Science & Technology, Canada (Commonwealth Union) – Quantum information is a specialized field within the broader domain of quantum physics that focuses on the study and manipulation of information using the principles of quantum mechanics. It deals with the use of quantum bits, or qubits, as the fundamental unit of information. Researchers across the world have actively explored practical applications and building quantum computers to harness the power of quantum information processing.
Utilizing laser technology, researchers have pioneered the most robust technique currently available for managing individual qubits composed of the chemical element barium. The ability to precisely manipulate a qubit represents a significant milestone in the pursuit of functional quantum computers.
This innovative approach, developed at the Institute for Quantum Computing (IQC) at the University of Waterloo, employs a diminutive glass waveguide to segregate laser beams and focus them at intervals of four microns, roughly four-hundredths of the width of a single human hair. The precision and simultaneous control achieved over each laser beam targeting its designated qubit surpass previous research endeavors.
Dr. K. Rajibul Islam, a professor at IQC and Waterloo’s Department of Physics and Astronomy, highlighted the method’s exceptional effectiveness in minimizing crosstalk, the unintended interference of light on adjacent ions. The relative intensity of crosstalk is a mere 0.01 percent, a benchmark considered among the finest in the quantum research community. Notably, unlike prior methods for establishing agile control over individual ions, the fiber-based modulators do not exert mutual influence on 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 scientists specifically focused on barium ions, which are gaining popularity in the realm of trapped ion quantum computing. Barium ions offer convenient energy states that can serve as the zero and one states of a qubit and can be manipulated using visible green light, in contrast to the higher-energy ultraviolet light required for manipulating other types of atoms for the same purpose. This unique characteristic allows the researchers to utilize off-the-shelf optical technologies that are not readily available for ultraviolet wavelengths.
To implement their approach, the researchers designed a waveguide chip capable of splitting a single laser beam into 16 distinct channels of light. Each channel is then directed into individual optical fiber-based modulators, providing independent and agile control over the intensity, frequency, and phase of each laser beam. Subsequently, the laser beams are precisely concentrated to their close spacing using an array of optical lenses, similar to a telescope. The researchers verified the accuracy of each laser beam’s focus and control by employing precise camera sensors for measurement.
“This work is part of our effort at the University of Waterloo to build barium ion quantum processors using atomic systems,” explained Dr. Crystal Senko, Dr Islam’s co-principal investigator as well as 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.”
The novel waveguide technique showcases an uncomplicated yet highly accurate means of control, offering substantial potential for manipulating ions to encode and process quantum data, as well as for integration into quantum simulation and computing applications.
The paper, titled “A Guided Light System for Precise Individual Addressing of Ba+ Qubits with Exceptionally Low Intensity Crosstalk (10^-4 Level),” has been authored by Ali Binai-Motlagh, Dr. Matt Day, Nikolay Videnov, Noah Greenberg, Senko, and Islam, and it has appeared in the journal Quantum Science and Technology.
