# Browsing by Subject "Physics, Applied"

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Item Open Access A hybrid ion-atom trap with integrated high resolution mass spectrometer(Review of Scientific Instruments, 2019-10-01) Jyothi, S; Egodapitiya, KN; Bondurant, B; Jia, Z; Pretzsch, E; Chiappina, P; Shu, G; Brown, KR© 2019 Author(s). In this article, we describe the design, construction, and implementation of our ion-atom hybrid system incorporating a high resolution time of flight mass spectrometer (TOFMS). Potassium atoms (39K) in a magneto optical trap and laser cooled calcium ions (40Ca+) in a linear Paul trap are spatially overlapped, and the combined trap is integrated with a TOFMS for radial extraction and detection of reaction products. We also present some experimental results showing interactions between 39K+ and 39K, 40Ca+ and 39K+, as well as 40Ca+ and 39K pairs. Finally, we discuss prospects for cooling CaH+ molecular ions in the hybrid ion-atom system.Item Open Access Analyzing X-ray tomographies of granular packings.(The Review of scientific instruments, 2017-05) Weis, Simon; Schröter, MatthiasStarting from three-dimensional volume data of a granular packing, as, e.g., obtained by X-ray Computed Tomography, we discuss methods to first detect the individual particles in the sample and then analyze their properties. This analysis includes the pair correlation function, the volume and shape of the Voronoi cells, and the number and type of contacts formed between individual particles. We mainly focus on packings of monodisperse spheres, but we will also comment on other monoschematic particles such as ellipsoids and tetrahedra. This paper is accompanied by a package of free software containing all programs (including source code) and an example three-dimensional dataset which allows the reader to reproduce and modify all examples given.Item Open Access Chiral quasiparticle tunneling between quantum Hall edges in proximity with a superconductor(Physical Review B, 2019-09-10) Wei, MT; Draelos, AW; Seredinski, A; Ke, CT; Li, H; Mehta, Y; Watanabe, K; Taniguchi, T; Yamamoto, M; Tarucha, S; Finkelstein, G; Amet, F; Borzenets, IV© 2019 American Physical Society. We study a two-terminal graphene Josephson junction with contacts shaped to form a narrow constriction, less than 100nm in length. The contacts are made from type-II superconducting contacts and able to withstand magnetic fields high enough to reach the quantum Hall regime in graphene. In this regime, the device conductance is determined by edge states, plus the contribution from the constricted region. In particular, the constriction area can support supercurrents up to fields of ∼2.5T. Additionally, enhanced conductance is observed through a wide range of magnetic fields and gate voltages. This additional conductance and the appearance of supercurrent is attributed to the tunneling between counterpropagating quantum Hall edge states along opposite superconducting contacts.Item Open Access Correction of beam hardening in X-ray radiograms.(The Review of scientific instruments, 2019-02) Baur, Manuel; Uhlmann, Norman; Pöschel, Thorsten; Schröter, MatthiasThe intensity of a monochromatic X-ray beam decreases exponentially with the distance it has traveled inside a material; this behavior is commonly referred to as Beer-Lambert's law. Knowledge of the material-specific attenuation coefficient μ allows us to determine the thickness of a sample from the intensity decrease the beam has experienced. However, classical X-ray tubes emit a polychromatic bremsstrahlung-spectrum. And the attenuation coefficients of all materials depend on the photon energy: photons with high energy are attenuated less than photons with low energy. In consequence, the X-ray spectrum changes while traveling through the medium; due to the relative increase in high energy photons, this effect is called beam hardening. For this varying spectrum, the Beer-Lambert law only remains valid if μ is replaced by an effective attenuation coefficient μeff which depends not only on the material but also on its thickness x and the details of the X-ray setup used. We present here a way to deduce μeff(x) from a small number of auxiliary measurements using a phenomenological model. This model can then be used to determine an unknown material thickness or in the case of a granular media its volume fraction.Item Open Access Detecting a Majorana-fermion zero mode using a quantum dot(Physical Review B - Condensed Matter and Materials Physics, 2011-11-16) Liu, DE; Baranger, HUWe propose an experimental setup for detecting a Majorana zero mode consisting of a spinless quantum dot coupled to the end of a p-wave superconducting nanowire. The Majorana bound state at