IP: teleportation?

[David Farber <dave () farber net>]

> Date: Thu, 27 Sep 2001 12:50:26 -0400
> To: farber () cis upenn edu (David Farber)
> From: Richard Jay Solomon <rsolomon () dsl cis upenn edu>
>
> http://www.nature.com/nsu/010927/010927-11.html#1
>
> > Trillion-atom triumph
> > Physicists take first step towards practical teleportation.
> > 27 September 2001
> > PHILIP BALL
> >
> > For the first time physicists have forged quantum entanglement between 
> > two large blobs of gas. The achievement brings closer the possibility of 
> > super-fast quantum computers and teleportation1.
> >
> > Eugene Polzik and his co-workers at the University of Aarhus in Denmark 
> > have entangled about a million million caesium atoms. Four was the 
> > previous record.
> >
> > "This work should pave the way for a new generation of experiments to 
> > teleport states of matter," says Ignacio Cirac, a quantum physicist at 
> > Austria's University of Innsbruck.
> >
> > Teleportation will not involve the wholesale deconstruction and 
> > reconstruction of humans, Star Trek-style. It should allow the 
> > arrangement of one set of quantum particles to reproduce more or less 
> > instantly that of a similar collection of distant particles. In this way 
> > a message encoded in photons of light could be transmitted from one place 
> > to another without sending the photons across the intervening space.
> >
> > Entanglement also underpins attempts to perform high-speed quantum 
> > computing. It is a property without any analogue in the everyday world.
> >
> > Quantum particles such as atoms or photons can exist in distinct states, 
> > like the head or tail of a coin. Such particles can also exist in a 
> > superposition - in both states at once - comparable to a coin spinning in 
> > the air before it lands.
> >
> > If we toss two coins at once, their outcomes are independent: if one is 
> > heads, the other could be heads or tails. Two entangled quantum 
> > particles, by contrast, have interdependent fates: if one is in a 'heads' 
> > state, for instance, the other must be in a 'tails' state.
> >
> > Maintaining this kind of superposition is very difficult and for any 
> > practical applications, entanglement has to embrace thousands, or even 
> > millions, of particles. How can something so sensitive be sustained?
> >
> > Polzik and colleagues forgo full entanglement, where the state of each 
> > particle depends on the state of every other particle. Instead, they 
> > generate two loosely entangled clouds of caesium gas, one with slightly 
> > more atoms in a 'heads' state and the other with slightly more in a 
> > 'tails' state. (These two states are actually defined by the directions 
> > of the atoms' magnetic fields.)
> >
> > The interdependence of these clouds is more resilient to measurements or 
> > interactions that alter the quantum states of just a few of the 
> > constituent atoms.
> >
> > It would be impossible to maintain full entanglement of this many atoms 
> > for longer than a million-billionth of a second. Polzik's team can keep 
> > their two clouds in a loose entanglement for half a millisecond. They 
> > hope to maintain it for longer in the future, and perhaps to achieve the 
> > same thing in the solid samples needed for making quantum computers.
> >
> >
> > References
> >
> > 1.      Julsgaard, B., Koxhekin, A. & Polzik, E. S. Experimental 
> > long-lived entanglement of two macroscopic quantum objects. Nature, 413, 
> > 400 - 403 , (2001).
> >
> >
> > © Nature News Service / Macmillan Magazines Ltd 2001
> > *       Not a tangled web
> > 6 September 2000
> > *       No hiding place for quantum bombs
> > 18 April 2000
> > *       Quantum juggling
> > 16 March 2000
> > *       How decoherence killed Schrödinger's cat
> > 20 January 2000
> > *       Everyone wins in quantum games
> > 18 October 1999
> > *       A cat through the eye of a needle
> > 14 October 1999
> > *       Entangled photons and quantum computers