Fluctuations and dissipation in a Bose-Einstein condensed photon gas

Bose-Einstein condensation, superfluidity and superconductivity are all related phenomena where particles behave as collective quantum systems. The behavior of such systems is treated using quantum statistics and their properties such as energy distribution or coherence are used to describe the system at a macroscopic level. These quantities are affected not only by the intrinsic features of the particles that constitute the quantum gas, but also by the interaction of these particles with their environment. The effect of a coupling of the quantum gas with its surroundings can be as drastic as completely changing its coherence properties or it might lead to a slight deviation from an equilibrium energy distribution. In this thesis, we investigate the effects caused by coupling a quantum gas of light with its environment. Quantum gases of light are realized in optical microcavities filled with a medium the photons couple to. If a strong coupling between the light and the medium is realized, the gas comprises mixed states of matter and light such as polaritons. Phenomena like lasing, Bose-Einstein condensation and superfluidity can be observed in such systems. In the opposite case, when the coupling of medium and photons is weak, no coherent coupling is established and the gas consists of pure photons. The latter situation can be experimentally realized in high quality optical microcavities filled with photo-excitable dye molecules. In this system it was shown that if the lifetime of the photons in the cavity are sufficiently long, they thermalize at the temperature of the dye solution. And if the density of the photons is increased beyond a critical point, a Bose-Einstein condensate of photons forms. A distinct feature of a condensate of photons in the dye-microcavity system compared to atom or polariton condensates is that the dye molecules act as a reservoir of particles, as well as energy. The photon gas exchanges particles with excited dye molecules and the coupling between the two is of statistical nature. It has been shown that Bose-Einstein condensation can coexist with unusually large particle number fluctuations in the so called grand-canonical statistical ensemble regime. In the first part of this thesis, we experimentally investigate the fluctuation-dissipation relation in a Bose-Einstein condensate of photons realized in the dye-microcavity. In equilibrium, thermally driven fluctuations are closely connected to how the system dissipates its excess energy or particles. This relation is so general that it has been observed in a variety of systems ranging from Brownian particles to quantum gases of atoms. However, its validity in Bose-Einstein condensates has not been shown. Despite being intrinsically in thermal equilibrium, fluctuations usually completely diminish in a Bose-Einstein condensate soon after the condensation threshold. We measure the second-order coherence of the photon Bose-Einstein condensate to search for the expected ratio of statistical number fluctuations and compressibility following the fluctuation-dissipation theorem. Another intriguing aspect of the photon condensate is introduced due to the imperfect reflectivity of the cavity mirrors. In the second part of this thesis we show that this openness can lead to the existence of new states of the condensate. Physical models often consider systems that are completely isolated from their environment, such as a gas of particles closed in a box. Real-life situations often deviate from these idealized scenarios and the system loses energy or particles to its surroundings. In contemporary physics, systems which are dissipatively coupled to the environment are actively studied in a broad range of research fields ranging from optics to biophysics. Here, we investigate the open-system dynamics of a photon condensate in grand-canonical ensemble conditions. We identify non-Hermitian phases of the system that are observed by abrupt changes in the dynamics of the condensate’s second-order coherence

Artificial olfaction with hollow core bragg fiber arrays

Ankara : Materials Science and Nanotechnology Program of The Graduate School of Engineering and Science of Bilkent Univesity, 2014.Thesis (Ph. D.) -- Bilkent University, 2014.Includes bibliographical references leaves 83-89.An optoelectronic nose for the analysis of alcohols (ethanol and methanol) in chemically complex environments is reported. The cross-responsive sensing unit of the optoelectronic nose is an array of three distinct hollow core infrared (IR) transmitting photonic band gap fibers (Bragg fibers), which transmit a specific band of IR light depending on their Bragg mirror structures. Presence of alcohol molecules in the optofluidic core quench the fiber transmissions if there is an absorption band of the analyte overlapping with the transmission band of the fiber. The cumulative response data of the fiber array enables rapid, reversible and accurate discrimination of alcohols in chemically complex backgrounds such as beer and fruit juice. In addition, we observed that humidity of the environment has no effect on the response of the optoelectronic nose, which is rarely achieved in gas sensing applications. Consequently, it can be reliably used in virtually any environment without precalibration for humidity or drying the analytes. To further improve the performance, we engineered the photonic bandgap of Bragg fibers by controlling the thickness profile of the fiber during the thermal drawing. Conical hollow core Bragg fibers were produced by thermal drawing under a rapidly alternating load, which was applied by introducing steep changes to the fiber drawing speed. In conventional cylindrical Bragg fibers, light is guided by omnidirectional reflections from interior dielectric mirrors with a single quarter wave stack period. In conical fibers, the diameter reduction introduced a gradient of the quarter wave stack period along the length of the fiber. Therefore, the light guided within the fiber encountered slightly smaller dielectric layer thicknesses at each reflection, resulting in a progressive blueshift of the reflectance spectrum. As the reflectance spectrum shifts, longer wavelengths of the initial bandgap cease to be omnidirectionally reflected and exit through the cladding, which narrows the photonic bandgap. A narrow transmission bandwidth is particularly desirable in hollow waveguide mid-infrared sensing schemes such as the optoelectronic nose. We carried out sensing simulations using the absorption spectrum of isopropyl alcohol vapor to demonstrate the importance of narrow bandgap fibers in chemical sensing applications.Öztürk, Fahri EmrePh.D

