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The
science-fiction fantasy of nanotechnology — building
novel structures, devices, and materials at the atomic
or molecular scale — is becoming a reality. For the
great potential of nanoscience and nanotechnology to be
fully realized, however, research efforts must cross many
disciplines, from electrical engineering, mechanical engineering,
materials science, and computer science to bioengineering,
chemistry, and physics.
Nowhere
is this cross-disciplinary approach fostered more than
at UC Berkeley. Each month, Lab Notes is proud
to present the work of nanotechnology researchers from
the College of Engineering and our collaborators across
the campus.
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Catching the Quantum Bus
by David Pescovitz
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version
The Stamper-Kurn Research Group: in front, J. Higbie, L. Sadler, K. Moore; in back, R. Johnson, D. Stamper-Kurn, B. Van Dusen.
Courtesy Stamper-Kurn Group
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While UC Berkeley engineers tackle the architectural challenges of building a quantum computer, experimental physicists at the university are helping design the basic building blocks necessary to make these miraculous machines a reality.
Arguably the next step after silicon-based microprocessors, quantum
computers promise to crank out calculations a billion times faster
than today's integrated circuits. By exploiting the unusual characteristics
of quantum mechanics, the tiny systems could help us quickly solve
problems that cripple even the fastest of today's supercomputers
— for example, determining the physical structure of proteins,
important in developing new drugs for diseases like cystic fibrosis.
The power of a quantum computer could also be harnessed to generate
uncrackable encryption codes for highly sensitive data.
Berkeley experimental physicist Dan Stamper-Kurn's contribution to the quantum computing challenge begins at the very bottom.
"The universe itself can be entirely described by quantum mechanics," Stamper-Kurn says. "But we don't have the tools to engineer a complicated quantum object."
The key ingredient in a quantum computer is the qubit, the
equivalent of the binary zero or one bit of a digital computer.
There are a variety of physical systems being considered as candidates
for qubits. For example, quantum scientists have intensely studied
the single neutral atom and developed precise tools for control
and detection of these particles. Indeed, controlling atoms' internal
and external motional states have led to several Nobel Prizes.
The power of quantum computers lies in a qubit's ability to exist
in a zero or one state, or a superposition somewhere in the middle,
or, oddly, both at one time. This quantum weirdness is what enables
quantum computers to process so much data at once. Essentially,
each qubit represents two values at one time. As more qubits are
strung together, the power of the quantum processor grows exponentially.
"The current frontier is attaining maximal control of collections of atoms, which amounts to the creation of a universal quantum computer," Stamper-Kurn says.
Reliably stringing the qubits together remains problematic, he explains. Essentially, the atoms act as quantum memory, but we're lacking quantum wires to connect the atoms together.
To make the equivalent of a silicon computer's bus, a group of connections between devices, Stamper-Kurn is applying his expertise in cavity quantum electrodynamics. He and his colleagues are making progress building tiny boxes, or cavities, that confine individual atoms and photons between tiny mirrors less than 100 microns apart.
Acting as a qubit,
the confined atom communicates its state — equivalent to a
zero, one, or, thanks to quantum physics, somewhere in between —
to the photon and vice versa. The bit of information is converted
into light that travels around the quantum
computer via traditional optics, landing in other cavities and sharing its information
with the qubits there.
"The term for this is a flying qubit," Stamper-Kurn says. "Combining flying qubits together with the atoms in the cavities creates what could be transistors for a quantum computer."
Stamper-Kurn Group's Deterministic Cavity Quantum Electrodynamics Research
"A Quantum Leap in Computing" by David Pescovitz (Lab Notes)
Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking
research underway today at the College of Engineering that will dramatically change our lives tomorrow.
Editor, Director of Public Affairs: Teresa Moore
Writer, Researcher: David Pescovitz
Designer: Robyn Altman
Subscribe or send comments to the Engineering Public Affairs Office: lab-notes@coe.berkeley.edu.
© 2003 UC Regents.
Updated 5/2/03.
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