Landau-Zener Research Articles

Utilizing direct Zener tunneling in Germanium for cryogenic quantum applications

The temperature-dependent electroluminescent properties of Ge-Diodes, especially the Ge-Zener-Emitter, with tunnel transitions are investigated. The direct band-gap behavior of Germanium below a temperature of 140 K is demonstrated, facilitated by Zener tunneling. Pulsed excitation of the Ge-Zener-Emitter results in an optical output power density of 6 μW, which is sufficient to excite quantum dots for single-photon emission. The peak energy of 0.86 eV suits the non-resonant excitation of InGaAs quantum dots at cryogenic temperatures. This paper presents a potential optical pump source for a quantum photonic integrated circuit.

Investigation of junction capacitance in Zener tunnelling tunnel diode partially depleted silicon on insulator

Junction capacitance variation in Zener Tunnelling Tunnel Diode Partially Depleted Silicon On Insulator (ZT-TDPDSOI), due to the geometry effects of source and drain are discussed in this paper. Electric field profile and a capacitance equivalent circuit are used to reveal the gate-source capacitance dependence on the P+ region in ZT-TDPDSOI. It is demonstrated how the inclusion of a P+ region below the source/drain region impacts the gate substrate capacitance using the hole concentration and valence band energy at the source channel junction. A decrease of 42 % was noted in gate-substrate capacitance for a P+ doping of 2*1020/cm3 and thickness of 0.05 μm under fixed biased condition. The use of the trapezoidal approximation is also suggested as an extraction technique for the depletion width.

Parity-Time Symmetric Holographic Principle.

Originating from the Hamiltonian of a single qubit system, the phenomenon of the avoided level crossing is ubiquitous in multiple branches of physics, including the Landau-Zener transition in atomic, molecular, and optical physics, the band structure of condensed matter physics and the dispersion relation of relativistic quantum physics. We revisit this fundamental phenomenon in the simple example of a spinless relativistic quantum particle traveling in (1+1)-dimensional space-time and establish its relation to a spin-1/2 system evolving under a PT-symmetric Hamiltonian. This relation allows us to simulate 1-dimensional eigenvalue problems with a single qubit. Generalizing this relation to the eigenenergy problem of a bulk system with N spatial dimensions reveals that its eigenvalue problem can be mapped onto the time evolution of the edge state with (N-1) spatial dimensions governed by a non-Hermitian Hamiltonian. In other words, the bulk eigenenergy state is encoded in the edge state as a hologram, which can be decoded by the propagation of the edge state in the temporal dimension. We argue that the evolution will be PT-symmetric as long as the bulk system admits parity symmetry. Our work finds the application of PT-symmetric and non-Hermitian physics in quantum simulation and provides insights into the fundamental symmetries.

Classical analogue to driven quantum bits based on macroscopic pendula

Quantum mechanics increasingly penetrates modern technologies but, due to its non-deterministic nature seemingly contradicting our classical everyday world, our comprehension often stays elusive. Arguing along the correspondence principle, classical mechanics is often seen as a theory for large systems where quantum coherence is completely averaged out. Surprisingly, it is still possible to reconstruct the coherent dynamics of a quantum bit (qubit) by using a classical model system. This classical-to-quantum analogue is based on wave mechanics, which applies to both, the classical and the quantum world. In this spirit we investigate the dynamics of macroscopic physical pendula with a modulated coupling. As a proof of principle, we demonstrate full control of our one-to-one analogue to a qubit by realizing Rabi oscillations, Landau-Zener transitions and Landau-Zener-Stückelberg-Majorana interferometry. Our classical qubit demonstrator can help comprehending and developing useful quantum technologies.

Enhancement of Zener tunneling rate via electron-hole attraction within a time-dependent quasi-Hartree-Fock method

Enhancement of Zener tunneling rate via electron-hole attraction within a time-dependent quasi-Hartree-Fock method

Photon‐Assisted Landau Zener Transitions in a Tunable Driven Rabi Dimer Coupled to a Micromechanical Resonator

AbstractEmploying the multiple Davydov D2 Ansätze with the time‐dependent variational principle, photon‐assisted Landau–Zener (LZ) transitions and qubit manipulation in a hybrid quantum electrodynamics device have been investigated. Modeled as a Rabi dimer, the device comprises of two interacting transmission‐line resonators, each coupled to a qubit. The qubits, driven by independent harmonic fields, are further modulated by a micromechanical resonator mimicked by a phonon mode. The impacts of two independent driving fields on the qubit dynamics are carefully examined. The energy diagram of the system and the photon number mobilization on the resonators are analyzed to explain the behavior of the LZ transitions and qubit dynamics while taking into account the influence of the single phonon mode. Results show that low phonon frequencies can alter the qubit dynamics, particularly in the absence of the driving fields, and a strong phonon coupling strength can significantly perturb the qubit dynamics, thanks to a high influx of phonon energy. Notably, only the photon frequency affects the oscillation frequency of qubit polarization. This study unveils the imperative roles that photons and phonons play in the Rabi dimer model.

