Superheated Bose-Einstein condensate exists above critical temperature

Apr 10, 2013 by Lisa Zyga feature
(a) Physicists created a BEC that can persist at up to 1.5 times hotter than the critical temperature at which it normally decays. (b) The BEC can survive in the superheated regime for more than a minute when different components of the boson gas are not in equilibrium. Credit: Alexander L. Gaunt, et al. ©2013 Macmillan Publishers Limited

(Phys.org) —At very low temperatures, near absolute zero, multiple particles called bosons can form an unusual state of matter in which a large fraction of the bosons in a gas occupy the same quantum state—the lowest one—to form a Bose-Einstein condensate (BEC). In a sense, the bosons lose their individual identities and behave like a single, very large atom. But while previously BECs have only existed below a critical temperature, scientists in a new study have shown that BECs can exist above this critical temperature for more than a minute when different components of the gas evolve at different rates.

The physicists, Alexander L. Gaunt, Richard J. Fletcher, Robert P. Smith, and Zoran Hadzibabic at the University of Cambridge in the UK, have published their study on the superheated BEC in a recent issue of Nature Physics.

As the physicists explain, a superheated BEC is reminiscent of superheated distilled water (water that has had many of its impurities removed), which remains liquid above 100 °C, the temperature at which it would normally boil into a gas. In both cases, the temperature—as defined by the average energy per particle ( or water molecule)—rises above a critical temperature at which the phase transition should occur, and yet it doesn't.

In BECs and distilled water, the inhibition of a phase transition at the critical temperature occurs for different reasons. In general, there are two types of . The boiling of water is a first-order phase transition, and it can be inhibited in clean water because, in the absence of , there is in an that "protects" the liquid from boiling away. On the other hand, boiling a BEC is a second-order phase transition. In this case, superheating occurs because the BEC component and the remaining thermal (non-condensed) component decouple and evolve as two separate equilibrium systems.

The physicists explain how this mechanism works in more detail. In equilibrium, a BEC can only exist below a critical transition temperature. If the temperature is increased towards the critical value, the BEC should gradually decay into the thermal component. The particles flow between the two components until they have the same chemical potential (a measure of how much energy it takes to add a particle to either component), or in other words, until they are in equilibrium with each other. However, maintaining this equilibrium relies on the interactions between the particles.

Here, the researchers demonstrated that in an optically trapped potassium-39 gas the strength of interactions can be reduced just enough so that the two components remain at the same temperature, but the particle flow between them is slowed down and their chemical potentials decouple. This condition makes it possible for the BEC to maintain a higher chemical potential than the surrounding thermal component, and thus survive far above its equilibrium transition temperature.

"The thing that prompted this work was a previous paper of ours on measuring the equilibrium BEC transition temperature as a function of the interparticle interaction strength," Smith told Phys.org. "At the time we noticed that something funny was happening at very low interaction strengths: the transition temperature seemed higher than it should be by up to 5%. We realized that this was probably due to non-equilibrium effects, but could not explain it fully. Also, the effect was much smaller than we demonstrated now. Only after fully understanding the equilibrium properties of a BEC in an interacting gas we could come back to this problem, demonstrate a much clearer effect, and explain it quantitatively."

In the new study, the experimentally demonstrated that a BEC could persist in the superheated regime (at temperatures above the ) for more than a minute. They also showed that that they could cause the BEC to rapidly boil away by strengthening the interatomic interactions to their normal levels, confirming the presence of the superheated state.

The scientists predict that extending a BEC's lifetime by tuning the interactions could have several applications.

"Generally, atomic BECs are increasingly used for applications such as atom interferometry and precision measurements, and might also find applications in quantum information processing and computing," Smith said. "For all those applications one wishes to preserve the coherent BEC for as long as possible, e.g., to perform a longer (hence more precise) measurement or more quantum-information type operations. Our work shows that it is possible to significantly extend the lifetime of a coherent BEC exposed to the experimentally unavoidable decohering thermal environment."

In the future, the researchers plan to further investigate the physical mechanism behind superheating.

