How fast can a quantum system evolve? We answer this question focusing on the role of entanglement and interactions among subsystems. In particular, we analyze how the order of the interactions shapes the dynamics.

Calculations of photon counting distributions and false probabilities are compared with measured data obtained using very weak laser pulses propagated over 10-km horizontal paths. Good agreement is obtained between theory and experiment using various simplifying assumptions and values of the refractive-index structure constant C_n² lying within an expected range.

It is well known that interactions between a coherent monochromatic radiation and a scattering media induce a speckle phenomenon. Spatial and temporal statistics of this speckle allow many applications in laser imaging. The main problem is the characterization of the backscattered media from the speckle pattern in biomedical imagery. In this paper, we present a stochastic approach based on Brownian motion theory in the approximation of the diffusion. Stochastic processes showing statistical scale law are, under some assumptions, called fractional Brownian motion (fBm) which is a generalization of ordinary Brownian motion (Bm) as defined by Mandelbrot and Van Ness. This extension is related to the existence of a long-range statistic dependence in the process. This dependence is quantified by the Hurst exponent H that is a 'scale factor' indicating the persistence (H>0.5), totally random (H=0.5) or the anti-persistence (H<0.5) nature of the process. Variogram analysis is a possible method to estimate the Hurst exponent. We applied this approach by estimation of the mean quadratic spatial difference, or diffusion function, for 2D analysis of speckle image. Hence, spatial speckle is characterize by extracting from diffusion function plot a set of three parameters; the Hurst exponent, the saturation of the variance and the characteristic element size. Applications of this method to characterization of test media are presented. We find that for all test media with different latex micro-ball concentrations (1%, 5% and 10%) the characteristic element size and the saturation of the variance discriminate media while Hurst exponent seems to be constant for all concentrations. This first results permit us to hope in application like skin lesion quantification in dermatology.

We present an overview of quantum noise in gravitational wave interferometers. Gravitational wave detectors are extensively modified variants of a Michelson interferometer and the quantum noise couplings are strongly influenced by the interferometer configuration. We describe recent developments in the treatment of quantum noise in the complex interferometer configurations of present-day and future gravitational-wave detectors. In addition, we explore prospects for the use of squeezed light in future interferometers, including consideration of the effects of losses, and the choice of optimal readout schemes.

We discuss the use of active control to reduce mirrors position fluctuations at the quantum level. Recent experiments have shown that it is possible to reduce the thermal motion of a mirror by cold damping. The mirror motion is measured with an optomechanical sensor based on an high-finesse optical cavity, and corrected by a feedback loop. We show that this approach can be extended to lock the mirror motion at the quantum level and we propose to use this quantum locking technique to reduce the noise in interferometric measurements such as gravitational-waves detectors. We analyze the back-action effects of the optomechanical sensor and show that quantum limits can be transferred from the sensor measurement to the interferometric one. This simple technique allows one to suppress the quantum effects of radiation pressure in the interferometer and to greatly enhance its sensitivity. The effect is furthermore insensitive to losses in the interferometer.

It is expected that interferometric gravitational wave detectors such as LIGO will be eventually limited by fundamental noise sources like shot noise and Brownian motion, as well as by seismic noise. In the commissioning process, other technical noise sources (electronics noise, alignment fluctuations) limit the sensitivity and are eliminated one by one. We propose here a way to correlate the noise in the output of the gravitational wave detector with other detector and environmental signals not through their linear transfer functions (often unknown), but through their statistical properties. This could prove useful for identifying the frequency bands dominated by different noise sources in the final configuration, and also to help the commissioning process.

We present a detailed study of how phase-sensitive feedback schemes can be used to improve the performance of optomechanical devices. Considering the case of a cavity mode coupled to an oscillating mirror by the radiation pressure, we show how feedback can be used to reduce the position noise spectrum of the mirror, cool it to its quantum ground state, or achieve position squeezing. Then, we show that even though feedback is not able to improve the sensitivity of stationary position spectral measurements, it is possible to design a nonstationary strategy able to increase this sensitivity.

We present methods of transforming the standard quadrature amplitude squeezing of a continuous-wave light beam to its Stokes parameters and transverse spatial modes statistics. These two states of light are called polarization squeezing and spatial squeezing, respectively. We present experimental results of the quadrature amplitude, polarization and spatial squeezing obtained with a common experimental setup based on optical parametric amplifiers. The transformations from quadrature amplitude to polarization and spatial squeezing are achieved with only simple linear optics.

It has been argued that continuous-variable quantum teleportation at optical frequencies has not been achieved because the source used was not 'truly coherent'. While arguing against Rudolph and Sanders, also accept that an 'absolute phase' is achievable, even if it has not been achieved yet. I will argue to the contrary that 'true coherence' or 'absolute phase' is always illusory, as the concept of absolute time on a scale beyond direct human experience is meaningless. All we can ever do is to use an agreed time standard. in this context, laser beam is fundamentally as good a 'clock' as any other. I explain in detail why this claim is true, and defend my argument against various objections. In the process I discuss super-selection rules, quantum work by myself and Berry and myself to show that a Heisenberg-limited laser with a mean photon number μ can synchronize M independent clocks each with a mean-square error of square root M/4μ radians².

