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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/6
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Publication Open Access Ground-state cooling of mechanical resonatorsby quantum reservoir engineering(Springer Nature, 2021) Department of Physics; Müstecaplıoğlu, Özgür Esat; Naseem, Muhammad Tahir; Faculty Member; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; 1674; N/ACooling a mechanical oscillator to its ground state underpins many applications ranging from ultra-precise sensing to quantum information processing. The authors propose a new scheme that addresses the problem of the simultaneous cooling of many mechanical resonators with nearby frequencies. Ground-state cooling of multiple mechanical resonators becomes vital to employ them in various applications ranging from ultra-precise sensing to quantum information processing. Here we propose a scheme for simultaneous cooling of multiple degenerate or near-degenerate mechanical resonators to their quantum ground-state, which is otherwise a challenging goal to achieve. As opposed to standard laser cooling schemes where coherence renders the motion of a resonator to its ground-state, we consider an incoherent thermal source to achieve the same aim. The underlying physical mechanism of cooling is explained by investigating a direct connection between the laser sideband cooling and ""cooling by heating"". Our advantageous scheme of cooling enabled by quantum reservoir engineering can be realized in various setups, employing parametric coupling of a cooling agent with the target systems. We also discuss using non-thermal baths to simulate ultra-high temperature thermal baths for cooling.Publication Open Access A note on the pp-wave solution of minimal massive 3D gravity coupled with Maxwell-Chern-Simons theory(Institute of Physics (IOP) Publishing, 2022) Cebeci, Hakan; Şentorun, Seçil; Department of Physics; Dereli, Tekin; Faculty Member; Department of Physics; College of Sciences; 201358In this work, we examine a family of pp-wave solutions of minimal massive 3D gravity minimally coupled with the Maxwell-Chern-Simons theory. An elaborate investigation of the field equations shows that the theory admits pp-wave solutions provided that there exist an anti-self duality relation between the electric and the magnetic components of the Maxwell two-form field. By employing Noether-Wald formalism, we also construct Noether charges of the theory within exterior algebra formalism.Publication Open Access Highly sensitive optical sensor for hydrogen gas based on a polymer microcylinder ring resonator(Elsevier, 2020) Eryürek, Mustafa; Department of Physics; Department of Chemistry; Department of Electrical and Electronics Engineering; Bavili, Nima; Balkan, Timuçin; Morova, Berna; Uysallı, Yiğit; Kaya, Sarp; Kiraz, Alper; Researcher; Researcher; PhD Student; Faculty Member; Faculty Member; Department of Physics; Department of Chemistry; Department of Electrical and Electronics Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; N/A; 116541; 22542A highly sensitive platform is demonstrated for hydrogen gas (H-2) sensing based on a polymer microcylinder ring resonator (PMRR) obtained by an optical fiber coated with an inner nanofilm of amorphous palladium (Pd) and an outer polymer layer of polydimethylsiloxane (PDMS) permeable to H-2. The sensing scheme is based on monitoring the spectral shifts of high-quality optical resonances called whispering gallery modes (WGMs) that propagate in the vicinity of the outer rim of the PDMS layer without being affected by the absorption and scattering losses caused by the Pd nanofilm. WGMs are excited by a single-mode tapered optical fiber evanescently coupled to the PMRR. The observed reversible spectral shifts of the WGMs are induced by changes in the diameter of the PDMS layer caused by expansion or contraction of the Pd nanofilm exposed to varying concentrations of H-2. Maximum spectral shift sensitivity of 140 pm/% H-2, a minimum response time of 95 s, and minimum limit of detection of similar to 60 ppm were measured for sensors prepared with different thicknesses of the amorphous Pd nanofilm and tested in the H-2 concentration range up to 1%, having nitrogen gas (N-2) as a carrier. Experiments were also conducted with Pd nanofilms annealed in air or N-2 atmosphere after the deposition. In both cases, smaller sensitivities were observed due to the formation of larger grains within the film, resulting in slower diffusion and reduced solubility of H in the Pd layer. The impacts of oxygen gas and humidity on sensor performance were also studied.Publication Open Access Fundamental transfer matrix and dynamical formulation of stationary scattering in two and three dimensions(American Physical Society (APS), 2021) Loran, Farhang; Department of Mathematics; Department of Physics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; Department of Physics; College of Sciences; 4231We offer a consistent dynamical formulation of stationary scattering in two and three dimensions (2D and 3D) that is based on a suitable multidimensional generalization of the transfer matrix. This is a linear operator acting in an infinite-dimensional