Aharonov-Bohm Ring Research Articles

Spin-polarized thermoelectrical currents induced in Aharonov-Bohm rings

We propose an interferometric device that generates spin-polarized electric currents based on an Aharonov-Bohm ring geometry. The device is driven by a temperature gradient and a magnetic flux without any voltage bias. Remarkably, no ferromagnetic contact is necessary once the two-path interference effects are present combined with a spin-orbit interaction. A large amplitude of spin current signal occurs where the charge current is small or even vanishing, thus easily creating pure spin currents by applying a magnetic field. Our proposal provides an ingredient of information processing devices in a generic caloritronic setup. Published by the American Physical Society 2024

Dipole polarizability of relativistic Aharonov-Bohm ring: Application to graphene nanorings

Dipole polarizability of relativistic Aharonov-Bohm ring: Application to graphene nanorings

Asymmetric transmission through a classical analogue of the Aharonov-Bohm ring

Asymmetric transmission through a classical analogue of the Aharonov-Bohm ring

Majorana Modes and Fano Resonances in Aharonov–Bohm Ring with Topologically Nontrivial Superconducting Bridge

Majorana Modes and Fano Resonances in Aharonov–Bohm Ring with Topologically Nontrivial Superconducting Bridge

Dynamic and static dipole polarizability of an Aharonov–Bohm ring

The properties of nanoscale rings are sensitive to Aharonov–Bohm fluxes threading the ring. In particular, neighboring angular momentum eigenstates become degenerate in cases of half-integer flux. Such degeneracies have a profound effect on the dipole polarizability leading to a divergent response. We analyze circular finite-width nanorings and derive a simple and compact expression for the polarizability valid for arbitrary ring geometry, frequency and magnetic flux. The dipole response is significantly reduced by finite-width effects, yet divergencies at half-integer flux are predicted irrespective of width. Finally, a non-divergent (but large) response is restored through a non-perturbative treatment of both magnetic and electric fields.

Emergence of a Bose polaron in a small ring threaded by the Aharonov-Bohm flux

The model of a ring threaded by the Aharonov-Bohm flux underlies our understanding of a coupling between gauge potentials and matter. The typical formulation of the model is based upon a single particle picture, and should be extended when interactions with other particles become relevant. Here, we illustrate such an extension for a particle in an Aharonov-Bohm ring subject to interactions with a weakly interacting Bose gas. We show that the ground state of the system can be described using the Bose-polaron concept—a particle dressed by interactions with a bosonic environment. We connect the energy spectrum to the effective mass of the polaron, and demonstrate how to change currents in the system by tuning boson-particle interactions. Our results suggest the Aharonov-Bohm ring as a platform for studying coherence and few- to many-body crossover of quasi-particles that arise from an impurity immersed in a medium.

Aharonov-Bohm Interference and Phase-Coherent Surface-State Transport in Topological Insulator Rings.

We present low-temperature magnetotransport measurements on selectively grown Sb2Te3-based topological insulator ring structures. These devices display clear Aharonov-Bohm oscillations in the conductance originating from phase-coherent transport around the ring. The temperature dependence of the oscillation amplitude indicates that the Aharonov-Bohm oscillations originate from ballistic transport along the ring arms. We attribute these oscillations to the topological surface states. Further insight into the phase coherence is gained by comparing with similar Aharonov-Bohm-type oscillations in topological insulator nanoribbons exposed to an axial magnetic field. Here, quasi-ballistic phase-coherent transport is confirmed for closed-loop topological surface states in the transverse direction enclosing the nanoribbon. In contrast, the appearance of universal conductance fluctuations indicates phase-coherent transport in the diffusive regime, which is attributed to bulk carrier transport. Thus, it appears that even in the presence of diffusive p-type charge carriers in Aharonov-Bohm ring structures, phase-coherent quasi-ballistic transport of topological surface states is maintained over long distances.

Generation and manipulation of pure spin current in a conducting loop coupled to an Aharonov–Bohm ring

In this work we put forward a new prescription for the generation and manipulation of non-decaying pure spin current (SC) in a Rashba spin–orbit (SO) coupled conducting loop which is attached to an Aharonov–Bohm (AB) ring. In presence of a single link between the rings, a SC is established in the flux-free ring, without accompanying any charge current (CC). The magnitude and direction of this SC are controlled by means of the AB flux, without tuning the SO coupling, which is the central aspect of our study. Employing a tight-binding framework we describe the two-ring quantum system, where the effect of magnetic flux is incorporated through Peierls phase factor. The specific roles of AB flux, SO coupling and the connectivity among the rings are critically investigated which yield several non-trivial signatures in energy band spectrum and pure SC. Along with SC, the phenomenon of flux-driven CC is also discussed, and at the end, different other effects like electron filling, system size and disorder are analyzed to make the present communication a self contained one. Our detailed investigation may provide some key aspects of designing efficient spintronic devices where SC can be guided in an other way.

