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©
Geoffrey Wheeler
NIST
physicist David Wineland adjusts an ultraviolet laser
beam used to manipulate ions in a high-vacuum "ion
trap" used to 'teleport' the quantum state of one
atom to another. |
Physicists
at the Commerce Department’s
National Institute of Standards
and Technology (NIST) have demonstrated “teleportation”
by transferring key properties of one atom to another atom
without using any physical link, according to results reported
in the June 17, 2004, issue of the journal Nature.
Unlike
the “beaming” of actual physical objects and people
between distant locations popularized in the Star Trek
science fiction series, the term “teleportation”
is how physicists describe a transfer of “quantum states”
between separate atoms. The quantum state of an atom is a
description of such things as its energy, motion, magnetic
field and other physical properties.
The NIST
experiments used laser beam manipulations to transfer quantum
states of one beryllium atom to another atom within a set
of microscale traps, with a 78 percent success rate. The technique
may prove useful for transporting information in quantum computers
of the future, which could use central processing elements
smaller than a cube of sugar to carry out massively complex
computations that are currently impossible.
If they
can be built, quantum computers—harnessing the strange
behavior of particles at the atomic scale—someday might
be used for applications such as code breaking of unprecedented
power, optimizing complex systems such as airline schedules,
much faster database searching and solving of complex mathematical
problems, and even the development of novel products such
as fraud-proof digital signatures.
|
Teleportation
takes place inside an ion trap made of gold electrodes
deposited onto alumina. The trap area is the horizontal
opening near the center of the image. |
The NIST
work and other research by the University of Innsbruck reported
in the same issue of Nature mark the first demonstrations
of teleportation using atoms. Systems using atoms are arguably
the leading candidate for storing and processing data in quantum
computers. Teleportation could increase computing speed and
efficiency by linking distant zones within a computer so that
data could be processed by physically separated quantum bits
(or qubits, the quantum form of the digital bits 1 and 0).
Quantum
computing with atomic qubits requires manipulation of information
contained in the quantum states of the atoms. “It’s
hard to quickly move qubits to share or process information.
But using teleportation as we’ve reported could allow
logic operations to be performed much more quickly,”
says NIST physicist David
Wineland, leader of the NIST work.
The NIST
group previously has demonstrated the building blocks for
a quantum computer based on atomic-ion traps. The new experiments,
which are computer controlled and perform teleportation in
about 4 milliseconds, incorporate most of the features required
for large-scale information processing systems using ion traps.
In addition, the experiments are relatively simple in design
and could be used as part of a series of logical operations
needed for practical computing.
The demonstration
described in the Nature paper exploited quantum properties
that are radically different from the properties observed
in the “normal” world. For example, ions can be
manipulated into a special state known as a “superposition”
in which they literally can be in two places at once. Similarly,
they also can hold information representing more than one
number at once, a common property of all qubits. Ions also
can be “entangled” with each other, so that their
behavior is related in predictable ways, as if they were connected
by an invisible force. Einstein called this “spooky
action at a distance.”
The NIST
experiments entangled a set of three ions, then destroyed
the quantum state in one ion and teleported it to another
one. The properties that were teleported included the “spin
state” of the ion (up, down or a superposition of the
two), and the “phase” (which has to do with the
relative positions of the peaks and troughs of an ion’s
wave properties). A clever approach was required because of
another unusual feature of the quantum world: measurements
always alter quantum states (for example, causing superpositions
to collapse). Therefore, the experiment teleported the quantum
state without measuring it.
The ions
were teleported inside a NIST-developed multi-zone trap, first
described in 2002. Lasers are used to manipulate the ion’s
spin and motion, and to entangle the ions by linking their
internal spin states to their external motion. A key technical
advance reported in the current paper is the capability to
entangle ions and then separate them in the trap (maintaining
entanglement) without generating much heat. This previously
led to uncontrolled motions that interfered with operations
and required additional cooling operations. The advance was
enabled in part by the use of smaller electrodes to generate
electric fields that move the ions between trap zones.
The research
was supported in part by the Advanced Research and Development
Activity and the National Security Agency.
More
information about NIST research on quantum computing can be
found at http://qubit.nist.gov.
A non-regulatory
agency of the U.S. Department of Commerce, NIST develops and
promotes measurement, standards, and technology to enhance
productivity, facilitate trade and improve the quality of
life.
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Created:
06/16//04
Last
updated:
06/17/2004
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