Plasmonic Zener tunneling in metal-dielectric waveguide arrays

We elucidate in this Letter plasmonic Zener tunneling (PZT) in metal-dielectric waveguide arrays (MDWAs) by using numerical simulations and theoretical analyses. PZT in MDWAs occurs at the waveguide entrance and wherever the beam completes Bloch oscillations, because the bandgap between the first and second bands is minimal at the center of the first Brillouin zone. This feature significantly differs from that of optical Zener tunneling in dielectric waveguide arrays. The dependence of the simulated tunneling rate on the gradient of the relative permittivity of the dielectric layers correlates with the tunneling theory, thus confirming the occurrence of PZT in MDWAs.     

Bloch oscillations in one-dimensional photonic crystal coupled microcavity composed of single-negative materials

We have studied the propagation properties of electromagnetic waves in one-dimensional photonic crystal coupled microcavity structure composed of single-negative materials. Two Wannier-Stark ladders can be obtained by employing only one type of microcavity. The dynamics behavior of a Gaussian pulse transmitting through the structure is simulated theoretically. We demonstrated for the first time that even in this multilayered structure completely made of single-negative materials, the optical Bloch oscillations and Zener tunneling can also be attained.     

Quantum‐optical analogies using photonic structures

Engineered photonic waveguides have provided in the past decade an extremely rich laboratory tool to visualize with optical waves the classic analogues of a wide variety of coherent quantum phenomena encountered in atomic, molecular or condensed‐matter physics. As compared to quantum systems, optics offers the rather unique advantage of a direct mapping of the wave function evolution in coordinate space by simple fluorescence imaging or scanning tunneling optical microscopy techniques. In this contribution recent theoretical and experimental advances in the field of quantum‐optical analogies are reviewed. Special attention is devoted to some relevant optical analogies based on the use of curved photonic structures, including: coherent destruction of tunneling in driven bistable potentials; coherent population transfer and adiabatic passage in laser‐driven multilevel atomic systems; quantum decay control and Zeno dynamics; electronic Bloch oscillations and Zener tunneling, Anderson localization and dynamic localization in crystalline potentials.     

Bloch oscillations and Zener tunneling in two-dimensional photonic lattices

We report on the first experimental observation of photonic Bloch oscillations and Zener tunneling in two-dimensional periodic systems. We study the propagation of an optical beam in a square lattice superimposed on a refractive index ramp. We observe oscillations of the beam inside the first Brilloin zone and tunneling of light from the first to the higher-order bands of the lattice band gap spectrum.     

Mode conversion, Bloch oscillations and Zener tunneling with light by means of the Sagnac effect

Propagation of light in a rotating optical ring resonator shows striking similarities with magnetic flux induced electron propagation in small metal rings. This correspondence leads us to predict the possibility of Bloch oscillations and Zener tunneling with light in sufficiently high-Q rotating ring resonators.     

Bloch-Zener oscillations across a merging transition of Dirac points

Bloch oscillations are a powerful tool to investigate spectra with Dirac points. By varying band parameters, Dirac points can be manipulated and merged at a topological transition toward a gapped phase. Under a constant force, a Fermi sea initially in the lower band performs Bloch oscillations and may Zener tunnel to the upper band mostly at the location of the Dirac points. The tunneling probability is computed from the low-energy universal Hamiltonian describing the vicinity of the merging. The agreement with a recent experiment on cold atoms in an optical lattice is very good.     

Visual observation of Zener tunneling

We experimentally investigate photonic Zener tunneling between the bands of a waveguide array by directly monitoring the propagating light inside this structure. For strong transverse index gradients we observe Zener breakdown as regular outbursts of radiation escaping from the Bloch oscillations. Tunneling to higher order photonic bands and Bloch oscillations in different bands have been detected.     

Tunable hybridization at midzone and anomalous Bloch-Zener oscillations in optical waveguide ladders

We have studied the optical oscillation and tunneling of light waves in optical waveguide ladders (OWLs) formed by two coupled planar optical waveguide arrays. For the band structure, a midzone gap is formed owing to band hybridization, and its wavenumber position can be tuned throughout the whole Brillouin zone, which is different from the Bragg gap. By imposing a gradient in the propagation constant in each array, Bloch-Zener oscillation (BZO) is realized with Zener tunneling between the bands occurring at the midzone, which is contrary to the common BZO with tunneling at the center or edge of the Brillouin zone. The occurrence of BZO is demonstrated by using the field-evolution analysis. The tunable hybridization at the midzone enhances the tunability of BZO in the OWLs. This Letter may offer new insights into the coherent phenomena in optical lattices.     

飞秒激光场中原子所受光学偶极力研究

通过求解全波矢布洛赫方程研究了两能级原子与飞秒超快激光脉冲的相互作用过程,计算了不同拉比频率取值下原子所受光学偶极力和粒子数布居随时间的演化情况,分析了光场失谐量对光学势分布情况的影响.研究发现:由飞秒激光场产生的横向光力的时间平均值并不等于零,而是随着拉比频率的增加呈现振荡的增大趋势;纵向光力的时间平均作用也并非是拉比频率的单调函数,而是随着拉比频率的增加呈现周期性的振荡分布特性;光学势的分布对光场的失谐量具有明显的依赖性,随着失谐量的变化,光学势的性质也随之发生了改变.     

Traversal time in periodically loaded waveguides

We derive general expressions for the transmission coefficient and the traversal time in waveguides periodically loaded with dielectric slabs. We apply the results to resonant tunneling between two regions below cut-off, with exponentially decaying modes. At the resonant frequencies, we found a relationship between the traversal time and the lifetime. We also study the photonic band gap in a periodic quarter wavelength structure. As in several experiments, we found superluminal velocities.     

