We have long been fascinated by the concept of absolute zero, the temperature at which everything comes to a complete stop, but physics tells us absolute zero cannot be reached but only approached - and the closer you get, the more interesting phenomena you find.
Three scientists from ESF's EUROCORES Programme EuroQUAM gave insight into this 'cool' matter at the event "The Amazing Quantum World of Ultra Cold Matter", held at this year's ESOF (Euroscience Open Forum) in Barcelona. It was co-organized by the European Science Foundation (ESF) and The Institute of Photonic Sciences (ICFO) within the collaborative research programme "Cold Quantum Matter" (EuroQUAM).
Maciej Lewenstein leads the quantum optics theory group at ICFO and is a Humboldt Research Prize Awardee. Introducing the basics of quantum mechanics, he explained without mathematics why laser light cools atoms and told the audience about recent developments in atomic, molecular and optical physics and quantum optics, toward reaching temperatures close to absolute zero.
"I expect major developments in fields like quantum information", said Lewenstein. He argued that while in classical physics absolute zero is in certain sense "boring", in the quantum world new, fascinating states of matter such as Bose-Einstein condensates arise at ultralow temperatures. Moreover, he elaborated on the tremendous advances in physics that have made such experiments possible, and which led to Nobel prizes in physics in 1997 and 2001. "Concerning Nobel Prizes in this area, it's only a question of who's next" predicted Lewenstein.
Christophe Salomon is Head of the cold Fermi gas group at Ecole Normale Supérieure, France and Principal Investigator for the ACES/PHARAO Space Clock Mission. He has received the "Three Physicists" prize (FR), the Mergier-Bourdeix Grand Prize of the French Academy of Sciences, the European Time and Frequency Prize, and the Philip-Morris Prize.
In his talk "Precision Time with Cold Atoms" he described an important application of cold atoms, the realization of ultra precise clocks. Using atomic fountains and microwave radiation, the SI unit of time, the second, is realised with an error of less than one second over 100 million years. Clocks operating in the optical domain show even better performances and cycles of light can now be easily counted with a femtosecond laser.
"In a few years clocks will be able to monitor local changes of the Earth gravitational potential by using relativity, which might help us forecast tsunamis, earthquakes, or global climate warming", said Salomon.
The third speaker, Christopher Foot, Professor of Physics at Oxford University, said, "The extraordinary behaviour of quantum systems". Small particles such as atoms and electrons behave in strange ways that often seem very weird when compared to our everyday experience of large 'ordinary' objects such as a tennis ball or football. For these very small objects the effects of quantum mechanics are manifested in striking ways, which Foot outlined.
A single quantum object can exist in two places at once - "It is in a state of indecision" said Foot. Additionally, there is a second property of quantum systems of two or more particles that is truly difficult to understand, known as entanglement. Indeed Einstein pointed out that this so-called "spooky action at a distance" is so bizarre that he thought there must be something wrong. Experiments have shown, however, that the quantum world really behaves in this peculiar way. "By understanding it we can do new things such as build quantum computers that, in the future, could store and process far more information than 'ordinary computers' and may outperform them in certain applications, e.g. cracking the encryption commonly used to transmit information electronically" explained Foot.
With current technology, quantum systems of many atoms at temperatures less than one millionth of a degree above absolute zero can be made. These systems can be controlled in such a way that they act like small quantum calculating machines, or 'quantum simulators', with which the quantum properties of a wide range of other interesting physical systems can be studied. Foot also gave an example of this type of experiment currently carried out in the EuroQUAM Programme, where laser beams are used to form 'optical lattices' that resemble crystals.
Spanish Anchorman and former Minister of European Relations in the Spanish Government Eduardo Punset moderated the event, and Jürgen Eschner, an experimentalist and group leader from ICFO, was the main organizer of this activity of EuroQUAM. "I think our biggest challenge in the coming years is to bring together knowledge and entertainment, and the speakers captivated the public here in Barcelona" said Punset. ESOF marked a unique opportunity for EuroQUAM to go public with its research and make cold quantum matter more graspable. "We have clearly conveyed the fascination that the EuroQUAM scientists have for the exciting fundamental phenomena and technological opportunities of ultra-cold matter" concluded Eschner.