Nonlinear Landau-Zener-Stückelberg-Majorana tunneling and interferometry of extended Bose-Hubbard flux ladders.

The nonlinear Landau-Zener-Stückelberg-Majorana (LZSM) tunneling dynamics and interferometry of an extended Bose-Hubbard flux ladder are studied. Based on the mean-field theory, the dispersion relation of the system is given, and it is found that loop structures periodically appear in the band structure and the nonlinear LZSM interference occurs naturally without Floquet engineering, which can be effectively modulated by atomic interactions. The nonlinear energy bands and the unique chirality feature of the flux ladder system can be identified through the dynamics of nonlinear Landau-Zener tunneling. Remarkably, the critical position of the noise in the interference pattern can be employed to identify the loop structure in the energy band, establishing an effective link between the nonlinear loop structure and LZSM interferometry. The position, intensity, symmetry, and width of interference patterns strongly depend on the magnetic field, atomic interactions, rung-to-leg coupling ratio, and energy bias, which provides an effective way to measure these parameters using the nonlinear LZSM interferometry. This paper further expands the dynamics of flux ladder systems to complex interaction regions and has potential applications in the precise measurement of related nonlinear systems.

Controlling qubit-oscillator systems using linear parameter sweeps

We investigate the dynamics of a qubit-oscillator system under the influence of a linear sweep of system parameters. We consider two main cases. In the first case, we consider sweeping the parameters between the regime of a weakly correlated ground state and the regime of a strongly correlated ground state, a situation that can be viewed as a finite-duration quench between two phases of matter: the normal phase and the superradiant phase. Excitations are created as a result of this quench. We investigate the dependence of the excitation probabilities on the various parameters. We find a qualitative asymmetry in the dynamics between the cases of a normal-to-superradiant and superradiant-to-normal quench. The second case of parameter sweeps that we investigate is the problem of a Landau–Zener sweep in the qubit bias term for a qubit coupled to a harmonic oscillator. We analyze a theoretical formula based on the assumption that the dynamics can be decomposed into a sequence of independent Landau–Zener transitions. In addition to establishing the conditions of validity for the theoretical formula, we find that under suitable conditions, deterministic and robust multi-photon state preparation is possible in this system.

Nonadiabatically Driven Subcritical Crack Nucleation in Solids

This paper discusses a subcritical crack nucleation mechanism in a brittle solid within a real range of applied stress. A medium deformed by uniaxial tension is considered as an open nonequilibrium system of nuclei and electrons. Structural relaxation of the medium begins with the excitation of dynamic displacements during nonadiabatic Landau–Zener transitions. Dynamic displacements induce the instability of the medium to the longitudinal displacement wave. The kinetics of structural relaxation is described by two nonlinear parabolic kinetic equations for dynamic order parameters. Conditions are derived for the existence of localized solutions (autosolitons). The excitation of autosolitons leads to local elongation and cross-sectional reduction of the specimen. The resulting neck is a subcritical crack.

Geometric Aspects of Nonlinear and Nonequilibrium Phenomena

We review recent developments in the research of nonlinear and nonequilibrium phenomena in solids focusing on their geometrical aspects. We start with introducing the basic concepts of geometrical phases of Bloch electrons and Floquet theory for periodically driven systems. Then we review recent attempts to engineer topological phases in nonequilibrium matters such as graphene, magnets, and superconductors irradiated with circularly polarized light. We next review a bulk photovoltaic effect of inversion broken materials focusing on the shift current response. The shift current is described with Berry connections and has a close relationship to the modern theory of polarization. We further review recent extensions of the shift current to correlated electron systems. Finally, we explain the geometric diabatic time evolution in the Zener tunneling process and its consequences on nonreciprocal transport.

