Teleport lifts quantum computing
Technology Research News
A leading candidate architecture for quantum
computing -- trapped ions -- has received a significant boost with a pair
of teleportation experiments that show is possible to reliably and readily
shuttle information within a quantum computer.
The experiments, from the University of Innsbruck in Austria and
the National Institute of Standards and Technology (NIST), have also advanced
the practice of teleportation.
Each team transported the states of charged atoms and showed that
it is possible to do so on demand. Previous teleportation experiments
used photons and were probabilistic, meaning each attempt had only a certain
probability of succeeding.
The method allows quantum bits, or qubits, to be stored before
and after teleportation so that quantum computers can process information,
move it to a different part of the computer and then process it further.
Teleportation is based on the strange phenomenon of entanglement,
which links the traits of particles like atoms and photons regardless
of the distance between the particles. When one of a pair of entangled
particles is observed, it assumes a definite state, and at the same instant,
the other particle assumes the opposite state.
Teleporting the state of a particle is akin to faxing a document
and in the process destroying the original. Teleportation requires three
particles. Two of the particles are entangled and one is held by the sender
and the other sent to the receiver.
The third particle is teleported when the sender brings it into
contact with her half of the entangled pair and measures both particles,
which transfers the quantum information of the third particle to the entangled
particle and in the process destroys the original. The sender then gives
the receiver via an ordinary communication line information about how
she measured the particles. The receiver performs the same measurement
on his half of the entangled pair, which converts it into a copy of the
The University of Innsbruck researchers teleported the quantum
states of calcium ions trapped in a radio-frequency electric field. Electrodes
shaped the field in a way that forced the ions into a row. The NIST researchers
used a similar setup to teleport the quantum states of beryllium ions.
Qubits formed from ions last much longer than qubits formed from
photons, which exist for a small fraction of a second and are difficult
to store. "In related experiments using our beryllium ion qubits, we have
observed [quantum] states to be preserved for longer than 10 minutes,"
said David Wineland, group leader for ion storage at NIST. This is more
than enough time to use the information in computing operations.
The ion teleportation schemes provide a means for moving information
within a quantum computer without having to move the ions themselves.
In most large-scale quantum processor schemes, moving information by moving
qubits directly takes a relatively long time, said Wineland. In contrast,
teleportation speed is determined by the time it takes to transmit classical
signals, which is limited only by the speed of light, he said.
Ion-based quantum computer architectures generally require that
quantum information be moved frequently. Trapped-ion quantum information
processors are likely to need several small quantum registers, or sets
of qubits, to store, process and error-check information, said Rainer
Blatt, a professor of physics at the University of Innsbruck. Information
could be readily transmitted between registers using teleportation, he
The experiments are significant because the quantum states of
ions, which are relatively massive particles, have been teleported, said
Steven van Enk, a researcher at Lucent Technologies' Bell Labs. "The advantage
is that the state of an ion can be stored for a long time," he said. Teleportation
has only previously been achieved using photons, which are massless particles
of light, and whole light beams.
In addition, the process is reliable, and the state that has been
teleported is available for another round of quantum information processing,
said van Enk. "The significance is that the experiments were done in setups
that are very promising candidates for quantum computing." The two teams
used different techniques, both of which can ultimately be used in quantum
computers, he added.
There are two big advantages to using teleportation to transfer
information within quantum computers, said van Enk. It makes it possible
to perform a two-ion operation on ions that are not close to one another,
and it increases the computer's error threshold, which means the computers
would be easier to make, he said. Without teleportation, the error threshold,
or acceptable error rate, is around one in 10,000, or 1 percent of 1 percent;
teleportation increases the error threshold to about 1 percent, making
the computer more resilient to errors, he said.
Practical applications for full quantum computers that have several
hundred thousand qubits are one or two decades away, but specialized applications
that require only a few qubits are two to five years away, and applications
that require 10 to 20 qubits are five to ten years away, said Blatt. "One
of the not-so-distant applications might be a quantum repeater, that is
a small quantum computer node for long distance quantum communication,"
Useful simulations of other quantum systems and practical applications
in quantum measurement be possible within the next decade, said Wineland.
A useful factoring machine is likely to take much longer, he added.
Blatt's research colleagues were Mark Riebe, Hartmut Häffner,
Christian F. Roos, Wolfgang Hänsel, Jan Benhelm, Gavin P. T. Lancaster,
Timo W. Körber, Christoph Becher and Ferdinand Schmidt-Kaler of the University
of Innsbruck, and Daniel F. V. James of the Los Alamos National Laboratory.
The work appeared in the June 17, 2004 issue of Nature. The research
was funded by the Austrian Science Fund (FWF), the Austrian Ministry for
Education, Science and Culture (bm:bwk), the Institute for Quantum Information
(IQI), the Advanced Research and Development Activity (ARDA), the European
Union (EU), and the Austrian Academy of Sciences.
Wineland's research colleagues were Murray Barrett, John Chiaverini,
Tobias Schaetz, Joe Britton, Wayne Itano, John Jost, Emanuel Knill, Chris
Langer, Dietrich Leibfried and Roee Ozeri. The work appeared in the June
17, 2004 issue of Nature. The research was funded by the Advanced
Research and Development Activity (ARDA), the National Security Agency
(NIST), and the National Institute of Standards and Technology (NIST).
Timeline: 1-2 decades
Funding: Government, Private
TRN Categories: Quantum Computing and Communications
Story Type: News
Related Elements: Technical paper, "Deterministic Quantum
Teleportation with Atoms," Nature, June 17, 2004; Technical paper, "Deterministic
Quantum Teleportation of Atomic Qubits", Nature, June 17, 2004.
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