Time reversal in quantum or classical systems described by an Hermitian Hamiltonian is a physically allowed process, which requires in principle inverting the sign of the Hamiltonian. Here we consider the problem of t...Time reversal in quantum or classical systems described by an Hermitian Hamiltonian is a physically allowed process, which requires in principle inverting the sign of the Hamiltonian. Here we consider the problem of time reversal of a subsystem of discrete states coupled to an external environment characterized by a continuum of states, into which they generally decay. It is shown that, by flipping the discrete-continuum coupling from an Hermitian to a non-Hermitian interaction, thus resulting in a non unitary dynamics, time reversal of the subsystem of discrete states can be achieved, while the continuum of states is not reversed. Exact time reversal requires frequency degeneracy of the discrete states,or large frequency mismatch among the discrete states as compared to the strength of indirect coupling mediated by the continuum. Interestingly, periodic and frequent switch of the discrete-continuum coupling results in a frozen dynamics of the subsystem of discrete states.展开更多
Recent experiments demonstrated that chiral symmetry breaking at an exceptional point(EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation...Recent experiments demonstrated that chiral symmetry breaking at an exceptional point(EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation model,we show here that unidirectional laser emission at an EP is a robust regime. Slight deviations from the EP condition can break preferential unidirectional lasing near threshold via a Hopf instability. However, abovea "second" laser threshold, unidirectional emission is restored.展开更多
On-chip integrated laser sources of structured light carrying fractional orbital angular momentum(FOAM)are highly desirable for the forefront development of optical communication and quantum information-processing tec...On-chip integrated laser sources of structured light carrying fractional orbital angular momentum(FOAM)are highly desirable for the forefront development of optical communication and quantum information-processing technologies.While integrated vortex beam generators have been previously demonstrated in different optical settings,ultrafast control and sweep of FOAM light with low-power control,suitable for high-speed optical communication and computing,remains challenging.Here we demonstrate fast control of the FOAM from a vortex semiconductor microlaser based on fast transient mixing of integer laser vorticities induced by a control pulse.A continuous FOAM sweep between charge 0 and charge+2 is demonstrated in a 100 ps time window,with the ultimate speed limit being established by the carrier recombination time in the gain medium.Our results provide a new route to generating vortex microlasers carrying FOAM that are switchable at GHz frequencies by an ultrafast control pulse.展开更多
The engineering of self-organized plasmonic metasurfaces is demonstrated using a maskless technique with defocused ion-beam sputtering and kinetically controlled deposition. The proposed reliable, cost-effective, and ...The engineering of self-organized plasmonic metasurfaces is demonstrated using a maskless technique with defocused ion-beam sputtering and kinetically controlled deposition. The proposed reliable, cost-effective, and controllable approach enables large-area （order of square centimeter） sub-wavelength periodic patterning with close-packed gold nanostrips. A multi-level variant of the method leads to high-resolution manufacturing of vertically stacked nanostrip dimer arrays, without resorting to lithographic approaches. The design of these self-organized metasurfaces is optimized by employing plasmon hybridization methods. In particular, preliminary results on the so-called gap-plasmon configuration of the nanostrip dimers, implementing magnetic dipole resonance in the near-infrared range, are reported. This resonance offers a superior sensitivity and field enhancement, compared with the more conventional electric dipole resonance. The translational invariance of the nanostrip configuration leads to a high filling factor of the hot spots. These advanced features make the large-area metasurface based on gap-plasmon nanostrip dimers very attractive for surface-enhanced linear and nonlinear spectroscopy （e.g., surface-enhanced Raman scattering） and plasmon-enhanced photon harvesting in solar and photovoltaic cells.展开更多
文摘Time reversal in quantum or classical systems described by an Hermitian Hamiltonian is a physically allowed process, which requires in principle inverting the sign of the Hamiltonian. Here we consider the problem of time reversal of a subsystem of discrete states coupled to an external environment characterized by a continuum of states, into which they generally decay. It is shown that, by flipping the discrete-continuum coupling from an Hermitian to a non-Hermitian interaction, thus resulting in a non unitary dynamics, time reversal of the subsystem of discrete states can be achieved, while the continuum of states is not reversed. Exact time reversal requires frequency degeneracy of the discrete states,or large frequency mismatch among the discrete states as compared to the strength of indirect coupling mediated by the continuum. Interestingly, periodic and frequent switch of the discrete-continuum coupling results in a frozen dynamics of the subsystem of discrete states.
基金National Science Foundation(NSF)(DMR-1506884)Army Research Office(ARO)(W911NF-15-1-0152)
文摘Recent experiments demonstrated that chiral symmetry breaking at an exceptional point(EP) is a viable route to achieve unidirectional laser emission in microring lasers. By a detailed semiconductor laser rate equation model,we show here that unidirectional laser emission at an EP is a robust regime. Slight deviations from the EP condition can break preferential unidirectional lasing near threshold via a Hopf instability. However, abovea "second" laser threshold, unidirectional emission is restored.
基金the support from the National Science Foundation(NSF)(ECCS-1932803,OMA-1936276,ECCS-1842612,DMR-1809518,and CNS-2011411)U.S.Army Research Office(ARO)(W911NF-19-1-0249 and W911NF-18-1-0348)+2 种基金Office of Naval Research MURI(N00014-20-1-2558)partially supported by the NSF through the University of Pennsylvania Materials Research Science and Engineering Center(MRSEC)(DMR-1720530)supported by the NSF National Nanotechnology Coordinated Infrastructure Program under grant NNCI-1542153.
文摘On-chip integrated laser sources of structured light carrying fractional orbital angular momentum(FOAM)are highly desirable for the forefront development of optical communication and quantum information-processing technologies.While integrated vortex beam generators have been previously demonstrated in different optical settings,ultrafast control and sweep of FOAM light with low-power control,suitable for high-speed optical communication and computing,remains challenging.Here we demonstrate fast control of the FOAM from a vortex semiconductor microlaser based on fast transient mixing of integer laser vorticities induced by a control pulse.A continuous FOAM sweep between charge 0 and charge+2 is demonstrated in a 100 ps time window,with the ultimate speed limit being established by the carrier recombination time in the gain medium.Our results provide a new route to generating vortex microlasers carrying FOAM that are switchable at GHz frequencies by an ultrafast control pulse.
文摘The engineering of self-organized plasmonic metasurfaces is demonstrated using a maskless technique with defocused ion-beam sputtering and kinetically controlled deposition. The proposed reliable, cost-effective, and controllable approach enables large-area （order of square centimeter） sub-wavelength periodic patterning with close-packed gold nanostrips. A multi-level variant of the method leads to high-resolution manufacturing of vertically stacked nanostrip dimer arrays, without resorting to lithographic approaches. The design of these self-organized metasurfaces is optimized by employing plasmon hybridization methods. In particular, preliminary results on the so-called gap-plasmon configuration of the nanostrip dimers, implementing magnetic dipole resonance in the near-infrared range, are reported. This resonance offers a superior sensitivity and field enhancement, compared with the more conventional electric dipole resonance. The translational invariance of the nanostrip configuration leads to a high filling factor of the hot spots. These advanced features make the large-area metasurface based on gap-plasmon nanostrip dimers very attractive for surface-enhanced linear and nonlinear spectroscopy （e.g., surface-enhanced Raman scattering） and plasmon-enhanced photon harvesting in solar and photovoltaic cells.
