In the future, it may be possible to use the control over the coupling of the quantum dots to build switches for quantum computers, or for encryption devices that will be based on quantum phenomena - that is, machines that can operate at the level of photons or individual quantum systems
A research group led by Prof. Gilad Haran From the Department of Chemical Physics - which included post-doctoral researcher Dr. Kotani Santosh, faculty scientist Dr. Ora Biton from the Department of Chemical Research Infrastructures, and Prof. Lev Chotunov from the Technion - created two-dimensional nanostructures in the shape of a bow tie, made of silver , have a spacing of about 20 nanometers (billionths of a meter) in their center. The researchers dipped the "bow ties" in a solution containing quantum dots (tiny semiconductor particles, six to eight nanometers in size, capable of absorbing and emitting light). During the immersion, some of the quantum dots were captured in the gaps in the center of the "bow ties".
Under exposure to light, the trapped dots created an electromagnetic coupling to the "bow ties". In this process, a mixed state was created: a light particle - a photon - that reached the device, was divided between the "bow tie" and the quantum dot. The coupling was so strong that it was observed even when only one quantum dot was trapped in the gap of the "bow tie". As a result, it was possible to cause the "butterfly ties" to go, as if by means of a switch, from one state to another: from the state that preceded the coupling to quantum dots, before exposure to light, to the mixed state characterized by strong coupling, after exposure to light.
In the future, it may be possible to use the control over the coupling of the quantum dots to build switches for quantum computers, or for encryption devices that will be based on quantum phenomena - that is, machines that can operate at the level of photons or individual quantum systems, such as atoms, molecules or quantum dots. Scientists predict that these devices will be many times more powerful than the current electronic computers or encryption systems, because quantum phenomena create situations that do not exist on a day-to-day basis, such as the possibility of a particle being in more than one place at the same time, and therefore being able to perform more than one calculation at the same time.
"This is only the first step of our coupling method, which we hope will contribute to the creation of quantum switches in the future," says Prof. Hearn. "A lot of research is still needed before it will be possible to build useful devices using this method, but we have shown that in principle, it is easy to apply our method, and most importantly - that it is applicable at room temperature. Now we are developing even smaller nanostructures in the shape of a bow tie, and are trying to create an even stronger and reversible coupling."
The institute's scientists were able to develop the "bow tie" system thanks to new developments in nano technologies, including electron beam lithography, with which they built the "butterfly ties" and inserted the quantum dots into the spaces in their center. The scientists analyzed the data with the help of relatively simple calculation programs, the availability of which makes redundant the much work that was required in the past by theorists to describe such systems. The scientists also relied on understanding electron oscillations created in metals using light, something that is now possible thanks to recently published research findings. These vibrations, which are the physical source of the coupling between the "bow ties" and the quantum dots, are especially strong on the surface of the metal. Therefore, in two-dimensional systems, the electric and magnetic field created by these oscillations is highly concentrated, especially when it is focused on the narrowest part of the "bow tie", similar to light focused on a narrow beam.
It is the high concentration of light that ensures the good control over the coupling, and this control is essential for future quantum applications. This is the first time that a system built for the purpose of studying strong coupling between light and a single quantum system succeeds in operating on such a tiny scale. This achievement now makes it possible, for the first time, to carry out additional experiments at the level of the individual quantum dots.
