We investigate the quantum signature scheme proposed by and Zeng and Keitel [Phys. Rev. A 65, 042312 (2002)]. It uses Greenberger-Horne-Zeilinger states and the availability of a trusted arbitrator. However, in our opinion the protocol is not clearly operationally defined and several steps are ambiguous. Moreover, we argue that the security statements claimed by the authors are incorrect.
Dynamic control of higher-order modes in hollow-core photonic crystal
fibers
T. G. Euser,
G. Whyte,
M. Scharrer,
J. S. Y. Chen,
A. Abdolvand,
J. Nold,
C. F. Kaminski,
P. St. J. Russell
We present a versatile method for selective mode coupling into higher-order modes of photonic crystal fibers, using holograms electronically generated by a spatial light modulator. The method enables non-mechanical and completely repeatable changes in the coupling conditions. We have excited higher order modes up to LP(31) in hollow-core photonic crystal fibers. The reproducibility of the coupling allows direct comparison of the losses of different guided modes in both hollow-core bandgap and kagome-lattice photonic crystal fibers. Our results are also relevant to applications in which the intensity distribution of the light inside the fiber is important, such as particle-or atom-guidance. (C) 2008 Optical Society of America
On the improvement of two-dimensional curvature computation and its
application to turbulent premixed flame correlations
R. S. M. Chrystie,
I. S. Burns,
J. Hult,
C. F. Kaminski
MEASUREMENT SCIENCE AND TECHNOLOGY
19
(12)
125503
(2008)
| Journal
Measurement of curvature of the flamefront of premixed turbulent flames is important for the validation of numerical models for combustion. In this work, curvature is measured from contours that outline the flamefront, which are generated from laser-induced fluorescence images. The contours are inherently digitized, resulting in pixelation effects that lead to difficulties in computing curvature of the flamefront accurately. A common approach is to fit functions locally to short sections along the flame contour, and this approach is also followed in this work; the method helps smoothen the pixelation before curvature is measured. However, the length and degree of the polynomial, and hence the amount of smoothing, must be correctly set in order to maximize the precision and accuracy of the curvature measurements. Other researchers have applied polynomials of different orders and over different segment lengths to circles of known curvature as a test to determine the appropriate choice of polynomial; it is shown here that this method results in a sub-optimal choice of polynomial function. Here, we determine more suitable polynomial functions through use of a circle whose radius is sinusoidally modulated. We show that this leads to a more consistent and reliable choice for the local polynomial functions fitted to experimental data. A polynomial function thus determined is then applied to flame contour data to measure curvature of experimentally acquired flame contours. The results show that there is an enhancement in local flame speed at sections of the flamefront with a non-zero curvature, and this agrees with numerical models.
Quantum filtering of optical coherent states
C. Wittmann,
D. Elser,
U. L. Andersen,
R. Filip,
P. Marek,
G. Leuchs
We propose and experimentally demonstrate nondestructive and noiseless removal (filtering) of vacuum states from an arbitrary set of coherent states of continuous variable systems. Errors, i.e., vacuum states in the quantum information are diagnosed through a weak measurement, and on that basis, probabilistically filtered out. We consider three different filters based on on-off detection, phase stabilized, and phase randomized homodyne detection. We find that on-off detection, optimal in the ideal theoretical setting, is superior to the homodyne strategy also in a practical setting.
Active laser radar systems with stochastic electromagnetic beams in
turbulent atmosphere
Yangjian Cai,
Olga Korotkova,
Halil T. Eyyuboglu,
Yahya Baykal
Propagation of stochastic electromagnetic beams through paraxial ABCD optical systems operating through turbulent atmosphere is investigated with the help of the ABCD matrices and the generalized Huygens-Fresnel integral. In particular, the analytic formula is derived for the cross-spectral density matrix of an electromagnetic Gaussian Schell-model (EGSM) beam. We applied our analysis for the ABCD system with a single lens located on the propagation path, representing, in a particular case, the unfolded double-pass propagation scenario of active laser radar. Through a number of numerical examples we investigated the effect of local turbulence strength and lens' parameters on spectral, coherence and polarization properties of the EGSM beam. (C) 2008 Optical Society of America
Propagation properties of anomalous hollow beams in a turbulent
atmosphere
Propagation of circular and elliptical anomalous hollow beams in a turbulent atmosphere is investigated in detail. Based on the extended Huygens-Fresnel integral, analytical formulae for the average irradiance of circular and elliptical anomalous hollow beams propagating in a turbulent atmosphere are derived. The irradiance and spreading properties of circular and elliptical anomalous hollow beams in a turbulent atmosphere and in free space are studied numerically. It is found that circular and elliptical anomalous hollow beams at short propagation distance in turbulent atmosphere have similar propagation properties to those of free space, while at long propagation distance, circular and elliptical anomalous hollow beams eventually become circular Gaussian beams in a turbulent atmosphere, which is much different from their propagation properties in free space. The conversion from an anomalous hollow beam to a circular Gaussian beam becomes quicker and the beam spot spreads more rapidly for a larger structure constant, a shorter wavelength and a smaller waist size of the initial beam. (C) 2008 Elsevier B.V. All rights reserved.
Temperature dependence of indirect-exciton luminescence in in-plane
magnetic field
M. Orlita,
G. H. Doehler,
R. Grill,
P. Hlidek,
S. Malzer,
J. Prochazka,
M. Zvara
JOURNAL OF LUMINESCENCE
128
(12)
1873-1875
(2008)
| Journal
We report on a magneto-luminescence on a double quantum well subject to an in-plane magnetic field. The attention is paid to the properties of interwell excitons, which are indirect in the real space and which become indirect in the reciprocal space as well when a finite in-plane magnetic field is applied. Such indirect exciton states become optically inactive unless some relaxation mechanisms of their momentum appear. The experiment is carried out on a sample where, as reported previously, the radiative recombination of indirect excitons is possible due to their localization or via collisions with structural defects. The experimental data presented here, measured at various temperatures, favour the latter mechanism which is less sensitive to the system temperature in comparison with the former one. (c) 2008 Elsevier B.V. All rights reserved.
