How do I solve physics problems faster

News portal - Ruhr University Bochum

A Danish-German research team has developed a tiny chip that is based on quantum technology and - if it were implemented on a larger scale - could surpass the computing power of a conventionally working supercomputer. The researchers showed that their nanochip can in principle achieve this so-called quantum advantage. In the chip, light particles, also called photons, are generated that can be used as flying quantum information units. The team from the University of Copenhagen and the Ruhr University Bochum reported on the development in the journal Science Advances, published online on December 9, 2020.

Quantum advantage through superposition of states

Quantum computers could solve some arithmetic tasks significantly faster than classic computers, since they could process information in parallel to a large extent. While a classic computer works with bits that have either the state zero or one, quantum computers would be based on qubits that can assume many different states at the same time. Research groups and IT companies around the world are working flat out on the development of a technology that will make the so-called quantum advantage a reality: a state in which a quantum technology can solve a certain arithmetic task faster than the most powerful supercomputers in the world.

The team around Prof. Dr. Peter Lohdahl from the Copenhagen Center for Hybrid Quantum Networks has now presented a chip that is just a hundredth as thick as a human hair and could achieve the quantum advantage. The nanochip produces stable photons in which the researchers can store quantum information. The quality of the individual photons must be so high that they are quantum-mechanically indistinguishable, i.e. practically identical. If enough of these photons are generated - and this is possible with the chip - arithmetic operations can be carried out that far exceed the computing power of a classic computer.

The expertise of the Bochum group led by Dr. Arne Ludwig and Prof. Dr. Andreas Wieck from the Chair of Applied Solid State Physics, who are experts in the manufacture of semiconductor structures with which quantum information can be stored and read out again.

The practical test requires a large financial investment

The newly developed chip has not yet passed the practical test, so the physicists have not yet solved any arithmetic task faster than a supercomputer. Carrying out such an experiment would be far beyond the financial resources of a university. "Put simply, the photons that our chip produces can be compared with the switching states on transistors in classic computers, but with quantum states," says Arne Ludwig. “For the practical test, the chip would now have to be built into a photonic circuit, i.e. correctly wired, so to speak. The technology for this already exists, but a lot of work, time and money would have to be invested in the implementation. "

In order to achieve the quantum advantage, the researchers would have to be able to use their technology to control around 50 of the qubits generated in the chip. This mark comes from experiments by the company Google, which had their quantum computer based on superconducting qubits undergo the practical test. In their current work with theoretical methods, the Danish-German team showed that it would be possible to control 50 qubits with light-based technology. Now they are looking for partners from industry who could upscale the chip for practical use.

Different types of qubits

There are different approaches for the development of quantum computers, the information units of which can be based on atoms, electrons or photons. Each technique has its advantages and disadvantages. According to the scientists, the greatest advantage of light-based technology is the fact that photonic technologies are already widely used in the telecommunications industry. When upscaling the technology, you could dock onto the existing infrastructure.

Quantum dots from Bochum

The Bochum team has continued to develop the manufacturing technology for quantum dots over the past eight years. These are structures in semiconductors that can emit qubits in the form of photons. Together with partners, they designed techniques to specifically load and unload qubits with information and to be able to transport information over long distances. Since the quantum dots are almost perfect at emitting single photons, they are ideal for light-based applications.

The work was supported by the Federal Ministry of Education and Research (funding numbers 16KIS0867 and Q.Link.X) and the German Research Foundation (Sonderforschungsbereich / Transregio 160, project number 383065199 and DFH / UFA CDFA-05-06).

Ravitej Uppu, Freja T. Pedersen, Ying Wang, Cecilie T. Olesen, Camille Papon, Xiaoyan Zhou, Leonardo Midolo, Sven Scholz, Andreas D. Wieck, Arne Ludwig, Peter Lodahl: Scalable integrated single-photon source, in: Science Advances , 2020, DOI: 10.1126 / sciadv.abc8268

Prof. Dr. Andreas Wieck
Applied Solid State Physics
Faculty of Physics and Astronomy
Ruhr-University Bochum
Tel .: +49 234 32 26726
Email: [email protected]

Dr. Arne Ludwig
Applied Solid State Physics
Faculty of Physics and Astronomy
Ruhr-University Bochum
Tel .: +49 234 32 25864
Email: [email protected]