Over the last half century, the components of computers have gotten
smaller by a factor of two every 18 months, a phenomenon known as
Moore's law. In
state-of-the-art computers, the smallest wires and transistors are
approaching 100 nm feature size, which is approximately 1000x the
diameter of an atom. Quantum mechanics is the theory of physics that
describes the behavior of matter and energy in extreme conditions,
such as short times and tiny distances. As transistors and wires
become smaller and smaller, they inevitably begin to behave in intrinsically
quantum mechanical ways. Thus, whereas the quantum mechanics of semiconductor
band theory has given us the microprocessors and laser diodes that
have fueled our information ageís computers and communication
systems, these technologies have not exhibited macroscopically quantum-mechanical
effects. This will no longer be true as we drive forward to ever
smaller and faster devices, and so it becomes essential to address
information science in a fully quantum mechanical setting, viz.,
we need quantum computers and quantum communications.
Quantum computers and quantum communication systems operate at the
level of individual quanta—atoms, photons, and electrons.
They store, process, and transmit information at the smallest possible
scales, and using the minimum possible energy. Even if Moore's
law persists, commercial quantum computers are not yet due on the
shelves for another few decades; nonetheless, prototype quantum computers
consisting of a small number of atoms and quantum communication systems
that use single photons have been built and operated. Quantum
mechanics is famously counterintuitive. (Einstein, despite making
great contributions to quantum mechanics, never fully accepted it.)
Quantum computers and communication systems exploit quantum weirdness
to do things that classical information technologies cannot. A quantum
computer could search databases and break codes that no classical
computer could search or break. Quantum communication systems
allow the creation of unbreakable codes, and could be used to teleport
the state of matter from one place to another. Quantum enhancements
to the Global Positioning System (GPS) could greatly enhance its
accuracy.
What more could quantum computers and quantum communication systems
do? Might quantum computers be able to solve harder problems than
code breaking? Could quantum communication channels convey information
at much higher rates than conventional radio frequency or optical
communication channels? What are the ultimate attainable accuraciesóbased
on the laws of physicsóof
measurement and sensing systems such as GPS? Despite much productive
research into the theory of quantum computation and quantum communication,
the answers to these questions are not known. The ultimate capabilities
of quantum computers and quantum communication systems, pressed to
their extremes, remain to be discovered. Our efforts to meet these
challenges will focus on three areas:
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