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In the 21st century, we are moving towards a true coming-of-age of technologies that use quantum-mechanical phenomena, such as entanglement and quantum many-body effects. Quantum technology (QT) applies quantum mechanical properties such as quantum entanglement, quantum superposition, and No-cloning theorem to quantum systems such as atoms, ions, electrons, photons, or molecules. Quantum bit is the basic unit of quantum information. Whereas in a classical system, a bit is either in one state or the another. However, quantum qubits can exist in large number of states simultaneously, property called Superposition.
Quantum entanglement is a phenomenon where entangled particles can stay connected in the sense that the actions performed on one of the particles affects the other no matter what’s the distance between them. No-cloning theorem tells us that quantum information (qubit) cannot be copied.
Quantum technologies have the potential to spur revolutions in computing, sensing, cryptography and beyond. By taking advantage of those properties, quantum computers can process information in new ways, potentially performing calculations far beyond the reach of even the fastest of today’s supercomputers. Quantum sensors far more powerful than those used today could be useful in applications ranging from medicine to seismology. And quantum cryptography could lead to intrinsically secure communication.
For all the promise, however, there are obstacles to overcome before these quantum technologies deliver their full potential. One problem is that quantum states are extremely fragile — the slightest disturbance can destroy them. And scientists still don’t fully understand how to model the complex correlations between particles in quantum systems. Those microscopic correlations are critically important because they ultimately determine the properties of a material at the macroscopic scale. This is driving the development of new materials and structures where such effects play a leading role.
As we are entering the Quantum Age, Researchers have turned to quantum materials. “Quantum materials” was a phrase originally invented by researchers in condensed matter physics. It’s an umbrella term referring to materials that have properties that cannot be easily described by classical, or low-level, quantum physics. Nowadays people generalize quantum materials to other things, including topological materials, low-dimensional materials, and engineered quantum materials.
When engineers and physicists make new materials in electronics, Typically, the sizes people are working with these days are mostly at the nanoscale or nanometer scale, which is a few billionths of a meter—a scale that’s related to the size of molecules, or a few tens of atoms. To work at this very small scale, special tools and techniques are needed. You need special tools to image the tiny structures or even to fabricate devices. Some of the techniques include electron beam microscopy, lithography, focus ion beam microscopy, and lithography. There are other things like scanning tunneling microscopy, atomic force microscopy, nano-scanning optical microscopy. Given the tiny sizes of these things—they’re even smaller than typical dust particles—people often will have to conduct observations and fabrication in a clean-room environment.
One of the major challenges in advancing semiconducting technology is that we need to continually decrease the size of nano-electronic components and devices. That leads to new challenges in the quantum limit. For instance, we have issues related to quantum conductance, quantum capacitance, quantum fluctuations as well as increasing heat dissipation. Now, if we incorporate quantum materials, we can actually introduce additional electrical and thermal conduction channels and provide protection barriers and layers to prevent atomic migration in nano devices and nano structures. These materials also have interesting properties you can use to develop additional functionalities.
Quantum materials
Quantum materials are broadly defined as all those versatile materials platforms that allow us to explore emergent quantum phenomena as well as their potential uses in future technology. Quantum materials is a broad term to put under the same umbrella materials that present strong electronic correlations and/or some type of electronic order (superconducting, magnetic order), or materials whose electronic properties are linked to non-generic quantum effects, such as topological insulators, Dirac electron systems such as graphene, as well as systems whose collective properties are governed by genuinely quantum behavior, such as ultra-cold atoms , cold excitons, polaritons, etc.
The last few decades have seen the discovery of materials with exotic properties few would have imagined. Superconductors exhibit zero resistivity up to 135 Kelvin. Multi-ferroic materials allow a magnetic field to write electric domains and an electric field to write magnetic domains. Colossal magnetoresistance materials change their electrical conductivity by orders of magnitude upon application of a magnetic field. Heavy fermion materials host electrons which behave thousands of times heavier than their actual mass, whereas the electrons in graphene behave as if they were massless. Existing materials display fractional charges in two dimensions, and the recently discovered topological insulators may extend these fractional charges into three dimensions.
