• Friday, February 4, 1:30PM, in Room S-240
  Michael Berry (Simons lecturer)
  H.H. Wills Physics Laboratory, Britain
  Quantum Mechanics, chaos, and the Riemann zeros
  Host: Abanov
• Monday, February 7, 4:00PM
  Mika Sillanpää
  Helsinki University of Technology
  Band engineering in Cooper-pair box: dispersive measurements of charge and phase
  Low-frequency susceptibility of the Cooper-pair box is investigated for use in various kinds of sensitive measurements. In a practical realization the box has been split into two, thus constituting a Cooper-pair transistor (SCPT). In this scheme we show how to perform a dispersive detection of the drain-source phase difference by measuring the input capacitance of the box. The measurement is done by studying the phase shift of a reflected microwave signal. The predictions have been verified experimentally. In the dual mode of operation, that is, while looked at the source or drain, the SCPT looks like an inductance which depends on the gate charge. This second scheme, called L-SET, is a novel radio-frequency electrometer, somewhat a reactive equivalent to the rf-SET. In experiment, we have achieved a charge sensitivity of 3E-5 e/rtHz and an input bandwidth of 100 MHz for a good device. Parametric gain, phase-sensitive detection and squeezing of 1/f noise have also been demonstrated in the L-SET scheme. Finally, we discuss theoretically how the inductance or capacitance could be used for non-demolition readout of the quantum state of the box. All of the measurements are performed without any quasiparticle generation.
  Host: Lukens
• Friday, February 11, 1:30PM
  J. W. Davenport
  Brookhaven National Lab
  Analytic Tight Binding Model: Application to NanoScale Metallic Clusters
  It seems not to be widely recognized that the simple cubic s band tight binding model can be exactly solved for finite clusters [1]. Even more surprising is the generalization to fcc and bcc clusters [2]. I derive these results in a novel way use them to calculate the density of states (DOS) for clusters ranging up to one million atoms. For clusters larger than 100,000 atoms, the DOS is essentially the same as the bulk. However, in the 1000 - 100,000 atom range there are substantial differences between the cluster and the bulk. The formulas are easily generalized to include 1 or 2 dimensions and mixed boundary conditions (periodic or finite) so that flat films, tubes, and surfaces can also be studied.
  [1] R. P. Messmer, Phys. Rev. B 15, 1811 (1977).
  [2] G-H. Ryu and H. Kim, Bull. Korean Chem. Soc, 12, 544 (1991).
  Host: Allen
• Friday, February 18, 1:30PM
  Andrey Chubukov
  University of Maryland
  Singular corrections to a Fermi liquid - 1D physics in D > 1
  I address the issue of the leading corrections to the Fermi liquid theory. I show that these corrections are universal in the sense that they come from fermions near the Fermi surface, and are non-analytic in D < 3, The non-analyticities emerge from the fundamental singularities in the dynamical bosonic response functions of a Fermi liquid. In 2D case, which I discuss in some detail, the non-analytic corrections include a T² term in the specific heat, linear in T terms in the effective mass and the uniform spin susceptibility c_s(Q = 0, T), and |Q| term in c_s(Q, T = 0). I show that all these non-analytic terms originate from effectively one-dimensional forward and backward scattering processes which involve fermions moving along the same line.
  Host: Abanov
• Friday, February 25, 1:30PM
  Robert Konik
  BNL
  Novel Kondo Physics in Quantum Dot Structures
  Quantum dots offer a highly engineered, highly tunable environment in which to realize strongly correlated, non-perturbative physics. In particular they offer the opportunity to realize Kondo-like behaviour in new ways. I will consider two examples of this type of physics. In the first I will consider quantum dot configurations possessing two interfering tunneling paths. This can be concretely realized by embedding a quantum dot in an Aharonov-Bohm ring. In the second case I will consider a double quantum dot system. In both cases a simplified Anderson-like model describing the dots can be argued to be exactly solvable. With this exact solvability, I am able to describe the strongly coupled transport properties of these systems.
  Host: Abanov
• Wednesday, March 2, 3:45PM
  Markus Büttiker
  Department of Theoretical Physics, University of Geneva, Switzerland
  Zero-temperature entanglement energetics
  Host: Averin
• Friday, March 4, 1:30PM
  Andrey Zheludev
  Oak Ridge National Laboratory
  Dynamics and quantum phase transitions in anisotropic S=1 spin chains.
  Anisotropic S=1 quantum spin chains with bond alternation are a deceptively simple model with a remarkably complex phase diagram. The ground state is either the Haldane-gap or dimerized spin-liquid phase, a quantum-critical XY phase, or an Ising-like ordered state. The two distinct spin-liquid phases differ in their "hidden" symmetries associated with antiferromagnetic string order. Even though the corresponding order parameter is not observable experimentally, the two cases can be told apart by looking for certain signatures in the excitation spectrum. Applying an external magnetic field to either type of spin liquid leads to a quantum phase transition driven by a "fully legitimate" 1D Bose condensation of magnons. The high-field magnetized state is a "quantum spin solid" where long-range order coexists with exotic excitations that have no analogues in conventional spin wave theory.
