Quantum Pumping Research Articles

Thermodynamics of adiabatic quantum pumping in quantum dots

Thermodynamics of adiabatic quantum pumping in quantum dots

Electroluminescence Rectification and High Harmonic Generation in Molecular Junctions.

The field of molecular electronics has emerged from efforts to understand electron propagation through single molecules and to use them in electronic circuits. Serving as a testbed for advanced theoretical methods, it reveals a significant discrepancy between the operational time scales of experiments (static to GHz frequencies) and theoretical models (femtoseconds). Utilizing a recently developed time-linear nonequilibrium Green function formalism, we model molecular junctions on experimentally accessible time scales. Our study focuses on the quantum pump effect in a benzenedithiol molecule connected to two copper electrodes and coupled with cavity photons. By calculating both electric and photonic current responses to an ac bias voltage, we observe pronounced electroluminescence and high harmonic generation in this setup. The mechanism of the latter effect is more analogous to that from solids than from isolated molecules, with even harmonics being suppressed or enhanced depending on the symmetry of the driving field.

Thouless pumping in Josephson junction arrays

Recent advancements in fabrication techniques have enabled unprecedented clean interfaces and gate tunability in semiconductor-superconductor heterostructures. Inspired by these developments, we propose protocols to realize Thouless quantum pumping in electrically tunable Josephson junction arrays. We analyze, in particular, the implementation of the Rice-Mele and the Harper-Hofstadter pumping schemes, whose realization would validate these systems as flexible platforms for quantum simulations. We investigate numerically the long-time behavior of chains of controllable superconducting islands in the Coulomb-blockaded regime. Our findings provide new insights into the dynamics of periodically driven interacting systems and highlight the robustness of Thouless pumping with respect to boundary effects typical of superconducting circuits.

High-Efficiency Red-Emitting Phosphor of Li0.5La0.5SrMgWO6: Mn4+, Pr3+

The 400–500 nm blue light and 630–750 nm red light play crucial roles in plant cultivation. In this work, a high efficiency red-emitting phosphor, Li0.5La0.5SrMgWO6:Mn4+, Pr3+, was synthesized through the solid-state reaction technique. The absorption and excitation spectra were measured, indicating that 467 nm was an suitable excitation wavelength for this material. Upon excitation with a 467 nm LED, the fluorescence characteristics were evaluated, revealing dual-band red emission peaks located at 621–654 nm and 695–710 nm. The quantum efficiency and pumping slope efficiency were measured to be 63% and 35%, respectively. Based on energy level theory and Tanabe-Sugano theory, the dual-band fluorescence mechanism was analyzed, revealing that cross relaxation phenomenon contributed to the high quantum efficiency. The temperature sensing property was also demonstrated. The relative sensitivity (Sr) exhibited a significant change from 0.05% K−1 to 0.85% K−1 with different temperatures. The phosphor’s high efficiency and exceptional temperature property confer it with extensive potential applications in the fields of plant cultivation and display technology.

High-harmonic generation in spin and charge current pumping at ferromagnetic or antiferromagnetic resonance in the presence of spin–orbit coupling

One of the cornerstone effects in spintronics is spin pumping by dynamical magnetization that is steadily precessing (around, for example, the z-axis) with frequency ω 0 due to absorption of low-power microwaves of frequency ω 0 under the resonance conditions and in the absence of any applied bias voltage. The two-decades-old ‘standard model’ of this effect, based on the scattering theory of adiabatic quantum pumping, predicts that component of spin current vector is time-independent while and oscillate harmonically in time with a single frequency ω 0 whereas pumped charge current is zero in the same adiabatic limit. Here we employ more general approaches than the ‘standard model’, namely the time-dependent nonequilibrium Green’s function (NEGF) and the Floquet NEGF, to predict unforeseen features of spin pumping: namely precessing localized magnetic moments within a ferromagnetic metal (FM) or antiferromagnetic metal (AFM), whose conduction electrons are exposed to spin–orbit coupling (SOC) of either intrinsic or proximity origin, will pump both spin and charge I(t) currents. All four of these functions harmonically oscillate in time at both even and odd integer multiples of the driving frequency ω 0. The cutoff order of such high harmonics increases with SOC strength, reaching in the one-dimensional FM or AFM models chosen for demonstration. A higher cutoff can be achieved in realistic two-dimensional (2D) FM models defined on a honeycomb lattice, and we provide a prescription of how to realize them using 2D magnets and their heterostructures.

