Quantum Rabi oscillation in cavity quantum electrodynamics is at the very heart of the interaction of an atomic system with a single electromagnetic field in a resonator. It has proved a powerful tool to entangle the atom with the field in the case of an empty cavity (vacuum Rabi oscillation). On the other side, as soon as the field is macroscopic, its state seems unaffected and one observes the well-known phenomenon of classical Rabi oscillation which only affects the atomic populations. We propose to experimentally investigate the frontier between those two behaviours, when one has to take into account the fluctations of the photon number. In order to do so, we let interact circular Rydberg atoms with a microwave resonator in which a mesocopic field is injected (a few tens of photons). We observe a strong correlation between specific atomic states and the phase of the injected field, which is measured by a homodyne technique. Those correlations explain in an easy way all the standard features of quantum Rabi oscillations (especially the collapses and revivals). Moreover they allow for the preparation of atom-field entangled state as well as non classical Schroedinger cat like states for the field.

For a diatomic molecule interacting with an off-resonant laser field it is shown how quantum vacuum fluctuations of the electromagnetic field act via spontaneous Raman processes on the molecular rotational degree of freedom. Furthermore, the inclusion of the molecule's centre-of-mass and the treatment of associated photon recoil effects is outlined. The obtained results form a basis for describing the combined centre-of-mass and rotational dynamics of the molecule in off-resonant, spatially varying laser fields, such as in the laser focus forming a dipole trap.

We investigate experimentally the number and phase quantum noises of the light emitted by an ultrastable nondegenerate optical parametric oscillator (OPO) above threshold. Strong intensity correlations at the photon level -- number-difference squeezing or twin beams -- have already been observed by several groups. We have recently observed the twin-beam interference of a classically phase-locked OPO and have shown that the phase-difference is antisqueezed, as expected from the number-phase Heisenberg (in)equality. In this paper we describe the realization of a stable classical measurement of the joint quadratures of an OPO, as part of our ongoing effort to generate ultrastable EPR light beams simultaneously squeezed in number difference and phase sum.

We study the possibility to reveal a weak coherent force acting on a movable mirror (probe) by coupling it to a radiation field (meter) in a cavityless configuration. We determine the sensitivity of such a model and we show that the use of entangled meter state greatly improves the ultimate detection limit. A comparison of the presented model with that involving optical cavity is also done.

We apply the quantum locking scheme recently proposed by Courty et al. [Phys. Rev. Lett. 90, 083601 (2003)] for the reduction of back action noise to the realistic case of a gravitational wave interferometer. We show that by applying an active control to each mirror of the interferometer it is possible to improve significatively its sensitivity by reducing the radiation pressure noise.

Output bits from an optical logic cell present noise due to the type of technique used to obtain the Boolean functions of two input data bits. We have simulated the behavior of an optically programmable logic cell working with Fabry Perot-laser diodes of the same type employed in optical communications (1550nm) but working here as amplifiers. We will report in this paper a study of the bit noise generated from the optical non-linearity process allowing the Boolean function operation of two optical input data signals. Two types of optical logic cells will be analyzed. Firstly, a classical “on-off” behavior, with transmission operation of LD amplifier and, secondly, a more complicated configuration with two LD amplifiers, one working on transmission and the other one in reflection mode. This last configuration has nonlinear behavior emulating SEED-like properties. In both cases, depending on the value of a “1” input data signals to be processed, a different logic function can be obtained. Also a CW signal, known as control signal, may be apply to fix the type of logic function. The signal to noise ratio will be analyzed for different parameters, as wavelength signals and the hysteresis cycles regions associated to the device, in relation with the signals power level applied. With this study we will try to obtain a better understanding of the possible effects present on an optical logic gate with Laser Diodes.

