Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A quantum logic gate between light and matter

10.04.2014

Scientists at MPQ successfully process quantum information with a system comprising an optical photon and a trapped atom.

When it comes to recognizing complex patterns or to decoding encrypted messages, conventional computers reach their limits. A whole new quality in the communication and processing of data is expected from a technology that exploits the special properties of quantum particles such as superposition and entanglement.


Central part of the experimental setup: A single atom is trapped in the narrow gap between two highly reflecting mirrors (light blue) that form an optical resonator. Reflection of single photons from the resonator implements a quantum logic operation between the atom and the photons. Graphic: Andreas Reiserer, MPQ, Quantum Dynamics Division.

Scientists around the world pursue a variety of different concepts towards the development of such a quantum computer. Prof. Gerhard Rempe, Director at the MPQ and head of the Quantum Dynamics Division, follows the strategy of combining two rather dissimilar techniques: quantum communication using photons, and information processing using stationary atoms.

His team has now for the first time realized a quantum logic gate between a single photon and a single atom (Nature, 10 April 2014). The development of this hybrid device could be a milestone on the path to a scalable and universal quantum computer.

Any modern computer operates according to a mathematical principle that was developed by German polymath Gottfried Wilhelm Leibniz more than 300 years ago: information can be encoded in the binary system and processed via the application of logic operators. Logic gates are based on this principle. They deterministically generate output signals for any combination of input signals according to a so-called truth table. Nowadays, computers contain many millions of logic gates in the form of electronic circuits.

In the experiment described here, the binary states 0 and 1 are represented by the two spin orientations of an atom (upwards or downwards), and by two polarization states of an optical photon (left or right circular), respectively.

In contrast to classical bits, these “quantum bits” can be in a coherent superposition of both states. In order to realize a quantum gate, the atom is trapped inside a cavity which is made of two high-finesse mirrors. The properties of the cavity are chosen in such a way that atom and cavity form a strongly coupled system. The light quanta are prepared as faint laser pulses containing less than one photon on average.

In a former experiment it has been shown that – by a proper choice of parameters – the light quanta are always reflected. What matters is the fact that for certain combinations of atomic and photonic input states the photons are reflected at the first mirror. For other combinations, however, they first enter the cavity, subsequently leaving it on the same path. Thereby, they experience a phase shift of 180 degrees. “This conditional phase shift is the prerequisite for the implementation of a truth table assigning output signals to any combination of input bits in a deterministic way, similar to a classical logic gate.”, Dr. Stephan Ritter explains.

“In our experiment we measure both the polarization of the reflected photons and the spin orientation of the atom after the gate operation. At present, we achieve an efficiency of about 70%. By further improving the mirror parameters this value could be significantly improved”, Andreas Reiserer says.

These measurements demonstrate that the hybrid atom-photon system can act as a classical logic gate. However, the true advantage of a quantum gate compared to a classical one is its ability to generate entangled states from separable input states. In order to test this specific behaviour, the scientists chose a combination of input bits that – according to the rules of quantum mechanics – must lead to an entangled state of atom and photon after the gate operation. Also in this case the gate mechanism worked as expected.

By successively sending two laser pulses onto the system the physicists could even achieve entanglement between the atom and two photons. By clever manipulation of the atom in a second step it was disentangled, leaving a pair of two entangled photons. “These measurements demonstrate the versatility of the gate mechanism that even provides an interaction between two photons”, Norbert Kalb says. “The mechanism should also allow generating entangled cluster states that consist of the atom and several photons.”

