“We need millions of quantum bits”
Currently, quantum computers only have a few dozen quantum computers. This means that they can basically demonstrate their functionality. But for practical tasks many more Qbits are needed. A German-British physicist explains how this could be achieved.
bAlready during his doctoral thesis in Australia, Winfried Hensinger set himself a challenging goal that he wanted to achieve in his life as a physicist: “I want to build a quantum computer.” Hensinger had long been a professor of quantum technologies at the University of Sussex when he finally met all the requirements in 2018 to start his own company.
An important aspect was the scientific breakthrough achieved in 2016. Hensinger is now coming to Hamburg with “Universal Quantum”, because the physicist with a British and German passport can benefit from generous funding for innovative quantum computer companies in this country.
There are dozens of research groups and companies around the world that are researching and developing quantum computers. To create the so-called quantum bits (Qbits), very different technologies are used. Which of them will ultimately emerge victorious and be best suited for commercial quantum computers is an open question. Naturally, every scientist places the greatest hope in the path of development that he himself follows.
In fact, the first quantum computers already exist that have fundamentally demonstrated their functionality. They were able to solve specific tasks using special quantum algorithms. The number of Qbits in these systems is usually only two digits.
“To be able to solve real problems with quantum computers in practice, we need millions of Qbits,” says Hensinger. For this reason, some of the technologies used so far would have no chance in the long term because they are not “scalable”.
“A technology is called scalable if it can be used not only to build systems with, say, 100 Qbits, but also by modular expansion to systems with 1,000, 10,000 or a million Qbits,” explains Hensinger. And that’s exactly what should be possible with the technology he prefers.
Hensinger quantum bits are represented by ions, that is, electrically charged ions found in an ion trap on microchips. “In 2005 I presented the first ion trap microchip,” says the British-German researcher. That same year he received his professorship in England.
“The main advantage of this technology is its scalability,” says Hensinger. “In Hamburg we want to build a quantum computer in which we connect four chips with electric fields using a new technology that we have invented. Then we build a truly modular system. And of course, a quantum computer could be built with millions of Qbits in exactly the same way. same way; then many more chips would simply be connected.”
Because if that works, then other modules should be attached using the same principle and a scalable quantum computer could be built. In similar approaches, researchers use laser light to communicate with the Qbits. But it seems impossible to try to do this with millions of Qbits at the same time.
Microwaves work with Qbits
“You can’t direct millions of laser beams at ion microchips,” says Hensinger, “but in 2016 we made a breakthrough. We have developed chips that produce non-homogeneous magnetic money within the processor area. You can then change the resonance frequency of the ion by simply displacing the ion in the inhomogeneous magnetic field using an applied voltage. This means that by applying a voltage you can determine if the ion can absorb microwaves. “The microwaves then change the state of the ion and therefore calculations can be performed simply by applying voltages.”
A big advantage of this quantum computing technology is that it basically works at room temperature. In contrast, the quantum computer developed by Google must be cooled to temperatures in the mikelvin range, that is, just above absolute zero of -273 degrees Celsius. This is complex and expensive and another obstacle to scaling up. Bringing millions of Qbits to such low temperatures is an almost impossible challenge to overcome.
And it’s this scalability that will ultimately require cooling for Hensinger’s chips. If there are millions of active ions there in the form of Qbits, the waste heat that will inevitably be generated will be too great. “We want to cool our chips to -200 degrees Celsius with helium gas,” says the physicist. “This can be done with little effort and very cost-effectively.”