Harvard University  >  Department of Physics  >  Condensed Matter Theory

Hans-Andreas Engel, Ph.D.Engel, Hansres, condensed matter theory, theoretical physics, Harvard university, spin, spintronics, quantum computer, finance, hedge fund, computation, information Hansres Engel

 
Address:  The D. E. Shaw Group
39th Floor, Tower 45
120 West Forty-Fifth Street
New York, NY 10036
e-mail:  engel@physics.harvard.edu


Currently I am working for the D. E. Shaw group in New York.

You can find the web page of Prof. Andreas Engel (my father) here.


Publications
Hanle Effect near Boundaries
Hans-Andreas Engel,
arXiv:0707.3762.

The Hanle effect describes suppression of spin polarization due to precession in a magnetic field. This is a standard spintronics tool and it gives access to the spin lifetime of samples in which spins are generated homogeneously. We examine the Hanle effect when spins are generated at a boundary of a diffusive sample by the extrinsic spin Hall effect. We show that the Hanle curve is spatially dependent and that the "apparent" spin lifetime, given by its inverse half-width, is shorter near the boundary even if the spin relaxation rate is homogenous.


Spin generation away from boundaries by nonlinear transport
Ilya G. Finkler, Hans-Andreas Engel, Emmanuel I. Rashba, and Bertrand I. Halperin,
Phys. Rev. B 75, 241202(R) (2007); see also cond-mat/0703654.

Spin polarization may be generated far from the boundaries of a sample by nonlinear effects of an electric current, in the presence of "extrinsic" spin-orbit interactions, even when such generation is forbidden in the linear regime. We present a Corbino model where spin accumulation results from a combination of current gradients, nonlinearity, and cubic anisotropy. Further, we show that even with isotropic conductivity, nonlinear effects in a low-symmetry sidearm geometry can generate spin polarization far away from boundaries. Finally, we find that drift from the boundaries dominates spin polarization patterns observed in recent experiments on GaAs by Sih et al. [Phys. Rev. Lett. 97, 096605 (2006)].


Quantum optical interface for gate-controlled spintronic devices
Hans-Andreas Engel, Jacob M. Taylor, Mikhail D. Lukin, Atac Imamoglu,
cond-mat/0612700.

We describe an opto-electronic structure in which charge and spin degrees of freedom in electrical gate-defined quantum dots can be coherently coupled to light. This is achieved via electron-electron interaction or via electron tunneling into a proximal self-assembled quantum dot. We illustrate potential applications of this approach by considering several quantum control techniques, including optical read-out of gate-controlled semiconductor quantum bits and controlled generation of entangled photon-spin pairs.


Out-of-plane spin polarization from in-plane electric and magnetic fields
Hans-Andreas Engel, Emmanuel I. Rashba, and Bertrand I. Halperin,
Phys. Rev. Lett. 98, 036602 (2007); see also cond-mat/0609078.

We show that the joint effect of spin-orbit and magnetic fields leads to a spin polarization perpendicular to the plane of a two-dimensional electron system with Rashba spin-orbit coupling and in-plane parallel dc magnetic and electric fields, for angle-dependent impurity scattering or nonparabolic energy spectrum, while only in-plane polarization persists for simplified models. We derive Bloch equations, describing the main features of recent experiments, including the magnetic field dependence of static and dynamic responses.


Tunable Noise Cross-Correlations in a Double Quantum Dot
D.T. McClure, L. DiCarlo, Y. Zhang, H.-A. Engel, C.M. Marcus, M.P. Hanson, A.C. Gossard,
Phys. Rev. Lett. 98, 056801 (2007); see also cond-mat/0607280.

We report measurements of the cross-correlation between current noise fluctuations in two capacitively coupled quantum dots in the Coulomb blockade regime. The sign of the cross-spectral density is found to be tunable by gate voltage and source-drain bias. Good agreement is found with a model of sequential tunneling through the dots in the presence of inter-dot capacitive coupling.


The Contrast Imaging Function for Tilted Specimens
Ansgar Philippsen, Hans-Andreas Engel, and Andreas Engel,
Ultramicroscopy 107, 202 (2007).

A theoretical description of the contrast-imaging function is derived for tilted specimens that exhibit weak-phase object characteristics. We show that the tilted contrast-imaging function (TCIF) is a linear transformation, which can be approximated by the convolution operation for small tilt angles or for small specimens. This approximation is not valid for electron tomography, where specimen tilts are above 60° and specimen dimensions amount to some 10 μm. The approximation also breaks down for electron crystallography, where atomic resolution is to be achieved. Therefore, we do not make this approximation and propose a generalized algorithm for inverting the TCIF. The implications of our description are discussed in the context of electron tomography, single particle analysis, and electron crystallography, and the improved resolution is quantitatively demonstrated.


