Quantum detector tomography applied to the human visual system: a feasibility study.

We show that quantum detector tomography can be applied to the human visual system to explore human perception of photon number states. In detector tomography, instead of using very hard-to-produce photon number states, the response of a detector to light pulses with known photon statistics of varying intensity is recorded, and a model is fitted to the experimental outcomes, thereby inferring the detector's photon number state response. Generally, light pulses containing a Poisson-distributed number of photons are utilized, which are very easy to produce in the lab. This technique has not been explored to study the human visual system before because it usually requires a very large number of repetitions not suitable for experiments on humans. Yet, in the present study we show that detector tomography is feasible for human experiments. Assuming a simple model for this accuracy, the results of our simulations show that detector tomography is able to reconstruct the model using Bayesian inference with as few as 5000 trials. We then optimize the experimental parameters in order to maximize the probability of showing that the single-photon accuracy is above chance. As such, our study opens the road to study human perception on the quantum level.

Artificial Coherent States of Light by Multiphoton Interference in a Single-Photon Stream.

Coherent optical states consist of a quantum superposition of different photon number (Fock) states, but because they do not form an orthogonal basis, no photon number states can be obtained from it by linear optics. Here we demonstrate the reverse, by manipulating a random continuous single-photon stream using quantum interference in an optical Sagnac loop, we create engineered quantum states of light with tunable photon statistics, including approximate weak coherent states. We demonstrate this experimentally using a true single-photon stream produced by a semiconductor quantum dot in an optical microcavity, and show that we can obtain light with g^{(2)}(0)→1 in agreement with our theory, which can only be explained by quantum interference of at least 3 photons. The produced artificial light states are, however, much more complex than coherent states, containing quantum entanglement of photons, making them a resource for multiphoton entanglement.

Observation of the Unconventional Photon Blockade.

We observe the unconventional photon blockade effect in quantum dot cavity QED, which, in contrast to the conventional photon blockade, operates in the weak coupling regime. A single quantum dot transition is simultaneously coupled to two orthogonally polarized optical cavity modes, and by careful tuning of the input and output state of polarization, the unconventional photon blockade effect is observed. We find a minimum second-order correlation g^{(2)}(0)≈0.37, which corresponds to g^{(2)}(0)≈0.005 when corrected for detector jitter, and observe the expected polarization dependency and photon bunching and antibunching; close by in parameter space, which indicates the abrupt change from phase to amplitude squeezing.

Electro-optic polarization tuning of microcavities with a single quantum dot.

We present an oxide aperture microcavity with embedded quantum dots which utilizes a three-contact design to independently tune the quantum dot wavelength and birefringence of the cavity modes. A polarization splitting tuning of ∼5 GHz is observed. For a typical microcavity polarization splitting, the method can be used to achieve perfect polarization degeneracy that is required for many polarization-based implementations of photonic quantum gates. The embedded quantum dot wavelength can be tuned into resonance with the cavity, independent of the polarization tuning.

Pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome: differential diagnosis of septic arthritis by regular detection of exceedingly high synovial cell counts.

Pyogenic arthritis, pyoderma gangrenosum and acne syndrome was diagnosed in a 42-year-old patient, after an unusual persistency of high synovial cell counts had been noticed. Clinical peculiarities and problems with diagnosing septic versus non-septic arthritis are discussed.

Purification of a single-photon nonlinearity.

Single photon nonlinearities based on a semiconductor quantum dot in an optical microcavity are a promising candidate for integrated optical quantum information processing nodes. In practice, however, the finite quantum dot lifetime and cavity-quantum dot coupling lead to reduced fidelity. Here we show that, with a nearly polarization degenerate microcavity in the weak coupling regime, polarization pre- and postselection can be used to restore high fidelity. The two orthogonally polarized transmission amplitudes interfere at the output polarizer; for special polarization angles, which depend only on the device cooperativity, this enables cancellation of light that did not interact with the quantum dot. With this, we can transform incident coherent light into a stream of strongly correlated photons with a second-order correlation value up to 40, larger than previous experimental results, even in the strong-coupling regime. This purification technique might also be useful to improve the fidelity of quantum dot based logic gates.