These diverse behaviors all trace to electron interactions. In conventional metals, electrons barely interact with each other: Fermi liquid theory describes their tendency to screen local charge so that electrons can be treated as isolated particles in a homogenous background. In contrast, the common feature to all of these exotic materials is that their electrons do interact, and we lack the broadly successful theoretical language to describe these ‘correlated electron materials.
In recent years, the notion of ‘Quantum Materials’ has emerged as a powerful unifying concept across diverse fields of science and engineering, from condensed-matter and cold-atom physics to materials science and quantum computing. Quantum Materials has a strong overlap with Condensed Matter Physics, although the latter is a broader field of research that encompasses classical, yet non-trivial, phenomena, such as soft condensed matter. The Condensed Matter Physics is study of systems in their ‘condensed’ phases that can be applied to an almost limitless range of problems such as magnetism, superconductivity and superfluidity.
Quantum materials exhibit a plethora of phenomena such as superconductivity, quantum-Hall effect, quantum spin-Hall, topological-Hall effect, and Dickie’s superradiance. Understanding how we control the manifestation of these properties in materials using knobs such as reduced dimensionality, quantum confinement, quantum coherence, the topology of wavefunctions, quantum fluctuations, electron-electron interactions, and spin-orbit coupling is crucial.
“Quantum materials mean they have properties that cannot be described by classical physics – we have to invoke quantum physics,” said Dr Amalia Coldea, a quantum materials researcher at the University of Oxford. “Often we refer to materials where there are very strong interactions between their components – you don’t know what properties they will have, and you can’t predict in advance.” Quantum materials have various quirky properties, some of which could contribute to future technological innovations like quantum computing – regarded by many as the next revolution in computer technology.
These quirky behaviors arise only at very cold temperatures, where they cannot be masked by the overwhelming forces of thermal energy. The most celebrated quantum materials are the high-temperature superconductors discovered in the 1980s, so named for their ability to conduct electrical current without resistance at temperatures well above those of traditional superconductors. Another classic example is the heavy fermion materials discovered in the late 1970s. In these, electrons appear to be effectively hundreds of times more massive than normal and, equally unusual, the effective electron mass seems to vary strongly as temperature changes.
Originally introduced to emphasize the exotic properties of unconventional superconductors, heavy-fermion systems, and multifunctional oxides, the definition of quantum materials has morphed into a much broader container that also encompasses research on topological properties, two-dimensional (2D) materials, and driven quantum systems. This convergence of diverse research areas is perhaps best exemplified by the coexistence of strong correlation, quantum criticality, and superconductivity in Moiré materials such as twisted bilayer graphene (TBG). With this example in mind, it is natural to broadly define quantum materials as all those versatile materials platforms that allow us to explore emergent quantum phenomena as well as their potential uses in future technology.
With a $4 million grant from the National Science Foundation, a team of researchers from Brown University and Dartmouth College will work to better understand the materials and the exotic quantum states that make these technologies possible. “We’re trying to understand these quantum materials and complex quantum states on a fundamental level that enables us to control and manipulate them in useful ways,” said Vesna Mitrovi, a professor of physics at Brown and principal investigator on the grant. “This new understanding will help us to identify which of these materials or states is useful for which applications, which in turn will help us to move quantum technology forward.” “The ability to measure these correlations gives us the ability to better understand and control these quantum states,” Mitrovi said. “That could enable the design of new technologies including error-tolerant quantum computers, for example.”
The framework through which these phenomena were first understood is the Landau–Ginzburg theory of phase transitions: by identifying a suitable order parameter that reflects the underlying symmetry of the system (such as a material’s density, to continue with our solid-state example), it is possible to pinpoint the conditions that are required for that symmetry to become manifest.
