Aharonov-Bohm Interferometer Research Articles

Nonreciprocity and thermoelectric performance in a double-dot Aharonov–Bohm interferometer

We investigate nonreciprocity and thermoelectric performance beyond the linear response regime in a double-dot Aharonov–Bohm interferometer that is connected to three reservoirs. In the presence of a magnetic flux (broken time-reversal symmetry), we find that the difference between the forward and reverse particle currents can reach the order of 10% under certain conditions. We also show that when the temperature gradient is reversed, the thermoelectric efficiency and output power both change; however, the discrepancies are minimal. Indeed, although breaking time-reversal symmetry can enhance the maximum efficiency, it reduces the maximum power in the present model. These results could be useful for the design of nanoscale thermoelectric devices.

Stepped graphene-based Aharonov–Bohm interferometers

Aharonov–Bohm interferences in the quantum Hall regime are observed when electrons are transmitted between two edge channels. Such a phenomenon has been realized in 2D systems such as quantum point contacts, anti-dots and p-n junctions. Based on a theoretical investigation of the magnetotransport in stepped graphene, a new kind of Aharonov–Bohm interferometers is proposed herewith. Indeed, when a strong magnetic field is applied in a proper direction, oppositely propagating edge states can be achieved in both terrace and facet zones of the step, leading to the interedge scatterings and hence strong Aharonov–Bohm oscillations in the conductance in the quantum Hall regime. Taking place in the unipolar regime, this interference is also predicted in stepped systems of other 2D layered materials.

Aharonov-Bohm Interferometer in a T-Shaped Quantum Dot Embedded in Majorana Bound States**Supported by the National Natural Science Foundation of China under Grant No. 11547203 and the Science Foundation of Civil Aviation Flight University of China under Grant Nos. J2015-35 and JG2019-19

We theoretically study the spin-dependent transport properties of an Aharonov-Bohm (AB) interferometer composed by a T-shaped quantum dot (QD) embedded in Majorana bound states (MBS). We use the equation of motion method to calculate the conductance across the interferometer. We note that the conductance exhibits sensitive dependence on the MBS-QD coupling strength as well as the polarization strength of the leads when the phase factor of AB ring changes periodically. The conductance shows a transition from resonance to anti-resonance when the MBS-QD coupling strength changes from small to large. Also, there is different p-dependence conductance when the leads alignment changes from parallel to anti-parallel. These findings suggest that such a model could be used for a sensitive detection of MBS interactions, exploiting the high sensitivity of conductance to the AB phase in the interferometer.

Broadband Optical Switch based on an Achromatic Photonic Gauge Potential in Dynamically Modulated Waveguides

We demonstrate that a photonic gauge potential, which arises from the phase degree of freedom in dynamic refractive-index modulation and hence is achormatic, can be used to achieve a broadband optical switch using the configuration of a photonic Aharonov-Bohm interferometer (ABI). The resulting ABI switch has a far larger bandwidth and lower cross talk than the conventional Mach-Zehnder interferometer. Using coupled-mode theory and full-wave numerical modeling, we compare the response of the two interferometers in the presence of nonidealities. Our results indicate the importance of the photonic gauge potential for broadband optical signal processing.

Fano Resonance in Transport Through Double Quantum Dot in Parallel

The transport properties of double quantum dot (DQD) in parallel are theoretically examined. This system simulates a mesoscopic ring with an embedded quantum dot, so‐called Aharonov–Bohm (AB) interferometer, by enlarging the line width in one of the quantum dots. We find that: 1) the Coulomb peak shows an asymmetric shape of Fano resonance when the DQD is coupled to external leads with single conduction channel; 2) the peak becomes more symmetric for the leads with multiple channels; and 3) the resonant shape is characterized by a single parameter which is determined by the structure of the leads. Our theory may explain the experimental results on the transport through the AB interferometer; an asymmetric Fano resonance was observed by one group while a symmetric Breit–Wigner resonance was observed by the other groups.

Fano resonance and power output in a quantum-dot-embedded Aharonov-Bohm ring subjected to THz irradiation

In this paper, we theoretically investigate the Fano resonance and thermoelectric transport in a nanoscale Aharonov-Bohm interferometer consisting of an InAs quantum dot coupled to two electrodes under THz irradiation. In the non-linear regime, the charge current shows a symmetric line shape at asymmetric THz frequency even in the presence of the Fano effect. Under asymmetric THz irradiation, the heat current presents the cooling effect. Interestingly, the heat current will change its sign and the cooling effect appears in different VG region if we switch the THz frequency asymmetric ratio of the two electrodes. This characteristic provides a new way of manipulating thermoelectric devices. In addition, with increasing strength or frequency of the THz field, a restricted zone of the output power would appear around the region VG=0.0. These results have potential for the application of thermoelectric devices under THz irradiation.

