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Important milestone in the establishment of a quantum computer



Important milestone in the establishment of a quantum computer

(a) Scanning electron image of one of the cast fabricated quantum point devices. Four quantum dots can be formed in the silicon (dark gray) using four independent control wires (light gray). These wires are the control buttons that activate the so-called quantum ports. (b) Schematic overview of the two-dimensional array unit. Each Qubit (red circle) can interact with the nearest neighbor in the two-dimensional network, and bypass a Qubit that fails for some reason. This layout is what “second dimension” means. Credit: University of Copenhagen

Quantum computer: One of the obstacles to progress in the search for a functioning quantum computer has been that the work units that go into a quantum computer and perform the actual calculations, qubits, have so far been done by universities and in small numbers. But in recent years, a pan-European collaboration, in collaboration with French microelectronics leader CEA-Leti, has explored everyday transistors – present in billions in all our mobile phones – for their use as qubits. The French company Leti makes giant waffles full of units, and after measurement, researchers at the Niels Bohr Institute, University of Copenhagen, have found that these industrially produced units are suitable as a qubit platform that can move to another dimension, a significant step for a functioning quantum computer. The result is now published in Nature communication.


Quantum dots in two-dimensional array is a leap ahead

One of the key features of the units is the two-dimensional range of quantum dots. Or more precisely, a two-to-two grid with quantum dots. “What we have shown is that we can realize single electron control in each of these quantum dots. This is very important for the development of a qubit, because one of the possible ways to make qubits is to use the spin of a single So to achieve this goal “Controlling the individual electrons and doing so in a 2-D range of quantum dots was very important to us,” said Fabio Ansaloni, a former Ph.D. student, now postdoctoral fellow at the Center for Quantum Devices, NBI.

The use of electron spin has proven to be beneficial for the implementation of qubits. In fact, their “quiet” nature makes spin in weak interaction with the noisy environment, an important requirement for achieving high-performance qubits.

Extending quantum computer processors to the second dimension has proven crucial for a more efficient implementation of quantum error correction routines. Quantum error correction will enable future quantum computers to be error tolerant of individual qubit errors during the calculations.

The importance of industrial scale production

Assistant Professor at the Center for Quantum Devices, NBI, Anasua Chatterjee adds: “The original idea was to make a series of spin qubits, get down to individual electrons and be able to control them and move them around. That way, it really is great that Leti was able to deliver the samples we used, which in turn enabled us to achieve this result.Much of the credit goes to the pan-European project consortium, and generous funding from the EU, and helped us slowly move from the level of a single quantum dot with a single electron to have two electrons, and now move on to the two-dimensional matrices.Two-dimensional matrices are a very big goal, because it’s starting to look like something you absolutely need to build a quantum So Leti has been involved in a series of projects over the years, all of which have contributed to this result. “

The credit for getting this far belongs to many projects across Europe

The development has been gradual. In 2015, researchers at Grenoble succeeded in creating the first spin qubit, but this was based on holes, not electrons. At that time, the performance of the units made in the “hole regime” was not optimal, and the technology has advanced so that the units now at NBI can have two-dimensional matrices in one electron regime. The progress is threefold, the researchers explain: “Firstly, it is a necessity to produce the units in an industrial foundry. The scalability of a modern, industrial process is important when we start making larger matrices, for example for small quantum simulators. Secondly, when you make a quantum computer, you need a two-dimensional array, and you need a way to connect the external world to each qubit.If you have 4-5 connections for each qubit, you quickly end up with an unrealistic number of wires out of But what we have managed to show is that we can have one port per electron, and you can read and control with the same port.And finally, by using these tools, we were able to move and exchange electrons easily in a controlled way around the matrix, a challenge in itself. “

Two-dimensional matrices can control errors

Checking for faults that occur in the devices is a chapter in itself. The computers we use today produce many errors, but they are corrected through what is called the repetition code. In a conventional computer you can have information in either 0 or 1. To make sure that the result of a calculation is correct, the computer repeats the calculation, and if a transistor makes a mistake, it is corrected by simple majority. If the majority of the calculations performed in other transistors point to 1 and not 0, 1 is selected as the result. This is not possible in a quantum computer since you cannot make an exact copy of a qubit, so quantum error correction works differently: state-of-the-art physical qubits do not have a low error rate yet, but if enough of them are combined in the 2-D array, can they keep each other in check, so to speak. This is another advantage of the now realized 2-D array.

The next step from this milestone

The result realized at the Niels Bohr Institute shows that it is now possible to control individual electrons, and perform the experiment in the absence of a magnetic field. So the next step will be to look for spins – spin signatures – in the presence of a magnetic field. This will be important for implementing single and two qubit ports between the individual qubits in the matrix. The theory has shown that a handful of single and two qubit ports, called a complete set of quantum ports, are enough to enable universal quantum computation.


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More information:
Fabio Ansaloni et al., Single electron operations in a foundry-produced range of quantum dots, Nature communication (2020). DOI: 10.1038 / s41467-020-20280-3

Delivered by the University of Copenhagen

Citation: Important milestone in the creation of a quantum computer (2020, December 28) retrieved December 28, 2020 from https://phys.org/news/2020-12-important-milestone-creation-quantum.html

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