Top PDF Single Photon Experiments and Quantum Complementarity

Single Photon Experiments and Quantum Complementarity

Single Photon Experiments and Quantum Complementarity

It will now be shown that Afshar’s setup is equivalent to Unruh’s setup. In brief Afshar has dual pinholes, a lens, and detectors that record photons streaming away from the pinhole images created at the image plane of the lens (Afshar [3]). Analogously to Unruh’s setup one closes pinhole 1 and sees that light goes only to image 2, then closes pinhole 2 and sees that light goes only to image 1. One may, analog- ously to Unruh’s setup, inconsistently postulate “which way” + pure state density matrix. However, one should note that, in the single pinhole experiments, at the image plane of the lens the zero light intensity outside the central Airy disc of the pinhole image is a result of destructive quantum interference. There are many faint higher order maxima and minima outside the central Airy disc resulting from quantum interference. In order for the two pinhole images to be resolv- able ∗ the image of the second pinhole must be outside the central Airy disc, and located in the first negative Airy ring of the first pinhole image (or further away). Therefore in the case of open pinhole 2 at image 1 there are destructively interfering quantum amplitudes contributed by pinhole 2 be- cause image 1 resides in an Airy minimum of image 2. In contrast at image 2 the waves from pinhole 2 will construc- tively interfere. If both pinholes are open and some of the waves coming from pinhole 1 cross-interfere with waves coming from pinhole 2 in the space before the lens, there will remain a contribution by pinhole 2 at image 1 that will compensate exactly the decrease of quantum waves contri- buted by pinhole 1 at image 1. Now one has to “choose”
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A Survey on Recent Security Trends using Quantum Cryptography

A Survey on Recent Security Trends using Quantum Cryptography

In telecommunication networks, light is routinely used to exchange information. For each bit of information, a pulse is emitted and sent down an optical fiber – a thin fiber of glass used to carry light signals – to the receiver, where it is registered and transformed back into an electronic signal. These pulses typically contain millions of photons. In quantum cryptography, one can follow the same approach, with the only difference that the pulses contain only a single photon. A single photon represents a very tiny amount of light (when reading this article your eyes register billions of photons Quantum cryptography solves the key distribution problem by allowing the exchange of a cryptographic key between two remote parties with absolute security, guaranteed by the laws of physics. This key can then be used with conventional cryptographic algorithms.
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A single molecule investigation of the photostability of quantum dots.

A single molecule investigation of the photostability of quantum dots.

From these experiments it is also apparent that the small reducing agent BME enhances the photoemissive properties of QDs by two distinct means: 1) by minimizing the photobleaching rate of QDs, and 2) by increasing the time when QDs are in their emitting fluorescent state. The improvement effect of BME upon the intermittency frequency in this case is evident from the observed increase of the relative fraction of QDs that are fluorescent. For example, at the start of illumination and in the absence of BME, less than 20% of the total number of the 705 nm QDs are emitting fluorescence within the expected fluorescence spectral range (.690 nm), and where the fraction of fluorescent QDs within this spectral window remaining constant for the first 10 seconds after which a steady decrease of fluorescent QDs emitting at .690 nm coincides with an increase in the number of QDs that emit in the spectral window ranging from 645–665 nm. In contrast, the fraction of fluorescent QDs in the expected spectral window (.690 nm) at the onset of the experiment is about 20% in the presence of 25 m M BME, 45% in the presence of 200 m M BME, and 75% in the presence of 1000 m M BME, respectively. This effect of BME on the QD intermittency is consistent with earlier results [8] while the effect of BME on minimizing the photobleaching of QDs is in contrast to previously published results which reported that BME does prevent blue shifting but not photobleaching of QDs emitting at 525 nm [20]. In agreement with published data [23], we also see a photo- enhancement effect such that the fraction of fluorescent QDs increases with time reaching about 35% (25 m M BME), 75%
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Braz. J. Phys.  vol.35 número2A

