arXiv subjects

Yanpeng Zhang

Publications and source records attributed to Yanpeng Zhang.

At least 55 records · Page 3Linked to original sources

arXiv2018

Inhibition of tunnelling and edge state control in polariton topological insulators

We address the inhibition of tunnelling in polariton condensates confined in a potential landscape created by a honeycomb array of microcavity pillars in the presence of spin-orbit coupling and Zeeman splitting in the external magnetic field. The coupling rate between the microcavity pillars can be strongly impacted even by weak out-of-phase temporal modulations of the depths of the corresponding potential wells. When such a modulation is implemented in truncated honeycomb arrays that realize a polariton topological insulator, which supports unidirectional edge states in the presence of spin-orbit coupling and Zeeman splitting, it allows controlling the velocity of the states. The origin of the phenomenon is the dynamical modulation with a proper frequency, which notably changes the dispersion of the system and the group velocity of edge states. We show that such a control is possible for modulation frequencies close to resonances for inhibition of tunnelling in a two-well configuration. Edge states considerably slow down, and even stop completely, when the modulation frequency approaches a resonant value, while above such frequency splitting of the edge states into wavepackets moving with different velocities occurs.

physics.optics↗

arXiv2018

Resonant edge-state switching in polariton topological insulators

Topological insulators are unique devices supporting unidirectional edge states at their interfaces. Due to topological protection, such edge states persist in the presence of disorder and do not experience backscattering upon interaction with defects. We show that despite the topological protection and the fact that such states at the opposite edges of a ribbon carry opposite currents, there exists a physical mechanism allowing to resonantly couple topological excitations propagating at opposite edges. Such mechanism uses weak periodic temporal modulations of the system parameters and does not affect the internal symmetry and topology of the system. We study this mechanism in truncated honeycomb arrays of microcavity pillars, where topological insulation is possible for polaritons under the combined action of spin-orbit coupling and Zeeman splitting in the external magnetic field. The temporal modulation of the potential leads to a periodic switching between topological states with the same Bloch momentum, but located at the opposite edges. The switching rate is found to increase for narrower ribbon structures and for larger modulation depth, though it is changing nonmonotonically with the Bloch momentum of the input edge state. Our results provide a promising realization of a coupling device based on topologically protected states. The proposed scheme can be used in other topological photonic and condensed matter systems, including Floquet insulators and graphene.

physics.optics↗

arXiv2017

Parity-time-symmetric optical lattice with alternating gain and loss atomic configurations

Since the spatially extended periodic parity-time (PT) symmetric potential can possess certain unique properties compared to a single PT cell (with only a pair of coupled gain-loss components), various schemes have been proposed to realize periodic PT-symmetric potentials based on optical lattices. Here, we experimentally construct a spatially periodic PT-symmetric optical potential based on gain-loss arrays induced in a coherently-prepared atomic medium. The gain and loss arrays are generated in alternating four-level N-type and three-level $Λ$-type configurations in the same atomic medium, respectively, which do not require discrete diffractions as demonstrated in the previous work [Phys. Rev. Lett. 117, 123601(2016)] and can be easier to realize with more relaxed operating conditions. The dynamical behaviors of the system are investigated by measuring the phase difference between two adjacent gain and loss channels. The demonstrated PT-symmetric optical lattice with easy accessibility and better tunability sets a new stage for further exploiting the peculiar physical properties in periodic non-Hermitian systems.

physics.optics↗

arXiv2017

Greatly enhanced intensity-difference squeezing for narrow-band quantum metrology applications