Anomalous pulse breakup in small-core photonic crystal fibers
A. Podlipensky,
P. Szarniak,
N. Y. Joly,
P. St. J. Russell
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
25
(12)
2049-2056
(2008)
| Journal
Detailed numerical and experimental studies of propagation of 110 fs laser pulses at 800 am in small-core photonic crystal fibers (gamma = 100 W (1) km(-1)) reveal that pulse breakup occurs in two distinct regimes defined by the input power. At low peak power (soliton order N <= g7) higher-order soliton fission occurs: individual solitons being ejected from the input pulse one after the other and are at-ranged in wavelength and in time by peak power. At higher levels of peak power (N>8), pulse breakup results in ejection of bound soliton pairs and the formation of single solitons that collide during propagation. (C) 2008 Optical Society of America
Polarization-dependent coupling to plasmon modes on submicron gold wire
in photonic crystal fiber
H. W. Lee,
M. A. Schmidt,
H. K. Tyagi,
L. Prill Sempere,
P. St. J. Russell
We present experimental results on coupling to surface plasmon modes on gold nanowires selectively introduced into polarization-maintaining photonic crystal fibers. Highly polarization- and wavelength-dependent transmission is observed. In one sample 24.5 mm long, the transmission on and off resonance differs by as much as 45 dB. Near-field optical images of the light emerging from such a gold-filled fiber show light guided on the wire at surface plasmon resonances. Finite element simulations are in good agreement with the experimental results. These gold-filled fibers can be potentially used as in-fiber wavelength-dependent filters and polarizers and as near-field tips for sub-wavelength-scale imaging. (C) 2008 American Institute of Physics.
Scintillation properties of non-circular flat-topped beams
Yangjian Cai
JOURNAL OF OPTICS A-PURE AND APPLIED OPTICS
10
(7)
075003
(2008)
| Journal
The scintillation properties of a flat-topped (FT) beam of non-circular (rectangular or elliptical) symmetry propagating in a weak turbulent atmosphere are investigated. Explicit expressions for the on-axis scintillation index of rectangular and elliptical FT beams in a weak turbulent atmosphere are derived. It is found that the scintillation index value of a rectangular or elliptical FT beam can be smaller than that of a circular Gaussian beam under certain conditions. The scintillation properties of non-circular FT beams are closely related to the beam parameters.
Anyon statistics with continuous variables
Jing Zhang,
Changde Xie,
Kunchi Peng,
Peter van Loock
We describe a continuous-variable scheme for simulating the Kitaev lattice model and for detecting statistics of Abelian anyons. The corresponding quantum optical implementation is solely based upon Gaussian resource states and Gaussian operations, hence allowing for a highly efficient creation, manipulation, and detection of anyons. This approach extends our understanding of the control and application of anyons and it leads to the possibility for experimental proof-of-principle demonstrations of anyonic statistics using continuous-variable systems.
Coupled whispering gallery mode resonators in the Terahertz frequency
range
S. Preu,
H. G. L. Schwefel,
S. Malzer,
G. H. Doehler,
L. J. Wang,
M. Hanson,
J. D. Zimmerman,
A. C. Gossard
We report on coupling of two whispering gallery mode resonators in the Terahertz frequency range. Due to the long wavelength in the millimeter to submillimeter range, the resonators can be macroscopic allowing for accurate size and shape control. This is necessary to couple specific modes of two or more resonators. Sets of polyethylene (PE) and quartz disk resonators are demonstrated, with medium (loaded) quality (Q)-factors of 40-800. Both exhibit coinciding resonance frequency spectra over more than ten times the free spectral range. Loading effects of single resonators are investigated which provide strong Q-factor degradation and red-shifts of the resonances in the 0.2% range. By coupling two resonators of the same size, we observe mode splitting, in very good agreement with our numerical calculations. (C) 2008 Optical Society of America.
Spectral shifts of general beams in turbulent media
H. T. Eyyuboglu,
Y. Cai,
Y. K. Baykal
JOURNAL OF OPTICS A-PURE AND APPLIED OPTICS
10
(1)
015005
(2008)
| Journal
Using the concept of generalized beam, by applying the extended Huygens-Fresnel principle, we derive the spectrum for partially coherent cosh-Gaussian, cos-Gaussian, Gaussian and annular Gaussian beams propagating in turbulent media. From this formulation, graphical outputs are constructed illustrating the variation of receiver plane spectra against propagation distance, turbulence strength, degree of partial coherence and transverse coordinate. The dependence of spectral shifts on source and propagation parameters is observed. Spectrum invariance conditions are deduced analytically and discussed for the particular case of a fundamental Gaussian beam.
Experimental generation of a partially coherent flat-topped beam
An efficient optical system is proposed to generate a partially coherent flat-topped (FT) beam theoretically. Furthermore, we report the experimental generation of a partially coherent FT beam based on the proposed optical system. The intensity distribution and the modulus of the square of the spectral degree of coherence of the generated partially coherent FT beam are measured. The experimental results are consistent with the theoretical results. (c) 2008 Optical Society of America.
Heat dissipative solitons in optical fibers
N. Akhmediev,
P. St. J. Russell,
M. Taki,
J. M. Soto-Crespo
PHYSICS LETTERS A
372
(9)
1531-1534
(2008)
| Journal
We propose a one-dimensional model governing the propagation of heat waves in an optical fiber (the "fiber fuse"). The model has solutions in the form of high temperature localized waves moving towards the input end of the fiber, fueled by the laser power. These waves can be ignited by local heating at any point along the fiber. The effect of such a wave is irreversible damage to the fiber core. The phenomenon was observed earlier by Hand and Russell, when locally heating a fiber through which CW light of modest intensity was propagating. This induced self-destruction of the optical fiber core. (c) 2007 Elsevier B.V. All rights reserved.
