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Publication Metadata only Terrestrial very-long-baseline atom interferometry: workshop summary(AIP Publishing, 2024) Abend, Sven; Allard, Baptiste; Alonso, Ivan; Antoniadis, John; Araujo, Henrique; Arduini, Gianluigi; Arnold, Aidan S.; Asano, Tobias; Augst, Nadja; Badurina, Leonardo; Balaz, Antun; Banks, Hannah; Barone, Michele; Barsanti, Michele; Bassi, Angelo; Battelier, Baptiste; Baynham, Charles F. A.; Beaufils, Quentin; Belic, Aleksandar; Beniwal, Ankit; Bernabeu, Jose; Bertinelli, Francesco; Bertoldi, Andrea; Biswas, Ikbal Ahamed; Blas, Diego; Boegel, Patrick; Bogojevic, Aleksandar; Boehm, Jonas; Boehringer, Samuel; Bongs, Kai; Bouyer, Philippe; Brand, Christian; Brimis, Apostolos; Buchmueller, Oliver; Cacciapuoti, Luigi; Calatroni, Sergio; Canuel, Benjamin; Caprini, Chiara; Caramete, Ana; Caramete, Laurentiu; Carlesso, Matteo; Carlton, John; Casariego, Mateo; Charmandaris, Vassilis; Chen, Yu-Ao; Chiofalo, Maria Luisa; Cimbri, Alessia; Coleman, Jonathon; Constantin, Florin Lucian; Contaldi, Carlo R.; Cui, Yanou; Ros, Elisa Da; Davies, Gavin; Rosendo, Esther del Pino; Deppner, Christian; Derevianko, Andrei; de Rham, Claudia; De Roeck, Albert; Derr, Daniel; Di Pumpo, Fabio; Djordjevic, Goran S.; Doebrich, Babette; Domokos, Peter; Dornan, Peter; Doser, Michael; Drougakis, Giannis; Dunningham, Jacob; Duspayev, Alisher; Easo, Sajan; Eby, Joshua; Efremov, Maxim; Ekelof, Tord; Elertas, Gedminas; Ellis, John; Evans, David; Fadeev, Pavel; Fani, Mattia; Fassi, Farida; Fattori, Marco; Fayet, Pierre; Felea, Daniel; Feng, Jie; Friedrich, Alexander; Fuchs, Elina; Gaaloul, Naceur; Gao, Dongfeng; Gardner, Susan; Garraway, Barry; Gauguet, Alexandre; Gerlach, Sandra; Gersemann, Matthias; Gibson, Valerie; Giese, Enno; Giudice, Gian F.; Glasbrenner, Eric P.; Guendogan, Mustafa; Haehnelt, Martin; Hakulinen, Timo; Hammerer, Klemens; Hanimeli, Ekim T.; Harte, Tiffany; Hawkins, Leonie; Hees, Aurelien; Heise, Jaret; Henderson, Victoria A.; Herrmann, Sven; Hird, Thomas M.; Hogan, Jason M.; Holst, Bodil; Holynski, Michael; Hussain, Kamran; Janson, Gregor; Jeglic, Peter; Jelezko, Fedor; Kagan, Michael; Kalliokoski, Matti; Kasevich, Mark; Kehagias, Alex; Kilian, Eva; Koley, Soumen; Konrad, Bernd; Kopp, Joachim; Kornakov, Georgy; Kovachy, Tim; Krutzik, Markus; Kumar, Mukesh; Kumar, Pradeep; Laemmerzahl, Claus; Landsberg, Greg; Langlois, Mehdi; Lanigan, Bryony; Lellouch, Samuel; Leone, Bruno; Poncin-Lafitte, Christophe Le; Lewicki, Marek; Leykauf, Bastian; Lezeik, Ali; Lombriser, Lucas; Luis Lopez-Gonzalez, J.; Lopez Asamar, Elias; Monjaraz, Cristian Lopez; Luciano, Giuseppe Gaetano; Mahmoud, M. A.; Maleknejad, Azadeh; Krutzik, Markus; Marteau, Jacques; Massonnet, Didier; Mazumdar, Anupam; McCabe, Christopher; Meister, Matthias; Menu, Jonathan; Messineo, Giuseppe; Micalizio, Salvatore; Millington, Peter; Milosevic, Milan; Mitchell, Jeremiah; Montero, Mario; Morley, Gavin W.; Mueller, Juergen; Ni, Wei-Tou; Noller, Johannes; Odzak, Senad; Oi, Daniel K. L.; Omar, Yasser; Pahl, Julia; Paling, Sean; Pandey, Saurabh; Pappas, George; Pareek, Vinay; Pasatembou, Elizabeth; Pelucchi, Emanuele; dos Santos, Franck Pereira; Piest, Baptist; Pikovski, Igor; Pilaftsis, Apostolos; Plunkett, Robert; Poggiani, Rosa; Prevedelli, Marco; Puputti, Julia; Veettil, Vishnupriya Puthiya; Quenby, John; Rafelski, Johann; Rajendran, Surjeet; Rasel, Ernst M.; Sfar, Haifa Rejeb; Reynaud, Serge; Richaud, Andrea; Rodzinka, Tangui; Roura, Albert; Rudolph, Jan; Sabulsky, Dylan O.; Safronova, Marianna S.; Santamaria, Luigi; Schilling, Manuel; Schkolnik, Vladimir; Schleich, Wolfgang P.; Schlippert, Dennis; Schneider, Ulrich; Schreck, Florian; Schubert, Christian; Schwersenz, Nico; Semakin, Aleksei; Sergijenko, Olga; Shao, Lijing; Shipsey, Ian; Singh, Rajeev; Smerzi, Augusto; Sopuerta, Carlos F.; Spallicci, Alessandro D. A. M.; Stefanescu, Petruta; Stergioulas, Nikolaos; Stroehle, Jannik; Struckmann, Christian; Tentindo, Silvia; Throssell, Henry; Tino, Guglielmo M.; Tinsley, Jonathan N.; Mircea, Ovidiu Tintareanu; Tkalcec, Kimberly; Tolley, Andrew J.; Tornatore, Vincenza; Torres-Orjuela, Alejandro; Treutlein, Philipp; Trombettoni, Andrea; Tsai, Yu-Dai; Ufrecht, Christian; Ulmer, Stefan; Valuch, Daniel; Vaskonen, Ville; Vazquez-Aceves, Veronica; Vitanov, Nikolay