This term the seminars will be held
on
Tuesdays at 3.00 pm in Room
0G.007, David Bates Building
(location), followed by tea/coffee and biscuits in
room 01.040 from 4.00 pm.
You are very welcome!
Seminar coordinator: Dr G Gribakin -
g.gribakin@qub.ac.uk
(Past
Seminars in 2000-2010)
Seminars
2011-2012:
Tuesday, 31 January 2012, 3:00 pm, room 0G.007,
David Bates Building
D. Sokolovski1,2 and E. Ya. Sherman1,2
1Departmento de Quimica-Fisica, Universidad del Pais
Vasco, UPV/EHU, E-48080 Leioa, Spain
2IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain
Measurement of noncommuting spin components using spin-orbit interaction
We propose a possible experiment aimed at a joint measurement of two
noncommuting spin-1/2 components and analyze its physical meaning. We
demonstrate that switching of a strong spin-orbit interaction, e.g., in a
solid-state or a cold-atom system, for a short time interval simulates a
simultaneous von Neumann measurement of the operators σx
and σy. With the spin dynamics mapped onto the quantum
coordinate-space motion, such an experiment determines averages of
σx and σy over the duration of the
measurement, however short the measurement may be. These time averages, unlike
the instantaneous values of σx and σy,
may be evaluated simultaneously to an arbitrary accuracy.
Tuesday, 20 December 2011
Prof Brian Kennedy, School of Physics, Georgia Institute of Technology, Atlanta
Quantum optics with interacting Rydberg atoms
For applications in quantum information processing, high speed sources of
single photons and entangled states are of great importance. We will discuss
recent ideas and scenarios, involving interacting Rydberg states of alkali
atoms, that are promising for these purposes.
Wednesday, 7 December 2011
Dr Fabio Sciarrino, Quantum Optics Group, Department of Physics
Sapienza University of Rome
Optical technologies for quantum information processing
Photons are a natural candidate for quantum information transmission,
quantum computing, optical quantum sensing, and metrology. In the last
few years, the Quantum Optics group of Roma has contributed to develop
different experimental photonic platforms to carry out quantum information
processing based on different photon degrees of freedom.
The standard encoding process of quantum information adopting the methods
of quantum optics is based on the two-dimensional space of photon
polarization. Very recently the orbital angular momentum (OAM) of light,
associated to the transverse amplitude profile, has been recognized as a
new resource, allowing the implementation of a higher-dimensional quantum
space, or a "qudit", encoded in a single photon. Our research topic is
based on the study of new optical devices able to couple the orbital and
spinorial components of the photonic angular momentum [1]. Such devices
allow to manipulate efficiently and deterministically the orbital angular
momentum degree of freedom, exploiting both the polarization and the OAM
advantages [2].
Another approach exploits integrated optical technology which may
represent an excellent experimental platform to carry out quantum
information processing. We report the realization of a laser written beam
splitter in a bulk glass able to support polarization encoded
information [3]. We demonstrated integrated quantum optical circuits, like
CNOT gate [3]. The maskless technique, the single step easy fabrication,
the possible three-dimensional layouts and the circular transverse
waveguide profile able to support the propagation of gaussian modes with
any polarization state make this approach promising to carry out optical
quantum information processing.
[1] E. Nagali et al., Phys. Rev. Lett. 103, 013601 (2009).
[2] E. Nagali, et al., Nature Photonics 3, 720 (2009);
E. Nagali, et al., Phys. Rev. Lett. 105, 073602 (2010).
[3] L. Sansoni, et al., Phys. Rev. Lett. 105, 200503 (2010);
A. Crespi et al. Nature Photonics (in press).
Thursday, 1 December 2011
Dr Simone Paganelli, Physics Department, Theoretical Physics Group: Quantum
Information Group, Autonomous University of Barcelona, Spain
Beyond pure state entanglement for atomic ensembles
Entanglement between macroscopic atomic ensembles induced by measurement
on an ancillary light system has proven to be a powerful method for
engineering quantum memories and quantum state transfer. The main ingredient
to produce such entanglement is the interface of atomic collective spins
with polarized light via the Faraday effect. At the quantum level, this
leads to an exchange of fluctuations between light and matter.
