The frequency domain susceptibility of all materials results from the collective response of absorptive resonances. The concomitant dispersive response follows according to the Kramers-Kronig relations for causal transfer functions. For an inhomogeneously broadened spectrum that comprises a collection of frequency-shifted homogeneously broadened absorption lines, analysis of the response is in principle straightforward and repetitive. The prospect that these regular resonant features might serve as a mathematical basis for constructing an arbitrary spectral susceptibility suggests the use of their mathematical lineshape as a mother wavelet in a wavelet basis.

The fabrication of spectral storage materials presents a great challenge of tailoring the optical properties of a solid at the atomic scale. We show that by a careful choice of a host material and the luminescent rare earth centers created in it, thin film structures can be fabricated using pulsed laser deposition. It is shown that these structures can be tailored to satisfy the material requirements for the power-gated spectral holeburning, one of the most successful techniques for the spectral storage. In the form of multilayer thin film structures, these tailored materials can provide surface storage densities exceeding a terabit per square inch. Possibilities of tailoring new rare earth centers that can further multiply the storage densities have been discussed. Experimental data has been presented for the fabrication and characterization of such impurity based europium centers in MgS and CaS by chemically controlled pulsed laser deposition.

In this paper, we present a new photonic technique for producing large time delay of radio-frequency (RF) modulated optical signals and its application in a novel true-time-delay (TTD) multiple beam-forming system for wideband RF phased-array antennas using Fourier optics. The RF signal to be delayed is modulated onto a broadband optical carrier in a frequency-mapped manner by an acousto-optic tunable filter (AOTF). Due to the phased-matched acousto-optic interaction and the moving nature of the acoustic waves in the AOTF, di.erent frequency components of the optical carrier are only modulated and Doppler-shifted by the corresponding frequencies of the modulating RF signal. Heterodyne detection between the modulated optical beam and a timealigned reference beam from the same light source can recover the modulating RF signal. When a small optical path length di.erence is introduced between the heterodyne beams, a large RF time delay magnified by the frequency ratio between the optics and the RF will be generated, which we refer to as the sluggish-light effect. Sluggish light has potential applications in TTD beam forming for wideband RF phased-array antennas and proof-of-concept experiments of the sluggish-light based TTD beam forming for an emulated 2- and 4-channel RF array will be presented in this paper.

Recent progress toward the development of scalable quantum computers based on nitrogen-vacancy (NV) color centers in diamond will be described. Scaling is accomplished through the long-range entanglement of few-qubit processing nodes using photons. Local operations within each processing node will be accomplished using electronically switchable dipole-dipole interactions. Significant progress has been made in the control of the optical transitions, enabling us to reach the level required to attempt long-range entanglement. In the meantime, long-term storage and two-qubit operations have been demonstrated using magnetic dipole-dipole coupling to proximal spins that are not nearest neighbors. Significantly, all the processing node demonstration were been done at room temperature where spin lifetimes were found to be exceptionally long.

Nitrogen-vacancy centers in diamond typically have spin-conserving optical transitions, a feature which allows for optical detection of the long-lived electronic spin states through fluorescence detection. However, by applying stress to a sample it is possible to obtain spin-nonconserving transitions in which a single excited state couples to multiple ground states. Here we describe two-frequency optical spectroscopy on single nitrogen-vacancy centers in a high-purity diamond sample at low temperature. When stress is applied to the sample it is possible to observe coherent population trapping with a single center. By adjusting the stress it is possible to obtain a situation in which all of the transitions from the three ground sublevels to a common excited state are strongly allowed. These results show that all-optical spin manipulation is possible for this system, and we propose that that by coupling single centers to optical microcavities, a scalable quantum network could be realized for photonic quantum information processing.

In the past europium doped materials have been tailored in our group, which could exhibit the highest spectral storage densities known to date. In these materials, europium exists in both doubly and triply ionized states. Therefore, it is necessary to control the relative concentration of Eu²⁺ and Eu³⁺. Due to accidental overlap of Eu²⁺ and Eu³⁺ optical transitions in this medium optical spectroscopy cannot be used to determine their relative concentration. For highly enriched europium samples, such a ratio can be determined by Mössbauer spectroscopy. However, at very low concentrations of the order of 0.01% of Eu in MgS that are necessary for these materials, conventional Mössbauer spectroscopy requires prohibitively long data acquisition times. In this article, we present and compare the ways of solving this problem with conventional and the time domain Mössbauer spectroscopy using Nuclear Forward Scattering. The synchrotron of the Advanced Photon Source at Argonne National Laboratory has been used as the source of high intensity, coherent and monochromatic gamma rays in NFS experiments. It is shown that in time domain Mössbauer spectroscopy the data acquisition times can be reduced by two orders of magnitude or more. This is of paramount importance for Mössbauer spectroscopy of very small samples or the samples with very low concentrations of the active isotope.