In optical coherence tomography (OCT), it is often assumed that the signal-to-noise ratio, at higher optical power regimes, is limited by beat noise. Nonetheless it was often noticed that the limiting value could not be experimentally achieved, despite minimizing the stray reflectance and increasing the optical source effective bandwidth. In this work we present a new model for the noise in a balanced OCT configuration, which accounts for the limited spectral response of fiber directional couplers, as well as imperfections in the photo-detectors. As a consequence, and due to different spectrum content between the two balanced-OCT outputs, excess photon noise is larger than previously considered. The model also allows for the determination of SNR optimized parameters for maximum performance of the balanced system, and can be applied to any coupler or broadband source. Results for optimized and non-optimized configurations, for different balanced detection configurations, implemented in an OCT system, are presented and discussed.

Photomixing in laser-assisted field emission offers promise as a new mechanism for generating terahertz radiation. A nanoscale field emission tip is much smaller than optical wavelengths, so the potential of the tip follows each cycle of the incident radiation. Electron emission responds to the total electric field (DC + radiation) in τ < 2 fs, and the current-voltage characteristics of field emission are highly nonlinear. Thus, two lasers cause current oscillations by photomixing, which can be tuned from DC to 500 THz (1/τ) by shifting the offset of the lasers. Photomixing is simulated as a stationary stochastic process in which the frequencies and phases of the incident optical radiation are random variables. The waveform of the current is determined by solving the time-independent Schroedinger equation at discrete time steps for which the potential barrier is a superposition of the incident radiation field and the static barrier. These samples satisfy the criteria of a Poisson process to allow for the discrete emission of electrons at the specified total current. The one-sided power spectral density is calculated with the FFT to produce periodogram estimates.

Soliton generation in optical fibers has been generally studied through the launch of pulses with sufficient power. Also, soliton generation can take place through modulation instability and with the amplification of noise. In this paper we will derive the gain of modulation instability and show soliton evolution through the amplification of a seeded noisy signal, which describes the generation of amplified ultrashort solitons from weak-modulated CW laser source by normalized numerical simulations.

Effective superselection rules severely alter the possible operations that can be implemented on a distributed quantum system. Superselection rules appear in e.g. the context of experiments with entangled cold gases: in this case all local operations have to conserve the local particle number. These superselection rules enforces us to reconsider the notion of nonlocality, as the new constraint implies limitations on the local operations that can be implemented. This gives rise to a novel form of nonlocality, and it is possible to associate a new nonlocal resource to it. In this paper we characterize this new resource, quantify it and discuss some applications.

We demonstrate a multipartite protocol that utilizes entanglement to securely distribute and reconstruct a quantum state. A secret quantum state is encoded into a tripartite entangled state and distributed to three players. By collaborating together, a majority of the players can reconstruct the state, whilst the remaining player obtains nothing. This (2,3) threshold quantum state sharing scheme is characterized in terms of fidelity (F), signal transfer (T) and reconstruction noise (V). We demonstrate a fidelity averaged over all reconstruction permutations of 0.73 ± 0.04, a level achievable only using quantum resources.

We report experimental generation of nonclassically correlated photon pairs from collective emission in a room temperature atomic vapor cell. The nonclassical feature of the emission is demonstrated by observing a violation of the Cauchy-Schwarz inequality. Each pair of correlated photons are separated by a controllable time delay up to 2 microseconds. This experiment demonstrates an important step towards the realization of the Duan-Lukin-Cirac-Zoller scheme for scalable long-distance quantum communication.

In the present work we review recent results concerning stochastic phenomena in semiconductor lasers with optical feedback which operate in the low-frequency fluctuation (LFF) regime. Under these conditions the output intensity of the laser shows an irregular pulsated behavior in the form of sudden intensity dropouts. In the first two sections we show numerically the existence of stochastic and coherence resonance in the dropout appearance. These resonances are caused by the help of external colored noise introduced through the pumping current of the laser. In the third section we describe a recently reported new type of stochastic resonance, where a nonlinear system shows a resonance at a frequency not present neither at its internal time scales nor at any external perturbation. This phenomenon, known as ghost resonance, is reported both numerically and experimentally.

