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Antiresonance and its application in triple-quantum-dot systems are studied theoretically using nonequilibrium Green’s function method. The presence or absence of antiresonance point can be used to determine whether quantum dot impurity exists in the system. For a tri-quantum-dot ring, the conversion between 0 and 1 for the conductance can be realized by adjusting the energy levels of quantum dots, which makes the system applicable as a quantum switch. The coupling strength can be measured according to the energy level of the antiresonance point. Once the intradot Coulomb interactions are taken into account, three new Fano antiresonances emerge in the conductance spectrum. Under the action of the magnetic field, two antiresonance points disappear simultaneously. Our work sheds lights onto the design and implementation of new quantum functional devices for electronic measurements.

Twist measurement based on the transmission of fixed wavelength of a helical long-period fiber grating is studied. The single-mode fiber is spiraled by a welding machine. There are two resonance dips near 1473 nm and 1517 nm, with the pitch length around 782 μm. The experimental results show that the transmission near 1473 nm decreases along with contra-direction twist and increases along with co-direction twist. In contrast, the transmission near 1517 nm decreases along with co-direction twist and increases along with contra-direction twist. The relationships between the twist and the resonance wavelength, the twist and the transmission of resonance dips, the twist and the transmission of fixed wavelengths are studied, respectively. They all show linear relationship with the twist, and the slopes are about 100 nm·mm/rad, 36 dB·mm/rad, and 46 dB·mm/rad, respectively. The dual-wavelength ratio is studied, and the ratio also shows linear relationship with the twist. The twist sensitivity of I1463.3 nm/I1526.5 nm is about 0.79 each 0.01 rad/mm. This has great potential application in twist sensors.

Employing the nonequilibrium Green’s function technique, electron transport characteristics through a laterally coupled triple-quantum-dot chain are investigated. The conductance versus electron energy is numerically calculated. Two anti-resonance points change into two anti-resonance bands with increasing the size of triple-quantum-dot chain. The widths of two anti-resonance bands are the same and can be regulated via adjusting the inter-dot tunneling coupling strength in the main chain or its attachment. Spin-polarized window emerges due to Zeeman splitting as an external magnetic flux is introduced. Our studies demonstrate that the system can be used as a quantum switch or an efficient spin filtering.

We present theoretically the quantum electronic transport through an interferometer asymmetrically coupled with triple quantum dots. Using the Keldysh non-equilibrium Green’s function method, the photon-assisted transport properties through the asymmetric quantum system are numerically analyzed. The sidebands of the photon-assisted tunneling process appear when driven by the time-modulated field. The average current spectra are simulated as a function of quantum dot energy to understand the roles of side-coupling strength and time-modulated field in sideband effect and electron tunneling. This is helpful in future design of the basic structures required for quantum computation applications.

We theoretically study the average current through a ring embedded with multiple quantum dots in each arm subjected to a time-dependent external field. A current resonance band can be observed in a six-quantum-dot system. In the presence of a time-dependent external field, mutual transformation occurs between the resonance band and antiresonance band, indicating an effective optically-controlled quantum switch can be realized in a wider quantum dot’s energy regime. As the Zeeman effect is introduced, the conversion between 100 and − 100% for spin polarization $$p$$ p can be realized by adjusting the frequency of time-dependent external field, suggesting a physical scheme of an optically-controlled spin filter. The present work sheds lights onto the design and quantum computation of future nano-devices.

In this paper, several four-quantum-dot topological structures are designed. The influence of the interdot coupling strength and intradot Coulomb interactions on the conductance is discussed. The location of the anti-resonance band can be manipulated by tuning the interdot coupling strength, which suggests a physical scheme of an effective quantum switch. The Fano anti-resonance peak may evolve into a resonance peak. For the particular value of the interdot coupling strength, two Fano anti-resonances collapse and bound states in the continuum are formed. Moreover, many-body effect makes the number of anti-resonance bands increase. This study provides a theoretical basis for the design of quantum computing devices.

Using the non-equilibrium Keldysh Green's function technique, electron transport properties through a two-terminal linear tri-quantum-dot molecule Aharonov-Bohm (A-B) interference are investigated. The conductance as a function of electron energy is numerically calculated. The influence of magnetic flux and interdot coupling strength on the conductance is researched. Fano resonances emerge in the conductance spectrum, and two bound states in the continuum form simultaneously when the interdot couplings take appropriate values. A conductance dip is observed and evolves into an antiresonance band with increasing magnetic flux. The system can be designed as a quantum switch by adjusting the intramolecular couplings.