We developed techniques to design higher efficiency diffractive optical elements (DOEs) with large numerical apertures (NA) for quantum computing and quantum information processing. Large NA optics encompass large solid angles and thus have high collection efficiencies. Qubits in ion trap architectures are commonly addressed and read by lasers¹. Large-scale ion-trap quantum computing² will therefore require highly parallel optical interconnects. Qubit readout in these systems requires detecting fluorescence from the nearly isotropic radiation pattern of single ions, so efficient readout requires optical interconnects with high numerical aperture. Diffractive optical element fabrication is relatively mature and utilizes lithography to produce arrays compatible with large-scale ion-trap quantum computer architectures. The primary challenge of DOEs is the loss associated with diffraction efficiency. This is due to requirements for large deflection angles, which leads to extremely small feature sizes in the outer zone of the DOE. If the period of the diffractive is between &lgr; (the free space wavelength) and 10&lgr;, the element functions in the vector regime. DOEs in this regime, particularly between 1.5&lgr; and 4&lgr;, have significant coupling to unwanted diffractive orders, reducing the performance of the lens. Furthermore, the optimal depth of the zones with periods in the vector regime differs from the overall depth of the DOE. We will present results indicating the unique behaviors around the 1.5&lgr; and 4&lgr; periods and methods to improve the DOE performance.

By using only two input signals of A and B, an all-optical half adder that utilizes a cross gain modulation in semiconductor optical amplifiers is demonstrated at 10 Gbps. The half adder utilizes two logic functions of SUM and CARRY, which can be demonstrated by using the XOR gate and the AND gate, respectively. The extinction ratios of SUM and CARRY are approximately 6.1 dB. No additional input beam such as clock signal or continuous wave light, which is required in many other all-optical logic gates, is used in this design concept.

We propose a secure display that limits the viewing space three-dimensionally by use of optically decodable encryption. A secret image is encrypted into a displayed image and a decoding mask. The decryption process is based on optical logic and performed without calculation. The secret is visible within the limited viewing space. However, the viewed results outside the viewing space look like random-dot pattern. When viewed at a distance different from the designed viewing distance, only the central area of the secret is faintly visible for a limited direction. When a user watches the secure display, in practice, the user's head prevents peeping at the secret. The relationships between the size and the position of the displayed image and the viewing space have been analyzed and confirmed experimentally. The proposed technique has been demonstrated by use of two-layered liquid-crystal displays. Furthermore, 3D displacement of the viewing space have been realized only by renewing the displayed image, i.e., without any mechanical movements. By using the decoding mask as the key for decryption, no one can view the secret image without the knowledge of the decoding mask pattern, and the viewed image is secure against prying eyes behind the viewer.

Contention resolution is one of the major design challenges in scaling the current packet switching architectures toward handling higher loads and different classes of traffic. This article explores an evolutionary path in packet switching technology toward Quantum Switching paradigm based on the principles of Quantum Information Processing, as a radical approach in addressing the contention resolution issue.

We compared experimentally the properties of optically controlled tunable time delay based on a Raman-assisted optical parametric amplifier (OPA) with different gain media of normal dispersion shifted fibers (DSF) and highly nonlinear fibers (HNLF). The Raman-assisted OPA using the DSF has previously been demonstrated to obtain large light delay for one single pulse. Position optimization of pump wavelength according to zero dispersion wavelength of the fibers results in narrow band gain spectrum through a parametric process. Stimulated Raman scattering further modifies the shape of the gain spectrum. The modified gain spectrum with sharper transitions leads to a large group index change so that large time delay can be achieved. In the paper, we experimentally demonstrated propagating 10Gbps return-to-zero (RZ) optical packets through slow-light fiber delay line based on the Raman-assisted OPA with above 100ps time delay. We also experimentally compared the gain, the bandwidth and the time delay versus variable pump powers for the Raman-assisted OPA by using 1km-long DSF and 1km-long HNLF as the gain medium, respectively. While smaller time delay was obtained in the slow-light scheme using HNLF due to its wider gain spectrum, lower pump power threshold was found compared to that using DSF. In the experiment, we found that the slow-light scheme has THz gain bandwidth and indicates that slow light could be achieved at higher bit rates with further optimized system parameters.

