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China Puts Atoms on a Chip
Dec 2008
SHANGHAI, China, Dec. 16, 2008 -- Researchers in China have successfully developed the country's first atom-chip system -- a milestone in ultracold atom research and quantum information storage technologies -- and at least one Nobel Prize laureate is impressed.

A research team from the Chinese Academy of Sciences (CAS) Shanghai Institute of Optics and Fine Mechanics (SIOM) announced Nov. 26 that they had successfully developed the atom-chip system for achieving Bose-Einstein condensation (BEC). While scientists in countries such as the US, France and Germany have already realized such a chip, China became only the second country in Asia (Japan was first) to achieve the milestone.
China's atom-chip system (Photo: Chinese Academy of Sciences)
German physicist Wolfgang Ketterle, who shared the 2001 Nobel Prize in Physics for synthesizing the first condensate, told China's state-run news agency Xinhua today that he was impressed by the country's progress. China is now "rapidly catching up with the frontiers of the field" and he expects Chinese physicists to "make major contributions (to the field of BEC) in the near future," Ketterle told Xinhua in an e-mail. Ketterle is now associate director of the Research Laboratory of Electronics and John D. MacArthur Professor of Physics at MIT.

According to professor and CAS member Wang Yuzhu, who led the research team, a BEC is a state of matter in which atoms are cooled to temperatures very near to absolute zero (0 K, about -273 °C or -459 °F). Under such conditions, a large fraction of the atoms will collapse into their lowest quantum state, and quantum effects become apparent on a macroscopic scale.

The SIOM team used lasers to cut Z- and U-shaped lines 100-µm wide on the gilded surface of a silicon-based chip and generated a magnetic field around the chip by electrifying the lines. The team said it had made over 3000 rubidium atoms condensate on a thumbnail-sized chip for five seconds at a temperature of almost absolute zero, the news agency reported.

Atom chips can be used to store and process quantum information, and in ultraprecise atomic clocks used in navigation and space flight, Wang told the news agency.

Predicted in the 1920s by Indian physicist Satyendra Bose and Albert Einstein, this exotic phenomenon was not observed until 1995 in dilute atomic gases for the first time.

Research has shown that atoms at the BEC state act at the same frequency, like photons in a laser, but stronger. Now, BEC is a subject of intense theoretical and experimental studies with wide application in atom frequency standards, atom interferometer as well as the storage and process of quantum information.

Traditional research apparatuses for BEC were usually expensive and huge, Wang told Xinhua. "The magnetic field loops alone could take up half the volume of a floor-standing air conditioner, making it very expensive and difficult to do experiments," he said.

With the help of modern technologies of semiconductor manufacturing and microelectromechanical systems (MEMS), some of them are now able to integrate the magnetic and optical systems into a silicon-based chip. When a surface electric current induces gradient magnetic fields on the chip, the atoms will be trapped and gradually frozen to extremely low temperatures. The BEC-on-a-chip not only is more stable and easier to carry, but can perform functions that traditional equipment could not.

Since it was established in 2003, the CAS group has installed China's first atom-chip optical electromechanical experimental setup including a ultrahigh vacuum system, an optical system, a frequency-stabilized laser device, an external magnetic field, along with high-resolution imaging and computer control systems for ultracold atom research. Their original design also involved an atom-chip capable of combining a magnetostatic trap with a high-frequency one.

Later they joined efforts with scientists from Zhejiang University to successfully prepare first such atom chip in China. With these chips researchers were able to carry out a series of cutting-edge experiments, such as laser cooling and chip-surface evaporative cooling of atomic gases, magneto-optical trapping, atomic waveguides, and the splitting of ultracold atom clouds. They finally managed to cool down the atoms -- 3000 of them in all -- to some 300 nK (nano kelvin), at which point the phase transition of BEC was obtained.

The work, chaired by Wang, was supported by the National Basic Research Program and performed by the atom-chip group under the Laboratory for Quantum Optics at SIOM.

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