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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access BCS theory of time-reversal-symmetric Hofstadter-Hubbard model(American Physical Society (APS), 2017) Umucalılar, Rıfat Onur; Department of Physics; Işkın, Menderes; Faculty Member; Department of Physics; College of Sciences; 29659The competition between the length scales associated with the periodicity of a lattice potential and the cyclotron radius of a uniform magnetic field is known to have dramatic effects on the single-particle properties of a quantum particle, e.g., the fractal spectrum is known as the Hofstadter butterfly. Having this intricate competition in mind, we consider a two-component Fermi gas on a square optical lattice with opposite synthetic magnetic fields for the components, and study its effects on the many-body BCS-pairing phenomenon. By a careful addressing of the distinct superfluid transitions from the semimetal, quantum spin-Hall insulator, or normal phases, we explore the low-temperature phase diagrams of the model, displaying lobe structures that are reminiscent of the well-known Mott-insulator transitions of the Bose-Hubbard model.Publication Open Access Macroscopic loop formation in circular DNA denaturation(American Physical Society (APS), 2012) Bar, Amir; Mukamel, David; Department of Physics; Kabakçıoğlu, Alkan; Faculty Member; Department of Physics; College of Sciences; 49854The statistical mechanics of DNA denaturation under fixed linking number is qualitatively different from that of unconstrained DNA. Quantitatively different melting scenarios are reached from two alternative assumptions, namely, that the denatured loops are formed at the expense of (i) overtwist or (ii) supercoils. Recent work has shown that the supercoiling mechanism results in a picture similar to Bose-Einstein condensation where a macroscopic loop appears at T-c and grows steadily with temperature, while the nature of the denatured phase for the overtwisting case has not been studied. By extending an earlier result, we show here that a macroscopic loop appears in the overtwisting scenario as well. We calculate its size as a function of temperature and show that the fraction of the total sum of microscopic loops decreases above T-c, with a cusp at the critical point.Publication Open Access Spectral singularities of complex scattering potentials and ınfinite reflection and transmission coefficients at real energies(American Physical Society (APS), 2009) Department of Mathematics; Department of Physics; Mostafazadeh, Ali; Researcher; Department of Mathematics; Department of Physics; College of SciencesSpectral singularities are spectral points that spoil the completeness of the eigenfunctions of certain non-Hermitian Hamiltonian operators. We identify spectral singularities of complex scattering potentials with the real energies at which the reflection and transmission coefficients tend to infinity, i.e., they correspond to resonances having a zero width. We show that a waveguide modeled using such a potential operates like a resonator at the frequencies of spectral singularities. As a concrete example, we explore the spectral singularities of an imaginary PT-symmetric barrier potential and demonstrate the above resonance phenomenon for a certain electromagnetic waveguide.Publication Open Access Understanding the link between inflammasome and apoptosis through the response of THP-1 cells against drugs using droplet-based microfluidics(American Chemical Society (ACS), 2022) Gençtürk, E.; Kasım, M.; Ülgen, K.O.; Department of Physics; Department of Electrical and Electronics Engineering; Kiraz, Alper; Morova, Berna; Faculty Member; Researcher; Department of Physics; Department of Electrical and Electronics Engineering; College of Sciences; College of Engineering; 22542; N/ADroplet-based microfluidic devices are used to investigate monocytic THP-1 cells in response to drug administration.Consistent and reproducible droplets are created, each of which acts as a bioreactor to carry out single cell experiments withminimized contamination and live cell tracking under an invertedfluorescence microscope for more than 2 days. Here, the effects ofthree different drugs (temsirolimus, rifabutin, and BAY 11-7082) on THP-1 are examined and the results are analyzed in the contextof the inflammasome and apoptosis relationship. The ASC adaptor gene tagged with GFP is monitored as the inflammasomereporter. Thus, a systematic way is presented for deciphering cell-to-cell heterogeneity, which is an important issue in cancertreatment. The drug temsirolimus, which has effects of disrupting the mTOR pathway and triggering apoptosis in tumor cells, causesTHP-1 cells to express ASC and to be involved in apoptosis. Treatment with rifabutin, which inhibits proliferation and initiatesapoptosis in cells, affects ASC expression byfirst increasing and then decreasing it. CASP-3, which has a role in apoptosis and isdirectly related to ASC, has an increasing level in inflammasome conditioning. Thus, the cell under the effect of rifabutin might befaced with programmed cell death faster. The drug BAY 11-7082, which is responsible for NF Kappa B inhibition, shows similar results totemsirolimus with more than 60% of cells having highfluorescence intensity (ASC expression). The microfluidic platform presentedhere offers strong potential for studying newly developed small-molecule inhibitors for personalized/precision medicine.Publication Open Access Photonic detection and characterization of DNA using sapphire microspheres(Society of Photo-optical Instrumentation Engineers (SPIE), 2014) Murib, Mohammed Sharif; Yeap, Weng-Siang; Martens, Daan; Bienstman, Peter; De Ceuninck, Ward; van Grinsven, Bart; Schoening, Michael J.; Michiels, Luc; Haenen, Ken; Ameloot, Marcel; Wagner, Patrick; Department of Physics; Serpengüzel, Ali; Faculty Member; Department of Physics; College of Sciences; 27855Publication Open Access Few-qubit quantum