quantum pot boils slower
Technology Research News
The Greek philosopher Zeno argued that
motion does not exist because at any given point in an arrow's flight,
it is not moving, and because it is still at all points of flight it never
Though mathematicians solved this paradox long ago by introducing the
concept of real numbers to describe quantities of duration and distance,
the notion of freezing motion by observing it turns out to be a very real
effect in the strange world of quantum physics.
Researchers at the University of Texas at Austin have demonstrated the
Quantum Zeno Effect and Anti-Zeno Effect in sodium atoms trapped in a
pair of laser beams.
The trapped sodium atoms escape over time, a process physicists call decay.
By observing the atoms repeatedly at very short time intervals the researchers
were able to either reduce or increase the probability that the atoms
would escape after a certain amount of time.
The Quantum Zeno Effect holds the tantalizing possibility of bolstering
the notoriously fragile quantum systems used in today's rudimentary quantum
Likewise, the related Anti-Zeno Effect could hinder certain quantum computing
schemes because the frequent measurements could hasten the demise of a
quantum computer's tenuous bits.
Quantum bits, or qubits,
can represent the ones and zeros of computing using distinct states of
atoms or subatomic particles like magnetic orientation. If large-scale
quantum computers can be built, they would be phenomenally fast for certain
applications like cracking codes and searching large databases.
The researchers induced the Quantum Zeno Effect by observing their quantum
system every microsecond, or millionth of a second. They brought about
the Anti-Zeno Effect by observing the system every five microseconds.
"Just by looking at the system periodically one can modify decay," said
Martin C. Fischer, who was a graduate student at the University of Texas
at Austin when the research was conducted. "If measurements are performed
at very short time intervals, the decay can be strongly suppressed, whereas
observations at intervals slightly larger can enhance the decay."
The Quantum Zeno Effect doesn't produce a specific slower rate of decay
but rather increases the probability that the atoms will be in the trap
at a given point in time. "We achieved about 40 percent larger probability
of survival at a certain time of decay, but that, of course, is not really
a fixed number," said Fischer.
Delaying the escape of trapped sodium atoms isn't itself useful for quantum
computing, but a better understanding of the Quantum Zeno Effect and Anti-Zeno
Effect could play a role in quantum computing, said Fischer.
Although it's early to speculate about applications in quantum computing,
the experiment does show that reduction of decay by measurement is possible,
said Fischer. "Quantum computing requires more elements, but this experiment
might provide an important ingredient," he said.
Preliminary investigations into using the Quantum Zeno Effect to make
sturdier quantum computers are not all that promising, said Paul Kwiat,
a physics professor at the University of Illinois at Urbana-Champaign.
"But there are new paradigms all the time," he added. "I wouldn't be surprised"
if in five years the effect could be used in quantum computing, said Kwiat.
"I also would not be surprised if it's not useful."
On the other hand, the Anti-Zeno Effect could be cause for concern, said
The equivalent of decay in a quantum computer, decoherence, occurs when
energy from the environment knocks qubits out of their quantum states.
Qubits are made from atoms or subatomic particles that are in the quantum
state of superposition, which is a mixture of the two states that are
used to represent the ones and zeros of computing. Controlling this mixture
allows quantum computers to examine all possible answers to a problem
at the same time.
Because it is challenging to stave off decoherence even for small numbers
of qubits, researchers are looking to use error correction schemes. But
quantum error correction schemes require frequent observations and some
researchers fear they could induce the Anti-Zeno Effect, said Kwiat.
Whether or not the Quantum Zeno Effect can be harnessed to improve quantum
computers, many researchers say it will be at least two decades before
practical quantum computers can be developed.
"I don't think I will see a functional quantum computer on a level that
could compete with conventional PCs in the next couple of decades. But
you never know," said Fischer.
Fischer's research colleagues were Braulio Gutiérrez-Medina and Mark G.
Raizen of the University of Texas at Austin. Their research has been accepted
for publication in the journal Physical Review Letters. The research was
funded by the National Science Foundation (NSF), the R. A. Welch Foundation
and the Sid W. Richardson Foundation.
Timeline: >20 years
Funding: Government; Private
TRN Categories: Quantum Computing
Story Type: News
Related Elements: Technical paper, "Observation of the Quantum
Zeno and Anti-Zeno effects in an unstable system," Physical Review Letters,
accepted for publication
Pen and paper networked
closer to computing
choices key for speech software
tales into animations
Watched quantum pot
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link