Observation of Four-Photon Orbital Angular Momentum Entanglement.

We demonstrate genuine multipartite quantum entanglement of four photons in their orbital angular momentum degrees of freedom, where a high-dimensional discrete Hilbert space is attached to each photon. This can encode more quantum information compared to the qubit case, but it is a long-standing problem to entangle more than two such photons. In our experiment we use pulsed spontaneous parametric down-conversion to produce the photon quadruplets, which allows us to detect about one four-photon event per second. By means of quantum state reconstruction and a suitable witness operator we find that the photon quadruplets form a genuine multipartite entangled symmetric Dicke state. This opens a new tool for addressing foundational questions in quantum mechanics, and for exploration of novel high-dimensional multiparty quantum information applications such as secret sharing.

Walsh modes and radial quantum correlations of spatially entangled photons.

Orthogonal sets of 2D transverse modes are key to controlling the spatial degree of freedom of light in a classical or quantum context. In contrast to the azimuthal part, which is easily accessible using orbital angular momentum modes, control of the radial part is more difficult. We show here that simple sets of orthogonal binary sequences, the Walsh functions, provide a workable solution for exploration of the radial space with phase-only spatial light modulation. We demonstrate this by measuring "sequency" quantum correlations between different radial Walsh modes of spatially entangled photon pairs and for numerically optimized versions thereof.

Spatial coherence and optical beam shifts.

A beam of light, reflected at a planar interface, does not follow perfectly the ray optics prediction. Diffractive corrections lead to beam shifts; the reflected beam is displaced (spatial Goos-Hänchen type shifts) and/or travels in a different direction (angular Imbert-Fedorov type shifts), as compared to geometric optics. How does the degree of spatial coherence of light influence these shifts? We investigate this issue first experimentally and find that the degree of spatial coherence influences the angular beam shifts, while the spatial beam shifts are unaffected.

Instability of higher-order optical vortices analyzed with a multi-pinhole interferometer.

Higher-order optical vortices are inherently unstable in the sense that they tend to split up in a series of vortices with unity charge. We demonstrate this vortex-splitting phenomenon in beams produced with holograms and spatial light modulators and discuss its generic and practically unavoidable nature. To analyze the splitting phenomena in detail, we use a multi-pinhole interferometer to map the combined amplitude and phase profile of the optical field. This technique, which is based on the analysis of the far-field interference pattern observed behind an opaque screen perforated with multiple pinholes, turns out to be very robust and can among others be used to study very 'dark' regions of electromagnetic fields. Furthermore, the vortex splitting provides an ultra-sensitive measurement method of unwanted scattering from holograms and other phase-changing optical elements.

Observation of orbital angular momentum sidebands due to optical reflection.

We investigate how the orbital angular momentum of a paraxial light beam is affected upon reflection at a planar interface. Theoretically, the unavoidable angular spread of the beam leads to orbital angular momentum sidebands, which are found to be already significant for a modest beam spread (0.05). In analogy to the polarization Fresnel coefficients, we develop an analytical theory based upon spatial Fresnel coefficients; this allows a straightforward prediction of the strength of the sidebands. We confirm this by experiment and numerical simulation.

Full-field quantum correlations of spatially entangled photons.

Spatially entangled twin photons allow the study of high-dimensional entanglement, and the Laguerre-Gauss modes are the most commonly used basis to discretize the single-photon mode spaces. In this basis, to date only the azimuthal degree of freedom has been investigated experimentally due to its fundamental and experimental simplicity. We show that the full spatial entanglement is indeed accessible experimentally; i.e., we have found practicable radial detection modes with negligible cross correlations. This allows us to demonstrate hybrid azimuthal-radial quantum correlations in a Hilbert space with more than 100 dimensions per photon.

Fiber transport of spatially entangled photons.

Entanglement in the spatial degrees of freedom of photons is an interesting resource for quantum information. For practical distribution of such entangled photons, it is desirable to use an optical fiber, which in this case has to support multiple transverse modes. Here we report the use of a hollow-core photonic crystal fiber to transport spatially entangled qubits.

