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"Quantum electronics"
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Nanoelectronics : a molecular view
\"This is a reference book for graduate students and researchers in the areas of nanomaterials, nanoelectronics, solid state physics and solid state devices. Segments of this book are also useful as textbook for a course in nanoelectronics\"-- Provided by publisher.
Book
Modulation of Recombination Radiation in Quantum Wires by Electric Field and the Possibility of Its Application in Quantum Electronics
The cross section for the process of single-photon recombination of free charge carriers in the 1D geometry of a thin quantum wire in a strong longitudinal electric field is calculated. It is established that the spectrum of recombination radiation is no less pure (close to sparse discrete) and stable than that of quantum dots. It is believed that the longitudinal classical degree of freedom “blurs” spectral lines due to the uncertainty in the kinetic energy of the longitudinal motion of carriers. It is shown that a strong electric field removes this uncertainty, while making it possible to vary both the frequency of radiation and the intensity of the recombination process. A complex oscillatory dependence of the recombination intensity on the uniform electric field strength is revealed. The natural directionality of the radiation along the wire in a strong field is an additional advantage. The semiclassical approach made it possible to establish that the recombination process is predominantly localized in the vicinity of particular points of the wire, where the dispersion relations for the emitted photon are satisfied. The electric field can affect the position of these points and modulate the spatial distribution, spectrum and anisotropy of recombination radiation. The theoretical results obtained are used to interpret extensive experimental studies on recombination radiation from CdSe filaments in an electric field.
Journal Article
Atomistic simulation of quantum transport in nanoelectronic devices
\"Computational nanoelectronics is an emerging multi-disciplinary field covering condensed matter physics, applied mathematics, computer science, and electronic engineering. In recent decades, a few state-of-the-art software packages have been developed to carry out first-principle atomistic device simulations. Nevertheless those packages are either black boxes (commercial codes) or accessible only to very limited users (private research codes). The purpose of this book is to open one of the commercial black boxes, and to demonstrate the complete procedure from theoretical derivation, to numerical implementation, all the way to device simulation. Meanwhile the affiliated source code constitutes an open platform for new researchers. This is the first book of its kind. We hope the book will make a modest contribution to the field of computational nanoelectronics\"-- Provided by publisher.
Book
Coherence and Indistinguishability of Single Electrons Emitted by Independent Sources
The on-demand emission of coherent and indistinguishable electrons by independent synchronized sources is a challenging task of quantum electronics, in particular regarding its application for quantum information processing. Using two independent on-demand electron sources, we triggered the emission of two single-electron wave packets at different inputs of an electronic beam splitter. Whereas classical particles would be randomly partitioned by the splitter, we observed two-particle interference resulting from quantum exchange. Both electrons, emitted in indistinguishable wave packets with synchronized arrival time on the splitter, exited in different outputs as recorded by the low-frequency current noise. The demonstration of two-electron interference provides the possibility of manipulating coherent and indistinguishable single-electron wave packets in quantum conductors.
Journal Article
Graphene nanoribbons for quantum electronics
Graphene nanoribbons (GNRs) are a family of one-dimensional (1D) materials with a graphitic lattice structure. GNRs possess high mobility and current-carrying capability, sizeable bandgap and versatile electronic properties, which make them promising candidates for quantum electronic applications. In the past 5 years, progress has been made towards atomically precise bottom-up synthesis of GNRs and heterojunctions that provide an ideal platform for functional molecular devices, as well as successful production of semiconducting GNR arrays on insulating substrates potentially useful for large-scale digital circuits. With further development, GNRs can be envisioned as a competitive candidate material in future quantum information sciences. In this Perspective, we discuss recent progress in GNR research and identify key challenges and new directions likely to develop in the near future.Graphene nanoribbons are an emerging class of 1D materials hosting rich quantum-confined and topological states. This Perspective discusses recent breakthroughs in graphene nanoribbon materials and devices, and identifies key challenges towards electronics and quantum information applications.
Journal Article
Cryogenic memory technologies
Cryogenic data storage technology is of use in superconducting single-flux quantum electronics and quantum computing. However, the lack of compatible cryogenic memory technology, which can operate at temperatures of 4 K (or lower), hinders the development of practical and scalable systems. Here we examine the development of cryogenic memory technologies. We explore three areas of memory technology: cryogenic non-superconducting memories (including those based on charge and resistance), superconducting memories (including those based on Josephson junctions, superconducting quantum interference devices and superconducting memristors) and hybrid memories (which use both superconducting and non-superconducting technologies). We consider the key challenges involved in the integration of such memories with single-flux quantum circuits and quantum computers. We also provide a comparison of the capabilities of the different technologies in the context of the requirements of superconducting electronics and quantum computing.
This Review examines the development of cryogenic memory technologies—including non-superconducting memories, superconducting memories and hybrid memories—and their potential application in superconducting single-flux quantum circuits and quantum computers.
