February 16, 2016

Controlling lasers to a millionth of a percent for trapped ion quantum computer

Jungsang Kim is trying to create a quantum computer by controlling the frequency of a laser to within a millionth of a percent.

According to David DiVincenzo, a prominent computer scientist at IBM, researchers must meet five criteria to create a true quantum computing device.

First, Kim needs a well-defined system that can represent different states. For example, classical computers use small electrical switches made out of semiconductors to indicate a 1 or a 0. But because an atom’s quantum spin can point in an infinite number of directions, controlling its state with a high degree of reliability is very difficult. Kim’s group has demonstrated this feat with an accuracy on par with anyone in the world.

Once an atom’s quantum state can be controlled, the system must be made quantum-mechanically coherent. If the atom interacts with the outside world even a little bit, it loses its “quantumness,” which is bad. Again, Kim’s laboratory has demonstrated this ability.

They have also demonstrated the ability to initialize their system to a well-defined starting state. For example, in a laptop, each bit starts in the same place – a zero – until data is written to the chip.

Fourth, a quantum processor needs enough components to produce a universal set of gates, which allows one to implement arbitrary computational tasks. Kim’s setup combines a simple two-quantum-bit gate with the ability to control each quantum bit’s state to accomplish that.

Last but not least, a quantum computer needs to have the ability to report its solution. To do that, there must be good quantum measurements, which again, Kim’s laboratory has already demonstrated.

“All of these criteria our system meets pretty much as well as anybody else’s can,” said Kim. “But those are just the components. If you want to build a computer, you have to put a large number of these things together in a way that you can control them and interact with them at will. And that system integration is something that we are currently working on.”

Kim hopes to demonstrate the first small string of “quantum vacuum tubes” within a year. After that, it will be up to the cutting-edge technologies developed for semiconductors and telecommunications to scale the system up.

“We do all of these quantum manipulations with atomic ions trapped on silicon chips, so we could actually start to think about systems where we have 100 atomic ions,” said Kim. “That’s a small processor, but we have ways of connecting multiple units to build large-scale systems. The result would be similar to data processing centers with thousands of processors linked together.”

In 2014, Dr Kim made Qubits based on trapped ions that were prepared and manipulated with record-breaking accuracy, offering a promising scalable platform for quantum computing.

SOURCE - Duke University

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