The polarization dynamics of a vertical cavity surface emitting laser is investigated as a nonlinear stochastic dynamical system. The polarization switches in the device are considered as activation processes in a two dimensional system with a saddle cycle; the optimal way of switching is determined as the solution of a boundary value problem. The theoretical results are in good agreement with the numerical simulations.

We have recently unveiled a new dynamics in Vertical-Cavity Surface-Emitting Lasers (VCSELs), induced by a time-delayed optical feedback [M. Sciamanna et al., Opt. Lett. 28, 1543-1545 (2003)]. The optical feedback is responsible for multiple polarization switchings as we increase the injection current. If the current is fixed close to a switching point, the VCSEL exhibits a bistable regime: the laser randomly hops between the two VCSEL linearly polarized (LP) modes, this mode hopping being driven by the laser spontaneous emission noise. Each hop is accompanied by delayed feedback induced instabilities such as rapid anticorrelated oscillations in the intensities of the two LP modes at the frequency of the external cavity (EC). These rapid delay-periodic oscillations therefore complement the slow polarization bistable mode-hopping. Here we summarize our previous theoretical and experimental conclusions and we report on further statistical studies of this optical feedback induced polarization mode-hopping in VCSELs. Interestingly, we show that the addition of an optimal amount of noise on the VCSEL injection current may give rise to coherence resonance. When the noise intensity is optimal, the delay-periodic oscillations in the VCSEL mode-hopping regime exhibit a maximal regularity, i.e. the VCSEL exhibits a sequence of regular pulses at the EC frequency. This almost periodic signal is generated by the interaction between the time-delay and the noise driven mode-hopping dynamics, without the need for an external periodic signal. Our results contribute to recent investigations of coherence resonance in non excitable systems and give evidence of coherence resonance in a realistic, optical bistable system with time-delay, that is, a mode-hopping VCSEL subject to optical feedback.

In this paper, we present the effect of grating structure on Relative Intensity Noise (RIN) in Distributed Feedback (DFB) laser diode. We analyze the noise in three types of grating shape including longitudinally uniform, concave and convex depth. It is shown that the concave grating against uniform and convex structure is suitable for reducing the Spatial Hole Burning (SHB) effect, but is not appropriate for low noise DFB lasers. According to the results of analysis, in uniform grating, RIN decreases when the corrugation depth increases. In concave and convex structure, grating depth is composed of fixed and variable parts. When fixed part of grating depth is constant, increasing variable amplitude of grating reduces RIN and when the variable part of grating is constant, increasing fixed part of grating reduces RIN. In all of the three type structures, RIN for the symmetric grating is lowest. Also with decreasing RIN, relaxation oscillation frequency decreases and when the SHB effect occurs, the rate of this decreasing is low. We conclude a special shape of grating that has low SHB effect and low noise in optical communication systems.

We find that, although inversion noise has only a marginal effect on the linewidth of a semiconductor laser in CW operation, in the presence of dynamics it may play a key role in determining the final dynamical state. It is therefore essential to include both field noise and carrier noise of realistic strength when analysing semiconductor laser dynamics. Next we investigate the influence of quantum noise, both field and carrier noise, on the highly complex nonlinear dynamics that arise in a single-mode semiconductor laser subject to filtered optical feedback. Our numerical study based on stochastic rate equations shows that for a wide range of filter widths the noise may lead to qualitatively different dynamics than predicted by a deterministic analysis. In particular, we find that certain attractors that are predicted in the absence of noise may no longer be available when the effects of noise are correctly incorporated, while others show remarkable robustness instead. In general, the results confirm that carrier noise in the laser can influence the dynamics quite substantially. Finally, we present numerical results of noise-induced pulsations in a semiconductor laser with optical injection. We show that, close to the locking edge, patterns of single, two and three pulses can be excited and we suggest that experimental study of this multi-pulse excitability be based on pulse timing statistics.

