The system consists of a large number of atoms trapped in an
optical lattice of laser beams. The researchers are creating
order by exciting the ensemble of particles with another laser
while at the same time allowing spontaneous emission into an
ultra-cold gas (red) in the environment. (c) IQOQI
In the online edition of Nature Physics, theoretical physicists
from the Institute for Quantum Optics and Quantum Information (IQOQI)
and the University of Innsbruck today are presenting a
completely new way of preparing quantum states in many-body
systems. This means that for the first time even excited
many-body states can be created in a targeted fashion, an
important step in the exploration of solid states.
Analysing many-body systems quantum-physically is of particular
interest because they can be used as models for exploring the
interior of solid states. Up to now the extremely high
complexity of solid matter denied any penetrating
quantum-physical gaze into it. Theoretical physicists around
Sebastian Diehl, Andrea Micheli, Barbara Kraus and Peter Zoller
at the Institute of Theoretical Physics at the University of
Innsbruck and at the Institute for Quantum Optics and Quantum
Information (IQOQI) of the Austrian Academy of Sciences (Oesterreichische
Akademie der Wissenschaften, OeAW) have now developed a new
theoretical proposal for preparing quantum states in many-body
systems. Their method employs a trick: in classical physics
dissipation describes, for instance, the transition from kinetic
energy to thermal energy through friction. 'Normally dissipation
dramatically raises the degree of disorder in any system, but we
are turning it around,' explained Sebastian Diehl. 'We use
dissipation to create a perfectly pure many-body state of
long-range order.'
The system that the scientists use to test their method
theoretically consists of a large number of atoms trapped in an
optical lattice of laser beams. The researchers are creating
order by exciting the ensemble of particles with another laser
while at the same time allowing spontaneous emission into an
ultra-cold gas in the environment (dissipation). 'In this
process the coherence of the exciting laser beam is transferred
into the atomic matter system,' Diehl summed up the idea behind
the new method. 'What is surprising and follows the laws of
quantum physics is the fact that while the atoms are manipulated
only locally, order is created throughout the entire system.'
'In this model system we are combining methods from quantum
optics and nuclear physics with techniques used in solid state
physics,' professor Peter Zoller, head of the research group,
explained. Such an interdisciplinary approach might also be
relevant for applications in quantum information processing. The
theoretical physicists now want to apply their idea to even more
complex systems, for example proposing experimental methods for
studying high temperature superconductivity, a very prominent
problem in solid state physics. Here their new method offers an
advantage that existing approaches lack. 'With our method it
becomes possible to prepare states that correspond to excited
many-body states. Conventional cooling of a particle system
could never achieve this in its pure form,' Sebastian Diehl and
his research colleagues emphasise.
In their research the scientists are receiving support from the
Austrian Science Fund (FWF), the Austrian Academy of Sciences
and the European Union.
Citation: Quantum states and phases in driven open quantum
systems with cold atoms. Diehl S, Micheli A, Kantian A, Kraus B,
Buechler HP, Zoller P. Nature Physics, Advanced Online
Publication 7 September 2008 (doi: 10.1038/nphys1073).
Source: Institute
for Quantum Optics and Quantum Information