The topological nature of the electronic states is the key concept in the most recent developments in understanding quantum materials. The quantum Hall effect, topological insulators, and topological superconductors are all characterized by nontrivial topologies in Hilbert space. The Berry phase, which describes the connection and curvature of the subspace of Hilbert space, plays the central role in the unified principle to describe this topological nature. Relativistic effects and consequent spin–orbit interactions are deeply connected to the Berry phase. They are also key to spintronics applications, where the electrical manipulation of spins is being pursued.
A common thread in the study of Quantum Materials is the concept of emergence, as advocated by P. W. Anderson in his famous article More is Different, by David Pines and Robert Laughlin in their article The theory of everything.Emergence is a concept developed for many-body systems, indicating the properties, phenomena, and functions that never appear in the individual elements but are realized only when a huge number of elements get together.
These collective electrons demonstrate various macroscopic quantum phenomena, the representative example of which is superconductivity. One of the big challenges in condensed matter physics is to increase the temperature (Tc) at which superconductivity can be observed to above room temperature. However, there are many other macroscopic quantum phenomena that are already observable above room temperature. One is magnetism (by the Bohr–van Leeuwen theorem), and the other is ferroelectricity. Remarkably, there are common features of these three macroscopic quantum phenomena: the order parameter, which is of quantum origin, behaves as a classical quantity, and the quantum topology plays a crucial role.
The metal–insulator transition (MIT) in solids is one of the most important features in quantum materials. Origins of the MIT are versatile, including simple bandgap closing, Anderson localization, and polaron self-trapping driven by electron–lattice interactions, but many are related to electron–electron interaction beyond the one-particle picture—generally called the Mott transition. At a finite temperature, preferably around and beyond room temperature, the MIT can provide useful functions, enabling gigantic, ultrafast switching of versatile physical properties, not only electrical conductivity but also other transport, magnetic and optical properties. The terminology ‘Mottronics’ was coined to represent the concept of electron technology exploiting the Mott transition.
Applications
All of these can lead to devices with better operation efficiency, faster speed, and lower energy consumption for smaller and smaller volumes. That’s becoming an important challenge, at least for nano-electronic applications. Of course, there are many other areas of applications. Quantum materials are not only useful for quantum technology but also for a wide range of applications, such as metrology, sustainability, biomedical and environmental applications, communications, and consumer products.
Currently, Quantum qubits are mostly made of superconductors, but they’re very low-temperature superconductors. There are many issues with that. They only operate at very, very low temperatures. That makes these qubits not very scalable. If we can advance interesting and good properties of higher-temperature superconductors, then it can certainly help the development of qubits.
Also, there are qubits already made of quantum materials. For example, people have used semiconductor quantum dots and cooled atoms as qubits. So, these are examples of real quantum materials already being used as qubits. And of course, qubits are directly related to quantum computation, explains Nai-Chang Yeh, Caltech’s Thomas W. Hogan Professor of Physics
Typical quantum dots and cooled atoms are not as well developed as the low-temperature superconducting qubits for quantum computation right now. But the application of quantum materials to qubits is certainly an area that can have impact on quantum computation.
Measurements of quantum and emergent phenomena towards applications: The novel properties of these materials enable us to study the rich physics of quantum and correlated material systems in detail. There is also a concentrated effort around the world to use them for developing disruptive new technologies to transform computation, communication, sensing, and metrology.
Researchers from Intel Corp. and the University of California, Berkeley, are looking beyond current transistor technology and preparing the way for a new type of memory and logic circuit that could someday be in every computer on the planet. In a paper appearing online Dec. 2018 in advance of publication in the journal Nature, the researchers propose a way to turn relatively new types of materials, multiferroics and topological materials, into logic and memory devices that will be 10 to 100 times more energy-efficient than foreseeable improvements to current microprocessors, which are based on CMOS (complementary metal-oxide-semiconductor).
