Entanglement becomes (almost) macroscopic

Researchers limit micrometer-size mechanical oscillators

Researchers have quantified the vibrations of two metal drums, each 15 microns in size, with quantum physisks. © Aalto University / Petja Hyttinen and Olli Hanhirova, ARKH Architects
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Size record in quantum physics: For the first time, physicists succeeded in interlocking objects of almost macroscopic size. The two groups of researchers generated a quantum-physical coupling between two vibrating objects that were about a dozen microns in size. The entanglement of these mechanical oscillators shifts the previous limit of this quantum physical phenomenon and opens up new applications, according to the researchers in the journal "Nature".

Albert Einstein called the phenomenon of entanglement "spooky long-distance effect". Because this quantum-physical peculiarity makes it possible to link the state of photons, atoms or ions with each other - no matter how far away they are from each other. The state change of one automatically triggers that of the entangled partner particle. This entanglement is the crucial basis for many applications in quantum physics, from quantum computers to quantum cryptography to quantum physical measurement methods.

In the macro world is over - so far

But so far there was a catch: similar to the quantum physical overlay, the entanglement could previously only be generated and detected in the realm of the smallest particles, but not in macroscopic objects. The reason: "For objects on a macroscopic scale, entanglement is very sensitive to environmental disturbances, " explain Caspar Ockeloen-Korppi from Aalto University and his colleagues.

Now, however, two research groups have managed to interlink mechanical systems on a micrometer scale - a team led by Ockeloen-Korppi and another team led by Ralf Riedinger from the University of Vienna. Both groups produced pairs of oscillators whose oscillations were each coupled to one another with respect to quantum physics. Both systems contain billions of atoms and are thus at the edge of the macro-world.

Vibrating micro eardrums

In the first experiment, the mechanical oscillators consist of thin aluminum discs of about 15 microns in diameter. These metal membranes swing up and down like tiny eardrums. Ockeloen-Korppi and his colleagues cooled these mini-drums down to just 0.1 degrees above absolute zero to minimize collisions with molecular motion. display

"The two vibrating oscillators are connected to a superconducting microwave circuit, " explains group leader Mika Sillanp of Aalto University. This creates the restriction of both objects and stabilizes them at the same time. "The electromagnetic fields in this circuit are used to absorb all thermal disturbances, so that only the quantum mechanical vibrations remain", says Sillanp .

From the behavior of the microwaves and the vibrations of the micro drums, the researchers were able to deduce that both were actually confined although there was no direct connection between the two oscillators. Surprisingly, too: The restriction of the micro drums lasted for up to half an hour. This is half an eternity, according to quantum physics.

Silicon beams with reduced oscillation

In the second experiment, Riedinger and his colleagues used two silicon strips as mechanical oscillators. Each about ten micrometer long B lkchen were fixed at both ends, but could swing in the middle. These oscillators were also cooled down to just above absolute zero. Tiny holes in the silicon bars allowed them to vibrate via light rays.

In this setup, the scientists observed a limitation: The two 20-centimeter apart and not directly connected silicon strips vibrated in a resonant, coupled mode, as the physicists report. After all, the cohesion time of the folded bar pairs lasted a few microseconds.

Applications in quantum communication

Both experiments show that it is quite possible to restrict even mechanical oscillators on the threshold to the macro world. "These experiments bring the exploration of the restriction into completely new areas, " explains Andrew Armor of the University of Nottingham in an accompanying commentary. "It will be fascinating to see how much greater such experiments can become over the next few decades."

But even the limited oscillators that are now demonstrated could have practical applications. For example, because the silicon beams from Riedinger and colleagues are coupled via an optical field, they are suitable for use in optical data transmission: "Our system can be inserted directly into real fiber-optic quantum networks, the work in the conventional optical telecommunications sector, "say the researchers. (Nature, 2018; doi: 10.1038 / s41586-018-0038-x, doi: 10.1038 / s41586-018-0036-z)

(Aalto University, Nature, 27.04.2018 - NPO)