How to manipulate light on superconducting chips

Posted by Thomas Anderson

Physicists at UC Santa Barbara are manipulating light on superconducting chips, forging new pathways to designing the quantum devices of the future – including super-fast and powerful quantum computers.

Indeed, a team in the lab of John Martinis, UCSB professor of physics, has made a discovery that provides new understanding in the quantum realm, with the findings published this week in the Physical Review Letters journal.

"As one crucial step of achieving controllable quantum devices, we have developed an unprecedented level of manipulating light on a superconducting chip," explained first author Yi Yin. Yin worked on the project when she was a postdoctoral fellow in the Martinis Lab from 2009 to 2012. She relocated to her native China last fall, where she is now a professor at Zhejiang University in the city of Hangzhou.

"In our experiment, we caught and released photons in and from a superconducting cavity by incorporating a superconducting switch," said Yin.

"By controlling the switch on and off, we were able to open and close a door between the confined cavity and the road where photons can transmit. The on/off speed should be fast enough with a tuning time much shorter than the photon lifetime of the cavity."

To be sure, not only can the switch be in an on/off state, it can also be opened continuously, like a shutter. Meaning, the research team was able to shape the released photons in different wave forms – a key element for the next step they want to accomplish: controlled photon transfer between two distant cavities.

Co-author Yu Chen, also a postdoctoral fellow in the Martinis lab, said this particular method of moving information around – sending and catching information – is one of the most important features of this research.

"In optics, people imagine sending information from Earth to a satellite and then back – really remote quantum communication," he said.

"The shutter controls the release of this photon. You need to perfectly transfer a bit of information, and this shutter helps you to do that."

Co-author Jim Wenner, a graduate student in the Martinis lab, offered up yet another application.

"Another one, again with communication, would be providing ways to transmit signals in a secure manner over long distances," said Wenner.

Interestingly, instead of another shutter, Yin used classical electronics to drive the photon. She then captured the signal in the superconducting cavity, in an area called the meander, or the resonator. The shutter subsequently controlled the release of the photon.

Wenner also noted that the resonator, a superconducting cavity, is etched on the flat, superconducting chip – which is about one quarter of an inch square. It is chilled to a temperature of about minus-273.12 degrees Celsius.