State of polarization of a stochastic electromagnetic beam in an optical
resonator
Olga Korotkova,
Min Yao,
Yangjian Cai,
Halil T. Eyyuboglu,
Yahya Baykal
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND
VISION
25
(11)
2710-2720
(2008)
| Journal
On the basis of the unified theory of coherence and polarization, we investigate the behavior of the state of polarization of a stochastic electromagnetic beam in a Gaussian cavity. Formulations both in terms of Stokes parameters and in terms of polarization ellipse are given. We show that the state of polarization stabilizes, except in the case of a lossless cavity, after several passages between the mirrors, exhibiting monotonic or oscillatory behavior depending on the parameters of the resonator. We also find that an initially (spatially) uniformly polarized beam remains nonuniformly polarized even for a large number of passages between the mirrors of the cavity. (C) 2008 Optical Society of America
Velocity of heat dissipative solitons in optical fibers
A. Ankiewicz,
Wenjing Chen,
P. St. J. Russell,
M. Taki,
N. Akhmediev
In the fiber fuse, a pulse of high temperature travels toward the input end of the fiber, where high-power laser light is launched into the fiber. At any point along the fiber, the soliton can be ignited. The fiber core is damaged in the process so that light cannot propagate beyond the hot spot. This phenomenon is an example of a dissipative soliton that can exist only in the presence of an external energy supply and internal loss, We analyze this phenomenon, derive an expression for the velocity of the soliton, and determine its width as functions of the physical parameters of the laser and the fiber material. (C) 2008 Optical Society of America
Scintillation of astigmatic dark hollow beams in weak atmospheric
turbulence
Yangjian Cai,
Halil T. Eyyuboglu,
Yahya Baykal
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND
VISION
25
(7)
1497-1503
(2008)
| Journal
The scintillation properties of astigmatic dark hollow beams (DHBs) in weak atmospheric turbulence were investigated in detail. An explicit expression for the on-axis scintillation index of an astigmatic DH13 propagating in weak atmospheric turbulence was derived. It was found that the scintillation index value of an astigmatic DH13 with suitable astigmatism (i.e., ratio of the beam waist size in the x direction to that in the y direction), dark size, beam waist size, and wavelength can be smaller than that of a stigmatic DH13 and that of stigmatic and astigmatic flat-topped, annular, and Gaussian beams in weak atmospheric turbulence particularly at long propagation ranges. Our results will be useful in long-distance free-space optical communications. (c) 2008 Optical Society of America
Quantum repeaters using coherent-state communication
Peter van Loock,
Norbert Lutkenhaus,
W. J. Munro,
Kae Nemoto
We investigate quantum repeater protocols based upon atomic qubit-entanglement distribution through optical coherent-state communication. Various measurement schemes for an optical mode entangled with two spatially separated atomic qubits are considered in order to nonlocally prepare conditional two-qubit entangled states. In particular, generalized measurements for unambiguous state discrimination enable one to completely eliminate spin-flip errors in the resulting qubit states, as they would occur in a homodyne-based scheme due to the finite overlap of the optical states in phase space. As a result, by using weaker coherent states, high initial fidelities can still be achieved for larger repeater spacing, at the expense of lower entanglement generation rates. In this regime, the coherent-state-based protocols start resembling single-photon-based repeater schemes.
Electronic noise-free measurements of squeezed light
Leonid A. Krivitsky,
Ulrik L. Andersen,
Ruifang Dong,
Alexander Huck,
Christoffer Wittmann,
Gerd Leuchs
We study the implementation of a correlation measurement technique for the characterization of squeezed light. We show that the sign of the covariance coefficient revealed from the time-resolved correlation data allow us to distinguish among squeezed, coherent, and thermal states. In contrast to the traditional method of characterizing squeezed light, involving measurement of the variation of the difference photocurrent, the correlation measurement method allows one to eliminate the contribution of the electronic noise, which becomes a crucial issue in experiments with dim sources of squeezed light. (C) 2008 Optical Society of America
Recent developments in quantum key distribution: Theory and practice
Wolfgang Mauerer,
Wolfram Helwig,
Christine Silberhorn
ANNALEN DER PHYSIK
17
(2-3)
158-175
(2008)
| Journal
Quantum key distribution is among the foremost applications of quantum mechanics, both in terms of fundamental physics and as a technology on the brink of commercial deployment. Starting from principal schemes and initial proofs of unconditional security for perfect systems, much effort has gone into providing secure schemes which can cope with numerous experimental imperfections unavoidable in real world implementations. In this paper, we provide a comparison of various schemes and protocols. We analyse their efficiency and performance when implemented with imperfect physical components. We consider how experimental faults are accounted for using effective parameters. We compare various recent protocols and provide guidelines as to which components propose best advances when being improved. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA. Weinheim.
Microdeflectometry - a novel tool to acquire three-dimensional
microtopography with nanometer height resolution
Gerd Haeusler,
Claus Richter,
Karl-Heinz Leitz,
Markus C. Knauer
We introduce "microdeflectometry," a novel technique for measuring the microtopography of specular surfaces. The primary data are the local slope of the surface under test. Measuring the slope instead of the height implies high information efficiency and extreme sensitivity to local shape irregularities. The lateral resolution can be better than 1 mu m, whereas the resulting height resolution is in the range of 1 nm. Microdeflectometry can be supplemented by methods to expand the depth of field, with the potential to provide quantitative 3D imaging with scanning-electron-microscope-like features. (C) 2008 Optical Society of America.
Experimental entanglement distillation of mesoscopic quantum states
Ruifang Dong,
Mikael Lassen,
Joel Heersink,
Christoph Marquardt,
Radim Filip,
Gerd Leuchs,
Ulrik L. Andersen
The distribution of entangled states between distant parties in an optical network is crucial for the successful implementation of various quantum communication protocols such as quantum cryptography, teleportation and dense coding(1-3). However, owing to the unavoidable loss in any real optical channel, the distribution of loss-intolerant entangled states is inevitably afflicted by decoherence, which causes a degradation of the transmitted entanglement. To combat the decoherence, entanglement distillation, a process of extracting a small set of highly entangled states from a large set of less entangled states, can be used(4-14). Here we report on the distillation of deterministically prepared light pulses entangled in continuous variables that have undergone non-Gaussian noise. The entangled light pulses(15-17) are sent through a lossy channel, where the transmission is varying in time similarly to light propagation in the atmosphere. By using linear optical components and global classical communication, the entanglement is probabilistically increased.
