Showing papers in "Journal of Modern Optics in 2007"
TL;DR: In this article, the design and characterization of InGaAs/InP single photon avalanche diodes (SPADs) for photon counting applications at wavelengths near 1.5 µm were reported.
Abstract: The paper reports on the design and characterization of InGaAs/InP single photon avalanche diodes (SPADs) for photon counting applications at wavelengths near 1.5 µm. It is shown how lower internal electric field amplitudes can lead to reduced dark count rates, but at the expense of degraded afterpulsing behaviour and larger timing jitter. Dark count rate behaviour provides evidence of thermally assisted tunnelling with an average thermal activation energy of ∼0.14 eV between 150 K and 220 K. Afterpulsing behaviour exhibits a structure-dependent afterpulsing activation energy, which quantifies how carrier de-trapping varies with temperature. SPAD performance simultaneously exhibits a dark count rate of 10 kHz at a detection efficiency of 20% with timing jitter of 100 ps at 200 K, and with appropriate performance tradeoffs, we demonstrate a 200 K dark count rate as low as 3 kHz, a detection efficiency as high as 45%, and a timing jitter as low as 30 ps.
181 citations
TL;DR: For any master equation which is local in time, whether Markovian, non-Markovian of Lindblad form or not, a general procedure is given for constructing the corresponding linear map from the initia...
Abstract: For any master equation which is local in time, whether Markovian, non-Markovian, of Lindblad form or not, a general procedure is given for constructing the corresponding linear map from the initia...
123 citations
TL;DR: The necessary performance of photodetectors used in these types of experiments, the current state of the art for different categories of detectors, and actual and future developments of single-photon counting detectors for single-molecule imaging and spectroscopy, are investigated.
Abstract: Single-molecule observation, characterization and manipulation techniques have recently come to the forefront of several research domains spanning chemistry, biology and physics. Due to the exquisite sensitivity, specificity, and unmasking of ensemble averaging, single-molecule fluorescence imaging and spectroscopy have become, in a short period of time, important tools in cell biology, biochemistry and biophysics. These methods led to new ways of thinking about biological processes such as viral infection, receptor diffusion and oligomerization, cellular signaling, protein-protein or protein-nucleic acid interactions, and molecular machines. Such achievements require a combination of several factors to be met, among which detector sensitivity and bandwidth are crucial. We examine here the needed performance of photodetectors used in these types of experiments, the current state of the art for different categories of detectors, and actual and future developments of single-photon counting detectors for single-molecule imaging and spectroscopy.
121 citations
TL;DR: In this paper, the quantum theory of rotation angles is generalized to non-integer values of the orbital angular momentum, which requires the introduction of an additional parameter, the orientation of a phase discontinuity associated with fractional values of angular momentum.
Abstract: The quantum theory of rotation angles [S.M. Barnett and D.T. Pegg, Phys. Rev. A 41 3427 (1990)] is generalized to non-integer values of the orbital angular momentum. This requires the introduction of an additional parameter, the orientation of a phase discontinuity associated with fractional values of the orbital angular momentum. We apply our formalism to the propagation of light modes with fractional orbital angular momentum in the paraxial and non-paraxial regime.
110 citations
TL;DR: In this paper, the authors discuss the advantages and limitations of the soft-photon approximation, which, they believe, provides most useful insights in the analysis of nonlinear ionization processes observed when atoms are in the simultaneous presence of intense and coherent IR and extreme ultraviolet (XUV) laser pulses.
Abstract: We address several questions related to the nonlinear ionization processes observed when atoms are in the simultaneous presence of intense and coherent infrared (IR) and extreme ultraviolet (XUV) laser pulses. This topic is of much interest in the context of the current development of new XUV and soft-X-ray coherent sources, either from high-order harmonics or from X-ray free-electron laser (XFEL) devices that can be synchronized with IR lasers. The theoretical description of this class of two- (more generally multi-) colour ionization processes is challenging for theory. Here, we discuss the advantages and limitations of the so-called “soft-photon approximation”, which, we believe, provides most useful insights in the analysis of these processes.
92 citations
TL;DR: In this article, the authors present a theoretical analysis and experimental study of the behavior of optical cavities filled with slow and fast light materials, and show that the fast-light material-filled cavities have properties useful for astrophysical applications such as enhancing the sensitivity-bandwidth product of gravitational wave detection and terrestrial measurement of Lense-Thirring rotation via precision gyroscopy.
