Researchers perform first direct measurement of Van der Waals force

Phys.org ^ | Jul 08, 2013 | Bob Yirka

[neverdem]

Enlarge Mapping out the van der Waals interaction between two atoms. (a) In the experiment of Béguin et al. two atoms are trapped in the foci of two laser beams separated by a distance R. (b) Depending on R, the excitation laser field can couple the ground state |gg of the atomic pair to states containing one atom in the Rydberg state (|gr and |rg, respectively), or to a state with both atoms populating the Rydberg state |rr. The energy of the latter state is strongly shifted because of the van der Waals interaction U_vdW between the atoms (see level diagram in the upper left), resulting in a distance-dependent coherent excitation dynamics of the atomic pair system. (c) By analyzing the time evolution of the atom-pair state, Béguin et al. deduce the van der Waals energy shift as a function of interatomic distance for different Rydberg states. Credit: Physics 6, 71 (2013) DOI: 10.1103/Physics.6.71

(Phys.org) —Researchers working at the French National Center for Scientific Research have for the first time, directly measured the Van der Waals force between two atoms. In their paper published in the journal Physical Review Letters, the team describes how they used lasers to hold two atoms steady and a third laser to measure the Van der Waals force between them.

The weak force between atoms, named after its discoverer Johannes Diderik van der Waals is evident in the behavior of many materials—it's what keeps most gas molecules together. Scientists have also discovered that it's also what allows a gecko's toes to stick to a smooth wall. But, because the weak force is only apparent when atoms are very close together, scientists have until now been unable to measure it directly.

In this new effort, the research team chose to use Rydberg atoms as part of their study. Such atoms are large and one of their electrons has a highly charged state. This makes them a good candidate for attempting to measure the Van der Waals force—they have more force between them than most other atom pairs and because of that can be measured at longer distances.

They started by firing a pair of lasers at twin Rydberg atoms. Doing so held them steady. Next, they fired a third laser at the two atoms causing them to oscillate at a desired frequency. By measuring the oscillations, the researchers were able to work out mathematically the Van der Waals force between them. More specifically, the researchers measured oscillations between ground and excited states, noting that the distance between the two atoms at the time of measurement was key—too close and the excitation of one of the atoms overwhelmed the other—too far and the force between the atoms became too weak to measure. Using the third laser as optic tweezers allowed for adjusting the distance between the two atoms, which ultimately led to just the right distance for measurement.

The team also noted that the technique used for measuring the Van der Waals force also led to the oscillating atoms evolving to a fully coherent state. This means the technique could be used to create quantum logic gates, which might prove useful in creating a quantum computer.

Explore further:

First single-molecule measurement of Van Der Waals interactions at metal-organic interface

More information: Direct Measurement of the van der Waals Interaction between Two Rydberg Atoms, Phys. Rev. Lett. 110, 263201 (2013) prl.aps.org/abstract/PRL/v110/i26/e263201

Abstract
We report the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. Working in a regime where the single-atom Rabi frequency for excitation to the Rydberg state is comparable to the interaction, we observe partial Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. Quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and observe its characteristic C6/R6 dependence. The measured C6 coefficients agree well with ab initio calculations, and we observe their dramatic increase with the principal quantum number n of the Rydberg state.

Journal reference: Physical Review Letters

[neverdem]

Hat tip SunkenCiv!

[saintgermaine]

Look who posted, not wrote this article...”neverdem”

A while back I tried to get the point across that by judging or assessing the nature of an article and who posted it or perhaps wrote it, you can get a fairly good idea what field such a person might be in or what their interests are, as I am quite sure some one as dumb as the “Anointed One” or the “Global Warming Freak” who was bestowed with a Nobel Price by his like minded socialist brethrens certainly would not even have the foggiest idea what Van der Waal forces are or couldn’t care less.

At the same token there are a lot of interesting people frequenting this site and along with it putting in their two Cents worth and you may learn a few things or two. This is another reason why I like this website and also donate to it and I encourage any one to do the same in order to keep it alive even if it is just a small amount.

Saintgermaine

[Telepathic Intruder]

Only interesting in an abstract sense until they can use this information to make something useful: a Van der Waals bomb!

[wastedyears]

In layman’s terms.........

[neverdem]

http://en.wikipedia.org/wiki/Van_der_Waals_force

Wikipedia is usually a good reference if the science topic is not politicized.

[Telepathic Intruder]

Van der Waals force: Basically all other intermolecular forces besides the major ones which produce an overall attractive or repulsive effect. Similar to the hydrogen bond which creates surface tension in water, forms rain drops, ice crystals, etc.

[tired&retired]

Per Wiki (No I didn’t stay at a Holiday Inn Express last night!!)

In physical chemistry, the van der Waals force (or van der Waals interaction), named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds, the hydrogen bonds, or the electrostatic interaction of ions with one another or with neutral molecules or charged molecules.

The term includes:

Force between two permanent dipoles (Keesom force)

Force between a permanent dipole and a corresponding induced dipole (Debye force)

Force between two instantaneously induced dipoles (London dispersion force).

It is also sometimes used loosely as a synonym for the totality of intermolecular forces. Van der Waals forces are relatively weak compared to covalent bonds, but play a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics. Van der Waals forces define many properties of organic compounds, including their solubility in polar and non-polar media.

The ability of geckos – which can hang on a glass surface using only one toe – to climb on sheer surfaces has been attributed to the van der Waals forces between these surfaces and the spatula (plural spatulae), or microscopic projections, which cover the hair-like setae found on their footpads. A later study suggested that capillary adhesion might play a role, but that hypothesis has been rejected by more recent studies. There were efforts in 2008 to create a dry glue that exploits the effect, and success was achieved in 2011 to create an adhesive tape on similar grounds. In 2011, a paper was published relating the effect to both velcro-like hairs and the presence of lipids in gecko footprints.

[1010RD]

Sadly, this information is lost on the masses. The greatest kings of any age didn’t enjoy the wealth that is now so common in this era of our country. Worse, they have no idea how wealth is generated. A laser acting as an optic tweezer for a single atom is beyond their comprehension.

Yet, here in America, despite all the socialism and the nearly $2 trillion in just regulatory costs on our economy, we still generate enough wealth to allow the 47% to live in luxury most of the rest of the world only dreams of. Yet, a charlatan from backwards Cook County Illinois can convince them that they live in a hell hole needing more central planning from his crony capitalists.

We must recapture education by freeing it from government. Only government money can sustain so many bad ideas. The marketplace would have killed them long ago.