April 20, 2012
The door to a completely new way of transmitting information is now open. Physicists at the Max Planck Institute of Quantum Optics in Garching have created an elementary quantum network by transmitting quantum information between two atoms trapped in optical resonators. Quantum information has fundamentally different characteristics to the conventional information with which today’s computers operate and which is transmitted via telephone lines or fibre-optic cables. The hope is that quantum information will make it possible to process information more efficiently in some applications. It must, however, be handled with extreme care in order that it not lose its quantum character. The Garching-based physicists are now the first to transmit quantum bits in the form of individual photons from one atom to the other via a 60-metre fibre-optic cable and to reliably store them in the receiver atom. This arrangement is not only suitable for exchanging data between computers, should they, in years to come, compute in quantum bits. It also enables fundamental insight into how quantum communication works, and it could, in future, allow physicists to investigate quantum systems that are not yet understood.
Breakthrough in quantum communication: Quantum information can now be transmitted between two individual atoms in resonators in a controlled way and reversibly stored in the atoms. G. Rempe, S. Ritter and a team from the Max Planck Institute of Quantum Optics have transported quantum bits in the form of individual photons in an elementary quantum network and thus taken a step forward in quantum information technology towards a quantum computer, quantum simulation and a quantum Internet.[less]
Breakthrough in quantum communication: Quantum information can now be transmitted between two individual atoms in resonators in a controlled way and reversibly stored in the atoms. G. Rempe, S. Ritter and a team from the Max Planck Institute of Quantum Optics have transported quantum bits in the form of individual photons in an elementary quantum network and thus taken a step forward in quantum information technology towards a quantum computer, quantum simulation and a quantum Internet.
It is possible that the progression from analogue to digital data processing has not been the last leap forward in information technology. Throughout the world, physicists are investigating the possibilities for processing quantum information. No one knows yet whether it will change our daily routine as much as digital information processing, as it is extremely fragile and its quantum properties disappear easily. However, it offers opportunities that are principally not available to conventional digital information. Physicists in the Quantum Dynamics Division headed by Gerhard Rempe at the Max Planck Institute of Quantum Optics in Garching are now the first to have transmitted quantum information in a controlled and reversible way.
One could say: the researchers let the individual atoms talk to each other in the language of individual quantum bits, which are transmitted by individual photons. The physicists in Garching succeeded in achieving something that is taken for granted in a conversation and also works in conventional data processing, but has not yet been possible at all in quantum communication. “Our approach is characterised by the fact that the system of atom and resonator can serve as transmitter and receiver. We can also store the information in the atoms and we can exchange it between them in a controlled and reversible way,” says Stephan Ritter, who was instrumental in facilitating the quantum dialogue. This means that any atom can speak the quantum language and transmit the information contained in it - without losing the sensitive quantum character of the information.
Physicists are also studying other systems for exchanging quantum information, such as ensembles of atoms or single atoms and molecules without a mirror. The special strong point of individual atoms in resonators is that they allow all operations, i.e. the sending, receiving and storage of quantum information, in equal measure.
One new development of fundamental interest is the fact that the Garching-based researchers can exchange quantum information in a controlled and reversible way - physicists use the term coherent. “We have created a breakthrough with our experiments in order to learn more about the fundamental properties of the quantum world,” says Gerhard Rempe, who, as a Director at the Max Planck Institute of Quantum Optics, headed the research. Since the researchers accurately control the exchange of quantum information and thus the quantum mechanical interactions between their networked atoms, they hope in the future to also be able to simulate quantum processes that physicists do not fully understand as yet. These include superconductivity - the flow of current with zero resistance - at relatively high temperatures. “A larger quantum network of the future could be particularly suitable for such quantum simulations because it’s particularly versatile,” says Stephan Ritter.
The atomic dialogue also opens up new prospects for the exchange and the processing of quantum information. Unlike conventional bits, quantum bits have the characteristic that the state which they are in is not determined as long as they are not measured. They are in a state which physicists call superposition state. This has a property that is hardly conceivable in our everyday world, which is governed by classical physics, because the result of a measurement on the superposition state is not determined right from the start, it is the measurement that makes the decision. The measurement changes the state in this sense.
The computing characteristics of quantum bits are based on this indecisiveness of the superposition state. A quantum bit therefore does not represent a zero or one, like a conventional bit, but has the possibility to be in both states at the same time. This characteristic can be used for ingenious and powerful computational methods, which are denied a conventional computer.