Nonlinear dynamics of semiclassical spin in a time-dependent magnetic field

The dynamics of magnetic nanoclusters (or molecules) with a large spin in a magnetic field whose strength varies in proportion to time is analyzed. Such a field breaks the symmetry relative to rotations through 2π, as well as clockwise and counterclockwise rotations, and induces a number of new coherent quantum effects in the spin dynamics, such as the formation of a band energy spectrum with continuous spin states or the emergence of “Bloch” oscillations in spin precession and interband Zener tunneling. Bloch oscillations are manifested in experiment as equidistant identical jumps on the magnetization curve. The interband Zener tunneling gives rise to additional jumps and peaks on the susceptibility of the system.     

Field-induced delocalization and Zener breakdown in semiconductor superlattices

We investigate the energy spectrum and the electron dynamics of a band in a semiconductor superlattice as a function of the electric field. Linear optical spectroscopy shows that, for high fields, the well-known localization of the Bloch states is followed by a field-induced delocalization, associated with Zener breakdown. Using time-resolved measurements, we observe Bloch oscillations in a regime where they are damped by Zener breakdown.     

Effect of the local field on transient processes in a dense ensemble of two-level atoms

Transient processes are analyzed based on modified Bloch equations describing the interaction of optical radiation with dense resonant media with allowance for dipole-dipole interaction between atoms (the local-field effect). An analytical solution to the equation for the population difference of resonant atomic levels, taking into account the up-conversion processes, is obtained for a rectangular pulse in the quasi-stationary approximation. Computer simulation is performed for the kinetics of the population difference of resonant atomic levels in the field of a long sine-shaped pulse. It is shown that the time dynamics of the population difference of resonant atomic levels manifests characteristic features inherent in the intrinsic optical bistability effect under an adiabatically slow variation of the acting field.     

Optical Absorption Spectra and Intraband Dynamics in Terahertz-Driven Semiconductor Superlattice

We have theoretically investigated the optical absorption spectrum and intraband dynamics by subjecting a superlattice to both a terahertz (THz)-frequency driving field and an optical pulse by using an excitonic basis.In the presence of a THz dc field, the satellite structures in the absorption spectra are presented. The satellite structure is a result from the THz nonlinear dynamics of Wannier-Stark ladder excitons. On the other hand, the coherent intraband polarization is investigated. We find that the excitonic Bloch oscillation is driven by the THz field and yields an intraband polarization that continues to oscillate at times much longer than the intraband dephasing time. The temporal evolution of the slowly varying components of the intraband polarization is dependent on the THz frequency.     

Quantum interference and population swapping in single quantum dots with V-type three-level

The quantum interference and Rabi oscillation of a V-type three-level system with two orthogonal sub-states in an elongated semiconductor quantum dot are discussed theoretically with optical Bloch equations when the system is driven by pulse-pair. Numerical calculations from the optical Bloch equations reveal that the quantum interference in the system is enhanced with the increasing of the energy decay or splitting. Furthermore, the populations swapping in two orthogonal sub-states can be realized though the direct transition is prohibited.     

Dynamics of Bloch–Zener Oscillations with Tuning Gap

In 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.     

Resonant interaction of light with a thin film of three-level atoms

Refraction of a double-frequency optical pulse at the interface between two linear dielectrics containing a thin film of resonant atoms is considered. The dynamics of the system is treated based on the model of three-level atoms with the V-type energy diagram. Refraction of short and long (compared with the Rabi oscillation period) pulses is analyzed with allowance for local-field effects. In both cases, the shape of the pulse corresponding to one carrier wave frequency is shown to depend on the energy of the pulse with the other carrier wave frequency. In particular, both the frequency and the depth of the amplitude modulation arising in the refracted pulse are changed.     

Bloch-wave packet control in truncated modulated optical lattices

We study the reflection of Bloch wave packets at the interface of an optical lattice possessing a shallow longitudinal out-of-phase refractive index modulation in the adjacent waveguides. We show that the relation between the transmitted and reflected energy flows can be efficiently controlled by tuning the frequency and depth of the modulation. Thus, complete beam reflection may be achieved for a set of resonant modulation frequencies at which light tunneling between adjacent guides of modulated lattice is inhibited.     

Resonant modes in quantum well structure of photonic crystals with different lattice constants

The resonant modes in a quantum well (QW) structure composed of three slabs of two dimensional (2D) photonic crystals with different lattice constants are analyzed with plane-wave-based transfer matrix method (TMM). It is found that the energy band of the well slab submerged into the band gap of barrier slab is discretized into quantized modes and the number of the resonant modes changes with the well slab thickness. A model structure of asymmetrical photonic QW consisting of two slabs of 2D photonic crystals with different lattice constants and one uniform dielectric slab in between is proposed and the resonant modes in it are investigated with the same method. A useful numerical simulation method for theoretical discussion as well as for practical application about photonic QW structure of photonic crystals with different lattice constants is proposed.     

Transient gain in photonic crystals

Using the optical response formula for photonic crystals and the Bloch equations, we analyze coherent emission in arbitrary two-dimensional photonic crystals. The transient emission depends not only on the photon density of the states, but also on the intensity and duration of the pump laser pulses. A transient gain exists if the pump pulse area is a certain value and the transition frequency is tuned to the band edge. The sharp structure of the density of states near the band edge leads to a dramatic enhancement of the transient emission intensity and an abrupt change in the oscillation of the emission field. PACS 42.70.Qs; 32.80.-t; 42.25.Bs