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Hamish Johnston: September 2008 Archives

rovibrational.jpg
The weakly bound rubidium molecules (upper image) are transferred into the rovibrational ground state with a STIRAP laser pulse. (Courtesy: Austrian Academy of Sciences).

By Hamish Johnston

Rovibrational ground states are a bit like buses — you wait a long time for nothing and then three come along one after another.

A few weeks ago, we reported on the first realization of a quantum gas of ultracold polar molecules by Deborah Jin, Jun Ye and colleagues at JILA in Boulder, Colorado.

The big challenge in creating the 350-nK gas was to put the potassium-rubidium molecules into their “rovibrational” ground state, where they have the smallest amount of rotational and vibrational energy allowed by quantum mechanics.

Normally, the molecules heat up the gas when they give up their excess rovibrational energy. Jin and Ye avoided this by using lasers to get the molecules to give up their energy as light that exits the gas without heating it — a technique called “stimulated Raman adiabatic passage” (STIRAP).

Now, Rudi Grimm and Johannes Hecker Denschlag at the Austrian Academy of Sciences have used the same technique to create an ultracold gas of rubidium-rubidium molecules in the “triplet” rovibrational ground state (Phys. Rev. Lett. 101 133305). Such a triplet state is interesting because the molecules have large magnetic moments, and therefore the gas could be useful as a “quantum simulator” of solid magnetic materials.

In the same issue of Physical Review Letters, Matthias Weidemueller and colleagues at Germany’s University of Freiburg explained how they created an ultracold gas of lithium-caesium molecules in the rovibrational ground state (Phys. Rev. Lett. 101 133304).

Like the potasium-rubidium, lithium-caesium molecules have electric dipole moments — which means that they could someday be used as quantum bits that are controlled by the simple application of an electric field.

By Hamish Johnston

Superfluid helium and magnetic fields are both in abundance in the Large Hadron Collider so it’s not surprising that some doomsayers have suggested that explosions called Bosenovae could occur in the accelerator’s cooling system.

Such explosions were first seen about ten years ago when an ultracold condensate of atoms was subjected to a carefully-selected magnetic field, which caused the normally-repulsive forces between atoms to become attractive. The condensate collapsed under these forces until it reached a critical density and then exploded outwards — much like an aging star becoming a supernova, but of course, on a much smaller scale.

So why couldn’t this happen in the LHC?

Well according to CERN’s Malcolm Fairbairn and Bob McElrath, this scenario is impossible because helium-4 atoms used to cool the LHC will simply not be attracted to each other when subject to any sort of magnetic field. The reason, according to the pair, is that the helium-4 nucleus does not have a magnetic moment and the atom has no unpaired electrons — both of which are needed to make the atoms attract each other.

By Hamish Johnston

If you asked me to name an “outspoken” particle physicist, I might choose Tommaso Dorigo of Italy’s University of Padova. Dorigo, you may recall, was embroiled in a controversy last year over the supposed sighting of the Higgs boson by the CDF collaboration at Fermilab.

Dorigo is a CDF member and had discussed preliminary results from the experiment on his blog, where they were picked up by the press and reported as evidence of the elusive Higgs. While these results had been previously reported at a conference, they had not been “approved” by Fermilab for mass consumption.

Needless to say, the CDF data did not provide strong evidence for the Higgs, and Dorigo has been criticized for discussing the results in public.

Now, Dorigo spends most of his time working on the LHC’s CMS experiment — so what does he have to say about the recent setbacks at CERN?

Nothing it seems, and he has even made a point of saying so in a recent blog posting .

Dorigo observes “CERN appears a bit up-tight about the latest events…”, and claims “my blog is targeted as a possible source of leaks”.

As a result, he has chosen to keep quiet: “And if I play fair, maybe I am allowed to survive here, and maybe one day I will stop being threatened every other day, in the name of protecting internal information of the experiments I am part of”.

Strong stuff…so, once burned, is Dorigo making the right choice?