In the presence of quantum noise a perfect EPR pair becomes imperfect and may be described by a non-maximally entangled pair. With non-maximally entangled state as a resource one cannot teleport an unknown state faithfully. Typically, one has to perform either local filtering or entanglement concentration and then follow the standard teleportation method. In this talk, we will present a new protocol that uses neither local filtering nor entanglement concentration to teleport an unknown state. We show that using non-maximally entangled measurements one can teleport an unknown state with unit fidelity but with a probability that is less than unit. Ours is a generalized quantum teleportation protocol that encompasses probabilistic as well as deterministic teleportation scenarios. We describe the probabilistic teleportation in terms of quantum operations and give explicit expressions for success and failure probabilities. This may have practical value in real experiments, and even may be tested with current technology.

A quantum communication architecture is being developed for long-distance, high-fidelity transmission and storage of Greenberger-Horne-Zeilinger states. This system uses an ultrabright narrowband source of polarization-entangled photons plus trapped-atom quantum memories, and it is compatible with long-distance transmission over standard telecommunication fiber. An error model for the preceding architecture is derived, and the use of quantum error correction or entanglement purification protocols to improve the performance of this quantum communication system is also discussed.

We show both numerically and experimentally that a semiconductor laser prepared in an excitable state and driven by two weak periodic signals with different frequencies is able to resonate at a ghost frequency, i.e., a frequency that is not present in the forcing signal. The small signal modulation together with the complex internal dynamics of the system produces this resonance. This is an eminently nonlinear effect that agrees with the recent theoretical predictions by Chialvo et. al. [PHys. Rec. E. 65, 050902(R),2002].

We study the effect of optical injection on the dynamical behavior of a laser whose frequency drifts randomly in time. When the autocorrelation time of these random fluctuations is larger than the ty ical time scales of the system dynamics,and the range of the frequency drift is larger than the injection locking range,the laser exhibits bursting behavior at irregular times,each burst being followed by relaxation oscillations towards the unlocked state. Numerical results from a simple model agree satisfactorily with the experimentally observed behavior of an injected fiber ring laser.

The vertical-cavity surface-emitting laser (VCSEL) is a novel type of semiconductor laser that is having a dramatic influence on many optical applications, including computing, communication, and sensing. Unfortunately, VCSELs suffer from a randomly fluctuating polarization whose dynamics are not fully understood. The model of stochastic polarization dynamics developed by San Miguel is rather complicated, and comparisons between experiment and simulations are quite difficult. One of the approaches to solve this problem was suggested in, where a simplified spin-eliminated linearized model (i.e., with dynamics reduced to that of a class-A laser) is used to analyze experimentally measured fluctuations and fluctuational switchings. In this talk, we present a recently developed technique that estimates the parameters of a nonlinear stochastic dynamical model by Bayesian inference, and demonstrate its application to the characterization of VCSELs. We start by considering the problem of diffusion of polarization in a potential well, onto which the dynamics of a class-A laser are usually mapped. We demonstrate the ability to infer laser parameters in numerical and analogue simulations, with the emphasis being placed on the role of large deviations. We specifically show that, contrary to one's intuition, the quality of inference can be improved by neglecting those data points in experimental time series that correspond to the rising part of large deviations. We then extend our technique to the full set of equations describing the polarization dynamics of a VCSEL in terms of the motion of its Stokes vector on the Poincare sphere. Application of this technique to other standard problems encountered in characterizing semiconductor lasers, such as the identification of laser parameters from measurements of relaxational oscillations, is also discussed.

The effects of optical feedback in edge-emitting semiconductor lasers and vertical cavity surface emitting lasers (VCSELs) have attracted considerable attention because the characteristics of both kind of lasers are very sensitive to the effects of reflected light. The phenomena arising in laser diodes subject to optical feedback can be classified according to operating five regimes conventionally identified as regimes I-V. Optical feedback also affects the noise properties of semiconductor lasers. There have been a number of investigations of the noise properties of semiconductor lasers and VCSELs subject to optical feedback. However, such work has been concerned with only some of the above-mentioned regimes of operation. A thorough experimental investigation of the effect of optical feedback in RIN of edge-emitting semiconductor lasers has yet to appear in the literature. In this paper, we present a detailed study of the effect of optical feedback on the average RIN of edge-emitting semiconductor lasers at different bias currents. An experimental study has been performed of the relative intensity noise (RIN) of a semiconductor laser in optical feedback regimes I to V. At low bias current, a low RIN is observed with low feedback feedback ratio, the RIN increased in the coherence collapse regime, then decreased again in regime V. The RIN in regime V is lower than that of the solitary laser. It is observed experimentally that an increase of the RIN occurs for intermediate levels of feedback. Such an increase in RIN appears to be related to enhanced intensity fluctuations. We will consider theoretical approaches to explaining the observed RIN characteristics.

Signal to noise ratio (SNR) is the most important figure of merit for comparing the performance of infrared detectors. When measuring SNR, it is vitally important that all of the noise sources be characterized, including those of the test apparatus. At low temperatures and/or high current, generation-recombination (G-R) noise is expected to be the main noise contributor. At high temperatures and low current, Johnson noise is expected to become comparable to the G-R noise. We present noise measurements under dark conditions on a Quantum Well Infrared Photodetector (QWIP) with careful attention to noise sources present in the measurement apparatus. The noise was dominated by Johnson noise at temperatures <40K, and by G-R noise at 77K and finite bias. A new method to measure noise in QWIPs is described.

