Robert Andrzej Żak
ContactDepartment of PhysicsUniversity of Basel Klingelbergstrasse 82 CH4056 Basel, Switzerland

Personal webpage: http://quantumtheory.physik.unibas.ch/zak/personal/
Short CV
2007  present  PhD student at the University of Basel 
2007  Master in Physics from the University of Warsaw 
Research interests
 Nuclear magnetism
 Strongly correlated systems
 Spintronics
 Quantum computation and quantum information theory
 Electron transport in nanostructures
Publications
Show all abstracts.1.  Spin susceptibility of interacting twodimensional electrons in the presence of spinorbit coupling 
Robert Andrzej Żak, Dmitrii Maslov, and Daniel Loss. Phys. Rev. B 82, 115415 (2010); arXiV:1005.1913.
A longrange interaction via virtual particlehole pairs between Fermiliquid quasiparticles leads to a nonanalytic behavior of the spin susceptibility $\chi$ as a function of the temperature ($T$), magnetic field ($\mathbf{B}$), and wavenumber. In this paper, we study the effect of the Rashba spinorbit interaction (SOI) on the nonanalytic behavior of $\chi$ for a twodimensional electron liquid. Although the SOI breaks the $SU(2)$ symmetry, it does not eliminate nonanalyticity but rather makes it anisotropic: while the linear scaling of $\chi_{zz}$ with $T$ and $\mathbf{B}$ saturates at the energy scale set by the SOI, that of $\chi_{xx}$ ($=\chi_{yy}$) continues through this energy scale, until renormalization of the electronelectron interaction in the Cooper channel becomes important. We show that the Renormalization Group flow in the Cooper channel has a nontrivial fixed point, and study the consequences of this fixed point for the nonanalytic behavior of $\chi$. An immediate consequence of SOIinduced anisotropy in the nonanalytic behavior of $\chi$ is a possible instability of a secondorder ferromagnetic quantum phase transition with respect to a firstorder transition to an $XY$ ferromagnetic state.
 
2.  Quantum computing with electron spins in quantum dots 
Robert Andrzej Żak, Beat Röthlisberger, Stefano Chesi, and Daniel Loss. Proceedings of the CLXXI International School of Physics 'Enrico Fermi': Quantum Coherence in Solid State Systems (Società Italiana di Fisica, 2009, 61 pages); La Rivista del Nuovo Cimento 33, 7 (2010); arXiv:0906.4045.
Several topics on the implementation of spin qubits in quantum dots are
reviewed. We first provide an introduction to the standard model of quantum
computing and the basic criteria for its realization. Other alternative
formulations such as measurementbased and adiabatic quantum computing are
briefly discussed. We then focus on spin qubits in single and double GaAs
electron quantum dots and review recent experimental achievements with respect
to initialization, coherent manipulation and readout of the spin states. We
extensively discuss the problem of decoherence in this system, with particular
emphasis on its theoretical treatment and possible ways to overcome it.
 
3.  Momentum dependence of the spin susceptibility in two dimensions: nonanalytic corrections in the Cooper channel 
Stefano Chesi, Robert Andrzej Żak, Pascal Simon, and Daniel Loss. Phys. Rev. B 79, 115445 (2009); arXiv:0811.0996.
We consider the effect of rescattering of pairs of quasiparticles in the
Cooper channel resulting in the strong renormalization of secondorder
corrections to the spin susceptibility in a twodimensional electron system. We
use the Fourier expansion of the scattering potential in the vicinity of the
Fermi surface to find that each harmonic becomes renormalized independently.
Since some of those harmonics are negative, the first derivative of the spin
susceptibility is bound to be negative at small momenta, in contrast to the
lowest order perturbation theory result, which predicts a positive slope. We
present in detail an effective method to calculate diagrammatically corrections
to the spin susceptibility to infinite order.
 
4.  Coulomb blockade of a threeterminal quantum dot 
Robert Andrzej Żak and Karsten Flensberg. Phys. Rev. B 77, 045329 (2008); arXiv:0711.1787.
We study an interacting singlelevel quantum dot weakly coupled to three
electrodes. When two electrodes are biased by voltages with opposite
polarities, while keeping the third lead (the stem) grounded, the current
through the stem is a measure of electronhole asymmetry of the dot. In this
setup we calculate the stem current for both metallic and ferromagnetic
(collinearly polarized) leads and discuss how the threeterminal device gives
additional information compared to the usual twoterminal setup. We calculate
both the sequential and cotunneling contribution for the currents. For the
latter part we include a regularization procedure for the cotunneling current,
which enables us to also describe the behavior at the charge degeneracy points.
 
5.  Samoistne powstawanie korków (Spontaneous creation of traffic jams) 
Robert Andrzej Żak Delta 375, 8 (2005)
Not available.
 
6.  Piłeczka w szklance wody (Plastic ball in a glass of water) 
Andrzej Hryczuk and Robert Andrzej Żak. Delta 353, 10 (2003)
Not available.
 
7.  Niebieski las (Blue forest) 
Robert Andrzej Żak and Andrzej Hryczuk. Delta 351, 4 (2003)
Not available.
 
8.  O unoszeniu się ciał na wodzie (About floating of bodies) 
Andrzej Hryczuk and Robert Andrzej Żak. Delta 347, 11 (2003)
Not available.
