Showing papers in "Journal of Modern Optics in 2001"
TL;DR: It is concluded that additional protection is necessary for currently implemented quantum key distribution systems against the large pulse attack, a new strategy of eavesdropping on quantum cryptosystems, which eliminates the need of immediate interaction with transmitted quantum states.
Abstract: In this paper so-called ‘large pulse attack’ is investigated. This attack is one of the possible methods of conventional optical eavesdropping, a new strategy of eavesdropping on quantum cryptosystems, which eliminates the need of immediate interaction with transmitted quantum states. It allows the eavesdropper to avoid inducing transmission errors that disclose her presence to the legal users. As an object of the eavesdropping, phase-state fibre optic schemes are considered. With large pulse attack, settings of transmitting and/ or receiving apparatus are interrogated by external high-power light pulses. Applicability conditions of this method are given. Type and amount of information learned by the eavesdropper is estimated, depending on parameters of the interrogating pulse and apparatus. An experimental set-up for an eavesdropping experiment is proposed and results of successful preliminary measurements are presented. It is concluded that additional protection is necessary for currently imple...
175 citations
TL;DR: In this article, the performance of three types of InGaAs/InP avalanche photodiodes was investigated for photon counting at 1550 nm in the temperature range of thermoelectric cooling.
Abstract: The performance of three types of InGaAs/InP avalanche photodiodes is investigated for photon counting at 1550 nm in the temperature range of thermoelectric cooling. The best one yields a dark count probability of 2.8 × 10−5 per gate (2.4 ns) at a detection efficiency of 10% and a temperature of -60°C. The afterpulse probability and the timing jitter are also studied. The results obtained are compared with those of other papers and applied to the simulation of a quantum key distribution system. An error rate of 10% would be obtained after 54 km.
158 citations
TL;DR: In this paper, the authors characterized the fluorescence behavior of silicon avalanche photodiodes in the experimentally simple passive quenching configuration and discuss implications for their use in quantum cryptography systems.
Abstract: Silicon avalanche photodiodes are the most sensitive photodetectors in the visible to near-infrared region for a wavelength <1000 nm. However, when they are used for single photon detection in a Geiger mode, they are known to emit light on the controlled breakdown used to detect a photoelectron. This fluorescence light might have serious impacts on experimental applications like quantum cryptography or single-particle spectroscopy. We characterized the fluorescence behaviour of silicon avalanche photodiodes in the experimentally simple passive quenching configuration and discuss implications for their use in quantum cryptography systems.
132 citations
TL;DR: In this paper, the angular momentum of the light from passing through a birefringent particle is measured by measuring the change in angular momentum, and the optical torque acting on it is measured.
Abstract: In recent years there has been an explosive development of interest in the measurement of forces at the microscopic level, such as within living cells, as well as the properties of fluids and suspensions on this scale, using optically trapped particles as probes. The next step would be to measure torques and associated rotational motion. This would allow measurement on very small scales since no translational motion is needed. It could also provide an absolute measurement of the forces holding a stationary non-rotating particle in place. The laser-induced torque acting on an optically trapped microscopic birefringent particle can be used for these measurements. Here we present a new method for simple, robust, accurate, simultaneous measurement of the rotation speed of a laser trapped birefringent particle, and the optical torque acting on it, by measuring the change in angular momentum of the light from passing through the particle. This method does not depend on the size or shape of the particle or the laser beam geometry, nor does it depend on the properties of the surrounding medium. This could allow accurate measurement of viscosity on a microscopic scale.
102 citations
TL;DR: In this paper, an optical interpretation for the Lie algebra's symmetry operators of the paraxial wave equation is proposed, where angular momentum operator is used to derive a relation for the expression of the angular momentum of an arbitrary light field in terms of angular harmonics.
Abstract: This paper proposes an optical interpretation for the Lie algebra's symmetry operators of the paraxial wave equation. In particular, the angular momentum operator is used to derive a relation for the expression of the angular momentum of an arbitrary light field in terms of angular harmonics. Furthermore, experimental results are presented demonstrating a filter that extracts angular harmonics from different Gauss-Laguerre modes.
