Researchers at QuTech have made a groundbreaking advancement in quantum computing by developing somersaulting spin qubits for universal quantum logic. This achievement has the potential to revolutionize the control of large semiconductor qubit arrays. Their research has been published in prestigious journals such as Nature Communications and Science.
In 1998, Loss and DiVincenzo introduced the concept of ‘quantum computation with quantum dots’. Although the idea of hopping spins for qubit logic was proposed in their work, experimental validation has been elusive until now. Over 20 years later, researchers at QuTech, a collaboration between the TU Delft and TNO, have successfully demonstrated that ‘hopping gates’ are not only possible but also exhibit state-of-the-art performance.
Making control simple
Quantum dots-based qubits have garnered global interest as they offer a promising platform for building quantum computers. Traditionally, control is achieved by trapping a single electron and utilizing a strong magnetic field to manipulate its spin using microwave signals.
However, the QuTech researchers have shown that universal qubit control can be achieved without the need for microwave signals. By utilizing baseband signals and minimal magnetic fields, they have simplified the control electronics required for future quantum processors.
From hopping to somersaulting qubits
The key to controlling spin involves hopping between quantum dots and a mechanism for rotating the spin. While the original magnet-based proposal faced practical challenges, the QuTech group innovatively utilized germanium, a semiconductor with intrinsic spin rotation capabilities. This breakthrough was detailed in a Nature Communications publication by Floor van Riggelen-Doelman and Corentin Déprez.
Germanium provides a unique feature where the simple act of hopping between quantum dots induces a torque that results in somersaulting spins. This property allows for effective qubit control, as demonstrated by Chien-An Wang in the Science paper.
Somersaulting qubits in a trampoline park
The team at QuTech progressed from controlling two spins in a four-quantum dot system to exploring hopping across multiple quantum dots, akin to somersaulting over numerous trampolines. Valentin John highlights the necessity of coupling large numbers of qubits with precision for quantum computing applications.
Francesco Borsoi emphasizes the importance of understanding the unique rotations induced by hopping spins between quantum dots. The team successfully developed control routines enabling hopping to any quantum dot within a 10-quantum dot array, facilitating the assessment of key qubit metrics in extended systems.
Team effort
Principal investigator Menno Veldhorst commends the collaborative effort of the team in achieving this milestone. He emphasizes the critical role of efficient control schemes for future quantum computers and the promising prospects of the new somersaulting spin qubit approach.