Theory of Spin Hall Effects in Semiconductors
Hans-Andreas Engel, Emmanuel I. Rashba, and Bertrand I. Halperin,
cond-mat/0603306;
Theory of Spin Hall Effects in Semiconductors, in Handbook of Magnetism and Advanced Magnetic Materials, H. Kronmüuller and S. Parkin (eds.). John Wiley & Sons Ltd, Chichester, UK, pp 2858-2877 (2007).

Spin Hall effects are a collection of phenomena, resulting from spin-orbit coupling, in which an electrical current flowing through a sample can lead to spin transport in a perpendicular direction and spin accumulation at lateral boundaries. These effects, which do not require an applied magnetic field, can originate in a variety of intrinsic and extrinsic spin-orbit coupling mechanisms and depend on geometry, dimension, impurity scattering, and carrier density of the system---making the analysis of these effects a diverse field of research. In this article, we give an overview of the theoretical background of the spin Hall effects and summarize some of the most important results. First, we explain effective spin-orbit Hamiltonians, how they arise from band structure, and how they can be understood from symmetry considerations; including intrinsic coupling due to bulk inversion or structure asymmetry or due to strain, and extrinsic coupling due to impurities. This leads to different mechanisms of spin transport: spin precession, skew scattering, and side jump. Then we present the kinetic (Boltzmann) equations, which describe the spin-dependent distribution function of charge carriers, and the diffusion equation for spin polarization density. Next, we define the notion of spin currents and discuss their relation to spin polarization. Finally, we explain the electrically induced spin effects; namely, spin polarization and currents in bulk and near boundaries (the focus of most current theoretical research efforts), and spin injection, as well as effects in mesoscopic systems and in edge states.


Small-angle impurity scattering and the spin Hall conductivity in 2D systems
A.V.Shytov, E.G.Mishchenko, H.-A.Engel, and B.I.Halperin,
Phys. Rev. B 73, 075316 (2006); see also cond-mat/0509702.

An arbitrarily small concentration of impurities can affect the spin Hall conductivity in a two-dimensional semiconductor system. We develop a Boltzmann-like equation that can be used for impurity scattering with arbitrary angular dependence, and for arbitrary angular dependence of the spin-orbit field b(k) around the Fermi surface. For a model applicable to a 2D hole system in GaAs, if the impurity scattering is not isotropic, we find that the spin Hall conductivity depends on the derivative of b with respect to the energy and on deviations from a parabolic band structure, as well as on the angular dependence of the scattering. In principle, the resulting spin Hall conductivity can be larger or smaller than the ``intrinsic value'', and can have opposite sign. In the limit of small angle scattering, in a model appropriate for small hole concentrations, where the band is parabolic and b ~ k3, the spin Hall conductivity has opposite sign from the intrinsic value, and has larger magnitude. Our analysis assumes that the spin-orbit splitting b and the transport scattering rate tau-1 are both small compared to the Fermi energy, but the method is valid for for arbitrary value of b*tau.


Theory of Spin Hall conductivity in n-doped GaAs
Hans-Andreas Engel, Bertrand I. Halperin, and Emmanuel I. Rashba,
Phys. Rev. Lett. 95, 166605 (2005); see also cond-mat/0505535.

We develop a theory of extrinsic spin currents in semiconductors, resulting from spin-orbit coupling at charged scatterers, which leads to skew scattering and side jump contributions to the spin Hall conductance. Applying the theory to bulk n-GaAs, without any free parameters, we find spin currents that are in reasonable agreement with recent experiments by Kato et al. [Science 306, 1910 (2004)].


Fermionic Bell-State Analyzer for Spin Qubits
Hans-Andreas Engel and Daniel Loss,
Science 309, 586 (2005);
see also J. Carlos Egues, Science Perspectives: Fingerprinting Spin Qubits; and Philip Ball, news@nature.com: Quantum computers go for a spin.

We propose a protocol and physical implementation for partial Bell-state measurements of Fermionic qubits, allowing for deterministic quantum computing in solid-state systems without the need for two-qubit gates. Our scheme consists of two spin qubits in a double quantum dot where the two dots have different Zeeman splittings and resonant tunneling between the dots is only allowed when the spins are antiparallel. This converts spin parity into charge information by means of a projective measurement and can be implemented with established technologies. This measurement-based qubit scheme greatly simplifies the experimental realization of scalable quantum computers in electronic nanostructures.


Fault-tolerant architecture for quantum computation using electrically controlled semiconductor spins
J. M. Taylor, H.-A. Engel, W. Dür, A. Yacoby, C.M. Marcus, P. Zoller, and M.D. Lukin,
Nature Physics 1, 177 (2005).