Intensity fluctuations in J-Bessel-Gaussian beams of all orders
propagating in turbulent atmosphere
H. T. Eyyuboglu,
E. Sermutlu,
Y. Baykal,
Y. Cai,
O. Korotkova
The scintillation index of a J (n) -Bessel-Gaussian beam of any order propagating in turbulent atmosphere is derived and numerically evaluated at transverse cross-sections with the aid of a specially designed triple integral routine. The graphical outputs indicate that, just like the previously investigated J (0)-Bessel-Gaussian beam, higher-order members of the family also offer favorable scintillation characteristics at large source sizes. This advantage is maintained against rising beam orders. Viewed along the propagation axis, beams with lower orders and smaller widths exhibit smaller values of the scintillation index at shorter propagation distances and large values at longer propagation distances. Further, it is shown that the scintillation index of the J (n) -Bessel-Gaussian beams (n > 0) is larger than that of the fundamental Gaussian and the J (0)-Bessel-Gaussian beams only near the on-axis points, while remaining smaller towards the edges of the beam.
An alternative theoretical model for an anomalous hollow beam
An alternative and convenient theoretical model is proposed to describe a flexible anomalous hollow beam of elliptical symmetry with an elliptical solid core, which was observed in experiment recently (Phys. Rev. Lett, 94 (2005) 134802). In this model, the electric field of anomalous hollow beam is expressed as a finite sum of elliptical Gaussian modes. Flat-topped beams, dark hollow beams and Gaussian beams are special cases of our model. Analytical propagation formulae for coherent and partially coherent anomalous hollow beams passing through astigmatic ABCD optical systems are derived. Some numerical examples are calculated to show the propagation and focusing properties of coherent and partially coherent anomalous hollow beams. (C) 2008 Optical Society of America.
Dead time correction in coincidence counting of photon pairs
M. S. Kang,
D-H Lee,
J. Lee,
J. Y. Lee,
S-K Choi,
H. S. Park
We describe two methods for evaluating the dead time of a time-to-amplitude converter (TAC). The dead time is obtained by measuring either the corresponding time interval in an oscilloscope trace or the relation between the single count rate and the coincidence count rate. Values for the TAC dead time are obtained in the range from 3.4 mu s to 14.3 mu s for the two methods with respective standard uncertainties of 2.9 x 10(-8) s and 3.3 x 10(-9) s. The TAC dead time is applied to the calibration of coincidence-counting measurements of optical transmission and photon-heralding efficiency.
Effect of detector dead times on the security evaluation of
differential-phase-shift quantum key distribution against sequential
attacks
We investigate limitations imposed by detector dead times on the performance of sequential attacks against a differential-phase-shift (DPS) quantum key distribution (QKD) protocol with weak coherent pulses. In particular; we analyze sequential attacks based on unambiguous state discrimination of the signal states emitted by the source and we obtain ultimate upper bounds on the maximal distance achievable by a DPS QKD scheme both for the case of calibrated and uncalibrated devices, respectively.
Partially coherent anomalous hollow beam and its paraxial propagation
Yangjian Cai,
Fei Wang
PHYSICS LETTERS A
372
(25)
4654-4660
(2008)
| Journal
Anomalous hollow beam is extended to the partially coherent case. Analytical propagation formulae for a partially coherent anomalous hollow beam passing through a paraxial ABCD optical system are derived. The propagation properties of a partially coherent anomalous hollow beam in free space and the focusing properties of a partially coherent anomalous hollow beam are studied numerically It is found that the. propagation and focusing properties of the partially coherent anomalous hollow beam are closely related to its initial coherence. (C) 2008 Elsevier B.V. All rights reserved.
Long-range spiralling surface plasmon modes on metallic nanowires
We discuss the characteristics of surface plasmon modes guided on metallic nanowires of circular cross-section embedded in silica glass. Under certain conditions such wires allow low-loss guided modes, full account being taken of ohmic losses in the metal. We find that these modes can be bound to the wire even when the real part of their axial refractive index is less than that of the surrounding dielectric. We assess in detail the accuracy of a simple model in which SPs are viewed as spiralling around the nanowire in a helical path, forming modes at certain angles of pitch. The results are relevant for understanding the behavior of light in twodimensional arrays of metallic nanowires in fiber form. (c) 2008 Optical Society of America.
Direct experimental observation of the single reflection optical
Goos-Hanchen shift
H. G. L. Schwefel,
W. Koehler,
Z. H. Lu,
J. Fan,
L. J. Wang
We report a precise direct measurement of the Goos-Hanchen shift after one reflection off a dielectric interface coated with periodic metal stripes. The spatial displacement of the shift is determined by image analysis. A maximal absolute shift of 5.18 and 23.39 mu m for TE and TM polarized light, respectively, is determined. This technique is simple to implement and can be used for a large range of incident angles. (C) 2008 Optical Society of America.
Observation of optomechanical multistability in a high-Q torsion balance
oscillator
We observe the optomechanical multistability of a macroscopic torsion balance oscillator. The torsion oscillator forms the moving mirror of a hemispherical laser light cavity. When a laser beam is coupled into this cavity, the radiation pressure force of the intracavity beam adds to the torsion wire's restoring force, forming an optomechanical potential. In the absence of optical damping, up to 23 stable trapping regions were observed due to local light potential minima over a range of 4 mu m oscillator displacement. Each of these trapping positions exhibits optical spring properties. Hysteresis behavior between neighboring trapping positions is also observed. We discuss the prospect of observing optomechanical stochastic resonance, aiming at enhancing the signal-to-noise ratio (SNR) in gravity experiments.
Generation of a high-quality partially coherent dark hollow beam with a
multimode fiber
Chengliang Zhao,
Yangjian Cai,
Fei Wang,
Xuanhui Lu,
Yuzhu Wang
We report the experimental generation of a high-quality partially coherent dark hollow beam (DHB) by coupling a partially coherent beam into a multimode fiber (MMF) with a suitable incidence angle. The interference experiment of the generated partially coherent DHB passing through double slits is demonstrated. It is found that the coupling efficiency of the MMF, the quality, and the coherence of the generated partially coherent DHB are closely controlled by the coherence of the input beam. (c) 2008 Optical Society of America.