Narrow-band intensity-difference squeezing beams have important applications in quantum metrology and gravitational wave detection. The best way to generate narrow-band intensity-difference squeezing is to employ parametrically-amplified four-wave mixing process in high-gain atomic media. Such IDS can be further enhanced by cascading multiple parametrically-amplified four-wave mixing processes in separate atomic media. The complicated experimental setup, added losses and required high-power pump laser with the increase of number of stages can limit the wide uses of such scheme in practical applications. Here, we show that by modulating the internal energy level(s) with additional laser(s), the degree of original intensity-difference squeezing can be substantially increased. With an initial intensity-difference squeezing of $-8.5\pm0.4$ dB using parametrically-amplified-non-degenerate four-wave mixing process in a three-level $Λ$-type configuration, the degree of intensity-difference squeezing can be enhanced to $-11.9\pm0.4$ dB/$-13.9\pm0.4$ dB (corrected for losses) when we use one/two laser beam(s) to modulate the involved ground/excited state(s). More importantly, a maximal noise reduction of $-9.7\pm0.4$ dB (only corrected for electronic noise) is observed below the standard quantum limit, which is the strongest reported to date in phase insensitive amplification in four-wave mixing. Applying the model to quantum metrology, the signal-to-noise ratio is improved by 23 dB compared to the conventional Mach-Zehnder interferometer under the same phase-sensing intensity, which is a 14-fold enhancement in rms phase measurement sensitivity beyond the shot noise limit. Our results show a low-loss, robust and efficient way to produce high degree of IDS and facilitate its potential applications.

physics.optics↗

arXiv2017

Edge states in dynamical superlattices

We address edge states and rich localization regimes available in the one-dimensional (1D) dynamically modulated superlattices, both theoretically and numerically. In contrast to conventional lattices with straight waveguides, the quasi-energy band of infinite modulated superlattice is periodic not only in the transverse Bloch momentum, but it also changes periodically with increase of the coupling strength between waveguides. Due to collapse of quasi-energy bands dynamical superlattices admit known dynamical localization effect. If, however, such a lattice is truncated, periodic longitudinal modulation leads to appearance of specific edge states that exist within certain periodically spaced intervals of coupling constants. We discuss unusual transport properties of such truncated superlattices and illustrate different excitation regimes and enhanced robustness of edge states in them, that is associated with topology of the quasi-energy band.

physics.optics↗

arXiv2016

Observation of electromagnetically induced Talbot effect in an atomic system

We experimentally demonstrate the Talbot effect resulting from the repeated self-reconstruction of a spatially intensity-modulated probe field under the Fresnel near-field regime. By launching the probe beam into an optically induced atomic lattice (established by interfering two coupling fields) inside a rubidium vapor cell, we can obtain an diffracted probe beam pattern from an formed electromagnetically induced grating (EIG) in a three-level $Λ$-type Doppler-free atomic configuration with the assistance of electromagnetically induced transparency (EIT). The EIG-based diffraction pattern repeats itself at the planes of integer multiple Talbot lengths, which agrees well with the theoretical prediction [Appl. Phys. Lett., 98, 081108 (2011)]. In addition, fractional EIT-induced Talbot effect was also investigated. Such experimentally demonstrated EIT Talbot effect in a coherently-prepared atomic system may pave a way for lensless and nondestructive imaging of ultracold atoms and molecules, and further demonstrating nonlinear/quantum beam dynamical features predicted for established periodic optical systems.

physics.optics↗

arXiv2016

Observation of Parity-Time Symmetry in Optically Induced Atomic Lattices

We experimentally demonstrate PT-symmetric optical lattices with periodical gain and loss profiles in a coherently-prepared four-level N-type atomic system. By appropriately tuning the pertinent atomic parameters, the onset of PT-symmetry breaking is observed through measuring an abrupt phase-shift jump between adjacent gain and loss waveguides. The experimental realization of such readily reconfigurable and effectively controllable PT-symmetric waveguide array structure sets a new stage for further exploiting and better understanding the peculiar physical properties of these non-Hermitian systems in atomic settings.

physics.optics↗

arXiv2016

Unveiling the link between fractional Schrödinger equation and light propagation in honeycomb lattice

We establish a link between the fractional Schrödinger equation (FSE) and light propagation in the honeycomb lattice (HCL) - the Dirac-Weyl equation (DWE). The fractional Laplacian in FSE causes a modulation of the dispersion relation of the system, which in the limiting case becomes linear. In the HCL, the dispersion relation is already linear around the Dirac point, suggesting a possible connection with the FSE. Here, we demonstrate this connection by describing light propagation in both FSE and HCL, using DWE. Thus, we propagate Gaussian beams according to FSE, HCL around the Dirac point, and DWE, to discover very similar behavior - the conical diffraction. However, if an additional potential is brought into the system, the link between FSE and HCL is broken, because the added potential serves as a perturbation, which breaks the translational periodicity of HCL and destroys Dirac cones in the dispersion relation.

