Researchers take step towards reliably processing quantum information

Researchers have found the most robust way for controlling individual qubits made of the chemical element barium using laser light. The capacity to manipulate a qubit reliably is a significant step towards realising future functioning quantum computers.

The Institute for Quantum Computing (IQC) at the University of Waterloo created this novel technology, which employs a thin glass waveguide to divide and focus laser beams four microns apart, or approximately four-hundredths of the breadth of a single human hair. Previous research has not been able to match the precision and extent to which each focused laser beam on its target qubit can be regulated in tandem.

“Our design limits the amount of crosstalk–the amount of light falling on neighbouring ions–to the very small relative intensity of 0.01 per cent, which is among the best in the quantum community,” said Dr K. Rajibul Islam, a professor at IQC and Waterloo’s Department of Physics and Astronomy.

“Unlike previous methods to create agile controls over individual ions, the fibre-based modulators do not affect each other.

“This means we can talk to any ion without affecting its neighbours while also retaining the capability to control each individual ion to the maximum possible extent. This is the most flexible ion qubit control system with this high precision that we know of anywhere, in both academia and industry.”

The researchers focused on barium ions, which are gaining popularity in the field of trapped ion quantum computation. Barium ions have suitable energy states that can be employed as the zero and one levels of a qubit and manipulated using visible green light, as opposed to the higher energy ultraviolet light required for the same manipulation with other atom types. This enables the researchers to employ commercially available optical technologies that were previously unavailable for UV wavelengths.

The researchers developed a waveguide circuit that separates a single laser beam into 16 distinct light channels. Each channel is then sent to its own optical fibre-based modulator, which provides independent control over the strength, frequency, and phase of each laser beam. Using a series of optical lenses akin to a telescope, the laser beams are then focused down to their narrow spacing.

The researchers confirmed the focus and control of each laser beam by monitoring them with accurate camera sensors.

“This work is part of our effort at the University of Waterloo to build barium ion quantum processors using atomic systems,” said Dr. Crystal Senko, Islam’s co-principal investigator and a faculty member at IQC and Waterloo’s Department of Physics and Astronomy.

“We use ions because they are identical, nature-made qubits, so we don’t need to fabricate them. Our task is to find ways to control them.” (ANI)