Abstract: We present a theoretical analysis and experimental study of the behaviour of optical cavities filled with slow- and fast-light materials, and show that the fast-light material-filled cavities, which can function as ‘white light cavities’, have properties useful for astrophysical applications such as enhancing the sensitivity-bandwidth product of gravitational wave detection and terrestrial measurement of Lense–Thirring rotation via precision gyroscopy.
77 citations
TL;DR: In this article, the authors propose to redefine the candela in terms of fundamental quantum optical entities, i.e. photons, and demonstrate equivalence with existing techniques, together with new possibilities which would result from further improvements in accuracy.
Abstract: The candela, the SI (systeme internationale) unit for optical radiation, has been one of the base units since the inception of the system. The latest definition was in 1979, when it was linked to the derived unit, the watt. Advances in optical technology and the needs of the communication sector suggest that it is timely that consideration be given to redefining the candela in terms of fundamental quantum optical entities, i.e. photons. Validation of this approach will require comparison against the most accurate conventional technique, cryogenic radiometry. A definition in terms of photon number and the requirements for demonstrating equivalence with existing techniques is discussed, together with new possibilities which would result from further improvements in accuracy. Work being carried out at the National Physical Laboratory (NPL) towards these goals is described, drawing on developments of photon-counting calibration techniques and low temperature measurements, and research into single photon sourc...
76 citations
TL;DR: In this paper, the authors investigate non-Gaussian states of light as ancillary inputs for generating nonlinear transformations required for quantum computing with continuous variables, and identify the main challenges to preparing an ideal cubic phase state and describe the gates implemented with the non-ideal prepared state.
Abstract: We investigate non-Gaussian states of light as ancillary inputs for generating nonlinear transformations required for quantum computing with continuous variables. We consider a recent proposal for preparing a cubic phase state, find the exact form of the prepared state and perform a detailed comparison to the ideal cubic phase state. We thereby identify the main challenges to preparing an ideal cubic phase state and describe the gates implemented with the non-ideal prepared state. We also find the general form of operations that can be implemented with ancilla Fock states, together with Gaussian input states, linear optics, squeezing transformations, and homodyne detection with feed forward, and discuss the feasibility of continuous variable quantum computing using ancilla Fock states.
76 citations
TL;DR: In this article, a scheme for a photon-counting detection system that can be operated at incident photon rates higher than otherwise possible by suppressing the effects of detector deadtime is presented.
Abstract: We present a scheme for a photon-counting detection system that can be operated at incident photon rates higher than otherwise possible by suppressing the effects of detector deadtime. The method uses an array of N detectors and a 1-by-N optical switch with a control circuit to direct input light to live detectors. Our calculations and models highlight the advantages of the technique. In particular, using this scheme, a group of N detectors provides an improvement in operation rate that can exceed the improvement that would be obtained by a single detector with deadtime reduced by 1/N, even if it were feasible to produce a single detector with such a large improvement in deadtime. We model the system for continuous and pulsed light sources, both of which are important for quantum metrology and quantum key distribution applications.
73 citations
TL;DR: In this paper, a frequency-chirped laser pulse with a Gaussian amplitude envelope was used to transfer a single trapped ion from the ground state S1/2 to the metastable state D5/2.
Abstract: We report adiabatic passage experiments with a single trapped ion. By applying a frequency-chirped laser pulse with a Gaussian amplitude envelope, we reach a transfer efficiency of 0.99(1) on an optical transition from the electronic ground state S1/2 to the metastable state D5/2. This transfer method is shown to be insensitive to the accurate setting of laser parameters, and therefore is suitable as a robust tool for ion-based quantum computing.
73 citations
TL;DR: In this article, the authors investigated the dependence of the transverse mode content in step-index fibres on the microbending value by means of diffractive optical elements, and the results obtained allow the designing of fiber sensors with advanced characteristics such as the dynamic range and accuracy.
Abstract: Use of diffractive optical elements (DOEs) in fibre sensors is very promising. This work is dedicated to the investigation of dependence of the transverse mode content in step-index fibres on the microbending value by means of diffractive optical elements. We describe the experimental set-up and methods of experimental data processing that afford precise measurements of mode power. The LP mode power dependencies on the fibre microbending value are obtained. The results obtained allow the designing of fibre sensors with advanced characteristics such as the dynamic range and accuracy.
TL;DR: In this paper, the authors present an analysis of the propagation of light pulses through materials possessing extreme values of the group velocity and present fundamental limitations to how many pulse widths a pulse of light can be delayed or advanced.