Braz. J. Phys. vol.35 número2A

But we can also investigate in a quantitative way under which circumstances molecules will appear as classical balls. The corresponding work has already been published in great detail [13, 17–19]. We will therefore only briefly summarize the general idea of these experiments. Our experiment is a pure ’de Broglie interferometer’, i.e. the internal state of the particle is the same in all possible arms. But which-path infor- mation can be obtained by emission or scattering of particles. It turns out that collisions with molecules in the background gas of the vacuum chamber is a most naturally occurring deco- herence scheme in matter wave interferometry. The colliding particle changes its path in dependence on the exact location of the binary encounter and thus carries information about the collision point (see Fig. 1b). But even in the absence of any residual gas decoherence can occur if the interfering object is sufficiently complex and hot. Such a molecule may emit thermal light, ranging from the visible to the infrared domain. A single photon with a wavelength comparable to the separa- tion of two superposed wave-packets of the diffracting mole- cule suffices to transmit precise information about the location of the emitting particle and thus to destroy the interference pattern. With increasing temperature the probability of pho- ton emission increases and the average wavelength decreases. Both effects smoothly reduce the molecular interference con- trast.
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Widefield Two-Photon Excitation without Scanning: Live Cell Microscopy with High Time Resolution and Low Photo-Bleaching.

Widefield Two-Photon Excitation without Scanning: Live Cell Microscopy with High Time Resolution and Low Photo-Bleaching.

However, since the peak intensity of illumination used in our two-photon widefield microscope is around three orders of magnitude less than Smith et al used in their experiments, it is highly unlikely that we are observing light-induced Ca 2+ transients. Indeed, the sensitivity of the observed Ca 2+ events to blockade of glutamatergic synaptic activity indicates that the events are synaptically driven and are presumably triggered by action potentials arriving at the neuronal cell body, the consequence of which is the transient increase in intracellular Ca 2+ level due to mem- brane potential depolarisation. The close similarity between the optical transients observed here and those recorded electrically in individual cells by the whole-cell path clamp technique in cur- rent clamp mode are a clear demonstration of the sensitivity, time resolution and usefulness of this method. We have concentrated here on the improved time resolution and remarkably low level of photo-bleaching, but, as already pointed out by Hwang et al, there may be other advan- tages over single-photon imaging, such as improved discrimination against auto-fluorescence and clearer imaging of dense tissues. We believe that the new method may have particular value with biological specimens, not only neuronal, where the longevity of the preparation under imag- ing conditions is more important than the precision of optical sectioning. This may include photoprotein-labelled cells within functioning tissues.
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Fast optical preparation, control, and readout of a single quantum dot spin

Fast optical preparation, control, and readout of a single quantum dot spin

Armed with tools for the sequential initialization and readout of a single spin, a number of future experiments are now possible. For example, a magnetic field in the Voigt configuration may be used to achieve an arbitrary phase shift on a single spin [23]. To observe the precession of the hole spin a preparation and readout pulse sequence would be applied. The data presented here strongly suggest that when a third circularly polarized control pulse with a pulse area of 2 is applied, an operation ^ U0; 2 ^  z will induce a relative phase shift of  between the hole spin states, resulting in a phase jump in the spin precession. The phase shift can then be controlled using the detuning of the laser [24].
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Braz. J. Phys.  vol.36 número3B

Braz. J. Phys. vol.36 número3B

The concept of dimensionality in semiconductor structures has been extremely successful during the last two decades: technological efforts have focused first on realization of quasi- two-dimensional quantum wells and have then shifted toward the fabrication of quasi-one and quasi-zero-dimensional struc- tures such as quantum wires and quantum dots (QD). An ar- tificial quantum dot molecule (QDM) is formed by two cou- pled QDs structures located close to each other [1]. The fab- rication of such structures on the nanometer scale presents a considerable technological challenge. Self-assembled quan- tum dots have emerged as one of simplest means of exploiting the physics and device applications. Self-assembly quantum dots are interesting systems in which is possible to study the electronic and excitonic confinement physics and also the in- teraction between the confined units or quantum dots, gain- ing information about the self-organization processes. Khaled Karrai et al. [2] showed that QDs in a self-assembled system can also possess electronic states that go far beyond the arti- ficial atom model. These states are a coherent hybridization of localized QD states and extended continuum states: they have no analogue in atomic physics. The states are gener- ated by emission by a photon from a quantum dot. Coher- ent coupling in quantum dots is interesting for applications as quantum gates, where coherence is important so that quan- tum information is not lost during the gate operation. Single charge excitations (excitons) in semiconductor quantum dots represent an attractive quantum bit since they can coherently manipulated using ultrafast laser pulses over time scales much shorter than their coherence times. However, our interest is in the coupling between the dots is focused in the hybridiza- tion and how these new states could affect the formation of a QDM. We calculate the exciton states of a QD and a QDM quantitatively, in order to obtain the exciton energies in these systems for single, double and triply charge excitons without and in the presence of an external magnetic field. For the QD we reproduce the experimental results reported in [2]. We also calculate the emission energies for the neutral molecule and for the charged QDM as function of the barrier width between the two dots and we find that the Coulomb interaction splits the emission spectra as expected. Additionally, in the triply
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The Brothers Q: multimode entangled photons with parametric down conversion