Information processing using quantum systems provides new paradigms for computation and communication and may yield insights into our understanding of the limits of quantum mechanics. However, realistic systems are never perfectly isolated from their environment, hence all quantum operations are subject to errors. Realization of a physical system for processing of quantum information that is tolerant of errors is a fundamental problem in quantum science and engineering. Here, we develop an architecture for quantum computation using electrically controlled semiconductor spins by extending the Loss–DiVincenzo scheme and by combining actively protected quantum memory and long-distance coupling mechanisms. Our approach is based on a demonstrated encoding of qubits in long-lived two-electron states, which immunizes qubits against the dominant error from hyperfine interactions. We develop a universal set of quantum gates compatible with active error suppression for these encoded qubits and an effective long-range interaction between the qubits by controlled electron transport. This approach yields a scalable architecture with favourable error thresholds for fault-tolerant operation, consistent with present experimental parameters.


Electron Spins in Dots and Rings: Coherence, Read Out, and Transport
Hans-Andreas Engel,
PhD thesis, University of Basel (2003), supervised by Daniel Loss, co-refereed by Christoph Bruder and Leonid Levitov;
Shaker, Aachen (2004, ISBN 3-8322-2770-9, available on amazon).
 

Controlling Spin Qubits in Quantum Dots
Hans-Andreas Engel, L.P. Kouwenhoven, Daniel Loss, and C.M. Marcus,
Quantum Information Processing 3, 115 (2004); see also cond-mat/0409294.

We review progress on the spintronics proposal for quantum computing where the quantum bits (qubits) are implemented with electron spins. We calculate the exchange interaction of coupled quantum dots and present experiments, where the exchange coupling is measured via transport. Then, experiments on single spins on dots are described, where long spin relaxation times, on the order of a millisecond, are observed. We consider spin-orbit interaction as sources of spin decoherence and find theoretically that also long decoherence times are expected. Further, we describe the concept of spin filtering using quantum dots and show data of successful experiments. We also show an implementation of a read out scheme for spin qubits and define how qubits can be measured with high precision. Then, we propose new experiments, where the spin decoherence time and the Rabi oscillations of single electrons can be measured via charge transport through quantum dots. Finally, all these achievements have promising applications both in conventional and quantum information processing.


Probing Single-Electron Spin Decoherence in Quantum Dots using Charged Excitons
Oliver Gywat, Hans-Andreas Engel, and Daniel Loss,
J. Supercond. 18, 175 (2005); see also cond-mat/0408451.

We propose to use optical detection of magnetic resonance (ODMR) to measure the decoherence time T2 of a single electron spin in a semiconductor quantum dot. The electron is in one of the spin 1/2 states and a circularly polarized laser can only create an optical excitation for one of the electron spin states due to Pauli blocking. An applied electron spin resonance (ESR) field leads to Rabi spin flips and thus to a modulation of the photoluminescence or, alternatively, of the photocurrent. This allows one to measure the ESR linewidth and the coherent Rabi oscillations, from which the electron spin decoherence can be determined. We study different possible schemes for such an ODMR setup, including cw or pulsed laser excitation.


Asymmetric Quantum Shot Noise in Quantum Dots
Hans-Andreas Engel and Daniel Loss,
Phys. Rev. Lett. 93, 136602 (2004); see also cond-mat/0312107.

We analyze the frequency-dependent noise of a current through a quantum dot which is coupled to Fermi leads and which is in the Coulomb blockade regime. We show that the asymmetric shot noise as function of frequency shows steps and becomes super-Poissonian. This provides experimental access to the quantum fluctuations of the current. We present an exact calculation for a single dot level and a perturbative evaluation of the noise in Born approximation (sequential tunneling regime but without Markov approximation) for the general case of many levels with charging interaction.


Measurement efficiency and n-shot read out of spin qubits
Hans-Andreas Engel, Vitaly Golovach, Daniel Loss, L.M.K. Vandersypen, J.M. Elzerman, R. Hanson, and L.P. Kouwenhoven,
Phys. Rev. Lett. 93, 106804 (2004); see also cond-mat/0309023.

We consider electron spin qubits in quantum dots and define a measurement efficiency e to characterize reliable measurements via n-shot read outs. We propose various implementations based on a double dot and quantum point contact (QPC) and show that the associated efficiencies e vary between 50% and 100%, allowing single-shot read out in the latter case. We model the read out microscopically and derive its time dynamics in terms of a generalized master equation, calculate the QPC current and show that it allows spin read out under realistic conditions.