The development of this hybrid quantum logic gate could be a big step towards a universal quantum computer. “Quantum communication, using flying photons, and data processing with atoms or ions have been regarded as separate research fields so far”, Prof. Gerhard Rempe says. “In our experiment we merge both techniques. In particular, our quantum gate could be easily implemented in a network in which atoms serve as stationary nodes for the storage of information, whereas photons transmit the information between these nodes, even over large distances. In this way we hope to contribute to the realization of a scalable quantum computer.” Olivia Meyer-Streng

Original publication:

Andreas Reiserer, Norbert Kalb, Gerhard Rempe, and Stephan Ritter
A quantum gate between a flying optical photon and a single trapped atom
Nature, 10 April 2014

Contact:

Prof. Dr. Gerhard Rempe
Director at Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching, Germany
Phone: +49 (0)89 / 32 905 -701 /Fax: -311
E-mail: gerhard.rempe@mpq.mpg.de

Dr. Stephan Ritter
Max Planck Institute of Quantum Optics
Hans-Kopfermann-Straße 1
85748 Garching, Germany
Phone: +49 (0)89 / 32 905 -728 /Fax: -395
E-mail: stephan.duerr@mpq.mpg.de

Dr. Olivia Meyer-Streng
Press & Public Relations
MPQ Garching, Germany
Phone: +49 (0)89 / 32 905 -213
E-mail: olivia.meyer-streng@mpq.mpg.de

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

Further reports about: MPQ Max-Planck-Institut Phone Quantenoptik Quantum combination photons polarization processing signals

More articles from Physics and Astronomy:

nachricht Rosetta’s comet contains ingredients for life
30.05.2016 | Universität Bern

nachricht Present-day measurements yield insights into clouds of the past
27.05.2016 | Paul Scherrer Institut (PSI)

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: Worldwide Success of Tyrolean Wastewater Treatment Technology

A biological and energy-efficient process, developed and patented by the University of Innsbruck, converts nitrogen compounds in wastewater treatment facilities into harmless atmospheric nitrogen gas. This innovative technology is now being refined and marketed jointly with the United States’ DC Water and Sewer Authority (DC Water). The largest DEMON®-system in a wastewater treatment plant is currently being built in Washington, DC.

The DEMON®-system was developed and patented by the University of Innsbruck 11 years ago. Today this successful technology has been implemented in about 70...

Im Focus: Computational high-throughput screening finds hard magnets containing less rare earth elements

Permanent magnets are very important for technologies of the future like electromobility and renewable energy, and rare earth elements (REE) are necessary for their manufacture. The Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, Germany, has now succeeded in identifying promising approaches and materials for new permanent magnets through use of an in-house simulation process based on high-throughput screening (HTS). The team was able to improve magnetic properties this way and at the same time replaced REE with elements that are less expensive and readily available. The results were published in the online technical journal “Scientific Reports”.

The starting point for IWM researchers Wolfgang Körner, Georg Krugel, and Christian Elsässer was a neodymium-iron-nitrogen compound based on a type of...

Im Focus: Atomic precision: technologies for the next-but-one generation of microchips

In the Beyond EUV project, the Fraunhofer Institutes for Laser Technology ILT in Aachen and for Applied Optics and Precision Engineering IOF in Jena are developing key technologies for the manufacture of a new generation of microchips using EUV radiation at a wavelength of 6.7 nm. The resulting structures are barely thicker than single atoms, and they make it possible to produce extremely integrated circuits for such items as wearables or mind-controlled prosthetic limbs.

In 1965 Gordon Moore formulated the law that came to be named after him, which states that the complexity of integrated circuits doubles every one to two...

Im Focus: Researchers demonstrate size quantization of Dirac fermions in graphene

Characterization of high-quality material reveals important details relevant to next generation nanoelectronic devices

Quantum mechanics is the field of physics governing the behavior of things on atomic scales, where things work very differently from our everyday world.

Im Focus: Graphene: A quantum of current

When current comes in discrete packages: Viennese scientists unravel the quantum properties of the carbon material graphene

In 2010 the Nobel Prize in physics was awarded for the discovery of the exceptional material graphene, which consists of a single layer of carbon atoms...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking 4.0: International Laser Technology Congress AKL’16 Shows New Ways of Cooperations

24.05.2016 | Event News

Challenges of rural labor markets

20.05.2016 | Event News

International expert meeting “Health Business Connect” in France

19.05.2016 | Event News

 
Latest News

3-D model reveals how invisible waves move materials within aquatic ecosystems

30.05.2016 | Materials Sciences

Spin glass physics with trapped ions

30.05.2016 | Materials Sciences

Optatec 2016: Robust glass optical elements for LED lighting

30.05.2016 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>