We have shown experimentally that dispersion due to an intra-cavity electromagnetically induced transparency or gain medium reduces the sensitivity of the cavity resonance frequency to a change in its length by a factor which is inversely proportional to the group index. Since the group index under atomic coherence can be made extremely large, the sensitivity of a long path length optical cavity can be reduced significantly. This can help in constructing highly frequency-stable cavities for various potential applications without taking additional measures for mechanical stability. The results also establish indirectly the opposite effect of increased sensitivity that can be realized for a negative dispersion corresponding to a group index close to a null value. These effects are discussed in the context of potential sensitivity enhancement of a rotation sensor.

We present a preliminary experimental study of optimized slow and stored light pulses in Rb vapor cells. We study the effciency of light storage as a function of pulse duration, storage time, retrieval field intensity, etc. We demonstrate a procedure based on time reversal for the optimization of the effciency for storage of light in atomic ensembles suggested in a recent theoretical paper [A.V. Gorshkov et al., e-print archive quant-ph/0604037 (2006)]. Experimental results are in a good qualitative agreement with theoretical calculations based on a simplified three-level model.

This paper presents the first demonstration of a white-light-cavity in a free-space cavity. Design of a whitelight- cavity has been proposed using negative dispersion in an intra-cavity medium to make the cavity resonate over a large range of frequencies and still maintain a high cavity build-up. The negative dispersion of the intra-cavity medium is caused by bi-frequency Raman gain in an atomic vapor cell. A significantly broad cavity response over a bandwidth greater than 20 MHz has been observed.

We review the current status of integrating optical quantum interference effects such as electromagnetically induced transparency (EIT), slow light, and highly efficient nonlinear processes on a semiconductor chip. A necessary prerequisite for combining effects such as slow light and related phenomena with the convenience of integrated optics is the development of integrated alkali vapor cells. Here, we describe the development of integrated rubidium cells based on hollow-core antiresonant reflecting optical waveguides (ARROWs). Hollow-core waveguides were fabricated on a silicon platform using conventional microfabrication and filled with rubidium vapor using different methods. Rubidium absorption through the waveguides was successfully observed which opens the way to integrated atomic and molecular on a chip. The realization of quantum coherence effects requires additional surface treatment of the waveguide walls, and the effects of the surface coating on the waveguide properties are presented.

We give exact solutions for correlated two-photon transport in one-dimensional waveguide coupled to a two-level system, using a Bethe-Ansatz-like approach. The S-matrix is explicitly constructed to account for the transport properties of the photons. We show that the scattering eigenstates of this system include a two-photon bound state that passes through the two-level system as a composite single particle. Also, the two-level system can induce effective attractive or repulsive interactions in space for photons. This general procedure can be applied to the Anderson model as well.

We present the methodology for designing the optimal gain profiles for slow-light systems under the given system constraints. Optimal system designs for the multiple Lorentzian gain lines make the gain spectrum uniform over larger bandwidth compared to the single-line gain system. The design procedure for the multiple-line gain systems is modified to make the gain spectrum uniform over arbitrarily broad bandwidth and applied to the design of the gain-only and gain+absorption slow-light media. The optimization of the triple-line gain system improves the delay-bandwidth product 1.7 times the delay-bandwidth product for the single-line gain system. For the broadband slow-light system, the optimal gain + absorption design and the optimal gain-only design improve the fractional delay performance by factors of 1.8 and 1.4, respectively, compared to the Gaussian noise pump broadened (GNPB) system.

We investigate an active Raman gain scheme for significant group velocity reduction. This scheme, which is fundamentally different from the electromagnetically induced transparency scheme, is capable of achieving ultraslow and distortion-free propagation of a pulsed probe field. The group velocity behavior is drastically different from the conventional electromagnetically induced transparency scheme, and the new scheme can be used to accurately determine the decoherence rate of a long-lived state. In addition, the Raman gain scheme has the advantage of being broadly tunable, an important feature that may have potential applications.

We theoretically predict strong coherent scattering in the backward direction from forward propagating fields only. It is achieved by applying laser fields with proper chosen detunings and an approprate spatial phase to excite a molecular vibrational coherence that corresponds to a wave propagating backwards. The applications of the technique to coherent scattering and remote sensing are discussed.

