Research Interests of EIIIa
The goal of our research is to develop spectroscopic methods and to apply these techniques to the investigation of
a variety of materials. Within this field, we emphasize high resolution
laser spectroscopy,
magnetic resonance,
and the combination of the two fields.
Our motivation for combining the two fields stems partly from the possibility to increase the
sensitivity
of magnetic resonance by several orders of magnitude. This possibility has resulted in some dramatic achievements,
like the demonstration of magnetic resonance of individual molecules.
Another motivation is selectivity: the addition of a laser beam greatly enhances the possibilities for distinguishing
signals that originate from different chemical species, different parts of the sample, or molecules with different orientation.
If you would like to know more about laser-assisted magnetic resonance, you may get an
introduction,
check out a description of the
physics
involved or browse through some
applications to various systems.
Recently, we have focused much of our work on
quantum information processing.
Using nuclear magnetic resonance, we implement simple quantum algorithms and investigate
how their execution can be optimized.
A number of projects are focused on the scalability of quantum information processors.
Current Projects
Raman heterodyne detection of NMR
Marko Lovric
Magnetic resonance transitions can be detected optically
by coherent Raman scattering, a process that may be considered as a frequency shift of an optical photon.
The frequency-shifted light is detected through optical heterodyning, which returns the RF signal.
The aim of our work is to improve these methods and make them applicable to a greater number of systems.
Details on optical superheterodyne detection
Literature :
Stokes / anti-Stokes Symmetry .
Raman heterodyne detection of EPR
Raman heterodyne detection can equally be applied to EPR transitions.
We have built the first instrument that is capable of optical heterodyne detection in the microwave region.
With this instrument, we have measured EPR spectra of transition metal ions in Ruby
and in different metalloproteins containing iron or copper ions.
Detection of the EPR spectrum through a coherent Raman process provides higher selectivity
than conventional detection: the dependence on the optical wavelength allows us to eliminate
signal contributions from impurities, while the dependence on the polarization of the laser beam
provides a possibility to determine the orientation of the g-tensor
with respect to the electric dipole moment and therefore to the molecular geometry.
Additional Details
Laser Assisted NMR of Individual GaAs Quantum Wells
Wieland Worthoff
NMR of quantum wells faces a twofold challenge: the number of spins in a layer of only a few nanometers
is significantly smaller than the detection limit of conventional NMR spectrometers.
Even if it were possible to detect this small number of spins, the signal would be completely covered
by the much larger signal from the identical spins in the substrate. Using lasers for excitation and
detection can overcome the sensitivity limit by enhancing the signal by several orders of magnitude.
Furthermore, the restriction of the signal to a specific optical wavelength selects a specific quantum well,
while the substrate signal is effectively suppressed.
Literature:
Coupling mechanisms for optically induced NMR in GaAs quantum wells
(Phys. Rev. B 65, 125301 (2002).)
Mapping of strain and electric fields in GaAs/AlGaAs quantum-well samples by laser-assisted NMR
(Phys. Rev. B 67, 085308 (2003). )
Molecular Quantum Computing
Ryszard Narkovich, Ingo Niemeyer, and Xing Rong
Research into the physics of computing has shown that some problems for which the computing time
grows exponentially with the size of the problem may be solved in polynomial time if the information
is represented in quantum mechanical states and computational steps implemented as Hamiltonian evolution.
We investigate the possibility to implement a quantum on the basis of individual molecules nanopositioned on surfaces.
More details are available in this
summary.
Literature:
A scalable architecture for spin-based quantum computers with a single type of gates
(Phys. Rev. A 65, 052309 (2002))
Two-qubit gates between noninteracting qubits in endohedral-fullerene-based quantum computation
(Phys. Rev. A 75, 012318 (2007))
NMR Quantum Computer
Xinhua Peng, in Collaboration with
Prof. Jiangfeng Du,
University of Science and Technology China, Hefei
Most physical realisations of quantum computers that have been suggested to date cannot be realised with current technology.
The major exception is nulcear magnetic resonance.
We use liquid-state NMR to implement various quantum algorithms and to
simulate quantum systems
on an NMR quantum computer.