We consider intensity-field correlation functions for a two-level atom in a degenerate optical parametric oscillator (OPO). Analytic results are obtained in the limit of weak driving fields using quantum trajectory methods. We find large violations of inequalities satisfied by classical fields. We compare our results to those of an ordinary OPO. We also calculate the second-order intensity correlation function for transmitted and fluorescent light, as well as for cross correlations. Here we report large violations of inequalities for the intensity cross-correlation functions in the weak field limit.

The photocurrent noise has been investigated in Quantum Well Infrared Photodetectors (QWIPs) having identical growth sequence, layer width and composition, but different number of wells. It has been found that the power spectral density exhibits characteristic features related to the discrete structure of the device. This behavior might be caused by the strong potential nonuniformity arising as a consequence of the imbalance between the current injected at the emitter and the stream of photoelectrons drifting through the structure, which is also responsible for the anomalies in the steady-state and transient photoconductivity. In the present work, we will add further evidence to our preliminary study by presenting results of the power spectral density obtained by numerical solution of the continuity equation of the electrons in the continuum state, with a discrete distribution of the electric field in the active region, instead of the homogeneous one valid for conventional photodetectors.

Steady state resonance fluorescence spectra from a two-level atom embedded in a photonic bandgap crystal and resonantly driven by a classical pump light are calculated. The photonic crystal is considered to be with a small bandgap which is in the order of magnitude of the Rabi frequency and is modeled by the anisotropic two-band dispersion relation. Non-Markovian noises caused by the non-uniform distribution of photon density states near the photonic bandgap are taken into account by a new approach which linearizes the optical Bloch equations by using the Liouville operator expansion. Fluorescence spectra that only exhibit sidebands of the Mollow triplet are found, indicating that there is no coherent Rayleigh scattering process.

Pulsed THz (T-ray) spectroscopy is an increasingly wide-spread tool for studying materials from physics to biology. Liquid transmission T-ray studies are valuable for understanding solvation dynamics of salts, exploring long-range structure in mixtures and probing biomolecules in suspension. In this paper the uncertainty in parameter estimation of liquid samples is shown to be dependent on the thickness change of the sample, and on the noise of the T-ray spectrometer. For many important liquids, such as water, with high THz absorption, we show that measurement uncertainty can be greatly decreased using a dynamically-modulated liquid sample, using differential T-ray time-domain spectroscopy (DTDS). Preliminary experiments support these calculations.

The ultraviolet quantum catastrophe of the zero-point fluctuations in an L-C circuit of finite Q is revisited. The zero-point energy is shown to approach the value hω₀/2 only in the limit of an infinite Q. A Fabry-Perot resonator, on the other hand, has bounded zero-point energies of its modes that are equal to hω₀/2 . We analyze the noise of an ultra-fast mode-locked laser when the slowly varying envelope approximation (SVEA) is not valid. It is found that quantum correlations exist that are not present in the SVEA. The correlations become evident in the spectrum of the zero-point uctuations.

There has been a significant progress in the X-ray generation technologies for various laboratory and production application by laser-Compton scheme and laser produced plasma. Femtosecond X-ray generation was performed by Compton scattering through interaction between a 3-ps electron beam and 100-fs laser photons in a 90 degree scattering configuration. The X-ray energy and pulse duration were estimated as 2.3keV and 280fs from the observed electron and laser beam parameters. The fluctuation of the X-ray output was measured as 25% rms during a 30-min operation, and analyzed as a function of fluctuations of parameters like timing between the electron and laser beam, electron beam charge, laser beam energy, pulse widths, and spatial stability. Further reduction of the fluctuation is possible by improvement of timing stability down to 100fs region. All optical synchronization scheme was proposed and component technologies are under development. The novel scheme employs optical control of linear accelerator and femtosecond lasers by optical locking of lasing between different laser oscillators. Two mode-locked Ti:sapphire lasers of different wavelengths were precisely synchronized by a simple feedback system employing sum frequency generation. The measured rms timing jitter between two lasers was 28fs. Clean EUV light source is strongly demanded for next generation lithography, with 13.5nm, 2%bw, 100W and high pulse stability of less than 1%. The most promising approach is to employ a liquid Xe jet of 10-30 micron-meter diameter as the plasma source with high repetition rate solid state laser. The laser pulse energy usually fluctuates more than a few % and liquid jet fluctuates of the position up to 10% of the diameter. Higher repetition rate plasma generation causes acoustic instability inside the liquid jet. All these obstacles prevent to achieve the desired EUV stability. Discussion will be given on these issues and new architecture is proposed to achieve a clean and stable EUV light source.

We report on an experiment to study the properties of subthreshold modes of a multiple quantum well diode laser in an external grating cavity configuration. Measurement of the radio frequency (rf) intensity noise near the external cavity mode spacing provides information about the intensity and phases of the adjacent subthreshold modes. The rf spectrum has a double peaked structure, as has been previously reported; and we also measure optical spectra with a Fabry-Perot etalon to isolate the individual side modes. In addition, we observe rf noise and optical spectra at higher multiples of the external cavity mode spacing. Our data are compared with previous theoretical models.

