The fields of quantum electronics (e.g., quantum dots and superconducting circuits) and optoelectronics have garnered much interest in the past few years. They deal with quantum and optical platforms in combination with electronic and condensed matter systems, which may serve as building blocks for a plethora of applications in quantum computing and optical technology. In this reprint, we reprint the articles of the Special Issue "Quantum and Optoelectronic Devices, Circuits and Systems", published in Electronics (MDPI).
The fields of quantum electronics (e.g., quantum dots and superconducting circuits) and optoelectronics have garnered much interest in the past few years. They deal with quantum and optical platforms in combination with electronic and condensed matter systems, which may serve as building blocks for a plethora of applications in quantum computing and optical technology. In this reprint, we reprint the articles of the Special Issue "Quantum and Optoelectronic Devices, Circuits and Systems", published in Electronics (MDPI).
Hybrid quantum circuits combine two or more physical systems, with the goal of harnessing the advantages and strengths of the different systems in order to better explore new phenomena and potentially bring about novel quantum technologies. This article presents a brief overview of the progress achieved so far in the field of hybrid circuits involving atoms, spins, and solid-state devices (including superconducting and nanomechanical systems). How these circuits combine elements from atomic physics, quantum optics, condensed matter physics, and nanoscience is discussed, and different possible approaches for integrating various systems into a single circuit are presented. In particular, hybrid quantum circuits can be fabricated on a chip, facilitating their future scalability, which is crucial for building future quantum technologies, including quantum detectors, simulators, and computers.
Ultrafast phenomena, optoelectronics, and superconductivity are acknowledged fields of technological importance and a very large amount of research has been performed in these areas in recent years. In modern, highly-advanced digital electronic circuits, the primary function of high-performance, high-speed signal processing is given to superconducting single-flux-quantum (SFQ) logical devices, based on resistively-shunted Josephson tunnel junctions. The development of this branch of digital electronics requires ultrafast, and ultra sensitive optical-to-electrical transducers for fiber optic interconnects, which must be able to transform to the electrical domain the input information coded in the form of a train of ultrafast optical pulses and, subsequently, feed it into the SFQ processor.
Quantum phenomena are typically observable at length and time scales smaller than those of our everyday experience, often involving individual particles or excitations. The past few decades have seen a revolution in the ability to structure matter at the nanoscale, and experiments at the single particle level have become commonplace. This has opened wide new avenues for exploring and harnessing quantum mechanical effects in condensed matter. These quantum phenomena, in turn, have the potential to revolutionize the way we communicate, compute and probe the nanoscale world. Here, we review developments in key areas of quantum research in light of the nanotechnologies that enable them, with a view to what the future holds. Materials and devices with nanoscale features are used for quantum metrology and sensing, as building blocks for quantum computing, and as sources and detectors for quantum communication. They enable explorations of quantum behaviour and unconventional states in nano- and opto-mechanical systems, low-dimensional systems, molecular devices, nano-plasmonics, quantum electrodynamics, scanning tunnelling microscopy, and more. This rapidly expanding intersection of nanotechnology and quantum science/technology is mutually beneficial to both fields, laying claim to some of the most exciting scientific leaps of the last decade, with more on the horizon.
Abstract Devices combining superconductors with semiconductors offer a wide range of applications, particularly in the growing field of quantum information processing. This is due to their ability to take advantage of both the extensive knowledge gathered in the field of semiconductors and the unique quantum properties of superconductors. This results in novel device concepts, such as structures generating and detecting entangled photon pairs as well as novel optical gain and laser realizations. In this review, we discuss the fundamental concepts and the underlying physical phenomena of superconductor–semiconductor optoelectronics as well as practical device implementations.
