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Abouraddy, A. F., B. E. A. Saleh, et al. (2001). "Quantum holography." Optics Express 9(10): 498-505.
We propose to make use of quantum entanglement for extracting holographic information about a remote 3-D object in a confined space which light enters, but from which it cannot escape. Light scattered from the object is detected in this confined space entirely without the benefit of spatial resolution. Quantum holography offers this possibility by virtue of the fourth-order quantum coherence inherent in entangled beams. (C) 2001 Optical Society of America.
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We demonstrate experimentally and theoretically that a coherent image of a pure phase object [implemented by a microelectromechanical system (MEMS) micromirror array] may be obtained by use of a spatially incoherent illumination beam. This is accomplished by employing a two-beam source of entangled photons generated by spontaneous parametric down-conversion. One of the beams probes the phase object while the other is scanned. Though each of the beams is, in and of itself, spatially incoherent, the pair of beams exhibits higher-order interbeam coherence.
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Aharonov, Y. and M. S. Zubairy (2005). "Time and the Quantum: Erasing the Past and Impacting the Future." Science 307(5711): 875-879.
The quantum eraser effect of Scully and Druhl dramatically underscores the difference between our classical conceptions of time and how quantum processes can unfold in time. Such eyebrow-raising features of time in quantum mechanics have been labeled "the fallacy of delayed choice and quantum eraser" on the one hand and described "as one of the most intriguing effects in quantum mechanics" on the other. In the present paper, we discuss how the availability or erasure of information generated in the past can affect how we interpret data in the present. The quantum eraser concept has been studied and extended in many different experiments and scenarios, for example, the entanglement quantum eraser, the kaon quantum eraser, and the use of quantum eraser entanglement to improve microscopic resolution.
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The linear-polarization correlation of pairs of photons emitted in a radiative cascade of calcium has been measured. The new experimental scheme, using two-channel polarizers (i.e., optical analogs of Stern-Gerlach filters), is a straightforward transposition of Einstein-Podolsky-Rosen-Bohm gedankenexperiment. The present results, in excellent agreement with the quantum mechanical predictions, lead to the greatest violation of generalized Bell's inequalities ever achieved.
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The correlation between fluorescence photons emitted by an optically pumped single molecule of pentacene in a p-terphenyl host has been investigated at short times. The correlation function shows photon antibunching, a unique feature of a nonclassical radiation field, which decreases if two molecules rather than one are pumped at the same time. The peculiarities of the correlation function for a three-level molecule are discussed and the theoretical description outlined.
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We generate a pair of entangled beams from the interference of two amplitude squeezed beams. The entanglement is quantified in terms of EPR paradox and inseparability criteria, with both results clearly beating the standard quantum limit. We experimentally analyze the effect of decoherence on each criterion and demonstrate qualitative differences. We also characterize the number of required and excess photons present in the entangled beams and provide contour plots of the efficacy of quantum information protocols in terms of these variables.
Bramon, A., R. Escribano, et al. (2004). Bell's inequality tests: from photons to B-mesons. ArXiv Quantum Physics e-prints: 0410122.
We analyse the recent claim that a violation of a Bell's inequality has been observed in the $B$--meson system [A. Go, {\em Journal of Modern Optics} {\bf 51} (2004) 991]. The results of this experiment are a convincing proof of quantum entanglement in $B$--meson pairs similar to that shown by polarization entangled photon pairs. However, we conclude that the tested inequality is not a genuine Bell's inequality and thus cannot discriminate between quantum mechanics and local realistic approaches.
Bramon, a., G. Garbarino, et al. (2004). "Quantitative complementarity in two-path interferometry." Physical Review A 69(2): 022112.
The quantitative formulation of Bohr's complementarity proposed by Greenberger and Yasin is applied to some physical situations for which analytical expressions are available. This includes a variety of conventional double-slit experiments, but also particle oscillations, as in the case of the neutral-kaon system, and Mott scattering of identical nuclei. For all these cases, a unified description can be achieved including a new parameter nu, which quantifies the effective number of fringes one can observe in each specific interferometric setup.