Optical properties of photonic crystal fiber with integral micron-sized
Ge wire
H. K. Tyagi,
M. A. Schmidt,
L. Prill Sempere,
P. St. J. Russell
Using a selective hole closure technique, individual hollow channels in silica-air photonic crystal fibers are filled with pure Ge by pumping in molten material at high pressure. The smallest channels filled so far are 600 nm in diameter, which is 10x smaller than in previous work. Electrical conductivity and micro-Raman measurements indicate that the resulting cm-long wires have a high degree of crystallinity. Optical transmission spectra are measured in a sample with a single wire placed adjacent to the core of an endlessly single-mode photonic crystal fiber. This renders the fiber birefringent, as well as causing strongly polarization-dependent transmission losses, with extinction ratios as high as 30 dB in the visible. In the IR, anti-crossings between the glass-core mode and resonances on the high index Ge wire create a series of clear dips in the spectrum transmitted through the fiber. The measurements agree closely with the results of finite-element simulations in which the wavelength dependence of the dielectric constants is taken fully into account. A toy model based on a multilayer structure is used to help interpret the results. Finally, the temperature dependence of the anti-crossing wavelengths is measured, the preliminary results suggesting that the structure might form the basis of a compact optical thermometer. Since Ge provides electrical conductance together with low-loss guidance in the mid-IR, Ge-filled PCF seems likely to lead to new kinds of in-fiber detector and sensor, as well as having potential uses in ultra-low-threshold nonlinear optical devices. (C) 2008 Optical Society of America
Design of highly transparent organic photodiodes
Edgar S. Zaus,
Sandro Tedde,
Tobias Rauch,
Jens Fuerst,
Gottfried H. Doehler
IEEE TRANSACTIONS ON ELECTRON DEVICES
55
(2)
681-684
(2008)
| Journal
In this brief, various approaches for the realization of transparent photodiodes based on bulk heterojunction blends of poly-3-hexylthiophene and [6,6]-phenyl C-61-butyric acid methyl ester are studied. The choice of the constituents of the device is discussed concerning transmittance and light-detecting properties as dark current and external quantum efficiency (EQE). Blending several light-absorbing materials makes tailoring of the transmittance spectrum possible. Transmittance of 36% of the incident light together with 46% EQE at a wavelength of 530 nm are promising results and show the potential for highly transparent, photodiodes based on organic layers.
Evanescent wave broadband cavity enhanced absorption spectroscopy using
supercontinuum radiation: A new probe of electrochemical processes
Mathias Schnippering,
Patrick R. Unwin,
Johan Hult,
Toni Laurila,
Clemens F. Kaminski,
Justin M. Langridge,
Roderic L. Jones,
Mikhail Mazurenka,
Stuart R. Mackenzie
An evanescent wave variant of broadband cavity enhanced absorption spectroscopy using a supercontinuum light source has been used to detect electrogenerated species at the silica-water interface. In proof-of-concept experiments [IrCl(6)](2-) was produced by electro-oxidation of [IrCl(6)](3-) in a thin layer electrochemical cell. Diffusion of the Ir(IV) across the cell to a silica interface was monitored yielding real-time concentrations within an evanescent field region at the interface. The optical response was compared with the electrochemical response during chronoamperometric step and cyclic voltammetric experiments and both were simulated by finite element modeling. The experiment is highly sensitive to interfacial processes and its wide spectral width and fast time resolution make it a potentially powerful tool for in situ spectroscopic monitoring of processes and intermediates in dynamical electrochemistry. (C) 2008 Elsevier B.V. All rights reserved.
Femto-Newton light force measurement at the thermal noise limit
The measurement of very small light forces has wide applications in many fields of physics. A common measurement method for small force detection is the determination of changes in the dynamic behavior of mechanical oscillators, either in amplitude or in frequency. The detection of slowly varying forces mostly requires long period oscillators, such as a torsion pendulum. We demonstrate the application of a macroscopic, low-noise, torsion balance oscillator for the detection of radiation pressure forces at the femto-Newton level. The system is "precooled" (removing excess seimic noise) to be only thermal noise limited. The demonstrated force sensitivity reaches the thermal limit. (C) 2008 Optical Society of America.
Demonstration of a Quantum Nondemolition Sum Gate
Jun-ichi Yoshikawa,
Yoshichika Miwa,
Alexander Huck,
Ulrik L. Andersen,
Peter van Loock,
Akira Furusawa
The sum gate is the canonical two-mode gate for universal quantum computation based on continuous quantum variables. It represents the natural analogue to a qubit C-NOT gate. In addition, the continuous-variable gate describes a quantum nondemolition (QND) interaction between the quadrature components of two light modes. We experimentally demonstrate a QND sum gate, employing the scheme by R. Filip, P. Marek, and U. L. Andersen [Phys. Rev. A 71, 042308 (2005)], solely based on off-line squeezed states, homodyne measurements, and feedforward. The results are verified by simultaneously satisfying the criteria for QND measurements in both conjugate quadratures.
Experimental generation of four-mode continuous-variable cluster states
Mitsuyoshi Yukawa,
Ryuji Ukai,
Peter van Loock,
Akira Furusawa
Continuous-variable Gaussian cluster states are a potential resource for universal quantum computation. They can be efficiently and unconditionally built from sources of squeezed light using beam splitters. Here we report on the generation of three different kinds of continuous-variable four-mode cluster states. In our realization, the resulting cluster-type correlations are such that no corrections other than simple phase-space displacements would be needed when quantum information propagates through these states. At the same time, the inevitable imperfections from the finitely squeezed resource states and from additional thermal noise are minimized, as no antisqueezing components are left in the cluster states.
Phase-preserving amplitude regeneration for a WDM RZ-DPSK signal using a
nonlinear amplifying loop mirror
K. Cvecek,
K. Sponsel,
C. Stephan,
G. Onishchukov,
R. Ludwig,
C. Schubert,
B. Schmauss,
G. Leuchs
We propose a modified nonlinear amplifying loop mirror (NALM) for phase-preserving 2R regeneration of wavelength division multiplexed (WDM) return-to-zero differential phase-shift-keyed signals. As proof of principle the regeneration capability of this NALM setup has been investigated experimentally for two 10 Gbit/s wavelength channels. A significant eye-opening improvement and a negative power penalty of 1.2 dB have been observed in both channels. (C) 2008 Optical Society of America.