Search for Hermite-Gauss mode rotation in cholesteric liquid crystals.

In theory, there are analogous transformations of light's spin and orbital angular momentum [Allen and Padgett, J. Mod. Opt. 54, 487 (2007)]; however, none have been observed experimentally yet. In particular, it is unknown if there exists for the orbital angular momentum of light an effect analogous to the spin angular momentum-based optical rotation; this would manifest itself as a rotation of the corresponding Hermite-Gauss mode. Here we report an experimental search for this effect in a cholesteric liquid crystal polymer, using strongly focussed, spin-orbit coupled light. We find that the relative phase velocities of the orbital modes constituting the Hermite-Gauss mode agree to within 10(-5).

Localized and delocalized modes in coupled optical micropillar cavities.

Optical micropillar Bragg cavities of different diameters and coupled by a small bridge have been realized experimentally by means of a focused ion beam system. The resonator modes in these coupled microcavities are either localized in one pillar or delocalized over the whole photonic structure, a fact that could be exploited to control the coupling between two spatially separated quantum dots, i.e. placed in different pillars, via the enhanced electromagnetic field in such a coupled microcavity. A simplified two dimensional simulation has been used to predict the resonant wavelengths and design the optical modes in these coupled Bragg cavities.

Patient acceptance of diagnostic laparoscopy.

PURPOSE: To assess patient acceptance of diagnostic conventional laparoscopy and minilaparoscopy under sedoanalgesia. MATERIALS AND METHODS: 120 consecutive patients undergoing diagnostic laparoscopy were enrolled prospectively in this study. Within the first week after diagnostic laparoscopy the patients were asked to answer a total of eight questions with regard to the acceptance of the procedure. RESULTS: The inconvenience of laparoscopy was assessed with a mean of 1.6 on a scale from 0 to 10 (0 = no inconvenience, 10 = very unpleasant). The discomfort in the two days following laparoscopy were graded with a mean of 2.1 on a scale from 0 to 10 (0 = no inconvenience, 10 = very unpleasant). There was no difference between conventional laparoscopy and minilaparoscopy. Only 10% of the patients described laparoscopy more inconvenient in comparison to diagnostic gastroscopy, whereas 29% of the patients assessed diagnostic gastroscopy more inconvenient. CONCLUSIONS: Diagnostic laparoscopy under sedoanalgesia is a very well tolerated procedure. There is no difference between conventional laparoscopy and minilaparoscopy.

Long-term results of Rehbein's procedure: a retrospective study in German-speaking countries.

AIM: In contrast to other countries, no collective study of Rehbein's procedure in German-speaking nations has been performed. Therefore, our intention was, analogously to Goto and Ikeda's (10) Japanese study in 1984, Kleinhaus's (13) study on Swenson's procedure in 1979, Bourdelat's (2) French-Canadian investigation into Duhamel's technique in 1997 and Martuciello's (11) and Teitelbaum's (16) follow-up in the year 2000, to perform a follow-up study of Rehbein's technique of deep anterior resection. METHODS: The data of 200 patients from 22 German-speaking centers in Switzerland, Austria and Germany were collected. These data were gathered by questionnaire and the children were followed up in the individual participating hospitals for at least 3.5 years after the procedure. The procedure was performed between 1993 and 1997, over a 5-year period. The questionnaire contained 74 items including anamnestic data, diagnostic postoperative treatment and reoperations. RESULTS: Concerning the incidence of anastomotic leaks and resolving anastomotic strictures there was no significant difference between the results in our series and those of the collective analyses made by Hofmann von Kap-herr (7), Holschneider (9) and Sherman (18). In 6.6 % of the 191 patients an anastomotic leak and in 9.9 % a rectal stricture, which had to be dilated, was observed. Concerning late complications, 22.8 % of the children suffered from constipation, 4.3 % from encopresis, 10.6 % from enterocolitis and only 0.5 % from enuresis. The frequency of constipation diminishes over the years. A comparison of the different large series in the literature clearly shows that the incidence of constipation is higher after Rehbein's procedure and the frequency of urinary incontinence and encopresis higher following Swenson's, Soave's and Duhamel's techniques. The incidence of enterocolitis is less after Rehbein's procedure than after Swenson's, Soave's and Duhamel's techniques. CONCLUSIONS: The different results in the literature are due to the individual experience of the author, the very different follow-up methods and the date of follow-up. Therefore, the different results are hard to compare with our study. Nevertheless, Rehbein's anterior resection still could be presented as an adequate and important method to treat Hirschsprung's disease.

