The way to quantum computing

It is most likely that a quantum computer race will be determined in the quantum bit (qubit) - the smallest quantum computer information unit. At present, combining multiple qubits with a computation device is one of the biggest challenges for quantum computer growth.

One main issue is what physical structures are suitable for qubits and which materials. Superconductor-based qubit development has progressed most far – but indications are growing that silicon halving technology can provide a promising alternative with decisive advantages in chip production.

What qubits are made of

The classic bit is our current computer's smallest data storage unit. Two values can be taken into account: A current flows ("one") or doesn't flow ("null") – either a current f flow. On the other hand, the quantum bit is not confined to both states: It may simultaneously assume an intermediate condition between one and zero known as the "overlay" This intermediate state is only taken to a fixed value at the time of measurement.

Whereas ordinary bits have at any given time a defined value, qubits only assume a defined value at the respective measuring moment. The vast computational strength that quantum computers can use for certain problems is based on this property.

This makes it much more difficult to store this quantum information - a simple "current on/off" is not sufficient. Rather, space and time are based on the fastest and smallest processes: A qubit may be applied with the quantum states of electrons or photons.

In the case of quantum silicon bits, one electron-electron spin - uses the intrinsic angular dynamic to store information. The quantum information is encrypted here in the rotational direction of the electron together with its quantum state. It is, of course, extremely fragile, because even the most slight disruptions in the atomic level can alter an electron's angular momentum and kill quantum information.

Two silicon electrons, the quantity gate. Two nanoelectrodes regulate the angular momentum of both electrons (VL and VR). The interaction between both electrons is coordinated by a third nano-electrode (VM). (Image: Constance University)

Coupling quantum bits Today's challenge:

An even harder task is to bind quantum bits because a single quantum bit is not enough to perform an arithmetic operation. Like normal computers, quantum computers need to be connected to a computer system by many (quantum) bits. The individual qubits must therefore be able to communicate. If the combined qubits are far off on the chip, one qubit must be carried with a kind of "quantum bus" to the neighborhood first in order to allow for a computer operation.

In spin-based qubit, it means that a particular electron's angular momentum needs to be precisely and with the minimum of perturbation transported or transferred to another electron – and not only once, but theoretically thousands and even millions of times. A challenge for science – linking the qubits is possibly currently the biggest hurdle in the quantum machine growth.

"It's all about whether you're setting up a single bit of quantum or teaming up tens, hundreds, or thousands of people. There may be interactions between hard-to-control qubits," - described Professor Guido Burkard at the University of Konstanz, a professor of physics of condensed theories and quantity knowledge.

At present, some 20-50 qubits are coupled in the most advanced quantum computing prototypes.

"It's already a great success. We still have a long way to go, though, before we submit. In order to perform practical arithmetic operations, thousands or millions are required." -Burkard says.

The potential of Silicon

Superconductor systems have to date been the most advanced quantum computer systems. Superconductor systems are extremely powerful, but must face limitations: They do not work at room temperature, but only above absolute zero (around -273 °C) at temperatures. Moreover, superconductors are relatively highly energy-intensive and comparatively large, so that only a limited number of supranational qubits fit into one chip.

Along with the further advancement of qubits, research on alternative systems is also underway. Silicon is one of the most promising materials: "We agree that silicone-based qubits are very promising." Guido Burkard explains.

Silicone-based quantity bits have the advantage that they are much smaller than superconductive devices since they are just a few nanometres. As a consequence, several more – possibly millions – can be installed in a computer chip.

"Industry has decades of experience with the technology of the silicon semiconductor. This profits greatly from the creation and production of silicone-based qubits – which is no small help," - explains Guido Burkard.

Guido Burkard's research team succeeded in developing the steady "quantum gate" for silicone qubits already in 2017 with Princeton University and Maryland University, a switching mechanism for initially two-qubit systems, able to operate all the basic operations of the quantum computer in the first place (Science, "Resonantly driven CNOT gate for electron spins").

A milestone that is now being developed by the physicists: "Now our job is to scale up, bind, and minimize the number of silicon qubits possible," said Burkard. He has now joined three major research networks in Europe, Germany, and Baden-Württemberg to achieve this aim with leading research teams in the field of qubit production.

QLSI (“Quantum Large-Scale Integration with Silicon”) Research Network is a Silicón-based Quantum Computer Project, which is being implemented as part of the European Union (EU) "Flagship" Quantum Technology Project, in the field of silicon-based quantum computer technology. The project brings together the expertise of 19 European research institutions led by the Grenoble CEA-Leti Research Institute (France).

"QLSI's job is simply to make the transition to complex switching systems, starting with individual silicon qubits," says Guido Burkard. In December 2020, the QLSI Research Network was launched and will finance $15 million over a four-year term.

The QUASAR research network is aimed at developing a semi-conductor "made in Germany" quantic processor based on electrons shuttling. In addition to its quantum knowledge, a quantum bus makes it possible to transport individual electrons over distances up to ten micrometers. The technology is based on electrodes linked by series that pulsate voltages "like a transport belt" from one end to the other.

The research center Jülich coordinates the QUASAR network and brings together research institutions and industrial partners from all over Germany. "QUASAR aims to gather national expertise in basic science research and the experience of industrial partners in the field of semiconductor technology," says Burkard, research group member of Guido Burkard's research team. The research staff is a project partner. QUASAR began in February 2021 with the funding of € € 7.5 million until 2025 from the Federal Ministry of Education and Research.

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Source- nanowerk