Nav: Home

New insights into the energy levels in quantum dots

June 25, 2020

Researchers from Basel, Bochum and Copenhagen have gained new insights into the energy states of quantum dots. They are semiconductor nanostructures and promising building blocks for quantum communication. With their experiments, the scientists confirmed certain energy transitions in quantum dots that had previously only been predicted theoretically: the so-called radiative Auger process. For their investigations, the researchers in Basel and Copenhagen used special samples that the team from the Chair of Applied Solid State Physics at Ruhr-Universität Bochum had produced. The researchers report their results in the journal Nature Nanotechnology, published online on 15 June 2020.

Lock up charge carriers

In order to create a quantum dot, the Bochum researchers use self-organizing processes in crystal growth. In the process, they produce billions of nanometer-sized crystals of, for example, indium arsenide. In these they can trap charge carriers, such as a single electron. This construct is interesting for quantum communication because information can be encoded with the help of charge carrier spins. For this coding, it is necessary to be able to manipulate and read the spin from the outside. During readout, quantum information can be imprinted into the polarization of a photon, for example. This then carries the information further at the speed of light and can be used for quantum information transfer.

This is why scientists are interested, for example, in what exactly happens in the quantum dot when energy is irradiated from outside onto the artificial atom.

Special energy transitions demonstrated

Atoms consist of a positively charged core which is surrounded by one or more negatively charged electrons. When one electron in the atom has a high energy, it can reduce its energy by two well-known processes: in the first process the energy is released in the form of a single quantum of light (a photon) and the other electrons are unaffected. A second possibility is an Auger process, where the high energy electron gives all its energy to other electrons in the atom. This effect was discovered in 1922 by Lise Meitner and Pierre Victor Auger.

About a decade later, a third possibility has been theoretically described by the physicist Felix Bloch: in the so-called radiative Auger process, the excited electron reduces its energy by transferring it to both, a light quantum and another electron in the atom. A semiconductor quantum dot resembles an atom in many aspects. However, for quantum dots, the radiative Auger process had only been theoretically predicted so far. Now, the experimental observation has been achieved by researchers from Basel. Together with their colleagues from Bochum and Copenhagen, the Basel-based researchers Dr. Matthias Löbl and Professor Richard Warburton have observed the radiative Auger process in the limit of just a single photon and one Auger electron. For the first time, the researchers demonstrated the connection between the radiative Auger process and quantum optics. They show that quantum optics measurements with the radiative Auger emission can be used as a tool for investigating the dynamics of the single electron.

Applications of quantum dots

Using the radiative Auger effect, scientists can also precisely determine the structure of the quantum mechanical energy levels available to a single electron in the quantum dot. Until now, this was only possible indirectly via calculations in combination with optical methods. Now a direct proof has been achieved. This helps to better understand the quantum mechanical system.

In order to find ideal quantum dots for different applications, questions such as the following have to be answered: how much time does an electron remain in the energetically excited state? What energy levels form a quantum dot? And how can this be influenced by means of manufacturing processes?

Different quantum dots in stable environments

The group observed the effect not only in quantum dots in indium arsenide semiconductors. The Bochum team of Dr. Julian Ritzmann, Dr. Arne Ludwig and Professor Andreas Wieck also succeeded in producing a quantum dot from the semiconductor gallium arsenide. In both material systems, the team from Bochum has achieved very stable surroundings of the quantum dot, which has been decisive for the radiative Auger process. For many years now, the group at Ruhr-Universität Bochum has been working on the optimal conditions for stable quantum dots.
-end-


Ruhr-University Bochum

Related Quantum Dots Articles:

What a pair! Coupled quantum dots may offer a new way to store quantum information
Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have for the first time created and imaged a novel pair of quantum dots -- tiny islands of confined electric charge that act like interacting artificial atoms.
Spinning quantum dots
A new paper in EPJ B presents a theoretical analysis of electron spins in moving semiconductor quantum dots, showing how these can be controlled by electric fields in a way that suggests they may be usable as information storage and processing components of quantum computers.
Towards high quality ZnO quantum dots prospective for biomedical applications
Scientists from Warsaw together with colleagues from Grenoble have moved a step closer to creating stable, high quality colloidal zinc oxide quantum dots (ZnO QDs) for use in modern technologies and nanomedicine.
Controlling the charge state of organic molecule quantum dots in a 2D nanoarray
Australian researchers have fabricated a self-assembled, carbon-based nanofilm where the charge state (ie, electronically neutral or positive) can be controlled at the level of individual molecules.
Modified quantum dots capture more energy from light and lose less to heat
Los Alamos National Laboratory scientists have synthesized magnetically-doped quantum dots that capture the kinetic energy of electrons created by ultraviolet light before it's wasted as heat.
Using quantum dots and a smartphone to find killer bacteria
A combination of off-the-shelf quantum dot nanotechnology and a smartphone camera soon could allow doctors to identify antibiotic-resistant bacteria in just 40 minutes, potentially saving patient lives.
Synthesizing single-crystalline hexagonal graphene quantum dots
A KAIST team has designed a novel strategy for synthesizing single-crystalline graphene quantum dots, which emit stable blue light.
US Naval Research Laboratory 'connects the dots' for quantum networks
Researchers at the US Naval Research Laboratory developed a novel technique that could enable new technologies that use properties of quantum physics for computing, communication and sensing, which may lead to 'neuromorphic' or brain-inspired computing.
Quantum rebar: Quantum dots enhance stability of solar-harvesting perovskite crystals
Engineering researchers have combined two emerging technologies for next-generation solar power -- and discovered that each one helps stabilize the other.
2D gold quantum dots are atomically tunable with nanotubes
Gold atoms ski along boron nitride nanotubes and stabilize in metallic monolayers.
More Quantum Dots News and Quantum Dots Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.