Lunchlecture VVTP by Leo Kouwenhoven
Technical University Delft 28-11-2014
As a part of the celebration of the birthday of the VVTP (Association for Applied Physics), Leo Kouwenhoven gave a lecture about his research on the Majoranas. He started his lecture with making sure the entire audience knew the definition of a Majorana. A Majorana is a particle that is also its own antiparticle. This property in itself is not that special, because there are more particles that are their own antiparticles, think about photons (light particles). The special thing about Majoranas is that they’re a member of the class of fermions, whereas all other particles that are their own antiparticles are members of the class bosons. ‘Mathematically’ you could write for the Majorana particle:
γ* = γ
The Majorana must have no energy, no charge and no spin to exist, and is therefore also named the niks-particle (niks = nothing in dutch). Another way of describing the Majorana is saying that it’s a superposition of an electron and a hole. He demonstrated a way to view the Majorana to us, by using a figure similar to the one below:
Where all the black circles are electrons and the white circles are holes. You must see this as a train of electrons that can all step to the right and to the left. If you take the superposition of the two states, namely the one with the hole on the right and the one with the hole on the left, you get the bottom figure, which is an analog for a Majorana.
After this theoretical background he talked about his research and about the question whether the Majorana particle has actually been detected. He said to be “pretty sure” he found the Majorana, but also noted that there’s not been an error analysis, so to be sure*, is going to take some time. Right now the signatures of the Majorana are found and confirmed by other research groups, and the combination of experiments is so far only consistend with the Majoranas. He closed his talk with an important future application of the Majorana, which is the quantum computer. This would be a computer where a bit doesn’t have to be 0 or 1, but can also be both, and this computer would therefore be extremely fast in calculation. At the very moment, companies such as Microsoft are interested in Leo’s work, because they realize that we could be standing on the edge of a major breakthrough in (quantum)computerscience.
Kasper Spoelstra – firstname.lastname@example.org
*5σ sure means that you have a probability of 99.9999% of being right.
Speaker: Uwe Sauer
Head of the Institute for Molecular System’s Biology, ETH Zurich
Subject: Coordination of central metabolix fluxes in microbes
Location: Bionanoscience Department, TU Delft
Date: Thursday, 4 december 2014, 16:00-17:00
Author: Jasper Veerman
Uwe Sauer is interested in the long term coordination of metabolism. For the past years, there seemed to be the general misconception that metabolism is just the workhorse of the cell. Metabolites turn out to also be important in, for example, intracellular signaling. Using labeled carbon atoms, Uwe Sauer’s group studies fluxes in the cell. This method allows to look at a molecule’s history. Combining this with quantitative physiology allows for modeling of the fluxes in the cell.
Using the above-mentioned approach, he studied the change in enzyme as compared to the flux difference in steady state. If these differences scale 1:1, then the change in enzyme is totally responsible for increased or decreased fluxes in the pathways (like . glucose catabolism). These cases mostly relate to full transcriptional regulation of fluxes. However, these cases are rare. In most cases – over 90% – we need additional factors, for example metabolic influences, to explain the change in fluxes.
In addition, the group studied active, dynamic allosteric interactions (ligand binding that changes the conformation of the active site of the enzyme). Due to their direct regulation of enzyme activity, they should dominate over transcription. By implementing allosteric interactions into the model that was already present, the model fitted the experimental results somewhat better. Allosteric interactions appear to account for some of the observed behavior of the pathways. However, other influences are still to be added for proper description of the pathways. Looking at cell metabolism is a good place to start.
Speaker: Leo Kouwenhoven (Department of Quantum Nanoscience, TU Delft)
Subject: Majorana particles
Location: Auditorium TU Delft
Date: Friday, November 28, 13:45-14:40
Author: Jasper Veerman
On Friday, November 28, Leo Kouwenhoven spoke about his work on Majorana particles. These particles, which are their own antiparticles, are rather special. They are fermions, but with the three unusual properties: no charge, no energy and no spin. The particles are the equal superposition of an electron and a hole (absence of an electron). This makes measuring them difficult, but not impossible. By connecting a semiconducting nanowire to a conductor on one side and a superconductor on the other side, Kouwenhoven’s group observed the above mentioned ‘3 times nothing’ criterion for some particles in the experiment. These particles, at the ends of the interface between the nanowire and the superconductor, are likely to be Majorana particles.
To demonstrate the use of this discovery, imagine two Majorana particles. If we exchange their places, we can understand that the conditions have changed. However, if we exchange them again – back into their original position – we would expect the net result to be ‘zero’. In contrast to this expectation, actual exchanges of Majorana particles result in a phase shift, meaning the particles have some memory of what has happened to them. This makes the Majorana particles interesting for application in a quantum computer, since the information in these interactions can be used to form bits. In practice, the particles function in pairs, making them more robust. The Dutch government and Microsoft are now funding Kouwenhoven’s group to develop this computer.
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This is the spot were we’d like to share the experiences of our Honours Programme students with you. Sharing the latest information on research within the Nanobiology field is essential for letting know the world about the importance of this exciting and new research field.
The Nanobiology Honours programma has started as of November 2014 for the first time ever. Six of our ambitious students with excellent study performances will have to attend several seminars from the Bionanoscience departments and Kavli Institute of TU Delft and the Biomedical Sciences departments of the Erasmus MC in Rotterdam.
Stay tuned for the latest exciting blogs of Kasper, Edgar, Jasper, Marloes, Max and Guus.
The Nanobiology Honours Programme team