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Influence of impurity on the rate of single photon superradiance and photon transport in disordered N qubit chain
摘要： We investigate the rate of superradiant emission for a number of artificial atoms (qubits) embedded in a one-dimensional open waveguide. More specifically, we study the 1D (N+1)- qubit chain where N qubits are identical with respect to their excitation frequency Ω but have different rates of spontaneous emission Γn, and a single impurity qubit which is different from N qubits by its excitation frequency ΩP and the rate of spontaneous emission ΓP . We performed exact diagonalization of Hamiltonian and showed that the system has two hybridized collective states one of which accumulates the widths of all qubits. The energy spectrum of these states and corresponding probabilities are investigated as a function of the frequency detuning between the impurity and other qubits in a chain. It is shown that the inclusion of the impurity qubit alters the resonance widths of the system if the total width overlaps the frequency detuning between qubits and the impurity. In this case the resonance widths experience a significant repulsion. The photon transmission through disordered N- qubit chain with the impurity qubit is also considered. It is shown that a single photon transport through this system is described by a simple expression which predicts for specific photon frequency the existence of a complete transmission peak and transparency window between frequencies Ω and ΩP .
关键词： superradiance,impurity,photon transport,qubit chain,non-Hermitian Hamiltonian
更新于2025-09-23 15:23:52
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[Springer Tracts in Modern Physics] Parity-time Symmetry and Its Applications Volume 280 || Parity-Time-Symmetric Optical Lattices in Atomic Configurations
摘要： In this chapter, we show how to theoretically design and experimentally construct exact parity-time (PT) symmetric optical lattices with gain and loss in atomic configurations. By making use of the advantages of light-induced atomic coherence in multi-level atomic systems, spatially extended gain and loss arrays with real-time reconfigurability and multiple-parameter tunability can be effectively obtained in hot atomic vapors. We have constructed periodically alternative gain-loss structures with two very different schemes based on spatially-arranged optical induction techniques. With the required symmetric/antisymmetric spatial distributions for the real/imaginary parts of the refraction index satisfied, PT-symmetric optical lattices can be achieved with easy controllability. The dynamic behaviors of light propagating inside the induced non-Hermitian optical lattices are investigated by measuring the relative phase difference between two adjacent gain and loss channels.
关键词： Light-Induced Atomic Coherence,Non-Hermitian Optical Lattices,Atomic Configurations,Parity-Time-Symmetric Optical Lattices,Gain and Loss
更新于2025-09-23 15:21:21
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Petermann-factor sensitivity limit near an exceptional point in a Brillouin ring laser gyroscope
摘要： Exceptional points are singularities of open systems, and among their many remarkable properties, they provide a way to enhance the responsivity of sensors. Here we show that the improved responsivity of a laser gyroscope caused by operation near an exceptional point is precisely compensated by increasing laser noise. The noise, of is enhanced because the laser mode spectrum loses the oft-assumed property of orthogonality. This occurs as system eigenvectors coalesce near the exceptional point and a bi-orthogonal analysis confirms experimental observations. While the results do not preclude other possible advantages of the exceptional-point-enhanced responsivity, they do show that the fundamental sensitivity limit of the gyroscope is not improved through this form of operation. Besides being important to the physics of microcavities and non-Hermitian photonics, these results help clarify fundamental sensitivity limits in a specific class of exceptional-point sensor.
关键词： Brillouin ring laser gyroscope,Petermann-factor,Exceptional points,sensitivity limit,non-Hermitian photonics
更新于2025-09-23 15:21:01
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Waveguide-induced coalescence of exceptional points
摘要： In non-Hermitian systems, multiple eigenstates can merge into one state at so-called exceptional points (EPs). This paper presents the coalescence of the multiple EPs based on a waveguide. For the ring cavities located at the second-order EPs with desired chiral modes, the waveguide provides unidirectional couplings among the modes of the second-order EPs, which merges the second-order EPs into one high-order EP. The principle of this framework and properties of this system are presented by analyzing the effective Hamiltonian of the system, a mode-coupling diagram, and numerical simulations.