94 citations
TL;DR: In this paper, the authors present a method for the compensation of the aberrations appearing when a lensless hologram of a microscopic object is reconstructed using a relatively low resolution device (CCD sensor).
Abstract: We present a digital method for the compensation of the aberrations appearing when a lensless hologram of a microscopic object is reconstructed. The digital hologram of the microscopic object is recorded on a relatively low resolution device (CCD sensor). An expansion of the hologram by interpolation of the recorded intensity is performed in order to increase the number of pixels. For digital reconstruction of the wavefronts the expanded hologram is multiplied by the reference wave followed by simulation of the diffraction using the Rayleigh-Sommerfeld propagation relation. Experimental results are presented.
80 citations
TL;DR: In this article, two eavesdropping strategies taking advantage of multiphoton pulses in faint laser QKD are presented, and they conclude that, as long as storage of qubits is technically impossible, faint LQD is not limited by this security issue, but mostly by the detector noise.
Abstract: The technological possibilities of a realistic eavesdropper are discussed. Two eavesdropping strategies taking advantage of multiphoton pulses in faint laser QKD are presented. We conclude that, as long as storage of qubits is technically impossible, faint laser QKD is not limited by this security issue, but mostly by the detector noise.
78 citations
TL;DR: In this paper, an experimental investigation of the emission characteristics for down-converted photons in order to investigate the possibility of high brightness sources for correlated photon pairs is presented, and possible ways to increase the collection efficiency for polarization entangled photon pairs are discussed.
Abstract: Type-II parametric down conversion in nonlinear optical crystals has turned out to be one of the most powerful methods to generate entangled photon pairs, and even allowed a large set of experiments on foundations of quantum mechanics and recent applications in quantum communication In this paper, we present an experimental investigation of the emission characteristics for down-converted photons in order to investigate the possibility of high brightness sources for correlated photon pairs Furthermore, we discuss possible ways to increase the collection efficiency for polarization entangled photon pairs
62 citations
TL;DR: A free space quantum cryptography system using weak laser pulses with polarization modulation by acousto-optic switching that is robust against transmission (and diffraction) losses up to 20 dB and the feasibility of exchanging keys to a low earth orbit satellite is analysed.
Abstract: We have designed and built a free space quantum cryptography system. It operates using weak laser pulses with polarization modulation by acousto-optic switching. The system also incorporates full key sifting and error correction between computers connected by a serial port. We have used this system to exchange keys over ranges up to 1.9km with absolute security. The system is robust against transmission (and diffraction) losses up to 20 dB. Building from this initial result we analyse the feasibility of exchanging keys to a low earth orbit satellite.
54 citations
TL;DR: Self-written waveguides have been observed in a variety of materials including glasses and polymers as mentioned in this paper, where the refractive index changes permanently under the influence of light that propagates through it.
Abstract: Self-written structures form dynamically in photosensitive media, in which the refractive index changes permanently under the influence of light that propagates through it. Self-written waveguides have been observed in a variety of materials including glasses and polymers. Detailed theoretical analysis of self-writing in germanosilicate glasses is in good agreement with experiments. We review recent experimental and theoretical progress in this field and indicate likely areas of future progress.
53 citations
TL;DR: In this article, the authors review recent attempts to elucidate the phenomenon of sonoluminescence in terms of fundamental principles, focusing mainly on the processes which generate the light, but other relevant facts, such as the bubble dynamics, must also be considered for the understanding of the physics involved.
Abstract: We review recent attempts to elucidate the phenomenon of sonoluminescence in terms of fundamental principles. We focus mainly on the processes which generate the light, but other relevant facts, such as the bubble dynamics, must also be considered for the understanding of the physics involved. Our emphasis is on single bubble sonoluminescence which in recent years has received much attention, but we also look at some of the excellent work on multiple bubble sonoluminescence and its spectral characteristics for clues. The weakly ionized gas models were recently studied most thoroughly and are remarkably successful when combined with a hydrodynamic bubble model, in terms of reproducing observed spectral shapes, intensities, optical pulse widths and the dependencies of these observables on the experimental parameters. Other radiation models, such as proton tunnelling radiation and the confined electron model, were not combined with hydrodynamic models and/or have freely adjustable parameters so that...