Most common monomode tunable laser diodes use carriers injection to change a bulky semi-conductor material's optical index (through absorption), with the aim of switching the emission wavelength, thanks to the phasis comb spectrum or Bragg filtering evolution. This index change existe in the active, phase and Bragg section. Independently, current injection in a laser diode involves the existance of a fundamental shot noise and of excess 1/f noise. This noise power creates optical index fluctuations in all of the 3 sections, and so modulates the laser's light field. As there is a close link between absorption and refraction index in semiconductors, through Kramers-Kronig relationships this modulation has an influence on both phase and amplitude of the laser field. The aim of this paper is to establish the correlations existing between electrical shot noise and 1/f noise of the tuning sections and the laser field's optical noise.

Semiconductor cascade lasers have larger photon noise than conventional single stage semiconductor lasers as a result of positive correlations in photon emission in different gain stages which are connected electrically in series. The photon noise of cascade lasers can be related to the photon noise of single stage lasers with scaled external circuit impedances. This scaling relation for the photon noise holds for bipolar as well as unipolar cascade lasers.

No abstract available.

We study collective spontaneous emission from arbitrary distributions of N two-state atoms using quantum trajectory theory and without an a priori single-mode assumption. Assuming a fully excited initial state, we calculate the angular distribution of the average integrated intensity. We investigate the dependence of the angular distribution of emission on the geometry of the atomic distribution. The formalism is developed around an unravelling of the master equation in terms of source mode quantum jumps. A modified boson approximation is made to treat the many-atom case, where it is found that strong directional superradiance occurs for a few hundred to a few thousand atoms. In order to illustrate important differences between our model and single-mode models we consider shot-to-shot intensity fluctuations and angular correlations in the emitted intensity.

Do non-Markovian diffusive stochastic Schroedinger equations (SSEs) for open quantum systems have a physical interpretation? In a recent paper we investigated this question using the orthodox interpretation of quantum mechanics. We found that the solution of a non-Markovian SSE at time t represents the state the system would be in at that time if a measurement was performed on the environment at that time, and yielded a particular result. However, the linking of solutions at different times to make a trajectory is, we concluded, a fiction. In this paper we show that such trajectories be interpreted using a non-standard interpretation of quantum mechanics, namely hidden variables theory. The simplest example is a non-Markovian SSE, which we call a position unraveling, which results from a description of the bath using Bohmian mechanics. We find that the noise function z(t) appearing in the non-Markovian SSE can be interpreted as a weighted sum of trajectories for the positions of the bath modes. The solution of the non-Markovian SSE is the state of the system 'conditioned' on values of the bath positions. It also determines the guiding wave for these positions. We also discuss previously used unravelings which have the Markovian limits of homodyne and heterodyne detection.

Measurement of the squeezed fluctuations of an optical field by the method of conditional homodyne detection is discussed. It is shown that conditional homodyne detection is able to distinguish qualitatively between vacuum-state squeezing and squeezed classical noise. Whereas for conventional squeezed-light detection, only a quantitative distinction can be made, based on the setting of the shot-noise level, under conditional detection, the presence of classical noise changes the actual shape of the measured correlation function. The correlations show a positive peak due to the unsqeezed classical noise frequencies, set inside the negative dip associated with the squeezed fluctuations. The width in time of the positive peak is the larger of the detector response time and the inverse of the classical noise bandwidth. The fundamental distinction between vacuum-state squeezing and squeezed classical noise is that there is no positive peak, even in the limiting form of a delta-function, when the unsqueezed frequencies correspond to vacuum state modes. Implications for the literal interpretation of vacuum fluctuations, such as is adopted in stochastic electrodynamics, are discussed. The ideas are presented in general terms and illustrated by an example which treats the generation and detection of broadband squeezed light, including finite-bandwidth classical noise, within the framework of the quantum trajectory theory of cascaded open systems.

Quantum equations of motion are developed for broadband soliton propagation with an instantaneous Kerr effect. New terms appear in the nonlinear Schroedinger equation. Hyperbolic secant soliton solutions exist. The initial pulse perturbations are evaluated.

Alternating two fair coin flipping games can create a winning game. Such a Parrondo game is a discrete model for a thermal ratchet. Recently we have constructed quantum versions of these coin flipping games that display the same 'paradoxical' behavior. In this paper we add noise to these quantum Parrondo games in order that they can be compared with continuum models of quantum ratchets. Simulation of these models reproduces one of the most interesting features of quantum ratchets: current inversion.

We present protocol that allows the generation of a maximally entangled state between individual atoms held in spatially separate cavities. Under ideal conditions, the scheme is deterministic. In a realistic setting, when the the atom-cavity interaction may be weak, and the detectors are imperfect, we show that the scheme is robust against experimental inefficiencies and yields probabilistic entanglement of very high fidelity.

A truel, or a three person generaliztion of a duel, is a popular model in game theory of a struggle of survival. The outcome is often sensitive to the precise rules under which the truel is performed and can be anti-intuitive. We propose a quantum scheme, along the lines of recent work in quantum game theory, for the problem of duels and truels. Interference amongst the players' strategies can arise leading to game equilibria different from the classical case.

