Quantum silicon processors are coming — Australian startup entangles quantum ‘transistors’ for the first time

Australian startup Diraq has published an article in Nature Communications, in which it has for the first time substantiated the possibility of producing quantum processors from silicon based on electron spin qubits. Diraq researchers have proven that the spin qubits they created correspond to quantum theory. The proof was obtained by violating Bell’s inequality, which confirms the true quantum nature of an entangled pair of electrons – its nonlocality.

Image source: AI generation Grok 3/3DNews

In a 1935 paper by Einstein, Podolsky, and Rosen, the authors reported discovering a “spooky” state of entanglement that they could not explain. They suggested that the quantum theory that had been created by that time might be incomplete, and that particles might have hidden parameters. This is called local realism. Meanwhile, EPR pairs of entangled particles exhibited the very “spookiness” that Einstein had described: they responded instantly to measurements of the state of one of them, regardless of the distance. For the creator of the theory of relativity with its postulate of the ultimate speed of light, this seemed unthinkable.

In 1964, physicist John Bell developed a way to test EPR pairs for hidden parameters. He proposed equations that, if violated, caused the system to exhibit quantum properties — it was described by a wave function and exhibited nonlocality. Otherwise, the system was considered classical and obeyed the laws of conventional physics, including general relativity. Since calculations and experiments in quantum mechanics give a coincidence of results with an accuracy of 12 decimal places, quantum mathematics is usually trusted absolutely. In the quantum world, the behavior of particles corresponds to the calculations performed.

For pairs of photons with both spin and polarization (these are also quantum properties), the first experiments on violating Bell’s inequality were conducted in the late 1970s and early 1980s. For electrons, according to the Australians’ article, such experiments have not yet been conducted in the proposed configuration on silicon. In other words, the quantum nature of silicon qubits has not yet been formally proven.

It is worth noting that Diraq, founded in 2022, grew out of a strong academic environment – the University of New South Wales (UNSW) in Sydney. Many research groups at this university are working on quantum platforms based on spin qubits. Diraq has significant experience, knowledge and a portfolio of patents.

The startup is developing a modified silicon field-effect transistor capable of controlling a single electron, or more precisely, its spin. The technology for producing such transistors and processors is called SiMOS (silicon-metal-oxide-semiconductor) by analogy with CMOS. The SiMOS process technology is implemented on the same industrial equipment that is used to produce conventional transistors and processors. According to the developers, each such transistor can be a qubit. Obviously, such a platform is ideally scalable to millions and millions of qubits.

In their work, Diraq demonstrated a violation of the Bell inequality with a result of S = 2.731. This value exceeds the classical limit (S ≤ 2), confirming the presence of quantum entanglement and non-local correlations between qubits. The system also demonstrated a Bell state fidelity of greater than 97% without correction of readout errors. This means that qubits in an entangled state retain their quantum nature with very high accuracy, which is critical for quantum computing. The system also operated at a relatively high temperature of 1.1 K, which is about 20 times higher than that of conventional superconducting qubits.

Andrew Dzurak, CEO of Diraq, commented on the findings: “Entanglement is perhaps the most profound property of quantum mechanics and the fundamental basis for quantum computing and quantum advantage. Using state-of-the-art tools to manipulate electron spin qubits in SiMOS quantum dots and improve their performance, our team at Diraq has broken Bell’s inequality, demonstrating the true quantum nature of entangled states. We believe this is the world’s first creation of electron spin qubits in quantum dots, and this success demonstrates the maturity of spin-based quantum computing in silicon.”