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We describe a new realization of Ghose, Home, Agarwal experiment on wave particle duality of light where some limitations of the former experiment, realized by Mizobuchi and Ohtake, are overcome. Our results clearly indicate that wave-particle complementarity must be understood between interference and "whelcher weg" knowledge and not in a more general sense. (C) 2004 Elsevier B.V. All rights reserved.
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Young's experiment is the quintessential quantum experiment. It is argued here that quantum interference is a consequence of the finiteness of information. The observer has the choice of whether that information manifests itself as path information or in the interference pattern or partly in both to the extent defined by the finiteness of information.
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The polarization state of biphoton light generated via colinear frequency-degenerate spontaneous parametric down-conversion is considered. A biphoton is described by a three-component polarization vector, its arbitrary transformations relating to the SU(3) group. A subset of such transformations, available with retardation plates, is realized experimentally. In particular, two biphoton beams, formed by colinearly polarized photons (type I) are transformed into a single biphoton beam formed by orthogonally polarized photons (type II). Polarized biphotons are suggested as ternary analogs of two-state quantum systems (qubits). [S1050-2947(99)51312-7].
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We report a proof-of-principle experimental demonstration of quantum lithography. Utilizing the entangled nature of a two-photon state, the experimental results have beaten the classical diffraction limit by a factor of 2. This is a quantum mechanical two-photon phenomenon but not a violation of the uncertainty principle.
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We report a quantum interference and imaging experiment which allows identifying the entanglement in momentum and position variables of a two-photon system. The measurements show indeed that the uncertainties in the sum of momenta and in the difference of positions of the entangled two-photon satisfy both EPR inequalities Delta(k(1)+k(2))<min(Deltak(1),Deltak(2)) and Delta(x(1)-x(2))<min(Deltax(1),Deltax(2)). These two inequalities, together, represent a nonclassicality condition. Our measurements provide a direct way to distinguish between quantum entanglement and classical correlation in continuous variables for systems of pairs of photons.
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A novel manifestation of nonlocality of quantum mechanics is presented It is shown that it is possible to ascertain the existence of an object in a given region of space without interacting with it. The method might have practical applications for delicate quantum experiments.
Epinasse, P. (2005). Bohr's Complementarity Principle Challenged After 80 Years. OE Magazine. 5: 8.
Described by Bohr's Complementarity Principle, wave-particle duality, which considers particle theory and wave theory to be equally valid, yet mutually exclusive, is being challenged after 80 years. No one since Einstein in his apparent loss to Bohr in their famous debate has been able to show both interference and which-way information in the same experiment—until now.
Shahriar S. Afshar, a visiting professor at Rowan University (Glassboro, NJ), carried out a novel version of the "double slit" single photon experiment initially conducted at the Institute for Radiation-Induced Mass Studies (IRIMS; Boston, MA) and Harvard University (Cambridge, MA) in the high-flux regime, which Afshar claims to show light behaving as both particles and waves at the same time. "Wave-particle duality as described by Bohr's Complementarity Principle is incorrect," Afshar explains. "The Measurement Theory must be updated to include non-perturbative measurement schemes. Specifically, the concept of wavefunction collapse and the role of the observer must be revised."
In the simple experiment, a converging lens focuses laser light from two pinholes onto two different photodetectors. A wire grid with wire spacings falling exactly on the dark fringes of the interference pattern from the two slits is positioned just before the lens, enabling an indirect measurement of the wave nature of light. Because there are no photons incident on the wires to be scattered into the wrong image, the photons falling on the detectors demonstrate that each of the photons originate in only one of the pinholes. Thus, one has measured in the same experiment both the complementary wave and particle nature of the light, violating Bohr's Complementarity Principle.
So far, the revised experiment has only been carried out with single photons, not electrons, neutrons, or other particles, and the results have yet to be peer-reviewed. The experiment may lead to applications in the development of interaction-free measurements of light.
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Galvez, E. J., C. H. Holbrow, et al. (2005). "Interference with correlated photons: Five quantum mechanics experiments for undergraduates." American Journal of Physics 73(2): 127-140.
