Scientists have created an improved, ultra-pure form of silicon that could one day be the basis for highly reliable “silicon spin qubits” in powerful quantum computers.
While bits in classical computers encode data as 1 or 0, qubits in quantum computers can be a superposition of these two states – meaning they can achieve a quantum state known as “coherence” and occupy 1’s and 0’s in parallel while processing calculations.
These machines could potentially be more powerful than the fastest supercomputers in the world but it would take about a million qubits to achieve that, the scientists said. The largest quantum computer today approximately 1000 qubits.
Connected: The world’s first fault-tolerant quantum computer launches this year ahead of a 10,000-qubit machine in 2026.
But a key challenge in quantum computing is that qubits are “noisy,” meaning they are highly susceptible to perturbations such as temperature changes, and must be cooled to nearly absolute zero. Otherwise, they easily lose information and fail in the middle of operations.
This means that even if we had a quantum computer with millions of qubits, many of them would be redundant even with error correction technologiesmaking the machine extremely inefficient.
Touching Silicon Quantum Computing
Qubits are usually made of superconducting metals such as tantalum and niobium because they possess almost infinite conductivity and almost infinite resistance.
But in a new study published May 7 in the journal Nature communication materialsresearchers proposed using a new, pure form of silicon – the semiconductor material used in conventional computers – as the basis for a qubit that is much more scalable than existing technologies.
Building qubits from semiconductor materials such as silicon, gallium or germanium has advantages over superconducting metal qubits, according to quantum computing company QuEra. Coherence times are relatively long, they are cheap to manufacture, they operate at higher temperatures and they are extremely small – meaning that a single chip can hold a huge number of qubits. But impurities in semiconductor materials cause decoherence during calculations, making them unreliable.
In the new study, the scientists proposed making a qubit from silicon-28 (Si-28), which they described as “the purest silicon in the world,” after removing the impurities found in natural silicon. These silicon-based qubits would be less prone to damage, they said, and could be manufactured down to the size of a pin head.
Natural silicon usually consists of three isotopes or atoms of different masses – Si-28, Si-29 and Si-30. Natural silicon works well in conventional computing because of its metalloid properties, but problems arise when using it in quantum computing.
In particular, Si-29, which makes up 5% of natural silicon, causes a “nuclear flip-flop effect” that leads to decoherence and loss of information. In the study, the scientists circumvented this by developing a new method for constructing silicon without the Si-29 and Si-30 atoms.
Cheaper, more scalable quantum computing
“What we’ve been able to do is effectively create a critical ‘brick’ needed to build a silicon-based quantum computer,” the study’s lead author Richard Curry, professor of advanced electronic materials at the University of Manchester, said in a statement. “This is a crucial step towards becoming a feasible technology that has the potential to transform humanity.”
Components for silicon-based quantum computers could, in theory, be built using the same methods used to make classical electronic chips that can fit billions of transistors on a tiny circuit board, the scientists said. Silicon qubits, or silicon-spinning qubits, are nothing new, but the quality of silicon has never been so pure, they added, as determined based on microscopic tests.
Silicon-based qubits can also be produced much more easily than other types of qubits due to existing chip manufacturing methods. And therefore quantum computers using them can be scaled to the region of millions of qubits much faster than competing methods, the researchers said.
“Now that we can produce extremely pure silicon-28, our next step will be to demonstrate that we can maintain quantum coherence for many qubits simultaneously,” project co-leader David Jamieson, a professor of physics at the University of Melbourne, said in a statement . “A reliable quantum computer with just 30 qubits would exceed the power of today’s supercomputers for some applications.”