Optical Detection of Single-Electron Spin Decoherence in a Quantum Dot
Oliver Gywat, Hans-Andreas Engel, Daniel Loss, R. J. Epstein, F. M. Mendoza, and D. D. Awschalom,
Phys. Rev. B 69, 205303 (2004); see also cond-mat/0307669.

We propose a method based on optically detected magnetic resonance (ODMR) to measure the decoherence time T2 of a single electron spin in a semiconductor quantum dot. The electron spin resonance (ESR) of a single excess electron on a quantum dot is probed by circularly polarized laser excitation. The photoluminescence is modulated due to the ESR which enables the measurement of electron spin decoherence. We study different possible schemes for such an ODMR setup.


Towards Quantum Communication with Electron Spins
D.S. Saraga, G. Burkard, J.C. Egues, H.-A. Engel, P. Recher, and D. Loss,
Turk J Phys 27 (5), 427 (2003).
Proceedings of the Quantum Computation at the Atomic Scale Conference, (Istanbul, 1-11 June, 2003).

We review our recent work towards quantum communication in a solid-state environment with qubits carried by electron spins. We propose three schemes to produce spin-entangled electrons, where the required separation of the partner electrons is achieved via Coulomb interaction. The non-product spin-states originate either from the Cooper pairs found in a superconductor, or in the ground state of a quantum dot with an even number of electrons. In a second stage, we show how spin-entanglement carried by a singlet can be detected in a beam-splitter geometry by an increased (bunching) or decreased (antibunching) noise signal. We also discuss how a local spin-orbit interaction can be used to provide a continuous modulation of the noise as a signature of entanglement. Finally, we review how one can use a quantum dot as a spin- lter, a spin-memory read-out, a probe for single-spin decoherence and ultimately, a single-spin measurement apparatus.


Single Spin Dynamics and Decoherence in a Quantum Dot via Charge Transport
Hans-Andreas Engel and Daniel Loss,
Phys. Rev. B 65, 195321 (2002); see also cond-mat/0109470.

We investigate the spin dynamics of a quantum dot with a spin-1/2 ground state in the Coulomb blockade regime and in the presence of a magnetic rf field leading to electron spin resonances (ESR). We show that by coupling the dot to leads, spin properties on the dot can be accessed via the charge current in the stationary and non-stationary limit. We present a microscopic derivation of the current and the master equation of the dot using superoperators, including contributions to decoherence and energy shifts due to the tunnel coupling. We give a detailed analysis of sequential and co-tunneling currents, for linearly and circularly oscillating ESR fields, applied in cw and pulsed mode. We show that the sequential tunneling current exhibits a spin satellite peak whose linewidth gives a lower bound on the decoherence time T2 of the spin-1/2 state on the dot. Similarly, the spin decoherence can be accessed also in the cotunneling regime via ESR induced spin flips. We show that the conductance ratio of the spin satellite peak and the conventional peak due to sequential tunneling saturates at the universal conductance ratio of 0.71 for strong ESR fields. We describe a double-dot setup which generates spin dependent tunneling and acts as a current pump (at zero bias), and as a spin inverter which inverts the spin-polarization of the current, even in a homogeneous magnetic field. We show that Rabi oscillations of the dot-spin induce coherent oscillations in the time-dependent current. These oscillations are observable in the time-averaged current as function of ESR pulse-duration, and they allow one to access the spin coherence directly in the time domain. We analyze the measurement and read-out process of the dot-spin via currents in spin-polarized leads and identify measurement time and efficiency by calculating the counting statistics, noise, and the Fano factor. We point out that single spin dynamics can also be accessed with STM techniques.


Detection of Single Spin Decoherence in a Quantum Dot via Charge Currents
Hans-Andreas Engel and Daniel Loss,
Phys. Rev. Lett. 86, 4648 (2001); see also cond-mat/0011193.

We consider a quantum dot attached to leads in the Coulomb blockade regime which has a spin 1/2 ground state. We show that by applying an ESR field to the dot-spin the stationary current in the sequential tunneling regime exhibits a resonance whose line width is determined by the single-spin decoherence time T2. The Rabi oscillations of the dot-spin are shown to induce coherent current oscillations from which T2 can be deduced in the time domain. We describe a spin-inverter which can be used to pump current through a double-dot via spin flips generated by ESR.


Benford's law for exponential random variables
Hans-Andreas Engel and Christoph Leuenberger,
Statistics & Probability Letters 63 (4), 361 (2003).

Benford's law assigns the probability log10(1+1/d) for finding a number starting with specific significant digit d. We show that exponentially distributed numbers obey this law approximatively, i.e., within bounds of 0.03.


