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Posted: Apr 28, 2016
Important effect observed in development of quantum storage
(Nanowerk News) Rare-earth materials are prime candidates for storing quantum information, because the undesirable interaction with their environment is extremely weak. Consequently however, this lack of interaction implies a very small response to light, making it hard to read and write data. Leiden physicists have now observed a record-high Purcell effect, which enhances the material’s interaction with light. Publication on April 25 in Nature Photonics ("Multidimensional Purcell effect in an ytterbium-doped ring resonator").
Ordinary computers perform calculations with bits—ones and zeros. Quantum computers on the other hand use qubits. These information units are a superposition of 0 and 1; they represent simultaneously a zero and a one. It enables quantum computers to process information in a totally different way, making them exponentially faster for certain tasks, like solving mathematical problems or decoding encryptions.
The difficult part now is to actually build a quantum computer in real life. Rather than silicon transistors and memories, you will need physical components that can process and store quantum information, otherwise the key to the whole idea is lost. But the problem with quantum systems is that they are more or less coupled to their environments, making them lose their quantum properties and become ‘classical’. Thermal noise, for example, can destroy the whole system. It makes quantum systems extremely fragile and hard to work with.
Yet, Leiden physicist Dirk Bouwmeester and his colleagues are taking on the challenge to devise a quantum system to serve as qubit. They plan to use the orbits of electrons around atomic nuclei as ones and zeros. Hitting many atoms with light will move one of the electrons up, giving scientists a way of writing data. This data can be read out with a second light pulse, forcing the electron to move down again, thereby emitting a light particle containing the information. If the atom also interacts with its surroundings, this storage principle does not work perfectly because part of the information is lost to the environment. First author Dapeng Ding uses so-called 'rare-earth ions' to avoid this quantum information leak. These particles can serve as stable storage for as long as ten seconds—an eternity in the otherwise very fragile quantum world. In comparison, other commonly used systems for quantum computer research decay within microseconds—over a million times more rapidly.
Alongside their incredible stability, rare-earth ions come with a problem; they interact only very weakly with light, making it difficult to write and read data. To resolve this problem, the physicists trapped light together with rare-earth ion ytterbium (Yb3+) in a so-called ring resonator. Much to their satisfaction, they saw that the ring resonator induced the Purcell effect, which enhances the interaction with light. This offsets the major pitfall of the use of rare-earth ions, and paves the way for Bouwmeester’s proposal to improve storage of quantum information.