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17 Jun 2002
Scientists have demonstrated a quantum-physics first, dynamic tunnelling.
Twenty years ago, quantum physicists predicted that it was possible to make a moving atom resist the laws of classical physics, and suddenly "flip" between different regions of space. This unexpected behavior, known as dynamic tunnelling, has now been demonstrated by two groups of US researchers.
Mark Raizen led a team at the University of Texas, Austin, (Sciencexpress, July 2001), while Winfried Hensinger and colleagues at Australia's University of Queensland collaborated with researchers from the National Institute of Standards and Technology, US (Nature, 412, 52-55).
Using similar optical techniques, each team cooled millions of atoms to just a few degrees above absolute zero and then trapped the atoms in a single quantum state, known as a Bose Einstein condensate. The atoms were confined by an "optical lattice" of criss-crossed laser beams.
To prove that dynamic tunnelling was more than a theoretical figment of physicists' imaginations, the teams loaded their super-cooled atoms into two separate quantum wells. They forced the laser lattice to oscillate as a standing wave between the two wells, and carefully monitored any effects that this had on the atoms' momentum. Each team noticed that, instead of moving from one well to the other, the atoms appeared to instantly "flip" between the two wells - a peculiarity that denotes dynamic tunnelling.
Both teams are eager to drive quantum studies forward and have already moved onto the next stage of their work, "chaos-assisted tunnelling." Mark Raizen and his group added "packets of chaos" to their optical-lattice set-up. "We observed that classical chaos increases the tunnelling rate of [the atoms]," said Raizen.
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