Browsing by Author "Decca, Ricardo S."
Now showing 1 - 10 of 14
Results Per Page
Sort Options
Item Classical symmetron force in Casimir experiments(APS, 2020-03) Elder, Benjamin; Vardanyan, Valeri; Akrami, Yashar; Brax, Philippe; Davis, Anne-Christine; Decca, Ricardo S.; Physics, School of ScienceThe symmetron is a typical example of screened modified gravity, wherein the symmetron force is dynamically suppressed in dense environments. This allows it to hide in traditional tests of gravity. However, the past decade has seen great experimental progress toward measuring screened forces in the laboratory or in space. Screening relies on nonlinearities in the equation of motion, which significantly complicates the theoretical analysis of such forces. Here, we present a calculation of the symmetron force between a dense plate and sphere surrounded by vacuum. This is done via semianalytical approaches in two limiting cases, based on the size of the sphere: large spheres are analyzed via the proximity force approximation, whilst small spheres are treated as screened test particles. In the intermediate regime we solve the problem numerically. Our results allow us to make contact with Casimir force experiments, which often employ a plate and sphere configuration for practical reasons, and may therefore be used to constrain symmetrons. We use our results to forecast constraints on the symmetron’s parameters for a hypothetical Casimir experiment that is based on the current state of the art. The forecasts compare favorably to other leading laboratory tests of gravity, particularly atom interferometry and bouncing neutrons. We thus conclude that near-future Casimir experiments will be capable of placing tight new bounds on symmetrons. Our results for the symmetron force are derived in a scale-invariant way, such that although we here focus on Casimir experiments, they may be applied to any other plate-sphere system, ranging from microscopic to astrophysical scales.Item Constraints On Spin Independent Forces At The ~100 Nm Range By Means Of A Micromechanical Oscillator(2014-06) Decca, Ricardo S.; Physics, School of SciencePreliminary data from improvements made in our experimental setup are presented. Forces measured with our setup are presented and possible origins for the systematics observed are discussed. The observed signal is most likely induced by an impulsive oscillation of the motor.Item Detectable Signature of Quantum Friction on a Sliding Particle in Vacuum(Wiley, 2021-05) Lombardo, Fernando C.; Decca, Ricardo S.; Viotti, Ludmila; Villar, Paula I.; Physics, School of ScienceSpatially separated bodies in a relative motion through vacuum experience a tiny friction force known as quantum friction (QF). This force has so far eluded experimental detection due to its small magnitude and short range. Quantitative details revealing traces of the QF in the degradation of the quantum coherence of a particle are presented. Environmentally induced decoherence for a particle sliding over a dielectric sheet can be decomposed into contributions of different signatures: one solely induced by the electromagnetic vacuum in the presence of the dielectric and another induced by motion. As the geometric phase (GP) has been proved to be a fruitful venue of investigation to infer features of the quantum systems, herein it is proposed to use the accumulated GP acquired by a particle as a QF sensor. Furthermore, an innovative experiment designed to track traces of QF by measuring the velocity dependence of corrections to the GP and coherence is proposed. The experimentally viable scheme presented can spark renewed optimism for the detection of non-contact friction, with the hope that this non-equilibrium phenomenon can be readily measured soon.Item Double-layer force suppression between charged microspheres(APS, 2018-02) Ether, D. S.; Rosa, F. S. S.; Tibaduiza, D. M.; Pires, L. B.; Decca, Ricardo S.; Maia Neto, P. A.; Physics, School of ScienceIn this paper we propose a protocol to suppress double-layer forces between two microspheres immersed in a dielectric medium, being one microsphere metallic at a controlled potential ψ M and the other a charged one either metallic or dielectric. The approach is valid for a wide range of distances between them. We show that, for a given distance between the two microspheres, the double-layer force can be totally suppressed by simply tuning ψ M up to values dictated by the linearized Poisson-Boltzmann equation. Our key finding is that such values can be substantially different from the ones predicted by the commonly used proximity force approximation, also known as the Derjaguin approximation, even in situations where the latter is expected to be accurate. The proposed procedure can be used to suppress the double-layer interaction in force spectroscopy experiments, thus paving the way for measurements of other surface interactions, such