Paraxial propagation of a partially coherent flattened Gaussian beam
through apertured ABCD optical systems
Yangjian Cai,
Xiang Lue,
Halil T. Eyyuboglu,
Yahya Baykal
By expanding the hard aperture function into a finite sum of complex Gaussian functions, some approximate analytical formulae for the cross-spectral density of a partially coherent flattened Gaussian beam (FGB) propagating through apertured aligned and misaligned ABCD optical systems are derived based on the generalized Collins formula. The results obtained by using the approximate analytical formula are in good agreement with those obtained by using the numerical integral calculation. As a numerical example, the focusing properties (including average irradiance distribution and focal shift) of a partially coherent FGB focused by an apertured thin lens are studied, and it is found that the focusing properties of a partially coherent FGB are closely related to its initial coherence and the aperture width. Our results provide an effective and fast way for studying the paraxial propagation of a partially coherent FGB through apertured ABCD optical systems. (C) 2008 Elsevier B.V. All rights reserved.
Hybrid quantum computation in quantum optics
P. van Loock,
W. J. Munro,
Kae Nemoto,
T. P. Spiller,
T. D. Ladd,
Samuel L. Braunstein,
G. J. Milburn
We propose a hybrid quantum computing scheme where qubit degrees of freedom for computation are combined with quantum continuous variables for communication. In particular, universal two-qubit gates can be implemented deterministically through qubit-qubit communication, mediated by a continuous-variable bus mode ("qubus"), without direct interaction between the qubits and without any measurement of the qubus. The key ingredients are controlled rotations of the qubus and unconditional qubus displacements. The controlled rotations are realizable through typical atom-light interactions in quantum optics. For such interactions, our scheme is universal and works in any regime, including the limits of weak and strong nonlinearities.
Shape reconstruction from gradient data
Svenja Ettl,
Juergen Kaminski,
Markus C. Knauer,
Gerd Haeusler
We present a generalized method for reconstructing the shape of an object from measured gradient data. A certain class of optical sensors does not measure the shape of an object but rather its local slope. These sensors display several advantages, including high information efficiency, sensitivity, and robustness. For many applications, however, it is necessary to acquire the shape, which must be calculated from the slopes by numerical integration. Existing integration techniques show drawbacks that render them unusable in many cases. Our method is based on an approximation employing radial basis functions. It can be applied to irregularly sampled, noisy, and incomplete data, and it reconstructs surfaces both locally and globally with high accuracy. (C) 2008 Optical Society of America.
Analysis and optimization of coupling to external cavities in feedback
experiments with vertical-cavity surface-emitting lasers
The feedback strength is a crucial parameter for feedback experiments using semiconductor lasers. In this article, the coupling efficiency of the field of vertical-cavity surface-emitting lasers (VCSELs) to external cavities containing one collimating lens has been analyzed in detail using ABCD-matrix methods. It is found that for a given set of parameters there are two distinct, experimentally realizable positions of the collimating lens which allow for optimal coupling, if the cavity length is sufficiently small. The predictions are verified in experiments using single-transverse-mode VCSELs. The obtained coupling efficiencies exceed 70%. (c) 2007 Elsevier B.V. All rights reserved.
Experimental continuous-variable cloning of partial quantum information
The fidelity of a quantum transformation is strongly linked with the prior partial information of the state to be transformed. We illustrate this interesting point by proposing and demonstrating the superior cloning of coherent states with prior partial information. More specifically, we propose two simple transformations that under the Gaussian assumption optimally clone symmetric Gaussian distributions of coherent states as well as coherent states with known phases. Furthermore, we implement for the first time near-optimal state-dependent cloning schemes relying on simple linear optics and feedforward.
Quantum dot microdrop laser
J. Schaefer,
J. P. Mondia,
R. Sharma,
Z. H. Lu,
A. S. Susha,
A. L. Rogach,
L. J. Wang
We report single-mode and multimode lasing from isolated spherical liquid microcavities containing CdSe/ZnS nanocrystal quantum dots. Lasing is observed at densities more than 2 orders of magnitude lower than previously demonstrated or theoretically predicted, assuming a uniform nanocrystal quantum dot distribution. Charged droplets, between 10 and 40 mu m in size, are electrodynamically levitated and optically pumped. Substantial laser signals at low thresholds are measured from the directional emission normal to the pump beam, owing to the high Q cavity modes.
Truncated su(2) moment problem for spin and polarization states
Tobias Moroder,
Michael Keyl,
Norbert Luetkenhaus
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
41
(27)
275302
(2008)
| Journal
We address the problem whether a given set of expectation values is compatible with the first and second moments of the generic spin operators of a system with total spin j. Those operators appear as the Stokes operator in quantum optics, as well as the total angular momentum operators in the atomic ensemble literature. We link this problem to a particular extension problem for bipartite qubit states; this problem is closely related to the symmetric extension problem that has recently drawn much attention in different contexts of the quantum information literature. We are able to provide operational, approximate solutions for very large spin numbers, and in fact the solution becomes exact in the limiting case of infinite spin numbers. Solutions for low spin numbers are formulated in terms of a hyperplane characterization, similar to entanglement witnesses, which can be efficiently solved with semidefinite programming.
Mechanical oscillators have a long tradition in measuring very small forces, particularly of gravitational nature. Oscillators have thermal energy of k(B)T/2 in each degree of freedom. Here, we demonstrate the dynamical cooling of a gram-sized oscillator to 300 mK in equivalent temperature, a reduction of noise by a factor of 10(6) compared to the seismic background level. A simple physical model is provided for the cooling process. We also demonstrate the dynamic control of the oscillator's eigenfrequency, aiming at providing a stationary reference point for position measurements. The method may find applications in precision measurements of weak forces. (C) 2008 American Institute of Physics.
Optical excitation and characterization of gigahertz acoustic resonances
in optical fiber tapers
Myeong Soo Kang,
Andre Brenn,
Gustavo S. Wiederhecker,
Philip St. J. Russell
Transverse acoustic resonances at gigahertz frequencies are excited by electrostriction in the few-micrometer-thick waists of low-loss optical fiber tapers of up to 40 cm long. A pump-probe technique is used in which the resonances are excited by a train of optical pulses and probed in a Sagnac interferometer. Strong radially symmetric acoustic resonances are observed and the dependence of their frequencies on taper thickness is investigated. Such easily reconfigurable acousto-optic interactions may have applications in the high-frequency mode locking of fiber lasers. (C) 2008 American Institute of Physics.
