Seeking Quantum Leap
In the Computing World
By JOHN MARKOFF
SANTA BARBARA, California — Modern computers are not unlike the
looms of the industrial revolution: They follow programmed
instructions to weave intricate patterns. With a loom, you see the
result in a cloth or carpet. With a computer, you see it on an
electronic display.
Now a group of physicists and computer scientists
funded by Microsoft is trying to take the analogy of interwoven
threads to what some believe will be the next great leap in
computing, so-called quantum computing.
If the scientists are right, their research could
lead to the design of computers that are far more powerful than
today’s supercomputers and could solve problems in fields as
diverse as chemistry, material science, artificial intelligence and
code-breaking.
They recently met to explore an approach to quantum
computing that is based on “braiding” exotic particles known as
anyons — what physicists describe as “quasiparticles” that exist in
just two dimensions rather than three — in order to form the
building blocks of a supercomputer that exploits the weird physical
properties of subatomic particles.
Conventional computing is based on a bit that can
be either a 1 or a 0, representing a single value in a computation.
But quantum computing is based on qubits, which simultaneously
represent both 0 and 1 values. If they are placed in an “entangled”
state — physically separated but acting as though they are
connected — with many other qubits, they can represent a vast
number of values simultaneously.
And the existing limitations of computing power are
thrown out the window. In the approach that Microsoft is pursuing,
which is described as “topological quantum computing,” precisely
controlling the motions of pairs of subatomic particles as they
wind around one another would manipulate entangled quantum bits.
Although the process of braiding particles takes place at subatomic
scales, it is evocative of the motions of a weaver overlapping
threads to create a pattern.
The mathematics of their motions would correct
errors that have so far proved to be the most daunting challenge
facing quantum computer designers.
First proposed by the physicist Richard Feynman in
1982, quantum computing has mostly been of interest to academics,
the National Security Agency and the Pentagon’s Defense Advanced
Research Projects Agency.
But in recent years, quantum computing has caught
the attention of the corporate world. While scientists have created
individual qubits, they are extremely fragile, and creating the
arrays of hundreds or thousands of circuits necessary to build a
useful quantum computer has proved daunting. Microsoft’s
topological approach is generally perceived as the most high-risk
because the type of anyon particle needed to generate qubits has
not been definitively proved to exist.
That may change soon. The company has been
exploring a long-hypothesized class of subatomic particles known as
Majorana fermions. Proving their existence would mean that it was
likely they could be used to form qubits.
Microsoft supported research, led by the physicist
Leo Kouwenhoven at the Delft University of Technology in the
Netherlands, that in 2012 produced the strongest evidence that the
long-predicted particles exist.
“They have really done something very special,”
said Charles M. Marcus, a physicist at the University of
Copenhagen.
His laboratory is now growing molecular-scale
nano-wires that will work like one-dimensional train tracks, making
it possible to control the movement of fermions around one
another.
Ensembles of these particles can be used to
construct qubits in the topological computing model proposed by the
mathematician Michael Freedman and the physicists Chetan Nayak and
Sankar Das Sarma in 2005.
Microsoft began supporting the effort after Dr.
Freedman approached Craig Mundie, one of Microsoft’s top
executives, and convinced him that there was a new path to quantum
computing based on ideas in topology originally proposed in 1997 by
the physicist Alexei Kitaev.
Mr. Mundie said the idea struck him as the kind of
gamble the company should be pursuing.
The researchers acknowledge that they have not yet
even made a working prototype of the basic element of their
system.
Many thought quantum computers would be useful only
for factoring huge numbers. But now many scientists believe that
quantum computers could tackle new kinds of problems.
When Mr. Mundie asked Dr. Freedman what he might do
with a working quantum computer, he said that the first thing he
would program it to do would be to model an improved version of
itself.
Today, The New York Times International Weekly, Saturday, July 5,
2014, Pg 11