Browsing by Author "Chen, Ting-Wei"

Now showing 1 - 11 of 11

Collective excitations, Nambu-Goldstone modes, and instability of inhomogeneous polariton condensates
(2013-11-08)
Chen, Ting-Wei
;
Cheng, Szu-Cheng
;
Hsieh, Wen-Feng
;
光電工程學系
;
Department of Photonics
We study nonequilibrium polariton condensates in a harmonic potential trap. After finding the steady-state density and supercurrent distributions of nonequilibrium condensates, we calculate the collective excitations of the system. From collective excitation spectra, we can identify the bifurcation of the stable and unstable modes in terms of the pumping spot size and power. There exist Nambu-Goldstone modes that reveal the pattern of the spontaneous symmetry breaking of the system. Moreover, the unstable mechanism associated with the inward supercurrent flow is characterized by the existence of a supersonic region within the condensate.
Dark solitons in a spinor microcavity-polariton condensate
(2016-10)
Chen, Ting-Wei
;
Jheng, Shih-Da
;
Hsieh, Wen-Feng
;
Cheng, Szu-Cheng
;
物理研究所
Dark solitons of a two-component condensate occurring in nonresonantly-pumped microcavity polaritons (spinor MPCs) with integer vorticities, referred to as integer dark solitons (IDSs), can be excited by a laser beam with tunable polarization and power. We investigate the physical properties of stationary IDSs in a pure spinor MPCs without defects. From the excitations of a IDS, we show that the soliton is stable when the pump power is higher than a critical value. When the pump polarization is in favor of one component, we find that the critical pump power for the stabilization becomes higher. The stable IDS exists below a critical pump polarization. A stable phase diagram of IDSs in terms of the pump condition, i.e., pump polarization and power, is thus obtained. (C) 2016 Elsevier Ltd. All rights reserved.
Drag and critical velocities in a nonresonantly pumped trapped polariton condensate with a rotating defect
(2016-01-19)
Cheng, Szu-Cheng
;
Chen, Ting-Wei
;
Jheng, Shih-Da
;
Hsieh, Wen-Feng
;
物理研究所
We model the superfluid properties of a trapped exciton-polariton condensate under non-resonant excitation subjected to a rotating defect. With increasing the linear velocity of rotating defect, the density modulation can be classified into superfluid-like regime, parabolic-like regime, Cherenkov regime and over-Cherenkov regime. The threshold-like behavior of drag force and the onset of turbulent fringes can define the critical velocity for the superfluidity. Based on the perturbative drag force in the Bogoliubov-type analysis, the rigid modes with gapped excitation spectrum have higher critical velocity than that of the soft modes. (C) 2015 Elsevier Ltd. All rights reserved.
Instability of a spontaneously formed multiple-flux vortex in polariton condensates
(2015-07-01)
Chen, Ting-Wei
;
Cheng, Szu-Cheng
;
Hsieh, Wen-Feng
;
光電工程學系
;
Department of Photonics
A spontaneously formed vortex can occur in an incoherently pumped microcavity-polariton condensate which is a non-equilibrium system. The stability of this vortex depends on the flux quanta that the vortex owns. In this paper, we have investigated the dynamics of spontaneously formed vortices with multiple-flux quanta in incoherently pumped microcavity-polariton condensates. From the excitation spectra of a spontaneously formed vortex, we can study the stability of the vortex under different pump strength. The vortices with flux quanta less than four are dynamically stable within a wide range of pump strength. However, when the flux quanta of a vortex is greater than three and the pump power is above a critical pump strength, some imaginary parts of excitation modes of the vortex become positive. The vortex then becomes dynamically unstable and Lends to split into several vortices with smaller flux quanta. (C) 2015 Elsevier Ltd. All rights reserved.
Nonequilibrium and nonlinear defect states in microcavity-polariton condensates
(2016-05-18)
Chen, Ting-Wei
;
Jheng, Shih-Da
;
Hsieh, Wen-Feng
;
Cheng, Szu-Cheng
;
物理研究所
The nonequilibrium and nonlinear defect modes (NNDMs), localized by a defect in a nonequilibrium microcavity-polariton condensate (MPC), are studied. There are three analytic solutions of NNDMs in a point defect: the bright NNDM, a bound state with two dark solitons for an attractive potential, and a gray soliton bound by a defect for a repulsive potential. We find that the stable NNDMs in a nonequilibrium MPC are the bright NNDM and gray soliton bound by a defect. The bright NNDM, which has the hyperbolic cotangent form, is a bright localized state existing in a uniform MPC. The bright NNDM is a unique state occurring in a nonequilibrium MPC that has pump-dissipation and repulsive-nonlinearity characters. No such state can exist in an equilibrium system with repulsive nonlinearity.