We describe five quantum mechanics experiments that have been designed for an undergraduate setting. The experiments use correlated photons produced by parametric down conversion to generate interference patterns in interferometers. The photons are counted individually The experimental results illustrate the consequences of multiple paths, indistinguishability, and entanglement. We analyze the results quantitatively using plane-wave probability amplitudes combined according to Feynman's rules, the state-vector formalism, and amplitude packets. The apparatus fits on a 2' x 4' optical breadboard. (C) 2005 American Association of Physics Teachers.
Gilchrist, A., K. Nemoto, et al. (2004). "Schroedinger cats and their power for quantum information processing." Journal of Optics B-Quantum and Semiclassical Optics 6(8): S828-S833.
We outline a toolbox comprised of passive optical elements, single photon detection and superpositions of coherent states (Schrodinger cat states). Such a toolbox is a powerful collection of primitives for quantum information processing tasks. We illustrate its use by outlining a proposal for universal quantum computation. We utilize this toolbox for quantum metrology applications, for instance weak force measurements and precise phase estimation. We show in both these cases that a sensitivity at the Heisenberg limit is achievable.
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We present some applications of high-efficiency quantum interrogation ("interaction-free measurement") for the creation of entangled states of separate atoms and of separate photons. The quantum interrogation of a quantum object in a superposition of object-in and object-out leaves the object and probe in an entangled state. The probe can then be further entangled with other objects in subsequent quantum interrogations. By then projecting out those cases in which the probe is left in a particular final state, the quantum objects can themselves be left in various entangled states. In this way, we show how to generate two-, three-, and higher-qubit entanglement between atoms and between photons. The effect of finite efficiency for the quantum interrogation is delineated for the various schemes.
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The photon statistics of the light emitted from an atomic ensemble into a single field mode of an optical cavity is investigated as a function of the number of atoms. The light is produced in a Raman transition driven by a pump laser and the cavity vacuum, and a recycling laser is employed to repeat this process continuously. For weak driving, a smooth transition from antibunching to bunching is found for about one intracavity atom. Remarkably, the bunching peak develops within the antibunching dip. The observed behavior is well explained by a model describing an ensemble of independent emitters.
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We are developing materials for classroom teaching about the quantum behavior of photons in beam splitters as part of a project to create five experiments that use correlated photons to exhibit nonclassical quantum effects vividly and directly. Pedagogical support of student understanding of these experiments requires modification of the usual quantum mechanics course in ways that are illustrated by the treatment of the beam splitter presented here. (C) 2002 American Association of Physics Teachers.
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We report a delayed "choice" quantum eraser experiment of the type proposed by Scully and Druhl (where the "choice" is made randomly by a photon at a beam splitter). The experimental results demon strate the possibility of delayed determination of particlelike or wavelike behavior via quantum entanglement. The which-path or both-path information of a quantum can be marked or erased by its entangled twin even after the registration of the quantum.
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I present the motivation for experiments which attempt to generate, and verify the existence of, quantum superpositions of two or more states which are by some reasonable criterion 'macroscopically' distinct, and show that various a priori objections to this programme made in the literature are flawed. I review the extent to which such experiments currently exist in the areas of free-space molecular diffraction, magnetic biomolecules, quantum optics and Josephson devices, and sketch possible future lines of development of the programme.
Leggett, A. J. (2005). "The Quantum Measurement Problem." Science 307(5711): 871-872.
Despite the spectacular success of quantum mechanics (QM) over the last 80 years in explaining phenomena observed at the atomic and subatomic level, the conceptual status of the theory is still a topic of lively controversy. Most of the discussion centers around two famous paradoxes (or, as some would have it, pseudoparadoxes) associated, respectively, with the names of Einstein, Podolsky, and Rosen (EPR) and with Schrodinger's cat. In this Viewpoint, I will concentrate on the paradox of Schrodinger's cat or, as it is often known (to my mind somewhat misleadingly), the quantum measurement paradox.
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We present a fully operational and consistent approach to complementarity. In contrast to previous approaches, in this proposal the duality relations emerge exclusively from the outcomes of simultaneous measurements performed on every run of the experiment and under the same experimental conditions. This can be done without assuming any definite relationship between the measurement performed and the complementary observables being studied.