  This rich behavior can be investigated experimentally by means of inelastic neutron scattering experiments on real quasi-one-dimensional systems. Particularly revealing were recent experiments on organometallic polymer crystals NDMAP (Haldane spin chains) [1] and NTENP (dimerized spin chains) [2]. The central new finding is that in the presence of magnetic anisotropy (but not in the Heisenberg case) the spin dynamics in the high-field phase is qualitatively different for Haldane and dimerized chains.
  [1] A. Zheludev, T. Masuda, B. Sales, D. Mandrus, T. Papenbrock, T. Barnes, S. Park, Phys. Rev. B 69, 144417 (2004). M. Hagiwara, L. P. Regnault, A. Zheludev, A. Stunault, N. Metoki, T. Suzuki, S. Suga, K. Kakurai, Y. Koike, P. Vorderwisch, J. H. Chung, cond-mat/0501207.
  [2] A. Zheludev et al., Phys. Rev. B 69, 054414 (2004); Phys. Rev. B 68, 134438 (2003); Phys. Rev. Lett. 88, 077206 (2002); Phys. Rev. B 63, 104410(2001). Y. Chen, Z. Honda, A. Zheludev, C. Broholm, K. Katsumata and S. M. Shapiro, Phys. Rev. Lett. 86, 1618 (2001).
  Host: Abanov
• Friday, March 11, 1:30PM
  Yuri Pashkin
  RIKEN/NEC
  Energy relaxation in superconducting charge qubits
  Josephson structures can behave as quantum two-level systems that was confirmed by oservation of coherent oscillations. Decoherence is one of the major hurdles that one must overcome in order to build quantum computing circuits with larger integration. Recently, we have measured energy relaxation time and its dependence on various parameters in superconducting charge qubits. The relaxation time equals to 5 ns at the qubit degeneracy point and rises up to a few hundred nanoseconds far from the degeneracy. The corresponding noise spectrum scales linearly with frequency. The noise magnitude cannot be explained by the standard spin-boson model. We suggest that this noise is caused by two-level fluctuators surrounding the qubit.
  Host: Averin
• Friday, March 18, 1:30PM
  Evgeny Il'ichev
  JENA Institute for Physical High Technology
  Continuous measurements of superconducting flux qubits
  Host: Averin
• Friday, April 8, 1:30PM
  Sami Mitra
  Physical Review Letters
  Physical Review Letters: The editorial office, growth in submissions, and proposed changes
  I will try to give a brief flavor of the APS Editorial Office and the review process for a typical submission to PRL. I also plan to discuss some changes that are being proposed primarily as a result of the recent report by the PRL Evaluation Committee.
  Host: Goldman
• Friday, April 22, 1:30PM
  M. P. Anantram
  NASA Ames Research Center
  Computational Modeling of Nanodevices
  Semi-classical methods of device modeling have worked well in conventional devices because the phase coherence and scattering length scales are much smaller than device dimensions, and detailed atomistic information is not needed to understand the basic device physics. Over the last decade, quantum mechanical methods developed by physicists in the 1960s have been adapted to model a number of emerging nanodevices. It is anticipated that these methods will become mainstream in device modeling. In this talk, I will provide an overview of our group's effort in modeling quasi-1D and 2D nanodevices using the non equilibrium Green's function method. The simulators developed have the capability to include scattering mechanisms, which turn out to be critical in nanodevices driven away from equilibrium. The device physics that we learn from practical application of these methods to carbon nanotubes and nanotransistors will be discussed. I will discuss the competing roles of 1D electrostatics, Schottky barriers, electron-phonon interaction and non crossing subbands, in determining the electrical properties of metallic carbon nanotubes. In the area of nanotransistors, I will discuss insights on the role of scattering away from the source injection barrier in determining the current-voltage characteristics.
  Host: Likharev
• Friday, April 29, 1:30PM
  Kevin S. Bedell
  Boston College
  Quantum Fluctuation Driven First Order Phase Transition in Weak Ferromagnetic Metals
  There has been much interest in the study of weak itinerant ferromagnetism since the discovery of superconductivity on the ferromagnetic side of the phase diagram of UGe2. In this talk I will describe some new results for the phase diagram of a weak ferromagnetic metal treated in the local Fermi liquid approximation. Some insight into these materials can be gained by studying the "Induced Interaction Model" developed by Gerry Brown and his collaborators, in the local limit. This approach reproduces the results expected for a local Fermi liquid in both the paramagnetic and ferromagnetic regime. However, a more dramatic prediction of this model is that a line of weak first order transitions separates the two phases. The basic point is that the exchange fluctuations due to the induced interaction suppresses the second order phase transition and drive it to a first order transition. In addition to this the induced interaction model predicts that a superconducting instability is possible on the ferromagnetic side but not on the paramagnetic side of the phase diagram. We also argue that at T = 0 the phase diagram ends at what is a "classic" example of a triple point, which we refer to here as a quantum triple point, QTP. These results describe some of the main features of the phase diagram of the itinerant (superconducting) ferromagnet, UGe2.
  Host: Allen

Send comments to Laszlo Mihaly; created 11/18/2004.