The principal obstacle to quantum information processing with many qubits is decoherence. One source of decoherence is spontaneous emission which causes loss of energy and information. Inability to control system parameters with high precision is another possible source of error. Strategies aimed at overcoming one kind of error typically increase sensitivity to others. As a solution we propose quantum computing with dissipation-assisted quantum gates. These can be run relatively fast while achieving fidelities close to one. The success rate of each gate operation can, at least in principle, be arbitrary close to one.

In semiclassical theory, light is a classical electromagnetic wave and the fundamental source of photodetection noise is the shot effect arising from the discreteness of the electron charge. In quantum theory, light is a quantum-mechanical entity and the fundamental source of photodetection noise comes from measuring the photon-flux operator. The Glauber coherent states are Gaussian quantum states which represent classical electromagnetic radiation. Quantum photodetection of these states yields statistics that are indistinguishable from the corresponding Poisson point-process results of semiclassical photodetection. Optical parametric interactions, however, can be used to produce other Gaussian quantum states, states whose photodetection behavior cannot be characterized semiclassically. A unified analytical framework is presented for Gaussian-state photodetection that includes the full panoply of nonclassical effects that have been produced via parametric interactions.

We have implemented a continuous measurement of the mean magnetic moment of an ensemble of atoms trapped in a far-off-resonance optical lattice, by detecting the Faraday rotation of one of the lattice beams after it has passed through the atom cloud. In a first demonstration experiment we have observed Larmor precession with high signal-to-noise ratio, and compared the performance of the measurement with a simple theory. Faraday spectroscopy offers an ideal method to monitor the atomic dynamics and will be applied to the study of quantum chaos in magneto-optical lattices. In principle the measurement sensitivity can be increased to the point where quantum backaction becomes significant, thereby opening the door to studies of quantum feedback, spin squeezing and the role played by quantum measurement in quantum/classical correspondence.

We give a short update of our research program on nonequilibrium statistical field theory applied to quantum processes in the early universe and black holes, as wel as the development of stochastic gravity theory as an extension of semiclassical gravity and an intermediary in the 'bottom-up' approach to quantum gravity.

Interference resulting from the measurement of four-time fourth-order correlation functions of a wave field is discussed. The fringes that are observed are peculiar because they have a statistical origin, and show the greatest contrast when the coherence time of the field is finite. This is demonstrated with a simple acoustic experiment. Random telegraph phase noise is used in this experiment to vary the field coherence in order to highlight the problem of interpreting this interference; for this noise the Gaussian moment theorem may not be invoked to reduce the description of the interference to one in terms of first order interference. A second example using the pseudorandom phase fluctuations that are encoded on GPS satellite transmissions is also presented.

The primary resource for quantum computation is Hilbert-space dimension. Whereas Hilbert space itself is an abstract construction, the number of dimensions available to a system is a physical quantity that requires physical resources. Avoiding a demand for an exponential amount of these resources places a fundamental constraint on the systems that are suitable for scalable quantum computation. To be scalable, the number of degrees of freedom in the computer must grow nearly linearly with the number of qubits in an equivalent qubit-based quantum computer.

Quantum optics has proved a fertile field for experimental tests of quantum information science, from experimental verification of the violation of the Bell inequalities to quantum teleportation. However it was long believed that quantum optics would not provide a practical path to efficient and scaleable quantum computation, and most current efforts to achieve a scaleable quantum computer have focussed on solid state implementations. This orthodoxy was challenged recently when Knill et al. showed that given single photon sources and single photon detectors, linear optics alone would suffice to implement efficient quantum computation. While this result is surprising, the complexity of the optical networks required is daunting. In this talk we propose an efficient scheme which is elegant in its simplicity. We indicate how fundamental single and two qubit gates can be achieved. By encoding the quantum information in multi-photon coherent states, rather than single photon states, simple optical manipulations acquire unexpected power. As an application of this new information processing ability we investigate a class of high precision measurements. We show how superpositions of coherent states allow displacement measurements at the Heisenberg limit. Entangling many superpositions of coherent states offers a significant advantage over a single mode superposition states with the same mean photon number.

The random matrix ensembles are applied to the quantum statistical two-dimensional systems of electrons. The quantum systems are studied using the finite dimensional real, complex and quaternion Hilbert spaces of the eigenfunctions. The linear operators describing the systems act on these Hilbert spaces and they are treated as random matrices in generic bases of the eigenfunctions. The random eigenproblems are presented and solved. Examples of random operators are presented with connection to physical problems.

Cascading of quadratic nonlinearity has been attracting great interests for its potential application to parametric devices, such as phase conjugators or effective Kerr media. In most configurations, the device consists of a single nonlinear element with uniform phase-mismatch. Cascading of several elements with different phase-mismatch has been theoretically investigated and predicted to improve performance of the device for classical applications. In this paper, amplitude squeezing in second-harmonic generation using cascaded quadratic nonlinear elements is numerically analyzed. The analyses are based on linearization of nonlinear coupling equations, where interacting fields are approximated as plane waves. Phase-mismatch of each element is varied independently and tolerance of squeezing performance to the fluctuation of the phase-mismatch is also investigated. It is predicted that the performance as a squeezing device can be also superior to that of a single element device, if a proper combination of the phase-mismatch of each element is chosen. For the fundamental wave, the tolerance to the fluctuation of the phase-mismatch will improve by nearly tenfold compared with the single element case. For the harmonic wave, squeezing beyond the limit of perfect phase-matched case (3dB) will be available, though the tolerance to the fluctuation of the phase-mismatch is quite small. These improvements can be attributed to the nonlinear phase rotation that keeps squeezed axis coincided with the amplitude phase in a stable manner.