Applied Materials and Arm Lead DARPA-Funded Research on a Correlated electron materials for Neuromorphic Switch for AI
Non-volatile memory and history-dependent analogue-like states are two elemental characteristics for synapse-simulating devices. Self-learning ability of the synapse is also a crucial attribute for cognitive computing. Spike-timing-dependent plasticity (STDP), in which the change of synapse weight (w) is a function (f1) of the time difference between postneuron (tpost) and preneuron (tpre) signals (w ¼ f1(tpost tpre)), is one common self-learning process in human brains. In biological systems, signal transmission and synapse learning are both generally regarded to occur concurrently in synapse-connected neuron pairs.
Current two-terminal metal–insulator–metal artificial synapses operate by separating the signal transmission and selflearning processes in time. Three-terminal synaptic devices, being able to realize both functions simultaneously, therefore offer a promising solution for efficient synapse simulation. Researchers have already demonstrated a three-terminal rare-earth nickelate thin-film transistor that mimics a biological synapse. By implementing such synaptic nickelate device, they successfully realize the first concurrent operation of signal transmission and STDP learning in correlated oxides, which provides a new opportunity and strategy to explore neuromorphic-correlated oxide electronics including programmable fluidic circuits.
DARPA has launched a project with Applied, Arm and Symetrix to develop a correlated electron switch. Correlated electron materials are materials that break some of the rules of classical band theory. These materials are really best considered as a type of quantum matter. ” Most of the materials we are studying in the context of this research should, according to classical theories, conduct electrons, but thanks to correlation they can also exhibit insulating properties under certain conditions due to electron-electron interactions that don’t happen according to traditional band theory. Welcome to the weird and wonderful world of quantum matter!”, write David Thompson, the Primary Investigator and Applied Materials’ Team Leader for the “Synapse and Neuron Correlated Electron Devices” Research Project funded in part by the Defense Advanced Research Projects Agency (DARPA).
Many of the other technologies looking at conductor-insulator switching necessarily require the motion of atoms and, in many cases, accompanying phase transitions. The promise of integrating correlated materials is that we’re looking at a purely electronic phase transition. We’re optimistic that if we can pin down the right material to integrate, then this will lead to unprecedented switching speeds since no atom migration is required. It’s also likely that reliability and endurance (how many times you can switch the device on and off before it fails) will be improved since a primary mode of failure involves atoms getting “stuck” at interfaces and defects when atomic motion is the basis of switching. Finally, the ability of the device to function at sub 1K temperatures is also embraced in the theory of these materials since we don’t need background kinetic energy to drive atomic motion.
At the heart of these new devices is the integrated quantum matter — in this case the correlated electron material. Manipulation of the composition of the material (the percentage and types of atoms), the phase and morphology (e.g. roughness and grain size of crystalline regions) and establishing the right interfaces at the electrodes connected to the material are at the heart of what Applied Materials does best.
Suffice it to say, it didn’t take long before the three parties saw real value in getting together on developing this new technology. Symetrix brings the general concept of the correlated electron switch and early learnings; Arm brings circuit designs and clearly defined requirements on how we need to optimize the device characteristics to disrupt compute at the edge with a disruptively low-power chip; and Applied does what we do best by demonstrating the path to manufacturing through enabling new materials and integration for a new device.
A UCF physicist has discovered a new material Neupane that has the potential to become a building block in the new era of quantum materials
A physicist at the University of Central Florida claims to have discovered a new material with the potential to become a building block in the new era of quantum materials. Quantum materials are composed of microscopically condensed matter and are expected to change our development of technology as we enter the “Quantum Age”.
The University’s assistant professor, Madhab Neupane, has spent his career researching these new materials, which are expected to become the foundation of the technology to develop quantum computers and long-lasting memory devices. He believes that these new devices will increase computing power for big data and greatly reduce the amount of energy required to power electronics.