The Brothers Q: multimode entangled photons with parametric down conversion

interference might include multimode interference of more than 2 photons, as well as the implementation of linear optical quantum logic gates using multimode interference. The theme of chapter 4 is Bell-state measurement: the discrimination of the four Bell states given in equation (2.31). Bell-state measurement is required in several quantum information tasks including quantum teleportation and quantum dense cod- ing. Previous methods of Bell-state anlalysis of polarization-entangled photon pairs utilize two-photon interference at a 50:50 beam splitter. One drawback to this method is that it requires detectors that are sensitive to photon number. At present, reli- able and efficient detectors that can distinguish between one and two photons are not yet available. Using multimode interference, this requirement on the detectors can be eliminated. An experiment was performed in which 3 classes of Bell states were discriminated by detecting in the coincidence basis with single photon detectors.
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Two-Photon Correlation Spectroscopy in Single Dendritic Spines Reveals Fast Actin Filament Reorganization during Activity-Dependent Growth.

Two-Photon Correlation Spectroscopy in Single Dendritic Spines Reveals Fast Actin Filament Reorganization during Activity-Dependent Growth.

The FRAP experiments confirmed (Fig 1) that most of the actin in spines is highly dynamic [20] (mobile fraction of ~79% composed of 65% mobile F-actin and 14% G-actin, S1 Table). The 2P-FCS analysis showed that both identified groups of mobile F-actin filaments within sin- gle spine heads, the very dynamic and much less dynamic group, became much more dynamic exclusively upon an increase in spine head volume during application of Tetraethylammonium (TEA), a protocol previously shown to chemically induce long-term potentiation. These changes indicate a reduction in filaments size of both groups which is further supported by their decreased molecular brightness. While upon spine head growth the calculated number of the less dynamic mobile filaments increased significantly within the fixed observation volume (Fig 2F), the total number of actin subunits (including all G-actin and F-actin subunits, S3A Fig) as well as the number of the much more dynamic filaments did not increase (Fig 2E). These observations suggest that during spine head growth longer filaments in the mobile F- actin fraction are cut into two to three times shorter filaments (Fig 4), albeit these newly formed “shorter” long filaments are still two orders of magnitude larger than a shorter, much more dy- namic filament sub-population (compare diffusion times in Fig 2C with 2D after potentiation). We propose that cutting longer fragments by proteins such as cofilin and cross-linking them by proteins such as α-actinin provides a very fast and efficient way to reorganize the actin net- work upon TEA induced spine growth (Fig 4). Our observations are in agreement with a model in which newly generated shorter filaments are used to “push” the spine head to its
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A SINGLE PHOTON SOURCE MODEL BASED ON QUANTUM DOT AND MICROCAVITY

