LINKOPING: “Our results do not yet have any obvious or direct applications. This is fundamental research that lays the foundation for future technologies in quantum information and Quantum computers. There is great potential for breakthrough discoveries in many different research fields,” said Wilhelm B. Xavier, a researcher Quantum communication at Linköping University, Sweden.
However, to understand what the researchers have demonstrated, we must start at the beginning.
One of the most absurd – yet essential – properties of quantum mechanics is that light can be both particles and waves. We refer to it. Wave-particle duality.
This theory dates back to the 17th century when Isaac Newton proposed that light consists of particles. Other contemporary scholars believed that light consists of waves. Newton eventually suggested that it could be both, without being able to prove it. In the 19th century, several physicists demonstrated in various experiments that light actually consists of waves.
But in the early 1900s, both Max Planck and Albert Einstein challenged the theory that light is just waves. However, it was not until the 1920s that physicist Arthur Compton was able to show that light also has kinetic energy, a property of a classical particle. The particles were named photons. Thus, it was concluded that light could be both particles and waves, just as Newton had suggested. Electrons and other elementary particles also exhibit this wave-particle duality.
But it is not possible to measure the same photon as both a wave and a particle. Depending on how photons are measured, either waves or particles appear. This is known as the principle of complementarity and was developed by Niels Bohr in the mid-1920s. This states that no matter what one decides to measure, the combination of wave and particle properties must be constant.
In 2014, a research team from Singapore demonstrated a mathematically direct connection between the complementarity principle and the degree of unknown information in a quantum system, known as so-called Entropic uncertainty. This relation means that for any combination of wave or particle characteristic of a quantum system, the unknown information quantity is at least a part of the information, i.e. the unmeasurable wave or particle.
Linköping University researchers, together with colleagues from Poland and Chile, have now succeeded in confirming the theory of the Singaporean researchers with the help of a new type of experiment.
“From our point of view, this is a very straightforward way to demonstrate fundamental quantum mechanical behavior. It’s a typical example of quantum physics where we can see the results, but we can’t imagine what’s going on inside the experiment. And yet it can be used. It’s very fascinating and almost borders on philosophy.” Guilherme B Xavier added.
In their new experimental setup, the Linköping researchers used photons moving in a circular motion, called orbital angular momentum, as opposed to the more common oscillating motion, which is up and down. The choice of orbital angular momentum allows practical use of the experiment in the future, as it may contain more information.
Measurements are made in an instrument commonly used in research, called a Interferometerwhere photons are shot at a crystal (beamsplitter) that splits the path of the photons into two new paths, which are then reflected to cross each other at another beam splitter and then measured. Be it as particles or waves. The status of this other device.
One thing that makes this experiment setup special is that the second beam splitter can be partially placed in the path of the light by the researchers. This makes it possible to measure light as waves, or particles, or a combination of these in a single setup.
According to the researchers, the results could have many future applications in quantum communication, metrology, and cryptography. But there is much more to explore at a fundamental level.
“In our next experiment, we want to observe the photon’s behavior if we change the configuration of the second crystal before the photon reaches it. This will show that we can securely encrypt this experimental setup in communication. can use to distribute keys, which is very exciting,” shared Daniel Spiegel-Lackson, a PhD student in the Department of Electrical Engineering.