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Ready for take-off!

Quantum computers are ready to take off, says David DiVincenzo. In our interview, the physicist explains what they will be used for and to what extent they could be useful or threatening.

Prof. DiVincenzo, how would you explain to me as a layperson what a quantum computer is?

A bit, the object of today’s information technology, consists either of the number 1 or the number 0. And there is no doubt whatsoever as to whether this object is a 1 or a 0. It’s like this pen: it’s either unquestionably here, or – if I put it somewhere else – it’s unquestionably there. Things are different in the quantum world: there, an object can be in one place and somewhere else at the same time. This contradicts our everyday experience as well as our intuition – just like other aspects of quantum physics. This is why quantum computers – which are based on the laws of quantum physics – are so difficult to understand. For example, the qubit, the object of quantum computing, can be both 0 and 1 at the same time. This property, among others, can be used to solve some tasks more rapidly than is possible with bits and digital computers.

Will quantum computers replace our computers in the future?

I don’t think that’s likely. Our digital computers are almost universally applicable. In many areas, a quantum computer will have no additional value compared to such computers. But scientists like me have for a while had our minds set on certain applications for which quantum computers will be far superior to conventional computers.

Ready to take off!Prof. David DiVincenzo is viewed as a pioneer in the field of quantum information. His name is associated with the development of criteria that a quantum computer must fulfil, the “DiVincenzo criteria”. The physicist is a director at Jülich’s Peter Grünberg Institute – Theoretical Nanoelectronics (PGI-2) and teaches at the JARA Institute for Quantum Information at RWTH Aachen University. In 2010, the American was awarded an Alexander von Humboldt Professorship, Germany’s most valuable international research prize.
Copyright: Forschungszentrum Jülich

What applications are these?

Firstly, the simulation of materials because they consist of atoms and electrons. These are components which obey the laws of quantum physics and we will therefore be better able to understand and predict their properties using quantum computers than we can now. Secondly, quantum computers may contribute to developing a novel network through which data may be exchanged more securely and partners can work together more securely than through the digital Internet. Thirdly, a quantum computer will be able to solve a series of complex mathematical problems more efficiently than conventional computers. This is of interest not only for pure mathematics, but also, for example, for the technology currently used to encrypt and decrypt data.

Speaking of decrypting data, this issue is the reason why there are concerns that quantum computers could be powerful weapons in the hands of intelligence agencies or criminals. What’s your reply to that?

Firstly, the Internet is by no means safe, even today – there is no need for quantum computers for that. Even the encryption technology that is currently used in Internet banking and messenger services will be so insecure in ten years’ time that it should be scrapped. But there is also some good news: there are already alternative means of encryption for such classic Internet services that could not be cracked even with a quantum computer. Hopefully, such methods will be operational on a wide scale in ten years. Additionally, pure quantum communication networks offer long-term security. It’s in the nature of these systems that any eavesdropping activity will be detected.

As far back as the early 1990s, there were reports that researchers had realized a quantum computer based on organic molecules. How far are we today?

The experiments conducted 20 years ago were well suited to demonstrate the principles of quantum mechanics and to produce individual qubits. As a result of theoretical deductions, I already predicted back then that quantum systems based on organic molecules could not be enlarged from a few qubits to 100 or more qubits. This limit in scalability was subsequently confirmed. At the end of the 1990s, theorists had the the idea of realizing qubits in solids, which was then achieved in the early 2000s. Today, there are solid-state systems which in my opinion can be upscaled from currently five or ten qubits to significantly more: the quantum computer is ready for take-off.

The US-based company D-Wave has already sold some specimens of a device that they call a quantum computer. But experts still argue whether it really is one. What’s your opinion?

The D-Wave computer has certain properties of a quantum computer. But I wouldn’t describe it as such. One reason for this is that its qubits can only take a superposition state between 0 and 1 for some nanoseconds (billionths of a second). This is why even future versions will solve very few tasks more efficiently than conventional computers.

You are concerned with quantum computers from the perspective of a theorist. What does that mean?

In contrast to practitioners, I am not bound to laboratory equipment, technology, or a method. Neither am I dependent on supercomputers or codes like other theorists. What I need is simply a piece of paper to write on, in order to develop ideas. I also think about how these ideas can be useful in experiments or how they can be applied.

Can you give an example of such an idea?

In current qubit experiments, components are used for signal processing which were described in a book as early as the 1960s. The more qubits are used in a system, the more of these centimetrelong circulators are necessary. I was reading up on something in that book some time ago when I had an idea for an alternative circulator, which works according to a completely different principle. Its great advantage is that it is smaller than the conventional circulator and a large number can be integrated on a single chip. Together with a postdoc, I’m further developing this idea. I now have a patent for it, and I’ve also written some publications on the topic.

The Interview was conducted by Frank Frick.

This Interview was published in the "effzett", (3/2016).