When an atom and two photons meet...

The world of computing, scientists and experts assure us, will change completely the day quantum computers come into operation and replace today's "normal" computers. An interview with Dr. Barak Dayan from the Weizmann Institute, who is establishing a new laboratory at the institute for the development of practical quantum devices

By: Yaki Dayan*

The world of computing, scientists and experts assure us, will change completely the day quantum computers come into operation and replace today's "normal" computers. Our entire world, they predict, will change beyond recognition. But in the meantime, the devices that produce individual quantum gates (in a certain institute they managed to create an 8-bit gate based on quantum computing) are large and cumbersome and take up large rooms full of equipment.

Dr. Barak Dayan, a senior researcher from the Weizmann Institute of Science, hopes that the new laboratory he is establishing at the institute will be able to develop practical quantum devices, which could lead to a breakthrough in the application of quantum computing. Barak has something to rely on. Only a few months ago he returned from a three-year stay at one of the undisputed centers of quantum optics, at the prestigious campus of Caltech in Los Angeles, under the leadership of Professor Jeff Campbell. During his stay there, Barak was able to successfully complete two unique experiments that promoted the practical side of quantum optics and were even published in two of the most prestigious journals in the field - "Science" and "Nature".

"When I started my doctoral thesis at the Weizmann Institute of Science, I was looking to do something interesting, original, and of an applied nature," says Dayan. "It was clear to me that the direction was in quantum optics, which is the cutting edge of physics research these days. In the beginning, like any researcher, I came up with a lot of interesting but incorrect ideas, and when I already found interesting ideas that were also theoretically correct, I saw that they were no longer original - someone had done them before, and the name of Jeff Kimball from Caltech came up again and again as someone who had already implemented these ideas. It intrigued me - who is my competitor who catches me all the time?" The continuation was clear. Upon completion of his PhD, Dayan went to Caltech to continue research under the guidance of the legendary Jeff Kimball.

When I visited Barak at Caltech several years ago, I was greeted by green lawns and impressive and beautiful buildings. In the basement of one of the buildings, far from the light of day, Dayan and his team worked on the development of a silicon chip that allows interaction between a single atom and a single photon. Unlike physicists who study a flux of photons (light) or clusters of atoms, researchers in quantum optics like to play with a single atom or a single photon. Only a very limited number of laboratories managed to reach the technological achievement of "imprisoning" a single atom and bringing a single photon close to it in order to measure the interactions between them. Dayan's first development was a first-of-its-kind technological achievement in the world of using a single silicon device manufactured at Caltech that enables this interaction, and replaces large and cumbersome instruments. In the future, such a development could help miniaturize the technology of personal computers. This achievement earned Dayan and his team publication in the prestigious "Nightsher" magazine in 2006.

Dayan was determined to move on, and accomplish one more thing before returning back to Israel. The challenge is to allow one photon to influence another photon. Photons in nature do not affect each other. When we look at someone else, the continuum of light between us is not interrupted by light crossing it on its way. He tried something else - to use a single atom to transfer information from one photon to another and create a reaction between them. Tried - and succeeded. "We were able to create a situation where a single photon passing by an atom allows the atom to create a barrier that lasts several billionths of a second, which blocks the passage of a photon that follows it. This exposure appears for a very short period of time and allows for the first time for one photon to interfere with the passage of another photon, through the mediation of the atom." To illustrate the phenomenon to his colleagues, Dayan uses an example taken from a popular cartoon series. Remember that roadrunner, a bird that always evades the prairie fox - the cutie - that tries to catch it? In one of the videos, the fox draws a tunnel opening on the side of the mountain. When the Roadrunner arrives, he manages, to the fox's surprise, to go through the tunnel. The surprised fox also tries to go through the painting - and runs into a rock.

"Why is it good? What can be done with it?” IM asking. Dayan smiles. He is used to this question. Think of today's world of communication, based on the transmission of information using light in optical fibers. Today, when information from Tel Aviv to Haifa reaches the switch in Herzliya, electronic equipment has to regulate the traffic so that information from another place can join or pass through the same medium. Today, the world of communication is trying to achieve branding based entirely on optics. Think of the day, he enthuses, when the photons arriving from Tel Aviv will be able to signal to the other photons "Wait a minute, we are passing". The transition from the experimental laboratory to application in the media is still a long way off, but this breakthrough resulted in publication in an even more prestigious journal, "Science", in April 2008.

With the completion of the experiment, Dayan finally left Caltech and returned to the Weizmann Institute of Science to establish a laboratory in quantum optics that continues to research and try to develop more practical devices. Dayan believes that the number of laboratories in the world with similar technology is smaller than the fingers of one hand. "So what's the next direction?" . "For me, the next challenge is to find a practical way to discover that a photon has passed here, without destroying it," Dayan answers. Today, we know that a photon passed by stopping it. What is it similar to? Let's put a concrete wall in the middle of the road, and when a car collides with it and crashes, we'll say - look, we found out that a car passed here. Today we know that light passes by blocking the photons and absorbing the energy that is emitted when they stop. "I know what I want to discover, but I don't yet know how to do it," concludes Dayan, "but when we manage to develop it, it will have fascinating applications."

Written as part of the "Science in Communication" course at the Technion