Abstract: We present an analysis of the propagation of light pulses through materials possessing extreme values of the group velocity. We begin with an analysis of the behaviour that occurs upon propagation through materials possessing simple Lorentzian gain or absorption lines or materials possessing sharp dips in gain or absorption features. We also describe how more complicated lineshapes can be used to tailor the dispersion of a slow-light system. We furthermore present an analysis of fundamental limitations to how many pulse widths a pulse of light can be delayed or advanced. We show how these mechanisms lead to different limits for slow and fast propagation media.
TL;DR: In this paper, the effect of electron tunnelling between the two fragments of the molecular ion has been investigated and it was shown that the high harmonic spectrum of high harmonic emission generated by an intense laser pulse that probes the molecular dissociation can be suppressed.
Abstract: We analyse S-matrix-type approaches to strong-field ionization by an intense few-cycle laser pulse. We derive simple modifications of approximate S-matrix-type approaches that either neglect the effect of the ionic potential after ionization, or treat this potential perturbatively. We show how these modifications eliminate some crucial problems and artefacts, such as the ‘curse of the displaced atom’, associated with the choice of gauge in the strong field approximation. We then discuss how these approximate S-matrix-type approaches should be applied to dissociating molecules using the example of H . We show that suppression of electron tunnelling between the two fragments of the molecular ion introduces dramatic changes in the spectrum of high harmonic emission generated by an intense laser pulse that probes the molecular dissociation. For large internuclear distances and even when the active electron is fully delocalized between the two fragments, the high harmonic spectrum loses all traces of the conve...
TL;DR: In this article, an analogue quantum simulator based on trapped atomic magnesium ions is described, and basic operations to implement quantum spin Hamiltonians like a one-dimensional quantum Ising model are discussed.
Abstract: Experiments directed towards the development of an analogue quantum simulator based on trapped atomic magnesium ions are described. We report on the required initialization including ground state cooling of 25Mg+ ions for the first time—parallel to the group at NIST/Boulder. We discuss basic operations to implement quantum spin Hamiltonians like a one-dimensional quantum Ising model and some challenges to be addressed in reaching for larger scale and higher dimensional devices.
TL;DR: In this paper, the authors demonstrate a scheme for quantum communication between the ends of an array of coupled cavities, where each cavity is doped with a single two level system and the detuning of the atomic level spacing and photonic frequency is appropriately tuned to achieve photon blockade in the array.
Abstract: We demonstrate a scheme for quantum communication between the ends of an array of coupled cavities. Each cavity is doped with a single two level system (atoms or quantum dots) and the detuning of the atomic level spacing and photonic frequency is appropriately tuned to achieve photon blockade in the array. We show that in such a regime, the array can simulate a dual rail quantum state transfer protocol where the arrival of quantum information at the receiving cavity is heralded through a fluorescence measurement. Communication is also possible between any pair of cavities of a network of connected cavities.
TL;DR: In this paper, the analogous geometric transformations for spin and orbital angular momentum states of light were considered and the possibility of equivalents to the Kerr, Pockels and Faraday electro-optic effects for spin angular momentum was raised, and the extent to which an image orientation of this type might be achieved by a coherent fiber bundle, twisted around its central axis.
Abstract: We consider the analogous geometric transformations for spin and orbital angular momentum states of light. Spin angular momentum is manifested as polarization and its possible transformations are typified by those introduced by waveplates and the rotation associated with optical activity. Orbital angular momentum is associated with the mode structure of the beam and, while the action of a waveplate is similar to that of a mode converter, the equivalent analogue of optical activity is not obvious. We reason that the equivalent is a rotation of the transmitted image. We consider the extent to which an image orientation of this type might be achieved by a coherent fibre bundle, twisted around its central axis. The possibility of equivalents to the Kerr, Pockels and Faraday electro-optic effects for orbital angular momentum is raised.
TL;DR: In this paper, the first set of two-photon images were captured by a photon counting CCD camera by means of jointly counting "reflected" photons from the object.
Abstract: Differing from the early principle demonstrations, this practical ghost imaging experiment reports the first set of two-photon images captured by a photon counting CCD camera by means of jointly counting ‘reflected’ photons from the object. Interestingly, the CCD camera was not ‘looking’ at the object at all. Instead, the CCD camera was facing the chaotic light source. The output of the CCD camera was used for coincidence registration of the two-photon joint-detection events with another photon counting detector which simply collects all randomly reflected photons from the surface of the object. It is also interesting to find that the observed two-photon images are ‘distortion-free’, i.e. any disturbances made along the light path has no effect on the quality of the image. These experimental observations are not only useful for practical field-applications, but also important from a fundamental point of view. It rejects the ‘projection shadow’ idea in a non-deniable way and further explores the two-photon...