Cytohistological discrepancies of cervico-vaginal smears and HPV status

Objectives: Discrepancies between abnormal cervical cytology or high-risk human papillomavirus (HR-HPV) status (cytolo-gy negative/HPV positive) and subsequent histological findings are a common occurrence. After using co-testing, the dis­crepancies between the HR-HPV status and cervical cytology have become an issue. In this study, we aimed to determine the characteristics of women with a discrepancy between histology and cytology/HR-HPV status, in terms of diagnosis, review and identification. Material and methods: A total of 52 women, patients of the University Hospital between 2013–2015, with cytohistologi­cal or HR-HPV status discrepancy were recruited for the study and retrospectively analyzed. The cytological samples were liquid-based Pap smears, classified according to the 2001 Bethesda system. The HR-HPV status was identified using the Hybrid Capture 2 HR-HPV DNA assay. The histological samples were obtained by cervical biopsy as well as large loop exci­sion of the transformation zone (LLETZ). Results: A cytohistological discrepancy was demonstrated in patients with (-)cytology/HR-HPV(+), ASCUS, LSIL, ASC-H, HSIL, AGC-NOS: 17.3%, 23.07%, 26.9%, 9.5%, 17.3% and 5.7%, respectively. When the degree of atypia in cytology increases, the concurrency of cervical cytology with biopsy also increases. A positive HR-HPV co-test result (19/24, 79.1%) was observed in nearly all CIN2 ≥ (+) cases. Our study emphasizes the significance of HR-HPV testing to determine CIN2 ≥ (+) cases, even in the presence of a normal cytological result. Conclusions: In case of cytohistological or HR-HPV discrepancies, a careful review of the HR-HPV status and the degree of cytological atypia should be performed before further intervention

Observation of a non-Hermitian phase transition in an optical quantum gas

Quantum gases of light, as photons or polariton condensates in optical microcavities, are collective quantum systems enabling a tailoring of dissipation from e.g. cavity loss. This makes them a tool to study dissipative phases, an emerging subject in quantum manybody physics. Here we experimentally demonstrate a non-Hermitian phase transition of a photon Bose-Einstein condensate to a new dissipative phase, characterized by a biexponential decay of the condensate's second-order coherence. The phase transition occurs due to the emergence of an exceptional point in the quantum gas. While Bose-Einstein condensation is usually connected to ordinary lasing by a smooth crossover, the observed phase transition separates the novel, biexponential phase from both lasing and an intermediate, oscillatory condensate regime. Our findings pave the way for studies of a wide class of dissipative quantum phases, for instance in topological or lattice systems.Comment: 10 pages, 4 figures, (additional 22 pages for supplementary information

Fluctuation-dissipation relation for a Bose-Einstein condensate of photons

For equilibrium systems, the magnitude of thermal fluctuations is closely linked to the dissipative response to external perturbations. This fluctuation-dissipation relation has been described for material particles in a wide range of fields. Here we experimentally probe the relation between the number fluctuations and the response function for a Bose-Einstein condensate of photons coupled to a dye reservoir, demonstrating the fluctuation-dissipation relation for a quantum gas of light. The observed agreement of the scale factor with the environment temperature both directly confirms the thermal nature of the optical condensate and demonstrates the validity of the fluctuation-dissipation theorem for a Bose-Einstein condensate.Comment: 5 pages, 4 figure

Observation of a non-hermitian phase transition in an optical quantum gas

Quantum gases of light, such as photon or polariton condensates in optical microcavities, are collective quantum systems enabling a tailoring of dissipation from, for example, cavity loss. This characteristic makes them a tool to study dissipative phases, an emerging subject in quantum many-body physics. We experimentally demonstrate a non-Hermitian phase transition of a photon Bose-Einstein condensate to a dissipative phase characterized by a biexponential decay of the condensate's second-order coherence. The phase transition occurs because of the emergence of an exceptional point in the quantum gas. Although Bose-Einstein condensation is usually connected to lasing by a smooth crossover, the observed phase transition separates the biexponential phase from both lasing and an intermediate, oscillatory condensate regime. Our approach can be used to study a wide class of dissipative quantum phases in topological or lattice systems

Sezaryen sırasında insidental olarak saptanan over tümörü

Overin müsinöz tümörleri, seröz over tümörlerinden sonra en sık karşımızı çıkan epitelyal over tümörlerindendir. Gebelik esnasında over tümörleri ile nadir olarak karşılaşmaktayız. Olguların bir kısmı, rutin antenatal takipler sırasında ultrasonografi ve fizik muayene ile tanı alırken, diğer bir kısmı ise insidental olarak sezaryen sırasında karşımıza çıkmaktadır. Bu olguda, 30 yaşında nullipar hastada, sezaryen ile doğumu gerçekleştirildiği esnada insidental olarak tespit edilen over tümöründen söz edilmiştir

Disappearance of Biodiversity and Future of Our Foods

“I. Uluslararası Organik Tarım ve Biyoçeşitlilik Sempozyumu 27-29 Eylül Bayburt