refrigerator for cooling a multi-qubit system(Nature Publishing Group (NPG), 2021) Arısoy, Onat; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We propose to use a few-qubit system as a compact quantum refrigerator for cooling an interacting multi-qubit system. We specifically consider a central qubit coupled to N ancilla qubits in a so-called spin-star model to be used as refrigerant by means of short interactions with a many-qubit system to be cooled. We first show that if the interaction between the qubits is of the longitudinal and ferromagnetic Ising model form, the central qubit is colder than the environment. We summarize how preparing the refrigerant qubits using the spin-star model paves the way for the cooling of a many-qubit system by means of a collisional route to thermalization. We discuss a simple refrigeration cycle, considering the operation cost and cooling efficiency, which can be controlled by N and the qubit–qubit interaction strength. Besides, bounds on the achievable temperature are established. Such few-qubit compact quantum refrigerators can be significant to reduce dimensions of quantum technology applications, can be easy to integrate into all-qubit systems, and can increase the speed and power of quantum computing and thermal devices.Publication Open Access Laser-inscribed diamond waveguide resonantly coupled to diamond microsphere(Multidisciplinary Digital Publishing Institute (MDPI), 2020) Le Phu, T.; Giakoumaki, A.; Bharadwaj, V.; Ramponi, R.; Eaton, S.M.; Department of Physics; Yavuz, Nurperi; Bayer, Mustafa Mert; Çirkinoğlu, Hüseyin Ozan; Serpengüzel, Ali; Master Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; N/A; N/A; 27855An all-diamond photonic circuit was implemented by integrating a diamond microsphere with a femtosecond-laser-written bulk diamond waveguide. The near surface waveguide was fabricated by exploiting the Type II fabrication method to achieve stress-induced waveguiding. Transverse electrically and transverse magnetically polarized light from a tunable laser operating in the near-infrared region was injected into the diamond waveguide, which when coupled to the diamond microsphere showed whispering-gallery modes with a spacing of 0.33 nm and high-quality factors of 105. By carefully engineering these high-quality factor resonances, and further exploiting the properties of existing nitrogen-vacancy centers in diamond microspheres and diamond waveguides in such configurations, it should be possible to realize filtering, sensing and nonlinear optical applications in integrated diamond photonics.Publication Open Access General formalism of local thermodynamics with an example: Quantum Otto engine with a spin-1/2 coupled to an arbitrary spin(American Physical Society (APS), 2015) Altıntaş, Ferdi; Department of Physics; Müstecaplıoğlu, Özgür Esat; Faculty Member; Department of Physics; College of Sciences; 1674We investigate a quantum heat engine with a working substance of two particles, one with a spin-1/2 and the other with an arbitrary spin (spin s), coupled by Heisenberg exchange interaction, and subject to an external magnetic field. The engine operates in a quantum Otto cycle. Work harvested in the cycle and its efficiency are calculated using quantum thermodynamical definitions. It is found that the engine has higher efficiencies at higher spins and can harvest work at higher exchange interaction strengths. The role of exchange coupling and spin s on the work output and the thermal efficiency is studied in detail. In addition, the engine operation is analyzed from the perspective of local work and efficiency. We develop a general formalism to explore local thermodynamics applicable to any coupled bipartite system. Our general framework allows for examination of local thermodynamics even when global parameters of the system are varied in thermodynamic cycles. The generalized definitions of local and cooperative work are introduced by using mean field Hamiltonians. The general conditions for which the global work is not equal to the sum of the local works are given in terms of the covariance of the subsystems. Our coupled spin quantum Otto engine is used as an example of the general formalism.Publication Open Access Graphene mode-locked femtosecond Cr:ZnSe laser at 2500 nm(Optical Society of America (OSA), 2013) Kim, J. W.; Bae, S.; Hong, B. H.; Rotermund, F.; N/A; Department of Physics; Çizmeciyan, Melisa Natali; Sennaroğlu, Alphan; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 23851We report, for the first time to our knowledge, femtosecond pulse generation from a graphene mode-locked Cr:ZnSe laser at 2500 nm. To minimize the insertion losses at the lasing wavelength, high-quality monolayer graphene transferred on a CaF2 substrate was used in the experiments. Once mode-locking was initiated, the laser generated a stable train of 226 fs pulses with a time-bandwidth product of 0.39. The mode-locked laser operated at a pulse repetition rate of 77 MHz and produced 80 mW output power with an incident pump power of 1.6 W. To our knowledge, this is the longest laser wavelength at which graphene-based passive mode-locking has been demonstrated to date.Publication Open Access Intrinsic pathology of self-interacting vector fields(American Physical Society (APS), 2022) Department of Physics; Ramazanoğlu, Fethi Mübin; Coates, Andrew; Faculty Member; Department of Physics; College of Sciences; 254225; N/AWe show that self-interacting vector field theories exhibit unphysical behavior even when they are not coupled to any external field. This means any theory featuring such vectors is in danger of being unphysical, an alarming prospect for many proposals in cosmology, gravity, high energy physics, and beyond. The problem arises when vector fields with healthy configurations naturally reach a point where time evolution is mathematically ill defined. We develop tools to easily identify this issue, and provide a simple and unifying framework to investigate it.