Optimal population transfer using adiabatic rapid passage in the presence of drive-induced dissipation

Adiabatic rapid passage (ARP) is extensively used to achieve efficient transfer or inversion of populations in quantum systems. Landau and Zener accurately estimated the transfer probability of ARP for a closed system and showed that this probability improved with higher drive amplitude. Recently, we found that, in open quantum systems, applying a strong drive can give rise to significant drive-induced dissipation (DID). Here, we investigate the effect of DID on the performance of ARP that is implemented using a linearly chirped pulse on a two-level system. From the Landau-Zener formula, the population transfer was known to be enhanced with increasing drive amplitude. However, here we show that, beyond a threshold value of the drive amplitude, the transfer probability is reduced because of the detrimental effect of DID. We show that the competition between the two processes results in an optimal behavior of the population transfer. We also propose a phenomenological model that helps explain such nonmonotonic behavior of the transfer. Using this model, we estimate the optimum time at which the maximum population transfer occurs. We extend the analysis for rectangular as well as Gaussian pulse profiles and conclude that a Gaussian pulse outperforms a rectangular pulse.

Cavity induced collective behavior in the polaritonic ground state

Cavity quantum electrodynamics provides an ideal platform to engineer and control light-matter interactions with polariton quasiparticles. In this work, we investigate collective phenomena in a system of many particles in a harmonic trap coupled to a homogeneous cavity vacuum field. The system couples collectively to the cavity field, through its center of mass, and collective polariton states emerge. The cavity field mediates pairwise long-range interactions and enhances the effective mass of the particles. This leads to an enhancement of localization in the matter ground state density, which features a maximum when light and matter are on resonance, and demonstrates a Dicke-like, collective behavior with the particle number. The light-matter interaction also modifies the photonic properties of the polariton system, as the ground state is populated with bunched photons. In addition, it is shown that the diamagnetic A^2A2 term is necessary for the stability of the system, as otherwise the superradiant ground state instability occurs. We demonstrate that coherent transfer of polaritonic population is possible with an external magnetic field and by monitoring the Landau-Zener transition probability.

Band topology and Bloch oscillation in an extended Creutz ladder

We study an extended Creutz ladder system, which supports topological phase transition as revealed by the change of topological invariant and by distinct pseudospin textures. With a linear force along the ladder, Bloch oscillation on topological bands is studied. At the topological phase transition point, the oscillation period is doubled due to band crossings and the wave packet evolves alternatively on the two bands. The magnitude of pseudospin polarizations in Bloch oscillation provide a dynamical identification of the topological feature. The local pseudospin polarizations along y − and z − axis are directly related to measurable inter-leg current and density difference. We also show the micromotion and non-adiabatic propagations of the Bloch wave packet. A small density oscillation beyond the description of Bloch oscillation is revealed. At avoided band crossings, the transition probability of the Landau-Zener tunneling is obtained. Our results exhibit a transparent framework to understand the properties of topological bands and of Bloch wave dynamics.

Predicting the minimum control time of quantum protocols with artificial neural networks

Quantum control relies on the driving of quantum states without the loss of coherence, thus the leakage of quantum properties into the environment over time is a fundamental challenge. One work-around is to implement fast protocols, hence the Minimal Control Time (MCT) is of upmost importance. Here, we employ a machine learning network in order to estimate the MCT in a state transfer protocol. An unsupervised learning approach is considered by using a combination of an autoencoder network with the k-means clustering tool. The Landau–Zener (LZ) Hamiltonian is analyzed given that it has an analytical MCT and a distinctive topology change in the control landscape when the total evolution time is either under or over the MCT. We obtain that the network is able to not only produce an estimation of the MCT but also gains an understanding of the landscape’s topologies. Similar results are found for the generalized LZ Hamiltonian while limitations to our very simple architecture were encountered.

Dynamics of dissipative Landau-Zener transitions in an anisotropic three-level system.

We investigate the dynamics of Landau-Zener (LZ) transitions in an anisotropic, dissipative three-level LZ model (3-LZM) using the numerically accurate multiple Davydov D2Ansatz in the framework of the time-dependent variational principle. It is demonstrated that a non-monotonic relationship exists between the Landau-Zener transition probability and the phonon coupling strength when the 3-LZM is driven by a linear external field. Under the influence of a periodic driving field, phonon coupling may induce peaks in contour plots of the transition probability when the magnitude of the system anisotropy matches the phonon frequency. The 3-LZM coupled to a super-Ohmic phonon bath and driven by a periodic external field exhibits periodic population dynamics in which the period and amplitude of the oscillations decrease with the bath coupling strength.

Gate-Controlled Quantum Interference Effects in a Clean Single-Wall Carbon Nanotube p-n Junction.

