A scalable quantum computer chip for atomic qubits has been built
for the first time by researchers at the University of Michigan
(Christopher Monroe, email@example.com), offering hopes for making
a practical quantum computer using conventional semiconductor
Exploiting the strange rules of the
atomic world, quantum computers could potentially break top-secret
codes and perform certain kinds of searches much more quickly than
conventional computers. The building blocks of quantum computers
are called "qubits," or quantum bits, made of such objects as atoms
or photons. Connecting multiple qubits via an electrostatic (or
other suitable) interaction could then result in a quantum computer,
similar to how wiring together individual transistors can make a
Unlike a conventional computer's bits, which
can have values of either 0 or 1, a qubit can possess a value of 0
and 1 simultaneously, analogous to a light switch that's on and off
at the same time. For their qubit the Michigan group chose an
individual cadmium ion, held in free space by a number of electrodes
inside a postage-stamp-sized gallium arsenide semiconductor chip.
There additional electric fields are able to manipulate the position
of the ion, and laser beams could control the qubit value in the
Ions pose an advantage over other potential qubits, such as
photons and electron dots, in that they are easier to isolate and
shield from external disturbances (noise) that can disrupt their
operation. An integrated semiconductor chip is a markedly
different environment for ion qubits, which were previously held in
hand-made ion traps that could not be easily scaled up or mass
The researchers have not yet demonstrated a quantum
computer based on this design, as it only consists of a single
qubit. Making a quantum computer would require scaling up a single
chip so that it contains enough electrodes to trap many ions
simultaneously (Stick et al.,
Nature Physics, January 2006).
This has been a busy month for announcements in the ion computing
realm: groups at the
National Institute of Standards and Technology in Boulder, Colo.
(Leibfried et al.,
Nature, December 1), and at Innsbruck University in Austria
(Häffner et al.,
Nature, December 1) independently reported
entangling up to eight ions, while the Michigan
group used another setup to perform a simple version of a quantum
search known as Grover's algorithm.
(Brickman et al., Physical Review
A, November 2005).
Stick et al.,
Nature Physics, January 2006.
Nature Physics is a new journal that began publication
in October 2005.