Through a collaboration between the University of Calgary, The City of Calgary and researchers in the United States, a group of physicists led by Wolfgang Tittel, professor in the Department of Physics and Astronomy at the University of Calgary, have successfully demonstrated teleportation of a photon (an elementary particle of light) over a straight-line distance of six kilometers using The City of Calgary’s fiber optic cable infrastructure. This accomplishment set a new record for distance of transferring a quantum state by teleportation.
“Such a network will enable secure communication without having to worry about eavesdropping, and allow distant quantum computers to connect,” says Tittel.
The experiment is based on the entanglement property of quantum mechanics, also known as “spooky action at a distance” — a property so mysterious that not even Einstein could come to terms with it.
“Being entangled means that the two photons that form an entangled pair have properties that are linked regardless of how far the two are separated,” explains Tittel. “When one of the photons was sent over to City Hall, it remained entangled with the photon that stayed at the University of Calgary.”
Next, the photon whose state was teleported to the university was generated in a third location in Calgary and then also travelled to City Hall where it met the photon that was part of the entangled pair.
“What happened is the disembodied transfer of the photon’s quantum state onto the remaining photon of the entangled pair, which is the one that remained six kilometers away at the university,” says Tittel.
The research could not be possible without access to the proper technology. One of the critical pieces of infrastructure that support quantum networking is accessible dark fiber. Dark fiber, so named because of its composition — a single optical cable with no electronics or network equipment on the alignment — doesn’t interfere with quantum technology. The City of Calgary is building and provisioning dark fiber to enable next-generation municipal services today and for the future.
As if teleporting a photon wasn’t challenging enough, Tittel and his team encountered a number of other roadblocks along the way. Due to changes in the outdoor temperature, the transmission time of photons from their creation point to City Hall varied over the course of a day — the time it took the researchers to gather sufficient data to support their claim. This change meant that the two photons would not meet at City Hall.
“The challenge was to keep the photons’ arrival time synchronized to within 10 pico-seconds,” says Tittel. “That is one trillionth, or one millionth of one millionth of a second.”
Secondly, parts of their lab had to be moved to two locations in the city. As Tittel explains, that was particularly tricky for the measurement station at City Hall, which included state-of-the-art superconducting single-photon detectors developed by the National Institute for Standards and Technology, and NASA’s Jet Propulsion Laboratory.
“Since these detectors only work at temperatures less than one degree above absolute zero the equipment also included a compact cryostat,” said Tittel.
This demonstration is arguably one of the most striking manifestations of a puzzling prediction of quantum mechanics, but it also opens the path to building a future quantum internet, the long-term goal of the Tittel group.