the end of the wire strongly influences the conductance through the quantum dot: Driving the wire through the topological phase transition causes a sharp jump in the conductance by a factor of 1/2. In the topological phase, the zero-temperature peak value of the dot conductance (i.e., when the dot is on resonance and symmetrically coupled to the leads) is e2/2h. In contrast, if the wire is in its trivial phase, the conductance peak value is e2/h, or if a regular fermionic zero mode occurs on the end of the wire, the conductance is 0. The system can also be used to tune Flensberg's qubit system to the required degeneracy point. © 2011 American Physical Society.Item Open Access Detecting photon-photon interactions in a superconducting circuit(Physical Review B - Condensed Matter and Materials Physics, 2015-10-06) Jin, LJ; Houzet, M; Meyer, JS; Baranger, HU; Hekking, FWJA local interaction between photons can be engineered by coupling a nonlinear system to a transmission line. The required transmission line can be conveniently formed from a chain of Josephson junctions. The nonlinearity is generated by side-coupling this chain to a Cooper pair box. We propose to probe the resulting photon-photon interactions via their effect on the current-voltage characteristic of a voltage-biased Josephson junction connected to the transmission line. Considering the Cooper pair box to be in the weakly anharmonic regime, we find that the dc current through the probe junction yields features around the voltages 2eV=n ωs, where ωs is the plasma frequency of the superconducting circuit. The features at n≥2 are a direct signature of the photon-photon interaction in the system.Item Open Access Generalized multipolaron expansion for the spin-boson model: Environmental entanglement and the biased two-state system(Physical Review B - Condensed Matter and Materials Physics, 2014-08-07) Bera, S; Nazir, A; Chin, AW; Baranger, HU; Florens, SWe develop a systematic variational coherent-state expansion for the many-body ground state of the spin-boson model, in which a quantum two-level system is coupled to a continuum of harmonic oscillators. Energetic constraints at the heart of this technique are rationalized in terms of polarons (displacements of the bath states in agreement with classical expectations) and antipolarons (counterdisplacements due to quantum tunneling effects). We present a comprehensive study of the ground-state two-level system population and coherence as a function of tunneling amplitude, dissipation strength, and bias (akin to asymmetry of the double-well potential defining the two-state system). The entanglement among the different environmental modes is investigated by looking at spectroscopic signatures of the bipartite entanglement entropy between a given environmental mode and all the other modes. We observe a drastic change in behavior of this entropy for increasing dissipation, indicative of the entangled nature of the environmental states. In addition, the entropy spreads over a large energy range at strong dissipation, a testimony to the wide entanglement window characterizing the underlying Kondo state. Finally, comparisons to accurate numerical renormalization-group calculations and to the exact Bethe ansatz solution of the model demonstrate the rapid convergence of our variationally optimized multipolaron expansion, suggesting that it should also be a useful tool for dissipative models of greater complexity, as relevant for numerous systems of interest in quantum physics and chemistry. © 2014 American Physical Society.Item Open Access Investigation of Supercurrent in the Quantum Hall Regime in Graphene Josephson Junctions(Journal of Low Temperature Physics, 2018-06-01) Draelos, A; Wei, MT; Seredinski, A; Ke, C; Watanabe, K; Taniguchi, T; Yamamoto, M; Tarucha, S; Borzenets, I; Amet, F; Finkelstein, G© 2018, Springer Science+Business Media, LLC, part of Springer Nature. In this study, we examine multiple encapsulated graphene Josephson junctions to determine which mechanisms may be responsible for the supercurrent observed in the quantum Hall (QH) regime. Rectangular junctions with various widths and lengths were studied to identify which parameters affect the occurrence of QH supercurrent. We also studied additional samples where the graphene region is extended beyond the contacts on one side, making that edge of the mesa significantly longer than the opposite edge. This is done in order to distinguish two potential mechanisms: (a) supercurrents independently flowing along both non-contacted edges of graphene mesa, and (b) opposite sides of the mesa being coupled by hybrid electron–hole modes flowing along the superconductor/graphene boundary. The supercurrent appears suppressed