Schizophrenic patients' subjective reasons for compliance and noncompliance with neuroleptic treatment.

Although several factors influencing schizophrenic patients' compliance with neuroleptic treatment have been investigated, the subjective reasons that patients are willing or reluctant to take medication have rarely been examined. In a follow-up study of a sample of schizophrenic patients currently undergoing psychiatric treatment in the city of Leipzig, 307 patients were asked about their subjective reasons for medication compliance or noncompliance by administering the Rating of Medication Influences (ROMI) Scale. The perceived benefit from medication proved to be the main reason for patients' compliance with neuroleptic treatment. Respectively, patient-reported noncompliance was mainly explained by negative side effects of medication. However, there were no statistically significant differences in responses between the patients receiving conventional versus second-generation antipsychotics. A positive relationship with the therapist and a positive attitude of significant others toward neuroleptic treatment contributed to patients' medication compliance. Reasons for noncompliance with neuroleptic treatment were lack of acceptance of the necessity of pharmacological treatment and lack of insight into the disease. The results emphasize the importance of psychoeducation in enhancing patient compliance with neuroleptic treatment.

[Causal beliefs of schizophrenic patients]. / Vorstellungen schizophrener Patienten über die Ursachen ihrer Erkrankung.

RESEARCH QUESTION: Aim of the study is to investigate whether the preference of schizophrenic patients for psychosocial causal explanations found in a previous study carried out in Hamburg can be observed elsewhere. Further aim of the study was to find out how stable patients' causal attributions are over time. Finally, we were interested to know to what degree patients' beliefs reflect those held by the general public. METHOD: Using an inventory comprising 15 items, we inquired about 105 schizophrenic patient's aetiological ideas at the time of discharge from hospital from inpatient or daycare treatment at 4 psychiatric hospitals in Germany. Follow-ups were carried out 3 months and 6 months later. RESULTS: Psychosocial factors, especially psychosocial stress, were most frequently held responsible for the onset of the illness. The possibility that biological factors might play a role in the causation of schizophrenia was considered more rarely by the patients. There were practically no regional variations as concerns aetiological beliefs. The tendency to endorse psychosocial stress factors was more pronounced among patients as compared with the general public. In total the causal beliefs proved to be quite stable over a time period of 6 months. DISCUSSION: Patients' causal beliefs are compared with findings of psychiatric research, and possible ways to bridge the gap between the two are discussed.

[Schizophrenia and delusions in middle aged and elderly patients. Epidemiology and etiological hypothesis]. / Schizophrenie und Wahn im höheren und hohen Lebensalter. Epidemiologie und ätiologische Hypothesen.

Knowledge of the similarities and differences between early- and late-onset schizophrenia and between late-onset schizophrenia and paranoid disorder of old age and very old age is fragmentary. We compared diagnosis, subtypes, syndromes and symptoms between first-episode schizophrenia (ICD-9: 295) and paranoid disorder (ICD-9: 297, 298.3/4.) over the life cycle in a population-based (N = 232) and a clinical first-admission sample (N = 1109). Apart from different age patterns of the sexes only two symptom groups were significantly different between early- and late-onset illness: paranoid and systematic delusions showed a linear increase, symptoms of disorganisation a linear decrease over the life cycle. Clearly different between early- and late-onset illness were the neurobiological and psychological risk factors, suggesting that both neurodevelopmental and neurodegenerative disorder causes psychopathology typical of schizophrenia. Late- (40 to 60) and very-late-onset (over 60) cases of both groups of illness showed the same symptom profiles, merely the number of symptoms being higher in the group diagnosed with schizophrenia. Age was the only factor significantly contributing to a clinico-diagnostic differentiation of schizophrenia from paranoid disorder beyond age 40.