Journal Article
Deep moiré potentials in twisted transition metal dichalcogenide bilayers
In twisted bilayers of semiconducting transition metal dichalcogenides, a combination of structural rippling and electronic coupling gives rise to periodic moiré potentials that can confine charged and neutral excitations1–5. Here we show that the moiré potential in these bilayers at small angles is unexpectedly large, reaching values above 300 meV for the valence band and 150 meV for the conduction band—an order of magnitude larger than theoretical estimates based on interlayer coupling alone. We further demonstrate that the moiré potential is a non-monotonic function of moiré wavelength, reaching a maximum at a moiré period of ~13 nm . This non-monotonicity coincides with a change in the structure of the moiré pattern from a continuous variation of stacking order at small moiré wavelengths to a one-dimensional soliton-dominated structure at large moiré wavelengths. We show that the in-plane structure of the moiré pattern is captured by a continuous mechanical relaxation model, and find that the moiré structure and internal strain, rather than the interlayer coupling, are the dominant factors in determining the moiré potential. Our results demonstrate the potential of using precision moiré structures to create deeply trapped carriers or excitations for quantum electronics and opto-electronics.The electrical potential created by a moiré pattern in twisted transition metal dichalcogenide bilayers can be surprisingly deep, trapping electrons that can possibly be used for opto-electronic or quantum simulation applications.
Journal Article
Supercurrent diode effect and magnetochiral anisotropy in few-layer NbSe2
Nonreciprocal transport refers to charge transfer processes that are sensitive to the bias polarity. Until recently, nonreciprocal transport was studied only in dissipative systems, where the nonreciprocal quantity is the resistance. Recent experiments have, however, demonstrated nonreciprocal supercurrent leading to the observation of a supercurrent diode effect in Rashba superconductors. Here we report on a supercurrent diode effect in NbSe
2
constrictions obtained by patterning NbSe
2
flakes with both even and odd layer number. The observed rectification is a consequence of the valley-Zeeman spin-orbit interaction. We demonstrate a rectification efficiency as large as 60%, considerably larger than the efficiency of devices based on Rashba superconductors. In agreement with recent theory for superconducting transition metal dichalcogenides, we show that the effect is driven by the out-of-plane component of the magnetic field. Remarkably, we find that the effect becomes field-asymmetric in the presence of an additional in-plane field component transverse to the current direction. Supercurrent diodes offer a further degree of freedom in designing superconducting quantum electronics with the high degree of integrability offered by van der Waals materials.
The supercurrent diode effect was recently observed in a Nb/V/Ta superlattice thin film with Rashba-type spin-orbit coupling. Here, the authors observe this effect in few-layer NbSe
2
crystals driven by valley-Zeeman-type spin-orbit coupling and find that the effect is proportional to out-of-plane magnetic field.
Journal Article
A quantum access network
An experimental demonstration of the concept of a ‘quantum access network’ based on simple and cost-effective telecommunication technologies yields a viable method for realizing multi-user quantum key distribution networks with efficient use of resources.
A key step towards secure information networks
Quantum key distribution (QKD) is a process allowing secure information exchange between a transmitter and receiver with access to both classical and quantum resources. Its use has been limited to niche applications in dedicated high-security networks, not least because it becomes extremely resource-intensive when multiple users require access to the system. Here, Bernd Fröhlich
et al
. outline the principles of a new QKD system, termed a 'quantum access network', based on simple and cost-effective optical telecommunication technologies. They then demonstrate the concept experimentally in a 64-user network in which, for simplicity and economy, all users share a single photon detector placed at a key node in the network. The authors suggest that this advance could lead to the adoption of quantum technologies as routine in the secure transmission of data.
The theoretically proven security of quantum key distribution (QKD) could revolutionize the way in which information exchange is protected in the future
1
,
2
. Several field tests of QKD have proven it to be a reliable technology for cryptographic key exchange and have demonstrated nodal networks of point-to-point links
3
,
4
,
5
. However, until now no convincing answer has been given to the question of how to extend the scope of QKD beyond niche applications in dedicated high security networks. Here we introduce and experimentally demonstrate the concept of a ‘quantum access network’: based on simple and cost-effective telecommunication technologies, the scheme can greatly expand the number of users in quantum networks and therefore vastly broaden their appeal. We show that a high-speed single-photon detector positioned at a network node can be shared between up to 64 users for exchanging secret keys with the node, thereby significantly reducing the hardware requirements for each user added to the network. This point-to-multipoint architecture removes one of the main obstacles restricting the widespread application of QKD. It presents a viable method for realizing multi-user QKD networks with efficient use of resources, and brings QKD closer to becoming a widespread technology.
Journal Article
Quantum tomography of electrical currents
In quantum nanoelectronics, time-dependent electrical currents are built from few elementary excitations emitted with well-defined wavefunctions. However, despite the realization of sources generating quantized numbers of excitations, and despite the development of the theoretical framework of time-dependent quantum electronics, extracting electron and hole wavefunctions from electrical currents has so far remained out of reach, both at the theoretical and experimental levels. In this work, we demonstrate a quantum tomography protocol which extracts the generated electron and hole wavefunctions and their emission probabilities from any electrical current. It combines two-particle interferometry with signal processing. Using our technique, we extract the wavefunctions generated by trains of Lorentzian pulses carrying one or two electrons. By demonstrating the synthesis and complete characterization of electronic wavefunctions in conductors, this work offers perspectives for quantum information processing with electrical currents and for investigating basic quantum physics in many-body systems.
Elementary excitations of electronic devices have potential use in quantum information but control and readout capabilities are not as developed as they are for more mature systems such as photonic qubits. Here the authors develop and demonstrate a tomographic protocol for electron and hole wavefunctions.
Journal Article