Barely a week goes by without reports of some new mega-hack that’s exposed huge amounts of sensitive information, from people’s credit card details and health records to companies’ valuable intellectual property. The threat posed by cyberattacks is forcing governments, militaries, and businesses to explore more secure ways of transmitting information.
For 15 years, scientists have tried to exploit the “miracle material” graphene to produce nanoscale electronics. On paper, graphene should be great for just that: it is ultra-thin—only one atom thick and therefore two-dimensional, it is excellent for conducting electrical current, and holds great promise for future forms of electronics that are faster and more energy efficient. In addition, graphene consists of carbon atoms – of which we have an unlimited supply.
In theory, graphene can be altered to perform many different tasks within e.g. electronics, photonics or sensors simply by cutting tiny patterns in it, as this fundamentally alters its quantum properties. One “simple” task, which has turned out to be surprisingly difficult, is to induce a band gap—which is crucial for making transistors and optoelectronic devices. However, since graphene is only an atom thick all of the atoms are important and even tiny irregularities in the pattern can destroy its properties.
“Graphene is a fantastic material, which I think will play a crucial role in making new nanoscale electronics. The problem is that it is extremely difficult to engineer the electrical properties,” says Peter Bøggild, professor atDTU Physics.
Shaking a physical system typically heats it up, in the sense that the system continuously absorbs energy. When considering a circular shaking pattern, the amount of energy that is absorbed can potentially depend on the orientation of the circular drive (clockwise/anti-clockwise), a general phenomenon known as circular dichroism.
In 2017, Nathan Goldman (ULB, Brussels), Peter Zoller (IQOQI, Innsbruck) and coworkers predicted that circular dichroism can be quantized in quantum systems (heating is then constrained by strict integers) forming a “topological state.” According to this theoretical prediction, the quantization of energy absorption upon circular driving can be directly related to topology, a fundamental mathematical concept that characterizes these intriguing states of matter.
Writing in Nature Physics, the experimental group of Klaus Sengstock and Christof Weitenberg (Hamburg), in collaboration with the team of Nathan Goldman, reports on the first observation of quantized circular dichroism. Following the theoretical proposal of Goldman, Zoller et al., the experimentalists realized a topological state using an ultracold atomic gas subjected to laser light, and studied its heating properties upon circular shaking of the gas. By finely monitoring the heating rates of their system, for a wide range of driving frequencies, they were able to validate the quantization law predicted by Goldman, Zoller et al. in 2017, in agreement with the underlying topological state realized in the laboratory.
Circa 2018
The experimental mastery of complex quantum systems is required for future technologies like quantum computers and quantum encryption. Scientists from the University of Vienna and the Austrian Academy of Sciences have broken new ground. They sought to use more complex quantum systems than two-dimensionally entangled qubits and thus can increase the information capacity with the same number of particles. The developed methods and technologies could in the future enable the teleportation of complex quantum systems. The results of their work, “Experimental Greenberger-Horne-Zeilinger entanglement beyond qubits,” is published recently in the renowned journal Nature Photonics.
Similar to bits in conventional computers, qubits are the smallest unit of information in quantum systems. Big companies like Google and IBM are competing with research institutes around the world to produce an increasing number of entangled qubits and develop a functioning quantum computer. But a research group at the University of Vienna and the Austrian Academy of Sciences is pursuing a new path to increase the information capacity of complex quantum systems.
The idea behind it is simple: Instead of just increasing the number of particles involved, the complexity of each system is increased. “The special thing about our experiment is that for the first time, it entangles three photons beyond the conventional two-dimensional nature,” explains Manuel Erhard, first author of the study. For this purpose, the Viennese physicists used quantum systems with more than two possible states—in this particular case, the angular momentum of individual light particles. These individual photons now have a higher information capacity than qubits. However, the entanglement of these light particles turned out to be difficult on a conceptual level. The researchers overcame this challenge with a groundbreaking idea: a computer algorithm that autonomously searches for an experimental implementation.