Lukishova, S. G., A. W. Schmid, et al. (2003). "Room temperature single-photon source: Single-dye molecule fluorescence in liquid crystal host." Ieee Journal of Selected Topics in Quantum Electronics 9(6): 1512-1518.
We report on new approaches toward an implementation of an efficient, room temperature, deterministically polarized, single-photon source (SPS) on demand-a key hardware element for quantum information and quantum communication. Operation of a room temperature SPS is demonstrated via photon antibunching in the fluorescence from single terrylene-dye molecules embedded in a cholesteric liquid crystal host. Using oxygen-depleted liquid crystal hosts, dye-bleaching was avoided over the course of more than 1 It of continuous 532-nm excitation. Liquid crystal hosts (including liquid crystal oligomers/polymers) permit further increase of the efficiency of the source: 1) by aligning the dye molecules along a direction preferable for maximum excitation efficiency; 2) by tuning a one-dimensional (1-D) photonic-band-gap microcavity of planar-aligned cholesteric (chiral nematic) liquid crystal layer to the dye fluorescence band.
Lvovsky, A. I. A., Thomas (2004). Conditionally prepared photon and quantum imaging. Quantum Communications and Quantum Imaging II, Denver, CO, USA, SPIE.
We discuss a classical model allowing one to visualize and characterize the optical mode of the single photongenerated by means of a conditional measurement on a biphoton produced in parametric down-conversion. The model is based on Klyshko’s advanced wave interpretation, but extends beyond it, providing a precise mathematical description of the advanced wave. The optical mode of the conditional photon is shown to be identical to the mode of the classical difference-frequency field generated due to nonlinear interaction of the partially coherent advanced wave with the pump pulse. With this “nonlinear advanced wave model” most coherence properties of the conditional photon become manifest, which permits one to intuitively understand many recent results, in particular, in quantum imaging.
Martinez-Linares, J. and D. A. Harmin (2004). "'Quality' of a which-way detector." Physical Review A 69(6): 062109.
We introduce a measure Q of the "quality" of a quantum which-way detector, which characterizes its intrinsic ability to extract which-way information in an asymmetric two-way interferometer. The "quality" Q allows one to separate the contribution to the distinguishability of the ways arising from the quantum properties of the detector from the contribution stemming from a priori which-way knowledge available to the experimenter, which can be quantified by a predictability parameter P. We provide an inequality relating these two sources of which-way information to the value of the fringe visibility displayed by the interferometer. We show that this inequality is an expression of duality, allowing one to trace the loss of coherence to the two reservoirs of which-way information represented by Q and P. Finally, we illustrate the formalism with the use of a quantum logic gate: the symmetric quanton-detecton system (SQDS). The SQDS can be regarded as two qubits trying to acquire which-way information about each other. The SQDS will provide an illustrating example of the reciprocal effects induced by duality between system and which-way detector.
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Research on fluorescent semiconductor nanocrystais (also known as quantum dots or qdots) has evolved over the past two decades from electronic materials science to biological applications. We review current approaches to the synthesis, solubilization, and functionalization of qdots and their applications to cell and animal biology. Recent examples of their experimental use include the observation of diffusion of individual glycine receptors in living neurons and the identification of lymph nodes in live animals by near-infrared emission during surgery. The new generations of qdots have far-reaching potential for the study of intracellular processes at the single-molecule level, high-resolution cellular imaging, long-term in vivo observation of cell trafficking, tumor targeting, and diagnostics.
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A quantum cryptographic channel using a 23 km long installed standard telecom optical cable is reported. The key is encoded in the polarization of very weak laser pulses of average photon number 0.12. The measured error rate is lower than 3.4%. The ability of the system to establish a quantum key at standard telecom wavelength (1300 nm) using installed cables is thus assessed.
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Niclass, C., A. Rochas, et al. (2004). "Toward a 3-D camera based on single photon avalanche diodes." Ieee Journal of Selected Topics in Quantum Electronics 10(4): 796-802.
