-dielectric systems for high-order dispersionless slow or stopped subwavelength light

A material platform of multilayered surface-plasmon-dielectric-polariton systems is introduced, along with a new physical mechanism enabling simultaneous cancellation of group-velocity and attenuation dispersion to extremely high orders for subwavelength light of any small positive, negative, or zero group velocity. These dispersion-free systems could have significant impact on the development of nanophotonics, e.g., in the design of efficient and very compact delay lines and active devices. The same dispersion-manipulation mechanism can be employed to tailor at will exotic slow-light dispersion relations.

Electromagnetically induced transparency and light storage in an atomic Mott insulator

We experimentally demonstrate electromagnetically induced transparency and light storage with ultracold 87Rb atoms in a Mott insulating state in a three-dimensional optical lattice. We have observed light storage times of approximately 240 ms, to our knowledge the longest ever achieved in ultracold atomic samples. Using the differential light shift caused by a spatially inhomogeneous far detuned light field we imprint a "phase gradient" across the atomic sample, resulting in controlled angular redirection of the retrieved light pulse.

Grating induced transparency (GIT) and the dark mode in optical waveguides

We propose and describe a new class of optical modes consisting of superposition of three waveguide modes which can be supported by a few-mode waveguide spatially modulated by two co-spatial gratings. These supermodes bear a close, but not exact, formal analogy to the three-level quantum states involved in EIT and its attendant slow light propagation characteristics. Of particular interest is the supermode which we call the dark mode in which, in analogy with the dark state of EIT, one of the three uncoupled waveguide modes is not excited. This mode has unique dispersion characteristics that translate into a slow light propagation which possesses high bandwidth-delay product and can form the basis for a new generation of optical resonators and lasers.

Three-channel all-optical routing in a Pr3+:Y2SiO5 crystal

We experimentally demonstrate a three-channel all-optical routing based on light storage in a Pr(3+):Y(2)SiO(5) crystal. By switching off the control field under the condition of electromagnetically induced transparency, the optical information of the probe light pulse can be stored in the crystal. When three retrieve control fields are switched on in the release process, the stored optical information from one light channel can be transferred (or distributed) into three different light channels. Also we show that this all-optical routing can be time-delayed. Such a multichannel all-optical routing in solids may have practical applications in quantum information and all-optical network.

Narrowband tunable filter based on velocity-selective optical pumping in an atomic vapor

We demonstrate a tunable narrowband filter based on optical-pumping-induced circular dichroism in rubidium vapor. The filter achieves a peak transmission of 14.6%, a linewidth of 80 MHz, and an out-of-band extinction of >or=35 dB. The transmission peak can be tuned within the range of the Doppler linewidth of the D1 line of atomic rubidium at 795 nm. While other atomic filters work at frequencies far from absorption, the presented technique provides light resonant with atomic media, useful for atom-photon interaction experiments. The technique could readily be extended to other alkali atoms.

Low-loss metamaterials based on classical electromagnetically induced transparency

We demonstrate theoretically that electromagnetically induced transparency can be achieved in metamaterials, in which electromagnetic radiation is interacting resonantly with mesoscopic oscillators rather than with atoms. We describe novel metamaterial designs that can support a full dark resonant state upon interaction with an electromagnetic beam and we present results of its frequency-dependent effective permeability and permittivity. These results, showing a transparency window with extremely low absorption and strong dispersion, are confirmed by accurate simulations of the electromagnetic field propagation in the metamaterial.

Detuned slow light in the Doppler broadened multi-level D2 line of Rubidium

We observed a detuned slow light phenomenon based on electromagnetically induced transparency in (87)Rb D2 line composed of multiple excited-hyperfine states within a Doppler-broadened linewidth. The results show that the maximum group delay of a probe occurs at off-detuned two-photon resonance frequency. The observed detuned group delay is analyzed with numerical calculations for a probe pulse interacting with the neighboring excited-states-modified Doppler broadening atoms for a fixed coupling field. The experimental results are in good agreement with the numerical calculations.