We present an experimental approach to study low light level absorption in a tapered optical fiber embedded in a rubidium atomic vapor medium. Our initial measurements demonstrates the potential of the system to realize extremely low light level quantum interference effects in the ultra small mode volume of the thin fiber, which is promising for many practical integrated device applications. The measurement shows saturated probe absorption using a low optical power of only ten nanowatt. Efforts are underway to use the fiber in a cloud of trapped rubidium atoms, which will circumvent the transit time limit for demonstrating a low photon optical switch via quantum interference.

A gyroscope based on Sagnac interferometer measures the rotation rate relative to an inertial frame of reference. Sagnac effect originally has been derived and experimentally demonstrated with optical waves. Later, matter wave based Sagnac interferometers were developed due to inherent sensitivity over a photon based system. However in any interferometer whether it is photon or matter wave based the resultant phase shift due to counter-rotating waves is independent of the wave velocity. Here we show that one can have a larger phase shift with slower matter waves using Aharonov-Bohm effect: the phase difference of the counter propagating waves is proportional to the inverse square of the particle velocity.

We have theoretically predicted and experimentally demonstrated an ultra-dispersive atomic prism made of coherently driven Rb atomic vapor. The prism posses spectral angular dispersion that six orders of magnetude higher than the prism made from optical glass; it is the highest spectral angular dispersion that has been ever shown (such angular dispersion allows one to resolve spatially light separated by a few kHz). The prism is working near the resonant frequency of atomic vapor, and its dispersion is optically controlled by coherent driving field.

Reduced density matrix descriptions are developed for linear and non-linear electromagnetic interactions of moving atomic systems, taking into account applied magnetic fields. Atomic collision processes are treated as environmental interactions. Applications of interest include electromagnetically induced transparency and related pump-probe optical phenomena in atomic vapors. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. The standard Born (lowest-order perturbation-theory) and Markov (short-memory-time) approximations are systematically introduced within the framework of the general nonperturbative and non-Markovian formulations. A preliminary semiclassical treatment of the electromagnetic interaction is introduced. However, the need for a fully quantum mechanical approach is emphasized. Compact Liouville-space operator expressions are derived for the linear and the general (n'th order) non-linear electromagnetic-response tensors occurring in a perturbation-theory treatment of the electromagnetic interaction. These expressions can be evaluated for coherent initial atomic excitations and for the full tetradic-matrix form of the Liouville-space self-energy operator representing the environmental interactions in the Markov approximation. Intense-field electromagnetic interactions can be treated by means of an alternative method, which is based on a Liouville-space Floquet representation of the reduced density operator. Collisional interactions between atoms in a vapor can be treated in various approximations for the self-energy operator and the influence of Zeeman coherences on the electromagnetic response can be incorporated.

In this work we considered temporal behavior of squeezing and amplitude-squared squeezing for a two two-level atoms in a finite-Q cavity with atom dissipation. The analytic expressions for squeezing parameters are obtained on the basis of master equation solution for coherent and squeezed input. Squeezing generation conditions are considered for various dissipation parameters values and coherent and squeezed initial input.

Peer-to-peer (P2P) optical communication network is presently attracting much attention in the application of smallscale network. We proposed a network element called as a node fabricated by optoelectronics hardware based on the optical bistable devices. These nodes can compose a self-organizing optical network being interconnected with each other. We also proposed an adaptive node with gate function which detects the differences of signal types as to the amplitude modulation (AM) signal in the network and switches their routings. Thus, the adaptive node allows optical P2P concurrent communications between multiple pairs of communicators in the network simultaneously. Moreover, we have proposed in the present work an optical nonblocking operation using the pseudorandom numbers fabricated into the above mentioned adaptive nodes. We have newly considered a switching scheme which identifies such pseudorandom numbers and forms automatically a signal propagation path so that the nodes with the same input pseudorandom numbers are to be linked. Since such a pseudorandom-number based switching may also prevent any irregular interception of established links among nodes, our scheme is proved to be a nonblocking operation. Therefore, this scheme allows multiple signals from input nodes to travel in the network simultaneously via only a single propagation path being established by the self-organized adaptive nodes. We have also demonstrated this switching operation experimentally by fabricating it into our optoelectronics hardware based on the optical bistable devices. As a consequence, nonblocking photonic switching scheme for P2P self-organized optical concurrent communications network has been achieved by our pseudorandom-number based adaptive nodes proposed by the present work.