Computing - Kwantumcomputer
U-M develops scalable and mass-producable
quantum computer chip
ANN ARBOR, Mich.---Researchers at the University of Michigan have produced what
is believed to be the first scalable quantum computer chip, which could mean
big gains in the worldwide race to develop a quantum computer.
Using the same semiconductor fabrication technology that is used in everyday
computer chips, researchers were able to trap a single atom within an integrated
semiconductor chip and control it using electrical signals, said Christopher
Monroe, U-M physics professor and the principal investigator and co-author of
the paper, "Ion Trap in a Semiconductor Chip." The paper appeared in the Dec.
11 issue of Nature Physics.
Quantum computers are promising because they can solve certain problems much
faster than any possible conventional computer, owing to the bizarre features
of quantum mechanics. For instance, quantum computers can process multiple inputs
at the same time in the same device, and quantum circuitry can be wired via the
quantum feature of entanglement, dubbed by Einstein as "spooky action-at-a-distance."
One of the most favored candidate quantum computer architectures is the use of
individual atoms to store quantum bits (qubits) of information, where each qubit
can hold the number 1 or 0, or even both 1 and 0 simultaneously, Monroe said.
Electrically charged atoms (ions) for such quantum computers are stored in what
are known as ion traps. Trapping is necessary in order to isolate the qubits
from the rest of the world, which is absolutely essential for the system to behave
quantum mechanically. It is well known how to program a quantum computer composed
of any number of trapped ions; the problem is to get the ions trapped in the
Current ion traps can only hold a few atoms or qubits, and are not easily scaled.
Rather, these ion traps are assembled laboriously by hand. Therefore, one of
the obstacles to perfecting the quantum computer is making a scalable integrated
quantum computer chip that can store thousands or more atomic ions. For this
reason, efforts in the area of quantum computing are now focused on making ion
traps on a chip that are scalable and mass producible, and can host larger numbers
"The semiconductor chip we demonstrated holds an individual atom in free space
inside the chip---we levitate the atom in the chip by applying certain electrical
signals to the tiny nearby electrodes," Monroe said. "We directly view this single
atom with specially-tuned lasers and a sensitive camera. This type of ion trap
has never been demonstrated at such a small level and in an integrated chip structure."
The chip produced at U-M is about as big as a postage stamp. It is etched with
electrodes using a process called lithography, which eliminates the need for
manual assembly. Each electrode is connected to a separate voltage supply, and
these various electrical voltages serve to control the ion by moving it in different
ways as it hovers in a space carved out of the chip.
Using existing microfabrication technology, the quantum chip developed at U-M
could be scaled up to include hundreds of thousands of electrodes, Monroe said.
"There is a worldwide race to build these (chips) right now, as such an integrated
chip structure shows a way to scale the quantum computer to bigger systems---just
like the microfabrication of conventional chips have given us the impressive
gains in conventional computing speed and power," Monroe said.
The next step is to build the chip bigger with many more electrodes, so that
it can store more ions. "There is still a great deal of work to be done in order
to learn how to control lots of ions in one of these chips. It won't be nearly
as easy as it was with conventional computer chips, but at least we know what
to do in principle," Monroe said.
Doctoral student Daniel Stick, in Monroe's group in the U-M Physics Department
and FOCUS Center (Frontiers in Optical, Coherent, and Ultrafast Science), led
this work in collaboration with the Laboratory for Physical Sciences at the University
For more information on Monroe's group, visit: http://iontrap.physics.lsa.umich.edu/
For more information about FOCUS: http://www.umich.edu/~focuspfc/
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