Curved Spacetime in Quantum Simulations – ScienceDaily


The theory of relativity works well when you want to explain cosmic phenomena – such as the gravitational waves that are created when black holes collide. Quantum theory works well when describing particle scale phenomena – such as the behavior of individual electrons in an atom. But the combination of the two in a completely satisfactory manner has yet to be achieved. The search for a “quantum theory of gravity” is one of the most important unsolved tasks of science.

This is partly because the mathematics in this field is very complex. At the same time, it is difficult to perform proper experiments: one has to create situations in which both phenomena of the theory of relativity play an important role, for example, space-time curved by heavy masses, and at the same time, quantum effects become visible, for example the double particle and nature wavelength of light.

At TU Wien in Vienna, Austria, a new approach has been developed for this: so-called “quantum simulations” are used to get to the bottom of these questions: instead of directly investigating the system of interest (i.e., quantum particles in curved space-time), one creates a “system typically” by which something about the actual system of interest can be known by analogy. Researchers have now shown that this quantum simulator works perfectly. The results of this international collaboration involving physicists from the University of Crete, Nanyang Technological University, and FU Berlin are now published in the scientific journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Learning from one system to another

The basic idea behind a quantum simulator is simple: many physical systems are the same. Even if they are completely different types of particles or physical systems at different levels, which, at first glance, have nothing to do with each other, these systems may be subject to the same laws and equations at a deeper level. This means that one can learn something about a particular system by studying another system.

“We take a quantum system that we know we can control and fine-tune in experiments,” says Professor Jörg Schmidmeier of the Atomic Institute at TU Wien. “In our case, these are very cold atomic clouds held and manipulated by an atomic chip with electromagnetic fields.” Suppose you have properly modified these atomic clouds so that their properties can be translated into another quantum system. In this case, you can learn something about the other system by measuring the atomic cloud model system—just as you can learn something about the oscillation of a pendulum from the oscillation of a mass attached to a metal spring: they are two different physical systems, but one can be translated into the other.

gravitational lens effect

says Mehmetamine Tajik of the Vienna Center for Quantum Science and Technology (VCQ) – TU Wien, first author of the current paper. In a vacuum, light propagates along what is called a “cone of light”. The speed of light is constant. At equal times, the light travels the same distance in each direction. However, if the light is affected by heavy masses, such as the gravity of the Sun, these light cones bend. Light paths are no longer perfectly straight in curved space-time. This is called the “gravitational lensing effect”.

The same can now be shown in atomic clouds. Instead of the speed of light, one examines the speed of sound. “We now have a system in which there is an effect that corresponds to space-time curvature or gravitational lensing, but at the same time, it is a quantum system that you can describe using quantum field theories,” says Mehmetamine Tajik. “With this, we have a completely new tool for studying the relationship between relativity and quantum theory.”

A model system for quantum gravity

Experiments show that the shape of light cones, lensing effects, reflections, and other phenomena can be manifested in these atomic clouds just as would be expected in relativistic cosmic systems. This is not only interesting for generating new data for basic theoretical research – solid-state physics and the search for new materials also face questions that have a similar structure and can therefore be answered by such experiments.

“We now want to better control these atomic clouds to determine more long-range data. For example, it is still possible to change the interactions between particles in a very targeted way,” explains Jörg Schmidmeyer. In this way, a quantum simulator can recreate physical situations that are too complex to compute even with supercomputers.

The quantum simulator thus becomes a new additional source of information for quantum research – in addition to theoretical calculations, computer simulations and direct experiments. In studying atomic clouds, the research team hopes to come across new phenomena that may not have been completely known yet, which also occur on a relativistic cosmic scale — but without looking at the tiny particles, they may never have been. Discover.


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