A three-dimensional (3-D) imager is presented, capable of computing the depth map as well as the intensity scale of a given scene. The heart of the system is a two-dimensional array of single photon avalanche diodes fabricated in standard CMOS technology. The diodes exhibit low-noise equivalent-power high-dynamic range, and superior linearity. The 3-D imager achieves submillimetric precision at a depth-of-field of a few meters. This precision was achieved by averaging over 10 000 measurements. The imager operates using a standard laser source pulsed at 50 MHz with 40-mW peak power and requires no mechanical scanning mechanisms or expensive optical equipment.
Oi, D. K. L. (2003). "Interference of quantum channels." Physical Review Letters 91(6): 067902.
We show how interferometry can be used to characterize certain aspects of general quantum processes and, in particular, the coherence of completely positive maps. We derive a measure of coherent fidelity, the maximum interference visibility, and the closest unitary operator to a given physical process under this measure.
Peters, a., K. Y. Chung, et al. (1997). "Precision atom interferometry." Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences 355(1733): 2223-2233.
The basic physical principles behind atom interferometers based on optical pulses of light are summarized. This method of atom interferometry is based on measurements in the time and frequency domain and is an inherently precise measurement technique. After a brief discussion of some of the important technical requirements for good fringe accuracy and visibility, rye describe an interferometer that has measured the acceleration of an atom due to gravity with a resolution better than one part in 10(10). The project that the absolute accuracy of our measurement will be of the order of a few parts in 10(9). The also describe an interferometer experiment that measures the recoil energy shift of an atom when it absorbs a photon. When combined with the value of the Rydberg constant and the mass ratios M-Cs/m(p) and m(p)/m(e), one can obtain a value for a, the fine structure constant. Currently, we have an experimental resolution Delta alpha/alpha similar to 10(-8) after two hours of integration time and are studying the systematic effects that affect the measurement.
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Pittman, T. B., Y. Shih, et al. (1995). "Optical Imaging by Means of 2-Photon Quantum Entanglement." Physical Review A 52(5): R3429-R3432.
A two-photon optical imaging experiment was performed based on the quantum nature of the signal and idler photon pairs produced in spontaneous parametric down-conversion. An aperture placed in front of a fixed detector is illuminated by the signal beam through a convex lens. A sharp magnified image of the aperture is found in the coincidence counting rate when a mobile detector is scanned in the transverse plane of the idler beam at a specific distance in relation to the lens.
Pittman, T. B., D. V. Strekalov, et al. (1996). "Two-photon geometric optics." Physical Review A 53(4): 2804-2815.
We report two-photon correlation experiments using spontaneous parametric down-conversion under a severe manipulation of the input pump field. Considering the case of passing the laser beam through a focusing lens before the down-conversion crystal, theoretical calculations and a series of imaging experiments demonstrate two-photon geometric optics effects. In particular, the imaging in coincidence counts of an aperture placed in one of the down-conversion beams is found to be the analog of a simple spherical mirror system, which displays a ''vacuum dispersion'' effect in that the object and image distances are wavelength weighted.
Pryde, G. J., J. L. O'Brien, et al. (2004). "Measuring a photonic qubit without destroying it." Physical Review Letters 92(19): 190402.
Measuring the polarization of a single photon typically results in its destruction. We propose, demonstrate, and completely characterize a quantum nondemolition (QND) scheme for realizing such a measurement nondestructively. This scheme uses only linear optics and photodetection of ancillary modes to induce a strong nonlinearity at the single-photon level, nondeterministically. We vary this QND measurement continuously into the weak regime and use it to perform a nondestructive test of complementarity in quantum mechanics. Our scheme realizes the most advanced general measurement of a qubit to date: it is nondestructive, can be made in any basis, and with arbitrary strength.
Ronnow, H. M., R. Parthasarathy, et al. (2005). "Quantum phase transition of a magnet in a spin bath." Science 308(5720): 389-392.
The excitation spectrum of a model magnetic system, LiHoF4, was studied with the use of neutron spectroscopy as the system was tuned to its quantum critical point by an applied magnetic field. The electronic mode softening expected for a quantum phase transition was forestalled by hyperfine coupling to the nuclear spins. We found that interactions with the nuclear spin bath controlled the length scale over which the excitations could be entangled. This generic result places a limit on our ability to observe intrinsic electronic quantum criticality.