as Casimir dispersion forces.Item The Effects of Refractive Index Mismatch on Multiphoton Fluorescence Excitation Microscopy of Biological Tissue(2010-08-31T18:42:10Z) Young, Pamela Anne; Rubart, Michael; Decca, Ricardo S.; Bacallao, Robert L.; Dunn, Kenneth WilliamIntroduction: Multiphoton fluorescence excitation microscopy (MPM) is an invaluable tool for studying processes in tissue in live animals by enabling biologists to view tissues up to hundreds of microns in depth. Unfortunately, imaging depth in MPM is limited to less than a millimeter in tissue due to spherical aberration, light scattering, and light absorption. Spherical aberration is caused by refractive index mismatch between the objective immersion medium and sample. Refractive index heterogeneities within the sample cause light scattering. We investigate the effects of refractive index mismatch on imaging depth in MPM. Methods: The effects of spherical aberration on signal attenuation and resolution degradation with depth are characterized with minimal light absorption and scattering using sub-resolution microspheres mounted in test sample of agarose with varied refractive index. The effects of light scattering on signal attenuation and resolution degradation with depth are characterized using sub-resolution microspheres in kidney tissue samples mounted in optical clearing media to alter the refractive index heterogeneities within the tissue. Results: The studies demonstrate that signal levels and axial resolution both rapidly decline with depth into refractive index mismatched samples. Interestingly, studies of optical clearing with a water immersion objective show that reducing scattering increases reach even when it increases refractive index mismatch degrading axial resolution. Scattering, in the absence of spherical aberration, does not degrade axial resolution. The largest improvements in imaging depth are obtained when both scattering and refractive index mismatch are reduced. Conclusions: Spherical aberration, caused by refractive index mismatch between the immersion media and sample, and scattering, caused by refractive index heterogeneity within the sample, both cause signal to rapidly attenuate with depth in MPM. Scattering, however, seems to be the predominant cause of signal attenuation with depth in kidney tissue. Kenneth W. Dunn, Ph.D., ChairItem Investigation of the separation dependent fluorescence resonant energy transfer between CdSe/ZnS quantum dots by near-field scanning optical microscopy(2010-02-02T17:37:27Z) Wang, Pu; Naumann, Christof A.; Dunn, Kenneth William; Decca, Ricardo S.; Atkinson, Susan J.A Near-field Scanning Optical Microscope (NSOM) is used to study the resonant energy transfer between different size CdSe/ZnS quantum dots (QDs). The NSOM system is used to bring the small QDs which are 6 nm in diameter close to 8 nm diameter QDs which are embed with PMMA on a cover glass. The PMMA is used to prevent the 8 nm QDs from aggregation, which allows us to locate one dot on the cover slide and have the potential to get the interaction of two individual dots. A systematic methodology is used to localize a single QD on the cover glass and align the small and large QDs. Since the ground energy state of the small QDs match the excitation energy level of the large QDs. When the small dots get excited, part of the energy transfers to the large QDs. As the separation between small and large QDs is changed in near-field range (20-50nm), the transition probability is observed, indicating that the FRET level changes as a function of separation between small and large QDs. Possible future improvements are also discussed.Item Isoelectronic determination of the thermal Casimir force(APS, 2016-05) Bimonte, G.; López, D.; Decca, Ricardo S.; Department of Physics, School of ScienceDifferential force measurements between spheres coated with either nickel or gold and rotating disks with periodic distributions of nickel and gold are reported. The rotating samples are covered by a thin layer of titanium and a layer of gold. While titanium is used for fabrication purposes, the gold layer (nominal thicknesses of 21, 37, 47, and 87 nm) provides an isoelectronic environment, and is used to nullify the electrostatic contribution but allow the passage of long wavelength Casimir photons. A direct comparison between the experimental results and predictions from Drude and plasma models for the electrical permittivity is carried out. In the models, the magnetic permeability of nickel is allowed to change to investigate its effects. Possible sources of errors, both in the experimental and theoretical sides, are taken into account. It is found that a Drude response with magnetic properties of nickel taken into account is unequivocally ruled out. The full analysis of the data indicates that a dielectric plasma response with the magnetic properties of Ni included shows good