We propose a technique that allows to laser cool a nanomechanical resonator mode to its motional ground state. The method is based on resonant laser excitation of a phonon sideband of an embedded self-assembled quantum dot. The strength of this sideband coupling is determined directly by the difference between the electron-phonon couplings of the initial and final states of the quantum dot (QD) optical transition. When compared with the analogous sideband-cooling of a trapped-ion (TI), we find novel quantum interference effects in the cooling cycle and that the finite Q-value can lead to regimes where the final occupancy is proportional to the initial one -- with their ratio determined by the product of the "effective Lamb-Dicke" parameter and the Q-value. The interactions underlying this cooling scheme also provide a tool-box for quantum state engineering in these systems.

We present results of comprehensive investigations of the intensity noise of continuous wave (CW) operated quantum cascade lasers (QCLs) under various operation conditions. These experiments are performed with the aim to measure and understand the intensity noise of QCLs, and furthermore to explore the potential to generate non-classical light, i.e. squeezed states of light with sub-shot intensity noise with these new devices. First, we measure the relative intensity noise (RIN) and find that the relative intensity noise behaviour of QCLs is different from that of bipolar edge emitting lasers and Vertical-Cavity Surface-Emitting Laser (VCSELs). These observations are explained by a semi-classical noise description in which the particular level scheme of the QCLs is incorporated via an effective cascaded three-level model. Second, we compare this intensity noise with respect to the shot-noise level in order to explore the possibility of generation of squeezed states of light in the mid-infrared spectral domain with QCLs. In our first experiments we find only an intensity noise 2 dB above the shot noise level. Finally, these experimental results, the possible origin of the observed non-successful sub-shot noise generation, as well as possibilities for future trends, applications and the limitations of these non-classical states of light with respect to sensing and spectroscopic applications are discussed.

We measure variations in optical and radio frequency (rf) noise for a diode laser operating single mode in an external grating cavity (EGC). The laser operates at fixed current and temperature; and its frequency is varied within a single EGC mode by changing the length of the EGC using a piezo-electric transducer. The major features of the rf noise spectrum are a doublet occurring near the EGC mode separation, and its multiples, and a low frequency rf continuum in the 0-100 MHz frequency range. The optical spectrum, which is measured using a scanning Fabry-Perot interferometer, consists of the lasing mode and subthreshold nonlasing sidemodes. The origin of these sidemodes is four-wave mixing in the laser crystal. As the laser frequency is varied within a given EGC mode, the features of the rf spectra and the optical sidemode spectra all vary systematically. Some of the observed variations can be explained simply and others cannot.

In this manuscript we analyze experimentally the noise effects on the modal dynamics of semiconductor lasers. Modal switching is the dominant feature of multimode semiconductor lasers. In bulk lasers, two modes coexisting for the same values of the parameters switch under the action of the noise present into the system (mode-hopping). In this kind of laser we give evidence of stochastic resonance of the mode-hopping under modulation of the laser pump. In quantum-well lasers the modal dynamics is radically different: it consists of a periodic switching among several longitudinal modes, following a well determined sequence from the bluest to the reddest mode in the optical spectrum. The switching dynamics of the modes obeys to a perfect antiphase leading to an almost constant total intensity output.

Spontaneous emission of an atom in contact with the modified radiation field of a Photonic band gap (PBG) material is known to present a typically non-Markovian behavior. In addition, the presence of a gap of forbidden frequencies in the photonic density of states (DOS), produces residual population of the excited level, and population inversion when the atomic system is driven by an external laser field. It's our aim to study those effects using non-Markovian Stochastic Schroedinger equations (NMSSE). This formalism permit us to describe the evolution of the atom in terms of a wave function, |ψ_t(z)], which due to the presence of the radiation field depends on a stochastic variable z_t. Having a singularity at the origin, the models of field correlation function usually found in literature, are not suitable to generate the corresponding z_t. We have proposed a new correlation function that do not have this problem, and reproduces all the important physical phenomena of the system under study. The results obtained with NMSSE are compared with those of the master equation, since the ensemble average of stochastic trajectories gives the reduced density matrix of the system, ρ_s. In addition, we propose a new non-Markovian master equation derived from the stochastic formalism, which in contrast to the current models of master equation preserves positivity for the problem under study.