A SINGLE PHOTON SOURCE MODEL BASED ON QUANTUM DOT AND MICROCAVITY

In this paper we are interested in studying a announced single photon source model, it consists on pyramidal quantum dot conception based on effective mass model, to calculate the photons energies emitted, the optimum dimensions of pyramid selected to obtain one photon at 1550 nm. We have developed a comparative study between photonic crystal and microdisk microcavities. We remark that the quality factor of photonic crystal microcavity Q= 45 is higher than quality factor of microdisk microcavity Q= 7226 . The second deduction is with the photonic crystal we have only one mode at 1550 nm but with microdisk structure we have others modes nearly than 1550 nm. These two points indicate that the photonic crystal microcavity is more appropriate to be used with quantum dot to form a announced single photon source. There is other kind of single photon source a heralded single photon source it consists on 2D active photonic crystal to generate photons at 1310 nm and 1550 nm with height coefficient efficiency around 70% of laser photons are converted at 1310 nm and 1550 nm. Where photons at 1310 nm and 1550 nm will be spatially separated; the photon at 1310 nm is the trigger to announce the photon at 1550 nm.
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Two-photon processes based on quantum commutators

Two-photon processes based on quantum commutators

We developed a new method to calculate two-photon processes in quantum mechanics that re- places the infinite summation over the intermediate states by a perturbation expansion. This latter consists of a series of commutators that involve position, momentum and hamiltonian quantum operators. We analyzed several single- and many-particle cases for which a closed form solution to the perturbation expansion exists, as well as more complicated cases for which a solution is found by convergence. Throughout the article, Rayleigh and Raman scattering are taken as examples of two-photon processes. The present method provides a clear distinction between the Thomson scat- tering, regarded as classical scattering, and quantum contributions. Such a distinction let us derive general results concerning light scattering. Finally, possible extensions to the developed formalism are discussed.
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Use of single photon emission computed tomography and magnetic resonance to evaluate central nervous system involvement in patients with juvenile systemic lupus erythematosus

Use of single photon emission computed tomography and magnetic resonance to evaluate central nervous system involvement in patients with juvenile systemic lupus erythematosus

neurological clinical history, neurological examination, electroencephalography, cere- brospinal fluid analysis, SPECT, and MR. Demographic and clinical data were obtained by a pediatric rheumatologist. Parents/pa- tients were asked about the neuropsychiatric manifestations which had been observed since the onset of the disease. A pediatric neurologist performed neurological exami- nation. Any neurological abnormality found in routine neurological exams, including signs of pyramidal or extrapyramidal involvement, and cerebellar, upper cortical function, neu- romuscular, or peripheral abnormalities was considered to be “neurological abnormal- ity”.
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COMPLEMENTARITY OF INFORMATION TECHNOLOGY AND MARKETING CAPABILITIES

COMPLEMENTARITY OF INFORMATION TECHNOLOGY AND MARKETING CAPABILITIES

E-marketing has the potential to create value in two ways. The first way is through providing a close connection to a company’s business processes and direct access to firm resources. One example of e-Marketing that connects customers to the firm business process is when a firm provides customized support for its customers through extranets (Trainor 2011). Usually, these extranets offer customers access to relevant information, product documentation and direct electronic communication with engineers. In this regard, customers become tightly integrated with the company’s product development lifecycle leading to much greater customer-firm information sharing and interaction. The extranet not only provide customers with a direct interface to firm’s resources, but also provides product management with a rich set of information regarding customer demands and product usage. This form of information exchange plays a critical role in developing and maintain a strong relationship with consumers (Jayachandran et al. 2005). E-marketing capabilities also create value by allowing employees to improve their focus on customers by synchronizing their activities and information in the organization. Outside–in information’s can be integrated with other customer records to improve overall sales productivity and organizational efficiency (Kim & Jae, 2007). Moreover, this valuable customer information can be used by marketers for a better understanding their customers expressed and latent needs (Slater & Narver, 1999). Trainor (2011) conceptualizes e-marketing capabilities as a multi-dimensional construct: Information Technology, Human and Business Resources.
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Arq. Bras. Cardiol.  vol.86 número1 en a08v86n1

Arq. Bras. Cardiol. vol.86 número1 en a08v86n1

Three days following stroke and after the Informed Consent was obtained from her husband and son, the patient was transferred to the Pró-Cardíaco Hospital. At admission, her blood pressure was 110 x 70 mmHg and her heart rate, 85 bpm. Neurological examination showed global aphasia, right faciobrachiocrural hemiparesis and hemihypoesthesia with ipsilateral Babinski’s sign. Deep refl exes were brisk and symmetrical. The National Institute of Health Stroke Scale (NIHSS), modifi ed Rankin Scale (mRS) and Barthel Index scores were 17, 4, and
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Braz. J. Phys.  vol.29 número4

