Entangled photons could promise lightning-speed computers

Using modern quantum physics, a research team from NASA's Jet
Propulsion Laboratory (JPL), Pasadena, CA, and the University of
Wales in the United Kingdom has discovered that entangled pairs of
light particles, called photons, can act as a single unit, but
perform with twice the efficiency.

Using a process called "entanglement," the research team proposes
that existing sources of laser light could be used to produce
smaller and faster computer chips than current technology allows.
Their paper appears in the today's issue of the journal Physical
Review Letters.

"Our economy constantly depends on faster and faster computers,"
said JPL researcher Dr. Jonathan Dowling, a co-author of the
paper. "This research potentially could enable us to continue
upgrading computers even after traditional manufacturing
procedures have been exhausted."

Currently, in a process known as optical lithography,
manufacturers use a stream of light particles to sculpt computer
chips. A chip is basically a grid of interconnected on-off
switches, called transistors, through which electric current flows
and enables computers to calculate. As companies crowd millions of
transistors into tinier chips, electric current travels shorter
distances, resulting in speedier processes.

Chipmakers shine a laser light onto photosensitive material to
create a stencil-like mask, which is used to carve silicon into
the components of transistors. However, the producers can only
provide transistors with dimensions as small as those of the
masks.

Today's state-of-the-art chips have transistors measuring between
180 and 220 nanometers, approximately 400 times narrower than the
width of a human hair. While traditional computers have the
ability to perform with transistors as small as 25 nanometers, or
3,000 times narrower than a human hair, this presents
manufacturing obstacles.

The light manufacturers use to produce today's transistors has a
wavelength of 248 nanometers. It becomes increasingly difficult to
use light with shorter wavelengths to produce transistors with
smaller dimensions. In fact, according to a central principle of
optics called the "Rayleigh criterion," 248-nanometer light can't
create features smaller than 124 nanometers.

However, this new research, still in its theoretical stage, could
provide a bypass of the Rayleigh criterion. The research team
proposes that entanglement would allow the use of existing sources
of laser light of 248 nanometers to produce computer chips with
dimensions of a fourth of the wavelength (62 nanometers) or
smaller compared to today's limits (124 nanometers).

Entanglement would allow researchers to use the intermingled
properties of two or more photons to obtain subwavelength spatial
resolutions. Albert Einstein called this intermingling of photons
process "spooky action at a distance" because the particles can
immediately influence each other over huge distances, even halfway
across the galaxy.

Here on Earth, entangled photons can be produced by passing a
light beam through a special crystal. In this quantum lithography
proposal, a pair of entangled photons enters a setup with two
paths. While the two particles travel together and act as a single
unit, it is impossible to determine which of the two paths the
pair has taken. In a strange effect of quantum mechanics, however,
each photon actually travels down both paths.

On each path, the photons act like a rippling wave with peaks and
valleys. After traveling on their own path for a while, the two
photons converge on a surface. Because the light particles making
up each wave were originally entangled, the result of adding the
photon waves together is to create patterns on the surface
equivalent to those made by a single photon with half the
wavelength.

This process, in essence, enables the entangled photon pair to
produce patterns twice as small on each side of a chip's surface
as can be created by the single photons in the conventional
optical lithography procedures. Entangling more than two photons
would improve results even further.

While a number of technical challenges remain, researchers are
already working on developing materials that would be required for
quantum lithography.

This research is part of the Revolutionary Computing Technology
project in the NASA/JPL Center for Integrated Space Microsystems
(CISM). CISM is supported by the Deep Space Systems Program in
NASA's Office of Space Science. JPL is managed for NASA by the
California Institute of Technology in Pasadena.

(Source: NASA News Press Release)

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