Scintillation advantages of lowest order Bessel-Gaussian beams
For a weak turbulence propagation environment, the scintillation index of the lowest order Bessel-Gaussian beams is formulated. Its triple and single integral versions are presented. Numerical evaluations show that at large source sizes and large width parameters, when compared at the same source size, Bessel-Gaussian beams tend to exhibit lower scintillations than the Gaussian beam scintillations. This advantage is lost however for excessively large width parameters and beyond certain propagation lengths. Large width parameters also cause rises and falls in the scintillation index of off-axis positions toward the edges of the received beam. Comparisons against the fundamental Gaussian beam are made on equal source size and equal power basis.
Average irradiance and polarization properties of a radially or
azimuthally polarized beam in a turbulent atmosphere
Yangjian Cai,
Qiang Lin,
Halil T. Eyyuboglu,
Yahya Baykal
Analytical formulas are derived for the average irradiance and the degree of polarization of a radially or azimuthally polarized doughnut beam (PDB) propagating in a turbulent atmosphere by adopting a beam coherence-polarization matrix. It is found that the radial or azimuthal polarization structure of a radially or azimuthally PDB will be destroyed (i.e., a radially or azimuthally PDB is depolarized and becomes a partially polarized beam) and the doughnut beam spot becomes a circularly Gaussian beam spot during propagation in a turbulent atmosphere. The propagation properties are closely related to the parameters of the beam and the structure constant of the atmospheric turbulence. (C) 2008 Optical Society of America.
Experimentally feasible quantum erasure-correcting code for continuous
variables
We devise a scheme that protects quantum coherent states of light from probabilistic losses, thus achieving the first continuous-variable quantum erasure-correcting code. If the occurrence of erasures can be probed, then the decoder enables, in principle, a perfect recovery of the original light states. Otherwise, if supplemented with postselection based on homodyne detection, this code can be turned into an efficient erasure-filtration scheme. The experimental feasibility of the proposed protocol is carefully addressed.
Experimental evidence for Raman-induced limits to efficient squeezing in
optical fibers
Ruifang Dong,
Joel Heersink,
Joel F. Corney,
Peter D. Drummond,
Ulrik L. Andersen,
Gerd Leuchs
We report new experiments on polarization squeezing using ultrashort photonic pulses in a single pass of a birefringent fiber. We measure what is to our knowledge a record squeezing of -6.8 +/- 0.3 dB in optical fibers, which when corrected for linear losses is -10.4 +/- 0.8 dB. The measured polarization squeezing as a function of optical pulse energy, which spans a wide range from 3.5-178.8 pJ, shows a very good agreement with the quantum simulations, and for the first time we see the proof experimentally that Raman effects limit and reduce squeezing at high pulse energy. (c) 2008 Optical Society of America.
Quasi-phase-matched high harmonic generation in hollow core photonic
crystal fibers
The potential of hollow core photonic crystal fiber as a nonlinear gas cell for efficient high harmonic generation is discussed. The feasibility of phase-matching this process by modulating the phase of ionization electrons using a counter-propagating laser field is shown. In this way, harmonics with energies of several hundreds of eV can be produced using fs-laser pump pulses of mu J energy. (C) 2008 Optical Society of America
Scintillation properties of dark hollow beams in a weak turbulent
atmosphere
The on-axis scintillation index for a circular dark hollow beam (DHB) propagating in a weak turbulent atmosphere is formulated, and the scintillation properties of a DHB are investigated in detail. The scintillation index for a DHB reduces to the scintillation index for a Gaussian beam, an annular beam and a flat-topped beam under certain conditions. It is found that the scintillation index of a DHB is closely related to the beam parameters and can be lower than that of a Gaussian beam, an annular beam and a flat-topped beam in a weak turbulent atmosphere at smaller waist sizes and longer propagation lengths.
Waveguiding and plasmon resonances in two-dimensional photonic lattices
of gold and silver nanowires
M. A. Schmidt,
L. N. Prill Sempere,
H. K. Tyagi,
C. G. Poulton,
P. St. J. Russell
We report the fabrication of triangular lattices of parallel gold and silver nanowires of high optical quality, with diameters down to 500 nm and length-to-diameter ratios as high as 100 000. The nanowires are supported by a silica glass matrix and are disposed around a central solid glass core, i.e., a missing nanowire. These centimeter-long structures make it possible to trap light within an array of nanowires and characterize the plasmon resonances that form at specific optical frequencies. Such nanowire arrays have many potential applications, e.g., imaging on the subwavelength scale.
Experimental observation of truncated fractional Fourier transform for a
partially coherent Gaussian Schell-model beam
Fei Wang,
Yangjian Cai,
Qiang Lin
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND
VISION
25
(8)
2001-2010
(2008)
| Journal
The truncated fractional Fourier transform (FRT) is applied to a partially coherent Gaussian Schell-model (GSM) beam. The analytical propagation formula for a partially coherent GSM beam propagating through a truncated FRT optical system is derived by using a tensor method. Furthermore, we report the experimental observation of the truncated FRT for a partially coherent GSM beam. The experimental results are consistent with the theoretical results. Our results show that initial source coherence, fractional order, and aperture width (i.e.. truncation parameter) have strong influences on the intensity and coherence properties of the partially coherent beam in the FRT plane. When the aperture width is large, both the intensity and the spectral degree of coherence in the FRT plane are of Gaussian distribution. As the aperture width decreases, the diffraction pattern gradually appears in the FRT plane, and the spectral degree of coherence becomes of non-Gaussian distribution. As the coherence of the initial GSM beam decreases, the diffraction pattern for the case of small aperture widths gradually disappears. (c) 2008 Optical Society of America.
We describe a generic way to improve a given linear entanglement witness by a quadratic, nonlinear term. This method can be iterated, leading to a whole sequence of nonlinear witnesses, which become stronger in each step of the iteration. We show how to optimize this iteration with respect to a given state and prove that in the limit of the iteration the nonlinear witness detects all states that can be detected by the positive map corresponding to the original linear witness.
