Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Quantum thermodynamics

05.12.2012
A better understanding of how atoms soak up their surroundings

No man is an island, entire of itself, said poet John Donne. And no atom neither. Even in the middle of intergalactic space, atoms feel the electromagnetic field---also known as the cosmic microwave background---left over by the Big Bang.


This shows the lattice of laser beams traps small numbers of ytterbium atoms in pancake-shaped "wells." A yellow laser excites the atoms so that they switch between lower (blue) and higher (yellow) energy levels.

Credit: NIST

The cosmos is filled with interactions that remind atoms they are not alone. Stray electric fields, say from a nearby electronic device, will also slightly adjust the internal energy levels of atoms, a process called the Stark effect. Even the universal vacuum, presumably empty of any energy or particles, can very briefly muster virtual particles that buffet electrons inside atoms, further shifting their energies; this form of self-interaction is known as the Lamb shift.

A new calculation by scientists at the Joint Quantum Institute (JQI) and the University of Delaware shows how still another influence, the warmth thrown off by nearby objects, can shift energy levels. Uncertainties in this "blackbody radiation shift" will soon impose limits on the accuracy of the best atomic clocks. Theoretical work on this subject will give scientists extra confidence when they come to redefine the second in coming years, a recalibration based on how ultracold atoms behave while sitting in special traps.

Modern timekeeping consists nowadays in reliably counting the cycles of light pouring out of those atoms and, more basic still, knowing what the atoms' intrinsic energy levels should be once all external influences are taken into account. On the experimental side, scientists slow the atoms to a near standstill in traps in order to minimize Doppler effects from the emitted light. This, and the ability to detect and count light oscillations at ever shorter wavelengths ---has led to atomic clocks with uncertainties as small as one part in 1017.

This research is Nobel-rich territory. To say nothing of earlier Nobels for atom cooling, the move from microwaves as the atomic "escapement" for clocks to light in the optical range (harder to measure but offering a precision hundreds of thousands of times better) earned several scientists the 2005 Nobel in Physics. One of 2012's Nobelists, David Wineland, is a pioneer in exploiting the properties of single ion held in a trap to develop clocks of the highest stability.

The precision of the clocks, however, is no better than knowledge of the internal energy levels of the atoms themselves, whether they are single ions or a gas of neutral atoms held in space by a network of laser beams---an arrangement called an optical lattice.

Some of the things that impose unwanted shifts on the atoms in a lattice, such as inter-atom collisions or the Stark effect, can be controlled. According to JQI Fellow Charles Clark, one of the largest irreducible parts in the uncertainty budget of an atomic clock is the blackbody radiation emitted by the very chamber enclosing the atoms. The atoms in the lattice might, by virtue of an elaborate cooling process, be at milli-kelvin or even micro-kelvin temperatures, but the surrounding vacuum chamber is generally at room temperature. One of the basic laws of thermodynamics says that material objects radiate heat---the higher the temperature the higher-energy the radiation. This shift is hard to measure experimentally and hard to calculate theoretically.

Coming to grips with this faint form of influence is the purpose of a new paper in the journal Physical Review Letters (**). Clark and his co-authors Marianna Safronova (a JQI Adjunct Fellow) and Sergey Porsev of the University of Delaware, look specifically at how ytterbium atoms are affected by blackbody radiation.

The rare-earth element ytterbium (Yb) is valued not so much for its mechanical properties but for its complement of internal energy levels. "A particular transition in Yb atoms, at a wavelength of 578 nm, currently provides one of the world's most accurate optical atomic frequency standards," said Safronova.

Although only important at a precision level of a part in 1015, accurate knowledge of the blackbody shift is more pertinent now that clocks are closing in on the part-per-1018 level of precision. That is, the uncertainty in the blackbody shift must be comparable to (and eventually lower than) the desired uncertainty of the clock. The new calculation by Safronova, Clark, and Porsev is the best yet since it includes the most complete treatment of the electron-electron correlations within the Yb atoms.

Clark estimates that the amount of uncertainty achieved in the value of an atomic energy level---about 2 times 10-18 --- corresponds to a clock uncertainty of about one second over the lifetime of the universe so far, 15 billion years.

The authors also studied the long-distance interactions among the Yb atoms and atoms of other species as well. This is critical to understanding the physics of dilute gas mixtures in general. Such mixtures are of interest, for example, in studying such things as quantum dipolar material (molecules which, though neutral, possess an electric dipole moment) and many-body quantum simulation. Besides applications in timekeeping and the study of ultracold chemistry, the results of the present work are important for the measurement of the weak force (through subtle parity effects---the process by which nature can tell left from right) and the search for the new physics beyond the standard model of the electroweak interactions.

###

(*)The Joint Quantum Institute is operated jointly by the National Institute of Standards and Technology in Gaithersburg, MD and the University of Maryland in College Park.

(**) "Ytterbium in quantum gases and atomic clocks: van der Waals interactions and blackbody shifts," M. S. Safronova, S. G. Porsev, and Charles W. Clark, Physical Review Letters, 7 December 2012.

Press contact at JQI: Phillip F. Schewe, pschewe@umd.edu, 301-405-0989. http://jqi.umd.edu/

Phillip F. Schewe | EurekAlert!
Further information:
http://www.umd.edu

More articles from Physics and Astronomy:

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>