scholarly journals Quantum Transport of Particles and Entropy

Entropy ◽  
2021 ◽  
Vol 23 (12) ◽  
pp. 1573
Author(s):  
Christoph Strunk
Keyword(s):  
Quantum Transport ◽  
Quantum Interference ◽  
Quantum Wires ◽  
Transport Coefficients ◽  
Building Blocks ◽  
Quantum Gases ◽  
Thermoelectric Effects ◽  
Entropy Flow ◽  
Unified View ◽  
Ideal Quantum

A unified view on macroscopic thermodynamics and quantum transport is presented. Thermodynamic processes with an exchange of energy between two systems necessarily involve the flow of other balancable quantities. These flows are first analyzed using a simple drift-diffusion model, which includes the thermoelectric effects, and connects the various transport coefficients to certain thermodynamic susceptibilities and a diffusion coefficient. In the second part of the paper, the connection between macroscopic thermodynamics and quantum statistics is discussed. It is proposed to employ not particles, but elementary Fermi- or Bose-systems as the elementary building blocks of ideal quantum gases. In this way, the transport not only of particles but also of entropy can be derived in a concise way, and is illustrated both for ballistic quantum wires, and for diffusive conductors. In particular, the quantum interference of entropy flow is in close correspondence to that of electric current.

Mechanically-Tunable Quantum Interference in Ferrocene-Based Single-Molecule Junctions

2020 ◽  
Author(s):  
María Camarasa-Gómez ◽  
Daniel Hernangómez-Pérez ◽  
Michael S. Inkpen ◽  
Giacomo Lovat ◽  
E-Dean Fung ◽  
...  
Keyword(s):  
Single Molecule ◽  
Quantum Interference ◽  
Degrees Of Freedom ◽  
Building Blocks ◽  
Ferrocene Derivative ◽  
Single Molecule Junctions ◽  
Molecule Junction ◽  
Single Molecule Junction ◽  
The Impact ◽  
D Orbitals

Ferrocenes are ubiquitous organometallic building blocks that comprise a Fe atom sandwiched between two cyclopentadienyl (Cp) rings that rotate freely at room temperature. Of widespread interest in fundamental studies and real-world applications, they have also attracted<br>some interest as functional elements of molecular-scale devices. Here we investigate the impact of<br>the configurational degrees of freedom of a ferrocene derivative on its single-molecule junction<br>conductance. Measurements indicate that the conductance of the ferrocene derivative, which is<br>suppressed by two orders of magnitude as compared to a fully conjugated analog, can be modulated<br>by altering the junction configuration. Ab initio transport calculations show that the low conductance is a consequence of destructive quantum interference effects that arise from the hybridization of metal-based d-orbitals and the ligand-based π-system. By rotating the Cp rings, the hybridization, and thus the quantum interference, can be mechanically controlled, resulting in a conductance modulation that is seen experimentally.<br>

scholarly journals Performance Analysis and Optimization for Irreversible Combined Carnot Heat Engine Working with Ideal Quantum Gases

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 536
Author(s):  
Lingen Chen ◽  
Zewei Meng ◽  
Yanlin Ge ◽  
Feng Wu
Keyword(s):  
Power Output ◽  
Thermal Efficiency ◽  
Combined Cycle ◽  
Quantum Gases ◽  
Carnot Cycle ◽  
Leakage Loss ◽  
Optimal Power ◽  
Heat Leakage ◽  
Working Medium ◽  
Ideal Quantum

An irreversible combined Carnot cycle model using ideal quantum gases as a working medium was studied by using finite-time thermodynamics. The combined cycle consisted of two Carnot sub-cycles in a cascade mode. Considering thermal resistance, internal irreversibility, and heat leakage losses, the power output and thermal efficiency of the irreversible combined Carnot cycle were derived by utilizing the quantum gas state equation. The temperature effect of the working medium on power output and thermal efficiency is analyzed by numerical method, the optimal relationship between power output and thermal efficiency is solved by the Euler-Lagrange equation, and the effects of different working mediums on the optimal power and thermal efficiency performance are also focused. The results show that there is a set of working medium temperatures that makes the power output of the combined cycle be maximum. When there is no heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are parabolic-like ones, and the internal irreversibility makes both power output and efficiency decrease. When there is heat leakage loss in the combined cycle, all the characteristic curves of optimal power versus thermal efficiency are loop-shaped ones, and the heat leakage loss only affects the thermal efficiency of the combined Carnot cycle. Comparing the power output of combined heat engines with four types of working mediums, the two-stage combined Carnot cycle using ideal Fermi-Bose gas as working medium obtains the highest power output.