This system allows very precise control of the evolution of the quantum system
and a large amount of fleibility in choosing the quantum system that is best suited for a given task.
In addition, we also use solid-state nuclear magnetic resonance.
The dipolar couplings that are present in these systems allow one to combine many spins
in such a way that they can be used as model quantum register with several thousand qubits.
We have used this system mostly to study decoherence phenomena, which represent a major difficulty
for the realisation of quantum computers of any type.
In the system that we studied,
we found
that the decoherence rate scales
roughly proportional to the square root of the number of qubits.
Furthermore, it turned out to be possible to reduce the decoherence rate
by modulating the system-environment interaction in a suitable way.
This allowed us to reduce the decoherence rate by almost two orders of magnitude,
for quantum register sizes of up to 5000 qubits.
Microresonators for ESR
Ryszard Narkovich
EPR resonators on the basis of standing-wave cavities are optimised for large samples. For small samples it is possible to design
different resonators that have much better power handling properties and higher sensitivity. Other parameters being equal, the
sensitivity of the resonator can be increased by minimising its size and thus increasing the filling factor. Like in NMR, it is possible to
use lumped elements; coils can confine the microwave field to volumes that are much smaller than the wavelength.
Our test resonators, which operate at a frequency of
14 GHz, have excellent microwave efficiency factors, achieving 20 ns π/2 EPR pulses with an input power of <1 mW.
The sensitivity increases roughly linearly with the inverse of the coil size.
Literature:
Planar microresonators for EPR experiments,
(J. Magn. Reson. 175, 275-284 (2005).)
Structure and Dynamic of Lamellar Bilayers
Svetlana Markova,
in collaboration with Prof. Roland Winter and Prof. Alfons Geiger, Department of Chemistry
Lamellar bilayers like cell membranes are essential elements of many biological systems.
We study the molecular forces that shape these structures and allow proteins and other
biomolecules to adhere to them.
Our experimental tools include a range of NMR experiments like pulsed field gradient diffusion NMR,
exchange spectra, MAS, and multiple pulse experiments.
Effect of Devitrification on Ion Dynamics
Reiner Küchler,
in collaboration with Prof. Otmar Kanert and Prof. Himanshu Jain (Lehigh University / USA)
The study of devitrification, the process of crystallization of glass, is not only of fundamental interest for understanding the dynamic properties of glasses, but may also lead to improved materials, such as glass-ceramics. Our investigations of devitrification of Lithium disilicate glass focus on the modification of the dynamics of mobile ions and the correlation of ionic mobility with structural modifications.
Preventive Arms Control and Nanotechnology
Jürgen Altmann, Christoph Weber, and Felix Gorschlüter
Nanotechnology deals with objects and structures the sizes of which are measured in nanometres.
It aims at the directed engineering of matter on the level of molecules and atoms.
Already the evolutionary nanotechnology which builds on present research promises fundamental thrusts of innovation:
faster and smaller computers, stronger and lighter materials, more effective engines, biological-artificial hybrids.
Visionary nanotechnology - which is still speculative - would be characterised by self-replicating systems
that could produce arbitrary goods. With nanotechnology, far-reaching consequences can be foreseen
for the civilian as well as for the military realm.
In the military, nanotechnology could bring about improvements of traditional weapons and systems,
but also new types of applications, e.g., micro fighting robots, specifically targeted chemical/biological weapons,
and implanted systems to analyse and affect body functions.
Building on a preceding analysis of microsystems technology,[1] the project explores the future developments
of nanotechnology under aspects of preventive arms control.
Present military research and development, in particular in the USA, and potential military applications
are listed and judged under criteria of preventive arms control.
On that basis areas are identified where preventive limitations may be advisable, and possible limitations discussed.
The project is being carried out in the framework of the
FONAS Joint Projects on Preventive Arms Control (PRK)
and funded by the Deutsche Stiftung Friedensforschung
(DSF).
[1] J. Altmann, Military Uses of Microsystem Technologies - Dangers and Preventive Arms Control, Münster:
agenda 2001