Slow and fast light in optical fibers using acoustooptic coupling between two co-propagating modes

We demonstrate numerically that acoustooptic interaction between two co-propagating modes in an optical fiber can be utilized to obtain optical delays. Both positive and negative delays of several pulse lengths can be obtained. Based on the simulations we consider relevant experimental parameters.

Coherent control of low loss surface polaritons

We propose fast all-optical control of surface polaritons by placing an electromagnetically induced transparency (EIT) medium at an interface between two materials. EIT provides longitudinal compression and a slow group velocity, while matching properties of the two materials at the interface provides strong transverse confinement. In particular, we show that an EIT medium near the interface between a dielectric and a negative-index metamaterial can establish tight longitudinal and transverse confinement plus extreme slowing of surface polaritons, in both transverse electric and transverse magnetic polarizations, while simultaneously avoiding losses.

Metamaterial analog of electromagnetically induced transparency

We demonstrate a classical analog of electromagnetically induced transparency in a planar metamaterial. We show that pulses propagating through such metamaterials experience considerable delay. The thickness of the structure along the direction of wave propagation is much smaller than the wavelength, which allows successive stacking of multiple metamaterial slabs leading to increased transmission and bandwidth.

Resonance beating of light stored using atomic spinor polaritons

We investigate the storage of light in atomic rubidium vapor using a multilevel-tripod scheme. In the system, two collective dark polariton modes exist, forming an effective spinor quasiparticle. Storage of light is performed by dynamically reducing the optical group velocity to zero. After releasing the stored pulse, a beating of the two reaccelerated optical modes is monitored. The observed beating signal oscillates at an atomic transition frequency, opening the way to novel quantum limited measurements of atomic resonance frequencies and quantum switches.

Bose-Einstein condensation of stationary-light polaritons

We propose and analyze a mechanism for Bose-Einstein condensation of stationary dark-state polaritons. Dark-state polaritons (DSPs) are formed in the interaction of light with laser-driven 3-level Lambda-type atoms and are the basis of phenomena such as electromagnetically induced transparency, ultraslow, and stored light. They have long intrinsic lifetimes and in a stationary setup, a 3D quadratic dispersion profile with variable effective mass. Since DSPs are bosons, they can undergo a Bose-Einstein condensation at a critical temperature which can be many orders of magnitude larger than that of atoms. We show that thermalization of polaritons can occur via elastic collisions mediated by a resonantly enhanced optical Kerr nonlinearity on a time scale short compared to the decay time. Finally, condensation can be observed by turning stationary into propagating polaritons and monitoring the emitted light.

Photon echoes generated by reversing magnetic field gradients in a rubidium vapor

We propose a photon echo quantum memory scheme using detuned Raman coupling to long-lived ground states. In contrast to previous three-level schemes based on controlled reversible inhomogeneous broadening that use sequences of pi pulses, the scheme does not require accurate control of the coupling dynamics to the ground states. We present a proof-of-principle experimental realization of our proposal using rubidium atoms in a warm vapor cell. The Raman resonance line is broadened using a magnetic field that varies linearly along the direction of light propagation. Inverting the magnetic field gradient rephases the atomic dipoles and re-emits the light pulse in the forward direction.

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.

Reversible quantum interface for tunable single-sideband modulation

Using electromagnetically induced transparency in a cesium vapor, we demonstrate experimentally that the quantum state of a light beam can be mapped into the long-lived Zeeman coherences of an atomic ground state. Two noncommuting variables carried by light are simultaneously stored and subsequently read out, with no noise added. We compare the case where a tunable single sideband is stored independently of the other one to the case where the two symmetrical sidebands are stored using the same electromagnetically induced transparency window.

Electromagnetically induced Bragg reflection with a stationary coupling field in a buffer rubidium vapor cell

An electromagnetically induced Bragg reflection with a stationary coupling field in an Rb vapor cell with a 6.67 kPa neon buffer gas was studied. When the coupling field was spatially modulated as a stationary wave, a transmission reduction of the probe field was observed, while simultaneously a reflected probe field was detected in the backward direction. Instead of absorbing a fraction of the probe laser in the Rb vapor, the modulated electromagnetically induced transparency medium reflected it, corresponding to a Bragg reflection. The spectrum in the 5S(1/2)-5P(1/2)Lambda-type system of (87)Rb atoms was investigated as a function of the coupling laser frequency detuning, the stationary coupling laser power, the vapor cell temperature, and the coupling laser power ratio.