Triggered single-photon sources produce the vacuum state with non-negligible probability, but produce a much smaller multiphoton component. We describe a method for increasing the probability of a single photon via a chain of beam splitters. This method has the drawbacks that it introduces a significant multiphoton component, and it can not be used to increase the probability for a single photon above 1/2. Part of the reason for these drawbacks is the incoherence in the photon sources. If the photon sources produced pure states rather than incoherent superpositions, it would be possible to obtain a perfect single photon output. The method for incoherent inputs is robust against detector inefficiencies, but sensitive to dark counts and the multiphoton component in the input.

Semiconductor lasers subject to optical feedback are of both scientific and technological importance. The laser and external mirror form a compound cavity which can be modeled using a coupled cavity approach. Using this approach we have calculated the longitudinal mode frequencies and the associated mode lifetimes of all the modes in the system. We have found that for a narrow range of external cavity reflectivities, the mode lifetimes become almost degenerate. In this regime the mode lifetimes become highly sensitive to variations in the refractive index of the laser and external cavity reflectivities. Close inspection of this regime has revealed ever finer detail, suggesting a fractal structure to the mode solutions. The calculations have been undertaken in the 'cold cavity' limit and indicate a catastrophic loss of mode discrimination, even in a system with no inherent material gain. In the short cavity limit the external reflectivity required to induce the loss of mode discrimination varies as a function of external cavity round-trip time.

Quantum error correction will be an indispensable ingredient of large-scale quantum computations. Conventional quantum error correction codes (QECC) have been devised with an independent-error model in mind, but one may expect that the noise affecting a system of qubits will, in general, exhibit nonzero correlations in time, or space, or both. This talk will present a brief introduction to the principles of quantum error correction, followed by a discussion of the performance of conventional QECCs in the presence of correlated noise.

We analytically show that it is possible to perform coherent imaging by using the classical correlation of two beams obtained by splitting incoherent thermal radiation. The case of such two classically correlated beams is treated in parallel with the configuration based on two entangled beams produced by parametric down-conversion, and a basic analogy is pointed out. The results are compared in a specific numerical example.

Understanding quantum noise is essential for accurately creating desired quantum states and for examining a given state's evolution in any protocol. Using spontaneous parametric downconversion, we can create a wide variety of single- and two-qubit polarization states, including nearly perfect Bell states, mixed states (i.e., "noisy" states) and maximally entangled mixed states (MEMS). To characterize these states we use several different measures, including fidelity, "tangle" and linear entropy. In the course of our experiments, we have discovered and numerically investigated an extreme imbalance in the sensitivity of these different two-qubit state measures. We have also experimentally realized a "Procrustean" filtering technique to remove noise from MEMS. For moderate amounts of filtering, the experimental procedure works as desired to increase the tangle and decrease the linear entropy. However, for large amounts of filtering, the process becomes dominated by perturbations in the starting density matrix. The final outcome is a pure (i.e., zero entropy) product state (i.e., zero entanglement).

Quantum trajectory equations are formulated for continuous variable teleportation, which model the generation of finite bandwidth squeezed light, the homodyne measurements carried out by Alice, and take into account the continuous feed-forward of Alice's measurement results to Bob. The formulation is multi-mode and provides direct access to correlation functions of the output field detected by Victor. Three unravellings of the dynamics are considered, corresponding to Victor's choice of direct, homodyne, or heterodyne detection of the output field. Numerical results for the teleportation of a vacuum-state input field are presented.