agreement with the data. Neither a Drude nor a plasma dielectric response provide a satisfactory description if the magnetic properties of nickel are disregarded.Item Measurement of the Casimir Force between 0.2 and 8 μm: Experimental Procedures and Comparison with Theory(MDPI, 2021) Bimonte, Giuseppe; Spreng, Benjamin; Maia Neto, Paulo A.; Ingold, Gert-Ludwig; Klimchitskaya, Galina L.; Mostepanenko, Vladimir M.; Decca, Ricardo S.; Physics, School of ScienceWe present results on the determination of the differential Casimir force between an Aucoated sapphire sphere and the top and bottom of Au-coated deep silicon trenches performed by means of the micromechanical torsional oscillator in the range of separations from 0.2 to 8 μm. The random and systematic errors in the measured force signal are determined at the 95% confidence level and combined into the total experimental error. The role of surface roughness and edge effects is investigated and shown to be negligibly small. The distribution of patch potentials is characterized by Kelvin probe microscopy, yielding an estimate of the typical size of patches, the respective r.m.s. voltage and their impact on the measured force. A comparison between the experimental results and theory is performed with no fitting parameters. For this purpose, the Casimir force in the sphere-plate geometry is computed independently on the basis of first principles of quantum electrodynamics using the scattering theory and the gradient expansion. In doing so, the frequency-dependent dielectric permittivity of Au is found from the optical data extrapolated to zero frequency by means of the plasma and Drude models. It is shown that the measurement results exclude the Drude model extrapolation over the region of separations from 0.2 to 4.8 μm, whereas the alternative extrapolation by means of the plasma model is experimentally consistent over the entire measurement range. A discussion of the obtained results is provided.Item Near-field studies of anisotropic variations and temperature-induced structural changes in a supported single lipid bilayer(American Physical Society, 2020-03) Johnson, Merrell A.; Decca, Ricardo S.; Physics, School of ScienceTemperature-controlled polarization modulation near-field scanning optical microscopy measurements of a single supported Lβ′ 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayer are presented. The effective retardance (S=2π(ne−no)tλ, where t is the thickness of the bilayer and λ is the wavelength of light used) and the direction of the projection of the acyl chains (θ) were measured simultaneously. We demonstrate how one is able to align the system over the sample and measure a relative retardance ΔS, a crucial step in performing temperature-controlled experiments. Maps of ΔS and θ, with a lateral resolution on the order of ∼100 nm are presented, highlighting variations deriving from changes in the average molecular orientation across a lipid membrane at room temperature. A discussion of how this information can be used to map the average three-dimensional orientation of the molecules is presented. From ΔS and the known thickness of the membrane t the birefringence (ne−no) of the bilayer was determined. Temperature-controlled measurements yielded a change of ΔS∼(3.8±0.3) mrad at the main transition temperature (Tm∼41∘C) of a single planar bilayer of DPPC, where the membrane transitioned between the gel Lβ′ to liquid disorder Lα state. The result agrees well with previous values of (ne−no) in the Lβ′ phase and translates to an assumed average acyl chain orientation relative to the membrane normal (⟨ϕ⟩∼32∘) when TTm. Evidence of super heating and cooling are presented. A discussion on how the observed behavior as Tm is approached, could relate to the existence of varying microconfigurations within the lipid bilyer are presented. This conversation includes ideas from a Landau-Ginzburg picture of first-order phase transitions in nematic-to-isotropic systems.Item Net energy up-conversion processes in CdSe/CdS (core/shell) quantum dots, a possible pathway to towards optical cooling(American Physical Society, 2022) Hua, Muchuan; Decca, Ricardo S.; Physics, School of ScienceAn investigation of the possibility of optical refrigeration (OR) on zinc-blende cadmium selenide/cadmium sulfide (CdSe/CdS) core/shell structure quantum dots (QDs) has been carried out. Quality samples were synthesized in our laboratory, and significant energy up-conversion photoluminescence (UCPL) was observed in these samples, showing the potential of generating net cooling effects. To better understand and predict the UCPL characteristics of the QDs, a semiempirical model has been developed, showing good agreement with our experimental results. The model takes into account the corresponding quantum yield and cooling efficiency, predicting the possibility of realizing optical refrigeration on a CdSe QD system.