Rubin, M. H. (2003). Simulating entangled sources by classically correlated sources and quantum imaging. arXiv.
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The transverse correlation between the pairs of photons produced in optical spontaneous parametric down-conversion is analyzed. The interesting features of the correlation arise from the form of the two-photon state generated in the process. The physics of the rings of radiation emerging from the crystal is described. We discuss the theory behind the recent experiments on two-photon geometric and physical optics.
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Atoms interacting with intense laser fields can emit electrons and photons of very high energies. An intuitive and quantitative explanation of these highly nonlinear processes can be found in terms of a generalization of classical Newtonian particle trajectories, the so-called quantum orbits. Very few quantum orbits are necessary to reproduce the experimental results. These orbits are clearly identified, thus opening the way for an efficient control as well as previously unknown applications of these processes.
Schaden, M. and L. Spruch (2004). "Diffraction in the semiclassical approximation to Feynman's path integral representation of the Green function." Annals of Physics 313(1): 37-71.
We derive the semiclassical approximation to Feynman's path integral representation of the energy Green function of a massless particle in the shadow region of an ideal obstacle in a medium. The wavelength of the particle is assumed to be comparable to or smaller than any relevant length of the problem. Classical paths with extremal length partially creep along the obstacle and their fluctuations are Subject to non-holonomic, constraints. If the medium is a vacuum, the asymptotic contribution from a single classical path of overall length L to the energy Green function at energy E is that of a non-relativistic particle of mass E/c(2) moving in the two-dimensional space orthogonal to the classical path for a time tau = L/c. Dirichlet boundary conditions at the surface of the obstacle constrain the motion of the particle to the exterior half-space and result in an effective time-dependent but spatially constant force that is inversely proportional to the radius of curvature of the classical path. We relate the diffractive, classically forbidden motion in the "creeping" case to the classically allowed motion in the "whispering gallery" case by analytic continuation in the curvature of the classical path. The non-holonomic constraint implies that the surface of the obstacle becomes a zero-dimensional caustic of the particle's motion. We solve this problem for extremal rays with piecewise constant curvature and provide uniform asymptotic expressions that are approximately valid in the penumbra as well as in the deep shadow of a sphere. (C) 2004 Elsevier Inc. All rights reserved.
Schwindt, P. D. D., P. G. Kwiat, et al. (1999). "Quantitative wave-particle duality and nonerasing quantum erasure." Physical Review A 60(6): 4285-4290.
The notion of wave-particle duality may be quantified by the inequality V-2 + K-2 less than or equal to 1, relating interference fringe visibility V, and path knowledge K. With a single-photon interferometer in which-polarization is used to label the paths, we have investigated the relation for various situations, including pure, mixed, and partially mixed input states. A quantum-eraser scheme has been realized that recovers interference fringes even when no which way information is available to erase. [S1050-2947(99)02911-X].
Sergienko, A. V., Y. Shih, et al. (1996). Two-photon geometric optical imaging and quantum cryptoFAX. Atomic and Quantum Optics: High-Precision Measurements, St. Petersburg, Russia, SPIE.
Shih, Y. (2003). "Entangled photons." Ieee Journal of Selected Topics in Quantum Electronics 9(6): 1455-1467.
Based on the quantum behavior of entangled photon pairs generated via spontaneous parametric down conversion, this paper reviews the concept of effective two-photon wavefunction or biphoton wavepacket and emphasize the very different physics associated with the entangled two-photon system and with its "individual" subsystems. Experimental approaches for Bell state preparation, pumped by continuous wave and ultrashort pulse, and the propagation of biphoton wavepacket in dispersive media are discussed.
Shih, Y., A. V. Sergienko, et al. (1995). "2-Photon Ghost Image and Interference-Diffraction." Fundamental Problems in Quantum Theory 755: 121-132.
Silberhorn, C., T. C. Ralph, et al. (2002). "Continuous variable quantum cryptography: Beating the 3 dB loss limit." Physical Review Letters 89(16): 167901.