"We are primarily interested in further fundamental understanding of the superheating phenomenon," Smith said. "The funny thing is that the system is simultaneously in equilibrium in some respects (e.g., the BEC and the thermal component have the same temperature, the BEC has an equilibrium shape for the given number of condensed atoms, etc.) and out of equilibrium in other ways (primarily the fact that the number of condensed atoms is much higher than expected in equilibrium). This poses new question about how we define equilibrium in a quantum system, which we would like to understand better. Practical applications might come later, fully exploiting their potential being reliant on more complete fundamental understanding.

"Also, it turns out that condensation in 2D systems is even more interesting than in 3D, and we plan to study superheating and other non- phenomena for an ultracold 2D Bose gas."

Explore further: Superabsorbing ring could make light work of snaps

More information: Alexander L. Gaunt, et al. "A superheated Bose-condensed gas." Nature Physics. DOI: 10.1038/NPHYS2587

Related: R. P. Smith, et al. "Effects of interactions on the critical temperature of a trapped Bose gas." Phys. Rev. Lett. 106, 250403 (2011) DOI: 10.1103/PhysRevLett.106.250403

Journal reference: Nature Physics search and more info website Physical Review Letters search and more info website

4.5 /5 (21 votes)

Related Stories

Ultracold atoms reveal surprising new quantum effects

Sep 06, 2012

Vienna University of Technology physicists have studied the transition of quantum systems towards thermal equilibrium. They detected an astonishingly stable intermediate state between order and disorder. ...

Flatland physics probes mysteries of superfluidity

Mar 25, 2009

(Physorg.com) -- If physicists lived in Flatland—the fictional two-dimensional world invented by Edwin Abbott in his 1884 novel—some of their quantum physics experiments would turn out differently (not ...

Atoms with quantum memory

Feb 28, 2013

Order tends towards disorder. This is also true for quantum states. Measurements at the Vienna University of Technology show that in quantum mechanics this transition can be quite different from what we experience ...

Matter-matter entanglement at a distance

May 27, 2011

(PhysOrg.com) -- Scientists at the Max Planck Institute of Quantum Optics prepare quantum mechanical entanglement of two remote quantum systems.

Entangled Light in Bose-Einstein Condensates

Apr 08, 2009

(PhysOrg.com) -- When physicists entangle light, they usually use nonlinear crystals as the source. However, it’s difficult to control the entanglement generation process in a bulk crystal, and so scientists ...

Recommended for you

What is Nothing?

5 hours ago

Is there any place in the Universe where there's truly nothing? Consider the gaps between stars and galaxies? Or the gaps between atoms? What are the properties of nothing?

On the hunt for dark matter

7 hours ago

New University of Adelaide Future Fellow Dr Martin White is starting a research project that has the potential to redirect the experiments of thousands of physicists around the world who are trying to identify the nature ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

Macksb
1 / 5 (1) Apr 10, 2013
This might be an instance of a "chimera state" in a system of coupled oscillators. See two papers by Daniel Abrams and Steven Strogatz. One in 2004, other in 2006. Both titles similar "Chimera states....coupled oscillators." See also "Cerium's Unusual Behavior" Phys Org Jan 27, 2011 article and comment by Macksb (crystal states). Bose Einstein state is a coupled oscillator system. In cerium case (2011 PhysOrg article), extreme pressure is critical element. In this BEC case, optical trapping is critical element.
behzzad
1 / 5 (1) May 22, 2013
My name is Behzad Simon Yousefzadeh. I have written two books. I have found a pattern in random numbers in 2004. This means by a proper filtration method we can predict what will be the end of tunnel. I am a complex data mine researcher. I can find a universal logic inside another unregulated logic. A dimensional approach to balance the power of universe.
My next research is to find logic inside tornado or twister. I have found a force inside the tornado in which by lasers guided hydrogen and another substance we can basically stop it or slow down the speed of a twister.
I need fund to continue my research. I need your help. I can help to solve the twister problems.
please send your donation to :

Mr. Behzad Simon Yousefzadeh
Post Office Box 5325
Sherman Oaks, CA 91413-5325