A reliable and ultra-powerful quantum computer could finally be on the horizon. Researchers from the University of Basel and the NCCR SPIN in Switzerland have achieved a significant advancement in quantum computing by controlling the interaction between two “hole spin qubits” inside a standard silicon transistor. This breakthrough, published in Nature Physics, could enable quantum computer chips to carry millions of qubits, drastically scaling up their processing power and potentially revolutionizing modern computing.

A qubit, or quantum bit, is the fundamental unit of data in quantum computing, analogous to a bit in conventional computing. Unlike a standard bit, which can be either a 0 or a 1, a qubit can exist in both states simultaneously due to quantum mechanics principles. This unique property allows quantum computers to perform complex calculations at speeds unattainable by today’s computers.

Hole spin qubits take this concept further. In the materials used for computer chips, electrons sometimes leave behind empty spaces or “holes” as they move. These holes, though not actual particles, behave like positively charged electrons. Researchers can manipulate the “spin” (intrinsic angular momentum) of these holes to represent data. The ability to control these spins electrically simplifies the design and scalability of quantum chips.

For both traditional and quantum computing, the interaction among bits or qubits is crucial for performing operations and solving problems. The Basel team has created a controlled interaction between two hole spin qubits, enabling them to influence each other’s states through a process known as a spin-flip. This interaction is essential for building complex quantum circuits capable of performing high-speed computations.

Current quantum computers have a limited number of qubits, restricting them to calculations that can often be done more efficiently by conventional computers. By effectively linking many qubits together—potentially millions on a single chip—quantum computers could surpass today’s machines, tackling currently unsolvable problems in areas like drug discovery, materials science, and cryptography.

Dr. Andreas Kuhlmann and his team used “FinFETs”—a type of transistor already employed in modern smartphones. FinFETs are produced using mature technology, making scaling up production to create quantum chips more feasible. Their method involves “exchange interaction,” a force that allows hole spins to interact, governed by electrostatics—the same principle that makes your hair stand up when you rub a balloon on your head. This interaction is electrically controllable and anisotropic, varying with the spin orientation, adding complexity and control to qubit operation.

This research brings us closer to realizing quantum computers capable of exceeding the boundaries of current computing technology. The work highlights the potential of hole spin qubits, which leverage the established fabrication of silicon chips and are highly scalable, fast, and robust.

“The anisotropy makes two-qubit gates possible without the usual trade-off between speed and fidelity,” Dr. Kuhlmann says. “Qubits based on hole spins not only leverage the tried-and-tested fabrication of silicon chips, but they are also highly scalable and have proven to be fast and robust in experiments. This principle now also makes it possible to couple a larger number of qubit pairs.”

With continued research and development, the dream of a quantum computer capable of surpassing current technological limits grows ever closer, unlocking new possibilities for computing and information science.

By Impact Lab