physics.optics↗

arXiv2016

Transport properties in the photonic super-honeycomb lattice - a hybrid fermionic and bosonic system

We report on transport properties of the super-honeycomb lattice, the band structure of which possesses a flat band and Dirac cones, according to the tight-binding approximation. This super-honeycomb model combines the honeycomb lattice and the Lieb lattice and displays the properties of both. The super-honeycomb lattice also represents a hybrid fermionic and bosonic system, which is rarely seen in nature. By choosing the phases of input beams properly, the flat-band mode of the super-honeycomb will be excited and the input beams will exhibit strong localization during propagation. On the other hand, if the modes of Dirac cones of the super-honeycomb lattice are excited, one will observe conical diffraction. Furthermore, if the input beam is properly chosen to excite a sublattice of the super-honeycomb lattice and the modes of Dirac cones with different pseudospins, e.g., the three-beam interference pattern, the pseudospin-mediated vortices will be observed.

physics.optics↗

arXiv2016

Coherent and incoherent nonparaxial self-accelerating Weber beams

We investigate the coherent and incoherent nonparaxial Weber beams, theoretically and numerically. We show that the superposition of coherent self-accelerating Weber beams with transverse displacement cannot display the nonparaxial accelerating Talbot effect. The reason is that their lobes do not accelerate in unison, which is a requirement for the appearance of the effect. While for the incoherent Weber beams, they naturally cannot display the accelerating Talbot effect but can display the nonparaxial accelerating properties, although the transverse coherence length is smaller than the beam width, based on the second-order coherence theory. Our research method directly applies to the nonparaxial Mathieu beams as well, and one will obtain similar conclusions as for the Weber beams, although this is not discussed in the paper. Our investigation identifies families of nonparaxial accelerating beams that do not exhibit the accelerating Talbot effect, and in addition broadens the understanding of coherence properties of such nonparaxial accelerating beams.

physics.optics↗

arXiv2016

Nonparaxial accelerating Talbot effect

We demonstrate the fractional Talbot effect of nonpraxial accelerating beams, theoretically and numerically. It is based on the interference of nonparaxial accelerating solutions of the Helmholtz equation in two dimensions. The effect originates from the interfering lobes of a superposition of the solutions that accelerate along concentric semicircular trajectories with different radii. Talbot images form along certain central angles, which are referred to as the Talbot angles. The fractional nonparaxial Talbot effect is obtained by choosing the coefficients of beam components properly. A single nonparaxial accelerating beam possesses duality --- it can be viewed as a Talbot effect of itself with an infinite or zero Talbot angle. These results improve the understanding of nonparaxial accelerating beams and the Talbot effect among them.

physics.optics↗

arXiv2016

New face-centered photonic square lattices with flat bands

We report two new classes of face-centered photonic square lattices with flat bands which we call the Lieb-I and the Lieb-II lattices. There are 5 and 7 sites in the corresponding unit cells of the simplest Lieb-I and Lieb-II lattices, respectively. The number of flat bands $m$ in the new Lieb lattices is related to the number of sites $N$ in the unit cell by $m=(N-1)/2$. Physical properties of the lattices with even and odd number of flat bands are different. We also consider localization of light in such Lieb lattices. If the input beam excites the flat-band mode, it will not diffract during propagation, owing to the strong localization in the flat-band mode. For the Lieb-II lattice, we also find that the beam will oscillate and still not diffract during propagation, because of the intrinsic oscillating properties of certain flat-band modes. The period of oscillation is determined by the energy difference between the two flat bands. This study provides a new platform for the investigation of flat-band modes.