Landau-Zener tunneling of qubit states and Aharonov-Bohm interferometry in double quantum wires

This paper gives a detailed description of a high-performance tunneling wire “flying qubit” for a quantum mechanical two-level system. We propose a simple double-wire interferometer setup and theoretically carry out the spectroscopy of these flying qubits. As such, we present a tight binding theoretical model which effectively mimicks the experimental setup and then compute the energy diagram and the Landau-Zener quantum tunneling probability under the effect of a sequence of magnetic pulses and gate voltages. At certain critical electrostatic gate voltages, the system exhibits a step rise in the Landau-Zener tunneling transition by playing a multi-crossing scenario in a privileged position of two geometric wires. We predict the consecutive modulations and precise the conservation of the Landau-Zener-Stückelberg-Majorana interference patterns mapped from the two-terminal of the double-wire system. A successful conversion of interferometry signals is identified within the two-path interferometer with higher intrinsic quantum correction errors. The latter is used quantitatively and qualitatively to achieve high-precision measurements beyond the standard Landau-Zener limit. The obtained results confirm the possibility of the construction of Aharonov-Bohm interferometers following the proposed model.

Aharonov-Bohm conductance oscillations and current equilibration in local n−p junctions in graphene

We consider a small p-type island defined within n-type graphene nanoribbon induced by potential of a floating electrode. In the quantum Hall conditions the island supports persistent currents localized at the $n-p$ junction. When coupled to the graphene edge the island acts as an Aharonov-Bohm interferometer. We evaluate the electrostatic potential induced by the floating gate within the ribbon near the charge neutrality point and consider equilibration of the currents at both sides of the junction. The incoherent equilibration is introduced by the virtual probes technique. We describe the evolution of the coherent Aharonov-Bohm conductance oscillations to the quantum Hall fractional plateaus due to the current equilibration.

Spin and charge Nernst effect in a four-terminal double-dot interferometer

We investigate the spin and charge Nernst effect of a four-terminal Aharonov–Bohm interferometer with Rashba spin–orbit interaction (RSOI). It is shown that a pure spin Nernst effect or a fully spin-polarized Nernst effect can be obtained by modulating the magnetic flux phase ϕ and the RSOI induced phase φ. It is also demonstrated that some windows of ϕ (or φ) for maintaining an almost fully spin-polarized Nernst effect exist and their width is under the control of the other phase. Moreover, for the charge Nernst coefficient Nc and spin Nernst coefficient Ns the relationship Nc(ϕ,φ)=−Ns(φ,ϕ) always holds. These results suggest that our proposal may act as a controllable thermospin generator.

Tunneling Aharonov-Bohm interferometer on helical edge states

We discuss transport through interferometer formed by helical edge states tunnel-coupled to metallic leads. We focus on the experimentally relevant case of relatively high temperature as compared to the level spacing and discuss a response of the setup to the external magnetic flux $\phi$ (measured in units of flux quantum) piercing the area encompassed by edge states. We demonstrate that tunneling conductance of the interferometer is structureless in ballistic case but shows a sharp antiresonances, as a function of magnetic flux $\phi$ - with the period 1/2 - in the presence of magnetic impurity. We interpret the resonance behavior as a coherent enhancement of backward scattering off magnetic impurity at integer and half-integer values of flux, which is accompanied by suppression of the effective scattering at other values of flux. Both enhancement and suppression are due to the interference of processes with multiple returns to magnetic impurity after a number of clockwise and counterclockwise revolutions around setup. This phenomenon is similar to the well-known weak-localization-induced enhancement of backscattering in disordered systems. The quantum correction to the tunneling conductance is shown to be proportional to flux-dependent "ballistic Cooperon". The obtained results can be used for flux-tunable control of the magnetic disorder in Aharonov-Bohm interferometers built on helical edge states.

