Controlling trapped ions for scalable quantum control

Researchers at the University of Waterloo’s Institute for Quantum Computing (IQC) have developed an algorithm that controls trapped ions for scalable quantum control.

This novel technology utilises the first known holographic optical engineering device to control trapped ion qubits, promising to aid the development of more precise controls of qubits. This will help the creation of quantum industry-specific hardware to further quantum simulation experiments as well as the potential of furthering quantum error correction processes for trapped ion qubits.

The results of the study were published in the journal npj Quantum Information.

“Our algorithm calculates the hologram’s profile and removes any aberrations from the light, which lets us develop a highly precise technique for programming ions,” said Chung-You Shih, lead author and PhD student at the University of Waterloo’s Institute for Quantum Computing.

The team at IQC have been trapping ions used in quantum simulation in the Laboratory for Quantum Information since 2019 but required a more accurate way to control them.

When a laser is aimed at an ion it can communicate with it and change its quantum state, thus establishing the necessary building blocks of quantum information processing. However, laser beams have irregularities and distortions that can result in a complicated, wide focus spot. This is complicated as the distance between trapped ions is a few micrometres.

In order to stimulate the ions, it is necessary that the laser beam profiles are accurately engineered. The team took a laser, blew its light up to 1cm wide and then delivered it via a digital micromirror device (DMD), which is programable and functions as a movie projector.

The DMD chip has two-million micron-scale mirrors on it that are separately controlled with electric voltage. Utilising an algorithm developed by Shih, the DMD chip is programmed to display a hologram pattern. The light generated from the DMD hologram can have its intensity and phase exactly controlled.

During the testing process, the researchers were able to control each ion with the holographic light. In previous experiments, ‘cross talk’ has been an issue, which meant that a laser focusing on one ion would result in light leaks on the surrounding ions.

In contrast, with this new device, the researchers were able to effectively differentiate any aberrations as a sensor. They can then cancel the aberrations by adjusting the hologram and obtain the lowest cross talk in the world.

“There is a challenge in using commercially available DMD technology,” Shih explained. “Its controller is made for projectors and UV lithography, not quantum experiments. Our next step is to develop our own hardware for quantum computation experiments.”

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