Evolution of the degree of polarization of an electromagnetic Gaussian
Schell-model. beam in a Gaussian cavity
Min Yao,
Yangjian Cai,
Halil T. Eyyuboglu,
Yahya Baykal,
Olga Korotkova
The interaction of an electromagnetic Gaussian Schell-model (EGSM) beam with a Gaussian cavity is analyzed. In particular, the evolution of the degree of polarization of the EGSM beam is investigated. The results show that the behavior of the degree of polarization depends on both the statistical properties of the source that generates the EGSM beam and the parameter of the cavity. (C) 2008 Optical Society of America
Interference between two coherently driven monochromatic terahertz
sources
S. Preu,
S. Malzer,
G. H. Doehler,
Q. Z. Zhao,
M. Hanson,
J. D. Zimmerman,
A. C. Gossard,
L. J. Wang
We report the interference between two phase-locked, continuous-wave, and coherent terahertz (Thz) photomixers. Both spatial and temporal coherence are observed with a narrow linewidth of less than 10 MHz. Phase locking is achieved by using one pair of lasers for both sources. The concept of optical narrow linewidth (fiber) distribution of the mixing signal opens various applications. We outline the necessary steps to extend this scheme for very long base line interferometric THz detection in the tens of kilometer range and for the improvement of spatial resolution for active stand-off THz imaging. (C) 2008 American Institute of Physics.
Cavity enhanced absorption spectroscopy of multiple trace gas species
using a supercontinuum radiation source
J. M. Langridge,
T. Laurila,
R. S. Watt,
R. L. Jones,
C. F. Kaminski,
J. Hult
Supercontinuum radiation sources are attractive for spectroscopic applications owing to their broad wavelength coverage, which enables spectral signatures of multiple species to be detected simultaneously. Here we report the first use of a supercontinuum radiation source for broadband trace gas detection using a cavity enhanced absorption technique. Spectra were recorded at bandwidths of up to 100 nm, encompassing multiple absorption bands of H2O, O-2 and O-2-O-2. The same instrument was also used to make quantitative measurements of NO2 and NO3. For NO3 a detection limit of 3 parts-per-trillion in 2 s was achieved, which corresponds to an effective 3 sigma sensitivity of 2.4 x 10(-9) cm(-1)Hz(-1/2). Our results demonstrate that a conceptually simple and robust instrument is capable of highly sensitive broadband absorption measurements. (C) 2008 Optical Society of America.
Coherent control of ultrahigh-frequency acoustic resonances in photonic
crystal fibers
G. S. Wiederhecker,
A. Brenn,
H. L. Fragnito,
P. St. J. Russell
Ultrahigh frequency acoustic resonances (2 GHz) trapped within the glass core (1 mu m diameter) of a photonic crystal fiber are selectively excited through electrostriction using laser pulses of duration 100 ps and energy 500 pJ. Using precisely timed sequences of such driving pulses, we achieve coherent control of the acoustic resonances by constructive or destructive interference, demonstrating both enhancement and suppression of the vibrations. A sequence of 27 resonantly-timed pulses provides a 100-fold increase in the amplitude of the vibrational mode. The results are explained and interpreted using a semianalytical theory, and supported by precise numerical simulations of the complex light-matter interaction.
Quantitative broadband chemical sensing in air-suspended solid-core
fibers
T. G. Euser,
J. S. Y. Chen,
M. Scharrer,
P. St. J. Russell,
N. J. Farrer,
P. J. Sadler
JOURNAL OF APPLIED PHYSICS
103
(10)
103108
(2008)
| Journal
We demonstrate a quantitative broadband fiber sensor based on evanescent-field sensing in the cladding holes of an air-suspended solid-core photonic crystal fiber. We discuss the fabrication process, together with the structural and optical characterization of a range of different fibers. Measured mode profiles are in good agreement with finite element method calculations made without free parameters. The fraction of the light in the hollow cladding can be tuned via the core diameter of the fiber. Dispersion measurements are in excellent agreement with theory and demonstrate tuning of the zero dispersion wavelength via the core diameter. Optimum design parameters for absorption sensors are discussed using a general parameter diagram. From our analysis, we estimate that a sensitivity increase of three orders of magnitude is feasible compared to standard cuvette measurements. Our study applies to both liquid and gas fiber sensors. We demonstrate the applicability of our results to liquid chemical sensing by measuring the broad absorption peak of an aqueous NiCl(2) solution. We find excellent agreement with the reference spectrum measured in a standard cuvette, even though the sample volume has decreased by three orders of magnitude. Our results demonstrate that air-suspended solid-core photonic crystal fibers can be used in quantitative broadband chemical-sensing measurements. (C) 2008 American Institute of Physics.
Absolute testing of the reference surface of a Fizeau interferometer
through even/odd decompositions
Absolute testing of spherical surfaces is a technological necessity because of increased accuracy requirements. In a Fizeau setup, the main part of the interferometer deviations thereby comes from the reference surface. We demonstrate the validity of an absolute testing procedure for the reference surface that has been proposed earlier. The procedure relies on the decomposition of the surface deviations into odd and even parts and could be used in partially coherent illumination. The odd deviations are obtained from a basic and a 180 degrees-rotated position of an auxiliary sphere, and the even deviations can be measured with the help of a cat's eye position in double pass using an opaque half screen in the interferometer aperture. (c) 2008 Optical Society of America
Testing quantum devices: Practical entanglement verification in
bipartite optical systems
We present a method to test quantum behavior of quantum information processing devices, such as quantum memories, teleportation devices, channels, and quantum key distribution protocols. The test of quantum behavior can be phrased as the verification of effective entanglement. Necessary separability criteria are formulated in terms of a matrix of expectation values in conjunction with the partial transposition map. Our method is designed to reduce the resources for entanglement verification. A particular protocol based on coherent states and homodyne detection is used to illustrate the method. A possible test for the quantum nature of memories using two nonorthogonal signal states arises naturally. Furthermore, closer inspection of the measurement process in terms of the Stokes operators reveals a security threat for quantum key distribution involving phase reference beams.
The scintillation index of a laser array beam is analytically derived and numerically evaluated for weak turbulence conditions. On-axis as well as off-axis positions of the receiver plane are considered. Our graphical illustrations prove that at longer propagation ranges and at some midrange radial displacement parameters, laser array beams exhibit less scintillations, when compared to a fundamental Gaussian beam. However, when compared among themselves, laser array beams tend to have reduced scintillations with rising numbers of beamlets, longer propagation wavelengths, at midrange radial displacement parameters, at intermediate Gaussian source sizes, at bigger inner scales and smaller outer scales of turbulence. However, in this improvement, the number of beamlets does not seem to have a major role.
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