V.; Vogt, Christian; von Klitzing, Wolf; Vukics, Andras; Walser, Reinhold; Wang, Jin; Warburton, Niels; Webber-Date, Alexander; Wenzlawski, Andre; Werner, Michael; Williams, Jason; Windpassinger, Patrick; Wolf, Peter; Woerner, Lisa; Xuereb, Andre; Yahia, Mohamed E.; Cruzeiro, Emmanuel Zambrini; Zarei, Moslem; Zhan, Mingsheng; Zhou, Lin; Zupan, Jure; Zupanic, Erik; Department of Physics; Müstecaplıoğlu, Özgür Esat; Department of Physics; College of SciencesThis document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more kilometer--scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions.Publication Metadata only Landau levels versus hydrogen atom(MDPI, 2024) Nounahon, Philippe; Popov, Todor; Department of Physics; Dereli, Tekin; Department of Physics; College of SciencesThe Landau problem and harmonic oscillator in the plane share a Hilbert space that carries the structure of Dirac's remarkable so(2,3) representation. We show that the orthosymplectic algebra osp(1|4) is the spectrum generating algebra for the Landau problem and, hence, for the 2D isotropic harmonic oscillator. The 2D harmonic oscillator is in duality with the 2D quantum Coulomb-Kepler systems, with the osp(1|4) symmetry broken down to the conformal symmetry so(2,3). The even so(2,3) submodule (coined Rac) generated from the ground state of zero angular momentum is identified with the Hilbert space of a 2D hydrogen atom. An odd element of the superalgebra osp(1|4) creates a pseudo-vacuum with intrinsic angular momentum 1/2 from the vacuum. The odd so(2,3)-submodule (coined Di) built upon the pseudo-vacuum is the Hilbert space of a magnetized 2D hydrogen atom: a quantum system of a dyon and an electron. Thus, the Hilbert space of the Landau problem is a direct sum of two massless unitary so(2,3) representations, namely, the Di and Rac singletons introduced by Flato and Fronsdal.Publication Metadata only Phase behaviour and dynamics of three-dimensional active dumbbell systems(Royal Society of Chemistry, 2024) Caporusso, C.B.; Negro, G.; Suma, A.; Digregorio, P.; Gonnella G; Cugliandolo, L.F.; Department of Physics; Carenza, Livio Nicola; Department of Physics; College of SciencesWe present a comprehensive numerical study of the phase behavior and dynamics of a three-dimensional active dumbbell system with attractive interactions. We demonstrate that attraction is essential for the system to exhibit nontrivial phases. We construct a detailed phase diagram by exploring the effects of the system's activity, density, and attraction strength. We identify several distinct phases, including a disordered, a gel, and a completely phase-separated phase. Additionally, we discover a novel dynamical phase, that we name percolating network, which is characterized by the presence of a spanning network of connected dumbbells. In the phase-separated phase we characterize numerically and describe analytically the helical motion of the dense cluster.Publication Metadata only Variational approach for the two-body problem in a multiband extended-Hubbard model(Elsevier Inc., 2024) ; Department of Physics; Işkın, Menderes; Department of Physics; ; College of Sciences;Considering a spin-up and a spin-down fermion in a generic tight-binding lattice with a multi-site basis, we investigate the two-body problem using a multiband extended-Hubbard model with finite-ranged hopping and interaction parameters. We derive a linear eigenvalue problem for the entire two-body spectrum, alongside a nonlinear eigenvalue problem for the bound states in the form of a self-consistency equation. Our results, based on an exact variational approach, suggest potential applications across various lattice geometries. As an illustration, we apply them to the linear-chain model and show that the resultant spin singlet and triplet bound states align well with the existing literature.Publication Metadata only Geometrical optimization of spin clusters for the preservation of quantum coherence(American Physical Society, 2024) ; Department of Physics; Gassab, Lea; Pusuluk, Orhan; Müstecaplıoğlu, Özgür Esat; Department of Physics; ; Graduate School of Sciences and Engineering; College of Sciences;We investigate the influence of geometry on the preservation of quantum coherence in spin clusters subjected