The precise control and deep understanding of quantum interference in carbon nanotube (CNT) devices are particularly crucial not only for exploring quantum coherent phenomena in clean one-dimensional electronic systems, but also for developing carbon-based nanoelectronics or quantum devices. Here, we construct a double split-gate structure to explore the Aharonov-Bohm (AB) interference effect in individual single-wall CNT p-n junction devices. For the first time, we achieve the AB modulation of conductance with coaxial magnetic fields as low as 3T, where the flux through the tube is much smaller than the flux quantum. We further demonstrate direct electric-field control of the nonmonotonic magnetoconductance through a gate-tunable built-in electric field, which can be quantitatively understood in combination with the AB phase effect and Landau-Zener tunneling in a CNT p-n junction. Moreover, the nonmonotonic magnetoconductance behavior can be strongly enhanced in the presence of Fabry-Pérot resonances. Our Letter paves the way for exploring and manipulating quantum interference effects with combining magnetic and electric field controls.

Analytic approach to the Landau–Zener problem in bounded parameter space

Three analytic solutions to the Schrödinger equation for the time-dependent Landau–Zener (LZ) Hamiltonian are presented. They correspond to specific finite-time driving paths in a bounded parameter space of a two-level system. Two of these paths go through the avoided crossing of levels, either with a constant speed or with variable speed that decreases in the region of reduced energy gap, the third path bypasses the crossing such that the energy gap remains constant. The solutions yield exact time dependencies of the excitation probability for the system evolving from the ground state of the initial Hamiltonian. The LZ formula emerges as an approximation valid within a certain interval of driving times for the constant-speed driving through the avoided crossing. For long driving times, all solutions converge to the prediction of the adiabatic perturbation theory. The excitation probability vanishes at some discrete time instants.

Modulating the Function of GeAs/ReS2 van der Waals Heterojunction with its Potential Application for Short-Wave Infrared and Polarization-Sensitive Photodetection.

Van der Waals heterojunction (vdWs) of 2D materials with integrated or extended superior characteristics, opening up new opportunities in functional electronic and optoelectric device applications. Exploring methods to achieve multifunctional vdWs heterojunction devices is one of the most promising prospects in this area. Herein, a diverse function of forward rectifying diode, Zener tunneling diode, and backward rectifying diodes are realized in GeAs/ReS2 heterojunction by modulating the doping level of GeAs. The tunneling diode presents an interesting trend forward negative differential resistance (NDR) behavior which may facilitate the application of multi-value logic. More importantly, the GeAs/ReS2 forward rectifying diode exhibits highly sensitive photodetection in the wide-spectrum range up to 1550nm corresponding to a short-wave infrared (SWIR) region. In addition, as two strong anisotropic 2D materials of GeAs and ReS2 , the heterojunction exhibits strong polarization-sensitive photodetection behavior with a dichroic photocurrent ratio of 1.7. This work provides an effective strategy to achieve multifunctional 2D vdW heterojunction devices and develops more possibilities to broaden their functionalities and applications.

Dynamics of Bloch–Zener Oscillations with Tuning Gap

AbstractIn this study, the transient dynamics of Bloch–Zener oscillations (BZOs) in a 1D qubit chain with a controllable band gap are explored. The chain consists of alternating site energies and is subjected to a constant external field. Several tight‐binding models were analyzed, including Bloch and Landau–Zener models, to understand the BZOs mechanism. The findings revealed that the band gaps played a crucial role in bridging the intriguing interplay between Bloch oscillations and Landau–Zener transitions. The motion of carriers in real and quasi‐momentum spaces is explored and the time evolution of occupancy in mini‐bands is calculated. A linearly time‐dependent way of tuning the gap is also proposed and non‐periodic motion is observed. When the chain is coupled to dispersionless optical phonons, strong coupling leads to large phonon displacements and localizes the carrier wave packets of the qubit states. The findings provide new insights into the behavior of BZOs in complex systems and suggest avenues for future studies.

Photonic Floquet Landau-Zener tunneling and temporal beam splitters.

Landau-Zener tunneling (LZT), i.e., the nonadiabatic transition under strong parameter driving in multilevel systems, is ubiquitous in physics, providing a powerful tool for coherent wave control both in quantum and classical systems. While previous works mainly focus on LZT between two energy bands in time-invariant crystals, here, we construct synthetic time-periodic temporal lattices from two coupled fiber loops and demonstrate dc- and ac-driven LZTs between periodic Floquet bands. We show that dc- and ac-driven LZTs display distinctive tunneling and interference characteristics, which can be harnessed to realize fully reconfigurable LZT beam splitter arrangements. As a potential application to signal processing, we realize a 4-bit temporal beam encoder for classical light pulses using a reconfigurable LZT beam splitter network. Our work introduces and experimentally demonstrates a new class of reconfigurable linear optics circuits harnessing Floquet LZT, which may find versatile applications in temporal beam control, signal processing, quantum simulations, and information processing.