Weizmann Institute of Science scientists present the rotating quantum microscope
One of the strangest properties of the quantum world is manifested in the fact that a particle is also a wave - that is, it exists in several places at the same time. Paradoxically, if we observe a particle, say an electron, we will confine it to one place and cause it to lose its quantum nature. Weizmann Institute of Science scientists managed to overcome this quantum strangeness and in the process developed a new way to observe quantum materials. in research published today in the scientific journal Nature They present to the world the quantum twisting microscope - Quantum Twisting Microscope or QTM for short - which follows the wavy behavior of electrons without causing them to collapse into a particle state. This technology will make it possible to create new quantum materials with unprecedented properties and applications, while at the same time observing the fundamental quantum nature of their electrons.
"We don't ask the electron personal questions, like 'Where are you?'" says the head of the research team Prof. Shachel Ilani From the Department of Condensed Matter Physics at the institute. "We simply perform an experiment that allows the electron to be in several places at the same time, and thus we manage to measure its very sensitive quantum behavior without destroying it."
Prof. Ilani explains that the wave behavior of electrons is already used in advanced materials called quantum materials, that is, those whose properties are determined by quantum phenomena. But in order to make the electrons perform different stunts - for example, in order to build new types of electronic devices - the scientists need to understand what exactly the electrons do in the material. And there is no better way to understand this, he says, than to show eyes.
"Biologists observe cells using optical microscopes, and astronomers study stars using telescopes. Now physicists will be able to examine materials using our quantum microscope and observe electrons in a way that is not possible with existing tools," says Prof. Ilani.
produce a quantum image
The ability of scientists to see electrons in matter took a leap forward about 40 years ago with the invention of the scanning tunneling microscope, for which the inventors were awarded the Nobel Prize in Physics in 1986. This microscope scans the surface of the material with an extremely thin needle, injects an electric current into it, and thus produces Gradually a picture of the distribution of electrons in the material.
"Biologists observe cells with the help of optical microscopes, astronomers study stars with the help of telescopes - and physicists will now be able to examine quantum materials using our microscope," say the researchers about the breakthrough technology they have developed
"Since this invention, many different methods have been developed to scan matter on a subatomic scale, but they all measure the properties of electrons in one place at any given time, so they can observe electrons mainly as particles; the wave nature can only be learned indirectly," explains Prof. Adi Stern, a colleague in Prof. Ilani's department. Prof. Stern participated in the research together with three other theoretical physicists from the same department: Prof. Binghai Yan, Prof. Yuval Org and Prof. Erez Berg. "The microscope we developed here produces a quantum image of the behavior of electrons in a material, that is, it allows for a direct imaging of the quantum electron waves," says Prof. Stern.
A new twist on spun materials
The QTM that was built by Alon Inbar, Dr. John Birkbek and Jivan Shaw in Prof. Ilani's laboratory is a completely new tool from a conceptual point of view. One of the main things that differentiates it from existing scanners is the needle. Instead of a needle with one or two atoms as in scanners existing, there is a surface about a thousand atoms wide; large enough to allow the electrons to flow with their quantum nature.
The surface gives QTM a role no less important than the possibility of observing materials: the ability to be used as a machine for the rapid production of new quantum materials. This role belongs to "twisttronics", a new field of nanomaterials research that was born about four years ago with a surprising discovery regarding graphene, a crystalline sheet of carbon only one atom thick. It turned out that if two layers of graphene are placed on top of each other in a slight rotation, or "twist" - and not in a precise and aligned match of the atomic networks in the two layers - the resulting "sandwich" takes on unexpected properties. Following this discovery, scientists began to develop different types of quantum materials, each with its own "spin".
The angle of rotation has been found to be the most critical variable for controlling the behavior of electrons in materials: a change of a tenth of a degree can transform them from an exotic superconductor to an unconventional insulator. But as critical as it is, this variable is also the most difficult to control, as each creation of a new angle requires the construction of a new "sandwich", a process that can take months. The QTM solves this problem by separating the two layers: one layer is attached to the scanning microscope needle, while the other is placed below it. The separation allows scientists to precisely control not only the level of pressure and the distance between the two layers, but also to rotate the upper surface with great precision, thereby changing the angle of rotation between the layers quickly and easily and creating an almost infinite number of materials that do not exist in nature.
"Our initial motivation was to solve the angle problem by building a new device that could rotate any two materials in relation to each other in a controlled and precise manner, thus producing a wide variety of new materials quickly," says Alon Inbar, the doctoral student who led the research in Prof. Ilani's laboratory. "While building this device, we discovered that it is possible to turn it into a powerful microscope that is able to simulate quantum electronic waves in a way that was impossible to imagine before."
Turning and tunneling
But how is the QTM's impressive imaging ability manifested? To use it as a microscope, scientists place an electrically insulating layer between the top surface and the material under examination, then send a stream of electrons through this layer. In the world we know, governed by the laws of classical physics, the electrons are not supposed to cross the barrier created by the insulating layer. But in the quantum world, at least some of them can pass through - a phenomenon known as "tunneling".
Unlike a standard tunneling microscope, where electrons can only cross in a single place, at the tip of the needle, the junction created in the QTM microscope is a two-dimensional surface, so the electron can choose to pass through multiple places. In a classical world, every passing electron will cross at one particular place. But in the quantum world, a single electron will traverse through all the places together at the same time. In such a process the electron can maintain its existence as a quantum wave as long as it cannot be said where it crossed. The QTM therefore makes it possible to directly examine the electrons in their natural state in the material - as quantum waves - and not by turning them into particles as has been done in all microscopes to date. This ability makes it possible to examine the form of organization of the electrons in the material, to map the material energetically and to diagnose the ways of "interference" of the waves, i.e. how the waves affect each other.
"Our microscope will give scientists a new 'lens' to examine and measure properties of quantum materials," says Inbar. "In fact, we have already examined some quantum materials at room temperature using the QTM and discovered new phenomena, but when we cool this microscope down to low temperatures we will be able to make breakthrough discoveries about some of the most exciting quantum effects."
As we look deeper into the quantum world, we will not only make new discoveries about nature, but also create technological effects on our daily lives. The quantum world is already knocking on our door with technologies in the making, from quantum computers to quantum control of chemical processes. The QTM promises to accelerate the arrival of these into implementation.