If a light beam crosses sequentially several polarized atomic ensembles,
then a homodyne measurement of light is able to projects the atomic ensembles
into an entangled state. A geometrical approach can be employed, making the
light impinge on samples with different angles to create different types of
entaglement. Such a scheme can be exploited to go beyond the pure state
paradigm and provides realistic experimental settings to address
multipartite mixed state entanglement in continuous variables. In particular,
it will be shown how it is possible to create bound entagled states.
Tuesday, 8 November 2011
Prof Ilya Fabrikant, Department of Physics and Astronomy,
University of Nebraska-Lincoln, Lincoln NE, USA, and Department of Physics
and Astronomy, The Open University, Walton Hall, Milton Keynes, UK
Semiclassical complex-time method for tunneling ionization
We apply the semiclassical propagation technique to tunneling ionization in
atomic and molecular systems. Semiclassical wave functions and the tunneling
flux are calculated from the solution of the classical equations of motion in
the complex time plane. We illustrate this method by rederiving the known
result for the decay rate of a negative ion in a weak electric field. We then
obtain numerical results for several molecules. In particular,
we investigate the presence of the molecular suppression effect
by calculating ionization rates of N2 versus Ar, O2 versus Xe, F2 versus Ar,
and CO versus Kr. Comparisons with other theories, including the
molecular-orbital-Ammosov-Delone-Krainov (MO-ADK) model and the strong-field
approximation, are given. We also analyze the dependence of the ionization
rate on the angle between the molecular axis and the field direction. The
theoretical results agree quite well with experiments for N2 and O2 but
give too low a value of the peak angle for CO2. Our calculations give small
values of the ionization rates for O2 and CO2 at small angles, in agreement
with the experiment. Other calculations, including the MO-ADK model and methods
involving a numerical integration of the time-dependent Schroedinger equation,
exhibit substantially weaker suppression at these angles.
Wednesday, 2 November 2011
Dr Simon Gardiner, Department of Physics, University of Durham
Quantum Chaos and Dynamical Depletion in an Atomic Bose-Einstein Condensate
Central to our understanding of weakly interacting atomic Bose-Einstein
condensates (BECs) is the concept of each atom being in approximately the
same motional state; this is manifest through the description of
zero-temperature BEC dynamics with the Gross-Pitaevskii equation (GPE).
Even at T=0 in a finite system there is always a finite noncondensate
fraction, and one expects strong dynamics within the BEC to cause
significant particle transfer from the condensate to the noncondensate
fraction under quite general circumstances. When such dynamical depletion
occurs rapidly, it has commonly been supposed to presage destruction of the
BEC as a coherent entity, however previous studies have been hampered by the
absence of a self-consistent treatment. One possibility is to use
a number-conserving treatment (where one works within the canonical
ensemble), to second order, which is the minimum order necessary to provide
consistent coupled condensate and noncondensate number dynamics for a finite
total number of particles. I will address the methodology and rationale for
such a canonical (as opposed to grand-canonical) treatment, and describe the
results considering a dynamical test-system based on the delta-kicked rotor.
Tuesday, 1 November 2011
Prof Sergei Sheinerman, St Petersburg State Maritime Technical University
Post-collision interaction in photoionization of atomic inner shells
followed by one- or two-electron emission
Post-Collision-Interaction (PCI) is known as a special kind of electron
correlation which is associated to the interaction between the charged
particles in a resonant process, i.e., the process which occurs through the
creation and decay of an intermediate quasistationary state. It provides a
rare example of a quantum three-body problem for which analytical results can
be obtained [1]. For the case of inner-shell photoionization, PCI reduces to the
interaction of the emitted photoelectron with the Auger electrons and with the
ion field which varies in the course of the Auger decay. This talk presents
an investigation of the PCI influence on the photoelectron spectrum which is
associated with an emission of one (single Auger decay) or two (double Auger
decay) Auger electrons [2]. Different features of the PCI in such processes are
illustrated by measurements and calculation for the case of Ar 2p and Kr 3d
inner shells photoionization.
[1] M. Yu. Kuchiev and S. A. Sheinerman, Post-collision interaction in atomic
processes, Sov. Phys. Usp. 32, 569-587 (1989).
[2] L. Gerchikov and S. A. Sheinerman, Post-collision-interaction distortion
of low-energy photoelectron spectra associated with double Auger decay,
Phys. Rev. A 84, 022503 (2011).
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