We consider two systems in the weak driving field limit. The first is an optical parametric oscillator, the transmitted field of which is highly bunched. We discuss a conditioned measurement of the second order intensity correlation function that yields antibunching. The second system we consider is a single two level atom inside a weakly driven cavity. Here we consider cross correlations between the transmitted and fluorescent fields. A strong asymmetry in delay time has been noted by Denisov et. al., here we find strong violations of a classical inequality for the cross correlation.

The quantum noise properties of laser diodes has been a topic of interest essentially since the first development of such devices. A particular recent focus for such activities has been created by work, initiated by Yamamoto and co-workers, directed at generating sub-Poissonian or squeezed light using these devices. Although there was a significant early success in experimentally demonstrating appreciable noise squeezing using laser diodes it was found that not all laser diode designs are suitable for this purpose. Subsequent work in the literature has indicated that a spectrally pure laser diode should be will be of great interest in this context. It is noted , however, that great care must also be taken to control the transverse mode structure of such lasers. Recent work has highlighted the "contamination" of the lasing mode which may arise due the noise of non-lasing modes in nominally single-mode lasers. In that work it was shown that excess noise due to non-orthogonal transverse modes - so-called Petermann excess noise - appears in the laser quantum intensity noise. In our previous work we have shown that such excess noise can be eliminated by suitable choice of laser structure: namely one with high-reflectivity facet mirrors.The identified low-noise symmetric high reflectivity ( SHR) structure had a practical limitation on the available optical output power. The aim of the present paper is to examine means for removing this limitation by the use of a one-dimensional array of SHR laser diodes. An analysis is performed of quantum noise enhancement due to asymmetric coupling between elements of a laser diode array. A general formalism is presented which facilitates the estimation of the quantum noise arising due to cross contamination between lasing modes of the array. Consideration is given to limiting cases where compact expressions are obtained for the asymmetry-induced excess noise.

Just as it is possible to stabilize the frequency of an electromagnetic field to an atomic resonance between energy eigenstates, so too is it possible to stabilize the amplitude (or 'brightness') of a field to atomic parametric resonances, the so-called Rabi-resonances. For ease of reference, and by analogy to the atomic clock, we have coined the term 'atomic candle' for this quantum-mechanical, amplitude-stabilization system. Though the atomic candle was originally developed to stabilize microwave power in gas-cell atomic clocks, thereby eliminating a source of timekeeping instability in these devices, the atomic candle's applications extend well beyond the area of precise timekeeping. Basically, the atomic-candle provides a means for detecting and controlling subtle amplitude changes in electromagnetic fields at very low Fourier frequencies (i.e., f < 0.1 Hz). In the present work, we discuss a number of atomic candle applications: laser stabilization, absorption/refractive-index measurements, observations of cavity mode stability over very long time scales (i.e., 50 days), and measurements of low-frequency absorption/scattering fluctuations along a propagation path.

Medium frequency (100kHz - 1MHz) measurements of electrical noise power spectrum densitiy in DBR tunable lasers show particular behaviour around threshold, compared to classical edge-emitting structures. In this paper, we consider structures in which tunability is made by current injection. Standard monomode (SMSR > 40 DB) non tunable DBR lasers Noise Level follow a global shot-noise tendancy, except around the laser threshold current level (called Ith). In these structures, a strong excess of noise is classically established at Ith. Next, at Ith+epsilon, the noise level goes down again to the shot noise level. In DBR tunable lasers, this behaviour is exactly the same, except that epsilon grows up when the current level in the Bragg section gets stronger. The aim of this paper is to establish a link between the 'epsilon' factor and the current level in the Bragg section.

In this paper, the noise properties of vertical cavity semiconductor optical amplifiers (VCSOAs) operated in reflection mode are studied. Expressions for noise sources contributing to the total noise detected at amplifier output are derived, based on the photon statistics master equations. The noise figure, defined as the degradation of signal-to-noise ratio (SNR), is analyzed using the assumption that spontaneous emission-signal beat noise dominates. The analysis shows that the noise figure of reflection mode VCSOAs has the same values as that in transmission mode as long as amplifier gain is high (G>>1). Furthermore, simulations depict the dependence of noise figure on device parameters and bias conditions, as well as reveal the importance of the low reflectivity front mirror and the high reflectivity rear mirror for low noise operation. In addition, the noise figure analysis results are compared with experimental measurements, in which amplified spontaneous emission (ASE) power is measured by an optical spectrum analyzer and the noise figure is obtained from the ASE power and the amplifier gain. The measured data are in good agreement with the theoretical predictions.

Phase-sensitive detection of resonance fluorescence, i.e., allowing the light emitted from an atom which is undergoing Rabi oscillations in free space to interfere with a coherent local oscillator (LO) beam, has drawn considerable attention throughout the history of quantum optics. Recently, phase-sensitive squeezing spectra for single-atom resonance fluorescence were observed for the first time using strongly-driven long-lived atoms. A measurement of phase-sensitive intensity correlations for this system will be presented. Using physical arguments I will construct the phase-sensitive two-time intensity autocorrelation function, and elucidate the role played by quantum fluctuations in phase-dependent resonance fluorescence.

