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EMERGING RESEARCH FRONTS - 2008

Ting Yu & Joseph Eberly talk with ScienceWatch.com and answer a few questions about this month's Emerging Research Front in the field of Physics.
Yu Article: Finite-time disentanglement via spontaneous emission
Authors: Yu, T;Eberly, JH
Journal: PHYS REV LETT, 93 (14): art. no.-140404 OCT 1 2004
Addresses: Univ Rochester, Rochester Theory Ctr Opt Sci & Engn, 601 Elmwood Ave, Rochester, NY 14627 USA.
Univ Rochester, Rochester Theory Ctr Opt Sci & Engn, Rochester, NY 14627 USA.
Univ Rochester, Dept Phys & Astron, Rochester, NY 14627 USA.

Why do you think your paper is highly cited?

In the last decade, the use of quantum mechanical principles to greatly enhance computing capabilities has begun to emerge from the domain of pure research, and the prospects are so attractive that interest has spread across many fields of physical science and engineering. Most approaches to this practical goal are based on preserving a high degree of correlation, called quantum entanglement, among the participating elements.

Decoherence is the term used to describe loss of entanglement, and in very simplified terms, we showed that ambient "noise" leads to decoherence that can attack entanglement in an unexpected way. In particular, it can cause entanglement to disappear non-smoothly, in a sense, abruptly. This non-smooth behavior is at variance with virtually all prior results, and our paper pointing it out triggered a still-ongoing surge of recalculations and confirmations, new theoretical examples, and more than one experimental observation to date.

Does it describe a new discovery, methodology, or synthesis of knowledge?

Our research does identify an effect not previously known in the long-established domain of relaxation studies, and in that sense it is a discovery. It is also obviously a synthesis of knowledge because the methods we used to obtain our predictions are commonly used by theoretical physicists everywhere.

Would you summarize the significance of your paper in layman's terms?

Practical use of quantum entanglement may lead to big advances in computational capabilities, for example speed. To go further requires a lesson in entanglement quantum physics, probably not what the reader is ready for. Let’s just say that entanglement describes an anomalously high degree of correlation among atoms or molecules or photons or spins in a many-body quantum system. This correlation can persist even if the two bodies are remotely located and completely out of contact with each other.

Only recently have experiments been able to enter this domain, because of the sensitivity of quantum waves. In principle, the preservation of this higher-than-normal correlation is what permits otherwise impossible tasks, but such high correlations are very fragile. We found that widely separated quantum systems in the presence of a very weakly noisy environment would lose their mutual entanglement in a new way, becoming exactly zero unexpectedly soon. This phenomenon, that entanglement is terminated in a finite time, is now commonly called entanglement sudden death (ESD).

How did you become involved in this research and were any particular problems encountered along the way?

It was almost accidental. We have joint experience in the behavior of noise-affected quantum systems, but for a while we were focused only on quantum noise-control in single units, overlooking the now-obvious fact that adding just one more unit would reveal interesting new time-dependent questions.

Where do you see your research leading in the future?

Entangled quantum memory networks will be valuable, and progress in developing them is occurring in a number of laboratories, but they are potentially sensitive to the consequences of ESD. Quantum transactions that can be operated at sufficiently high speed can ignore ESD, as a first approximation. However, a quantum memory should preserve correlation indefinitely. After ESD, there is no way presently known to reconstruct a usefully entangled state. This makes it desirable to have the onset time for ESD predictable, but so far there is no generic guide to such a time, so we guess there still is a lot of work to be done in this direction.

Do you foresee any social or political implications for your research?

It will be a much greater surprise than the discovery of ESD if there turn out to be implications for our research into social and political domains.

Ting Yu, Ph.D.
Scientist and Asst. Prof. of Physics
Department of Physics and Astronomy
University of Rochester
Rochester, NY, USA

J. H. Eberly, Ph.D.
Andrew Carnegie Professor of Physics and Professor of Optics
Director, Rochester Theory Center
Department of Physics and Astronomy
University of Rochester
Rochester NY, USA



2008 : February 2008 : Ting Yu & Joseph Eberly