Imaging a Coupled Quantum Dot - Quantum Point Contact System

We performed measurements on a quantum dot and a capacitively coupled quantum point contact by using the sharp metallic tip of a low-temperature scanning force microscope as a scanned gate. The quantum point contact served as a detector for charges on the dot or nearby. It allowed us to distinguish single electron charging events in several charge traps from charging events on the dot. We analyzed the tip-induced potential quantitatively and found its shape to be independent of the voltage applied to the tip within a certain range of parameters. We estimate that the trap density is below 0.1% of the doping density and that the interaction energy between the quantum dot and a trap is a significant portion of the dot's charging energy. Possibly, such charge traps are the reason for frequently observed parametric charge rearrangements.Comment: 6 pages, 5 figure

A novel policy making proposition for EV charging infrastructure management at HEI's

This paper is based on real time EV charging infrastructure development that took place at Brunel University, which is located in west of London, UK. The aim of this paper is to establish the policy making process that has stages of an initial student-staff interest survey, records of the consultation process with EV owners, results of competitive benchmarking with other HEI's and the discussion on Type 2 Mode 3 charging stations which are 240V, 32A, 7kW, 50Hz compliant with IEC 62196 and ISO 14443 Mifare standards. The first time ever PAYG concept of POD Point Ltd is explained. Benefits of using PAYG concept for charging EV are mentioned. Various other factors that played major role were also considered as follows: deciding the tariff of the electricity used by the EV owners, charging cable compatibility with charging station, hours of operation, creation of new enforcement rules and recommendations to provide incentives that recognise and motivate EV community

Electron-electron interaction and charging effects in graphene quantum dots

We analyze charging effects in graphene quantum dots. Using a simple model, we show that, when the Fermi level is far from the neutrality point, charging effects lead to a shift in the electrostatic potential and the dot shows standard Coulomb blockade features. Near the neutrality point, surface states are partially occupied and the Coulomb interaction leads to a strongly correlated ground state which can be approximated by either a Wigner crystal or a Laughlin like wave function. The existence of strong correlations modify the transport properties which show non equilibrium effects, similar to those predicted for tunneling into other strongly correlated systems.Comment: Extended version accepted for publication at Phys. Rev.

Optimal Charging of Electric Vehicles in Smart Grid: Characterization and Valley-Filling Algorithms

Electric vehicles (EVs) offer an attractive long-term solution to reduce the dependence on fossil fuel and greenhouse gas emission. However, a fleet of EVs with different EV battery charging rate constraints, that is distributed across a smart power grid network requires a coordinated charging schedule to minimize the power generation and EV charging costs. In this paper, we study a joint optimal power flow (OPF) and EV charging problem that augments the OPF problem with charging EVs over time. While the OPF problem is generally nonconvex and nonsmooth, it is shown recently that the OPF problem can be solved optimally for most practical power networks using its convex dual problem. Building on this zero duality gap result, we study a nested optimization approach to decompose the joint OPF and EV charging problem. We characterize the optimal offline EV charging schedule to be a valley-filling profile, which allows us to develop an optimal offline algorithm with computational complexity that is significantly lower than centralized interior point solvers. Furthermore, we propose a decentralized online algorithm that dynamically tracks the valley-filling profile. Our algorithms are evaluated on the IEEE 14 bus system, and the simulations show that the online algorithm performs almost near optimality ($<1$ relative difference from the offline optimal solution) under different settings.Comment: This paper is temporarily withdrawn in preparation for journal submissio

Enhanced energy transfer in a Dicke quantum battery

We theoretically investigate the enhancement of the charging power in a Dicke quantum battery which consists of an array of $N$ two-level systems (TLS) coupled to a single mode of cavity photons. In the limit of small $N$, we analytically solve the time evolution for the full charging process. The eigenvectors of the driving Hamiltonian are found to be pseudo-Hermite polynomials and the evolution is thus interpreted as harmonic oscillator like behaviour. We find that there exists a universal flip duration in this process, regardless to the number of TLSs inside the cavity. Then we demonstrate that the average charging power when using a collective protocol is $\sqrt{N}$ times larger than the parallel charging protocol as for transferring the same amount of energy. Unlike previous studies, we point out that such quantum advantage does not originate from entanglement but dues to the coherent cooperative interactions among the TLSs. Our results provide intuitive quantitative insight into the dynamic charging process of a Dicke battery and can be observed under realistic experimental conditions.Comment: 8 Pages, 3 figure

Evidence for Charging Effects in CdTe/CdMgTe Quantum Point Contacts

Here we report on fabrication and low temperature magnetotransport measurements of quantum point contacts patterned from a novel two-dimensional electron system - CdTe/CdMgTe modulation doped heterostructure. From the temperature and bias dependence we ascribe the reported data to evidence for a weakly bound state which is naturally formed inside a CdTe quantum constrictions due to charging effects. We argue that the spontaneous introduction of an open dot is responsible for the replacement of flat conductance plateaus by quasi-periodic resonances with amplitude less than 2e^{2}/h, as found in our system. Additionally, below 1 K a pattern of weaker conductance peaks, superimposed upon wider resonances, is also observed.Comment: 4 pages, 4 figure