We demonstrate that secure quantum key distribution systems based on continuous variable implementations can operate beyond the apparent 3 dB loss limit that is implied by the beam splitting attack. The loss limit was established for standard minimum uncertainty states such as coherent states. We show that, by an appropriate postselection mechanism, we can enter a region where Eve's knowledge on Alice's key falls behind the information shared between Alice and Bob, even in the presence of substantial losses.
Skagerstam, B.-S. (1998). Topics in Modern Quantum Optics. The 17th Symposium on Theoretical Physics — APPLIED FIELD THEORY. Seoul, Korea, arXiv.
Skagerstam, B.-S. (1996). Interaction-Free Measurements. arXiv.
Storey, P. and C. Cohentannoudji (1994). "The Feynman Path-Integral Approach to Atomic Interferometry - A Tutorial." Journal De Physique Ii 4(11): 1999-2027.
Many problems of current interest in atomic interferometry lend themselves to a path integral treatment. We present a practical guide to solving such problems, taking as examples the gravitational experiments of Kasevich and Chu, and the atomic equivalents of the Sagnac and Aharonov-Bohm effects.
Strekalov, D. V., A. V. Sergienko, et al. (1995). "Observation of 2-Photon Ghost Interference and Diffraction." Physical Review Letters 74(18): 3600-3603.
Tan, E. K., J. Jeffers, et al. (2003). "Retrodictive states and two-photon quantum imaging." European Physical Journal D 22(3): 495-499.
We use retrodictive quantum theory to analyse two-photon quantum imaging systems. The formalism is particularly suitable for calculating conditional probability distributions.
Tan, E. K., J. Jeffers, et al. (2004). "Retrodictive states and two-photon quantum imaging (vol 22, pg 495, 2003)." European Physical Journal D 29(2): 309-309.
Taylor, E. F. and D. F. Styer (2000). cT Executor program, version 3.
Taylor, E. F., S. Vokos, et al. (1998). "Teaching Feynman's sum-over-paths quantum theory." Computers in Physics 12(2): 190-199.
We outline an introduction to quantum mechanics based on the sum-over-paths method originated by Richard P. Feynman. Students use software with a graphics interface to model sums associated with multiple paths for photons and electrons, leading to the concepts of electron wavefunction, the propagator, bound states, and stationary states. Material in the first portion of this outline has been tried with an audience of high-school science teachers. These students were enthusiastic about the treatment, and we feel that it has promise for the education of physicists and ether scientists, as well as for distribution to a wider audience. (C) 1998 American Institute of Physics.
Treussart, F., A. Clouqueur, et al. (2001). "Photon antibunching in the fluorescence of a single dye molecule embedded in a thin polymer film." Optics Letters 26(19): 1504-1506.
We used scanning confocal microscopy to study the fluorescence from a single terrylene molecule embedded in a thin polymer film of polymethyl methacrylate, at room temperature, with a high signal-to-background ratio. The photon-pair correlation function g((2))(tau) exhibits perfect photon antibunching at tau = 0 and a limit of 1.3, compatible with bunching associated with the molecular triplet state. Application of this molecular system to a triggered single-photon source based on single-molecule fluorescence is investigated. (C) 2001 Optical Society of America.
Unruh, W. (2004). Shahriar Afshar — Quantum Rebel?
Valencia, A., G. Scarcelli, et al. (2005). "Two-photon imaging with thermal light." Physical Review Letters 94(6): 063601.
We report the first experimental demonstration of two-photon imaging with a pseudothermal source. Similarly to the case of entangled states, a two-photon Gaussian thin lens equation is observed, indicating EPR type correlation in position. We introduce the concepts of two-photon coherent and two-photon incoherent imaging. The differences between the entangled and the thermal cases are explained in terms of these concepts.
Walborn, S. P., M. O. T. Cunha, et al. (2003). "Quantum erasure - In quantum mechanics, there are two sides to every story, but only one can be seen at a time. Experiments show that "erasing" one allows the other to appear." American Scientist 91(4): 336-343.
Walborn, S. P., M. O. T. Cunha, et al. (2002). "Double-slit quantum eraser." Physical Review A 65(3): 033818.
