Beam Me Up Scotty? A Q&A about Quantum Teleportation with H. Jeff Kimble

[David Farber <dave () farber net>]

Begin forwarded message:

From: dewayne () warpspeed com (Dewayne Hendricks)
Date: February 15, 2008 3:44:13 AM EST
To: Dewayne-Net Technology List <xyzzy () warpspeed com>
Subject: [Dewayne-Net] Beam Me Up Scotty? A Q&A about Quantum  
Teleportation with H. Jeff Kimble

[Note:  This item comes from friend Ken DiPietro.  DLH]

February 14, 2008
Beam Me Up Scotty? A Q&A about Quantum Teleportation with H. Jeff Kimble
Why the effect is nothing like Star Trek

By JR Minkel
<http://www.sciam.com/article.cfm?id=why-teleporting-is-nothing-like-star-trek&print=true 
>

The sci-fi dream (or utter fantasy) of getting from one place to  
another instantaneously continued this February 14, with the opening  
of Doug Liman's film Jumper, based on the novel by Steven Gould. We  
asked quantum physicist H. Jeff Kimble of the California Institute of  
Technology to explain how physicists understand quantum teleportation,  
which turns out to be more relevant to computing than to commuting.  
Note: This is an expanded version of a Q&A published in the March 2008  
print edition of Scientific American.

Scientific American: What's the biggest misconception about  
teleportation?
Jeff Kimble: That the object itself is being sent. We're not sending  
around material stuff. If I wanted to send you a Boeing 757, I could  
send you all the parts, or I could send you a blueprint showing all  
the parts, and it's much easier to send a blueprint. Teleportation is  
a protocol about how to send a quantum state—a wave function—from one  
place to another.

Is transmitting a quantum state hard to do?
The most straightforward way to do it would be to imagine it was an  
electron: just shoot the electron from point A to point B and it takes  
its quantum state with it. But that’s not always so good, because the  
state gets messed up in the process.

How does teleportation get around the disruption of the quantum state?
The special resource that enables teleportation is entanglement.  
You're Alice [in location A], and I hand you an electron in an unknown  
quantum state. Your job is to send the quantum state (not the  
electron) to location B, which is Bob. If you try to measure it  
directly, you necessarily disturb it.

You and Bob also share a pair of electron—you have one, Bob has the  
other—and they're in an entangled state such that if yours is spinning  
up, his is spinning down and conversely.

You make a joint measurement of two electrons—the one I handed you and  
the one you're sharing with Bob. And that gives you two bits of  
information. You call up Bob on the cell phone and give him those two  
bits, and he uses them to manipulate his electron. And bingo, in the  
ideal case he can perfectly re-create the state of the electron that I  
handed you.

Why doesn't Alice just copy the quantum state and store the copy?
There are uncertainty relations like Heisenberg's uncertainty  
principle. When I hand my electron to Alice, what she might think to  
do is just keep a copy—clone it. The more information she tries to get  
about the state, the less good is the teleportation. If she tries to  
keep a perfect copy, then Bob would create a state that is perfectly  
random.

Why would you want to transmit a quantum state? What are the  
applications?
Imagine you want to build a quantum computer. A quantum computer is  
going to have parts just like a computer on your desktop. They have to  
be wired together quantum mechanically. The quantum memory's got to  
talk to the quantum processor. Teleportation is just a fancy quantum  
wire.

[snip]

-------------------------------------------
Archives: http://www.listbox.com/member/archive/247/=now
RSS Feed: http://www.listbox.com/member/archive/rss/247/
Powered by Listbox: http://www.listbox.com