physics.optics↗

arXiv2016

$\mathcal{PT}$ symmetry in a fractional Schrödinger equation

We investigate the fractional Schrödinger equation with a periodic $\mathcal{PT}$-symmetric potential. In the inverse space, the problem transfers into a first-order nonlocal frequency-delay partial differential equation. We show that at a critical point, the band structure becomes linear and symmetric in the one-dimensional case, which results in a nondiffracting propagation and conical diffraction of input beams. If only one channel in the periodic potential is excited, adjacent channels become uniformly excited along the propagation direction, which can be used to generate laser beams of high power and narrow width. In the two-dimensional case, there appears conical diffraction that depends on the competition between the fractional Laplacian operator and the $\mathcal{PT}$-symmetric potential. This investigation may find applications in novel on-chip optical devices.

physics.optics↗

arXiv2016

Controllable circular Airy beams via dynamic linear potential

We investigate controllable spatial modulation of circular autofocusing Airy beams, under action of different dynamic linear potentials, both theoretically and numerically. We introduce a novel treatment method in which the circular Airy beam is represented as a superposition of narrow azimuthally-modulated one-dimensional Airy beams that can be analytically treated. The dynamic linear potentials are appropriately designed, so that the autofocusing effect can either be weakened or even eliminated when the linear potential exerts a "pulling" effect on the beam, or if the linear potential exerts a "pushing" effect, the autofocusing effect can be greatly strengthened. Numerical simulations agree with the theoretical results very well.

physics.optics↗

arXiv2016

A monogamy equalities of complementarity relation and distribute entanglement for multi-qubit pure states

We propose a method to detect genuine quantum correlation for multi-qubit pure states. We then derive a complementarity relations for pure quantum states of N qubits. We prove that in all many-qubit systems there exist strict monogamy laws for quantum correlations. On the other hand, it is known that the entanglement monogamy equality proposed by Coffman, Kundu, and Wootters is in general not true for multiqubit states. Inducing from the CKW equality, we find a proper form of entanglement monogamy equality for arbitrary quantum states. The total quantum correlation of qubit k with the remaining qubits Rk can be characterizes. Furthermore, the quantum correlation of qubit mn with the remaining qubits Rmn can also be obtained. Furthermore, some monogamy relations have been obtained.

quant-ph↗

arXiv2016

Diffraction-free beams in fractional Schrödinger equation

We investigate the propagation of one-dimensional and two-dimensional (1D, 2D) Gaussian beams in the fractional Schrödinger equation (FSE) without a potential, analytically and numerically. Without chirp, a 1D Gaussian beam splits into two nondiffracting Gaussian beams during propagation, while a 2D Gaussian beam undergoes conical diffraction. When a Gaussian beam carries linear chirp, the 1D beam deflects along the trajectories $z=\pm2(x-x_0)$, which are independent of the chirp. In the case of 2D Gaussian beam, the propagation is also deflected, but the trajectories align along the diffraction cone $z=2\sqrt{x^2+y^2}$ and the direction is determined by the chirp. Both 1D and 2D Gaussian beams are diffractionless and display uniform propagation. The nondiffracting property discovered in this model applies to other beams as well. Based on the nondiffracting and splitting properties, we introduce the Talbot effect of diffractionless beams in FSE.

physics.optics↗

arXiv2015

Dispersion relations of strained as well as complex Lieb lattices

We investigate the dispersion relations of strained as well as complex Lieb lattices systematically based on the tight-binding method when the nearest-neighbor approximation is adopted. We find that edge states will no appear for strained Lieb lattices and $\mathcal{PT}$-symmetry Lieb lattice cannot be obtained.

physics.optics↗

arXiv2015

Photonic Floquet Topological Insulator in an Atomic Ensemble

We demonstrate the photonic Floquet topological insulator (PFTI) in an atomic vapor with nonlinear susceptibilities. The interference of three coupling fields splits the energy levels periodically to form a periodic refractive index structure with honeycomb symmetry that can be adjusted by the choice of frequency detunings and intensities of the coupling fields, which all affect the appearance of Dirac cones in the momentum space. When the honeycomb lattice sites are helically ordered along the propagation direction, we obtain a PFTI in the atomic vapor in which an obliquely incident beam moves along the zigzag edge without scattering energy into the PFTI, due to the confinement of the edge states. The appearance of Dirac cones and the formation of PFTI is strongly affected by the nonlinear susceptibilities; i.e. the PFTI can be shut off by the third-order nonlinear susceptibility and re-opened up by the fifth-order one.

physics.optics↗