Hybrid normal-superconducting Aharonov-Bohm quantum thermal device

We propose and theoretically investigate the behavior of a ballistic Aharonov-Bohm (AB) ring when embedded in a N-S two-terminal setup, consisting of a normal metal (N) and superconducting (S) leads. This device is based on available current technologies and we show in this work that it constitutes a promising hybrid quantum thermal device, as a quantum heat engine and quantum thermal rectifier. Remarkably, we evidence the interplay of single-particle quantum interferences in the AB ring and of the superconducting properties of the structure to achieve the hybrid operating mode for this quantum device. Its efficiency as a quantum heat engine reaches of the Carnot efficiency, and we predict a thermal rectification factor attaining 350%. These results make this device highly promising for future phase-coherent caloritronic nanodevices.

Topology and its detection in a dissipative Aharonov-Bohm chain

In a recent experiment, a dissipative Aharaonov-Bohm (AB) chain was implemented in the momentum space of a Bose-Einstein condensate. Formed by a series of dissipative AB rings threaded by synthetic magnetic flux, the chain exhibits the non-Hermitian skin effect, necessitating the non-Bloch band theory to account for its topology. In this work, we systematically characterize topological features of the dissipative AB chain, particularly beyond the experimentally realized parameter regime. Further, we show that an atom-injection spectroscopy is not only capable of revealing topological edge states, as has been demonstrated in the experiment, but also the general band structure of the system. We then discuss alternative dynamic detection schemes for the topological edge states. Given the generality of the model and the detection schemes, our work is helpful to future study of topological models with non-Hermitian skin effects across a variety of quantum simulators.

Nonlinear regime for enhanced performance of an Aharonov–Bohm heat engine

Thermal transport and quantum thermodynamics at the nanoscale are nowadays garnering increasing attention, in particular, in the context of quantum technologies. Experiments relevant for quantum technology are expected to be performed in the nonlinear regime. In this work, we build on previous results derived in the linear response regime for the performance of an Aharonov–Bohm (AB) interferometer operated as a heat engine. In the nonlinear regime, we demonstrate the tunability, large efficiency, and thermopower that this mesoscopic quantum machine can achieve, confirming the exciting perspectives that this AB ring offers for developing efficient thermal machines in the fully quantum regime.

Constructing Low-Dimensional Quantum Devices Based on the Surface State of Topological InsulatorsSupported by the National Key R&D Program of China (Grant No. 2017YFA0303301), the National Natural Science Foundation of China (Grant Nos. 11921005 and 11574007), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000), and Beijing Municipal Science and Technology Commission, China (Grant No. Z191100007219013).

We propose a new method to construct low-dimensional quantum devices consisting of the magnetic topological insulators. Unlike previous systems based on locally depleting two-dimensional electron gas in semiconductor heterojunctions, magnetization provides a simpler and rewriteable fabrication way. The motion of electrons can be manipulated through the domain wall formed by the boundary between different magnetic domains. Here, three devices designed by local magnetization are presented. For the quantum point contact, conductance exhibits quantized plateaus with the increasing silt width between two magnetic domains. For the quantum dot, conductance shows pronounced peaks as the change of gate voltage. Finally, for the Aharonov–Bohm ring, conductance oscillates periodically with the external magnetic field. Numerical results show that the transport of these local magnetization systems is identical to that of the previous systems based on depleting two-dimensional electron gas, and the only difference is the approach of construction. These findings may pave the way for realization of low-power-consumption devices based on magnetic domain walls.

Can a bright soliton model reveal a genuine time crystal for a finite number of bosons?

We analyze time crystal effects in a finite system of bosons which form a bright soliton clump on the Aharonov-Bohm ring. In the large particle number limit, N → ∞, this setup corresponds to the Wilczek model, where it is known that the time crystal behavior cannot be observed in the ground state of the system because a spontaneously formed soliton does not move. Here, we show that while the spontaneous formation of a moving soliton in the ground state can occur for , the soliton decays before it makes a single revolution along the ring and the time crystal dynamics is impossible.

Non-Hermitian Aharonov-Bohm effect in the quantum ring

We investigate the topological properties, energy spectrum, and persistent currents of a non-Hermitian ring with anti-Hermitian hopping terms. It is demonstrated that the anti-Hermitian hopping can effectively induce a synthetic gauge field. As the magnetic flux of the synthetic gauge field threads through the ring, the non-Hermitian system exhibits an Aharonov-Bohm effect. For the case of a non-Hermitian ring in the topological phase, the system, having an energy spectrum structure with a real gap, supports an imaginary persistent current. For the trivial case, a non-Hermitian system with an imaginary gap supports a real persistent current. Furthermore, we also investigate the transport property of a non-Hermitian Aharonov-Bohm ring connected by two semi-infinite leads. We find that the transmission coefficient shows the Aharonov-Bohm quantum oscillation as a function of the synthetic gauge field.

