Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Quantum Odyssey in an Ion Trap

31.08.2009
MPQ scientists demonstrate quantum walks with single trapped ions.

Many classical algorithms in computer science include so called "random walks", where possible ways to solve a problem are chosen at random. Algorithms of that kind are found in fields like physics, biology, economics, and even psychology.


In a quantum labyrinth all possible paths are in a state of superposition and can be taken simultaneously. This gives rise to interferences that lead to strange phenomena such as the self-encounter of the quantum walker. Due to these \"tricks\" the exit out of the maze, e.g. die solution of an algorithm or the most efficient way of energy transfer in plants, can be found dramatically faster than with classical methods. MPQ / Tobias Schätz

In quantum systems these decisions become obsolete because all possible paths are in a state of superposition and can be followed at the same time. As a consequence interferences occur that give rise to new phenomena.

E.g., at crossings a quantum walker can encounter himself. Quantum walks could substantially speed up algorithms used for quantum systems. But they can also lead to new insight into the behavior of mesoscopic systems that mark the border between the classical and the quantum mechanical world. In a "proof-of-principle"-experiment, using an ion trap, Dr. Tobias Schätz, leader of the Junior Research Group "Quantum Simulations" at Max Planck Institute of Quantum Optics in Garching near Munich, and his collaborators were now able to unambiguously demonstrate the difference between the classical and the quantum mechanical "Odyssey" of an ion (Physical Review Letters, 28. August 2009).

Every time we arrive at a crossroad, we have to choose - perhaps by flipping a coin - the route to tackle. After several crossings and choices we will have followed a few out of many possible paths, maybe some of them more frequently than others.

A quantum walker in contrast does not have to decide - indeed there is no choice. At each coin toss a superposition of head and tail is generated, allowing the walker to follow all the possible paths simultaneously. As a consequence strange phenomena may show up. E.g., if paths recombine again at subsequent crossings, the walker can meet himself - and due to interference - increase his probability to be at this crossing or even disappear.

In the experiment described here a single magnesium ion stored in an electromagnetic trap plays the role of the quantum walker. Its motional ground state represents the initial state of the walk. By irradiation of radiofrequency pulses a superposition of electronic states gets excited. This simulation of the coin toss results in a superposition of "left" and "right" decision. Now ultraviolet light of a well chosen frequency gives the ion the necessary "push" to get moving. Depending on its particular electronic state the ion gets pushed to the left or to the right, whereby a superposition of the two permitted motions is generated. Therefore, quantum walks are connected with a high degree of entanglement between the two values of the coin and the two motion possibilities of the ion.

Three times the actions "coin toss" and "change of position" are repeated; this is the least requirement for the observation of quantum effects. Once this quantum evolution is completed the state of the coin and the particular end position of the ion gets detected. This procedure exploits the fact that only one of the coin states allows the ion to fluoresce. From the statistics of about a thousand measurements the physicists infer how often the ion has moved to the right or to the left. The experimental data clearly confirm the theoretical prediction of an unbalance between the two directions, in contrast of what would be expected for a classical system.

In this experiment the group of Dr. Schätz has clearly revealed the difference of a quantum system to its classical counterpart by allowing the walker/ion to take all classical paths simultaneously: Quantum interferences enforce asymmetric, non-classical distributions in the highly entangled coin and position states. Yet the number of repetition steps is limited by non-linear effects. To overcome these restrictions the scientists now propose an altered protocol that would make it possible to scale the quantum walk to many, in principle to several hundreds of steps.

Quantum walks are predicted to be of fundamental interest for many "applications". Searching for the right path might get dramatically boosted in efficiency if one does not have to try out randomly each individual one but all of them simultaneously. This mind puzzling behaviour could, for example, help to enhance the power of search algorithms in computational science. But it is, for example, also suspected to be responsible for the high efficiency of energy transfer on multiple paths in plants, far beyond what human beings reach with their yet classical approach.

[Tobias Schätz/Olivia Meyer-Streng]

Original publication:
H. Schmitz, R. Matjeschk, C. Schneider, J. Glückert, M. Enderlein, T. Huber and T. Schätz
"Quantum walk of a trapped ion in phase space"
Physical Review Letters, 28. August 2009
Contact:
Dr. Tobias Schätz
Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching
Phone: +49 - 89 / 32905 - 199
Fax: +49 - 89 / 32905 - 311
E-mail: tobias.schaetz@mpq.mpg.de
Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics
Phone: +49 - 89 / 32905 - 213
Fax: +49 - 89 / 32905 - 200
E-mail: olivia.meyer-streng@mpq.mpg.de

Dr. Olivia Meyer-Streng | Max-Planck-Institut
Further information:
http://www.mpq.mpg.de

More articles from Physics and Astronomy:

nachricht Physicists Design Ultrafocused Pulses
27.07.2017 | Universität Innsbruck

nachricht CCNY physicists master unexplored electron property
26.07.2017 | City College of New York

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Physicists Design Ultrafocused Pulses

Physicists working with researcher Oriol Romero-Isart devised a new simple scheme to theoretically generate arbitrarily short and focused electromagnetic fields. This new tool could be used for precise sensing and in microscopy.

Microwaves, heat radiation, light and X-radiation are examples for electromagnetic waves. Many applications require to focus the electromagnetic fields to...

Im Focus: Carbon Nanotubes Turn Electrical Current into Light-emitting Quasi-particles

Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers

Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...

Im Focus: Flexible proximity sensor creates smart surfaces

Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.

At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...

Im Focus: 3-D scanning with water

3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects

A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

 
Latest News

Programming cells with computer-like logic

27.07.2017 | Life Sciences

Identified the component that allows a lethal bacteria to spread resistance to antibiotics

27.07.2017 | Life Sciences

Malaria Already Endemic in the Mediterranean by the Roman Period

27.07.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>