Double Quantum Dot System Research Articles

Optical Control of Coherent Population Transfer in Asymmetric Double Quantum-Dot System

Optical Control of Coherent Population Transfer in Asymmetric Double Quantum-Dot System

Electron Transport Through Two Branch Interferometer with Rashba Spin Orbit Interaction

In this paper, a theoretical model for electron transport through two branch interferometer with one quantum dot in each of its arms has been considered. Both a magnetic flux applied on the circuit and the Rashba spin orbit interaction inside the two dots are taken into account, Rashba spin-orbit interaction contribution are exhibited obviously in the double quantum dots system for the thermoelectric effect, by varying the temperature of the leads , we calculate the conductance (G) and the thermopower (S).

Formation of Fano resonance in double quantum dot system

Transient electron dynamics and the Fano resonance formation over time in transport through a two quantum dot system in a T-shape geometry (2QD-T) are analyzed for free electrons. Time evolution of the transport characteristics are different for a weak and a strong inter-dot coupling with respect to the dot-electrode coupling. When the dot–dot coupling is weak, we find that transport dynamics is governed by two channel tunneling processes with two different relaxation times and buildup of the Fano resonance is developed much slower, with the longer relaxation time. In the opposite limit, the transmission evolves with a single relaxation time, from the single peak resonance structure into the structure with two asymmetric peaks. One observes large dot-electrode charge oscillations, which can temporarily change direction of transient currents. We find also that the time evolution of entanglement is different in both coupling regimes; in particular rapid Rabi oscillations caused by coherent electron transfer between the 2QD states can be seen for the strong dot–dot coupling.

Coherent current correlations in a double-dot Cooper pair splitter

Exact analytical formulas are derived, by means of Keldysh Green functions, for currents and current correlation functions in a Cooper pair splitter modelled on a double quantum dot system coherently coupled to a superconductor and two normal metallic electrodes. Confining to the subspace with the inter-dot singlet we show perfect entanglement of split electrons in two separated crossed Andreev reflection processes. The studies are focused on the noise power spectrum in a whole bias voltage range. In particular, in the large voltage limit shot noise dominates and its spectrum exhibits two extraordinary side dips related to resonant inter-level current correlations caused by coherent electron-hole recombination processes accompanied by emission and absorption of photons. In the linear response limit we derived the frequency dependent admittance which shows different interference patterns for the cross and the auto current correlations.

Non-Markovian Dynamics of Geometric Quantum Discord in a Double Quantum Dot System

In this paper, we study the geometric quantum discord dynamics of the double quantum dot charge qubit in the non-Markovian environment. We apply the non-perturbative non-Markovian quantum state diffusion method to obtain the exact master equation of the double quantum dot system coupled to two independent non-zero temperature electronic baths. Then, we use this master equation to investigate the effects of non-Markovianity, inter-dot coupling strength and bath temperature on the dynamics of geometric quantum discord. Our studies show that the geometric quantum discord of a double quantum dot system can be modified and enhanced in some cases via these factors.

Recombination rates of the double quantum dot solar cell structure

This work proposes a double quantum dot structure as an intermediate-band layer to developing solar cell performance for the first time. The continuity-current equation is coupling with the density matrix equations, which are solved numerically to obtain the quantum efficiency. This modeling will calculate the momentum matrix elements of transitions, consider the orthogonalized plane wave for wetting layer- quantum dot transitions, and covers more characteristics than the rate equations by considering all the possible interactions between the states. The results simulate both the excitonic and nonexcitonic (electron-hole) cases. The work emphasizes adding the double quantum dot layer, which gives flexibility in choosing the energy difference between states controlling the recombination rates. The work refers to the importance of orthogonalized plane-wave in solar cell work. In both models, the band-band recombination is high for slight energy differences between the states, confirms the importance of the double quantum dot system to manipulate transitions between states and obtain higher rates. For the electron-hole model, the leakage is high due to the fast recombination of holes. The discrimination between occupations of states is increasing under the excitonic model due to growing hole occupation. In both models, reducing the quantum dot - quantum dot recombinations and increasing all other recombinations will increase the quantum efficiency. The high quantum dot band-to-band rate increases the quantum efficiency. In the excitonic model, lower rates than in the electron-hole model are enough for high quantum efficiency.

Thermal rectification and negative differential thermal conductance based on a parallel-coupled double quantum-dot

We investigate the heat flow transport properties of a parallel-coupled double quantum-dot system connected to two reservoirs with a temperature bias in the Coulomb blockade regime. We demonstrate that the effects of thermal rectification and negative differential thermal conductance (NDTC) exist in this system and analyze the influences of energy level difference and Coulomb interaction on the thermal rectification and NDTC. We find that this system can achieve a high thermal rectification ratio and NDTC when the asymmetry factor of the system is enhanced.

Two coupled double quantum-dot systems as a working substance for heat machines.