We predict the appearance of purely quantum effects within a radiation field upon reflection on a movable mirror. The model of an optical cavity having an oscillating end mirror is employed, and the role of thermal noise associated to this mechanical motion is studied.

We show how to beat the `fundamental' noise limits in optical lithography using entangled quantum states. In this talk we will give the theoretical background to optical lithography and its quantum formulation. A proof-in-principle experimental demonstration is described.

In the weak-field limit, resonant absorption is viewed as a passive process: an optical field impinges on an atom, and within some cross-sectional area the atom has a high probability for absorbing the radiant energy. Absorption, however, is a dynamic process. Consequently, though a singlemode laser is highly monochromatic, the field's phase noise (i.e., quantum noise) generates fluctuations in the atom's absorption cross section. Laser phase noise (PM) thereby gives rise to absorption cross-section noise, and hence fluctuations in the medium's transmitted light intensity (AM). Following a brief overview of the PM-to-AM conversion process, we consider the role of collisions on PM-to-AM conversion efficiency in the weak-field regime. Specifically, the relative-intensity-noise of a diode laser, tuned to the Rb D1 transition, was measured after it passed through a rubidium/nitrogen vapor. Varying the nitrogen pressure, we found that rapid collisional dephasing decreased the efficiency of PM-to-AM conversion. Examining the rubidium hyperfine transition lineshape as a function of nitrogen pressure, we then found that pressure-broadening increased the transition's signal-to-noise ratio when limited by the PM-to-AM conversion process.

Analytical expressions for the intensity and frequency/phase noise of single mode semiconductor lasers based on quantum-mechanical rate equations are derived. Correlated photons, electrons, and phase Langevin noise sources and their auto and cross-correlation relations are presented along with a novel self-consistent normalized laser model that includes the laser's correlated noise sources. A Symbolically Defined Device (SDD) is constructed using the proposed normalized model and implemented in Agilent's Advanced Design System (ADS) CAD tool. Dynamic laser characteristics are predicted using the SDD implementation for 1300 nm InGaAsP/InP lasers. The results of time domain dynamic simulations of photons, carriers, optical output power, and phase - with and without the effects of the noise - are presented. Simulation results are used to show the effects of random noise on both the phase and optical power output of semiconductor lasers. Simulation results are analyzed to demonstrate the resonance frequency shift dependence on the bias current levels, the relation between the frequency response and the bias current and the dependence of the laser line width broadening on the frequency fluctuations. Comparison between the presented results and other published results (simulations and measurements) show good agreement while achieving simulation time enhancement. The suitability of the proposed models for the study and characterization of the performance of complete systems in both circuit and system simulations is examined.

The spectral purity of laser radiation is a key point in the performance of coherent optical network. As 850nm VCSELs are being used in short distance interconnections, the evaluation of the frequency noise level is essential. Using a Fabry-Perot cavity as a frequency discriminator, the frequency noise spectrum is being investigated in the medium frequency and high frequency range (up to 1GHz). Frequency noise spectra show a 1/fn part in the medium frequency domain and a traditional white noise part in the high frequency domain. The aim of this paper is to present our measurements concerning 850nm-selectively-oxidized VCSELs and to investigate the different factors which have a quantitative influence on the frequency noise spectrum.

The knowledge of the noise levels is important for pump laser diodes as it allows to study and to locate the noise sources and their origin. 980 nm fresh and aged pump laser have been characterized by using electrical and optical noise measurements. In this work, we present the electrical and optical noises at low - medium frequency for fresh pump laser diodes emitting at 980 nm (reference laser), and we study the parametric evolution and the defects generated in aged 980nm single-mode ridge lasers, stressed during 400hrs at 50°C and high current injection (500 mA) (aged laser). The dynamic resistance, above threshold current, is not constant. It shows a proportionality of about RdμI-1/2. The injection of the carriers is associated to space charge limited current effect (SCLC). The study of the electrical and optical noise which represents the fluctuations of intensity at low and medium frequency is very significant of degradation of the active layer. The spectra are dominated by 1/f (fliker) noise at very weak current. And at weak current, the Current Noise Spectrale Density (CNSD) at 10 Hz is dominated by I^3/2. The deffect is associated with carrier transport controlled by the interfaces n⁺n^- and p⁺p^- and the trapping defect density near the n⁺n^- and p⁺p^- interfaces, also it due to pinching of the space charge limited current SCLC effect An excess noise due to longitudinal mode hopping is related with output power fluctuations.

