Using transistors as qubits, EU-backed researchers have achieved an important milestone in the quest to make the industrial manufacture of quantum processors possible.
Around the world, the race is underway to create quantum computers that will meet the needs of future science and industry. To achieve this goal, quantum technology needs to be scaled up so as to progress beyond the small-scale quantum computers currently being made only in controlled academic environments. However, the fragility of quantum bits, the basic unit of information in a quantum computer, also known as known as qubits, has until now served as an obstacle to scalability.
A research team from the University of Copenhagen, Denmark, and the French technology research institute CEA-Leti have now proposed a new method that will enable the manufacture of electron spin-based quantum processors industrially. Supported by the EU-funded QLSI, MOS-QUITO and Spin-NANO projects, the researchers found that ordinary transistors found in all our mobile phones could be used as qubits. The team’s findings are published in the journal ‘Nature Communications’.An important aspect of this research was the development of a 2D array of quantum dots – nanosize semiconductor crystals that are able to transport electrons. Quantum dots present an effective solution to control the spin of a single electron. “What we have shown is that we can realize single electron control in every single one of these quantum dots,” explained lead author Fabio Ansaloni of the University of Copenhagen in a news item posted on the ‘Phys.org’ website. “This is very important for the development of a qubit, because one of the possible ways of making qubits is to use the spin of a single electron. So reaching this goal of controlling the single electrons and doing it in a 2-D array of quantum dots was very important for us.” With 2D arrays, significant progress can be made towards correcting errors in quantum computing.The researchers use silicon transistor fabrication methods to create quantum dot-enabled silicon spin qubits. In their paper, they “demonstrate single-electron occupations in all four quantum dots of a 2 x 2 split-gate silicon device fabricated entirely by 300-mm-wafer foundry processes.” As the scientists in the ‘Phys.org’ news item state, “[f]irst, producing the devices in an industrial foundry is a necessity. The scalability of a modern, industrial process is essential as we start to make bigger arrays, for example for small quantum simulators. Second, when making a quantum computer, you need an array in two dimensions, and you need a way of connecting the external world to each qubit. If you have 4-5 connections for each qubit, you quickly end up with a[n] unrealistic number of wires going out of the low-temperature setup. But what we have managed to show is that we can have one gate per electron, and you can read and control with the same gate. And lastly, using these tools we were able to move and swap single electrons in a controlled way around the array, a challenge in itself.”
Joint lead author Anasua Chatterjee of the University of Copenhagen acknowledged the EU’s “generous funding” through the QLSI (Quantum Large Scale Integration in Silicon), MOS-QUITO (MOS-based Quantum Information TechnOlogy) and Spin-NANO (Nanoscale solid-state spin systems in emerging quantum technologies) projects. “Two dimensional arrays is a really big goal, because that’s beginning to look like something you absolutely need to build a quantum computer,” Chatterjee concluded.
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