关键词： unidirectional couplings,exceptional points,high-order EP,non-Hermitian systems,waveguide
更新于2025-09-23 15:21:01
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Tunable topological charge vortex microlaser
摘要： The orbital angular momentum (OAM) intrinsically carried by vortex light beams holds a promise for multidimensional high-capacity data multiplexing, meeting the ever-increasing demands for information. Development of a dynamically tunable OAM light source is a critical step in the realization of OAM modulation and multiplexing. By harnessing the properties of total momentum conservation, spin-orbit interaction, and optical non-Hermitian symmetry breaking, we demonstrate an OAM-tunable vortex microlaser, providing chiral light states of variable topological charges at a single telecommunication wavelength. The scheme of the non–Hermitian-controlled chiral light emission at room temperature can be further scaled up for simultaneous multivortex emissions in a flexible manner. Our work provides a route for the development of the next generation of multidimensional OAM-spin-wavelength division multiplexing technology.
关键词： data multiplexing,orbital angular momentum,chiral light emission,non-Hermitian symmetry breaking,vortex light beams,spin-orbit interaction,microlaser,telecommunication wavelength
更新于2025-09-23 15:21:01
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Photonic Topological Insulating Phase Induced Solely by Gain and Loss
摘要： We reveal a one-dimensional topological insulating phase induced solely by gain and loss control in non-Hermitian optical lattices. The system comprises units of four uniformly coupled cavities, where the successive two have loss; the others experience gain, and they are balanced under two magnitudes. The gain and loss parts are effectively dimerized, and a bulk band gap, topological transition, midgap topological edge, and interface states in finite systems can all be achieved by controlled pumping. We also clarify non-Hermitian topological invariants and edge states in gapless conditions.
关键词： Topological Transition,Photonic Topological Insulating Phase,Non-Hermitian Optical Lattices,Midgap Topological Edge States,Gain and Loss Control
更新于2025-09-23 15:21:01
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Non-Hermitian approach for quantum plasmonics
摘要： We examine the limits of applicability of a simple non-Hermitian model for exciton/plasmon interactions in the presence of dissipation and dephasing. The model can be used as an alternative to the more complete Lindblad density matrix approach and is computationally and conceptually simpler. We find that optical spectra in the linear regime can be adequately described by this approach. The model can fail, however, under continuous optical driving in some circumstances. In the case of two quantum dots or excitons interacting with a plasmon, the model can also describe coherences and entanglement qualitatively when both dissipation and dephasing are present and quantitatively in the limit with no dephasing. The approach, within a single excitation manifold, is also applied to assess the role of disorder for 50 quantum dots interacting with a plasmon, where we find that, on average, large enough disorder can help stabilize the ensemble average of the open quantum system toward a dark quasi-steady-state much faster than without disorder. While such single excitation manifold calculations in this size limit can readily be done with either the non-Hermitian or Lindblad forms, as one goes to larger Hilbert space sizes, the computational and storage advantages of the non-Hermitian approach can become more useful.
关键词： optical spectra,coherences,entanglement,non-Hermitian model,quantum plasmonics,exciton/plasmon interactions,Lindblad density matrix,disorder
更新于2025-09-23 15:19:57
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Quantum Fisher information of a two-level system controlled by non-Hermitian operation under depolarization
摘要： We investigated the dynamics of quantum Fisher information for a two-level system controlled by a non-Hermitian operation under the depolarization, and the non-Hermitian operation is described by a special Hamiltonian in which both the PT-symmetric zone and the PT-symmetry broken zone are considered. Our results show that the non-Hermitian operation can effectively control the evolutionary behavior of quantum Fisher information of the system. Especially, through a proper choice of the non-Hermiticity parameter combining with the optimal input state and a low depolarizing probability, quantum Fisher information of the system can be significantly increased by the non-Hermitian operation. According to the quantum Cramér–Rao inequality, the inverse of quantum Fisher information provides the lower bound of the error of the parameter estimation. Our investigation also shows that the non-Hermiticity in the operation which is performed on the initial state is robust against the depolarizing decoherence, and the precision of parameter estimation can be remarkably enhanced by applying an appropriate non-Hermitian operation.
