Quantum Nanoscience is a novel research field in which quantum effects, such as quantum state superposition, entanglement and coherence, are studied in nanoscale systems. Coherent quantum effects at the nanoscale are relatively uncharted territory. Therefore, at this point in time much of quantum nanoscience is dedicated to understanding the mechanisms of decoherence, with the aim to preserve and maximize coherence. Eventually, this will result in the development of nanostructures that can be used for emerging quantum technologies, such as quantum computing, quantum communication, and quantum sensing. These quantum technologies drive the so-called second quantum revolution.
While quantum nanoscience is a bridge between quantum materials and quantum technologies, it also plays an even more profound role. Nanoscale artificial systems of matter with engineered quantum states cannot only be realized in ion traps and ultracold atomic gases, but also at surfaces of condensed matter. Although fabricated at the surface of a material as a template, these artificial nanostructures transcend the concept of a crystalline material: They are metastable structures that are fabricated by placing the building blocks (atoms, molecules, 1D wires, 2D sheets) in precisely defined positions. Such designed and crafted artificial structures are a nearly universal playground in which concepts of quantum technology can be explored and exploited, without being constrained by the existence and stability of suitable materials.
Coming from traditional nanoscience (“functional nanostructures at surfaces”), we use our extensive knowledge in surface science and nanoscience to contribute to quantum nanoscience and its primary goal: the manipulation and exploitation of quantum-coherent functionality in nanostructures.
In particular, our profile as a surface science institute with a strong focus on scanning probe microscopy, as well as method and instrument development, puts us in an excellent position to address each of the four pillars of quantum nanoscience:
- Exploring quantumness: we use the experimental platform of scanning probe microscopies (SPM) at low temperatures to investigate quantum coherence, or more generally quantumness, in diverse nanostructures on atomic length scales and in the time domain.
- Materials: we investigate interfaces between materials that bestow quantum functionality, such as topological insulators, superconductors or ferromagnets.
- Tools: we develop novel instruments and microscopies that provide access to the quantum-coherent functionalities of nanostructures. Examples are the Jülich Multi-tip SPMs, the Jülich Millikelvin SPM, and scanning quantum dot microscopy.
- Devices: we fabricate and study model devices as metastable artificial structures with purpose-engineered quantum states, in part by using artificial intelligence.
Second Quantum Revolution
The first quantum revolution, which took place at the beginning of the 20th century, revealed the rules that govern physical reality. During this time, the foundations of quantum mechanics were laid. In the 100+ years since then, quantum mechanics was applied to many fields of research, among which the physics of condensed matter, including molecules, solid-state materials, surfaces and interfaces, is particularly important. The profound description of solid-state materials as well as surface and interface phenomena resulted in several technologies on which our modern way of life is based, most prominently information technology.
While some of the constitutive properties of quantum mechanics, such as the discreteness of states, are already utilized in today’s information technology devices, others, most notably coherence and entanglement, are not yet exploited broadly. But these are the features of quantum mechanics that are profoundly different from classical physics, i.e. show a high level of “quantumness” and therefore have the highest potential to lead to disruptive technologies. Recently, the scientific community has started their technological utilization for information technology, and because the implications that emerge are so momentous, this is often referred to as the second quantum revolution (Jonathan P. Dowling and Gerard J. Milburn, Quantum Technology: The second quantum revolution).
In course of the second quantum revolution we will learn to exploit quantum state superposition, coherence and entanglement to develop new ground-breaking information technologies, specifically quantum computing, quantum communication, and quantum sensing.
Since the first quantum revolution, scientists have known the rules of quantum mechanics and have built devices that followed these rules, leading to inventions such as the laser and the transistor. In contrast, in the new quantum technologies the system behaviour of complex quantum mechanical systems is engineered for a given purpose. Quantum technology thus allows us to wilfully organise and control the components of a complex system that is governed by the laws of quantum physics, thereby fully exploiting the quantum nature of the underlying states. These might by highly unnatural coherent or entangled quantum states of our own design that most probably exist nowhere else in the universe. These new man-made quantum states have novel properties of sensitivity and nonlocal correlation that have wide applications to the development of computers, communications systems, sensors and compact metrological devices.
Thus, although quantum mechanics as a science has matured long time ago, quantum engineering as a technology is now emerging in its own right. However, in spite of being technologies, quantum technologies remain so close to the core of modern physics that for many years to come research towards quantum technologies will require the perfection, and in some cases even the first-ever performance, of fundamental experiments in quantum physics. This is true in the fields of quantum materials and, especially, quantum nanoscience.
Some of the approaches to quantum technology use highly artificial systems of matter such as ultracold atoms or ions in traps, or even photons. Other approaches are based on condensed matter, i.e., the relevant quantum states exist in materials. Many of the materials that are relevant for quantum technology are commonly referred to as quantum materials – materials with emergent phenomena arising from electron-correlation and/or non-trivial topologies of their wave functions. Strong correlation of the electron leads to the emergence of conceptually new quantum states, and non-trivial topologies of the wave functions can guarantee the exceptional stability of such states. Evidently, both properties, especially in combination, are very interesting when it comes to tailoring functionalities for quantum technology.