Exchange fluctuation theorems for strongly interacting quantum pumps

We derive a general quantum exchange fluctuation theorem for multipartite systems with arbitrary coupling strengths by taking into account the informational contribution of the back-action of the quantum measurements, which contributes to the increase in the von-Neumann entropy of the quantum system. The resulting second law of thermodynamics is tighter than the conventional Clausius inequality. The derived bound is the quantum mutual information of the conditional thermal state, which is a thermal state conditioned on the initial energy measurement. These results elucidate the role of quantum correlations in the heat exchange between multiple subsystems.

(Ann. Phys. 4/2023)

Annalen der PhysikVolume 535, Issue 4 2370007 Cover PictureFree Access (Ann. Phys. 4/2023) First published: 13 April 2023 https://doi.org/10.1002/andp.202370007AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Graphical Abstract Quantum Pumping When quasiparticles of Weyl/multi-Weyl and nodal-line semimetals are subjected to a time-periodic potential well, the presence of the oscillating potential of frequency ω creates equispaced Floquet side-bands. Using the Floquet theory and the scattering matrix approach, in the zero-temperature non-adiabatic pumping limit, characteristic Fano resonance patterns are found in the transmission coefficients, which depend on the nature of the dispersion. See article number 2200460 for more details. Volume535, Issue4April 20232370007 RelatedInformation

Floquet Transmission in Weyl/Multi‐Weyl and Nodal‐Line Semimetals through a Time‐Periodic Potential Well

AbstractA quantum pumping protocol through which the quasiparticles of Weyl/multi‐Weyl and nodal‐line semimetals are subjected to a time‐periodic rectangular potential well is considered. The presence of an oscillating potential of frequency ω creates equispaced Floquet side‐bands with spacing . As a result, a Fano resonance is observed when the difference in the Fermi energy (i.e., the energy of the incident quasiparticle), and the energy of one of the (quasi)bound state levels of the well, coincides with the energy of an integer number of photons (each carrying energy quantum ). Using the Floquet theory and the scattering matrix approach in the zero‐temperature non‐adiabatic pumping limit, characteristic Fano resonance patterns are found in the transmission coefficients. The inflection points in the pumped shot noise spectra also serve as a proxy for the corresponding Fano resonances. Therefore, the pumped shot noise is also numerically evaluated. Finally, the existence of the Fano resonance points is correlated to the (quasi)bound states of the well, by explicitly calculating the bound states of the static well (which are a subset of the bound states of the driven system). Since semimetals with anisotropic dispersions are considered, all the features observed depend on the orientation of the potential well.

Quantum pumping through the surface states of a topological insulator

We investigate quantum charge pumping through the surface states of a topological insulator (TI), i.e., ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. We consider a device with two oscillating potentials for the generation of a dc current in the adiabatic pumping regime. Applying the exchange magnetic field, we show that the device can work as a memory read-out. Also, we show that by applying a static gate voltage the pumping device can work as a field-effect transistor. In addition, the pumped current obtained in our proposed device is significantly (more than three orders of magnitude) greater than the pumped current obtained previously for TI-based devices. These properties show that ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ can be considered a good candidate for the fabrication of nanoelectronic devices based on TI as well as low-power and low-energy consumption devices in quantum computing.

Symmetric Finite-Time Preparation of Cluster States via Quantum Pumps.

It has recently been established that clusterlike states-states that are in the same symmetry-protected topological phase as the cluster state-provide a family of resource states that can be utilized for measurement-based quantum computation. In this Letter, we ask whether it is possible to prepare clusterlike states in finite time without breaking the symmetry protecting the resource state. Such a symmetry-preserving protocol would benefit from topological protection to errors in the preparation. We answer this question in the positive by providing a Hamiltonian in one higher dimension whose finite-time evolution is a unitary that acts trivially in the bulk, but pumps the desired cluster state to the boundary. Examples are given for both the 1D cluster state protected by a global symmetry, and various 2D cluster states protected by subsystem symmetries. We show that even if unwanted symmetric perturbations are present in the driving Hamiltonian, projective measurements in the bulk along with feed-forward correction is sufficient to recover a clusterlike state.

