Researchers Simulate Lattice Gauge Theories in a Quantum Computer to Understand Fundamental Processes

The primary building blocks of matter are the elementary particles, whose properties are explained in the Standard Model of particle physics. An advanced step in confirming the Standard Model was the finding of the Higgs boson in 2012 at the CERN.

It is difficult to understand many aspects of this theory due to the complex nature and it is hard to examine the same with classical computers. This obstacle may be overcome by quantum computers as certain elementary particle physics can be stimulated in a quantum system that is well controlled. That is what physicists from the University of Innsbruck and the Institute for Quantum Optics and Quantum Information (IQOQI) at the Austrian Academy of Sciences have done. Lattice gage theories have been simulated in a quantum computer by Rainer Blatt’s and Peter Zoller’s research groups and are internationally first. They have reported their study in the Nature journal.

Simulation of particle-antiparticle pairs using a quantum computer

The interaction among elementary particles, like quarks and gluons can be explained using gage theories, and they are the basis for our understanding of fundamental processes.

Dynamical processes, for example, the collision of elementary particles or the spontaneous creation of particle-antiparticle pairs, are extremely difficult to investigate. However, scientists quickly reach a limit when processing numerical calculations on classical computers. For this reason, it has been proposed to simulate these processes by using a programmable quantum system.

Christine Muschik, Theoretical Physicist, IQOQI

Although a number of fascinating concepts have been suggested, till date it has not been possible to realize them.

"We have now developed a new concept that allows us to simulate the spontaneous creation of electron-positron pairs out of the vacuum by using a quantum computer," states Muschik.

Four electromagnetically trapped calcium ions regulated by laser pulses constitutes the quantum system.

"Each pair of ions represent a pair of a particle and an antiparticle," explains Esteban A. Martinez, experimental physicist. "We use laser pulses to simulate the electromagnetic field in a vacuum. Then we are able to observe how particle pairs are created by quantum fluctuations from the energy of this field. By looking at the ion's fluorescence, we see whether particles and antiparticles were created. We are able to modify the parameters of the quantum system, which allows us to observe and study the dynamic process of pair creation."

Combining various fields of physics

The physicists from Innsbruck have constructed a bridge between two separate fields in physics with this experiment. Atomic physics experiments have been used to solve queries in high-energy physics. Quantum simulations can be achieved by small teams in tabletop experiments. However, most theoretical physicists research on the extremely complicated theories of the Standard Model and experiments are performed at highly costly facilities, like the Large Hadron Collider at CERN.

These two approaches complement one another perfectly. We cannot replace the experiments that are done with particle colliders. However, by developing quantum simulators, we may be able to understand these experiments better one day.

Peter Zoller, Theoretical Physicist, University of Innsbruck

Rainer Blatt, experimental physicist continues, "Moreover, we can study new processes by using quantum simulation. For example, in our experiment we also investigated particle entanglement produced during pair creation, which is not possible in a particle collider." The physicists hope that future quantum simulators would be able to answer vital questions in high-energy physics that cannot be handled by traditional methods.

Foundation for a new field of research

The idea to unite atomic and high-energy physics was suggested a few years back. It has been executed experimentally with this work for the first time.

This approach is conceptually very different from previous quantum simulation experiments studying many-body physics or quantum chemistry. The simulation of elementary particle processes is theoretically very complex and, therefore, has to satisfy very specific requirements. For this reason it is difficult to develop a suitable protocol.

Peter Zoller, Theoretical Physicist, University of Innsbruck

The conditions were similarly demanding for the experimental physicists.

"This is one of the most complex experiments that has ever been carried out in a trapped-ion quantum computer," states Blatt. "We are still figuring out how these quantum simulations work and will only gradually be able to apply them to more challenging phenomena."

The theoretical and experimental proficiency of the physicists in Innsbruck was critical for the discovery. Both Zoller and Blatt highlight that they have been performing research on quantum computers since many years and have gained plenty of experience in their execution. Innsbruck has turned out to be one of the foremost centers of research in quantum physics. The experimental and theoretical branches collaborate at a high level in Innsbruck, which permits them to get novel insights into the basic phenomena.

The scientists receive funds from the European Union and the Federation of Austrian Industries Tyrol, the Deutsche Akademie der Naturforscher Leopoldina, the Austrian Science Fund (FWF), and the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences to mention a few.