Because of its strange consequences the quantum mechanical phenomenon of entanglement has been called “spooky action at a distance” by Albert Einstein. For several years physicists have been developing concepts how to use this phenomenon for practical applications such as absolutely safe data transmission. For this purpose, the entanglement which is generated in a local process has to be distributed among remote quantum systems.
A team of scientists around Prof. Gerhard Rempe, Director at the Max Planck Institute of Quantum Optics and head of the Quantum Dynamics Division, has now demonstrated that two remote atomic quantum systems can be prepared in a shared “entangled” state (Physical Review Letters, Advance Online Publication, 26 May 2011): one system is a single atom trapped in an optical resonator, the other one a Bose-Einstein condensate consisting of hundreds of thousands of ultracold atoms. With the hybrid system thus generated, the researchers have realized a fundamental building block of a quantum network.
In the quantum mechanical phenomenon of “entanglement” two quantum systems are coupled in such a way that their properties become strictly correlated. This requires the particles to be in close contact. For many applications in a quantum network, however, it is necessary that entanglement is shared between two remote nodes (“stationary” quantum bits). One way to achieve this is to use photons (“flying” quantum bits) for transporting the entanglement. This is somewhat analogous to classical telecommunication, were light is used to transmit information between computers or telephones. In the case of a quantum network, however, this task is much more difficult as entangled quantum states are extremely fragile and can only survive if the particles are well isolated from their environment.
The team of Professor Rempe has now taken this hurdle by preparing two atomic quantum systems located in two different laboratories in an entangled state: on the one hand a single rubidium atom trapped inside an optical resonator formed by two highly reflective mirrors, on the other hand an ensemble of hundreds of thousands of ultracold rubidium atoms which form a Bose Einstein condensate (BEC). In a BEC, all particles have the same quantum properties so that they all act as a single “superatom”.First, a laser pulse stimulates the single atom to emit a single photon. In this process, internal degrees of freedom of the atom are coupled to the polarisation of the photon, so that both particles become entangled. The photon is transported through a 30 m long optical fibre into a neighbouring laboratory where it is directed to the BEC. There, it is absorbed by the whole ensemble. This process converts the photon into a collective excitation of the BEC. “The exchange of quantum information between photons and atomic quantum systems requires a strong light-matter interaction”, explains Matthias Lettner, a doctoral student working on the experiment. “For the single atom, we achieve this by multiple reflections between the two resonator mirrors, whereas for the BEC the light-matter interaction is enhanced by the large number of atoms.”
In a subsequent step, the physicists prove that the single atom and the BEC are really entangled. To this end, the photon absorbed in the BEC is retrieved with the help of a laser pulse and the state of the single atom is read out by generating a second photon. The entanglement of the two photons reaches 95 % of the maximally possible value, thus showing that the entanglement of the two atomic quantum systems must have been equally good, or even better. Moreover, the entanglement is detectable for approximately 100 microseconds.
“A BEC is very well suited as a quantum memory because this exotic state does not suffer from any disturbances caused by thermal motion”, says Matthias Lettner. “This makes it possible to store and retrieve quantum information with high efficiency and to conserve this state for a long time.”
In this experiment, the team of Professor Rempe has realized a building block for a quantum network consisting of two remote, entangled, stationary nodes. This is a milestone on the way to large-scale quantum networks in which, for example, quantum information can be transmitted absolutely safe. In addition, such networks might help realizing a universal quantum computer in which quantum bits can be exchanged with photons between nodes designed for information storage and processing.
Original publication:M. Lettner, M. Mücke, S. Riedl, C. Vo, C. Hahn, S. Baur, J. Bochmann, S. Ritter, S. Dürr, and G. Rempe
Dr. Olivia Meyer-Streng | Max-Planck-Institut
OU-led team discovers rare, newborn tri-star system using ALMA
27.10.2016 | University of Oklahoma
First results of NSTX-U research operations
26.10.2016 | DOE/Princeton Plasma Physics Laboratory
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
27.10.2016 | Materials Sciences
27.10.2016 | Physics and Astronomy
27.10.2016 | Life Sciences