Normal mode splitting and four-wave mixing in Kerr-nonlinear optical system containing coupled double quantum dot

We theoretically investigate the four wave mixing (FWM) and normal mode splitting (NMS) in coupled double quantum dots cavity system in the presence of a third-order Kerr nonlinear medium. The FWM generated in the system has narrow spectral width and this can be tuned by nonlinear medium strength, the coupling strength between two coupled quantum dots and pump strength. Further, we study NMS that can also be tuned by various physical parameters and show that energy exchange between different modes is possible. The proposed model have potential applications in the field of quantum information processing.

Fermi's Golden Rule for Spontaneous Emission in Absorptive and Amplifying Media.

We demonstrate a fundamental breakdown of the photonic spontaneous emission (SE) formula derived from Fermi's golden rule, in absorptive and amplifying media, where one assumes the SE rate scales with the local photon density of states, an approach often used in more complex, semiclassical nanophotonics simulations. Using a rigorous quantization of the macroscopic Maxwell equations in the presence of arbitrary linear media, we derive a corrected Fermi's golden rule and master equation for a quantum two-level system (TLS) that yields a quantum pumping term and a modified decay rate that is net positive. We show rigorous numerical results of the temporal dynamics of the TLS for an example of two coupled microdisk resonators, forming a gain-loss medium, and demonstrate the clear failure of the commonly adopted formulas based solely on the local density of states.

Role of coherence in quantum-dot-based nanomachines within the Coulomb blockade regime

During the last decades, quantum dots within the Coulomb blockade regime of transport have been proposed as essential building blocks for a wide variety of nanomachines. This includes thermoelectric devices, quantum shuttles, quantum pumps, and even quantum motors. However, in this regime, the role of quantum mechanics is commonly limited to provide energy quantization while the working principle of the devices is ultimately the same as their classic counterparts. Here, we study quantum-dot-based nanomachines in the Coulomb blockade regime, but in a configuration where the coherent superpositions of the dots' states plays a crucial role. We show that the studied system can be used as the basis for different forms of "true" quantum machines that should only work in the presence of these coherent superpositions. We analyze the efficiency of these machines against different nonequilibrium sources (bias voltage, temperature gradient, and external driving) and the factors that limit it, including decoherence and the role of the different orders appearing in the adiabatic expansion of the charge/heat currents.

Moiré edge states in twisted bilayer graphene and their topological relation to quantum pumping

We study the edge states of twisted bilayer graphene and their topological origin. We show that the twisted bilayer graphene has special edge states associated with the moir\'{e} pattern, and the emergence of these moir\'{e} edge states is linked with the sliding Chern number, which describes topological charge pumping caused by relative interlayer sliding. When one layer of the twisted bilayer is relatively slid with respect to the other layer, the edge states are transferred from a single band to another across the band gap, and the number of the edge states pumped in a sliding cycle is shown to be equal to the sliding Chern number of the band gap. The relationship can be viewed as a manifestation of the bulk-edge correspondence inherent in moir\'{e} bilayer systems.

Transport fluctuation relations in interacting quantum pumps

The understanding of out-of-equilibrium fluctuation relations in small open quantum systems has been a focal point of research in recent years. In particular, for systems with adiabatic time-dependent driving, it was shown that the fluctuation relations known from stationary systems do no longer apply due the geometric nature of the pumping current response. However, the precise physical interpretation of the corrected pumping fluctuation relations as well as the role of many-body interactions remained unexplored. Here, we study quantum systems with many-body interactions subject to slow time-dependent driving, and show that fluctuation relations of the charge current can in general not be formulated without taking into account the total energy current put into the system through the pumping process. Moreover, we show that this correction due to the input energy is nonzero only when Coulomb-interactions are present. Thus, fluctuation response relations offer an until now unrevealed opportunity to probe many-body correlations in quantum systems. We demonstrate our general findings at the concrete example of a single-level quantum dot model, and propose a scheme to measure the interaction-induced discrepancies from the stationary case.

