Today’s most advanced quantum computers possess only a few hundred qubits. This limits them to performing calculations that conventional computers are already capable of and can often do more efficiently. For quantum computing to advance, researchers must find a way to accommodate millions of qubits on a single chip.

Electrons and Holes

To solve the problem of arranging and linking thousands of qubits, researchers at the University of Basel and the NCCR SPIN rely on a type of qubit that uses the spin (intrinsic angular momentum) of an electron or a hole. A hole is essentially a missing electron in a semiconductor. Both holes and electrons possess spin, which can adopt one of two states: up or down, analogous to 0 and 1 in classical bits. Compared to an electron spin, a hole spin has the advantage that it can be entirely electrically controlled without needing additional components like micromagnets on the chip.

Two interacting hole spin qubits. When a hole (magenta/yellow) tunnels from one site to the other its spin (arrow) rotates on account of the so-called spin-orbit coupling, leading to anisotropic interactions depicted by the surrounding bubbles. Credit: NCCR SPIN

In 2022, Basel physicists demonstrated that the hole spins in an existing electronic device can be trapped and used as qubits. These “FinFETs” (fin field-effect transistors) are built into modern smartphones and are produced in widespread industrial processes. Now, a team led by Dr. Andreas Kuhlmann has succeeded for the first time in achieving a controllable interaction between two qubits within this setup.

Fast and Precise Controlled Spin-Flip

A quantum computer needs “quantum gates” to perform calculations. These represent operations that manipulate the qubits and couple them with each other. As the researchers report in the journal SciTechDaily