Quantum Computing Advances: Closer to Millions of Qubits Chips

We’re one step closer to quantum chips with millions of qubits. This experiment is a success. To address symbolic problems, a quantum computer needs to have several million qubits. Physicists at the University of Basel have successfully developed a two-qubit logic gate in a silicon transistor. The prototypes of quantum computers developed by IBM, Google, Intel, or Honeywell, among other companies, have few qubits. Their complexity has been increasing over the past five years, but still, their qubits are not enough for us to stop considering them prototypes and start facing a truly significant range of problems. Their ability to correct their own errors is at stake.

This experiment draws a horizon where chips with millions of qubits appear. The search for the high scalability that will presumably make fully functional quantum computers possible can be addressed by resorting to very different strategies. One of them involves refining the manufacturing technology of silicon transistors currently used by integrated circuit manufacturers to produce a chip capable of aggregating many qubits. A group of researchers from the University of Basel, in Switzerland, has pursued this approach in an extraordinarily promising experiment. They have successfully developed a two-qubit logic gate inside a conventional silicon transistor. Their strategy involves using a type of qubit that utilizes the spin of an electron or the spin of a hole (a hole essentially identifies the absence of an electron in a semiconductor). Spin is an intrinsic property of elementary particles, like electric charge, derived from their angular momentum. The first experimental evidence confirming its existence came in 1922 thanks to the experiments of German physicists Otto Stern and Walther Gerlach.

The reason why it is not easy to precisely understand what spin is is that it is a quantum phenomenon, so it is not entirely correct to describe it as a conventional rotational movement in space. Nevertheless, the description I have proposed in the previous paragraph is often used for didactic purposes because it helps us to intuitively grasp what we are talking about. In any case, the quantum nature of this property anticipates something important: measuring it is difficult.