Phase diagram of microcavity polariton condensates with a harmonic potential trap
(2014-01-01)
Chen, Ting-Wei
;
Wei, Ming-Dar
;
Cheng, Szu-Cheng
;
Hsieh, Wen-Feng
;
光電工程學系
We theoretically explore the phase transition in inhomogeneous exciton-polariton condensates with variable pumping conditions. Through Bogoliubov excitations to the radial-symmetric solutions of complex Gross-Pitaevskii equation, we determine not only the bifurcation of stable and unstable modes by the sign of fluid compressibility but also two distinct stable modes which are characterized by the elementary excitations and the stability of singly quantized vortex. One state is the quasi-condensate BKT phase with Goldstone flat dispersion; the other state is the localized-BEG phase which exhibits linear-type dispersion and has an excitation energy gap at zero momentum. (C) 2013 Elsevier Ltd. All rights reserved.
Quantum fluctuations and stability of vortex lattices in a nonresonantly pumped exciton-polariton condensate
(2017-03-01)
Chen, Ting-Wei
;
Jheng, Shih-Da
;
Jiang, T. F.
;
Cheng, Szu-Cheng
;
物理研究所
The dynamics of an exciton-polariton condensate (EPC) subject to harmonic confinement can cause spontaneously formed vortices to arrange into a triangular vortex lattice. The stability of such a spontaneously formed vortex lattice is still unknown. We investigate the quantum fluctuations of vortex lattices in a rapidly rotating EPC with a rotation frequency close to the harmonic trap. In such a large condensate, we find that a vortex lattice with a triangular structure is stable, whereas one with a square structure becomes unstable. This result indicates that a driven-dissipative vortex array with strong quantum fluctuations can occur in an EPC.
Stability and excitations of spontaneous vortices in polariton condensates
(2013-07-01)
Chen, Ting-Wei
;
Chiang, Yu-Ling
;
Cheng, Szu-Cheng
;
Hsieh, Wen-Feng
;
光電工程學系
We study the dynamics of spontaneously formed vortices in incoherently pumped homogeneous microcavity polariton condensates (MPC). We find vortices are stable and appear spontaneously without stirring or rotating MPCs by the numerical modeling using complex Gross-Pitaevskii equation. The center of the vortex core contains some background of reservoir polaritons and the visibility increases with the pump strength. The vortex radius is inversely proportional to the square root of the condensate density or the pump strength. Finally, vortices formed by low pumping power exhibit short lifetime because of the existence of excitations without costing energy. (c) 2013 Elsevier Ltd. All rights reserved.
Stable gray soliton pinned by a defect in a microcavity-polariton condensate
(2015-09-21)
Chen, Ting-Wei
;
Hsieh, Wen-Feng
;
Cheng, Szu-Cheng
;
光電工程學系
;
光電工程研究所
We study the spatially localized dark state, called dark soliton, in a one-dimensional system of the non-resonantly pumped microcavity-polariton condensate (MPC). From the recent work by Xue and Matuszewski [Phys. Rev. Lett. 112, 216401 (2014)], we know that the dark soliton in the pure MPC system is unstable. But we find that a dark soliton pinned by a defect in the impure MPC becomes a gray soliton and can be stabilized by the presence of a defect. Moreover, the stable regime of the gray soliton is given in terms of the defect strength and pump parameter. (C) 2015 Optical Society of America
The synchronization and stability of spinor polariton condensates
(2016-04)
Chen, Ting-Wei
;
Jheng, Shih-Da
;
Hsieh, Wen-Feng
;
Cheng, Szu-Cheng
;
物理研究所
By taking account of the spin degree of freedom with varying the Zeeman splitting, we explore the possible synchronized states of spinor polariton condensates formed in a semiconductor microcavity. The interplay among nonlinear interactions, spin-flipping rates and energy splitting is theoretically investigated. Besides a minimum transverse field induced spin-flipping rate required to form the synchronized state, we find that the interaction effect between polaritons is the dominant factor. Therefore, with the manipulation of the energy splitting between the two spin states, the spinor condensate initially synchronized with "elliptical" polarization may become two separated desynchronized and "circularly" polarized condensates. Moreover, the region and stability of synchronized states are discussed for various asymmetric pumping configurations. (C) 2016 Elsevier Ltd. All rights reserved.
Vortex and trapped states of microcavity-polariton condensates in a harmonic trap
(2016-05)
Chen, Ting-Wei
;
Jhen, Shih-Da
;
Hsieh, Wen-Feng
;
Cheng, Szu-Cheng
;
物理研究所
We investigate the vortex and trapped states of a microcavity-polariton condensate in a harmonic trap under non-resonant excitation. The stationary states of the microcavity-polariton condensate are obtained from the complex Gross-Pitaevskii equation numerically. From the excitations of vortices and trapped states, the boundaries separating stable and unstable states are plotted in the phase diagram shown by pump powers versus pump-spot sizes. Our analysis provides physical parameters for experiments of creating stable vortices and trapped states in a trapped microcavity-polariton condensate. (C) 2016 Elsevier B.V. All rights reserved.