Fidelity criterion for quantum-domain transmission and storage of coherent states beyond the unit-gain constraint

We generalize the experimental success criterion for quantum teleportation (memory) in continuous-variable quantum systems to be suitable for a non-unit-gain condition by considering attenuation (amplification) of the coherent-state amplitude. The new criterion can be used for a nonideal quantum memory and long distance quantum communication as well as quantum devices with amplification process. It is also shown that the framework to measure the average fidelity is capable of detecting all Gaussian channels in the quantum domain.

An efficient method of all-optical buffering with ultra-small core photonic crystal fibers

We propose a new method of all-optical buffering with ultra-small core photonic crystal fibers (PCFs) based on stimulated Brillouin scattering. The large refractive index contrast between the near-hollow cladding and the pure-silica core contributes to high nonlinearity of the PCF. Considering the unusual gain spectrum of the ultra-small core PCF, we numerically investigate the influence of these factors to the buffering efficiency. A PCF with a length of 1 meter and a core diameter of 1.06 micrometer is simulated as the storage medium in this paper. It is shown that we can obtain a good buffering efficiency under a very low control power of 2 watt, which promises a significant improvement for the all-optical communication system.

Reversible quantum optical data storage based on resonant Raman optical field excited spin coherence

A method of reversible quantum optical data storage is presented using resonant Raman field excited spin coherence, where the spin coherence is stored in an inhomogeneously broadened spin ensemble. Unlike the photon echo method, in the present technique, a 2pi Raman optical rephasing pulse area is used and multimode (parallel) optical channels are available in which the multimode access gives a great benefit to quantum information processors such as quantum repeaters.

Electromagnetically induced transparency-like effect in the degenerate triple-resonant optical parametric amplifier

We investigate experimentally the absorptive and dispersive properties of the triple-resonant optical parametric amplifier (OPA) for the degenerate subharmonic field. In the experiment the subharmonic field is utilized as the probe field and the harmonic wave as the pump field. We demonstrate that the electromagnetically induced transparency (EIT)-like effect can be simulated in the triple-resonant OPA when the cavity linewidth for the harmonic wave is narrower than that for the subharmonic field. However, this phenomenon cannot be observed in a double-resonant OPA. The narrow transparency window appears in the reflected field. Especially in the measured dispersive spectra of the triple-resonant OPA, a very steep variation of the dispersive profile of the subharmonic field is observed, which can result in a slow light as that observed in an atomic EIT medium.

Double resonance optical pumping effects in electromagnetically induced transparency

We present the double resonance optical pumping (DROP) effect of ladder-type electromagnetically induced transparency (EIT) in the 5S1/2-5P3/2-5D5/2 transition of 87Rb atoms. When many atoms of the ladder-type atomic system are simultaneously resonant with the two laser fields, the population of one ground state can be optically pumped into another ground state through intermediate states and excited states. In this paper, we reveal that most previous results for the ladder-type EIT include the DROP effect. When the probe laser is very weak and the coupling laser is strong, we can observe the double structure transmittance spectrum, a narrow spectrum due to the EIT and a broad spectrum due to the DROP, in the 5S1/2(F=2)-5P3/2(F'=3)-5D5/2(F"=4) cycling transition.

The quantum internet

Quantum networks provide opportunities and challenges across a range of intellectual and technical frontiers, including quantum computation, communication and metrology. The realization of quantum networks composed of many nodes and channels requires new scientific capabilities for generating and characterizing quantum coherence and entanglement. Fundamental to this endeavour are quantum interconnects, which convert quantum states from one physical system to those of another in a reversible manner. Such quantum connectivity in networks can be achieved by the optical interactions of single photons and atoms, allowing the distribution of entanglement across the network and the teleportation of quantum states between nodes.

