This PDF file contains the front matter associated with SPIE Proceedings Volume 7727, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We study quantum intensity correlations produced using four-wave mixing in a room-temperature rubidium vapor cell. An extensive study of the effect of the various parameters allows us to observe very large amounts of non classical correlations.

In the last years we have proposed the use of the mechanism of spontaneous symmetry breaking with the purpose of generating perfect quadrature squeezing. Here we review previous work dealing with spatial (translational and rotational) symmetries, both on optical parametric oscillators and four-wave mixing cavities, as well as present new results. We then extend the phenomenon to the polarization state of the signal field, hence introducing spontaneous polarization symmetry breaking. Finally we propose a Jaynes-Cummings model in which the phenomenon can be investigated at the singlephoton- pair level in a non-dissipative case, with the purpose of understanding it from a most fundamental point of view.

The coupling of mechanical oscillators with light has seen a recent surge of interest, as recent reviews report. ^1,2 This coupling is enhanced when confining light in an optical cavity where the mechanical oscillator is integrated as backmirror or movable wall. At the nano-scale, the optomechanical coupling increases further thanks to a smaller optomechanical interaction volume and reduced mass of the mechanical oscillator. In view of realizing such cavity nanooptomechanics experiments, a scheme was proposed where a sub-wavelength sized nanomechanical oscillator is coupled to a high finesse optical microcavity. ³ Here we present such an experiment involving a single nanomechanical rod precisely positioned into the confined mode of a miniature Fabry-Pérot cavity. ⁴ We describe the employed stabilized cavity set-up and related finesse measurements. We proceed characterizing the nanorod vibration properties using ultrasonic piezo-actuation methods. Using the optical cavity as a transducer of nanomechanical motion, we monitor optically the piezo-driven nanorod vibration. On top of extending cavity quantum electrodynamics concepts to nanomechanical systems, cavity nano-optomechanics should advance into precision displacement measurements near the standard quantum limit ⁵ , investigation of mechanical systems in their quantum regime, non-linear dynamics ⁶ and sensing applications.

Different adiabatic passage methods are applied as part of a state mapping scheme in multilevel trapped systems. The aim is to achieve full population transfer from the rotational states of a trapped molecular ion to its translational states. Our analysis is based on numerical simulations with the master equation. We discuss how the resolved sideband condition, and spontaneous emission have an adverse effect on the efficiency for stimulated Raman adiabatic passage. Use of adiabatic rapid passage techniques, with two-photon Raman transitions results in higher efficiencies that can exceed 97%.

A new developed for storing quantum information on atomic polaritons being at thermal equilibrium is developed for the first time. We propose a new type of spatially periodic structure - polaritonic crystal (PolC) formed by trapped two-level atoms interacting with quantum electromagnetic field in one-dimensional array of tunnelcoupled microcavities, which allows polaritons to be fully localized. The quantum degeneracy and phase transition to superfluid (Bardeen-Cooper-Schrieffer-type) state for low branch polaritons is discussed. The principal result is that the group velocity of polaritons depends essentially on the order parameter of the system, i.e. on the average photon number in the cavity array. An algorithm for the spatially distributed writing, storing, and retrieving of quantum optical information using polariton wave packet propagated in the cavity array is examined. To take into account decoherence processes in polaritonic system the quantum Brownian particle model is discussed as well.

A novel method of multi-bit quantum optical data storage is presented, where the storage time can be lengthened far beyond the spin phase-decay time in a reversible spin inhomogeneous system excited by consecutive resonant Raman optical data pulses. The ultralong storage time is obtained by an optical population locking mechanism of modified rephasing process. This gives potentials to quantum repeaters utilizing quantum memories for long distance quantum communications, in which ultralong storage time plays a major role.

Few-photon systems are best described by their wave function rather than by the usual quantum field formalism. In this work, we develop a photon wave function (PWF) formalism suitable for analyzing a wide variety of quantum optical problems related to propagation, diffraction and imaging with quantum states of light. We establish a generalized Huygens-Fresnel (GH-F) principle that describes the propagation of any paraxial N-photon state. This tool is very helpful for predicting photo-detection correlations in space and time due to an initial N-particle entanglement, even in complex situation. The effect of lenses, beam splitters, filters ... on the photon paths can be easily taken into account. We apply the PWF formalism and the GH-F principle to three specific problems in quantum optics. First, we revisit the Hong-Ou-Mandel two-photon interference effect and analyze the effect of photon shape mismatch in space, time and polarization using the PWF formalism. Second, we show how to use the GH-F principle to analyze "ghost" imaging and diffraction experiments with entangled photon pairs such as those realized by Strekalov et al. [Phys. Rev. Lett. 74, 3600 (1995)] and Pittman et al. [Phys. Rev. A 52, R3429 (1995)] in the nineties. Finally, we use the GH-F principle to analyze the resolution enhancement in a recent quantum imaging proposal based on N incoherent single-photon sources [Phys. Rev. Lett. 99, 133603 (2007) and Phys. Rev. A 80, 013820 (2009)].

