Do quantum computers still exist

The long way to the high-speed computer Quantum computer: "We are in a transition phase"

It sounded like a technical revolution when Google announced in autumn 2019 that they could demonstrate what is known as quantum superiority with a quantum computer they had developed. This means that he has performed an arithmetic operation that a conventional computer would not have been able to solve in a realistic time frame - that would take years or even millennia. Google's innovation was impressive, but computer technology hasn't revolutionized it yet. So what about the development of a universal quantum computer? Or even one that could eventually replace our laptop at home? Experts are clearly slowing down this thought: the quantum laptop is definitely still a long way off - if it is ever possible.

But why do we actually need a quantum computer that can calculate at previously unimaginable speeds? There are some areas where it would make a real difference; in research for new drugs, for example, in materials research, in optimization processes or modeling. Some experts believe that entire processes can even be simulated in nature. And then they could crack current encryption methods in cryptography or make new methods possible, which is also one reason why the military and intelligence services, among others, are interested in the technology. But experts are also hoping for advantages and new possibilities for many other applications, such as in the area of ​​machine learning.

Hybrid transition phase

But the quantum computer that can do all of this is far from just around the corner, slows Immanuel Bloch, Professor of Experimental Physics at the Ludwig Maximilians University in Munich and Director of the Max Planck Institute for Quantum Optics. So far, only small calculations have been made on all quantum computers. "Nothing yet that knocks you off your feet," he said in an interview with the Science Media Center. So there are still only the first demonstrations, but the road to a universal quantum computer is still quite long. But the goal is clear: a completely error-corrected, programmable quantum computer.

Developing a fully error-corrected quantum computer is the great challenge for the next ten or twenty years.

Prof. Dr. Immanuel Bloch

Nevertheless, the applications of the small systems are still exciting. Because they let the experts learn: What is possible, for example, when programming algorithms? Perhaps the new "killer application" has not yet been found, speculates Bloch.

His colleague Peter Zoller - Professor of Theoretical Physics at the Center for Quantum Physics at the University of Innsbruck and Head of Research at the Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences - points out that today's technologies are already a significant step forward. Fifteen years ago, basic research demonstrated the first small components in the laboratory. With the "small" quantum computers from Google, IBM or from the research laboratories, a completely new phase has begun in the past few years that will last for another ten or fifteen years. It is a transition phase, explains Zoller.

We will build machines that will have tens to several hundred quantum bits of the order of magnitude and that have not yet been error-corrected, but on which one can still do quantum calculations.

Professor Peter Zoller

It will not happen in the same way as in the vision, in which you have complex algorithms. We are still a long way from that, but already in a way that we can scratch our quantum superiority. Research will be concerned with such "intermediate scale quantum devices" for the next 15 years or so. The applications must be adapted to the hardware as it is currently developing. According to Zoller, a hybrid approach also plays an important role: by combining conventional with quantum computers, hybrid algorithms could also be developed.

Wherever qubits do math, mistakes happen

The distant goal is a quantum computer that is scalable, programmable and error-corrected. Scalable means that it can be expanded to hundreds or thousands of qubits without uncontrollably frequent errors. Since it works with completely different physical laws than conventional computers, programming also has to be completely reinvented. And then at best he has to correct his own mistakes.

The mistakes that a quantum computer makes when calculating are the biggest unsolved problem. To understand this, you have to dive into the crazy world of quantum physics: errors happen wherever qubits do their math.

The term is derived from the physical term "quantum" and the "bit" used in computer technology. The quantum is the smallest possible value of a physical quantity - i.e. the smallest unit that something consists of, such as atoms, photons (light particles) or electrons - roughly like the pixels in a digital photo. The quantum world has its own physical laws, some of which even contradict our everyday knowledge and which are still not fully understood today. A qubit can, for example, be a charged atom - an ion - or an electron in a circuit. They are the basic arithmetic unit in a quantum computer.

Conventional computers calculate with bits in a binary system. That means there are only two states: power on (0) or power off (1). This is different with qubits. Because due to the laws of quantum physics, you can take both of these states at the same time - and all the others that lie in between.

You can think of it as a coin that rotates on its own axis: you only know whether it is heads or tails when it stops. As long as it rotates, however, it is all at the same time. The qubits only work as long as they are in this state. Physicists call this superposition. This enables the qubits to process 0 and 1 in parallel. If several qubits are interlaced, the number of values ​​processed at the same time increases exponentially. A few hundred qubits can theoretically process more numbers than there are particles in the universe.