The material Neupane discovered alongside his team is Hf2Te2P, a chemically composed of hafnium, tellurium and phosphorus. It’s the first material that has multiple quantum properties, meaning there is more than one electron pattern that develops within the electronic structure, giving it a range of quantum properties.
“With the discovery of such an incredible material, we are at the brink of having a deeper understanding of the interplay of topological phases and developing the foundation for a new model from which all technology will be based off, essentially the silicon of a new era,” Neupane added. The University states that once these quantum phenomena are better understood and can be engineered, the new technologies that come out of it are expected to change the world, much like electronics did at the end of the 20th century.
“New Quantum-World Material ‘Stumbled Upon’ That Cannot Be Described by Classical Physics”
An international team of physicists has “stumbled upon” an entirely new material, which they have called “Weyl-Kondo semimetal,” that belongs to a category of substances known as quantum materials. Rice University theoretical physicist Qimiao Si and colleagues at the Rice Center for Quantum Materials in Houston and the Vienna University of Technology in Austria make predictions that could help experimental physicists create a quantum material with an assorted collection of properties seen in disparate materials like topological insulators, heavy fermion metals and high-temperature superconductors.
All these materials fall under the heading of “quantum materials,” ceramics, layered composites and other materials whose electromagnetic behavior cannot be explained by classical physics. As scientists don’t necessarily have the theories to predict the behaviour of quantum materials, often they create them experimentally first and measure them to observe their properties. For the time being, however, researchers working on quantum materials are trying to understand how they work and how more useful ones can be produced.
“We really just stumbled upon a model in which, suddenly, we found that the mass had gone from like 1,000 times the mass of an electron to zero,” said Dr Lai. This is a characteristic of “Weyl fermions”, elusive particles first proposed over 80 years ago. “We had the material and the theory developing in parallel,” said Prof Silke Buehler-Paschen, who led the Vienna team. Prof Buehler-Paschen and her team experimented with structures made from the metals cerium, bismuth and palladium in very specific combinations. This work then fed into theoretical work being done by Dr Hsin-Hua Lai and his team at Rice University, who realised the potential to create an entirely new material.
While this research is still of interest primarily to other quantum researchers, Prof Buehler-Paschen is clear about where it could ultimately lead. “Currently we design these materials to find new effects,” she said. “We search for them because these effects could be very useful, with technological applications like quantum computing.” The research was supported by the National Science Foundation, the Army Research Office, the Welch Foundation, RCQM and the Austrian Science Fund.
Artificial neuromorphic electronics that mimic the working principle of neural synapses implement a unique computing paradigm emphasizing cognitive computing capability. Synapse-motivated device networks make high power-efficiency and fast parallel processing feasible due to inherent architectural characteristics. For instance, a simple signal—transmission action between neurons through a synapse only consumes a millionth of the energy required to execute the equivalent action in a traditional von Neumann computing system.
UChicago scientists programmed an IBM quantum computer to become a type of material called an exciton condensate.
For several years, Mazziotti has been watching as scientists around the world explore a type of state in physics called an exciton condensate. Physicists are very interested in these kinds of novel physics states, in part because past discoveries have shaped the development of important technology; for example, one such state called a superconductor forms the basis of MRI machines.
Though exciton condensates had been predicted half a century ago, until recently, no one had been able to actually make one work in the lab without having to use extremely strong magnetic fields. But they intrigue scientists because they can transport energy without any loss at all—something which no other material we know of can do. If physicists understood them better, it’s possible they could eventually form the basis of incredibly energy-efficient materials.
To make an exciton condensate, scientists take a material made up of a lattice of particles, cool it down to below -270 degrees Fahrenheit, and coax it to form particle pairs called excitons. They then make the pairs become entangled—a quantum phenomenon where the fates of particles are tied together. But this is all so tricky that scientists have only been able to create exciton condensates a handful of times. “An exciton condensate is one of the most quantum-mechanical states you can possibly prepare,” Mazziotti said. That means it’s very, very far from the classical everyday properties of physics that scientists are used to dealing with.
