Beyond qubits: unlocking the potential of quantum computing

Quantum computers are powerful computational devices that rely on quantum mechanics, or the science of how particles like electrons and atoms interact with the world around them. These devices could be used to solve certain kinds of computational problems in a shorter amount of time, with scientists hoping that quantum computing could be the next great advance in computing. However, existing limitations have prevented the technology from hitting its true potential — for these computers to work, the basic unit of information integral to their operation, known as quantum bits (or qubits), needs to be stable and fast.

Qubits are represented by simple binary quantum states and by various physical implementations. One candidate is a trapped electron that levitates in a vacuum. However, controlling the quantum states, especially the vibrational motions, of trapped electrons can be difficult. In a paper published in Physical Review Research, researchers identified possible solutions to some of the limitations of qubits for quantum computing. The researchers looked at two different hybrid quantum systems: an electron-superconducting circuit and an electron–ion coupled system. Both systems were able to control the temperature and the movement of the electron.

Assistant Professor Alto Osada at the Komaba Institute for Science at the University of Tokyo said that the researchers found a way to cool down and measure the motion of an electron levitated in a vacuum, or a trapped electron, both in the quantum regime. “With the feasibility of quantum-level control of the motion of trapped electrons, the trapped electron becomes more promising and attractive for quantum-technology applications, such as quantum computing,” Osada said.

The proposed systems that the researchers focused on included an electron trapped in a vacuum called a Paul trap interacting with superconducting circuits and a trapped ion. Because ions are positively charged and electrons are negatively charged, when they are trapped together, they move toward each other because of a phenomenon called Coulomb attraction. Because the electron has such a light mass, the interactions between the electron and circuit and the electron and the ion were particularly strong. The researchers also found that they could control the temperature of the electron using microwave fields and optical lasers.

The researchers also measured the success of their calculations through the phonon mode of the electron. Phonon refers to a unit of energy that characterises a vibration, or in this case, the oscillation of the trapped electron. The desirable result was a single-phonon readout and ground-state cooling (the frozen state of the electron). Researchers were able to accomplish these through their two hybrid systems they analysed. “Highly efficient and high-fidelity quantum operations are available in the trapped-electron system. This novel system manifests itself as a new playground for the development of quantum technologies,” Osada said.

The researchers noted that additional experimental research will need to be done to see if their methods can be implemented and applied to quantum computing. They also plan to demonstrate their idea with a proof-of-concept experiment. “We are planning to examine our schemes using electrons trapped in a microwave cavity. Through this research, we will be able to get another step closer toward precise quantum operations and toward the implementation of quantum computation,” Osada said.

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