Sampling the conformational space of membrane protein surfaces with the AFM
Simon Scheuring, Daniel J. Müller, Henning Stahlberg, Hans-Andreas Engel, and Andreas Engel,
Eur. Biophys. J. 31 172 (2002).

The atomic force microscope acquires topographs of single native membrane proteins at subnanometer resolution. Owing to the high signal-to-noise ratio, such images allow the conformational space of membrane protein surfaces to be sampled. This is demonstrated by topographs of porin OmpF, aquaporin-Z, and bacteriorhodopsin, all recorded at a lateral resolution of <7 Å and a vertical resolution of ~1 Å. The amplitudes of the domain movements were estimated from a large number of single molecule topographs and the corresponding energy landscapes calculated. To visualize the motion of protein domains, movies were generated by similarity ranking of the observed protein configurations.


Electron spins for spintronics and quantum communication in quantum dots and wires
Daniel Loss, Patrik Recher, and Hans-Andreas Engel,
XXXVI Rencontres de Moriond, Electronic Correlations: From meso- to nano-physics, 525 (2001).

Electron spins in nanostructures such as quantum dots and wires have promising applications for spintronics, quantum computing and quantum communication. We give a brief introduction to the quantum computing proposal using electron spins in quantum dots. A quantum dot in the Coulomb blockade regime, attached to leads and in the presence of a magnetic field is used to study single-spin effects. With an ESR source, the spin can be coherently controlled, leading to Rabi-oscillations of the dot spin. It is shown that the intrinsic single-spin decoherence time T2 is directly accessible via a stationary charge current through the dot. In addition, we show that the quantum dot acts as an efficient spin filter, single-spin read-out device or as a spin pump. Finally, we consider mobile non-local spin entangled electrons as needed for quantum communication. We propose how to create such EPR pairs by means of Andreev tunneling at a superconductor-normal junction and discuss experimental setups in which spin entanglement and non-locality may be detected via transport measurements.


Electron spins in quantum dots for spintronics and quantum computation
Hans-Andreas Engel, Patrik Recher, and Daniel Loss,
Solid State Commun. 119, 229-236 (2001).

Coherent manipulation, filtering, and measurement of electronic spin in quantum dots and other nanostructures have promising applications in conventional and in quantum information processing and transmission. We present an overview of our theoretical proposal to implement a quantum computer using electron spins in quantum dots as qubits. We discuss all necessary requirements towards a scalable quantum computer including one- and two qubit gates and read in/out tasks. We then present some concepts for promising single quantum dot devices which eventually could be used as building blocks for sophisticated spintronic devices. We show how a single quantum dot can act as an efficient spin filter. Further, in combination with an ESR source, a quantum dot can be used as a single spin memory or as a spin pump. In addition, the sequential tunneling current through a quantum dot in the presence of an ESR field can exhibit a resonance whose line width is determined by the decoherence time T2 of a single dot-spin. Finally, we consider mobile non-local spin entangled electrons as needed for quantum communication. We propose how to create such EPR pairs by means of Andreev tunneling at a superconductor-normal junction and discuss experimental setups in which spin entanglement may be detected via transport measurements.


Spintronics and Quantum Dots for Quantum Computing and Quantum Communication
Guido Burkard, Hans-Andreas Engel, and Daniel Loss,
Fortschritte der Physik 48, 965 (2000) (special issue on Experimental Proposals for Quantum Computation), eds. H.-K. Lo and S. Braunstein; see cond-mat/0004182.

Control over electron-spin states, such as coherent manipulation, filtering and measurement promises access to new technologies in conventional as well as in quantum computation and quantum communication. We review our proposal of using electron spins in quantum confined structures as qubits and discuss the requirements for implementing a quantum computer. We describe several realizations of one- and two-qubit gates and of the read-in and read-out tasks. We discuss recently proposed schemes for using a single quantum dot as spin-filter and spin-memory device. Considering electronic EPR pairs needed for quantum communication we show that their spin entanglement can be detected in mesoscopic transport measurements using metallic as well as superconducting leads attached to the dots.


Berry-Phase gemessen
Hans-Andreas Engel and Daniel Loss,
Physik Journal 1 (6), 19 (2002).

Conductance fluctuations in diffusive rings: Berry phase effects and criteria for adiabaticity
Hans-Andreas Engel and Daniel Loss,
Phys. Rev. B 62, 10238 (2000); see also cond-mat/0002396.