TL;DR: In this paper, the fundamental solitary wave in a cubic-quintic nonlinear medium is investigated both numerically and variationally, and an equivalent particle model is used to understand the behaviour of the numerical solutions, and while a super-Gaussian trial function has only a limited range of applicability in the variational analysis, a supersech trial function is found to match the numerical solution well for all input powers.
Abstract: Fundamental solitary waves in a cubic-quintic nonlinear medium are investigated both numerically and variationally. An equivalent particle model is used to understand the behaviour of the numerical solutions, and while a super-Gaussian trial function is found to have only a limited range of applicability in the variational analysis, a super-sech trial function is found to match the numerical solutions well for all input powers. Various limits are also investigated.
TL;DR: In this paper, a 250 μm diameter fiber of ytterbium-doped ZBLAN was cooled by 13 K from room temperature in vacuum to limit the thermal load on the fibre.
Abstract: A 250 μm diameter fibre of ytterbium-doped ZBLAN was cooled by 13 K from room temperature. The cooling was performed in vacuum to limit the thermal load on the fibre. 0.85 W of laser light at 1015 nm was coupled into the fibre. The ytterbium ions absorbed this light, and the excited atoms thermalized phononically and on average emitted light at a wavelength of 996 nm. Since the quantum efficiency of the transition was high, this resulted in a net loss of energy from the glass, producing net bulk cooling.
TL;DR: In this article, a method is described to spatially transform the annular profile of an arbitrary high-order Laguerre-Gaussian (LG) laser mode into an ultranarrow annulus using a combination of an axicon and a lens.
Abstract: A method is described to spatially transform the annular profile of an arbitrary high-order Laguerre-Gaussian (LG) laser mode into an ultranarrow annulus using a combination of an axicon and a lens. The method is shown to conserve the azimuthal phase variation of the illuminating LG mode. The thin annular (hollow) light beam generated possesses orbital angular momentum and is suitable for experimental studies with cold atoms.
TL;DR: In this article, the authors used the violation of the Bell inequality to quantify the degree of entanglement in two qubit systems and showed that the violation can be used as a measure of the extent of entrapment.
Abstract: Entanglement is a critical resource used in many current quantum information schemes. As such entanglement has been extensively studied in two qubit systems and its entanglement nature has been exhibited by violations of the Bell inequality. Can the amount of violation of the Bell inequality be used to quantify the degree of entanglement? What do Bell inequalities indicate about the nature of entanglement?
TL;DR: In this paper, the dependence of the Rayleigh range on the spot size of the beam and on the spectral degree of coherence of the light in the plane of the waist is investigated.
Abstract: The concept of the Rayleigh range, well known in the theory of coherent beams, is generalized to a class of partially coherent beams. Curves are presented which show the dependence of the Rayleigh range on the spot size of the beam and on the spectral degree of coherence of the light in the plane of the waist.
TL;DR: In this article, a model for the interferogram from double beam interference microscopes, which takes into account the coherence effects, is presented, based on the general imaging theory of a lens in defocus.
Abstract: A theoretical model for the interferogram from double beam interference microscopes, which takes into account the coherence effects, is presented. The model is based on the general imaging theory of a lens in defocus. For the case of zero relative lateral displacements between the reference and object beams a simplified expression is found for the defocus and path length dependence of the interferogram. Based on this expression the characteristics of the interferogram are studied and special attention is devoted to explaining the dependence of the fringe size on the objective numerical aperture, and the effect of the spatial and temporal coherence. For the Linnik microscope in which two objectives and a beam splitter cube are used, the effect of the mismatch between chromatic aberrations of the two objectives, and the effect of glass dispersions and misalignment of the beam splitter cube are investigated. Experimental results using the Linnik microscope are presented and they confirm the proposed...
TL;DR: In this article, the generalized master equation for a two-level atom driven by a strong classical field and damped into a "tailored" reservoir with a non-flat density of modes is derived under the Born-Markov approximation.