TL;DR: In this paper, a line-shaped directivity diagram of angular size 120° and uniform intensity is generated by using a mirror to form a vector function of one argument, which is then used to generate the directivity diagrams.
Abstract: We design a mirror to form a directivity diagram defined as a vector function of one argument. An analytical solution for the problem of generating a line-shaped directivity diagram from a point source is derived. The mirror calculation reduces to solving an ordinary differential equation. A mirror to generate the line-shaped directivity diagram of angular size 120° and uniform intensity is designed.
TL;DR: In this article, the authors exploit recent progress in the technology of silicon single-photon avalanche diodes (SPADs) and in the design of associated electronic circuits.
Abstract: New detector modules exploit recent progress in the technology of silicon single-photon avalanche diodes (SPADs) and in the design of associated electronic circuits. SPAD detectors with diameter up to 100 µm, good photon detection efficiency (48% peak at 550 nm wavelength) and low dark counting rate are used in these modules. Monolithic integrated active-quenching circuits (iAQC) and fast time-pickoff circuits ensure efficient photon counting and timing, with better than 50 ps FWHM time resolution and less than 50 ps centroid shift for counting rates up to 4 Mc/s. Experimental tests of the module performance and an application example are presented.
TL;DR: In this article, the concept of characteristic squeezing modes applied to a travelling-wave optical parametric amplifier pumped by an ultrashort pulse is discussed, which provides an elegant and intuitive picture of quantum statistical properties of parametric fluorescence.
Abstract: We discuss the concept of characteristic squeezing modes applied to a travelling-wave optical parametric amplifier pumped by an ultrashort pulse. The characteristic modes undergo decoupled single-mode squeezing transformations, and therefore they form a useful basis to describe the evolution of the entire multimode system. This provides an elegant and intuitive picture of quantum statistical properties of parametric fluorescence. We analyse the efficiency of detecting quadrature squeezing, and present results of numerical calculations for a realistic nonlinear medium.
TL;DR: In this article, the adiabatic loading of a Bose-Einstein condensate into an optical lattice potential was investigated, and it was shown that the limiting time scale is related to the redistribution of atoms across the lattice by single-particle tunnelling.
Abstract: We experimentally investigate the adiabatic loading of a Bose–Einstein condensate into an optical lattice potential. The generation of excitations during the ramp is detected by a corresponding decrease in the visibility of the interference pattern observed after free expansion of the cloud. We focus on the superfluid regime, where we show that the limiting time scale is related to the redistribution of atoms across the lattice by single-particle tunnelling.
TL;DR: In this paper, bound states at long-range (R∼5 μm) for pairs of Cs atoms in the 89D and neighbouring states were analyzed, due to avoided crossings between the van der Waals pair interaction potentials.
Abstract: We analyse bound states at long-range (R∼5 μm) for pairs of Cs atoms in the 89D and neighbouring states. These wells are due solely to avoided crossings between the van der Waals pair interaction potentials. The depth of the wells is ∼40 MHz, and vibrational spectra consist of hundreds of bound states. We present detailed calculations of the properties of two of these wells at different electric fields (∼ mV cm− 1), since the electric field changes the well depth and shape. We estimate bound-state lifetimes μs, lineshapes, and two-photon excitation and detection rates ∼Hz from the 6P state at a temperature of T = 40 μK for these molecules.
TL;DR: The Quantum Eye of OWL (QuantEYE) as mentioned in this paper has been developed as a possible focal plane instrument for the future OverWhelmingly Large Telescope (OWL) of the European Southern Observatory.
Abstract: A programme has been started to investigate photon properties that are not currently exploited in astronomical instruments, namely second- and higher-order coherence functions encoded in their arrival time, and the orbital angular momentum. This paper expounds the first results achieved in the study of a novel astronomical photometer capable of pushing time tagging towards the picosecond region. This conceptual device has been developed as a possible focal plane instrument for the future OverWhelmingly Large Telescope (OWL) of the European Southern Observatory. This instrument has been named QuantEYE, that is, the Quantum Eye of OWL.
TL;DR: In this article, the authors report the results of research and development of a single photon avalanche detector (SPAD) for use in the harsh and hostile conditions of outer space, which was developed for space projects related to the synchronization of timescales via a space clock using optical pulses.