This special issue of physica status solidi (b) on single electron control contains a series of articles dealing with the manipulation and detection of single electrons. Based on the tremendous experimental and theoretical progress achieved within this field during the last years, the generation of single electrons on demand in coherent conductors and the full control over the quantum states of single electrons is now within reach. The knowledge of such techniques is an absolute prerequisite for the implementation of schemes for the controlled transfer of quantum information in electronic setups. The transfer of quantum information was up to now mostly applied in quantum-optical setups. Such quantum technologies are expected to open up a whole new field for basic science but also for future applications in quantum communication and quantum sensing. The idea to put in place this special issue arose during a focus session on “single-particle sources for electronic devices”, which we organized at the DPG spring meeting of the condensed matter section in Regensburg on March 7, 2016. During the focus session, it became evident that the advancement of this research field had been quite dramatic during the last years and that it would be helpful for the scientific community to document this progress in a special issue. The focus session in Regensburg included 6 invited and 8 contributed talks. Most of the research groups, which were active in that focus session at the DPG spring meeting, and several other groups have now contributed with manuscripts to this special issue. The leading role of European groups in the field of single-electron control is evident from the fact that most of the contributions are of European origin. Within Europe, in these days, a number of different activities are started to advance quantum technologies, to mention only as a prominent example, the announcement and planning of the 3rd EU Flagship Program on Quantum Technologies. The purpose of this issue is, among others, to bring the field of single-electron control to the attention of the scientific community interested in quantum technologies. This issue includes 10 feature articles, allowing the readers to get a broad overview, but also 11 original research papers, thereby presenting the most recent advancements of the field. The subjects that are covered range from the physics of single-electron wave packets, thermodynamics with single electrons, studies of entanglement and electron quantum optics, up to the realization of feedback control and investigations of single-electron charge transfer. Contributions from experimental groups and from theory groups are almost balanced, representing a complete picture of the field. We hope that all readers will find this issue interesting and stimulating. We dedicate this special issue to Prof. Dr. Tobias Brandes, who unexpectedly passed away on 2 February 2017 at the age of 50. With him we lost an excellent scientist with great international recognition who impressed by his extraordinary kindness and his modest, open and friendly way in meeting people. Throughout his whole scientific carreer, Tobias has worked to bridge the gap between coherent solid-state devices, as e.g. in the quantum Hall effect or in quantum dots, and quantum optics. A focus of his research were quantum mechanical aspects of dynamical effects in solid-state devices. After having studied physics at the University of GÖttingen, Tobias worked at a number of different places, in Germany, Japan and the UK, before he moved to the Technical University of Berlin as a full professor in 2016. Within this special issue one of his last manuscripts is published which deals with feedback control applied to single-electron devices. Feedback control, as he had in mind in some of his recent publications, is therefore also visualized in the picture of the title page of this issue. With the sudden death of Tobias, the whole scientific community lost a great scientist and we all lost a good friend. Janine Splettstoesser Rolf J. Haug Guest Editors
Matter-based two-level quantum systems are fundamental building blocks of quantum technologies, underpinning applications in quantum computing, simulation, communication, and sensing. Today, most of these two-level quantum systems, including Rydberg atoms, trapped ions, superconducting circuits, molecules, and quantum dots, involve transition frequencies in microwave or optical domains. However, extending their transition frequency to the THz spectral range could provide numerous benefits, leveraging the unique properties of THz radiation. Here, we show that an hBN-encapsulated graphene double quantum dot realizes a two-level system with a transition frequency in the THz spectral range. Using low-temperature transport spectroscopy in the dark combined with modeling based on nonequilibrium Green's function formalism, we demonstrate the formation of an artificial molecule, featuring bonding and antibonding states separated by an energy of up to 0.6 meV, corresponding to a resonance frequency of 0.145 THz. This approach provides direct access to important parameters of open double quantum dot systems, including tunneling rates, offering a practical alternative to conventional techniques such as photon-assisted tunneling, which are challenging to implement at THz frequencies. The realized 2D-material-based THz two-level system, compatible with direct on-chip integration, could serve as a key building block for future THz quantum technologies. Furthermore, by involving a single-electron transition, coupling these devices to a THz resonator could enable the exploration of ultra-strong light-matter interactions at the fundamental limit of a single transition coupled to a single cavity, beyond the reach of existing THz quantum systems based on collective transitions.