Researchers Demonstrate Quantum Teleportation and Memory in Tandem

In research that may be a key step toward real-life quantum communication—the transmission of information using atoms, photons, or other quantum objects—researchers created an experiment in which a quantum bit of information is transported across a distance of seven meters and briefly stored in memory. This is the first time that both quantum memory and teleportation, as the information transfer is known, have been demonstrated in a single experiment.

The experiment was performed by scientists from the University of Heidelberg in Germany, the University of Science and Technology of China, and the Atomic Institute of the Austrian Universities in Austria. The work was led by Prof. Jian-Wei Pan, a physicist at the University of Heidelberg.

A quantum bit, or qubit, is the most basic unit of quantum information. It takes the form of a particular configuration, or “state,” of an atom or photon. Unlike a traditional computer bit, the most basic piece of information a computer can store, qubits represent the superposition of “0” and “1,” rather than either a 0 or 1. Additonally, a qubit cannot be copied in the traditional sense. It can only be transferred, without leaving any trace of the original.

Quantum teleportation is the way to transfer an unknown quantum state to a distant location without getting any information about the state in the course of this transfer. When a qubit is teleported across a distance, the process is remarkable in that the sending and receiving qubits are not physically connected in any way, and do not “know” of each other's existence. But through a quantum phenomenon called entanglement, one qubit is nonetheless able to assume the quantum state of another without physically interacting with it.

In the present research, described in the January 20 online edition of Nature Physics, an unknown quantum state of a photonic qubit is transferred into quantum memory via teleportation and is stored by two clusters of rubidium atoms. Each cluster contains approximately one million atoms, collected by a magneto-optical trap. The teleported photonic qubit can be stored in memory and read out up to eight microseconds (millionths of a second) before the state is lost.

“Such an interface to map the quantum states of photons onto the quantum states of matter, and to retrieve them without destroying the quantum character of the stored information, is an essential part of future quantum technologies,” said Pan to PhysOrg.com. “It represents an important step towards efficient and scalable connection of quantum networks.”

The quantum states carried by the photonic qubits are encoded in the photons' polarization, or the alignment of the photons' emitted electric fields. Each rubidium cluster encodes the information as a collective spin state over all of the electrons in the cluster. Like other unchangeable properties like mass and charge, spin, or angular momentum, is an intrinsic characteristic of an electron.

First, the research group entangled the polarization state of the photons and the spin state of the atom clusters. This entanglement is then exploited to teleport the unknown state of a single photonic qubit onto an atomic qubit seven meters away. This is done by taking a simultaneous measurement of the entangled photons and the photon to be teleported. Taking that measurement entangles the two photons and projects the second photon's state onto the atom clusters.

This setup does have some serious problems. The quantum memory duration is very short and the probability that the photon will be teleported is low. Therefore, the researchers say that “significant improvements” need to be made before the scheme could be used in practical applications.

Citation: Yu-Ao Chen, Shuai Chen, Zhen-Sheng Yuan, Bo Zhao, Chih-Sung Chuu, Jörg Schmiedmayer & Jian-Wei Pan Nature Physics advance online publication, 20 January 2008 (DOI:10.1038/nphys832).

Copyright 2008 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Related stories:

Qubits and Branes Share Surprising Features
What do black holes and entangled particles have in common? Until about a year ago, physicists thought that the two entities existed in completely separate worlds. Then, in 2007, physicist Michael Duff from Imperial College London demonstrated a correlation between the entanglement of three qubits and the entropy of a black hole. In the past year, several studies have demonstrated even more connections.
Unknown molecule opens the door to quantum computing
The odd behavior of a molecule in an experimental silicon computer chip has led to a discovery that opens the door to quantum computing in semiconductors.
Physicists Store Images in Vapor
Books are written on solid pieces of paper for an obvious reason: the atoms in a solid don’t move around much, keeping the words and pictures in place for centuries. Trying to store letters and images in a gas medium, on the other hand, seems a little far-fetched. Atoms in a gas are constantly moving around, which would move the images around with them.
Researchers untangle quantum quirk
Quantum computing has been hailed as the next leap forward for computers, promising to catapult memory capacity and processing speeds well beyond current limits. Several challenging problems need to be cracked, however, before the dream can be fully realized.
Researchers take step toward creating quantum computers using entangled photons in optical fibers
For now, full-fledged quantum computers are the stuff of science fiction — in last summer’s blockbuster movie Transformers, the bad guys use quantum computing to break into the U.S. Army's secure files in just 10 seconds flat.
The future of computing -- carbon nanotubes and superconductors to replace the silicon chip
The future of computing is under the spotlight at the Institute of Physics’ Condensed Matter and Materials Physics conference at the Royal Holloway College of the University of London on 26-28 March.
Silicon chips for optical quantum technologies
A team of physicists and engineers has demonstrated exquisite control of single particles of light – photons – on a silicon chip to make a major advance towards the long sought after goal of a super-powerful quantum computer.
Physicists Bring Quantum Computing Closer to Reality
Researchers at the U. S. Department of Energy’s Ames Laboratory, the University of California, Santa Barbara, and Microsoft Station Q have made significant advancements in understanding a fundamental problem of quantum mechanics – one that is blocking efforts to develop practical quantum computers with processing speeds far superior to conventional computers. Their respective theoretical and experimental studies investigate how microscopic objects lose their quantum-mechanical properties through interactions with the environment.

News discussion:

Physics news