Quantum memory for communication networks of the future

November 8, 2010
The photo shows the experimental setup for a quantum information experiment. The table is filled with optical elements such as mirrors, lenses and wave plates, which are used to guide and manipulate infrared light. Inside each of the two metal cylinders is a glass cell with caesium atoms. The two cylinders are magnetic shields which protect the atoms from magnetic fields. Shown in the upper right corner is a pair of detectors which are used to make measurements of the infrared light. Credit: Quantop

Researchers from the Niels Bohr Institute at the University of Copenhagen have succeeded in storing quantum information using two 'entangled' light beams. Quantum memory or information storage is a necessary element of future quantum communication networks. The new findings are published in Nature Physics.

Quantum networks will be able to protect the security of information better than the current conventional communication networks. The cornerstone of quantum communication is a phenomenon called entanglement between two quantum systems, for example, two light beams. means that the two light beams are connected to each other, so that they have well defined common characteristics, a kind of common knowledge. A can – according to the laws of quantum mechanics, not be copied and can therefore be used to transfer data in a secure way.

In professor Eugene Polzik's research group Quantop at the Niels Bohr Institute researchers have now been able to store the two entangled light beams in two quantum memories. The research is conducted in a laboratory where a forest of mirrors and optical elements such as wave plates, beam splitters, lenses etc. are set up on a large table, sending the light around on a more than 10 meter long labyrinthine journey. Using the optical elements, the researchers control the light and regulate the size and intensity to get just the right wavelength and polarisation the light needs to have for the experiment.

The illustration shows the two quantum memories. Each memory consists of a glass cell filled with caesium atoms, which are shown as small blue and red balls. The light beam is sent through the atoms and the quantum information is thus transferred from the light to the atoms. Credit: Quantop

The two entangled light beams are created by sending a single blue through a crystal where the blue light beam is split up into two red light beams. The two red light beams are entangled, so they have a common quantum state. The quantum state itself is information.

The two light beams are sent on through the labyrinth of mirrors and optical elements and reach the two memories, which in the experiment are two glass containers filled with a gas of caesium atoms. The atoms' quantum state contains information in the form of a so-called spin, which can be either 'up' or 'down'. It can be compared with computer data, which consists of the digits 0 and 1. When the light beams pass the atoms, the quantum state is transferred from the two light beams to the two memories. The information has thus been stored as the new quantum state in the atoms.

"For the first time such a memory has been demonstrated with a very high degree of reliability. In fact, it is so good that it is impossible to obtain with conventional memory for light that is used in, for example, internet communication. This result means that a quantum network is one step closer to being a reality", explains professor Eugene Polzik.

Explore further: Researchers Demonstrate 'Quantum Data Buffering' Scheme

More information: dx.doi.org/10.1038/NPHYS1819

Related Stories

Researchers Demonstrate 'Quantum Data Buffering' Scheme

February 12, 2009

(PhysOrg.com) -- Pushing the envelope of Albert Einstein's "spooky action at a distance," known as entanglement, researchers at the Joint Quantum Institute (JQI) of the Commerce Department's National Institute of Standards ...

Physicists Demonstrate Three-Color Entanglement

October 7, 2009

(PhysOrg.com) -- For the first time, physicists have demonstrated the quantum entanglement of three light beams, all of different wavelengths. Entanglement of two light beams of different wavelengths has already been demonstrated, ...

Quantum electronics: Two photons and chips

January 20, 2006

Scientists at Toshiba Research Europe Limited (Cambridge, UK) believe they are on to a way of producing entangled twins of photons using a simple semiconductor electronic device. Such a chip-based source of entangled photons ...

Shining light in quantum computing

September 12, 2006

University of Queensland scientist Devon Biggerstaff is investigating ways to manipulate light in a process that will help shape future supercomputers and communication technology.

Recommended for you

Mapping the edge of reality

April 28, 2017

Australian and German researchers have collaborated to develop a genetic algorithm to confirm the rejection of classical notions of causality.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.