Quantum feedback control is the control of the dynamics of a quantum system by feeding back (in real time) the results of monitoring that system. For systems with linear dynamics, the control problem is amenable to exact analysis. In these cases, the quantum system is equivalent to a stochastic system of classical phase-space variables with linear drift and constant diffusion, and with a measured current (e.g. a homodyne photocurrent) linear in the system variables. However, the classical evolution is constrained in order to represent valid quantum evolution. We quantify this in terms of a linear matrix inequality (LMI) relating the drift and diffusion (a sort of zero temperature fluctuation-dissipation theorem), and another LMI for the covariance matrix of the possible conditioned states (i.e. under all possible monitoring schemes consistent with the master equation). For manipulable systems (i.e. where the experimenter has arbitrary control over the parameters in a Hamiltonian linear in the system variables) the covariance of the conditioned state is all that is needed to calculate the effectiveness of the feedback. In this case the double optimization problem reduces to a semidefinite program, which can be solved efficiently in general. We illustrate this with an example drawn from quantum optics.

We investigate the dynamics of short linear chains consisting of two-level systems (atoms) coupled by the electromagnetic field. The environment of photon modes acts as a source of noise and leads to the disappearance of the initially present multipartite entanglement. The rate of this process (entanglement degradation) depends on the separation of the atoms, and also on the initial state. By the aid of the appropriate entanglement witnesses we show that this rate is exceptionally low for the so-called subradiant states. Below one resonant wavelength of atomic separation the effect of the environmental noise is weaker than the dipole-dipole interaction and multipartite entanglement can be formed in the initial stage of the time evolution.

A protocol for considering decoherence in quantum games is presented. Results for general two-player, two-strategy quantum games subject to decoherence are derived and some specific examples are given. Decoherence in other types of quantum games is also considered. As expected, the advantage that a quantum player achieves over a player restricted to classical strategies is diminished for increasing decoherence but only vanishes in the limit of maximum decoherence when the results of the game are randomized.

In many optical and atomic systems it is now possible to monitor an individual quantum system with high signal to noise and feed back by altering the system dynamics in real time. This motivates further development of quantum mechanical descriptions of feedback control. We discuss recent work on closed loop control of open quantum systems, focusing on general linear systems for which the statistics of the problem are Gaussian. Such systems may be realized with linear optics, parametric amplifiers and homodyne detection. This problem allows a direct comparison with the classical linear, quadratic cost, Gaussian noise (LQG) optimal control problem. This highlights the key distinction between the quantum and classical theories for linear systems: that increased measurement sensitivity may run counter to the control objectives since it increases the backaction noise. While in an idealized classical control problem it is always preferable to obtain a better sensor, quantum mechanical problems generically have an optimal sensitivity since quantum mechanical measurements irreducibly disturb the system. The general theory will be illustrated by reference to specific simple examples.

The issue of estimating how "macroscopic" a superposition state is, can be addressed by analysing the rapidity of the state's evolution under a preferred observable, compared to that of the states forming the superposition. This fast evolution, which arises from the larger dispersion of the superposition state for the preferred operator, also represents a useful characteristic for interferometric applications. This approach can be compared to others in which a superposition's macroscopality is estimated in terms of the fragility to dissipation.

The application of stochastic cooling to trapped atoms is theoretically studied. We develop a quantum-field approach and investigate the fundamental limits of stochastic cooling, being determined by quantum-noise effects such as atom-number fluctuations and measurement back action. Moreover, using a spatially resolved operation, acting only on a fraction of the atomic cloud, is shown to lead to additional noise effects.

We consider the use of feedback control during a measurement to increase the rate at which a quantum system is purified, and more generally the rate at which near-pure states may be prepared. We derive the optimal bang-bang algorithm for rapid state preparation from an initial completely mixed state when the measurement basis is unrestricted, and evaluate its performance numerically. We also consider briefly the case in which the measurement basis is fixed with respect to the state to be prepared, and describe the qualitative structure of the optimal bang-bang algorithm.

