Very special rules apply in the nanoworld – the laws of quantum physics. And because Robert J. Schoelkopf and Jörg Wrachtrup have been exploiting them in a very ingenious way, for example to make headway with quantum information technology, the Alexander von Humboldt Foundation and the Max-Planck-Gesellschaft have decided to honour them this year with the Max Planck Research Award. Robert Schoelkopf researches and teaches at Yale University; he developed qubits from superconducting electronic circuits. Qubits could form the smallest computing units of a quantum computer, which might in future solve various tasks significantly faster than conventional computers. Jörg Wrachtrup is professor at the University of Stuttgart and Fellow of the Max Planck Institute for Solid State Research; with his research on single electrons and nuclear spins in diamonds, he opens up, for example, not only new possibilities in electronics, but also for extremely accurate biological investigations. Each award winner will receive 750,000 euros which may be used to fund research chosen by the award winner as well as collaborative efforts with German or foreign scientists.
The laws of quantum physics allow phenomena which are inconceivable in our normal world. Two or more quantum particles can assume a state where they know of each other, although they do not communicate with each other. This entanglement can be used to develop new approaches in data processing, for example in a quantum computer that can search large sets of data much more quickly than a conventional computer entanglement also plays a role in the contributions Jörg Wrachtrup and Robert J. Schoelkopf have made to quantum nanoscience and thus to quantum information technology, for which the two researchers are to receive the Max Planck Research Award 2014.
The Max Planck Research Award is one of the most generously endowed science prizes in Germany. It is financed by the German Federal Ministry for Education and Research, and awarded annually by the Alexander von Humboldt Foundation and the Max-Planck-Gesellschaft to one scientist working abroad and one working in Germany. The call for nominations rotates on an annual basis between subfields within the natural and engineering sciences, life sciences and humanities.
Single spins in diamonds for a nano-nuclear magnetic resonance tomograph
spins in solid bodies, mainly in diamonds, but also in other materials such as silicon carbide. Spin is a quantum mechanical property of electrons and atomic nuclei, for example, and turns these particles into tiny magnetic needles that can align themselves in an external magnetic field. The amount of energy required to change the orientation also depends on the chemical environment of the spin. Nuclear magnetic resonance tomography thus provides, for example, a detailed image of the various tissues in the human body.
Jörg Wrachtrup, professor at the University of Stuttgart and Fellow of the Max Planck Institute for Solid State Research, was the first to succeed in reading out the orientation of a single spin in a diamond and controlling it. In a diamond, the single spins can be found where a nitrogen atom instead of a carbon atom is incorporated into its crystal lattice. The spin of such an NV centre – short for Nitrogen Vacancy centre – reacts very sensitively to other spins in its vicinity. Wrachtrup’s team, and meanwhile several other research groups around the world as well, is thus working on a nuclear magnetic resonance tomograph with a spectrum of possible applications ranging from nanotechnology through to cell biology.
“These quantum sensors can provide us with completely new insights into materials on the nanometre scale,” says Jörg Wrachtrup. “I even think it is realistic to use it in cell biology or even in living tissue.” For Jörg Wrachtrup, the prize money associated with the Max Planck Research Award comes just in time, as it can be used to fund a project over a longer period as well. He can envisage using the funds to further develop the quantum sensors for these difficult applications.
The spins of the NV centres are suitable not only as the probes of a nanoscopic nuclear magnetic resonance tomograph, but also as quantum bits or qubits, i.e. as the smallest computing unit of a quantum computer. This is down to the fact that the “0” and “1” of a data bit can be stored in the orientation of the spin. Jörg Wrachtrup’s team has already created a simple computing register from entangled qubits with one of these NV centres and used it to execute basic operations of a quantum computation.
Computing with zero resistance
Just as Jörg Wrachtrup is considered to be a pioneer of quantum spintronics, Robert W. Schoelkopf, professor at Yale University, is one of the inventors of the superconducting qubits. Superconductors transport electricity with zero electrical resistance. The qubits which Robert Schoelkopf developed with his colleagues Michel Devoret and Steve Girvin at Yale University consist of superconducting electronic circuits. At very low temperatures, these circuits can behave in a certain sense like a single atom: even though roughly a thousand billion electrons move on their trajectories in an electric circuit without hindrance, the circuit can assume defined energy states that are very similar to those of an atom. The lowest two can encode the “0” and “1” of a data bit, playing the same role as the orientation of the spin in a magnetic field.
With the superconducting qubits, which have diameters of a few micrometres or even millimetres, Schoelkopf’s team has shifted the boundaries of the quantum regime from the nano-dimension towards larger objects. Physicists have long assumed that the sometimes bizarre quantum effects can be observed only in extremely small dimensions. They thought that larger systems would have too many interactions which destroy the usually fragile quantum states, which are of interest for applications in a novel type of information processing. Currently, physicists are still testing how large systems can actually be and yet still be subject to the laws of quantum physics. Robert Schoelkopf has set a benchmark with the superconducting qubits in this search for the boundaries of the quantum world.
“We succeeded in making our superconducting qubits very robust against interferences from the outside,” explains Schoelkopf. He and his colleagues have meanwhile also used entangled electric circuits with zero resistance to produce elementary quantum registers which execute simple computing operations and form the nucleus of a quantum computer. It is thus not surprising that the superconducting qubits have created a promising starting position for themselves among the possible candidates for the smallest computing unit of a quantum computer. Jörg Wrachtrup adds: “It is a further honour that I will receive the Max Planck Research Award together with Robert Schoelkopf, who has opened up a completely new field with the superconducting qubits.”
The award presentation will take place on November 27, 2014 in Berlin. The invitation to the media will be issued shortly.