Abstract: The generalized master equation for a two-level atom driven by a strong classical field and damped into a ‘tailored’ reservoir with a non-flat density of modes is derived under the Born-Markov approximation. To derive the master equation the dressing transformation on the atomic operators is performed first and next the dressed operators are coupled to the reservoir and the corresponding damping rates are calculated. The modifications introduced by a strong field and/or by the reservoir with the non-flat density of modes lead to non-standard terms in the master equation, some of which are reminiscent of terms known for squeezed vacuum reservoirs. The optical Bloch equations based on this generalized master equation are obtained and solved for the steady state. The solutions are discussed from the point of view of both bare and dressed atoms. Analytical formulas for the fluorescence and probe absorption spectra are obtained and illustrated graphically.
TL;DR: In this paper, a multiple-scale perturbation method is developed to study the optical solitons described by a perturbed nonlinear Schrodinger equation, and the phase of the soliton pulse is defined.
Abstract: A multiple-scale perturbation method is developed to study the optical solitons described by a perturbed nonlinear Schrodinger equation. We show that, by properly defining the phase of the soliton pulse, we can obtain corrections to the pulse where a standard soliton perturbation approach fails. A comparison is made with results obtained by other methods as well as with numerical simulations.
TL;DR: In this article, the authors studied the propagation of flattened Gaussian beams through a paraxial optical ABCD system with hard-edge aperture and derived approximate closed-form equations of FGBs for the apertured case by means of the expansion of the circ function into a finite sum of complex Gaussian functions.
Abstract: The propagation of flattened Gaussian beams through a paraxial optical ABCD system with hard-edge aperture is studied. Approximate closed-form equations of FGBs for the apertured case are derived by means of the expansion of the circ function into a finite sum of complex Gaussian functions. The advantages of the method as compared with the straightforward integration of the Collins formula are discussed and illustrated with numerical examples.
TL;DR: A new quantum cryptography protocol with continuous variables for the construction of secret quantum keys based on pairs of Einstein-Podolsky-Rosen entangled quadratures is studied.
Abstract: We study a new quantum cryptography protocol with continuous variables for the construction of secret quantum keys. The protocol is based on pairs of Einstein-Podolsky-Rosen entangled quadratures o...
TL;DR: In this article, a polarization-based receiver for quantum key distribution incorporating an InGaAs/InP single photon avalanche photodiode (SPAD) was constructed to investigate the potential for increasing the transmission distance in long-wavelength QKD systems beyond the 50km range.
Abstract: A polarization-based receiver for quantum key distribution incorporating an InGaAs/InP single photon avalanche photodiode (SPAD) has been constructed to investigate the potential for increasing the transmission distance in long wavelength quantum key distribution systems beyond the 50km range.
TL;DR: In this article, the authors investigated the individual and aggregate electromagnetic scattering matrices, and their relations with conservation laws, reciprocity and the optical theorem, and showed that for scatterer centred transfer matrices the conservation laws and reciprocity are automatically satisfied regardless of whether or not sufficient multipolarities were retained in the description of individual scatterers.
Abstract: For systems of multiple spheres, we investigate in detail the ‘individual’ and aggregate electromagnetic scattering matrices, and their relations with conservation laws, reciprocity and the optical theorem. In order for these relations to adopt their simplest form, care is taken to completely extract both incoming and outgoing phase factors in the definitions. We illustrate that the ‘individual’ cross-sections in an aggregate are defined only in terms of part of the total field, and consequently do not individually obey conservation laws or reciprocity; these relations should be satisfied for the scattering by the entire aggregate. We demonstrate that for scatterer centred transfer matrices, the conservation laws and reciprocity are automatically satisfied regardless of whether or not sufficient multipolarities were retained in the description of individual scatterers. Derivations and results are worked out in a particularly compact and transparent formalism, including magnetic permeability contr...
TL;DR: In this article, three different schemes for producing Schrodinger cat states in Bose-Einstein condensates are outlined and the effects of loss in each of them compared and compared.
Abstract: Three different schemes for producing Schrodinger cat states in Bose-Einstein condensates are outlined and the effects of loss in each of them compared. The first scheme involves coupled interacting condensates and proves to be very fragile to loss. This is improved upon with a second scheme which first evolves a cat state in phase space and then rapidly transforms it to a number cat state. Finally a third scheme is discussed which makes use of number correlated condensates and is remarkably robust to loss. It may prove to be valuable for experimentally creating such states.