Electron transport characteristics through a system consisting of a series of triangular quantum dot rings are studied utilizing the non-equilibrium Green’s function. In the presence of a magnetic field, an additional anti-resonance point occurs in the conductance spectrum. As the number of triangular quantum dot rings increases, two anti-resonance points evolve into two well-defined insulating bands. The insulating band disappears as the magnetic flux takes an appropriate value, and therefore, an effective magnetically-controlled quantum switch can be achieved. If a Zeeman magnetic field is introduced, a spin-polarized window (SPW) can be formed, suggesting a physical scheme of a spin filtering. As the intradot Coulomb interactions are taken into consideration, more SPWs can be obtained. This work sheds lights onto the design of future quantum devices.

We design a four-quantum-dot system subjected to a time-dependent external field. The average current through the quantum dot system is obtained by using the method of non-equilibrium Green's function. By adjusting either the amplitude or frequency of the time-dependent external field, the average current can be converted between zero and non-zero. Based on this property, the system can be designed as an optically-controlled quantum switch device. When the asymmetric time-dependent external field is irradiated to the left and right electrodes, negative current can be observed in the current spectrum, i.e., the photon-electron pumping effect. The present work sheds lights onto design and quantum computation of future nano-devices.

We report the conductance and average current through a triple-quantum-dot interferometer coupled with two ferromagnetic leads using the nonequilibrium Green’s function. The results show that the interference between the resonant process and the non-resonant process leads to the formation of Fano resonance. More Fano resonances can be observed by applying a time-dependent external field. As a Zeeman magnetic field is applied, the spin-up electron transport is depressed in a certain range of electron energy levels. A spin-polarized pulse device can be realized by adjusting the spin polarization parameters of ferromagnetic leads. Moreover, the I–V characteristic curves show that under the influence of Fano resonance, the spin polarization is significantly enhanced by applying a relatively large reverse bias voltage. These results strongly suggest that the spin-polarized pulse device can be potentially applied as a spin-dependent quantum device.

A four quantum dots structure is designed. The influence of the interdot coupling strength, energy levels of quantum dots, magnetic flux and intradot Coulomb interactions on the conductance is discussed. An antiresonance point exactly emerges at the location of the energy level of side-coupled quantum dots (SCQD). The conversion between resonance band and antiresonance band can be achieved as parallel-coupled di-quantum dots with or without SCQD, which suggests a physical scheme of an effective quantum switch. The Breit–Wigner resonant and Fano antiresonant peaks may merge into one resonant band. By means of the mathematical formula, we analyze how the resonance band is formed. By varying intradot Coulomb interaction, the resonance band may evolve into a Fano antiresonance with an ultra-narrow width. This study provides theoretical basis for the design of quantum computing devices.

T-shape double quantum dot molecule A–B interference with the action of time-dependent external field is designed. Using the Keldysh non-equilibrium Green's function method, spin-dependent average current as a function of quantum dot energy is obtained. The magnitude and position of average current resonance peaks can be controlled by adjusting interdot coupling strength, frequency and amplitude of time-dependent electric field. The conversion between zero and non-zero value for average current can be realized under the condition with or without the action of time-dependent external field, respectively, which is the basis for the design of controlled quantum switch. Under the combined action of the external magnetic flux and Rashba spin–orbit coupling strength, the spin-polarized average current can be observed. Dc current–voltage characteristics are researched.

Electron transport through a triple-quantum-dot ring in various kinds of dot-lead coupling configurations has been investigated using the nonequilibrium Green’s function technique. The conductance is numerically calculated as a function of the dots’ levels. The appearance of Fano resonance and the formation of bound state in the continuum strongly depend on the configuration of dot-lead coupling strengths. Moreover, a striking conductance dip is found and the conductance spectrum can be interchanged by tuning extra magnetic flux.

A three-quantum-dot spin filter based on nonequilibrium Greenʼs function technique is proposed with external magnetic flux, Rashba spin orbit interaction, and intradot coulomb interaction taken into consideration. Numerical results indicate a spin filter can be made efficient by adjusting external magnetic flux and Rashba spin orbit interaction. Moreover, the formation of a resonance band is discussed through calculation. It is observed that the possibility of transition from one peak to other three peaks in the conductance spectrum increases with increasing interdot coupling strength.

