SCIENTIFIC REPORT:

Aim and Purpose

Nuclear physics research has entered a new era with the recent developments

of facilities that provide access to high intensity radioactive nuclear

beams; an area in which Europe is a major stakeholder (GSI, HIE-ISOLDE,

GANIL). At these facilities it is nuclear collisions and reactions that provide

the primary probes of the new physics, such as novel structural changes,

through dynamical excitations of nucleonic, collective and cluster degrees

of freedom. In parallel, new and innovative detection systems are allowing

measurements of unprecedented exclusivity and precision, including those using

intense stable beams. These and the increased intensity rare radioactive

beam capabilities require investigations of the role of hitherto inaccessible degrees

of freedom and new dynamical considerations in the nuclear structure

and collision dynamics. Combining fully reaction dynamics and many-body

structure information is a major outstanding problem across disciplines.

Quantifying the role and the importance of decoherence in quantum

many-body systems is now pervasive in modern science and studies of quantum

measurement and quantum information. The concept of a reduced (but

not closed) quantum system evolving in the presence of weak couplings to

complex states is common throughout disciplines. Collisions of composite

nuclei have conventionally been treated as closed quantum systems, assuming

a state-truncated model space. In reality however their evolution involves

intrinsic excitations to innumerable available open channels. The assumed

model space for any practical, conventional calculation is inevitably limited

to a number of most relevant excitations, defining the reduced quantum system.

All other states (each individually very weakly coupled to the reduced

system by residual interactions) constitutes the external environment in this

case and which may be specific to particular degrees of freedom of the system

and the collision dynamics, such as weak binding or isospin asymmetry, and

the collision energy. Among such environments are (i) high level-densities

of one- and multi-nucleonic excitations, (ii) the breakup continua of decay

channels (e.g. for weakly-bound nuclei).

Many of the key questions posed are common across disciplines and applicable

techniques have been advanced very significantly in other areas of

few- and many-body physics and chemistry. Molecular physics, for example,

covers a wide range of regimes involving ultrafast electronic and vibrational

decoherence, as well as situations where collective environmental

modes create approximate decoherence-free subspaces. Recent experiments

on photosynthetic light-harvesting systems provide strong evidence for the

protection of excitonic coherence by the protein environment. Accordingly,

the available theoretical approaches include Markovian and non-Markovian

master equations as well as explicit, high-dimensional quantum and mixed

quantum-classical calculations of the combined system and environment.

The main aims of the Workshop were:

   To both review and assess methods, recent investigations and implications

of quantum decoherence in atomic, molecular and other areas,

and to relate these to the nuclear physics context; providing both theoretical

and experimental perspectives.

   To create essential links between the nuclear physics community and

practitioners in other areas of science aimed at understanding fundamental

aspects of quantum physics, such as the role of decoherence and

the quantum-to-classical transition.

   To initiate inter-disciplinary exchanges and the transfer of expertise, to

foster collaborations, and facilitate the formation of younger- researcher

networks.

Results and Highlights  The workshop brought together researchers

(both theorists and experimenters) from a wide range of disciplines (electron

and molecular interferometry, quantum optics, atomic and molecular physics,

quantum information, quantum biology and nuclear physics) that span the

subject of quantum decoherence in dynamics of few- and many-body quantum

systems.

Researchers from fields other than nuclear physics presented methodologies

and experiments for the study of decoherence in quantum dynamics.

Nuclear scientists reported on theoretical methods and experimental capabilities

in nuclear structure and reaction dynamics. They discussed, with

researchers of other disciplines the use of specific techniques (their strengths

and weaknesses) that might be used to identify nuclear scenarios where quantum

decoherence may play a crucial role. E.g. complex atomic nuclei have

proven to be outstanding laboratories for researching quantum decoherence

effects, with the interplay of multiple, complicated degrees of freedom in the

processes involved.

Conclusions   The workshop was a great success, as expressed by many

delegates. While quantum decoherence is topical across various disciplines,

it is hardly investigated at all in low-energy nuclear physics phenomena.

Thus, the workshop has opened a new window for the nuclear physics community.

In the workshop, the communication between the participants was

impressive, reflected in deep and stimulating discussions during and after

the daily presentations. The workshop has been a very positive experience

for everyone. New collaborations and exchange of ideas have been initiated,

for instance, between nuclear theorists and researchers from other areas regarding

methodologies for investigating the open (nuclear) system dynamics.

A collaboration meeting on nuclear fusion (involving theorists and experimenters)

has been planned, which could take place in 2011. It is expected

that such a meeting will help tackle urgent (unsolved) problems in low-energy

nuclear collision dynamics. It could also access, through realistic quantitative

models, the usefulness of a consistent treatment of open (nuclear) system

dynamics that includes quantum decoherence effects.

Optional The talks can be browsed from the website:

                http://www.nucleartheory.net/Decoherence