We propose the use of modal engineered tapered optical fibers for single photon interferometry experiments. Tapered optical fibers (TOF) can be designed to function as tunable Mach-Zehnder (MZ) type modal single photon interferometer. The MZ design criteria of tunability, visibility, and wavelength range are inherently interconnected in TOF's, which makes the design complex. Moreover, novel TOF related design criteria, like loss minimization, have to be taken into account. Design guidelines can be based on a semi-analytical approach assuming multiple two mode beat equations for different mode power amplitudes. Linearization permits to obtain a set of simple and robust analytical relations that correlate the TOF design parameter with the TOF and MZI optical properties. By focusing on the tunability, we have demonstrated a device that permits to be tuned between local minima and maxima.

ABSTRACT The results of frequency-modulation (FM) spectroscopy of coherent dark resonances from the Zeeman sublevels of the transition F=2 ↔ F=1 of D₁ line in absorption of ⁸⁷Rb atoms are presented and discussed in detail. By contrast with the conventional spectroscopy of coherent dark resonances employing two laser beams, relative frequency of which can be varied, these data has been obtained with the help of a single frequency-modulated laser field. Variation of the modulation frequency plays then similar role with variation the relative frequency in conventional spectroscopy. Experimental data are fit to the theoretical calculations, which are based on the theory of FM spectroscopy of coherent dark resonances recently developed by us. Feasibility of using such experimental technique for accurate measurements of magnetic fields is also discussed.

In the space of mixed states the Schrödinger-Robertson uncertainty relation holds though it can never be saturated. Two tight extensions of this relation in the space of mixed states exist; one proposed by Dodonov and Man'ko, where the lower limit on the uncertainty depends on the purity of the state, and another where the uncertainty is bounded by the von Neumann entropy of the state proposed by Bastiaans. Driven by the needs that have emerged in the field of quantum information, in a recent work we have extended the puritybounded uncertainty relation by adding an additional parameter characterizing the state, namely its degree of non-Gaussianity. In this work we alternatively present a extension of the entropy-bounded uncertainty relation. The common points and differences between the two extensions of the uncertainty relation help us to draw more general conclusions concerning the bounds on the non-Gaussianity of mixed states.

Quantum multipartite entanglement is a striking phenomenon predicted by quantum mechanics when several parts of a physical system share the same quantum state that cannot be factorized into the states of individual subsystems. The Gaussian quantum states are usually characterized by the covariance matrix of the quadrature components. A powerful formalism for treating the Gaussian states is that of the symplectic eigenvalues. In particular, a quantitative measure of multipartite entanglement is the so-called logarithmic negativity, related to the symplectic eigenvalues of the partially transposed covariance matrix. Considering only global variances of the field quadratures one completely neglects the spatiotemporal properties of the electromagnetic field. We propose, following the spirit of quantum imaging, to generalize the theory of multipartite entanglement for the continuous variable Gaussian states by considering the local correlation matrix at two different spatiotemporal points [see manuscript for characters] and [see manuscript for characters] with [see manuscript for characters] being the transverse coordinate. For stationary and homogeneous systems one can also introduce the spatiotemporal Fourier components of the correlation matrix. The formalism of the global symplectic eigenvalues can be straightforwardly generalized to the frequency-dependent symplectic eigenvalues. This generalized theory allows, in particular, to introduce the characteristic spatial area and time of the multipartite entanglement, which in general depend on the number of "parties" in the system. As an example we consider multipartite entanglement in spontaneous parametric down-conversion with spatially-structured pump. We investigate spatial properties of such entanglement and calculate its characteristic spatial length.

We study the transmission of classical information via optical Gaussian channels with a classical additive noise under the physical assumption of a finite input energy including the energy of classical signal (modulation) and the energy spent on squeezing the quantum states carrying information. Multiple uses of a certain class of memory channels with correlated noise is equivalent to one use of parallel independent channels generally with a phase-dependent noise. The calculation of the channels capacity implies finding the optimal distribution of the input energy between the channels. Above a certain input energy threshold, the optimal energy distribution is given by a solution known in the case of classical channels as water-filling. Below the threshold, the optimal distribution of the input energy depends on the noise spectrum and on the input energy level, so that the channels fall into three different classes: the first class corresponds to very noisy channels excluded from information transmission, the second class is composed of channels in which only one quadrature (q or p) is modulated and the third class corresponds to the water-filling solution. Although the non-modulated quadrature in the channels of the second class is not used for information transmission, a part of the input energy is used for the squeezing the quantum state which is a purely quantum effect. We present a complete solution to this problem for one mode and analyze the influence of the noise phase dependence on the capacity. Contrary to our intuition, in the highly phase-dependent noise limit, there exists a universal value of the capacity which neither depends on the input energy nor on the value of noise temperature. In addition, similarly to the case of lossy channels for weak thermal contribution of the noise, there exists an optimal squeezing of the noise, which maximizes the capacity.