关键词： Non-Hermitian dynamics,Quantum Fisher information,Parameter estimation
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Atlanta, GA, USA (2019.7.7-2019.7.12)] 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Slow light at the nanoscale based on active epsilon-near-zero plasmonic waveguides
摘要： Plasmonic waveguides exhibit an effective epsilon-near-zero (ENZ) response at their cut-off frequency. In this work, we demonstrate the formation of an exceptional point (EP) in a nanoscale open and lossy (non-Hermitian) nanophotonic system consisting of an array of periodic nanowaveguides loaded with a very low gain coefficient material. We theoretically analyze the obtained EP, as well as its topological properties, by using a transmission-line model adapted to the plasmonic properties of the proposed device. The dispersion of the active ENZ mode and the group velocity are thoroughly investigated. Reflectionless transmission (perfect loss compensation) and ultraslow group velocity values at the nanoscale are realized at the EP, which coincides with the ENZ cut-off frequency of the proposed plasmonic system. This special spectral degeneracy (EP) is a unique feature of the presented nanoscale symmetric plasmonic ENZ configuration, different from most of the previous works that were mainly focused on asymmetric bulky micron-scale active photonic configurations.
关键词： Plasmonic waveguides,epsilon-near-zero (ENZ),non-Hermitian,exceptional point (EP),group velocity,nanophotonic system
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Photon Correlations in PT-Symmetric Waveguide Systems
摘要： Parity-Time (PT)-symmetric systems have been intensely studied since their first description by Bender & Boettcher in 1998 [1]. Especially in photonics, numerous PT-symmetric effects and systems were investigated [2]. However, all of these experiments used classical light or single photons. Here, we present the first observation of two-photon interference in a lossy directional coupler and its associated Hong-Ou-Mandel (HOM) dip. In optics, PT symmetric potentials can be realized by enforcing a symmetric real part of the refractive index and an antisymmetric imaginary part (gain/loss) [3]. Notably, the transition to the quantum-optical regime precludes one from deploying gain [4], thus, we make use of entirely passive systems: By choosing an appropriate loss distribution, the behaviour of the system can be separated into a global loss factor and the desired non-Hermitian dynamics [5]. In this vein, the object of our following considerations is a passive PT-symmetric coupler in which two waveguides interact over a distance z, see Fig. 1 A. Rapid microscopic undulations of the waveguide trajectory serve to introduce effectively constant Markovian losses, resulting in the desired complex index distribution (B). Fig. 1. (A) In a pair of coupled waveguides, rapid undulations introduce bending losses and the (B) effective complex index distribution. (C) Dependence of the two-photon coincidence on the propagation length in the coupler. In contrast to the Hermitian case, PT-symmetry systematically displaces the dip minimum towards shorter propagation lengths, as indicated by the vertical dashed red line. In the experiment (D), corresponding coincidence data were obtained for Hermitian and PT-symmetric couplers. We achieved a dip with a visibility of 87±2 % and the minimum at 3 cm in the Hermitian case, and in the PT case 90±4 % at a position of 2.75 cm. We theoretically describe light propagation in the lossy directional coupler by a quantum master equation in Lindblad form. Our rigorous approach provides information on the full quantum state of the system. It is based on a Lie algebra treatment that provides us with an eigen-decomposition of the density matrix. The analytical solution holds for the unbroken PT-symmetry case, i.e. for losses that do not exceed twice the coupling. The resulting coincidence function for a |1,1> input state is plotted in Fig. 1 C: In the Hermitian case, the HOM dip occurs at exactly half the coupling length. In contrast, the interference minimum occurs after a shorter propagation length in the PT-symmetric system, as the vertical dashed line indicates. For the experiment, a set of lossy directional couplers of identical couplings with different propagation lengths was implemented to sample light at different z positions. A corresponding set of conventional Hermitian couplers served as baseline reference. Our measurements were executed with pairs of indistinguishable photons obtained by type-I spontaneous parametric down conversion, the coincidences at the sample output were recorded by avalanche photo detectors. In conclusion, our theoretical and experimental findings indicate that the asymmetric loss distribution in the PT-symmetric case can systematically accelerate the quantum interference dynamics in comparison to the Hermitian case.
关键词： PT-symmetric systems,two-photon interference,quantum optics,non-Hermitian dynamics,Hong-Ou-Mandel dip
更新于2025-09-12 10:27:22