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Science

The next communication innovation? Quantum teleportation

TOKYO -- No need for cables and transmission speeds a million times faster than today's optical communications. That is the promise of quantum teleportation, in which data is teleported rather than physically transmitted.

Highly efficient quantum teleportation was realized using this experimental apparatus built by Akira Furusawa, fashioned from more than 500 mirrors and lenses.

    The technology, which relies on information from one photon being shared instantly with another, distant photon, is far from being ready for prime time. But significant experimental results have already been achieved, including seminal work by University of Tokyo professor Akira Furusawa, 52, a leader in the fields of quantum mechanics and quantum computing.

     Don't be fooled by the familiarity of the term.

     As popularized by science fiction and made famous by "Star Trek," teleportation imagines the instantaneous transportation of physical objects from one place to another.

     But nothing physical gets moved in quantum teleportation: The only thing transferred is quantum information, with the quantum state of one photon instantaneously affecting the state of another photon at a remote location.

     Conceptually, it is a little like sending a fax, but sending the quantum information destroys the original, due to the laws of quantum physics.

Sorry, Einstein

Furusawa conducted his first successful experiments with quantum teleportation in 1998. He was on leave from his job at Nikon Research Laboratory and studying in the U.S. at the California Institute of Technology in the laboratory of Jeff Kimble.

     The report of that success in the journal Science attracted global attention because the experiments were based on the theory of quantum entanglement, which a skeptical Albert Einstein believed was invalid.

     Quantum entanglement is a phenomenon that occurs for pairs of photons or other particles created at the same time. No matter how far apart the two "entangled" particles eventually lie, at the instant that the quantum information of one is altered, the information of the other also changes.

     Einstein himself first put forth the idea of quantum entanglement but doubted that it really existed, dismissing the phenomenon as "spooky action at a distance." Furusawa's quantum teleportation experiments have proved otherwise.

     For the experiments, Furusawa built an apparatus comprising over 100 lenses and a number of devices for extracting photons. He used this setup to create pairs of photons from individual photons and then to confirm that when specific information was added to one photon of the pair, that information was instantaneously conveyed to the other.

     "We can now validate the theory that Einstein argued against," he said.

     Furusawa's expertise is in the physical properties of semiconductor materials, but when he joined Nikon after completing his postgraduate studies, he began research in the field of quantum optics. "I wanted to do something that nobody else was doing," he said. He decided to go to the U.S. in 1996 to study at Caltech with Kimble, who was at the forefront of quantum optics, because he "wanted to experience working in the world's top lab."

     His background in semiconductor materials proved invaluable, allowing him to present his quantum teleportation experiments at an international conference on quantum optics just two years after moving to the U.S. "I was really just a dabbler in quantum optics, but I understood systematically the circuitry and control mechanisms required for the experiments." 

     With that success in hand, Furusawa decided to return to Japan in 1998, only to learn that Nikon was closing the Nikon Research Laboratory due to the recession. Frustrated, he quit Nikon in 2000 and applied for an assistant professor position at the University of Tokyo. He got the job partly because Science magazine had selected quantum teleportation as one of the top ten breakthroughs of 1998. "I was extremely lucky," Furusawa said with a grin.

Clearing hurdles

In modern optical communication, pulses of light transmitted along bundles of optical fibers carry information. But because the light weakens, or attenuates, over distance, it needs to be amplified along its journey using repeaters. This process consumes enormous amounts of electric power.

     This energy consumption would be reduced significantly by the advent of quantum computers, since such machines could read information even from attenuated light.

     Given the inevitable march toward ever-greater amounts of data being processed and transmitted at ever-faster speeds, the development of quantum computers is considered a need of the times.

     Since joining the University of Tokyo, Furusawa has continued to expand the possibilities for quantum teleportation in ways that will help bring such computers closer to reality.

     In 2004, he demonstrated a so-called quantum teleportation network with quantum entanglement shared between three parties, and in 2009 he broadened this network to nine parties.

     In August of 2013, Furusawa developed a way to improve the transfer efficiency of quantum teleportation. "The ability to transfer information in a highly efficient manner can dramatically increase data processing capabilities and lead to the practical use of quantum computers," he explained.

     In conventional setups for quantum teleportation, only photons carry information and not even 1% of the information can be sent. But by also using optical waves to carry information, Furusawa was able to boost the transfer efficiency to some 60%.

     For the August experiments, Furusawa put all of his experience and knowledge to the task of designing the needed apparatus, building an optical table fitted with over 500 lenses, mirrors and other optical equipment. Though haphazard in appearance, the various mirrors and lenses were all precisely positioned for the passage of laser light.

     Another important advance came in November of 2013, when Furusawa adopted the method of optical multiplexing to generate quantum entanglement of 16,000 "modes," which was three orders of magnitude larger than the previous largest entangled state of 14 entangled modes.

     Because quantum computers manipulate information as quantum bits, or qubits, rather than regular bits, they promise data-crunching capabilities far surpassing even the most powerful of today's supercomputers.

     The November achievement by Furusawa was important because it crossed one more hurdle toward the practical development of quantum computers. More entangled states allow for larger-volume transmission and processing of information, and according to Furusawa "there is no longer any limit to how many entangled states can be created."

     Of course, Furusawa is not alone in his studies, and research toward the realization of quantum computers is picking up steam elsewhere in Japan as well.

     NTT Basic Research Laboratories has devised a way to eliminate the time lag that arises during the course of processing by aligning the photons used for computations.

     Riken and NEC, meanwhile, have developed technology to more accurately read information. By using circuits made from a superconducting material to prevent noise that can alter the states of qubits, this setup can determine those states with 90% accuracy.

     Furusawa has boundless enthusiasm, but he is also realistic. "We are still a long way off," he cautions.

     Furusawa notes that quantum computers are important not just because of their data-crunching capabilities. "We are in the midst of an information explosion, and the electricity consumed by computers is on the rise. If we can realize quantum computers, we can reduce the number of servers in operation and achieve high-performance, low-energy communications. We can realize a communications network that is kinder to the Earth."

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