This paper presents a conceptual design for quantum heat machines using a pair of coupled double quantum dots (DQDs), each DQD with an excess electron to interact, as an working substance. We define a compression ratio as the ratio between the Coulomb couplings which describes the interaction between the electrons during the isochoric processes of the quantum Otto cycle and then we analyze the arising of different regimes of operations of our thermal machine. We also show that we may change the operation mode of an Otto engine when considering the effects due to the quantum tunneling of a single electron between each individual DQD.

Spin polarization rate calculation for T-shaped double quantum dots coupled to (C- terminated ScC(1 1 1) surface) leads

The device considered in our study is the T-shaped double quantum dots system embedded between two ferromagnetic (C-terminated ScC (111) surface) leads. The theoretical treatment is achieved using the time-evolution operator approach. The role of the time-dependent external field, spin-dependent coupling interaction and energy spacing on the dots in spin transport through the device considered in our study has studied. The spin accumulation on the quantum dots, the spin and total currents and the spin polarization rate of the device have calculated. The imprint of the leads density of states is very obvious in the time window calculation which increases with the energy spacing and the frequency of the time-dependent external field. Our results indicate that time-dependent external field and spin-dependent coupling interaction play important role in manufacturing full spin polarization and controlling the spin polarization rate in the device. Controlling the spin transport features have many potential applications in spin-based quantum devices such as quantum computing and spin filter devices.

Flexible Control of Two-Channel Transmission and Group Delay in an Optomechanical System with Double Quantum Dots Driven by External Field.

With the presence of a driving field applied to double quantum dots and a control field applied on the cavity, the transmission performance and group delay effect of a probe field have been theoretically studied in a hybrid optomechanical system (HOMS). Due to the interaction between the mechanical mode and the double quantum dots system, double optomechanically induced transparency (OMIT) arises in the HOMS. With the assistance of a driving field, the system can be tuned to switch on any one of the two OMIT windows, switch on both of the two OMIT windows or switch off both of the two OMIT windows by dynamically adjusting control of the optical field and the driving field. Furthermore, the transmitted probe fields of the two OMIT windows can be tuned to be absorbed or amplified with proper parameters of the driving field and control field. Moreover, the transmission properties of the two OMIT windows are asymmetrical. One can obtain the maximum group delay time of the probe field by optimizing the amplitude and phase of the driving field. These results provide a new way for constructing optically controlled nanostructured photonic switch and storage devices.

Nonlocality and coherence in double quantum dot systems

We examine the relationship among the fidelity, quantum coherence and Bell nonlocality in double quantum dot systems (DQDs) using transmission line resonator (TLR). We show how the physical quantities depend on the main parameters of the physical model and initial state parameter of the DQD. Moreover, we evaluate the total quantum correlation in DQDs using the skew information and display the time dependence of the quantum coherence and correlation on the main physical parameters.

Floquet state depletion in ac-driven circuit QED

We perform Floquet spectroscopy in a GaAs double quantum dot system coupled to a high-impedance superconducting resonator. By applying microwave induced consecutive passages under a double resonance condition, we observe novel Landau-Zener-St\"uckelberg-Majorana interference patterns that stem from a cavity-assisted interference pattern modified by the depletion of the ground state. Our experimental results reveal the stationary state behavior of a strongly driven two-level system, and are consistent with the simulations based on our theoretical model. This study provides an excellent platform for investigating the dynamics of Floquet states in the presence of strong driving.

Thermoelectric Transport in a Double-Quantum-Dot Coupled to Majorana Zero Modes

Thermoelectric transport through a double-quantum-dot (DQD) connected to the left and right leads is theoretically investigated in the framework of non-equilibrium Green’s function technique. We consider that the dots are also coupled to Majorana zero modes (MZMs) prepared at the two ends of a topological superconductor nanowire. It is found that the sign change of thermopower, which is promising in the detection of MZMs, can be realized by tuning several system’s parameters related to the MZMs, such as the coupling strength between the dots and the MZMs, the direct coupling between the MZMs, or even the magnetic flux penetrating through the structure. The above parameters also lead to significant enhancement of the thermopower and thermoelectric figure of merit (FOM), which indicates the conversion efficiency between heat and electrical energies. We also find that in this DQD system, both the thermopower and FOM are simultaneously enhanced by the MZMs around the electron-hole symmetric point, an ideal phenomenon in applications of thermoelectric effect. In addition, the thermoelectric effect is remarkably enhanced by the direct hybridization between the MZMs, which is very different from the case in single-dot structure.

Micro-scale photon source in a hybrid cQED system* *Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0301700), the National Natural Science Foundation of China (Grant Nos. 61922074, 11674300, 61674132, 11625419, and 11804327), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB24030601), and the Anhui Initiative in Quantum Information Technologies,

Coherent photon source is an important element that has been widely used in spectroscopy, imaging, detection, and teleportation in quantum optics. However, it is still a challenge to realize micro-scale coherent emitters in semiconductor systems. We report the observation of gain in a cavity-coupled GaAs double quantum dot system with a voltage bias across the device. By characterizing and analyzing the cavity responses to different quantum dot behaviors, we distinguish the microwave photon emission from the signal gain. This study provides a possibility to realize micro-scale amplifiers or coherent microwave photon sources in circuit quantum electrodynamics (cQED) hybrid systems.