function space which we can represent as a 2 x 2 matrix with operator entries. This operator encodes the information about the scattering properties of the potential and enjoys an analog of the composition property of its one-dimensional ancestor. Our results improve an earlier attempt in this direction [Phys. Rev. A 93, 042707 (2016)] by elucidating the role of the evanescent waves. We show that a proper formulation of this approach requires the introduction of a pair of intertwined transfer matrices, each related to the time-evolution operator for an effective nonunitary quantum system. We study the application of our findings in the treatment of the scattering problem for delta-function potentials in 2D and 3D and clarify its implicit regularization property which circumvents the singular terms appearing in the standard treatments of these potentials. We also discuss the utility of our approach in characterizing invisible (scattering-free) potentials and potentials for which the first Born approximation provides the exact expression for the scattering amplitude.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 Instability of vectorized stars(American Physical Society (APS), 2022) Department of Physics; Coates, Andrew; Ramazanoğlu, Fethi Mübin; Researcher; Faculty Member; Department of Physics; College of Sciences; Graduate School of Sciences and Engineering; N/A; 254225; N/AIn recent papers it has been shown that a large class of vectorization mechanisms in gravity, which involve the vector fields becoming apparently tachyonic in some regime, are actually dominated by ghosts and nonperturbative behavior. Despite this, vectorized compact object solutions have previously been found, which raises the question of how, and if, the newly discovered ghosts are quenched in these cases. Here we develop the tools to study the perturbations of vectorized compact objects, and demonstrate that they suffer from ghosts and gradient instabilities as well. Thus, these vectorized objects do not represent the stable end point of a quenched instability unlike their scalarized counterparts in the spontaneous scalarization literature.Publication 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 Atom-dimer and dimer-dimer scatterings in a spin-orbit-coupled Fermi gas(American Physical Society (APS), 2021) Department of Physics; Işkın, Menderes; Faculty Member; Department of Physics; College of Sciences; 29659Using the diagrammatic approach, here we study how spin-orbit coupling (SOC) affects the fermion-dimer and dimer-dimer scattering lengths in the Born approximation, and we benchmark their accuracy with the higher-order approximations. We consider both isotropic and Rashba couplings in three dimensions and show that the Born approximation gives accurate results in the 1/(mαas)≪-1 limit, where m is the mass of the fermions, α is the strength of the SOC, and as is the s-wave scattering length between fermions. This is because the higher-loop contributions form a perturbative series in the 1/(mαas)<0 region that is controlled by the smallness of the residue Z of the dimer propagator. In sharp contrast, since Z grows with the square root of the binding energy of the dimer in the 1/(mαas)>0 region, all of the higher-loop contributions are of similar order.Publication Open Access Exciton recycling via InP quantum dot funnels for luminescent solar concentrators(Tsinghua University, 2021) Ow-Yang, Cleva W.; N/A; N/A; Department of Physics; Department of Electrical and Electronics Engineering; Jalali, Houman Bahmani; Sadeghi, Sadra; Toker, Işınsu Baylam; Han, Mertcan; Sennaroğlu, Alphan; Nizamoğlu, Sedat; PhD Student; Master Student; Faculty Member; Faculty Member; Department of Physics; Department of Electrical and Electronics Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştırmaları Merkezi (KUYTAM); Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; N/A; 23851; 130295Luminescent solar concentrators (LSC) absorb large-area solar radiation and guide down-converted emission to solar cells for electricity production. Quantum dots (QDs) have been widely engineered at device and quantum dot levels for LSCs. Here, we demonstrate cascaded energy transfer and exciton recycling at nanoassembly level for LSCs. The graded structure composed of different sized toxic-heavy-metal-free InP/ZnS core/shell QDs incorporated on copper doped InP QDs, facilitating exciton routing toward narrow band gap QDs at a high nonradiative energy transfer efficiency of 66%. At the final stage of non-radiative energy transfer, the photogenerated holes make ultrafast electronic transitions to copper-induced mid-gap states for radiative recombination in the near-infrared. The exciton recycling facilitates a photoluminescence quantum yield increase of 34% and 61% in comparison with semi-graded and ungraded energy profiles, respectively. Thanks to the suppressed reabsorption and enhanced photoluminescence quantum yield, the graded LSC achieved an optical quantum efficiency of 22.2%. Hence, engineering at nanoassembly level combined with nonradiative energy transfer and exciton funneling offer promise for efficient solar energy harvesting.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.