Manipulating quantum coherence of charge states in interacting double-dot Aharonov–Bohm interferometers

We investigate the dynamics of charge-state coherence in a degenerate double-dot Aharonov–Bohm interferometer with finite inter-dot Coulomb interactions. The quantum coherence of the charge states is found to be sensitive to the transport setup configurations, involving both the single-electron impurity channels and the Coulomb-assisted ones. We numerically demonstrate the emergence of a complete coherence between the two charge states, with the relative phase being continuously controllable through the magnetic flux. Interestingly, a fully coherent charge qubit arises at the double-dots electron pair tunneling resonance condition, where the chemical potential of one electrode is tuned at the center between a single-electron impurity channel and the related Coulomb-assisted channel. This pure quantum state of charge qubit could be experimentally realized at the current–voltage characteristic turnover position, where differential conductance sign changes. We further elaborate the underlying mechanism for both the real-time and the stationary charge-states coherence in the double-dot systems of study.

Asymmetric lasing at spectral singularities

Scattering coefficients can diverge at spectral singularities. In such situation, the stationary solution becomes a laser solution with outgoing waves only. We explore a parity-time (PT)-symmetric non-Hermitian two-arm Aharonov-Bohm interferometer consisting of three coupled resonators enclosing synthetic magnetic flux. The synthetic magnetic flux does not break the PT symmetry, which protects the symmetric transmission. The features and conditions of symmetric, asymmetric, and unidirectional lasing at spectral singularities are discussed. We elucidate that lasing affected by the interference is asymmetric; asymmetric lasing is induced by the interplay between the synthetic magnetic flux and the system's non-Hermiticity. The product of the left and right transmissions is equal to that of the reflections. Our findings reveal that the synthetic magnetic flux affects light propagation, and the results can be applied in the design of lasing devices.

Buildup of Fano resonances in the time domain in a double quantum dot Aharonov-Bohm interferometer

In this paper, we investigate the transient quantum transport in a nanoscale Aharonov-Bohm interferometer consisting of laterally coupled double quantum dots (DQDs) coupled to the source and drain electrodes. The tran- sient linear conductance is derived at arbitrary temperature of the leads. The resulting transient conductance can be divided into three terms contributed from different transport channels. From the transient linear conductance and the reduced density matrix elements of the DQD system, we show the buildup of Fano resonances in the time domain.

Detecting coupling of Majorana bound states with an Aharonov–Bohm interferometer

We study the transport properties of an interferometer composed by a quantum dot (QD) coupled with two normal leads and two one-dimensional topological superconductor nanowires (TNWs) hosting Majorana bound states (MBS) at their ends. The geometry considered is such that one TNW has both ends connected with the QD, forming an Aharonov–Bohm (AB) interferometer threaded by an external magnetic flux, while the other TNW is placed near the interferometer TNW. This geometry can alternatively be seen as a long wire contacted across a local defect, with possible coupling between independent-MBS. We use the Green’s function formalism to calculate the conductance across normal current leads on the QD. We find that the conductance exhibits a half-quantum value regardless of the AB phase and location of the dot energy level, whenever the interferometer configuration interacts with the neighboring TNW. These findings suggest that such a geometry could be used for a sensitive detection of MBS interactions across TNWs, exploiting the high sensitivity of conductance to the AB phase in the interferometer.

Antiresonance and decoupling in electronic transport through parallel-coupled quantum-dot structures with laterally-coupled Majorana zero modes

We theoretically investigate the electronic transport through a parallel-coupled multi-quantum-dot system, in which the terminal dots of a one-dimensional quantum-dot chain are embodied in the two arms of an Aharonov–Bohm interferometer. It is found that in the structures of odd(even) dots, all their even(odd) molecular states have opportunities to decouple from the leads, and in this process antiresonance occurs which are accordant with the odd(even)-numbered eigenenergies of the sub-molecule without terminal dots. Next when Majorana zero modes are introduced to couple laterally to the terminal dots, the antiresonance and decoupling phenomena still co-exist in the quantum transport process. Such a result can be helpful in understanding the special influence of Majorana zero mode on the electronic transport through quantum-dot systems.