in extended junctions, suggesting the latter mechanism.Item Open Access Mesoscopic Anderson box: Connecting weak to strong coupling(Physical Review B - Condensed Matter and Materials Physics, 2012-04-27) Liu, DE; Burdin, S; Baranger, HU; Ullmo, DWe study the Anderson impurity problem in a mesoscopic setting, namely the "Anderson box," in which the impurity is coupled to finite reservoir having a discrete spectrum and large sample-to-sample mesoscopic fluctuations. Note that both the weakly coupled and strong coupling Anderson impurity problems are characterized by a Fermi-liquid theory with weakly interacting quasiparticles. We study how the statistical fluctuations in these two problems are connected, using random matrix theory and the slave boson mean-field approximation (SBMFA). First, for a resonant level model such as results from the SBMFA, we find the joint distribution of energy levels with and without the resonant level present. Second, if only energy levels within the Kondo resonance are considered, the distributions of perturbed levels collapse to universal forms for both orthogonal and unitary ensembles for all values of the coupling. These universal curves are described well by a simple Wigner-surmise-type toy model. Third, we study the fluctuations of the mean-field parameters in the SBMFA, finding that they are small. Finally, the change in the intensity of an eigenfunction at an arbitrary point is studied, such as is relevant in conductance measurements. We find that the introduction of the strongly coupled impurity considerably changes the wave function but that a substantial correlation remains. © 2012 American Physical Society.Item Open Access Nonequilibrium quantum transport through a dissipative resonant level(Physical Review B - Condensed Matter and Materials Physics, 2013-06-21) Chung, CH; Le Hur, K; Finkelstein, G; Vojta, M; Wölfle, PThe resonant-level model represents a paradigmatic quantum system which serves as a basis for many other quantum impurity models. We provide a comprehensive analysis of the nonequilibrium transport near a quantum phase transition in a spinless dissipative resonant-level model, extending earlier work. A detailed derivation of a rigorous mapping of our system onto an effective Kondo model is presented. A controlled energy-dependent renormalization-group approach is applied to compute the nonequilibrium current in the presence of a finite bias voltage V. In the linear-response regime V→0, the system exhibits as a function of the dissipative strength a localized-delocalized quantum transition of the Kosterlitz-Thouless (KT) type. We address fundamental issues of the nonequilibrium transport near the quantum phase transition: Does the bias voltage play the same role as temperature to smear out the transition? What is the scaling of the nonequilibrium conductance near the transition? At finite temperatures, we show that the conductance follows the equilibrium scaling for VT. We furthermore provide different signatures of the transition in the finite-frequency current noise and ac conductance via a recently developed functional renormalization group (FRG) approach. The generalization of our analysis to nonequilibrium transport through a resonant level coupled to two chiral Luttinger liquid leads, generated by fractional quantum Hall edge states, is discussed. Our work on the dissipative resonant level has direct relevance to experiments on a quantum dot coupled to a resistive environment, such as H. Mebrahtu,. © 2013 American Physical Society.Item Open Access Pb-Graphene-Pb josephson junctions: Characterization in magnetic field(IEEE Transactions on Applied Superconductivity, 2012-06-14) Borzenets, IV; Coskun, UC; Mebrahtu, H; Finkelstein, GWe fabricate superconductor-graphene-superconductor Josephson junctions with superconducting regions made of lead (Pb). The critical current through graphene may be modulated by the external magnetic field; the resulting Fraunhofer interference pattern shows several periods of oscillations, suggesting that the junction is uniform. Deviations from the perfect Fraunhofer pattern are observed, and their cause is explained by a simulation that takes into account the sample design. © 2002-2011 IEEE.Item Open Access Postponing the dynamical transition density using competing interactions(Granular Matter, 2020-08-01) Charbonneau, P; Kundu, JSystems of dense spheres interacting through very short-ranged attraction are known from theory, simulations and colloidal experiments to exhibit dynamical reentrance. Their liquid state can thus be fluidized at higher densities than possible in systems with pure repulsion or with long-ranged attraction. A recent mean-field, infinite-dimensional calculation