We study Berry phase effects on conductance properties of diffusive mesoscopic conductors, which are caused by an electron spin moving through an orientationally inhomogeneous magnetic field. Extending previous work, we start with an exact, i.e. not assuming adiabaticity, calculation of the universal conductance fluctuations in a diffusive ring within the weak localization regime, based on a differential equation which we derive for the diffuson in the presence of Zeeman coupling to a magnetic field texture. We calculate the field strength required for adiabaticity and show that this strength is reduced by the diffusive motion. We demonstrate that not only the phases but also the amplitudes of the h/2e Aharonov-Bohm oscillations are strongly affected by the Berry phase. In particular, we show that these amplitudes are completely suppressed at certain magic tilt angles of the external fields, and thereby provide a useful criterion for experimental searches. We also discuss Berry phase-like effects resulting from spin-orbit interaction in diffusive conductors and derive exact formulas for both magnetoconductance and conductance fluctuations. We discuss the power spectra of the magnetoconductance and the conductance fluctuations for inhomogeneous magnetic fields and for spin-orbit interaction.



Invited Talks
Out-of-plane spin polarization from in-plane electric and magnetic fields
  • Condensed Matter Theory Seminar, Department of Physics, Harvard University, September 29, 2006.

    Theory of Spin Hall Effect in GaAs
  • Spintech IV, Maui, Hawaii, June 18, 2007.
  • Festkörperkolloquium, Department of Physics, TU Munich, November 9, 2006.
  • APS March Meeting 2006, R19.001, Baltimore, March 15, 2006.
  • Condensed Matter and Surface Science Colloquium, Ohio University, September 22, 2005.
  • Condensed Matter Theory Seminar, Basel University, June 15, 2005.

    Fermionic Bell state analyzer for spin qubits
  • Quantum/Nanophysics Seminar, Department of Physics and Astronomy, Dartmouth College, October 5, 2006.
  • Group seminar, Westervelt Lab, Harvard University, May 25, 2005.


    • Efficiency of qubit measurements and readout of spin qubits via charge detection
  • CeNS Joint Workshop "Nanoscience: linking disciplines," Venice, September 27 - October 1, 2004.


    • Asymmetric Quantum Shot Noise in Quantum Dots
  • Group seminar, Quantum Transport group, TU Delft, March 12, 2004.
  • Condensed Matter Seminar, Department of Applied Physics, Yale University, February 6, 2004.
  • Condensed Matter Theory Seminar, Department of Physics, Harvard University, February 5, 2004.
  • Condensed Matter Theory Seminar, Institute for Theoretical Physics, RWTH Aachen, January 20, 2004.


    • Detection of Single Spin Decoherence in a Quantum Dot via Charge Currents
  • IPMC seminar, Institute for complex matter, EPFL Lausanne, November 18, 2003.
  • Group seminar, Nanophysics, ETH Zürich, August 22, 2003.
  • Condensed matter seminar, Basel, November 5, 2001.
  • Nano-Physics & Bio-Electronics - A new Odyssey, Dresden, Aug 6-31, 2001.
  • Solid State Quantum Computing Workshop, Warsaw, April 26-29, 2001.
  • Group seminar, Quantum Transport group, TU Delft, January 17, 2001.



    • Contributed Talks
    Out-of-plane spin polarization from in-plane electric and magnetic fields
  • ICN+T International conference on nanoscience and technology, No. 387, Basel, August 2, 2006.

    Theory of Spin Hall conductivity in n-doped GaAs
  • Kids Semiar, Department of Physics, Harvard University, May 10, 2005.


    • Fermionic Bell state analyzer for spin qubits
  • Group Seminar, Ulloa Group, Ohio University, September 23, 2005.
  • APS March Meeting 2005, P17.003, Los Angeles, March 23, 2005.


    • Asymmetric Quantum Shot Noise in Quantum Dots
  • APS March Meeting 2004, Y37.008, Montreal, March 26, 2004 .


    • Measurement efficiency and n-shot read out of spin qubits
  • QSIT Meeting, Flums, Switzerland, March 6, 2004.
  • SPS Meeting, Neuchâtel, Switzerland, March 3-4, 2004.
  • APS March Meeting 2004, B37.010, Montreal, March 22, 2004.
  • RTN Network Meeting, Munich, November 21, 2003.


    • Detection of Single Spin Decoherence in a Quantum Dot via Charge Currents
  • SPS Meeting, Basel, Switzerland, March 20-21, 2003.
  • APS March Meeting 2003, X19.006, Austin, USA, March 3-7, 2003.
  • Nanoscience Workshop: CFN Karlsruhe / NCCR, Emmendingen, Germany, October 7-8, 2002.
  • NCCR Nanoscale Science Workshop, Pontresina, Switzerland, September 4-6, 2002.
  • DPG-Frühjahrstagung, HL 10.3, Regensburg, Germany, March 11-15, 2002.
  • SPS Meeting, Lausanne, Switzerland, February 28 - March 1, 2002.



