How quantum phenomena perform key services

Text: Rainer Kayser

In his quest to understand quantum phenomena, with his pioneering work Martin Plenio has paved the way for their application in information technol-ogy. At the Center for Quantum Engineering, which is currently being estab-lished at the University of Ulm, Plenio will – in addition to quantum information technology – also be working on quantum effects in biology.

In the world of atoms, the rules of classical physics fail to apply; instead atoms are governed by the laws of quantum physics. As it is impossible to break up matter – and also energy – into infinitely smaller particles, it occurs in tiny portions called “quanta”. Depending on the particular view, these minuscule components of matter sometimes appear in the form of a wave, sometimes as particles; they can occupy two or more different states simultaneously, and particles that are far removed from each other remain in contact in a way that defies our general understanding of the world.

Martin Plenio feels very much at home in this world. “I try to understand quantum phenomena so that they can be used in technology”, explains the physicist who, born in Kassel, will now be returning to Germany from Imperial College in London. In his research, Plenio is mainly focusing on quantum information technology, i. e. applying quantum phenomena to the areas of data processing and data transfer. To give an example, quantum computers, which make use of overlapping states in multiparticle quantum systems, would be able to perform calculations a great deal faster than conventional computers.

Plenio‘s work has earned him the highest international acclaim. The Humboldt Professorship now allows him to make a smooth transition to the Center for Quantum Engineering at the University of Ulm, which is currently being established. For his work, he can practically take his entire working group from London to Germany with him. “Another advantage for us lies in the fact that there are many high-calibre experimental physicists to collaborate with in the future”, the scientist, who many years ago went to London on a Feodor Lynen Research Fellowship from the Alexander von Humboldt Foundation, is pleased to say.

A theoretical physicist, Plenio, who always keeps an open mind for possible alternatives, relies heavily on experimental testing in his work: “Even though I‘m not in the lab myself, I collaborate very closely with experimental physicists.” This means that my theoretical musings can be instantly tested by way of practical experiments. And reciprocally, the results from the experiments can be immediately incorporated in the theory again.

Revolution in IT and energy technology

Particularly his work on what is known as entanglement has earned the quantum physicist an outstanding reputation in academic circles. It is a phenomenon in which two or more particles can only be described as a complete system. In other words, the particle states are connected irrespective of their spatial distance. Initially dismissed by Albert Einstein as “spooky action at a distance,” numerous experiments have since successfully proven that entanglement does, in fact, exist.

The fact is that this understanding of entanglement has an immediate practical use as is shown by the following example: In the case of photons, which resemble the energy quanta of light – or, generally speaking, electromagnetic radiation – entanglement mostly refers to polarisation, i. e. the vibration direction of the electromagnetic field. This means that measuring the polarisation of a photon of an entangled pair will thus immediately also determine the polarisation of the other photon. Entangled photon pairs like these play a significant role in a new area called coding technology, for example. In the field referred to as quantum cryptography, entangled photons guarantee secure transmission of the key – any attempt to eavesdrop on the connection will destroy the quantum correlation and thus immediately reveal that the wires are being tapped. Among other things, Plenio and his colleagues have developed a new method for the efficient production of entangled particles that are far removed from each other – a step of paramount importance in quantum cryptography.

Plenio‘s work on the further development of entanglement theory and particularly of entanglement measures ranks among his outstanding research achievements. “It allows us to measure the strength of the quantum correlation”, the scientist explains, “and in this way we can estimate how secure these quantum information processes are.” In Ulm Plenio primarily intends to develop the theoretical and experimental basic principles that are necessary to control quantum phenomena in atoms, ions and photons – a principle for technical application. Secondly he plans to investigate the function of quantum phenomena in the field of biology. This is because quantum effects are immensely important in the process of photosynthesis, for example. The many different infl uences that originate from the environment (dubbed noise by physicists) are supposed to have a disruptive effect here. However, in his research Plenio was able to show that the opposite is, in fact, the case: “Nature seems to actually take advantage of the infl uence that noise has on quantum effects by using it to improve energy transport.” This decisively increases the efficiency of the energy transport in plants and bacteria. “We are taking a completely new approach, and it is turning into a red-hot field of research thanks to the progress we are currently making in our experiments.” The in-depth process knowledge gained from these experiments could help develop far superior solar cells. Thus it is possible that quantum phenomena will not only revolutionise the field of information technology but also energy technology.