TL;DR: In this paper, the authors present a one-dimensional quantization scheme for the electromagnetic field in arbitrary planar absorbing and dispersive dielectrics, taking into account explicitly the finite extent of media.
Abstract: We present a one-dimensional quantization scheme for the electromagnetic field in arbitrary planar absorbing and dispersive dielectrics, taking into account explicitly the finite extent of media. The complete form of the electric field operator includes a part that corresponds to the free fields incident from the vacuum towards the medium and a particular solution which can be expressed by using the classical Green-function integral representation of the electromagnetic field. By expressing the classical Green function in terms of the light modes of the dielectric structure, we obtain a natural generalization to absorbing media of the familiar method of mode expansion which strictly applies to non-absorbing media. As an application of our mode expansion, we obtain general quantum-optical input-output relations relating the output photon operators in vacuum to the input photon operators and to the reservoir noise operators. The input-output relations obtained are uniquely determined by the knowled...
TL;DR: In this article, the Fourier transform and the wavelet transform were used to process the fringe carrier pattern resulting from speckle-shearing inteferometry, in which the carrier frequency is modulated by deformation of a bending plate.
Abstract: The Fourier transform (FT) and the wavelet transform (WT) methods are used to process the fringe carrier pattern resulting from speckle-shearing inteferometry, in which the carrier frequency is modulated by deformation of a bending plate. Both the amount and the sign of the first derivative of the out-of-plane displacement can be obtained by these two transform techniques in the whole field. Phase distributions of the deflection slope are compared, which shows the wavelet analysis gives a better solution with noise reduction and without deficiency of filter window choice as for that in the Fourier transform. Meanwhile, the phase values in the path along the maximum WT amplitudes give a direct map of the second derivative patterns of the deflection, which presents the same image as that given by the shearing subtraction of the phase patterns from the inverse Fourier transformation but avoids the processing of unwrapping for the phase reconstruction.
TL;DR: Dedicated security analysis against realistic attacks is used to optimize the system parameters in order to maximize the secrecy capacity for the communication over the 20km distance.
Abstract: We report on a realization of a fully automated 20km quantum key distribution system incorporating real time error correction and privacy amplification protocols carried out via the Internet. Dedicated security analysis against realistic attacks is used to optimize the system parameters in order to maximize the secrecy capacity for the communication over the 20km distance.
TL;DR: Luminescence data from potassium niobate crystals are reported which show intensity and/or wavelength variations on heating, or cooling, through the phase transition temperatures as mentioned in this paper, which can clearly identify the structural changes between the various crystalline phases.
Abstract: Luminescence data from potassium niobate crystals are reported which show intensity and/or wavelength variations on heating, or cooling, through the phase transition temperatures. The luminescence signals can clearly identify the structural changes between the various crystalline phases. The transition temperatures differ between heating and cooling. They were recorded near 247 and 491 K (heating) or 220 and 478 K (cooling). The hysteresis indicates the presence of metastable material, (e.g. a supercooled structure). The data resolve the previously cited differences in transition temperatures for KNbO3 from different laboratories. The luminescence signals show further details in the variations of spectra, intensity and transition discontinuities of the luminescence which are related to material quality between samples, even from a single supplier. The luminescence data underline the sensitivity of these crystals to structural damage from electron, X-ray or thermal treatments and offer the opportu...
TL;DR: In this article, the authors re-elaborate on the theme of the Wigner rotation as an anholonomy or geometric phase, and show that this geometric phase can be easily observed in multilayers.
Abstract: We re-elaborate on the theme of the Wigner rotation as an anholonomy or geometric phase, and show that this geometric phase can be easily observed in multilayers. We compute the value of the Wigner angle from the parameters of a compound multilayer and propose a simple optical experiment to determine it.
TL;DR: In this paper, the status of commercially available InGaAs/InP avalanche photodiodes for use as single-photon counters in the telecom wavelength region of 1550 nm is described.
Abstract: We describe the status of commercially available InGaAs/InP avalanche photodiodes for use as single-photon counters in the telecom wavelength region of 1550 nm.