The researchers developed a new qubit hosted in a laser-cooled, radioactive barium ion - a "goldilocks ion" that has nearly ideal properties for realizing ultra-low error rate quantum devices. The techniques they have developed, say the researchers, make it easier to build quantum computers that outperform classical computers for important tasks, including the design of new materials and pharmaceuticals.
Currently, the most powerful quantum computers are "noisy intermediate-scale quantum" (NISQ) devices that are very sensitive to errors. For such devices, say the researchers, error in preparation and measurement of qubits is particularly onerous: for 100 qubits, a 1% measurement error means a NISQ device will produce an incorrect answer about 63% of the time.
However, using the "goldilocks ion" allowed the researchers to achieve a preparation and measurement error rate of about 0.03% - lower than any other quantum technology to date. The development of this exciting new qubit, say the researchers, should impact almost every area of quantum information science and paves the way for large-scale NISQ devices.
The radioactive ion - 133Ba+ - has been identified as a promising system in quantum networking, sensing, timing, simulation, and computation. It is a manufactured radioisotope that possesses several unique and desirable properties that are not found in any naturally occurring species, which make it a nearly ideal qubit.
Specifically, say the researchers, the barium electronic structure provides transitions in the visible part of the electromagnetic spectrum, enabling the use of the high-power lasers, low-loss fibers, high quantum efficiency detectors, and other optical equipment not available to many ion species currently in use. The nuclear structure of 133Ba+ provides a robust hyperfine clock state qubit that is easy to initialize and detect, yet protects the qubit coherence during shuttling and storage.
These features, say the researchers, make it compatible with existing traps and in many ways superior to species currently in use, particularly for a quantum charge-coupled