We report a quantum eraser experiment which actually uses a Young double slit to create interference. The experiment can be considered an optical analogy of an experiment proposed by Scully, Englert, and Walther [Nature (London) 351, 111 (1991)]. One photon of an entangled pair is incident on a Young double slit of appropriate dimensions to create an interference pattern in a distant detection region. Quarter-wave plates, oriented so that their fast axes are orthogonal, are placed in front of each slit to serve as which-path markers. The quarter-wave plates mark the polarization of the interfering photon and thus destroy the interference pattern. To recover interference, we measure the polarization of the other entangled photon. In addition, we perform the experiment under "delayed erasure'' circumstances.
Wheeler, J. A. (1978). The "Past" and the "Delayed-Choice" Double-Slit Experiment. Mathematical Foundations of Quantum Theory. A. R. Marlow. New York, Academic Press: 9-48.
Wheeler, J. A. and R. P. Feynman (1945). "Interaction with the Absorber as the Mechanism of Radiation." Reviews of Modern Physics 17: 157-181.
"We must, therefore, be prepared to find that further advance into this region will require a still more extensive renunciation of features which we are accustomed to demand of the space time mode of description."-Niels Bohr<SUP>1</SUP>
White, A. G., D. F. V. James, et al. (2002). "Exploring Hilbert space: Accurate characterization of quantum information." Physical Review A 65(1): 012301.
We report the creation of a wide range of quantum states with controllable degrees of entanglement and entropy using an optical two-qubit source based on spontaneous parametric down-conversion. The states are characterized using measures of entanglement and entropy determined from tomographically determined density matrices. The tangle-entropy plane is introduced as a graphical representation of these states, and the theoretic upper bound for the maximum amount of entanglement possible for a given entropy is presented. Such a combination of general quantum state creation and accurate characterization is an essential prerequisite for quantum device development.
White, A. G., J. R. Mitchell, et al. (1998). ""Interaction-free" imaging." Physical Review A 58(1): 605-613.
Using the complementary wavelike and particlelike natures of photons, it is possible to make "interaction-free" measurements where the presence of an object can be determined with no photons being absorbed. We investigated several "interaction-free" imaging systems, i.e., systems that allow optical imaging of photosensitive objects with less than the classically expected amount of light being absorbed or scattered by the object. With the most promising system, we obtained high-resolution (10-mu m), one-dimensional profiles of a variety of objects (human hair, glass and metal wires, and cloth fibers) by raster scanning each object through the system. We discuss possible applications and the present and future limits for interaction-free imaging.
Wootters, W. K. and W. H. Zurek (1979). "Complementarity in the double-slit experiment: Quantum nonseparability and a quantitative statement of Bohr's principle." Physical Review D 19(2): 473-484.
A detailed analysis of Einstein's version of the double-slit experiment, in which one tries to observe both wave and particle properties of light, is performed. Quantum nonseparability appears in the derivation of the interference pattern, which proves to be surprisingly sharp even when the trajectories of the photons have been determined with fairly high accuracy. An information-theoretic approach to this problem leads to a quantitative formulation of Bohr's complementarity principle for the case of the double-slit experiment. A practically realizable version of this experiment, to which the above analysis applies, is proposed.
Wu, C. S. and I. Shaknov (1950). "The Angular Correlation of Scattered Annihilation Radiation." Physical Review 77: 136-136.
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Zbinden, H., J. Brendel, et al. (2001). "Experimental test of nonlocal quantum correlation in relativistic configurations." Physical Review A 63(2): 022111.
We report on an experimental investigation of the tension between quantum nonlocality and relativity. Entangled photons are sent via an optical fiber network to two villages near Geneva, separated by more than 10 km where they are analyzed by interferometers. The photon pair source is set as precisely as possible in the center so that the two photons arrive at the detectors within a time interval of less than 5 ps (corresponding to a path length difference of less than 1 mm). One detector is set in motion so that both detectors, each in its own inertial reference frame, are first to do the measurement! The data always reproduces the quantum correlations, making it thus more difficult to consider the projection postulate as a compact description of real collapses of the wave function.