Fano-Kondo resonance versus Kondo plateau in an Aharonov-Bohm ring with an embedded quantum dot

We theoretically examine the transport through an Aharonov-Bohm ring with an embedded quantum dot (QD), the so-called QD interferometer, to address two controversial issues regarding the shape of the Coulomb peaks and measurement of the transmission phase shift through a QD. We extend a previous model [B. R. Bulka and P. Stefanski, Phys. Rev. Lett. 86, 5128 (2001); W. Hofstetter, J. Konig, and H. Schoeller, ibid. 87, 156803 (2001)] to consider multiple conduction channels in two external leads, L and R. We introduce a parameter p_{\alpha} (|p_{\alpha}| \le 1) to characterize a connection between the two arms of the ring through lead \alpha (=L, R), which is the overlap integral between the conduction modes coupled to the two arms. First, we study the shape of a conductance peak as a function of energy level in the QD, in the absence of electron-electron interaction U. We show an asymmetric Fano resonance for |p_{L,R}| = 1 in the case of single conduction channel in the leads and an almost symmetric Breit-Wigner resonance for |p_{L,R}| < 0.5 in the case of multiple channels. Second, the Kondo effect is taken into account by the Bethe ansatz exact solution in the presence of U. We precisely evaluate the conductance at temperature T=0 and show a crossover from an asymmetric Fano-Kondo resonance to the Kondo plateau with changing p_{L,R}. Our model is also applicable to the multi-terminal geometry of the QD interferometer. We discuss the measurement of the transmission phase shift through the QD in a three-terminal geometry by a "double-slit experiment." We derive an analytical expression for the relation between the measured value and the intrinsic value of the phase shift.

Quantum Simulations with Complex Geometries and Synthetic Gauge Fields in a Trapped Ion Chain

In recent years, arrays of atomic ions in a linear RF trap have proven to be a particularly successful platform for quantum simulation. However, a wide range of quantum models and phenomena have, so far, remained beyond the reach of such simulators. In this work we introduce a technique that can substantially extend this reach using an external field gradient along the ion chain and a global, uniform driving field. The technique can be used to generate both static and time-varying synthetic gauge fields in a linear chain of trapped ions, and enables continuous simulation of a variety of coupling geometries and topologies, including periodic boundary conditions and high dimensional Hamiltonians. We describe the technique, derive the corresponding effective Hamiltonian, propose a number of variations, and discuss the possibility of scaling to quantum-advantage sized simulators. Additionally, we suggest several possible implementations and briefly examine two: the Aharonov-Bohm ring and the frustrated triangular ladder.

Microreversibility and the statistics of currents in quantum transport.

For the statistics of currents in quantum transport, microreversibility is shown to provide a way to obtain the statistical cumulants at the order n+1 from the measurement of the cumulants at the order n or lower. This fundamental result is based on relations generalizing the fluctuation-dissipation theorem and the Onsager-Casimir reciprocal relations from linear toward nonlinear transport properties, as a consequence of the time-reversal symmetry of the underlying microscopic Hamiltonian dynamics. The method is demonstrated in detail in the case of multiterminal Aharonov-Bohm rings. Within the independent electron approximation, the cumulant generating function, which fully specifies the statistics of the nonequilibrium currents, is obtained from the scattering matrix of these circuits. The time-reversal symmetry relations are explicitly shown to express the cumulants at equilibrium up to the fourth order in terms of lower-order cumulants and their nonequilibrium responses in the presence of an external magnetic field.

Synthetic dimensions and topological chiral currents in mesoscopic rings

The recently-introduced concept of "synthetic dimensions" allows for the realization of higher-dimensional topological phenomena in lower-dimensional systems. In this work we study the complementary aspect that synthetic dimensions provide a natural route to topological states in mesoscopic hybrid devices. We demonstrate this for the current induced into a closed one-dimensional Aharonov-Bohm ring by the interaction with a dynamic mesoscopic magnet. The quantization of the magnetic moment provides a synthetic dimension that complements the charge motion around the ring. We present a direct mapping that places the combined ring-magnet system into the class of quantum Hall models, and demonstrate that topological features, combined with the magnet's anisotropy, can lead to clear signatures in the persistent current of the single-particle ground state.

Phonon-Assisted Transport through Double-Dot Aharonov-Bohm Interferometer in Kondo Regime

The effect of electron-phonon coupling on transport through a pair of strongly correlated quantum dots embedded in the Aharonov-Bohm ring is considered in the mean field slave boson Kotliar-Ruckenstein approach. It is shown that coupling with phonons opens transport gap in the region of double occupancy. Low-bias conductance and thermopower provide information on electron-phonon coupling strength.

Kondo-assistant Aharonov-Bohm transport in a quantum dot-Majorana wire system

We investigate the Kondo-assistant Aharonov-Bohm (AB) transport in a Quantum dot (QD) coupled with a topological Majorana wire. We noted that the conductance exhibits sensitive dependence on the phase factor of AB ring when the wire-QD coupling strength changes. The DOS resonance split when the coupling strength changes from small to large. The current is determined by the Kondo transport characteristics presented by the quantum dots (QDs). Also, the transport results show different p-dependence properties under parallel and anti-parallel leads alignment. We believe that these results can be helpful for understanding the Majorana-QD coupling properties as well as the detection of the Majorana bound states.