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Curated by RSF Research Staff

Fireworks coming out from Bose-Einstein Condensates

Scattering is a usual method to probe matter and its interactions. For example, in ultracold atomic gases, this method made possible to investigate quantum many-body systems. Also, on colliding Bose–Einstein condensates, previous experiments have already revealed matter–wave interference, haloes of scattered atoms. And more recently, researchers showed that stimulating an ultracold collective of atoms from a Bose–Einstein condensate causes it to emit a burst of matter-wave jets, blowing like fireworks.

The Bose-Einstein condensates could be called the fifth state of matter, the other four being gases, liquids, solids and plasmas. in short, a Bose-Einstein condensate represents a group of atoms cooled nearly to absolute zero. In this state, these atoms are hardly moving relative to each other having almost no free energy.  Consequently, they all acquire the same energy states and become like physically identical, the whole group acting as if it was a single atom. This new state of matter has very interesting properties presenting microscopic quantum phenomena like wavefunction interference.

Back to the scattering method, the interplay between spontaneous and stimulated scattering events underpins many interesting physical phenomena. When the scattering rate exceeds a certain threshold, stimulated processes can intensify leading to the exponential amplification of the number of outgoing particles. A well-known example is the laser, in which a sufficient rate of stimulated emission results in a coherent wave of photons. Similarly, the team lead by Professor Cheng Chin from University of Chicago found a very surprising behavior from a Bose-Esintein condensate.

This is a very fundamental behavior that we have never been seen before; it was a great surprise to us.

Professor of physics Cheng Chin, University of Chicago, USA

The researchers showed that runaway stimulated collisions in Bose–Einstein condensates cause the collective emission of matter-wave jets that resemble fireworks. Runaway stimulated scattering occurs only when outgoing atoms stimulate further collisions faster than they escape the condensate. They observed that the structures and atom occupancies of the jets stem from the quantum fluctuations of the condensate. To be more precise, these jets are coming from the parametric amplification of the vacuum fluctuation. These results are revealing the quantum nature of matter-wave emission.

If you'd asked almost anyone to predict what would happen, they would have said that these collisions would just send atoms flying off in random directions. But what we see instead are thousands of bosons bunching together to leave in the same direction.

Logan W. Clark, University of Chicago, USA

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