Fluctuations in the field of a 2^nd order nonlinear multi-mode parametric downcoverter exhibit nonclassical correlations in the transverse plane. We present results of measurements of the classical pattern for a degenerate, multi-mode parametric optical parametric oscillator (OPO) operating above threshold. We also present results of autocorrelation measurements of intensity fluctuations in the transverse plane both in the near field and in the far field with the OPO operating both below and above threshold -- a method we believe will ultimately enable us to display the nonclassical correlations of the OPO output.

Single photon count distributions at the outputs of a Mach-Zehnder interferometer are highly dependent on the phase difference between the two arms of the apparatus, so photocount records can be used to estimate an unknown optical phase. Experimental results have shown that phase information can be inferred from the data even at low mean input intensities of ⪅10 photons. Here we consider the optimal Bayesian parameter estimate for the model used by a previous frequentist analysis. In the limit of high input intensity the observation is well-modelled as an intensity measurement of a classical wave in Gaussian measurement noise, however in the low intensity regime this simple model does not apply. It seems that no generally valid closed-form estimator for this problem exists without making the Gaussian approximation. Moreover the 2π radian ambiguity in phase estimates presents a problem in defining cost functions to compare estimator performance, and we consider two reasonable alternatives. We present a numerical study of the experiment along with a novel numerical approach to this problem which out-performs the existing estimators and with a squared error that approaches the Cramer-Rao lower bound previously derived in the literature, in the limit where that bound is valid.

The effect of intensity fluctuations on laser-induced coupling of electronic and vibrational states of a trapped ion is studied analytically. Different types of noise relevant to the experiments are considered. The resulting decoherence phenomenology is shown to present nontrivial characteristics. Noise color leads to nonexponential decay of the coherences: after the initial decay, determined by the probability distribution, a transient period specific to the noise spectrum is apparent; at large times, exponential decay sets in for widely different noise properties. The detection of these features in the evolution of an initial coherent state of the vibrational mode is discussed.

Imaging digital systems are widely used nowadays. CCD and CMOS sensors are embedded in a lot of metrologic devices for metrology in a lot of devices. One of these applications is the characterization of laser beams. For these kinds of applications, it is necessary to use cameras with high dynamic range. Some algorithms have been proposed in the past for this purpose. But, normally they enhance not only the dynamic range but the noise sensor too. In this paper we have applied an automatic algorithm to classify the different noise processes appearing in a CCD matrix. The method is based on a principal component expansion of the covariance matrix of some frames taken with the camera. It is possible to classify not only non-uniformity noise of the detector matrix, but also those contributions due to electronics and electronic interference and vibrations. Some of these noise processes represent only a very low amount of the total noise. A method to filter these noises is also presented.

In this paper, we propose and demonstrate a new and original model for theoretical calculation of the noise power spectral density (NPSD) in phase-modulated optical links. The phase modulation is operated in the RF frequency range by an external phase modulator. The NPSD is derived for the first time in interferometric systems, by considering all effects such as the 1/f FM noise of the laser, and white noise applied to light from a 1550 nm DFB laser, with phase modulation. The results show for the first time the influence of the phase modulation index, modulation frequency, and interferometric delay in the phase-to-intensity noise conversion. Theoretical calculations and experimental results of conversion of FM-noise to intensity noise in an optical link are shown with good agreement.

We show how the probabilistic interpretation of quantum mechanics leads to unavoidable quantum noise, even for deterministic evolution of the quantum state. Far from being a nuisance, this consequent quantum randomness is at the heart of new concepts in technology. We discuss explicitly the quantum random number generator based on the partitition noise at the beam splitter. Another application of quantum noise is quantum cryptography, where the randomness of the detection event leads to the generation of a random cryptographic key at two locations without the necessity of transporting that key from A to B. Finally, we will show how quantum noise is an intrinsically important part of quantum teleportation, and we conclude with a brief discussion of the possibilities of free-space quantum communication.