    • Posters
    Theory of Spin Hall conductivity in n-doped GaAs
  • Frontiers in Nanoscale Science and Technology Workshop, NSEC, San Francisco, January 26-28, 2006.

    Fermionic Bell state analyzer for spin qubits
  • Gordon Research Conference on Quantum Information Science, Ventura, CA, February 27 - March 4, 2005.


    • Measurement efficiency and n-shot read out of spin qubits
  • Solid State Quantum Information Processing Conference, Amsterdam, December 15-18, 2003.
  • RTN Network Meeting, Munich, November 21, 2003.
  • NCCR Nanoscale Science Review Panel Site Visit, Basel, October 20, 2003.

    • This poster corresponds to the publication Phys. Rev. Lett. 93, 106804 (2004) (see above).

    Spin coherence and ESR on quantum dots
  • NCCR Nanoscale Science Review Panel Site Visit, May 19-20, 2003.
  • TNT 2002 Conference, Santiago de Compostela (E), September 9-13, 2002.
  • NCCR Nanoscale Science Workshop, Pontresina, Switzerland, September 4-6, 2002.
  • Gordon Research Conference on Magnetic Nanostructures, Il Ciocco, Lucca, Italy, May 12-17, 2002.
  • Workshop on Nanoscience, Twannberg, October 16-19, 2001.
  • Spintech-I (Conference and School on Spintronics and Quantum Information Technology), Maui, Hawaii, May 13-18, 2001.

    • This poster corresponds to the publication Phys. Rev. Lett. 86, 4648 (2001) (see above). The poster can be downloaded as GZipped PS (156 kB).

    Berry phase effects in diffusive rings
  • Hasliberg workshop on nanoscience 4, Hasliberg, October 16-20, 2000.
  • WE-Heraeus-Ferienkurs Nanophysik, Dresden, September 19-29, 2000.

    • This poster corresponds to the publication Phys. Rev. B 62, 10238 (2000) (see above). The poster can be downloaded as GZipped PS (371 kB).


    Scientific Visits
    Delft University of Technology, 15-19 January 2001
    Guest in the Quantum Transport group.


    IT Projects
    Overview
    Besides activities in physics, I have been working on a broad spectrum of IT (information technology) projects. These involved mastering several programming languages (C/C++, Java, Perl, VB, SQL), scripting languages (JavaScript, ColdFusion, PHP), IT concepts (client/server communication, GUI design, API development, 2D/3D graphics, Internet/Intranet, HTML, CSS, XML, PDF, Flash ...), databases (Oracle, mySql, Access, FileMaker), and UNIX server administration (IRIX and Linux).
    These projects include:

    Open source software
    I am often using open source software. When I stumble over bugs or find some trivial features missing, I tend to fix or implement them and to submit patches to the open source project. This is very useful for me, since I will never be annoyed by such bugs for a second time. Projects I contributed to include mozilla (find me on the credit list), wget, mingw, PyX, mplayer, and gnome-terminal.

    Learning Software
    An training/learning application, which runs within Internet Explorer (ActiveX). This application provides knowledge in form of questions, which are organised hierarchically. These questions can be accessed in various ways, such as browsing or as mock exam. Four different types of questions (multiple/single choice, cloze, assigning) are currently implemented. The application contains an administration interface, for adding and modifying questions.
    A high integration into an Internet/Intranet environment is achieved as follows. Updated versions of the question database can be downloaded by the users. (No online connection is required for the learning process.) Further, online exams can be executed: An administrator composes questions and starts a new exam session. Then, users can register for this exam and answer the given questions. The administrator can continuously monitor the progress of the students with detailed statistical information.


    CMS - Content Management System
    For several projects I have developed indivudual content management systems (CMS). The implemented features range from remotely managing a simple list of news articles or flash movies to sophisticated Java frontends for efficient manipulation of arbitrary databases over the internet.


    Simple CGI scripts
    Various small CGI scripts, mostly written in Perl. Most of them are used to access and modify a simple database for web page creation (see CMS section) or to extend given appications with additional features. For example, this page and other pages of condensed matter group members can be edited by its owners through a simple Web-interface.


    Intranet database interfaces
    I have developed several web interfaces for accessing databases over an intranet. For example, I have developed a software for managing contracts (say, license, R&D, etc.). This application runs on a Netscape server and uses an Oracle database. Access to the application is integrated into the user management of the Netscape server. For printing convenience, all views of the database can be converted into the PDF (Adobe Acrobat) format in real time. This results in a great improvement of the printing quality versus directly printing a HTML page out of the web browser. Further, automatical notifiers are implemented. Then, responsible persons can be reminded automatically by email, if there are due payments or a contract is about to expire.