Holographic quantum computing

We propose to use a single mesoscopic ensemble of trapped polar molecules for quantum computing. A "holographic quantum register" with hundreds of qubits is encoded in collective excitations with definite spatial phase variations. Each phase pattern is uniquely addressed by optical Raman processes with classical optical fields, while one- and two-qubit gates and qubit readout are accomplished by transferring the qubit states to a stripline microwave cavity field and a Cooper pair box where controllable two-level unitary dynamics and detection is governed by classical microwave fields.

Plasmon-induced transparency in metamaterials

A plasmonic "molecule" consisting of a radiative element coupled with a subradiant (dark) element is theoretically investigated. The plasmonic molecule shows electromagnetic response that closely resembles the electromagnetically induced transparency in an atomic system. Because of its subwavelength dimension, this electromagnetically induced transparency-like molecule can be used as a building block to construct a "slow light" plasmonic metamaterial.

Ultrawide-bandwidth slow-light system based on THz plasmonic graded metallic grating structures

We explore a novel mechanism for slowing down THz waves based on metallic grating structures with graded depths, whose dispersion curves and cutoff frequencies are different at different locations. Since the group velocity of spoof surface plasmons at the cutoff frequency is extremely low, THz waves are actually stopped at different positions for different frequencies. The separation between stopped waves can be tuned by changing the grade of the grating depths. This structure offers the advantage of reducing the speed of the light over an ultrawide spectral band, and the ability to operate at various temperatures, but demands a stringent requirement for the temperature stability.

Storing images in warm atomic vapor

Reversible and coherent storage of light in an atomic medium is a promising method with possible applications in many fields. In this work, arbitrary two-dimensional images are slowed and stored in warm atomic vapor for up to 30 micros, utilizing electromagnetically induced transparency. Both the intensity and the phase patterns of the optical field are maintained. The main limitation on the storage resolution and duration is found to be the diffusion of atoms. A technique analogous to phase-shift lithography is employed to diminish the effect of diffusion on the visibility of the reconstructed image.

Enhanced light trapping based on guided mode resonance effect for thin-film silicon solar cells with two filling-factor gratings

An approach of enhanced light-trapping in a thin-film silicon solar cell by adding a two-filling-factor asymmetric binary grating on it is proposed for the wavelength of near-infrared. Such a grating-on-thin-film structure forms a guided-mode resonance notch filter to couple energy diffracted from an incident wave to a leakage mode of the guided layer in the solar cell. The resonance wave coupled between two-filling-factor gratings would laterally extend the optical power and induce multiple bounces within the active layer. The resonance effect traps light in the cell enhancing its absorption probability. A dynamic light-trapping behaviour in solar cells is observed. A photon dwelling time is proposed for the first time to quantify the light-trapping effect. Moreover, the light absorption probability is also quantified. As compared the grating-on-thin-film structure with the one of planar silicon thin film, simulation results reveal that it is 3-fold enhancement in the light absorption within a spectral range of 920-1040 nm. Moreover, such an enhancement can be maintained even the incident angle of near-IR broadband light wave varies up to +/-40 degrees.

Delay of squeezing and entanglement using electromagnetically induced transparency in a vapour cell

We demonstrate experimentally the delay of squeezed light and entanglement using Electromagnetically Induced Transparency (EIT) in a rubidium vapour cell. We perform quadrature amplitude measurements of the probe field and find no appreciable excess noise from the EIT process. From input squeezing of 3.2+/-0.5 dB at low sideband frequencies, we observed the survival of 2.0+/-0.5 dB of squeezing at the EIT output. By splitting the squeezed light on a beam-splitter, we generated biased entanglement between two beams. We transmit one of the entangled beams through the EIT cell and correlate the quantum statistics of this beam with its entangled counterpart. We experimentally observed a 2.2+/-0.5 micros delay of the biased entanglement and obtained a preserved degree of wavefunction inseparability of 0.71+/-0.01, below the unity value for separable states.

Storage and retrieval of multimode transverse images in hot atomic Rubidium vapor

We report on the experimental realization of the storage of images in a hot vapor of Rubidium atoms. The images are stored in and retrieved from the long-lived ground state atomic coherences. We show that an image impressed onto a 500 ns pulse can be stored and retrieved up to 30 mus later. The image storage is made robust to diffusion by storing the Fourier transform of the image.