By Hamish Johnston

Have rocket scientists built ‘financial weapons of mass destruction’?…

The answer is yes — at least according to the investment guru Warren Buffett, who has been warning for some time that complex financial instruments such as ‘derivatives’ are far too complicated for mere mortals to understand. Indeed, five years ago Buffett described derivatives as a “financial weapons of mass destruction”.

Now that derivatives have apparently helped bring down one of the world’s largest investment banks, should the rest of us be blaming the rocket scientists — PhD physicists and other bright sparks — who helped develop these financial instruments and the mathematical algorithms needed to make sense of them?

In an 1999 editorial, then Physics World editor Peter Rodgers weighed the pros and cons of physicists abandoning careers in research for high-paying jobs in finance. Would the raised profile of physics in society offset the loss of talented people from academia?

What Peter didn’t ask was: “What if the rocket scientists make a mess of it?”.

Avarice, not algorithms, is of course to blame for the credit crunch, but one can’t help wondering if this is the end of the love affair between physics and finance?

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Ready for action at the LHC (Courtesy: BBC).
By Hamish Johnston

Clearly the world didn’t end earlier today when the first protons made their way around the LHC.

But what if something unexpected had happened…what if physicists (including our own Jon Cartwright) started vanishing and what if something was lurking in the accelerator tunnel…who would we turn to?

Torchwood’s Captain Jack, of course, who will be leaping from the tallest toroids later today in a special radio edition of the Dr Who spin-off set at the LHC.

You can listen to Torchwood: Lost Souls on BBC Radio 4 today at 14.15 BST and for the next seven days as a podcast.

And for more LHC fun, check out this story in The Sun: Boffins in ‘Doomsday’ rap

By Hamish Johnston

You would have to be living under a rock in the UK not to know that the Large Hadron Collider will be fired up next week at CERN in Geneva. BBC Radio 4 is dedicating an entire day of programming to the LHC (called ‘Big Bang Day’), and this is being promoted with great fervour across the corporation’s many TV and radio outlets.

This morning Chris Llewellyn Smith,former director general of CERN, was on Radio 4’s Today Programme to reassure listeners that the world will not be destroyed by a black hole — or turn into a “strange goo” — when the LHC is switched on.

Meanwhile over on Radio 5 Live, CERN physicist John Ellis was chatting about his new paper  ‘Review of the safety of LHC collisions’ with host Nicky Campbell. This is surely the first time that an article in the Journal of Physics G: Nuclear and Particle Physics has been deemed to have the same news value as the latest exploits of Newcastle United’s ex-manager Kevin Keegan.

Indeed, one could be forgiven for thinking that the LHC is ‘brought to you by the BBC’. In today’s Times, gossip columnist Adam Sherwin suggested that the LHC start-up date was pushed back to 10 September because BBC superstar Andrew Marr — who will be presenting live from CERN on the day — is on holiday this week. The BBC has denied exerting undue control over the world’s largest physics experiment.

Another ‘quality daily’, The Independent, ran the headline ‘It’s sex and drugs and particle physics as D:Ream star recreates the Big Bang’ earlier this week. For those too young to remember, the article refers to Brian Cox, who is sort of a Liam Gallagher of particle physics and one of the many stars that the BBC will be rolling out next week.

And leave it to The Sun to say: ‘End of the world due in nine days’ …unless Andrew Marr decides to extend his holiday, of course.

By Hamish Johnston

On 16 August Usain Bolt sprinted to gold in the 100 m dash at the Beijing Olympics, setting a new world record of 9.69 s.

But could he have gone faster? Many people think so because after the first 80 m of the race, when it was clear that he would win, the Jamaican appeared to stop trying and begun celebrating.

Now, four physicists in Norway have analysed video of the race and concluded that he could have covered the 100 m in as little as 9.55 s (plus or minus 0.04 s) if he had maintained his pre-celebration acceleration.

In a second calculation, the physicists argue that if Bolt had started to flag in the final 20 m — but still matched the acceleration of runner-up Richard Thompson — Bolt still would have finished in 9.61 s (plus or minus 0.04 s).

Cynics have suggested that Bolt held back so he would have a better chance at cracking the world record again, but the world’s fastest man remains silent on exactly why he appears to have stopped trying.

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