predicts that the dynamical arrest of the fluid can be further delayed by adding a longer-ranged repulsive contribution to the short-ranged attraction. We examine this proposal by performing extensive numerical simulations in a three-dimensional system. We first find the short-ranged attraction parameters necessary to achieve the densest liquid state, and then explore the parameter space for an additional longer-ranged repulsion that could further enhance reentrance. In the family of systems studied, no significant (within numerical accuracy) delay of the dynamical arrest is observed beyond what is already achieved by the short-ranged attraction. Possible explanations are discussed.Item Open Access Retrapping current, self-heating, and hysteretic current-voltage characteristics in ultranarrow superconducting aluminum nanowires(Physical Review B - Condensed Matter and Materials Physics, 2011-11-08) Li, P; Wu, PM; Bomze, Y; Borzenets, IV; Finkelstein, G; Chang, AMHysteretic I-V (current-voltage) curves are studied in narrow Al nanowires. The nanowires have a cross section as small as 50 nm2. We focus on the retrapping current in a down-sweep of the current, at which a nanowire re-enters the superconducting state from a normal state. The retrapping current is found to be significantly smaller than the switching current at which the nanowire switches into the normal state from a superconducting state during a current up-sweep. For wires of different lengths, we analyze the heat removal due to various processes, including electron and phonon processes. For a short wire 1.5μm in length, electronic thermal conduction is effective; for longer wires 10μm in length, phonon conduction becomes important. We demonstrate that the measured retrapping current as a function of temperature can be quantitatively accounted for by the self-heating occurring in the normal portions of the nanowires to better than 20% accuracy. For the phonon processes, the extracted thermal conduction parameters support the notion of a reduced phase-space below three dimensions, consistent with the phonon thermal wavelength having exceeded the lateral dimensions at temperatures below ∼1.3 K. Nevertheless, surprisingly the best fit was achieved with a functional form corresponding to three-dimensional phonons, albeit requiring parameters far exceeding known values in the literature. © 2011 American Physical Society.Item Open Access Stabilizing spin coherence through environmental entanglement in strongly dissipative quantum systems(Physical Review B - Condensed Matter and Materials Physics, 2014-03-18) Bera, S; Florens, S; Baranger, HU; Roch, N; Nazir, A; Chin, AWThe key feature of a quantum spin coupled to a harmonic bath - a model dissipative quantum system - is competition between oscillator potential energy and spin tunneling rate. We show that these opposing tendencies cause environmental entanglement through superpositions of adiabatic and antiadiabatic oscillator states, which then stabilizes the spin coherence against strong dissipation. This insight motivates a fast-converging variational coherent-state expansion for the many-body ground state of the spin-boson model, which we substantiate via numerical quantum tomography. © 2014 American Physical Society.Item Open Access Subkelvin lateral thermal transport in diffusive graphene(Physical Review B, 2019-03-29) Draelos, AW; Silverman, A; Eniwaye, B; Arnault, EG; Ke, CT; Wei, MT; Vlassiouk, I; Borzenets, IV; Amet, F; Finkelstein, G© 2019 American Physical Society. In this work, we report on hot carrier diffusion in graphene across large enough length scales that the carriers are not thermalized across the crystal. The carriers are injected into graphene at one site and their thermal transport is studied as a function of applied power and distance from the heating source, up to tens of micrometers away. Superconducting contacts prevent out-diffusion of hot carriers to isolate the electron-phonon coupling as the sole channel for thermal relaxation. As local thermometers, we use the amplitude of the universal conductance fluctuations, which varies monotonically as a function of temperature. By measuring the electron temperature simultaneously along the length we observe a thermal gradient which results from the competition between electron-phonon cooling and lateral heat flow.Item Open Access Surface-enhanced Raman scattering nanosensors for in vivo detection of nucleic acid targets in a large animal model(Nano Research, 2018-08-01) Wang, HN; Register, JK; Fales, AM; Gandra, N; Cho, EH; Boico, A; Palmer, GM; Klitzman, B; Vo-Dinh, T© 2018, Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature. Although nanotechnology has led to important advances in in vitro