Employing the non-equilibrium Green’s function technique, we have obtained the formula for dc current of two one-dimensional multi-quantum dot arrays, which couple to each other via tunneling coupling between two quantum dots connected to four leads, respectively. The retarded Green’s function is a staircase type, terminating at the four leads. Furthermore, the four quantum dots case is demonstrated. The influence of inter-dot coupling strength and quantum dot energy level on the transmission probability for TL, TM and TN branches is investigated. A non-resonant band is observed. By adjusting energy levels of quantum dots, a resonance emerges in the region of the non-resonance band. The system can be used as a quantum switch.

Making use of the equation of motion method and Keldysh Green's function technique, we have developed a calculation method by which an analytical formula for the current under dc bias is obtained and the transmission probabilities are numerically studied for a T-shaped four-quantum dot (QD) system connected to three terminals. The results are explained in terms of the localization properties of the confined states in the system.

We have obtained the formula for dc current of a four-terminal quantum dot arrays consisting of six quantum dots, by using the nonequilibrium Keldysh Green's function technique. The transmission probability T ( ω ) as a function of electron energy ω and the differential conductance as a function of the chemical potential of the input terminal are numerically calculated.

Making use of the equation of motion method and Keldysh Green function technique, we obtain a general current formula for a quantum-dot-ring with one of the dots connected to two electron reservoirs under a DC bias voltage. The transmission probability T ( ω ) as a function of electron ω curve is presented, which displays oscillation structure. The resonant states of the system are found to distribute within an interval centered at e 0 (the dot energy level) with a width of two times the tunnel coupling amplitude between two neighboring dots, the number of the resonant peaks agrees with N (the number of the dots) when inter-dot tunnel coupling is sufficiently large and an odd–even behavior appears at the Fermi energy.

The nonequilibrium Keldysh Green function technique is used to study the electronic transport property of a four-quantum-dot ring system in a four-terminal configuration. A general formula for the current under dc bias is obtained; the linear conductance characteristic is numerically studied.

Using the non-equilibrium Green’s function technique, conductance through a parallel-coupled double quantum dot (PCDQD) with a side-coupled quantum dot system is investigated. The evolution of the conductance strongly depends on the coupling between the side-coupled quantum dot and PCDQD. Moreover, the conductance as a function of the level of side-couple quantum dot is investigated. Numerical results indicate the lineshape of Fano resonance can be modulated by adjusting the interdot coupling strength.

The thermoelectric and the thermospin transport properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and thermoelectric figure of merit, of a parallel coupled double-quantum-dot Aharonov—Bohm interferometer are investigated by means of the Green function technique. The periodic Anderson model is used to describe the quantum dot system, the Rashba spin—orbit interaction and the Zeeman splitting under a magnetic field are considered. The theoretical results show the constructive contribution of the Rashba effect and the influence of the magnetic field on the thermospin effects. We also show theoretically that material with a high figure of merit can be obtained by tuning the Zeeman splitting energy only.

Using the nonequilibrium Keldysh Green function technique, the influence of intradot Coulomb interactions on conductance for a parallel-coupled triple quantum dot system is investigated. The conductance as a function of electron energy is numerically calculated. The combined effect of the intradot Coulomb interaction and the magnetic flux leads to an intricate conductance lineshape. Moreover, both the magnetic flux and the interdot coupling strength may modulate the Fano effect.

Based on the Green's function technique and the equation of motion approach, this paper theoretically studies the thermoelectric effect in parallel coupled double quantum dots (DQDs), in which Rashba spin—orbit interaction is taken into account. Rashba spin—orbit interaction contributions, even in a magnetic field, are exhibited obviously in the double quantum dots system for the thermoelectric effect. The periodic oscillation of thermopower can be controlled by tunning the Rashba spin—orbit interaction induced phase. The interesting spin-dependent thermoelectric effects will arise which has important influence on thermoelectric properties of the studied system.

We design a coupled-quantum-dot bridge of two quantum-dot arrays coupled to each other via one quantum dot between two quantum-dot arrays, connected to four electron reservoirs. By using the nonequilibrium Green's function, the current formula of the system is obtained. The transmission probability T(ω) as a function of electron energy ω is numerically calculated.