scholarly journals Silicon-based spin and charge quantum computation

2005 ◽  
Vol 77 (2) ◽  
pp. 201-222 ◽  
Author(s):  
Belita Koiller ◽  
Xuedong Hu ◽  
Rodrigo B. Capaz ◽  
Adriano S. Martins ◽  
Sankar Das Sarma
Keyword(s):  
Quantum Computation ◽  
Quantum Interference ◽  
Quantum Computer ◽  
Building Blocks ◽  
Shallow Donor ◽  
Molecular Ions ◽  
Conduction Band Edge ◽  
Tunnel Coupling ◽  
Qubit Operations ◽  
Silicon Based

Silicon-based quantum-computer architectures have attracted attention because of their promise for scalability and their potential for synergetically utilizing the available resources associated with the existing Si technology infrastructure. Electronic and nuclear spins of shallow donors (e.g. phosphorus) in Si are ideal candidates for qubits in such proposals due to the relatively long spin coherence times. For these spin qubits, donor electron charge manipulation by external gates is a key ingredient for control and read-out of single-qubit operations, while shallow donor exchange gates are frequently invoked to perform two-qubit operations. More recently, charge qubits based on tunnel coupling in P+2 substitutional molecular ions in Si have also been proposed. We discuss the feasibility of the building blocks involved in shallow donor quantum computation in silicon, taking into account the peculiarities of silicon electronic structure, in particular the six degenerate states at the conduction band edge. We show that quantum interference among these states does not significantly affect operations involving a single donor, but leads to fast oscillations in electron exchange coupling and on tunnel-coupling strength when the donor pair relative position is changed on a lattice-parameter scale. These studies illustrate the considerable potential as well as the tremendous challenges posed by donor spin and charge as candidates for qubits in silicon.

scholarly journals A unified view of density-based methods for semi-supervised clustering and classification

2019 ◽  
Vol 33 (6) ◽  
pp. 1894-1952 ◽  
Author(s):  
Jadson Castro Gertrudes ◽  
Arthur Zimek ◽  
Jörg Sander ◽  
Ricardo J. G. B. Campello
Keyword(s):  
Supervised Classification ◽  
Clustering Algorithms ◽  
Building Blocks ◽  
Large Collection ◽  
Supervised Clustering ◽  
The Core ◽  
Density Based Clustering ◽  
Clustering And Classification ◽  
Unified View ◽  
New Framework

Abstract Semi-supervised learning is drawing increasing attention in the era of big data, as the gap between the abundance of cheap, automatically collected unlabeled data and the scarcity of labeled data that are laborious and expensive to obtain is dramatically increasing. In this paper, we first introduce a unified view of density-based clustering algorithms. We then build upon this view and bridge the areas of semi-supervised clustering and classification under a common umbrella of density-based techniques. We show that there are close relations between density-based clustering algorithms and the graph-based approach for transductive classification. These relations are then used as a basis for a new framework for semi-supervised classification based on building-blocks from density-based clustering. This framework is not only efficient and effective, but it is also statistically sound. In addition, we generalize the core algorithm in our framework, HDBSCAN*, so that it can also perform semi-supervised clustering by directly taking advantage of any fraction of labeled data that may be available. Experimental results on a large collection of datasets show the advantages of the proposed approach both for semi-supervised classification as well as for semi-supervised clustering.

The Side Effect of Spin Precession and Quantum Interference in a Four-Terminal Nano Device with Rashba Spin-Orbit Coupling

2012 ◽  
Vol 496 ◽  
pp. 351-354
Author(s):  
Hui Xian Wang ◽  
Li Ben Li ◽  
Da Wei Kang
Keyword(s):  
Side Effect ◽  
Quantum Interference ◽  
Quantum Wires ◽  
Combined Effect ◽  
Spin Precession ◽  
Spatial Distributions ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Rashba Spin ◽  
Coherent Transmission

We propose a four-terminal nano device made of quantum wires with Rashba spin-orbit (SO) coupling. In each terminal there are several independent channels formed with quantum wires. The coherent transmission of electrons in such a nano system is a combined effect of quantum interference and spin precession. When defining two opposite terminals as source and drain leads, the charge and spin currents in channels of other two terminals exhibit spatial distributions which reflect the competition between spin precession and quantum interference during the tunneling of electrons. Since the four-terminal nano device is geometrically simple for the moving paths of charge and spin, our investigation may shed some light on the basic physical picture on this issue.

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