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Scientists teleport two different objects



 
 
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  #12  
Old October 6th 06, 03:38 AM posted to sci.space.policy
Wayne Throop
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Default Scientists teleport two different objects

: Alan Anderson
: An object (particle, photon, whatever) disappears from one location.

Nope. It stays right where it was. It's quantum state is rooned, that's all.

: An absolutely identical object (particle, photon, whatever) appears at
: another location.

Nope. It stays right where it was also; it just aquires the state
that the first got rooned. I does not call that teleportation,
nor have any truck with them as does. Well, other than to respectfully
(or sometimes not so respectfully; I am only mortal) disagree with them.

See for example http://www.its.caltech.edu/~qoptics/teleport.html
which says (among other things)

In quantum teleportation, an unknown quantum state is faithfully
transferred from a sender (Alice) to a receiver (Bob). To perform
the teleportation, Alice and Bob must have a classical communication
channel and must also share quantum entanglement -- in the protocol
we employ*, each possesses one half of a two-particle entangled
state. Alice makes an appropriate projective measurement (Bell
measurement) of the unknown state together with her component of the
shared entangled state. The result of this measurement is a random
piece of classical information which Alice sends to Bob over their
classical communication channel. Bob uses this information to
choose a unitary transformation which he performs on his component
of the shared entangled state, thus transforming it into an output
state identical to the original (unknown) input.

Note particularly the bits about the classical communication channel
involved in the process.


Wayne Throop http://sheol.org/throopw
  #14  
Old October 6th 06, 05:14 AM posted to sci.space.policy
Wayne Throop
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Posts: 1,062
Default Scientists teleport two different objects

: Alan Anderson
: I choose to indulge in the semantic shortcut of considering the act of
: moving the quantum state from one object to another to be just as good
: as moving the object which has that state. I further choose to believe
: that we can disagree on this topic without either of us being
: objectively wrong.

Well OK, but note that the only novel thing is the xfer of *quantum*
state; classical or nigh-classical states could be moved in that way
(ie, an atom emits a photon, another one somewhere else absorbs it and
gets the "same" excited state the original had), but nobody says they
"teleported" the atom. I don't quite see why quantum-ness deserves the
upgrade in terminology.


Wayne Throop http://sheol.org/throopw
  #15  
Old October 6th 06, 09:56 AM posted to sci.space.policy
[email protected][_1_]
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Default Scientists teleport two different objects


Wayne Throop wrote:
: Alan Anderson
: I choose to indulge in the semantic shortcut of considering the act of
: moving the quantum state from one object to another to be just as good
: as moving the object which has that state. I further choose to believe
: that we can disagree on this topic without either of us being
: objectively wrong.

Well OK, but note that the only novel thing is the xfer of *quantum*
state; classical or nigh-classical states could be moved in that way
(ie, an atom emits a photon, another one somewhere else absorbs it and
gets the "same" excited state the original had), but nobody says they
"teleported" the atom. I don't quite see why quantum-ness deserves the
upgrade in terminology.


Assuming that tech wasn't a major issue and extremely high (but finite)
effort can be applied to the task, does this actually allow a perfect
copy ?

My (limited) understanding of the process is that it is a method to
just bypass Heisenberg. However, the copy is not perfect as it is a
digital process. In effect, what it allows is that the position and
velocity of every particle in a person's body to be "measured" to any
finite accuracy (though the measurement doesn't actually require
observing the particle directly). This position and velocity can then
be applied to the target atomic particles.

Presumably, the amount of classical bits transmitted and entangled bits
required are equal. Also, the number of bits is equal to the
"measurement" resolution.

In principle, the process could be applied directly to quarks rather
than dealing with protons and neutrons. In fact, the lower down the
particle scale, the more accurate the reproduction.

OTOH, it is likely that a person's personhood is based purely on the
configuration of atoms in the brain and EM fields (maybe). Maybe there
is a need to also copy any photons floating around in the brain . In
fact, it is not really the atoms, people have no problem with the fact
that the atoms that make up their bodies are constantly changing. It
is the patten that counts.

  #18  
Old October 9th 06, 03:09 AM posted to sci.space.policy
Alan Anderson
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Posts: 335
Default Scientists teleport two different objects

" wrote:

Can it not be used to copy the position of an atom ?

For example, if I have 3 entangled photons, can I copy the position of
an atom to 3 bits of resolution ?

Step one: confirm the source atom is in a volume much larger than
Heisenberg's limit.

Step two: Do some fancy measurements in conjunction with the photons.
The measurements would be a binary search or something.

Step three: Use the other half of the photons + results of measurement
to position the other atom.

This then copies the atom's position ... but only to 3 bits of accuracy.


I can't tell what you're asking. Your words do not match anything I
know of regarding quantum teleportation.

What quantum teleportation does is to transfer the quantum state of a
target object to to a destination object with perfect fidelity. That
would be something like its polarization or its spin. It has to lose
the original state in the process, so it isn't able to "copy" anything.

(Position can already be measured to an arbitrary precision using
classical methods, though you lose information on momentum as you gain
it in position and vice versa.)
  #19  
Old October 9th 06, 04:20 PM posted to sci.space.policy
[email protected]
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Posts: 24
Default Scientists teleport two different objects


RobH wrote:
Scientists teleport two different objects
POSTED: 4:36 p.m. EDT, October 4, 2006

[fun with quantum entanglement]


Am I correct in thinking that this technology is FTL, and not subject
to any kind of range restriction or interference/ signal blockage?

Can we therefore imagine that some future interplanetary mission might
take with it a lump of entangled particles (having left the entangled
'mates' of those particles back on Earth), allowing the spacecraft and
mission control to exchange data instantaneously, no matter how far
away the craft travels?

What would the bandwidth be like? Presumably it would be 1 bit per
entangled particle pair, but is there any restriction on the rate at
which these bits can be sent other than the speed at which the the
computers involved can 'read' and 'write' the particles? However, I
suppose there would be a finite amount of data that could be
transmitted in this way, defined by the amount of entagled particles
available to the ship. What would we call that, 'banddepth'? Given that
these particles are at an atomic scale though, I imagine a just a few
grams of material would be enough for many billions of bits of data.

The advantages of eliminating comm-lag for manned space travel are
obvious, but I could see that even on unmanned missions this would do
away with a lot of hassles associated with traditional radio
transmissions.

Or have I misunderstood completely? The only future applications the
articles I've read seem to be interested in are secure data
communication (very exciting for gov, mil and biz I'm sure but...
well.... *yawn* ) and "beam me up scotty" style teleportation (which,
let's face it, ain't gonna happen).

I find it hard to believe that such a potentially revolutionary
technology (a) really is as useful as I understand it to be and (b)
isn't generating more of a buzz.

Someone please correct my misconceptions (if I have expressed any).

 




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