Photon-assisted electronic and spin transport through two T-shaped three-quantum-dot molecules embedded in an Aharonov–Bohm interferometer**Project supported by the National Natural Science Foundation of China (Grant Nos. 11447132 and 11504042), the Natural Science Foundation of Heilongjiang, China (Grant No. A201405), 111 Project to Harbin Engineering University, China (Grant No. B13015), Chongqing Science and Technology Commission Project, China (Grant Nos. cstc2014jcyjA00032 and

We investigate the time-modulated electronic and spin transport properties through two T-shaped three-quantum-dot molecules embedded in an Aharonov–Bohm (A–B) interferometer. By using the Keldysh non-equilibrium Green’s function technique, the photon-assisted spin-dependent average current is analyzed. The T-shaped three-quantum-dot molecule A–B interferometer exhibits excellent controllability in the average current resonance spectra by adjusting the interdot coupling strength, Rashba spin–orbit coupling strength, magnetic flux, and amplitude of the time-dependent external field. Efficient spin filtering and multiple electron-photon pump functions are exploited in the multi-quantum-dot molecule A–B interferometer by a time-modulated external field.

Transport through hybrid superconducting/ferromagnetic double-path junction

In this paper we study a double-path junction formed by a ferromagnetic and a superconductor lead. The first path connects the superconductor and ferromagnet directly while the second path connects these metals through a quantum dot. The whole system works as an Aharonov–Bohm interferometer allowing the study of the interference between these two paths under the presence of spin imbalance and Andreev bound states. We considered the effect of Fano interference on the electronic transmittance through the quantum dot and observed two regimes of conduction depending on the strength of the direct coupling. For the weak coupling regime, the transmittance presented the usual four resonances due to the Andreev bound states whereas for the strong coupling regime the profile was inverted and resonances became anti-resonances. However, even in the strong coupling regime it was possible to observe a central resonance due to the interference between the Andreev bound states. We have also studied the signatures of Fano interference on the average occupation within the quantum dot. The spin accumulation was analyzed and how it depends on the direct coupling and an external magnetic field applied to the system. The results obtained may be used in a possible experimental implementation of this system in order to probe spin related effects in ferromagnetic superconductor nanostructures.

Spin-dependent thermoelectric effect and spin battery mechanism in triple quantum dots with Rashba spin–orbital interaction**Project supported by the National Natural Science Foundation of China (Grant Nos. 11274208 and 11447170).

We have studied spin-dependent thermoelectric transport through parallel triple quantum dots with Rashba spin–orbital interaction (RSOI) embedded in an Aharonov–Bohm interferometer connected symmetrically to leads using nonequilibrium Green’s function method in the linear response regime. Under the appropriate configuration of magnetic flux phase and RSOI phase, the spin figure of merit can be enhanced and is even larger than the charge figure of merit. In particular, the charge and spin thermopowers as functions of both the magnetic flux phase and the RSOI phase present quadruple-peak structures in the contour graphs. For some specific configuration of the two phases, the device can provide a mechanism that converts heat into a spin voltage when the charge thermopower vanishes while the spin thermopower is not zero, which is useful in realizing the thermal spin battery and inducing a pure spin current in the device.

Unidirectional perfect absorber.

This study proposes a unidirectional perfect absorber (UPA), which we realized with a two-arm Aharonov-Bohm interferometer, that consists of a dissipative resonator side-coupled to a uniform resonator array. The UPA has reflection-less full absorption on one direction, and reflectionless full transmission on the other, with an appropriate magnetic flux and coupling, detuning, and loss of the side-coupled resonator. The magnetic flux controls the transmission, the left transmission is larger for magnetic flux less than one-half flux quantum; and the right transmission is larger for magnetic flux between one-half and one flux quantum. Besides, a perfect absorber (PA) can be realized based on the UPA, in which light waves from both sides, with arbitrary superposition of the ampli- tude and phase, are perfectly absorbed. The UPA is expected to be useful in the design of novel optical devices.

Quantum coherence of the molecular states and their corresponding currents in nanoscale Aharonov-Bohm interferometers

By considering a nanoscale Aharonov-Bohm (AB) interferometer containing a parrallel-coupled double dot coupled to the source and drain electrodes, we investigate the AB phase oscillations of transport current via the bonding and antibonding state channels. The results we obtained justify the experimental analysis given in [Phys. Rev. Lett. \textbf{106}, 076801 (2011)] that bonding state currents in different energy configurations are almost the same. On the other hand, we extend the analysis to the transient transport current components flowing through different channels, to explore the effect of the parity of bonding and antibonding states on the AB phase dependence of the corresponding current components in the transient regime. The relations of the AB phase dependence between the quantum states and the associated current components are analyzed in details, which provides useful information for the reconstruction of quantum states through the measurement of the transport current in such systems. With the coherent properties in the quantum dot states as well as in the transport currents, we also provide a way to manipulate the bonding and antibonding states by the AB magnetic flux.