The loose change from the arXiv this week:
Archive for October, 2007
Ya’ll heard about lunar laser ranging last week: them laser legends can now bounce enough photons off the moon to calculate its distance to within a few millimetres (we’re still waitin’ to hear how many millimetres it is)
This week, Victor “Brum” Brumberg at the Institute of Applied Astronomy in St Petersburg, Russia, and chums have worked out why this is useful: so we can land humans on the moon (nobody’s told Brum Brum that we done that already but no matter.)
Brum Brum’s dream is that we use the distance measurements to calculate the moon’s orbit to the precision required by general relativity. In fact the measurements are so accurate they could provide a test of relativity.
The new data will also allow us to go a-landin and explorin on the surface with unprecedented accuracy. And when we can do that we can plant shinier reflectors on the surface (the last one’s were left by Armstrong and co). That’ll give us even better measurements presumably allowing us to land with even more precision and so on in an infinite progression of lunar tomfoolery.
Ref: arxiv.org/abs/0710.1450: Prospects in the Orbital and Rotational Dynamics of the Moon with the Advent of Sub-centimeter Lunar Laser Ranging
If ya follow quantum game theory, you could be forgiven for thinking that quantum players always trounce their classical counterparts like T Rex versus the cavemen.
But it ain’t so. After some egg scratchin’ physicists have realised that quantum games are actually entirely different from classical games and so it ain’t fair to compare them. And even when they do compare em, quantum players usually cannot win against classical players because the classical player often destroys any quantum advantage his opponent can muster.
For example, in a coin flipping game, some theorists have suggested that a quantum player can outwit her classical opponent by putting the coin into a superposition of states. But she wouldn’t have to play long to find that the classical player destroyed the superposition whenever he touched the coin.
(There are a subset of games involving quantum telepathy in which a quantum player can outwit a classical player using entanglement but we ain’t talkin about those here.)
So Nati “Aha” Aharon and Lev “Itate” Vaidman at Tel Aviv University in Israel ask whether a quantum player can ever beat a classical player in anything resembling a decent game that doesn’t rely on entanglement.
The answer says Aha Aharon is yes, albeit in a rather contrived situation. The game involves one player placing a particle in one of three places and the second player attempting to work out what the first player has done. It turns out that if the first player puts the particle into a superposition of states, so it exists in all three places at once, then she will always win against classical player.
Who are they tryin’ to kid? That ain’t quantum playing, it’s quantum cheatin. Pull a stunt like that at a poker table and you’d be dribbling in an alley behind the casino before you can say “quantum teleportation”.
Ref: arxiv.org/abs/0710.1721 :Can Quantum Mechanics help to Win Games?
Dark matter is highly sought-after but like the unicorn, it is an elusive match for its hunters.
Physics bods have been a-huntin’ for dark matter here on Earth for some time now. They’ve set an impressive number of traps all over the planet and and found zilch.
So they’ve asked the astrobods to help out by looking for indirect evidence. If dark matter particles ever bang into each other, they might annihilate leaving a signature that we can see (or so the thinking goes).
Today, Dan “Super” Hooper from the Fermi National Accelerator in Illinois gives us the low down on the various candidates that the eggheads are looking at.
They’ve looked at the unexplained excess of positrons in cosmic rays, at the unexplained excess of 511KeV photons coming out of the galactic bulge, at the unexplained excess of gamma rays at energies above 1GeV coming from within our galaxy and from outside it and the unexplained excess of microwave emissions from the centre of the Milky Way as measured by the WMAP spacecraft.
None of these signals is particularly strong but that don’t bother dark matter theorists: if it don’t have a current explanation, it’s gotta be dark matter, right?
Whatever happened to that old fashioned notion of hypothesis testing.
I know what ya’ll thinkin and I’ll wager it includes the words “clutching” and “straws”. Myself? I’m rootin’ for the unicorn.
Ref: arxiv.org/abs/0710.2062: Indirect Searches For Dark Matter
The world has gone crazy over metamaterials cos they can be used to build invisibility cloaks, as ya’ll saw just the other week. There’s usually some drawback the media coverage never tells ya which means that we ain’t gonna see no Harry Potter-type invisibility cloaks any time soon. But that hasn’t stopped the living God of metamaterials, John “Now-You-See-Him” Pendry at Imperial College in London UK, from dreamin up ever more ingenious designs.
This week, he and a few pals have gone and built a metamaterial that works for light with zero frequency. That’s egghead-talk for a magnetic field. The material is a thin layer of lead squares pasted onto a cover slip and cooled to superconducting temperatures. This actually prevents a magnetic field from passing through it.
