In this report we review the present state of the art of the control of propagating quantum states at the single-electron level and its potential application to quantum information processing. We give an overview of the different approaches that have been developed over the last few years in order to gain full control over a propagating single-electron in a solid-state system. After a brief introduction of the basic concepts, we present experiments on flying qubit circuits for ensemble of electrons measured in the low frequency (DC) limit. We then present the basic ingredients necessary to realise such experiments at the single-electron level. This includes a review of the various single-electron sources that have been developed over the last years and which are compatible with integrated single-electron circuits. This is followed by a review of recent key experiments on electron quantum optics with single electrons. Finally we will present recent developments in the new physics that has emerged using ultrashort voltage pulses. We conclude our review with an outlook and future challenges in the field.
In this report we review the present state of the art of the control of propagating quantum states at the single-electron level and its potential application to quantum information processing. We give an overview of the different approaches that have been developed over the last few years in order to gain full control over a propagating single-electron in a solid-state system. After a brief introduction of the basic concepts, we present experiments on flying qubit circuits for ensemble of electrons measured in the low frequency (DC) limit. We then present the basic ingredients necessary to realise such experiments at the single-electron level. This includes a review of the various single-electron sources that have been developed over the last years and which are compatible with integrated single-electron circuits. This is followed by a review of recent key experiments on electron quantum optics with single electrons. Finally we will present recent developments in the new physics that has emerged using ultrashort voltage pulses. We conclude our review with an outlook and future challenges in the field.
In this report we review the present state of the art of the control of propagating quantum states at the single-electron level and its potential application to quantum information processing. We give an overview of the different approaches that have been developed over the last few years in order to gain full control over a propagating single-electron in a solid-state system. After a brief introduction of the basic concepts, we present experiments on flying qubit circuits for ensemble of electrons measured in the low frequency (DC) limit. We then present the basic ingredients necessary to realise such experiments at the single-electron level. This includes a review of the various single-electron sources that have been developed over the last years and which are compatible with integrated single-electron circuits. This is followed by a review of recent key experiments on electron quantum optics with single electrons. Finally we will present recent developments in the new physics that has emerged using ultrashort voltage pulses. We conclude our review with an outlook and future challenges in the field.
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
Abstract As a foundational technology in quantum information science (QIS), the manipulation and detection of quantum spins enable precise control, opening new avenues for significant advancements. Early research focused on macroscopic ensemble quantum systems, where electron spin resonance is used to coherently address electron spins within different ensembles. However, the low initialization efficiency and readout sensitivity of such systems hinder their further development. Unlocking the full potential of quantum technology, it is essential to achieve single‐spin precision. Various quantum systems, including color centers, quantum dots, atoms, and molecules, have been demonstrated the capability for single‐spin manipulation. The successful control of spin quantum states in these systems through diverse techniques has paved the way for new ideas and boundless possibilities in QIS. This review provides a comprehensive overview of recent significant advances in the field and explores future development directions, aiming to shed light on the ongoing evolution of QIS.
The second quantum revolution of the 20th century contributed to a technological expansion in solid-state physics. Modern nanofabrication coupled to material processing techniques have facilitated the development of on-demand single-electron sources. With their remarkable precision, they are currently used for metrology purposes and hold key potential for the recent field of research of electron quantum optics, including a promising candidate for quantum information: the electron flying qubit. These quantum bits are created by short voltage pulses and manipulation of their quantum state occurs on-the-fly. The shortest voltage pulse reported so far attains 27 ps, on-chip, in a cryogenic environment. However, suffering from attenuation and dispersion in coaxial lines, accessibility to electronic quantum regimes at faster time scale remains out-of-reach.On the contrary, empowered by the advent of ultrafast lasers and progress in photonics and plasmonics, photo-conductive-switch technology can allow the generation of electromagnetic pulses with picosecond duration. The large bandwidth of these THz opto-electronic technologies could overcome the technical bottleneck faced by standard electronic equipment. While they have been widely developed for room temperature applications, demonstrations of their integration along-side a quantum architecture in a cryogenic environment are still limited. The realisation of such an experiment would unlock new research directions for studying the dynamics of solid-state electronic quantum devices.In this manuscript, we present the development of an experimental setup to generate picosecond voltage pulses in a cryogenic environment for flying qubit applications. A femtosecond laser generates pulses that are injected into optical fibres and integrated at low temperatures. Fabricated on the surface of Low Temperature grown GaAs (LT-GaAs), a photoconductive-switch is co-integrated to the quantum circuit formed on a high mobility two-Dimensional Electron Gas (2DEG). Owing to the extremely fast opto-electronic response of the LT-GaAs, the photo-conductive device converts optical pulses into voltage pulses with a duration as short as a few picoseconds. Using a THz CoPlanar Waveguide (CPW) circuit, the pulse is conveyed toward the 2DEG, where it is used as an ultra-short single-electron source.To perform pump-probe measurement and resolve the dynamic profile of such pulses, an original experimental setup, involving piezo-electric positioners and alignment protocols at low-temperatures, was implemented. As proof of concept, we first report the characterisation at 300 K of electronic pulses with 1.9 ps duration. In a second step, we cool down the system to 4 K and measure 2.3 ps wide pulses, thus expanding the proof of concept to cryogenic environments. Then, by integrating a 2DEG structure along-side the THz circuit, we were able to excite THz plasmons in a Fabry-Pérot cavity. The characteristic frequency of their fundamental mode was compared to an analytical model that revealed information about the carrier density of the electron gas under illumination. In parallel, extensive developments were carried out on the design of CPWs in order to minimise undesirable signal reflections as well as dispersion losses. Finally, with the prospect of measuring and controlling the propagation of picosecond electron pulse in quantum channels directly with ultrafast THz electrostatic gates, the fabrication of the next generation of devices was initiated. This work will pave the way for on-chip integration of picosecond voltage pulses into quantum nanoelectronics devices and ultrafast control of electronic flying qubits.
Abstract In recent years, the use of integrated technologies for applications in the field of quantum information processing and communications has made great progress. The resulting devices feature valuable characteristics such as scalability, reproducibility, low cost and interconnectivity, and have the potential to revolutionize our computation and communication practices in the future, much in the way that electronic integrated circuits have drastically transformed our information processing capacities since the last century. Among the multiple applications of integrated quantum technologies, this review will focus on typical components of quantum communication systems and on overall integrated system operation characteristics. We are interested in particular in the use of photonic integration platforms for developing devices necessary in quantum communications, including sources, detectors and both passive and active optical elements. We also illustrate the challenges associated with performing quantum communications on chip, by using the case study of quantum key distribution—the most advanced application of quantum information science. We conclude with promising perspectives in this field.