JÜLICH, Germany, May 28, 2021 — Quantum systems are considered extremely fragile. Even the smallest interactions with the environment can result in the loss of sensitive quantum effects. In the renowned journal Science, however, researchers from TU Delft, RWTH Aachen University and Forschungszentrum Jülich now present an experiment in which a quantum system consisting of two coupled atoms behaves surprisingly stable under electron bombardment. The experiment provide an indication that special quantum states might be realised in a quantum computer more easily than previously thought.
The so-called decoherence is one of the greatest enemies of the quantum physicist. Experts understand by this the decay of quantum states. This inevitably occurs when the system interacts with its environment. In the macroscopic world, this exchange is unavoidable, which is why quantum effects rarely occur in daily life. The quantum systems used in research, such as individual atoms, electrons or photons, are better shielded, but are fundamentally similarly sensitive.
“Systems subject to quantum physics, unlike classical objects, are not sharply defined in all their properties. Instead, they can occupy several states at once. This is called superposition,” Markus Ternes explains. “A famous example is Schrödinger’s thought experiment with the cat, which is temporarily dead and alive at the same time. However, the superposition breaks down as soon as the system is disturbed or measured. What is left then is only a single state, which is the measured value,” says the quantum physicist from Forschungszentrum Jülich and RWTH Aachen University.
Copyright: Forschungszentrum Jülich / Ralf-Uwe Limbach
Given this context, the experiment that researchers at TU Delft have now carried out seems all the more astonishing. Using a new method, they succeeded for the first time in real-time observing how two coupled atoms freely exchange quantum information, switching back and forth between different states in a flip-flop interaction.
“Each atom carries a small magnetic moment called spin. These spins influence each other, like compass needles do when you bring them close. If you give one of them a push, they will start moving together in a very specific way,” explains Sander Otte, head of the Delft team that performed the experiment.
On a large scale, this kind of information exchange between atoms can lead to fascinating phenomena. Various forms of quantum technologies are based on these. A classical example is superconductivity: the effect where some materials lose all electrical resistivity below a critical temperature.
Unconventional approach
Copyright: Enrique Sahagún, Scixel
To observe this interaction between atoms, Otte and his team chose a rather direct way: Using a scanning tunnelling microscope, they placed two titanium atoms next to each other at a distance of just over one nanometre – one millionth of a millimetre. At that distance, the atoms are just able to feel each other’s spin. If you would now twist one of the two spins, the conversation will start by itself.
Usually, this twist is performed by sending very precise radio signals to the atoms. This so-called spin resonance technique – which is quite reminiscent of the working principle of an MRI scanner found in hospitals – is used successfully in research on quantum bits. Among other things, quantum bits in certain types of quantum computers are programmed in such a way. However, the method has a disadvantage. “It is simply too slow,” says PhD student Lukas Veldman, lead author on the Science publication. “You have barely started twisting the one spin before the other starts to rotate along. This way you can never investigate what happens upon placing the two spins in opposite directions.”
Further information:
Peter Grünberg Institute, Quantum Nanoscience (PGI-3)
Source: Forschungszentrum Jülich
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2021-05-28 18:04:45Z
CBMiYGh0dHBzOi8vd3d3LmhwY3dpcmUuY29tL29mZi10aGUtd2lyZS9xdWFudHVtLW5hbm9zY2llbmNlLWV4cGVyaW1lbnQtaW4tc2NpZW5jZS1yYWlzZXMtcXVlc3Rpb25zL9IBAA
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