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Distant Atoms Cooperate by Sharing Light

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Atoms can work collectively, rather than independently, to share light, an international team has found. The discovery has important implications for applications in advanced quantum devices.

Researchers demonstrated light sharing, or "photon-mediated interaction," between artificial atoms confined to a one-dimensional quantum system. Quantum physicists have long discussed such a possibility, but this is the first experimental observation of the effect. The team included scientists from ETH Zurich, who performed the experiment, and theoretical scientists from the Université de Sherbrooke in Quebec and the University of Calgary in Alberta.


The chip containing the superconducting circuits used in the experiment had a design identical to this one. Courtesy of Barry Sanders.


Getting artificial atoms to work collectively could lead to control of microwave fields in superconducting circuits with benefits, including ways to protect quantum information against "noise" or signal damage, said Barry Sanders, professor of physics and astronomy at the U of C and director of the university's Institute for Quantum Science and Technology.

"I think what we've shown is going to be critical for future applications. It's an unobserved effect that has been discussed for decades, and we see it with excellent agreement between theory and experiment," Sanders said.

The two artificial atoms “showed a coherent exchange interaction, something not seen before for distant quantum systems in an open environment,” said Arjan van Loo, a Ph.D. student in the Quantum Device Lab at ETH Zurich.

The key to the approach was to do the experiment in one dimension rather than in three, where the interaction between atoms is weak and declines significantly with distance.

Realizing such fundamental interactions between individual quantum systems in one dimension is crucial to advancing quantum-based devices, and is expected to be useful for routing quantum information along one-dimensional waveguides on devices used for quantum information processing or quantum communication, they said.

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 This illustration shows the artificial atoms or "qubits" alongside the one-dimensional waveguide, or transmission line. Courtesy of Barry Sanders.


This research shows that "man-made electrical circuits can now be engineered in such a way to exhibit behavior that is not possible in 'natural' quantum systems," said Alexandre Blais, associate professor of physics at Université de Sherbrooke.

Confining two artificial atoms to one dimension using a waveguide greatly increased the possibility that the two systems would interact and enabled measurement of the interaction. Using superconducting circuits, the team put two artificial atoms alongside the waveguide and sent a microwave field through the waveguide.

At a distance of approximately 2 cm – much larger than typically expected for quantum systems – the two atomlike systems formed a type of weakly bound molecule, due to the exchange of photons.

"We also observed how the superconducting circuits either synchronize to emit radiation much more efficiently displaying superradiance, or how the circuits trap radiation, turning the two systems dark, as they do not emit photons anymore," said Andreas Wallraff, professor of solid-state physics at ETH Zurich.

The paper, “Photon-mediated interactions between distant artificial atoms,” appears this week in Science Express. (DOI: 10.1126/science.1244324)

For more information, visit: www.ucalgary.ca  

Published: November 2013
Glossary
astronomy
The scientific observation of celestial radiation that has reached the vicinity of Earth, and the interpretation of these observations to determine the characteristics of the extraterrestrial bodies and phenomena that have emitted the radiation.
photon
A quantum of electromagnetic energy of a single mode; i.e., a single wavelength, direction and polarization. As a unit of energy, each photon equals hn, h being Planck's constant and n, the frequency of the propagating electromagnetic wave. The momentum of the photon in the direction of propagation is hn/c, c being the speed of light.
quantum
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
superradiance
Directional and coherent radiation pulses that result from an ensemble of coherently prepared states in an optical medium.
waveguide
A waveguide is a physical structure or device that is designed to confine and guide electromagnetic waves, such as radio waves, microwaves, or light waves. It is commonly used in communication systems, radar systems, and other applications where the controlled transmission of electromagnetic waves is crucial. The basic function of a waveguide is to provide a path for the propagation of electromagnetic waves while minimizing the loss of energy. Waveguides come in various shapes and sizes, and...
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