“We need millions of quantum bits.”
Quantum computers currently only have a few dozen quantum computers. This means they can basically prove their functionality. But for practical tasks, many more Qbits are needed. A German-British physicist explains how this can be achieved.
BAlready during his doctoral work in Australia, Winfried Hensinger set himself an ambitious goal that he wanted to achieve in his life as a physicist: “I want to build a quantum computer.” Sussex when he finally met all the requirements to start his own business in 2018.
An important aspect was the scientific breakthrough achieved in 2016. Hensinger is now coming to Hamburg with “Universal Quantum”, as the physicist with British and German passports can benefit from generous funding for innovative quantum computing companies in the country.
There are dozens of research groups and companies around the world engaged in quantum computing research and development. Very different technologies are used to implement so-called quantum bits (Qbits). Which one will ultimately prevail and perform best in commercial quantum computers remains an open question. Naturally, every scientist places his greatest hopes on the development path he himself follows.
In fact, the first quantum computers already exist and have essentially proven 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 solve real-world problems with quantum computers in practice, we need millions of Qbits,” says Hensinger. For this reason, some of the technologies implemented so far would not have a chance in the long run because they are not “scalable”.
“We call a technology scalable if it can be used not only to build systems with, say, 100 Qbits, but also through modular expansion to systems with 1,000, 10,000 or a million Qbits,” explains Hensinger. And that’s exactly what his preferred technology should be able to do.
Hensinger quantum bits are represented by ions, which are electrically charged ions that are located in an ion trap on microchips. “I presented the first microchip with an ion trap in 2005,” says the British-German researcher. In the same year he received a chair in England.
“The key advantage of this technology is its scalability,” says Hensinger. “In Hamburg, we want to build a quantum computer in which we will connect four chips with electric fields, using a new technology that we have invented. We then build a truly modular system. And of course you could build a quantum computer with millions of Qbits in exactly the same way; it would then be enough to connect many more chips.
Because if it worked, other modules would have to be docked in the same way and a scalable quantum computer could be built. In a similar way, researchers use laser light to communicate with Qbits. However, trying to do this with millions of Qbits at once seems hopeless.
Microwave ovens work with Qbits
“You can’t direct millions of laser beams at ion microchips,” says Hensinger, “but in 2016 we achieved a definite breakthrough. We have developed chips that produce non-uniform magnetic money in the processor zone. The resonant frequency of the ion can then be changed by simply moving the ion in a non-uniform magnetic field with an applied voltage. This means that by applying a voltage, you can determine whether an ion can absorb microwaves. The microwaves then change the state of the ions so that calculations can be performed by simply applying a voltage.
The big advantage of this quantum computer technology is that it essentially operates at room temperature. In turn, the quantum computer developed by Google must be cooled to temperatures of the order of millikelvins – that is, slightly above absolute zero, or minus 273 degrees Celsius. This is complex and expensive, and is another obstacle to scaling. Getting millions of Qbits to reach such low temperatures is an almost impossible challenge.
And it is this scalability that will ultimately require cooling of Hensinger’s chips. If millions of ions are active there in the form of Qbits, the waste heat that will inevitably be created will simply be too much. “We want to cool our chips to minus 200 degrees Celsius using helium,” says the physicist. “It can be done with little effort and very cost-effectively.”