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. More info
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.
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.
Now the difficult part is to actually build a quantum computer in real life. Rather than silicon transistors and memories, you will need physical components that can process an 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 take 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.
Vincent Traag from the Centre for Science and Technology Studies will give an LCN2 seminar on April 29th at 16:00 in room HL214, titled 'Methods & algorithms for detecting communities in large networks'.
modular structure: groups of densely connected nodes with few connections between the groups. Nodes in such groups often have something in common, and enrich our understanding of complex networks. Finding such so-called communities in large networks is far from trivial. One of the best-known methods for community detection is modularity, which specifies a quality function of a partition. However, modularity suffers from a well-known flaw, known as the resolution limit: it tends to oversimplify, and lump together several (sub)communities in one large community. We here show that only few quality functions can address this issue. One of the best algorithms for optimising modularity is the Louvain algorithm. We here show that it can lead to arbitrarily badly connected communities---in addition to the resolution limit of modularity. In particular, it can lead to disconnected communities. We here introduce a new algorithm, and show it not only addresses this caveat, but also that it asymptotically ensures that no subset of any community can be moved to another community. Finally, we introduce a fast local move subroutine, speeding up the algorithm 5-10 times.
Preliminary LCN2 Seminar Schedule - 2016
January 29, 16:00-17:00, HL214
February 27, 16:00-17:00, HL106
April 29, 16:00-17:00, HL214
May 27, 16:00-17:00, HL214
On May 1st, we are delighted to welcome Prof. Charles Kane as this year’s Lorentz Professor. Kane is a world-renowned American physicist who has made major contributions to theoretical condensed matter physics. He is most famously known for discovering topological More info
insulators in the mid-2000’s. For his work on this subject he received the Dirac Medal of the International Centre for Theoretical Physics in 2012, along with two colleagues.
During his stay in Leiden, Kane will give a series of three lectures titled 'Symmetry, Topology and Phases of Matter' in the De Sitter room (Oort building).
May 17th, 13:45-15:30 I. Topological Band Theory of Insulators and Semimetals
May 24th, 13:45-15:30 II. Topological Superconductivity
May 31st, 13:45-15:30 III. Topological Mechanics
The lectures will provide a pedagogical introduction to topological band theory and discuss its application to symmetry protected electronic states including topological insulators, semimetals and superconductors. Would it be possible to apply related ideas to mechanical systems?
Milan Allan’s research group has created a timelapse of their efforts to build their scanning tunneling microscope (STM), called Tamagotchi. An STM allows researchers to see the electronic structure of materials with atomic precision. Allan’s group wants to understand the More info
strangeness of exotic quantum materials, and use their STM for that purpose.