Toy Houses Built From Light

A team of physicists from the University of Calgary has discovered how to use quantum entanglement to stack light particles.

By manipulating the quantum entanglement, the team mounted up to two photons on top of one another to construct a variety of quantum states of light. In fact, the researchers say they can build two-story quantum toy houses of any style and architecture.

"This ability to prepare or control complex quantum objects is considered the holy grail of quantum science," said Andrew MacRae, a co-author of the paper and a doctoral physics student at the university. "It brings us closer to the onset of the new era of quantum information technology."

According to the group, this new generation of technology is expected to endow us with qualitatively new capabilities, including measurement instruments of extraordinary sensitivity, dramatically faster computers, secure communications systems and enhanced control over chemical reactions.

"Light is a particularly interesting quantum object because it's an excellent communication tool," said Alexander Lvovsky, a professor in the department of physics and astronomy. "No matter what future quantum computers will be made of, they'll talk to each other using photons."

The researchers used mirrors and lenses to focus a blue laser beam into a specialized crystal. The crystal takes high-energy blue photons and converts them into a quantum superposition of lower energy red photons, which emerge in two directions, or "channels." By measuring one of the channels using ultrasensitive single-photon detectors, the physicists prepare the desired quantum state in the other.

Such an operation is possible because the photons in the two channels are entangled: A measurement made in one channel would result in an immediate change in the other, regardless of whether the particles were an arm's length apart or light-years away. Albert Einstein called this quantum weirdness "spooky action at a distance."

"Quantum light is like an ocean and it's full of mysteries and treasures. Our task is to conquer it. But, so far, physicists were able to control only a tiny island in this ocean. What we have done is to make this island bigger," Lvovsky said.

The results of their research are published in the online edition of Nature Photonics.

For more information, visit: www.ucalgary.ca