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 Hubble observes one-of-a-kind star nicknamed 'Nasty'
22.05.2015 | NASA/Goddard Space Flight Center

nachricht Basel Physicists Develop Efficient Method of Signal Transmission from Nanocomponents
22.05.2015 | Universität Basel

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: Basel Physicists Develop Efficient Method of Signal Transmission from Nanocomponents

Physicists have developed an innovative method that could enable the efficient use of nanocomponents in electronic circuits. To achieve this, they have developed a layout in which a nanocomponent is connected to two electrical conductors, which uncouple the electrical signal in a highly efficient manner. The scientists at the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have published their results in the scientific journal “Nature Communications” together with their colleagues from ETH Zurich.

Electronic components are becoming smaller and smaller. Components measuring just a few nanometers – the size of around ten atoms – are already being produced...

Im Focus: IoT-based Advanced Automobile Parking Navigation System

Development and implementation of an advanced automobile parking navigation platform for parking services

To fulfill the requirements of the industry, PolyU researchers developed the Advanced Automobile Parking Navigation Platform, which includes smart devices,...

Im Focus: First electrical car ferry in the world in operation in Norway now

  • Siemens delivers electric propulsion system and charging stations with lithium-ion batteries charged from hydro power
  • Ferry only uses 150 kilowatt hours (kWh) per route and reduces cost of fuel by 60 percent
  • Milestone on the road to operating emission-free ferries

The world's first electrical car and passenger ferry powered by batteries has entered service in Norway. The ferry only uses 150 kWh per route, which...

Im Focus: Into the ice – RV Polarstern opens the arctic season by setting course for Spitsbergen

On Tuesday, 19 May 2015 the research icebreaker Polarstern will leave its home port in Bremerhaven, setting a course for the Arctic. Led by Dr Ilka Peeken from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) a team of 53 researchers from 11 countries will investigate the effects of climate change in the Arctic, from the surface ice floes down to the seafloor.

RV Polarstern will enter the sea-ice zone north of Spitsbergen. Covering two shallow regions on their way to deeper waters, the scientists on board will focus...

Im Focus: Gel filled with nanosponges cleans up MRSA infections

Nanoengineers at the University of California, San Diego developed a gel filled with toxin-absorbing nanosponges that could lead to an effective treatment for skin and wound infections caused by MRSA (methicillin-resistant Staphylococcus aureus), an antibiotic-resistant bacteria. This "nanosponge-hydrogel" minimized the growth of skin lesions on mice infected with MRSA - without the use of antibiotics. The researchers recently published their findings online in Advanced Materials.

To make the nanosponge-hydrogel, the team mixed nanosponges, which are nanoparticles that absorb dangerous toxins produced by MRSA, E. coli and other...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International symposium: trends in spatial analysis and modelling for a more sustainable land use

20.05.2015 | Event News

15th conference of the International Association of Colloid and Interface Scientists

18.05.2015 | Event News

EHFG 2015: Securing health in Europe. Balancing priorities, sharing responsibilities

12.05.2015 | Event News

 
Latest News

Mesoporous Particles for the Development of Drug Delivery System Safe to Human Bodies

22.05.2015 | Materials Sciences

Computing at the Speed of Light

22.05.2015 | Information Technology

Development of Gold Nanoparticles That Control Osteogenic Differentiation of Stem Cells

22.05.2015 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>