diagnostics, the development of nanosensors for in vivo detection remains very challenging. Here, we demonstrated the proof-of-principle of in vivo detection of nucleic acid targets using a promising type of surface-enhanced Raman scattering (SERS) nanosensor implanted in the skin of a large animal model (pig). The in vivo nanosensor used in this study involves the “inverse molecular sentinel” detection scheme using plasmonics-active nanostars, which have tunable absorption bands in the near infrared region of the “tissue optical window”, rendering them efficient as an optical sensing platform for in vivo optical detection. Ex vivo measurements were also performed using human skin grafts to demonstrate the detection of SERS nanosensors through tissue. In this study, a new core–shell nanorattle probe with Raman reporters trapped between the core and shell was utilized as an internal standard system for self-calibration. These results illustrate the usefulness and translational potential of the SERS nanosensor for in vivo biosensing. [Figure not available: see fulltext.].Item Open Access Transport signatures of Majorana quantum criticality realized by dissipative resonant tunneling(Physical Review B - Condensed Matter and Materials Physics, 2014-06-27) Zheng, H; Florens, S; Baranger, HUWe consider theoretically the transport properties of a spinless resonant electronic level coupled to strongly dissipative leads, in the regime of circuit impedance near the resistance quantum. Using the Luttinger liquid analogy, one obtains an effective Hamiltonian expressed in terms of interacting Majorana fermions, in which all environmental degrees of freedom (leads and electromagnetic modes) are encapsulated in a single fermionic bath. General transport equations for this system are then derived in terms of the Majorana T-matrix. A perturbative treatment of the Majorana interaction term yields the appearance of a marginal, linear dependence of the conductance on temperature when the system is tuned to its quantum critical point, in agreement with recent experimental observations. We investigate in detail the different crossovers involved in the problem, and analyze the role of the interaction terms in the transport scaling functions. In particular, we show that single barrier scaling applies when the system is slightly tuned away from its Majorana critical point, strengthening the general picture of dynamical Coulomb blockade. © 2014 American Physical Society.Item Open Access Tunable quantum phase transitions in a resonant level coupled to two dissipative baths(Physical Review B - Condensed Matter and Materials Physics, 2014-02-18) Liu, DE; Zheng, H; Finkelstein, G; Baranger, HUWe study tunneling through a resonant level connected to two dissipative bosonic baths: one is the resistive environment of the source and drain leads, while the second comes from coupling to potential fluctuations on a resistive gate. We show that several quantum phase transitions (QPT) occur in such a model, transitions which emulate those found in interacting systems such as Luttinger liquids or Kondo systems. We first use bosonization to map this dissipative resonant level model to a resonant level in a Luttinger liquid, one with, curiously, two interaction parameters. Drawing on methods for analyzing Luttinger liquids at both weak and strong coupling, we obtain the phase diagram. For strong dissipation, a Berezinsky-Kosterlitz-Thouless QPT separates strong-coupling and weak-coupling (charge localized) phases. In the source-drain symmetric case, all relevant backscattering processes disappear at strong coupling, leading to perfect transmission at zero temperature. In fact, a QPT occurs as a function of the coupling asymmetry or energy of the resonant level: the two phases are (i) the system is cut into two disconnected pieces (zero transmission), or (ii) the system is a single connected piece with perfect transmission, except for a disconnected fractional degree of freedom. The latter arises from the competition between the two fermionic leads (source and drain), as in the two-channel Kondo effect. © 2014 American Physical Society.Item Open Access Ultra-sharp metal and nanotube-based probes for applications in scanning microscopy and neural recording.(Journal of applied physics, 2012-04-12) Borzenets, IV; Yoon, I; Prior, MM; Donald, BR; Mooney, RD; Finkelstein, GThis paper discusses several methods for manufacturing ultra-sharp probes, with applications geared toward, but not limited to, scanning microscopy (STM, AFM) and intra-cellular recordings of neural signals. We present recipes for making tungsten, platinum/iridium alloy, and nanotube fibril tips. Electrical isolation methods using Parylene-C or PMMA are described.