a thermal environment. Assuming weak interspin coupling, we explore the various buffer network configura yons that can be embedded in a plane. Our findings reveal that the connectivity of the buffer network is crucial indetermining the preservation duration of quantum coherence in an individual central spin. Specifically, we observe that the maximal planar graph yields the longest preservation time for a given number of buffer spins. Interestingly, our results demonstrate that the preservation time does not consistently increase with an increasing #umber of buffer spins. Employing a quantum master equation in our simulations, we further demonstrate that a Cetrahedral geometry comprising a four-spin buffer network provides optimal protection against environmental Tects.Publication Metadata only Cooper pairing, flat-band superconductivity, and quantum geometry in the pyrochlore-Hubbard model(American Physical Society, 2024) ; Department of Physics; Işkın, Menderes; Department of Physics; ; College of Sciences;We investigate the impacts of the quantum geometry of Bloch states, specifically through the band -resolved quantum -metric tensor, on Cooper pairing and flat -band superconductivity in a three-dimensional pyrochloreHubbard model. First we analyze the low-lying two -body spectrum exactly, and show that the pairing order parameter is uniform in this four -band lattice. This allows us to establish direct relations between the superfluid weight of a multiband superconductor and (i) the effective mass of the lowest -lying two -body branch at zero temperature, (ii) the kinetic coefficient of the Ginzburg-Landau theory in proximity to the critical temperature, and (iii) the velocity of the low -energy Goldstone modes at zero temperature. Furthermore, we perform a comprehensive numerical analysis of the superfluid weight and Goldstone modes, exploring both their conventional and geometric components at zero temperature.Publication Metadata only Er3+:YLiF4 channeled waveguide laser near 2.7-2.8 μm fabricated by femtosecond laser inscription(Optica Publishing Group, 2024) Tonelli, Mauro; Department of Physics; Ayevi, Berke; Morova, Yağız; Sennaroğlu, Alphan; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Sciences;We report, for the first time to our knowledge, a demonstration of robust waveguide lasing near 2.7-2.8 mu m in an erbium -doped fluoride host. Femtosecond laser inscription was employed to fabricate 50- and 70-mu m diameter channeled waveguides inside an Er3+:YLiF4 crystal. The best power performance was obtained with the 70-mu m diameter waveguide and 16% transmitting output coupler. The propagation loss and refractive index contrast were measured as 0.23 dB/cm and 7.1 x 10-4, respectively, for the 70-mu m diameter waveguide. Both self-Q-switched (SQS) and continuous-wave (CW) operations could be obtained. During the SQS operation, as short as 240-ns pulses with average power of 51 mW, repetition rate of 368 kHz, and power slope efficiency of 15.2% were generated at the wavelength of 2717 nm with 465 mW of the pump power. During the CW operation, as high as 66 mW of output power was achieved at 2808 nm by using 460 mW of pump power at 798 nm, with a power slope efficiency of 19.6%. (c) 2024 Optica Publishing GroupPublication Metadata only A novel machine learning method for the design optimization of diamond waveguides fabricated by femtosecond laser writing(Elsevier, 2024) Ince, Faik Derya; Ozel, Tugrul; Department of Physics; Morova, Yağız; Sennaroğlu, Alphan; Department of Physics; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); College of Sciences;We report on a novel machine learning method for the design optimization of femtosecond (fs) laser written dielectric waveguides. Experimental results previously obtained from the optical characterization of fs laser written depressed cladding diamond waveguides have been used to form statistically generated regression models. Design variables such as core diameter and number of written tracks were varied to both minimize the propagation loss as well as to establish a full-factorial experimental design. The regression models were used to conduct a multi-objective optimization study to optimize the competing objectives such as maximizing the refractive index contrast