August 18, 2015

Twin paradox on a chip

(August 18, 2015)  Per Delsing and his team want to combine theoretical calculations with experiments on superconducting circuits to gain an understanding of how things fit together at the nano level. Among other things, they plan to simulate objects that move very rapidly, almost at the speed of light, and demonstrate the “twin paradox” on a microchip.

Stuck on the wall of Per’s office is a piece of paper on which is written: “It is easier to control a photon than it is to bring up four daughters.”
“That’s right,” says Per, who is Professor of Experimental Physics at Chalmers University of Technology, without a second’s hesitation.

But then again, he is a wiz at controlling photons – small particles of light. Among other things, his research team has succeeded in generating photons directly out of a vacuum. In their project, which has received funding from the Knut and Alice Wallenberg Foundation, they are using photons to demonstrate the twin paradox in a new way. The paradox is a thought experiment stemming from Einstein’s special theory of relativity, and has occupied the minds of physicists for more than a hundred years.
Per, who happens to be a twin himself, explains:
“The twin paradox says that if I take a space journey in a high-speed rocket and then return, as an effect of acceleration I will be much younger than my twin brother. This effect has been measured in various ways. What we want to do now is to demonstrate this on a microchip.”
In other words, instead of traveling into space, his research team will move photons a very short distance at nano level.

“But the photons travel so quickly, close to the speed of light, which is difficult for us to reach in reality. And this is why we can achieve an effect even though this space journey only takes place on the actual chip.”

The trick – a superconducting circuit
The team is using a special type of superconducting electric circuit called SQUID, which stands for Superconducting Quantum Interference Device, which has been made in Chalmers’ advanced clean room. When Per’s team showed in 2011 how to create photons out of a vacuum, they used the specially designed SQUIDs as ultra-high-speed mirrors to generate light particles.
In addition to the twin paradox, the project aims to study two other new physical phenomena on microchips: “photon condensation” and “frequency combs”.
“We always work on the boundaries of what is possible and what is new. The grant will enable us to realize these ideas and see how far we can go. The Foundation has also given us great freedom to use the resources as we ourselves see fit.”

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