Abstract: The paper reports the results of research and development of a single photon avalanche detector (SPAD) for use in the harsh and hostile conditions of outer space. The photon counting detector was developed for space projects related to the synchronization of timescales via a space clock using optical pulses. The detector is based on a SPAD manufactured on silicon using the K14 process, and operated in an active quenching mode. Its operation over an extreme temperature range and under high optical overload has been tested together with its sensitivity to radiation in space. The technology demonstrator of the detectors for the China Laser Time Transfer mission was developed and tested. The mission launch is expected in the year 2008.
TL;DR: In this article, disentanglement and decoherence rates for a pair of three-level atoms subjected to multi-local and collective pure dephasing noise acting in a preferred basis were derived.
Abstract: We relate disentanglement and decoherence rates in a pair of three-level atoms subjected to multi-local and collective pure dephasing noise acting in a preferred basis. The bipartite entanglement decay rate, as bounded from above by the negativity, is found to be greater than or equal to the dephasing-decoherence rates characterized by the decay of off-diagonal elements in the corresponding full density matrix describing the system or the reduced density matrix describing either qutrit, extending previous results for qubit pairs subject to such noise.
TL;DR: In this paper, a 48-element monolithic matrix detector, designed for parallel fluorescence detection, has been fabricated in silicon and tested, and the pixel detection efficiency is remarkably uniform over the array: it has a peak of 48% at 530 nm and it is higher than 30% over all the visible range.
Abstract: A 48-element monolithic matrix detector, designed for parallel fluorescence detection, has been fabricated in silicon and tested. The pixels are single photon avalanche diodes (SPADs) with 50 µm diameter, ordered in a 6× 8 array with 240 µm pitch. The photon detection efficiency is remarkably uniform over the array: it has a peak of 48% at 530 nm and it is higher than 30% over all the visible range. Low dark counting rate (DCR) is obtained in operation at moderately low temperature (−15°C with thermoelectric cooling): the individual pixel DCR is 60 c s−1 for about 40% of the elements and it is below 5700 c s−1 in the rest of the array. It was verified that the afterpulsing probability is below 1% and that the optical crosstalk probability between elements is lower than 0.2%. Based on this matrix detector, we have developed a versatile and compact (20 cm× 8 cm × 4 cm) photon counting module that can be easily interfaced to a PC via USB link.
TL;DR: In this article, a method for separating the correlated signal from the background signal that appropriately handles deadtime effects is presented, including consideration of pulse timing and afterpulsing issues that arise in typical avalanche photodiode (APD) detectors.
Abstract: When photon-counting detectors are calibrated in the presence of a background signal, deadtime effects can be significant and must be carefully accounted for to achieve high accuracy. We present a method for separating the correlated signal from the background signal that appropriately handles deadtime effects. This method includes consideration of pulse timing and afterpulsing issues that arise in typical avalanche photodiode (APD) detectors. We illustrate how these effects should be accounted for in the calibration process. We also discuss detector timing issues that should be considered in detector calibration.
TL;DR: In this article, three different formulations of the strong-field approximation for high-harmonic generation in diatomic molecules, based on length, velocity and acceleration form for the recombination amplitude, were analyzed.
Abstract: We analyse three different formulations of the strong-field approximation for high-harmonic generation in diatomic molecules, based on length, velocity and acceleration form for the recombination amplitude. We compare the predictions for the two-centre interference with those from the time-dependent Schrodinger equation. We find that the velocity form gives the closest agreement with the exact results while being the simplest from a computational point of view.
TL;DR: In this paper, trapped, laser-cooled rubidium atoms are transferred between two strongly focused, horizontal, orthogonally intersecting laser beams and the transfer efficiency is studied as a function of the vertical distance between the beam axes.
Abstract: Trapped, laser-cooled rubidium atoms are transferred between two strongly focused, horizontal, orthogonally intersecting laser beams. The transfer efficiency is studied as a function of the vertical distance between the beam axes. Optimum transfer is found when the distance equals the beam waist radius. Numerical simulations reproduce well the experimental results.
TL;DR: In this paper, the phase of either the coupling or probe fields can be changed to enhance the EIT by changing either the phase or probe field phase to increase the absorption rate.
Abstract: In this paper, we investigate various aspects of electro-magnetically induced transparency (EIT) that are associated with quantum interference In the first half of this paper, we investigate two cascade schemes and demonstrate two possible absorption pathways in one, which leads to interference, and only one pathway in the other scheme, which does not exhibit EIT In the second part of this paper, we demonstrate how EIT can be changed into enhanced absorption by changing the phase of either the coupling or probe fields