while minimizing the propagation loss and V-number by using a genetic algorithm. Optimization was subject to a nonlinear Rayleigh range constraint to ensure that the structure was in the waveguiding regime. Results from the optimization revealed the optimum variables to achieve low-loss and nearly single-mode guiding for a fs laser written diamond waveguide. Using the solution sets of design parameters resulting from the optimization study and their corresponding objective function values, important correlations between the design parameters and the objective functions have been revealed. With this regard, it has been shown that the number of written tracks is a much more dominant parameter, when compared to core diameter, during the design of a fs laser written circular depressed cladding diamond waveguide. The proposed method should be applicable not only to diamond waveguides but also to a wide range of dielectric waveguides fabricated by fs laser writing.Publication Metadata only Signature of topology via heat transfer analysis in the Su-Schrieffer-Heeger (SSH) model(IOP Publishing Ltd, 2024) Upadhyay, Vipul; Naseem, M. Tahir; Marathe, Rahul; Department of Physics; Müstecaplıoğlu, Özgür Esat; Department of Physics; ; College of Sciences;In this work, we explore how thermodynamics can be a potential tool for identifying the topological phase transition. Specifically, we focus on a one-dimensional Su-Schrieffer-Heeger (SSH) chain sandwiched between two fermionic baths. To investigate distinctive thermodynamic signatures associated with the topological phase, we employ heat flow analysis. Our results, derived using a global master equation, unveil a significant suppression of heat flow as we transition from the trivial to the topological phase. This decline in heat flow can be attributed to the reduction in transmission coefficients of non-zero energy modes within the topological phase. It may serve as an indicator of a phase transition. Furthermore, we investigate the heat flow asymmetry to search for phase transition indicators. Interestingly, no asymmetry is observed when employing fermionic baths. However, upon substituting fermionic baths with bosonic ones, we report a non-zero heat flow asymmetry. For SSH model with few fermionic sites, this asymmetry is more pronounced in the topological phase compared to the trivial phase. Therefore, the observed behavior of the heat diode provides an additional means of distinguishing between the topological and trivial phases. Finally, we delve into the contributions from both bulk and edge effects in heat flow and rectification to explore the impact of small system sizes on our findings.Publication Metadata only Reorganization of brain connectivity across the spectrum of clinical cognitive decline(SPRINGER-VERLAG ITALIA SRL, 2024) Dal, Demet Yüksel; Yıldırım, Zerrin; Gurvit, Hakan; Acar, Burak; Department of Physics; Kabakçıoğlu, Alkan; Department of Physics; ; College of Sciences;Clinical cognitive decline, leading to Alzheimer's Disease Dementia (ADD), has long been interpreted as a disconnection syndrome, hindering the information flow capacity of the brain, hence leading to the well-known symptoms of ADD. The structural and functional brain connectome analyses play a central role in studies of brain from this perspective. However, most current research implicitly assumes that the changes accompanying the progression of cognitive decline are monotonous in time, whether measured across the entire brain or in fixed cortical regions. We investigate the structural and functional connectivity-wise reorganization of the brain without such assumptions across the entire spectrum. We utilize nodal assortativity as a local topological measure of connectivity and follow a data-centric approach to identify and verify relevant local regions, as well as to understand the nature of underlying reorganization. The analysis of our preliminary experimental data points to statistically significant, hyper and hypo-assortativity regions that depend on the disease's stage, and differ for structural and functional connectomes. Our results suggest a new perspective into the dynamic, potentially a mix of degenerative and compensatory, topological alterations that occur in the brain as cognitive decline progresses.