Making building blocks for a quantum computer can now also be done in a factory

The first qubits of the assembly line are a fact. These building blocks for quantum computers were produced for the first time using the same mass production technology as today’s computer chips. Scaling up production is an important step towards a serious quantum computer.

Quantum computers are promising because, thanks to the quantum properties of qubits, they can perform certain calculations simultaneously and therefore super fast. The promise is that in the future they will be able to calculate the behavior of molecules, for example, in order to predict the effect of certain drugs.

But for a quantum computer with significant performance you quickly need a million qubits. Most of the qubits that researchers worldwide are working on are still being made one by one in cleanrooms, dust-free areas, of research institutes. This is very accurate, but also very slow.

Qubits that seem suitable for upscaling are so-called spin qubits, which consist of an electron that is trapped in a kind of cage made with semiconductor material. “Researchers have been writing for years that these qubits are ideal for scaling up because they are small and can be produced by the existing semiconductor industry that makes computer chips,” says Anne-Marije Zwerver of the QuTech institute in Delft. “Now we have finally proved that to be true.” For this, QuTech researchers worked together with engineers from chip manufacturer Intel. Their results appeared in the journal last week Nature Electronics

A cool trick

To make a spin qubit, you start with a quantum dot that acts as a cage. Quantum dot structures are very similar to transistors you find on a computer chip. They are both made of the semiconductor material silicon with tiny pieces of metal on top through which electric currents can flow. That agreement made it a breeze for experienced Intel engineers to create quantum dots with their mass-production technology. But this turned out to be less simple than expected.

The structures are slightly different from those of transistors and qubits are very sensitive. The question was whether the rougher, inflexible mass-production machines were capable of making these precise structures without disrupting the system. For years, the Intel engineers and the QuTech researchers ping-ponged back and forth with designs and prototypes of quantum dots. And now it worked. The researchers created qubits using exactly the same machine that Intel uses for large-scale chip production. “And its quality is comparable to the best qubits we currently make in our research labs,” says Zwerver.

We have gone from a maximum of twenty qubits to tens of thousands per production round

Anne-Marije Zwerver QuTech

“It’s as if we were writing calligraphy before and now we can print texts,” she continues. “We were very precise and flexible in what we can make in our cleanrooms, but it was slow. With industrial technology we are faster and it produces more working qubits. We have gone from a maximum of twenty qubits to tens of thousands per production round.”

“It is a promising development,” says physicist Carlo Beenakker of Leiden University. “They have shown that mass production for qubits is possible. And that is necessary for a credible quantum computer that is more than a toy. The next step is to actually do the math.”

Thousands of individual qubits are not quantum computers. For that you have to let them work together and be able to manage. Also, these qubits still crash after a few microseconds. “Our next step is to link two or three of these qubits together to perform small quantum calculations. Then we have to scale that up to more,” says Zwerver. “Ultimately, we also want to make the controlling electronics more efficient by building it into the chip with the qubits.” In this way, the researchers hope step by step to get closer to a serious quantum computer, with parts of the assembly line of the current semiconductor industry.

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