The HADAMARD principle is known in optics as a multiplex technique. It describes the mode with the most advantageous increase of the signal-to-noise ratio (SNR) in terms of scanning (Fellget advantage). The maximum increase of SNR, we call it gain, is (n+1)/(2On), where n is the number of multiplexing. It is valid in the case of pure detector noise. The multiplex encoding Hadamard pattern in case of n = 7 is 1110100, whereby 1 stands for a switched on channel performed by a field selector. The signals of all (switched on) channels are detected by a single detector. n measurement steps with a cyclic change of the pattern is necessary to perform the Hadamard transformation and to get the result of each individual channel. In case of n = 7 the theoretical gain is 1.51. For all possible multiplex pattern (1100000, 1110000 and so on) the gain is theoretically investigated. A multiplexing advantage (gain > 1) is reached only by the Hadamard pattern, the inverse Hadamard pattern and for (0111111)-pattern (gain=1.08). Most of the multiplex pattern are disadvantageous. The reason for maximum gain of the HADAMARD transformation is analysed theoretically. Signal fluctuations during the measurement caused by fluctuations of the illumination or by the object under test, reduce the multiplex gain, too. So the limits for realizing a gain are estimated theoretically. Essential is the transformation procedure and its influence on the error propagation. The results could be verified by experiments with array spectrometeres. Requirements are derived by numerical simulation concerning the stability of the signals to be multiplexed. It is simulated the needed stability of the signals with increasing order of multiplexing. So the increase of the multiplex gain is limited by signal fluctuations. A realized 96 channel spectral reader is presented as a modern application of an optical multiplexing arrangement. ! M. Harvid, N. J. A. Sloane, Hadamard Transform Optics, Academic Press, 1979 ! R.A. De Verse, R.M. Hammaker, W. G. Fately, J.A.Graham, J.D.Tate, "Spectrometry and imaging using a digital micromirror array" American Laboratory, Vol. 30, 21, pp. 112-120, 1998 ! R. Riesenberg, A. Wuttig, B. Harnisch, "Optical MEMS Technology for Multiplexing in High-End Micro-Scpectrometers", Proc. SPIE 4928, 6-14, 2002 ! A. Wuttig, R. Riesenberg, “Hyperspectral imager with a facile MEMS”, Proc. SPIE 4881A, 2002, to be published ! R. Riesenberg, G. Nitzsche, W. Voigt, 'HADAMARD Encoding and other optical Multiplexing', VDI-Berichte 1694, pp. 345-350, 2002 ! A. Wuttig, R. Riesenberg, G. Nitzsche, “Subpixel Analysis of Double Array Grating Spectrometer”, Proc. SPIE 4480, pp. 334-344, 2002 ! A. Wuttig, R. Riesenberg, G. Nitzsche, “Integral Field and Multi Object Spectrometry with MEMS”, Proc. SPIE 4480, pp. 367-376, 2002 ! R. Riesenberg, G. Nitzsche, A. Wuttig, B. Harnisch, “Micro Spectrometer and MEMS for Space” in “Smaller Satellites: Bigger Business?”, edited by M. Rycroft, N. Crosby, Kluwer Academic Publisher, pp. 403-406, 2002 ! R. Riesenberg, A. Wuttig, “Optical sensors with MEMS, slit masks and micromechanical devices”, Proc. SPIE 4561, pp. 315-322, 2001 ! R. Riesenberg, “MicroMechanical Slit Positioning System as a transmissive spatial Light Modulator”, Proc. SPIE 4457, pp.197-203, 2001 ! R. Riesenberg, J. Lonschinski, “HADAMARD-Minispectrometer made by a Micro Device”, Proc. “3rd Round Table on Micro/NanoTechnologies for Space”, ESTEC, Noordwijk, The Netherlands, pp. 291 - 297, 2000 ! R. Riesenberg, U. Dillner, "HADAMARD Imaging Spectrometers“, Proc. SPIE 3753, pp. 203-213, 1999 ! R. Riesenberg, Th. Seifert, "Design of spatial Light Modulator Microdevices - Micro Slit Arrays“, Proc. SPIE 3680, Part One, pp. 406-414, 1999 ! R. Riesenberg, W. Voigt, J. Schoneich, "Compact Spectrometers made by Micro System Technology“, Sensor 97, Proc. Vol. 2, pp. 145-150,1997

Relaxation of a two-level system (TLS) into a resonant infinite-temperature reservoir with a Lorentzian spectrum is studied. The reservoir is described by a complex Gaussian-Markovian field coupled to the nondiagonal elements of the TLS Hamiltonian. The theory can be relevant for electromagnetic interactions in microwave high-Q cavities and muon spin depolarization. Analytical results are obtained for the strong-coupling regime, ₀>ν, where Ω₀ is the rms coupling amplitude (Rabi frequency) and ν is the width of the reservoir spectrum. In this regime, the population difference and half of the initial coherence decay with two characteristic rates: the most part of the decay occurs at t < (Ω₀ν)^-1/3 the relaxation becomes reversible for t ~ Ω₀^-1/3, whereas for t > (Ω₀²ν)^-1/3 the relaxation becomes irreversible and is practically over. The other half of the coherence decays with the rate on the order of ν, which may be slower by orders of magnitude than the time scale of the population relaxation. The above features are explained by the fact that at t < ν^-1 the reservoir temporal fluctuations are effectively one-dimensional (adiabatic). Moreover, we identify the pointer basis, in which the reduction of the state vector occurs. The pointer states are correlated with the reservoir, being dependent on the reservoir phase.

In this work, we give a description of the process of teleportation between Alice in an inertial frame, and Rob who is in uniform acceleration with respect to Alice. The fidelity of the teleportation is reduced due to Unruh radiation in Rob's frame. In so far as teleportation is a measure of entanglement, our results suggest that quantum entanglement is degraded in non inertial frames.