Nonequilibrium free energy and information flow of a double quantum-dot system with Coulomb coupling* *Project supported by the National Natural Science Foundation (Grant No. 11805159), the First Batch of National First-class Undergraduate Courses of China (2020), the Natural Science Foundation of Fujian Province, China (Grant No. 2019J05003), and Teaching Research Program of Thermodynamics and Statistical Physics in the Institution of

We build a double quantum-dot system with Coulomb coupling and aim at studying connections among the entropy production, free energy, and information flow. By utilizing concepts in stochastic thermodynamics and graph theory analysis, Clausius and nonequilibrium free energy inequalities are built to interpret local second law of thermodynamics for subsystems. A fundamental set of cycle fluxes and affinities is identified to decompose two inequalities by using Schnakenberg’s network theory. Results show that the thermodynamic irreversibility has energy-related and information-related contributions. A global cycle associated with the feedback-induced information flow would pump electrons against the bias voltage, which implements a Maxwell demon.

Spin and charge localisation due to the interplay of Ac gate voltage and spin–orbit interaction

ABSTRACT We investigate the effects of a time-dependent gate voltage on a spin–orbit interaction (SOI) coupled interacting double quantum dot (DQD) system. For a tunnel coupled detuned DQD with two interacting electrons, SOI couples triplet and hybridised singlet state (1,1)–(0,2) through spin nonconserving transition. In order to explore the effects of Ac gate voltage on charge localisation, we initiate the system in the vicinity of the singlet–triplet avoided crossing and investigate the interplay of the Ac gate voltage and SOI on the charge and spin dynamics of the system. We show that the triplet state (1,1) charge configuration can be frozen by tuning the Ac frequency leading to charge localisation and dynamical spin locking with a redefined spin–orbit field in terms of gate voltage.

Quantum holography in ladder-plus-Y double quantum dot system

This work studies quantum holography in a ladder-plus-Y double quantum dot system. The density matrix theory is used to model the system and an analytical solution of the susceptibility is done. Different parameters and situations are examined in this study. A comparison with the classical holograph is examined. A coincidence with the transmission amplitude is shown means that good holography of the object is performed.

Voltage Control of Electromagnetically Induced Grating in Asymmetric Double Quantum Dot System

Voltage Control of Electromagnetically Induced Grating in Asymmetric Double Quantum Dot System

Electron transfer properties of double quantum dot system in a fluctuating environment* *Project supported by the Natural Science Foundation of Shandong Province, China (Grant No. ZR2014AM030).

Using the innovative method of the additional Bloch vector, the electron transfer properties of a double quantum dot (DQD) system measured by a quantum point contact (QPC) in a fluctuating environment are investigated. The results show that the environmental noises in transverse and longitudinal directions play different roles in the dynamical evolution of the open quantum systems. Considering the DQD with symmetric energy level, the Fano factor exhibits a slight peak with the increase of transverse noise amplitude σ T, which provides a basis for distinguishing dynamical phenomena caused by different directional fluctuation noises in symmetric DQD structures by studying the detector output. In the case of asymmetric DQD, the dependence of a detector current involving the level displacement is distinct when increasing the transverse noise damping coefficient τ T and the longitudinal noise damping coefficient τε respectively. Meanwhile, the transverse noise damping coefficient τ T could significantly reduce the Fano factor and enhance the stability of the quantum system compared with the longitudinal one. The Fano factors with stable values as the enhancement of noise amplitudes show different external influences from the detector measurement, and provide a numerical reference for adjusting the noise amplitudes in both transverse and longitudinal directions appropriately in a microscopic experimental process to offset the decoherence effect caused by the measurements. Finally, the research of average waiting time provides unique insights to the development of single electron transfer theory in the short-time limit.

G-tensor resonance in double quantum dots with site-dependent g-tensors

Pauli spin blockade (PSB) has long been an important tool for spin read-out in double quantum dot (DQD) systems with interdot tunneling t. In this paper we show that the blockade is lifted if the two dots experience distinct effective magnetic fields caused by site-dependent g-tensors g L and g R for the left and right dot, and that this effect can be more pronounced than the leakage current due to the spin–orbit interaction (SOI) via spin-flip tunneling and the hyperfine interaction (HFI) of the electron spin with the host nuclear spins. Using analytical results obtained in special parameter regimes, we show that information about both the out-of-plane and in-plane g-factors of the dots can be inferred from characteristic features of the magneto-transport curve. For a symmetric DQD, we predict a pronounced maximum in the leakage current at the characteristic out-of-plane magnetic field which we term the g-tensor resonance of the system. Moreover, we extend the results to contain the effects of strong SOI and argue that in this more general case the leakage current carries information about the g-tensor components and SOI of the system.