In a groundbreaking study, a group of University of Chicago scientists announced they were able to turn IBM’s largest quantum computer into a quantum material itself. Graduate students LeeAnn Sager and Scott Smart wrote a set of algorithms that treated each of Rochester’s quantum bits as an exciton. A quantum computer works by entangling its bits, so once the computer was active, the entire thing became an exciton condensate.
“It was a really cool result, in part because we found that due to the noise of current quantum computers, the condensate does not appear as a single large condensate, but a collection of smaller condensates,” Sager said. “I don’t think any of us would have predicted that.” Mazziotti said the study shows that quantum computers could be a useful platform to study exciton condensates themselves. “Having the ability to program a quantum computer to act like an exciton condensate may be very helpful for inspiring or realizing the potential of exciton condensates, like energy-efficient materials,” he said.
Europium Molecular Crystals reported in March 2022
Europium molecular crystals, a rare-earth-based material, could provide a robust platform for photonic quantum technologies. The work of a research team from the National Centre for Scientific Research (CNRS), the University of Strasbourg, Chimie ParisTech-PSL, and the Karlsruhe Institute of Technology (KIT) demonstrated the quantum capabilities of this material, the ultranarrow optical transitions of which support optimal interaction with light.
Rare-earth ions show promise as solid-state systems for building light-matter interfaces at the quantum level due to their ability to show long-lived quantum states. However, few crystalline materials have exhibited an environment that is quiet enough to fully exploit the quantum properties of rare-earth ions. Molecular systems can provide such an environment, but they generally lack spin states.
Moreover, when molecular systems do have spin states, they show optical lines that are too broad to allow a reliable link to be established between spins and light. Europium molecular crystals are a combination of rare-earth ions and molecular systems. These crystals have linewidths in the tens of kilohertz range — orders of magnitude narrower than those of other molecular systems. The researchers took advantage of this property to demonstrate the potential of europium molecular crystals to provide efficient optical spin initialization, coherent storage of light using an atomic frequency comb, and optical control of ion-ion interactions for the implementation of quantum gates.
The ultranarrow linewidths of europium molecular crystals translated into a long-lasting quantum state, and the researchers exploited this property to demonstrate the storage of a light pulse inside the crystals. They believe that the results of their experiments show the potential of these rare-earth molecular crystals to become a platform for photonic quantum technologies that would combine highly coherent emitters with the versatile capabilities of molecular materials in the areas of composition, structure, and integration.
Communication between quantum systems over long distances depends on their ability to effectively interact with light. So far, it has been challenging to find a material that can fully exploit the quantum properties of light. Molecular crystals are of increasing interest as a means to develop quantum computers that can communicate with each other using fiber optic networks.
Using AI/ML for searching and designing new Quantum Materials
As the library of quantum materials grows larger, it is becoming increasingly important to be able to leverage modern data science techniques to catalogue, search, and design new quantum materials. Machine learning (ML) and related artificial intelligence algorithms are expected to play a central role in this area. ML techniques can assist the high-throughput search for suitable materials for given applications, by harvesting the massive amount of raw data generated and stored by the computational materials science community. ML is particularly useful to identify patterns within large amounts of complex data, and many groups started to explore these methodologies for extracting knowledge and insight from materials databases.
ML is also seen as a powerful tool to advance the identification of quantum phase transitions and to deepen our understanding of many-body physics and quantum topological matter. This nascent field holds great promise and is expected to play a fundamental role in progressing towards new materials solutions for next-generation QTs.
References and Resources also include:
https://news.uchicago.edu/story/uchicago-scientists-turn-ibm-computer-quantum-material
https://www.photonics.com/Articles/Europium_Molecular_Crystals_Clear_a_Path_for/a67883