    Financial Chart generation
    Historical financial data is stored in a simple database on a web-server. This data can be updated via a web browser. Then, a small Java program visualizes the data as charts, which are generated for arbitrary time periods. Such dynamical charts can be integrated as images (or even as applet) into any web site. The charts feature high-quality graphics, in particular anti-aliased text and lines. This increases readability and gives the charts a smoother look.


    Stereo Graphics
    High quality stereo graphics can be displayed with a standard CRT monitor as follows. The images for the left eye and the right eye are shown in an alternating sequence, switching with the frame rate of the monitor (up to 120 Hz). Synchronously, glasses with a LCD shutter cover right and left eye, resp., such that each eye sees only every other frame. Thus, a different image can be presented for each eye, allowing a 3D viewing sensation.
    For this, the computer needs to render the scene from the different viewpoints of each eye. While such rendering does not affect the logic of any 3D software, one still needs to adjust the hardware and to take care of rendering the scene twice. In order to enable an easy access to this powerful display method, I have developed simple API for SGI computers. This API allows to switch stereo mode on and to recover previous setting after use, automatically choosing the best display method of the available hardware.


    Molecular Modeling Challenge
    A 3D Game written for the 100th anniversary of Roche. A screenshot is available (43 k).


    Molecular Inventor
    An API extension of OpenInventor, which provides an object-oriented toolkit for displaying molecular structures in 3D. My job on this project was to implement a first prototype of Molecular Inventor, while I was working for Michael Waldherr-Teschner and Chris Henn for the chemical marketing team of SGI in Basel. Later, Mark Benzel cleaned up the source code to build Molecular Inventor version 1.0, leaving the API mostly unchanged.
    «Molecular Inventor version 1.0 is an object-oriented 3D molecular visualization development kit. It extends the capabilities of Open Inventor to facilitate the development of interactive 3D molecular graphics software applications and extends the standard Open Inventor file format for communicating 3D data between collaborative applications. Chemistry professionals can now take advantage of SGI tools that allow for annotation in 3D, live video conferencing and using a virtual whiteboard over high-bandwidth networks and media-rich information sharing through intranets and the World Wide Web.» (1996)



    Other Activities
    Swiss Study Foundation
    During my time as student, I was an awarded member of the Swiss Study Foundation (Schweizerische Studienstiftung).
    «The Swiss Study Foundation is a private, nonprofit foundation, active in universities, technical colleges, art colleges and music academies. Its objective is to seek out exceptionally gifted and responsible young people, whose personality, abilities, creativity and intellect show promise of outstanding achievement in the fields of social sciences, science, technology or the arts, and to support them throughout their studies. Their studies will be distinguished by their breadth and intensity in accordance with the motto promotion and advancement.»
    I have participated in seminars/workshops on mathematics (Maienfeld, 1997), bioinformatics (1999), ethics (Balsthal, June 15-16, 2002 and Bern, May 4, 2002), economics (2000 ), communications (Ligerz, April 5-7, 2002 and Bern, April 27, 2002), politics (Ligerz, 2003), and rhetorics (Balsthal, 2003) and in some smaller activities. Now I am a member of the Alumni organization.


    Choir
    From 1995-2004 I was singing in the Choir of the University of Basel. Every June, we performed in concert with the university orchestra. Further, there were concerts in advent. I participated in performing the following works: Brahms: "Ein deutsches Requiem" (1996); Mendelssohn: "Paulus" (1997); Mozart: "Requiem" and "Davide penintente" (1998); Dvorák: "Stabat Mater" (1999); Mendelssohn: "Lobgesang" (2000); Carl Orff: "Carmina Burana" (2001); Mozart: "Missa brevis in B major" (2001); Hermann Suter: "Le Laudi" (2002); Joseph Haydn: "Theresienmesse" (2002); Joseph Haydn: "Die Schöpfung" (2003); Johann Sebastian Bach: "Missa a-Dur" (2003); and Johannes Brahms: "Gesang der Parzen," "Drei weltliche Gesänge," and "Nänie" (2004).

    Sports
    Concerning the swiss national sport: I am a keen skier, spending a considerable amount of my spare time on the skifields in the alps. Usually I can be found in challenging terrain, downhill skiing or telemark skiing (for advice to avoid common telemark accidents, click here). Otherwise, if I get the opportunity to swim through nice underwater scenery, I go Scuba diving.

    Traveling
    I enjoy traveling to other countries. My journeys have taken me around Europe and to USA, Canada, New Zealand, Nepal, Israel, Egypt, Jordan, Mexico, Guatemala, Australia, Malaysia, Thailand, Vietnam, Ecuador, Sri Lanka, Ghana, Togo, and Benin.