ELFT HÍRADÓ

[Edina Szirmai <eszirmai AT phy.bme.hu>]

                                    MEGHÍVÓ

 az "Egzotikus Kvantum Fázisok" Lendület kutatócsoport
                        következő szemináriumára


                                 Asbóth János
               (MTA Wigner Fizikai Kutatóközpont)


Localization, Diffusion, Topological Phases in 2-D quantum walks

The hallmark property of Quantum Walks is that they spread ballistically,
<x^2> \propto t^2, faster than the diffusive, <x^2> \propto t spreading of
random walks. This gives them a "quantum speedup", which can be exploited
in quantum algorithms. In the presence of time-independent disorder,
however, 1- and 2-dimensional (1D and 2D) quantum walks are expected to
suffer Anderson localization, whereby their spread stops completely, <x^2>
\to \const, except for a few exceptions.

Simulating the 2D split-step Hadamard walk, we have found [1] that -
contrary to earlier simulation results [2] -  it does not undergo Anderson
localization, instead, over long timescales, it spreads diffusively. We
explained this phenomenon by showing that this quantum walk is an iterative
dynamical system tuned to a critical point at a topological phase
transition. The role of the Chern number is here taken over[3] by the
Rudner invariant[4]. In the talk, I will explain this explanation.


[1]: J. M. Edge and J. K. Asboth, accepted to PRB,
http://arxiv.org/abs/1411.7691
[2]: J. Svozilik, R. D. J. Leon-Montiel, and J. P. Torres, PRA 86, 052327
(2012)
[3]: J. K. Asboth and J. M. Edge, PRA 91, 022324 (2015)
[4]: M. S. Rudner, N. H. Lindner, E. Berg, and M. Levin, PRX 3, 031005
(2013)


Az előadás helye:  BME F III. épület, mfsz, szemináriumi szoba.
Ideje: 2015. március 2. hétfő, 14:15.

Minden érdeklődőt szeretettel várunk!

                                         Szirmai Edina



-- 
Edina Szirmai
Department of Theoretical Physics,
Budapest University of Technology and Economics
Budafoki ut 8.
Budapest, Hungary
Tel:(+36-1) 463-4107
Fax:(+36-1) 463-3567
www.phy.bme.hu/~eszirmai