The radar cross section σ_C is an objective measure of the "radar visibility" of an object. As such, σ_C is an important concept for the correct characterization of the operational performance of radar systems. Furthermore, σ_C is equally essential for the design and development of stealth weapon systems and platforms. Recent years have seen the theoretical development of quantum radars, that is, radars that operate with a small number of photons. In this regime, the radar-target interaction is described through photon-atom scattering processes governed by the laws of quantum electrodynamics. As such, it is theoretically inconsistent to use the same σ_C to characterize the performance of a quantum radar. In this paper we define a quantum radar cross section σ_Q based on quantum electrodynamics and interferometric considerations. We discuss the theoretical challenges of defining σ_Q, as well as computer simulations of σ_C and σ_Q for simple targets.

Photon sources for multi-photon entanglement experiments are commonly based on the process of spontaneous parametric down conversion. Due to the probabilistic photon production, such experiments suffer from low multiphoton count rates. To increase this count rate, we present a novel SPDC pump source based on a femtosecond UV enhancement cavity that increases the available pump power while maintaining a high repetition rate of 80MHz. We apply the cavity as photon source for realizing symmetric, multi-partite entangled Dicke states, which are observed with a high rate and high fidelity. We characterize the observed Dicke states of up to six photons using efficient tools exploiting the state's symmetries.

We demonstrate an integrated semiconductor ridge microcavity source of counterpropagating twin photons at room temperature in the telecom range. Based on type II parametric down conversion in a counterpropagating phase matching scheme with transverse pump, the device generates around 10^-11 pairs/pump photons having a 0.3 nm bandwidth for a 1 mm long waveguide. The emission spectrum shows the existence of two equally probable processes, which is a preliminary step to the direct generation of Bell states. The twin character of the photons of each pair is demonstrated via a temporal correlation measurement. These results open the way to the demonstration of several interesting features associated to the counterpropagating geometry, such as the control of the frequency correlation degree via the spatial and spectral properties of the pump beam.

We demonstrate electrically pumped single-photon emission in the visible spectral range from InP quantum dots embedded in a resonant cavity LED device structure. The electroluminescence from a single QD can be observed up to 120 K. Our devices can also be operated using pulsed electrical excitation. The successful injection of carriers is verified by time-correlated photon counting experiments and the pulsed signature in second-order autocorrelation measurements.

Color centers in diamond are very promising candidates among the possible realizations for practical singlephoton sources because of their long-time stable emission at room temperature. The popular nitrogen-vacancy center shows single-photon emission, but within a large, phonon-broadened spectrum (≈ 100 nm), which strongly limits its applicability for quantum communication. By contrast, Ni-related centers exhibit narrow emission lines at room temperature. We present investigations on single color centers consisting of Ni and Si created by ion implantation into single crystalline IIa diamond. We use systematic variations of ion doses between 10⁸ cm^-2 and 10¹⁴ cm^-2 and energies between 30 keV and 1.8MeV. The Ni-related centers show emission in the near infrared spectral range (≈ 770 nm to 787 nm) with a small line-width (≈ 3 nm FWHM). A measurement of the intensity correlation function proves single-photon emission. Saturation measurements yield a rather high saturation count rate of 77.9kcounts/s. Polarization dependent measurements indicate the presence of two orthogonal dipoles.

The dual nature of photons is well known but in spite of several years of work its foundation is not well understood. In the present paper, a fresh approach is proposed according to which fields and particles are transformed into each other and propagate together. This is explained by considering the field quantization process with the help of annihilation and creation operators. Thus, at every point in space and time the sum of the energies associated with electric, magnetic fields and photons is conserved. The present investigation supports the recently observed experimental data related with sub wavelength interference and its regain by detecting photons with the help of the photon-echo process.

This paper reports on trapping and laser-cooling of singly-ionized strontium ions in a linear Paul trap. We demonstrate loading of large ion clouds containing as much as 10⁶ ions and laser cooling down to the Coulomb crystal transition. We observe the spatial segregation of the different Sr+ isotopes due to the mass-dependent Paul trap stiffness. Sympathetic cooling of the different isotopes is demonstrated, either by laser-cooling of ⁸⁸Sr+ (83% abundance) or of ⁸⁶Sr+ (10% abundance). These demonstrations open the way to the use of a large ion Coulomb crystal for quantum optics and quantum information experiments, where the strong confinement, the long lifetime, and the absence of perturbation by cooling lasers are crucial.

Single cesium atom prepared in a large-magnetic-gradient magneto-optical trap (MOT) has been efficiently loaded into a microscopic far-off-resonance optical trap (FORT, or optical tweezer), and the atom can be transferred back and forth between two traps with high efficiency. The intensity noise spectra of tweezer laser are measured and the heating mechanisms in optical tweezer are analyzed. To prolong the lifetime of single atom trapped in optical tweezer, laser cooling technique is utilized to decrease atom's kinetic energy, and the effective temperature of single atom in tweezer is estimated by the release-and-recapture (R&R) method. Thanks to laser cooling, typical lifetime of ~ 130.6 ± 1.8 s for single atom in tweezer is obtained. These works provides a good starting point for coherent manipulation of single atom.