first programmable quantum computer created
RMJon23
Ultracold beryllium ions tackle 160 randomly chosen programs
By Laura Sanders Web edition : Monday, November 23rd, 2009
Using a few ultracold ions, intense lasers and some electrodes,
researchers have built the first programmable quantum computer. The
new system, described in a paper to be published in Nature Physics,
flexed its versatility by performing 160 randomly chosen processing
routines.
Earlier versions of quantum computers have been largely restricted to
a narrow window of specific tasks. To be more generally useful, a
quantum computer should be programmable, in the same way that a
classical computer must be able to run many different programs on a
single piece of machinery.
The new study is “a powerful demonstration of the technological
advances towards producing a real-world quantum computer,” says
quantum physicist Winfried Hensinger of the University of Sussex in
Brighton, England.
Researchers led by David Hanneke of the National Institute of
Standards and Technology in Boulder, Colo., based their quantum
computer on two beryllium ions chilled to just above absolute zero.
These ions, trapped by an electromagnetic field on a gold-plated
alumina chip, formed the quantum bits, or qubits, analogous to the
bits in regular computers represented by 0s and 1s. Short laser bursts
manipulated the beryllium ions to perform the processing operations,
while nearby magnesium ions kept the beryllium ions cool and still.
Hanneke and colleagues programmed the computer to do operations on a
single beryllium ion and on both of the beryllium ions together. In
the quantum world, a single qubit can represent a mixture of 0 and 1
simultaneously, a state called a superposition. A laser pulse
operation could change the composition of the mixture within the
qubit, tipping the scales to make the qubit more likely to become a 1
when measured.
Both of the qubits together could be entangled, a situation where the
two qubits are intimately linked, and what happens to one seems to
affect the fate of the other. Different combinations of one- and two-
qubit operations made up various programs. “We put all these pieces
together and asked, what can we do with the circuit?” Hanneke says.
Hanneke and colleagues chose 160 programs for the quantum computer to
run. “We picked them, quite literally, at random,” Hanneke says. “We
really wanted to sample all possible operations.”
The researchers ran each program 900 times. On average, the quantum
computer operated accurately 79 percent of the time, the team reported
in their paper, which was published online November 15. “Getting this
kind of control over a quantum system is really interesting from a
physics perspective,” Hanneke says.
Earlier research has estimated that to be useful, a quantum computer
must operate accurately 99.99 percent of the time. Hanneke says that
with stronger lasers and other refinements, the system’s fidelity may
be improved.
Experimental physicist Boris Blinov says that one of the most exciting
things about the new study is that the quantum computer may be scaled
up. “What’s most impressive and important is that they did it in the
way that can be applied to a larger-scale system,” says Blinov, of the
University of Washington in Seattle. “The very same techniques they’ve
used for two qubits can be applied to much larger systems.”