Electronic Design

Ion Trap Marks A Step Toward Practical Quantum Computing

Aquantum computer would be nothing less than a marvel. Unlike conventional two-state computers, it would encode information as quantum bits, or qubits. A qubit can be a 1 or a 0, simultaneously both 1 and 0, or some point in between.

Since a quantum computer could function in multiple states simultaneously, it would be millions of times more powerful than today's most robust supercomputers. Able to perform vast numbers of operations simultaneously, it would be ideal for such processor-intense activities as breaking data encryption codes or searching large databases.

Quantum computing works on an atomic scale, exploiting the unusual behavior of the smallest particles of matter and light. A key stumbling block to building a functional machine is finding a way to build one using real-world fabrication processes. A research team at the National Institute of Standards and Technology (NIST) believes it can surmount this barrier with an easily manufacturable trap that harnesses electrically charged atoms—ions—for use as qubits.

David Wineland, the team's leader, says the new device marks the first functional ion trap with components arranged in a "chip-like" geometry (see the figure). The trap's horizontal single electrode layer will make it much easier to manufacture than previous ion traps that used two or three layers of electrodes, he says. He also notes that the device can trap up to a dozen magnesium ions without generating significant heat from electrode voltage variations.

Wineland says the planar trap was created using standard micro-fabrication technologies. "We deposited gold electrodes on a quartz substrate using lithographic techniques," he says, noting that gold is an excellent conductor and quartz is a good, low-loss dielectric.

"These features are important to suppress power dissipation from the applied RF and dc electric potentials, which are required for trapping," he says. Laser beams are used to create magnesium ions from the metal vapor and then cool them. The electrodes confine the ions 40 µm above the electrode plane.

The initial work has gone well, says Wineland. "At the lowest level, this should allow us to perform more complex algorithms using larger numbers of ion qubits." Yet he notes that that while the team has been able to develop the basic gates and operations required for quantum computation, precision must still be improved.

"We think this can be accomplished by the control of classical parameters, such as laser beam intensity, but it is a significant technical challenge," he says. Beyond that, the team will have to work its way through some functional roadblocks. "In addition to being able to store more ion qubits, we will also need to be able to simultaneously manipulate many laser beams and simultaneously detect many ions for parallel processing."

Wineland believes a useful quantum computer will eventually be built, but it may take at least another decade of research. "I wouldn't advise anybody to invest in startup companies right now," he quips.

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