Braz. J. Phys. vol.29 número4

grown on InP substrates have been widely used as ac- tive layers in optoelectronic devices, mainly in long wavelength semiconductor lasers and electroabsorption modulators for optical communication systems. The introduction of a biaxial strain into the active region of multiple-quantum well laser diodes and modulators resulted in improved electro-optic performances as com- pared with similar ones employing lattice-matched qua- ternary materials[1]. Although high quality InGaAsP strained layers have been successfully obtained by dif- ferent growth techniques, the strain relaxation mech- anisms involved in these structures are still unclear. If a critical thickness is exceeded, plastic relaxation of the elastic energy can occur through generation of mis t dislocations. More recently, relaxation through elastic mechanisms was observed in tensile strained In- GaAsP/InP structures, where the strain relief takes place via surface undulations along [110]direction. This elastic relaxation process was found to be strongly de- pendent on the growth temperature and on the growth rate[2-4]. It has been reported evidence of strain re- covery in partially relaxed InGaAs/GaAs single quan-
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Braz. J. Phys.  vol.31 número3

Braz. J. Phys. vol.31 número3

the single and two-photon wavepakets as partiular ases of the most general interferene proess.. The variable wavelength has no impliation on the energy of the individual photons neither [r]

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Assessment of network inference methods: how to cope with an underdetermined problem.

Assessment of network inference methods: how to cope with an underdetermined problem.

reveal associations among genes, not causal relationships. Never- theless, gene associations could still be used for confirming or rejecting edges, even though the direction of the edges cannot be determined. Furthermore, the nature of the gene regulations, i.e. whether a gene activates or inhibits the expression of another gene, has been ignored. Certain regulatory motifs, such as coherent and incoherent FFLs, might therefore be more difficult to infer from from single gene KO/KD experiments [23]. Also, gene compen- satory effects, where the effects of perturbing a gene could be masked by other regulator genes, would add further complications, namely in the inference of the fan-in motifs. While all of these factors would certainly enlarge the non-inferability part of the GRN, the G NI described above should provide a reasonable, albeit
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Aplicabilidade dos Critérios de Adequação em Cintilografia Miocárdica.

Aplicabilidade dos Critérios de Adequação em Cintilografia Miocárdica.

10. Douglas PS, Khandheria B, Stainback RF, Weissman NJ, Brindis RG, Patel MR, et al; American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group; American Society of Echocardiography; American College of Emergency Physicians; American Society of Nuclear Cardiology; Society for Cardiovascular Angiography and Interventions; Society of Cardiovascular Computed Tomography; Society for Cardiovascular Magnetic Resonance; American College of Chest Physicians; Society of Critical Care Medicine. ACCF/ASE/ACEP/ASNC/SCAI/SCCT/SCMR 2007 appropriateness criteria for transthoracic and transesophageal echocardiography: a report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group, American Society of Echocardiography, American College of Emergency Physicians, American Society of Nuclear Cardiology, Society for Cardiovascular Angiography and Interventions,
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Quantum Quasi-Paradoxes and Quantum Sorites Paradoxes

Quantum Quasi-Paradoxes and Quantum Sorites Paradoxes

There can be generated many paradoxes or quasi-paradoxes that may occur from the combination of quantum and non-quantum worlds in physics. Even the passage from the micro-cosmos to the macro-cosmos, and reciprocally, can generate unsolved questions or counter-intuitive ideas. We define a quasi-paradox as a statement which has a prima facie self-contradictory support or an explicit contradiction, but which is not completely proven as a paradox. We present herein four elementary quantum quasi-paradoxes and their corresponding quantum Sorites paradoxes, which form a class of quantum quasi-paradoxes.
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Braz. J. Phys.  vol.32 número2A

Braz. J. Phys. vol.32 número2A

A photon Green's funtion theory is used to inorporate Bethe- Salpeter-like many body orre-.. tions in the the omputations of nonlinear optial spetra of semiondutor quantum well lasero[r]

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