Why would anybody need a metamaterial that screens magnetic fields? There are all kindsa researchers playin around with tiny magnetic fields or with experiments in which they don’t want no magnetism at all. Their work is swamped by larger fields nearby. So a magnetic field cloak might be a useful device to have around.
And unlike other cloaking ideas, the technology is up and running now.
Ref: arxiv.org/abs/0710.1227: A DC Magnetic Metamaterial
What’s in a name? Quite a lot, it turns out. Researchers are working out how to extract data such as ya sex, nationality, age and even ya social and economic status by looking at nothing but yer name.
This week, Stasinos “King” Konstantopoulos at the National Center for Scientific Research in Athens, Greece gives us a curious glimpse into the kind of techniques that he and others are using.
He starts with a crazy game for ya’ll. Given a list of 15,00 names of people from 13 European countries, how accurately could you identify the nationality of each person?
Humans experienced in this art can reach accuracies of 43 per cent (them long winter evenings must fly by). But King Kon has developed some software that does the job just as well by looking at the length of the names and the types and frequency of accent marks used in each language. Turns out the number and types of accents in your name and its length is a pretty good signature of your nationality.
King Kon then says that since the popularity of names changes with time, he can get a reasonable idea of a person’s age–there ain’t many Hildas in the under-80s age group for example. Sex identification is usually straightforward in most languages. Names also give social and economic status clues. King Kon says look at the example of Paddy versus Patrick III. He also says some idea of a person’s religious and cultural background might also slip out: “Rene Antonius Maria Eijkelkamp and Abdelhali Chaiat are both Dutch football players, but certain educated guesses can be made about their cultural back grounds from their names alone.”
So if yer ain’t adopted a pseudonym already, better get one quick. By any other name, ya’ll bound to smell as sweet.
Ref: arxiv.org/abs/0710.1481 :What’s in a Name?
What kinda stuff is best at hosting ghostly bits of quantum information? It’s an important question cos we can’t tell what the next generation of quamputers will be like until we know what they gonna be made of.
Photons are one option cos they can store qubits for relatively long periods (unlike ions and electrons which get stripped of their qubits by any stray electric or magnetic field). The trouble with photons is that they don’t interact easily with each other so its hard to process the quantum information they store.
Another option are qubits in the form of neutral atoms which are naturally protected from the ravages of stray fields (cos they are neutral) and can be easily made to interact with each other to carry out information processing. The trouble with neutral atoms is that it’s easy to lose them, like spilt ball bearings.
So the dream option is to process the qubits as neutral atoms and transport them as photons.
This week Ed “57 Varieties” Hinds at Imperial College in London UK and his crew have unveiled a device that might just make that possible. It’s a microcavity connected to photon waveguides carved into a silicon chip. The idea is that a single atom sits in the cavity where physicists do their quantum data processing. They then transfer the qubit to a photon and ship it out through the waveguides. Simple when ya know.
Except, they don’t yet know how. This is just proof of principle hardware. The team has put it through its paces and says it performs with a throaty growl and a kick like a vodka martini. But a quamputer, it ain’t. That’ll come later.
“These results constitute first steps towards building an optical micro-cavity network on a chip for applications in quantum information processing,” says 57 Varieties in the paper.
The really excitin’ thing is that the device is scalable. It’s small and, in theory at least, easy to connect to other cavities on the same chip using the waveguides. So it should be straightforward to build two or more cavities onto a chip, link ‘em together with optical waveguides and start a-computin’ and a-calculatin’.
And if 57 Varieties and his gang do that, we might see some half-decent quamputing at Imperial in the next few years.
Ref: arxiv.org/abs/0710.2116: Atom Detection and Photon Production in a Scalable, Open, Optical Microcavity
The best of the rest from the physics preprint server
The Big Apple has had its toes watered by storms surges from passing hurricanes on many an occasion. But how to hold back the waters in future?
Alexander “Bonkin” Bolonkin reckons the best way to protect the city is to rap it in a textile storm surge barrier, a kinda giant gag.
Sounds good to me. When can they start?
Ref: arxiv.org/abs/0710.0195: Protection of New York City Urban Fabric With Low-Cost Textile Storm Surge Barriers
This looks impressive:
“The Apache Point Observatory Lunar Laser-ranging Operation has achieved one-millimeter range precision to the moon”
So c’mon fellas: how many millimeters is it?
Ref: arxiv.org/abs/0710.0890: APOLLO: the Apache Point Observatory Lunar Laser-ranging Operation: Instrument Description and First Detections