Even–odd chain effect and quantum pumping effect induced spatial spin filter on a Y-shaped zigzag silicene nanoribbon junction

We propose a possible spatial spin filter on a Y-shaped zigzag silicene nanoribbon (ZSNR) junction with different even(odd)-chain electrodes by applying three pumping electric fields. By means of the tight-binding model and Keldysh Green’s function method, we calculate the spin-dependent tunneling currents on the middle–left (M–L) and middle–right (M–R) terminals of Y-shaped ZSNR junction, and find that this spin pump not only can generate a pure spin current and a 100% polarized spin current at a zero bias, but also can spatially separate spin up and spin down currents on its even(odd)-chain M–L(R) terminals. The spatial spin filtering phenomena might come from the combination of the even–odd chain effect and single photon-assisted pumping process. The pumped spin up(down) current and its ON(OFF) transport states on M–L(R) terminal of the Y-shaped ZSNR junction can be modulated by almost all the device’s parameters such as the Fermi level, pumping frequency, spin–orbit coupling, staggered lattice potential and magnetization distribution. We also explore the possible way to close the spatial spin filtering behaviors in the device. Our findings might be useful for producing and separating 100% polarized spin up and down currents on multi-terminal silicene nanodevices.

Adiabatic pumping driven by a moving kink in a buckled graphene nanoribbon with implications for a quantum standard for the ampere

A quantum pump in buckled graphene ribbon with armchair edges is discussed numerically. By solving the Su-Schrieffer-Heeger model and performing the computer simulation of quantum transport we find that a kink adiabatically moving along the metallic ribbon results in highly-efficient pumping, with a charge per kink transition close to the maximal value determined by the Fermi velocity in graphene. Remarkably, insulating nanoribbon show the quantized value of a charge per kink ($2e$) in relatively wide range of the system parameters, providing a candidate for the quantum standard ampere. We attribute it to the presence of a localized electronic state, moving together with a kink, whose energy lies within the ribbon energy gap.

Topological phase transitions of Thouless charge pumping realized in helical organic molecules with long-range hopping

Recent studies indicated that helical organic molecules, such as DNA and $\alpha$-helical protein, can behave as Thouless quantum pumps when a rotating electric field is applied perpendicularly to their helical axes. Here we investigate the influence of long-range hoppings on this topological pumping of electrons in single-helical organic molecules. Under variation of the long-range hoppings governed by a decay exponent $\mu$, we find an energy gap in the molecular band structure closes at a critical value $\mu_c$ of the decay exponent and reopens for $\mu$ deviating from $\mu_c$. The relevant bulk bands in a pumping cycle acquire different Chern numbers in the strong ($\mu<\mu_c$) and weak ($\mu>\mu_c$) long-range hopping regimes, with a sudden jump at criticality. This topological phase transition is also shown to separate two distinct behaviors of the midgap end states in the pumping process. The end states carry quantized current pumped by the rotating electric field and the current forms a plateau by sweeping the Fermi energy over the gap. In the strong hopping phase, the quantized current plateau is positive, which is reversed to a negative one with smaller amplitude in the weak hopping phase. However, the reversal is a smooth crossover, not a sharp transition, due to the finite sizes of the molecules. We show that these transport characteristics of the topological phase transition could also be observed at finite temperatures.

Topological quantum pumping in spin-dependent superlattices with glide symmetry

Topological charge pumping represents an important quantum phenomenon that shows the fundamental connection to the topological properties of dynamical systems. Here, we introduce a pumping process in a spin-dependent double-well optical lattice with glide symmetry. In the dynamic process, the glide symmetry protects the band touching points and topological properties of the system are characterised by the non-Abelian Berry curvature. By engineering suitable form of interaction between different spin components, the model not only demonstrates topological phase transition, but also shows hybridisation between the spatial and temporal domain with novel topological features captured by the Wilson line along the synthetic directions. Our work provides a new model based on ultracold atoms towards the implementation of versatile topological matters and topological phenomena.

Photovoltaic effect generated by spin-orbit interactions

An AC electric field applied to a junction comprising two spin-orbit coupled weak links connecting a quantum dot to two electronic terminals is proposed to induce a DC current and to generate a voltage drop over the junction if it is a part of an open circuit. This photovoltaic effect requires a junction in which mirror reflection-symmetry is broken. Its origin lies in the different fashion inelastic processes modify the reflection of electrons from the junction back into the two terminals, which leads to uncompensated DC transport. The effect can be detected by measuring the voltage drop that is built up due to that DC current. This voltage is an even function of the frequency of the AC electric field and is {\em not} related to quantum pumping.