| 1. |
- Giustina, Marissa, et al.
(author)
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Significant-Loophole-Free Test of Bells Theorem with Entangled Photons
- 2015
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In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 115:25, s. 250401-
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Journal article (peer-reviewed)abstract
- Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bells theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bells inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74 x 10(-31), corresponding to an 11.5 standard deviation effect.
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| 2. |
- Holmberg, Patrik, 1971-
(author)
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Laser processing of Silica based glass
- 2015
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Doctoral thesis (other academic/artistic)abstract
- The main topic of this thesis work is photosensitivity and photo-structuring of optical fibers and bulk glass. Although research in the field of photosensitivity in glass and optical fibers has been ongoing for more than three decades, the underlying mechanisms are still not well understood. The objective was to gain a better understanding of the photo-response by studying photosensitivity from a thermodynamic perspective, as opposed to established research focusing on point defects and structural changes, and strain and stress in optical fibers. Optical fibers was mainly used for experimental studies for two reasons; first, photosensitivity in fibers is more pronounced and more elusive compared to its bulk counterpart, and secondly, fibers provide a simplified structure to study as they experimentally can be seen as one-dimensional.Initially, ablation experiments on bulk glass were performed using picosecond infrared pulses. With a design cross section of 40x40 μm, straight channels were fabricated on the top (facing incident light) and bottom side of the sample and the resulting geometries were analyzed. The results show a higher sensitivity to experimental parameters for bottom side ablation which was ascribed to material incubation effects. Moreover, on the top side, the resulting geometry has a V-shape, independent of experimental parameters, related to the numerical aperture of the focusing lens, which was ascribed to shadowing effects.After this work, the focus shifted towards optical fibers, UV-induced fiber Bragg gratings (FBGs) and thermal processing with conventional oven and with a CO2 laser as a source of radiant heat.First, a system for CO2 laser heating of optical fibers was constructed. For measuring the temperature of the processed fibers, a special type of FBG with high temperature stability, referred to as "Chemical Composition Grating" (CCG) was used. A thorough characterization and temperature calibration was performed and the results show the temperature dynamics with a temporal resolution of less than one millisecond. The temperature profile of the fiber and the laser beam intensity profile could be measured with a spatial resolution limited by the grating length and diameter of the fiber. Temperatures as high as ~ 1750 °C could be measured with corresponding heating and cooling rates of 10.500 K/s and 6.500 K/s.Subsequently, a thorough investigation of annealing and thermal regeneration of FBGs in standard telecommunication fibers was performed. The results show that thermal grating regeneration involves several mechanisms. For strong regeneration, an optimum annealing temperature near 900 C was found. Two different activation energies could be extracted from an Arrhenius of index modulation and Braggv iwavelength, having a crossing point also around 900 °C, indication a balance of two opposing mechanisms.Finally, the thermal dynamics and spectral evolution during formation of long period fiber gratings (LPGs) were investigated. The gratings were fabricated using the CO2 laser system by periodically grooving the fibers by thermal ablation. Transmission losses were reduced by carefully selecting the proper processing conditions. These parameters were identified by mapping groove depth and transmission loss to laser intensity and exposure time.
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| 3. |
- Joshi, Siddarth Koduru, et al.
(author)
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Space QUEST mission proposal : experimentally testing decoherence due to gravity
- 2018
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 20
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Journal article (peer-reviewed)abstract
- Models of quantum systems on curved space-times lack sufficient experimental verification. Some speculative theories suggest that quantum correlations, such as entanglement, may exhibit different behavior to purely classical correlations in curved space. By measuring this effect or lack thereof, we can test the hypotheses behind several such models. For instance, as predicted by Ralph et al [5] and Ralph and Pienaar [1], a bipartite entangled system could decohere if each particle traversed through a different gravitational field gradient. We propose to study this effect in a ground to space uplink scenario. We extend the above theoretical predictions of Ralph and coworkers and discuss the scientific consequences of detecting/failing to detect the predicted gravitational decoherence. We present a detailed mission design of the European Space Agency's Space QUEST (Space-Quantum Entanglement Space Test) mission, and study the feasibility of the mission scheme.
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| 4. |
- Mühlberger, Korbinian
(author)
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Temperature measurements on silicon core fibers during CO2 laser processing
- 2022
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Doctoral thesis (other academic/artistic)abstract
- This thesis presents temperature measurements on silicon core optical fibers during CO2 laser processing. Silicon core fibers are a new type of fiber offering a unique platform to combine the optoelectronic properties of silicon and the possibilities of the optical fiber platform. This makes them a promising candidate for many applications, such as mid-IR detection and transmission, studies of nonlinear optical devices, or fiber amplifiers. Today, two hurdles limit their usage: high optical transmission losses and complicated coupling into the core due to its high refractive index. The first task of this thesis work was to find suitable postprocessing of the as-drawn fibers in order to decrease optical transmission losses. The goal was to improve the fibers by the liquid-phase recrystalliza[1]tion method. In this method, the core of the fiber is heated to a temperature above its melting point by a laser beam. By scanning the beam along the fiber, a melt zone is moved through the fiber. When the silicon solidifies, it recrystallizes into a single crystal with lower optical losses. Successively, a fully computer-controlled setup was developed for fiber processing. Furthermore, a lab-size fiber draw tower was built to fabricate specialty fibers, especially silicon core fibers. Here, a CO laser acts as the heat source. The developed draw tower is very flexible and can be used to manufacture ample amounts of many fiber types quickly. It is known that the cooling rate at which the silicon core solidifies is a crucial parameter for the final transmission losses. Yet, it has so far only been estimated from black-body radiation. Here, an interferometric method was developed, allowing for in-situ temperature measurements in silicon core optical fibers. The method relies on probing the fiber with a laser beam during processing and observing the interference pattern caused by glass reflections. A suitable calibration of the interference pattern with temperature allowed to remotely monitor the fiber temperature in real-time during processing with high precision.
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