Résultats de recherche pour « Dark State »

We identify form-stable coupled excitations of light and matter ("dark-state polaritons") associated with the propagation of quantum fields in electromagnetically induced transparency. The properties of dark-state polaritons such as the group velocity are determined by the mixing angle between light and matter components and can be controlled by an external coherent field as the pulse propagates. In particular, light pulses can be decelerated and "trapped" in which case their shape and quantum state are mapped onto metastable collective states of matter. Possible applications of this reversible coherent-control technique are discussed.

An ideal and reversible transfer technique for the quantum state between light and metastable collective states of matter is presented and analyzed in detail. The method is based on the control of photon propagation in coherently driven three-level atomic media, in which the group velocity is adiabatically reduced to zero. Form-stable coupled excitations of light and matter (``dark-state polaritons'') associated with the propagation of quantum fields in electromagnetically induced transparency are identified, their basic properties discussed and their application for quantum memories for light analyzed.

We consider the optomechanical system consisting of an atom-cavity system coupled with a mechanical resonator, and expand the notion of quasi-dark state to the optomechanical system. We theoretically prove that even if both the one-mode light of the cavity and the one-mode Bose field of the mechanical resonator interact with the atom, each of a dark state and a quasi-dark state has an individual chance to appear when an interaction between the one-mode light and the one-mode Bose field exists. We then come up with a duality between the dark state and the quasi-dark state.

We propose a new type of laser resonator based on imaginary energy-level splitting (imaginary coupling or quality factor Q-splitting) in a pair of coupled microcavities. A particularly advantageous arrangement involves two microring cavities with different free-spectral ranges in a configuration wherein they are coupled by far-field interference in a shared radiation channel. A novel Vernier-like effect for laser resonators is designed in which only one longitudinal resonant mode has a lower loss than the small-signal gain and can achieve lasing while all other modes are suppressed. This configuration enables ultrawidely tunable single-frequency lasers based on either homogeneously or inhomogeneously broadened gain media. The concept is an alternative to the common external cavity configurations for achieving tunable single-mode operation in a laser. The proposed laser concept builds on a high-Q "dark state," which is established by radiative interference coupling and bears a direct analogy to parity-time symmetric Hamiltonians in optical systems. Variants of this concept should be extendable to parametric-gain-based oscillators, enabling widely tunable single-frequency light sources.

We study a disordered ensemble of quantum emitters collectively coupled to a lossless cavity mode. The latter is found to modify the localization properties of the ``dark'' eigenstates, which exhibit a character of being localized on multiple noncontiguous sites. We denote such states as semilocalized and characterize them by means of standard localization measures. We show that those states can very efficiently contribute to coherent energy transport. Our paper underlines the important role of dark states in systems with strong light-matter coupling.

Abstract Restriction of intramolecular motion (RIM), as the working mechanism of aggregation‐induced emission (AIE), cannot fully explain some heteroatom‐containing systems. Now, two excited states are taken into account and a mechanism, restriction of access to dark state (RADS), is specified to elaborate RIM and complete the picture of AIE mechanism. A nitrogen‐containing molecule named APA is chosen as a model compound; its weak fluorescence in solution is ascribed to the easy access from the bright (π,π*) state to the close‐lying dark (n,π*) state. By either metal complexation or aggregation, the dark state is less accessible due to restriction of the molecular motion leading to the dark state and elevation of the dark state energy, thus the bright state emission is restored. RADS is powerful in elucidating the AIE effect of molecules with excited states favoring non‐radiative decay, including overlap‐forbidden states such as (n,π*) and CT states, spin‐forbidden triplet states, and so on.

We report on the experimental realization of a conservative optical lattice for cold atoms with a subwavelength spatial structure. The potential is based on the nonlinear optical response of three-level atoms in laser-dressed dark states, which is not constrained by the diffraction limit of the light generating the potential. The lattice consists of a one-dimensional array of ultranarrow barriers with widths less than 10 nm, well below the wavelength of the lattice light, physically realizing a Kronig-Penney potential. We study the band structure and dissipation of this lattice and find good agreement with theoretical predictions. Even on resonance, the observed lifetimes of atoms trapped in the lattice are as long as 44 ms, nearly 10^{5} times the excited state lifetime, and could be further improved with more laser intensity. The potential is readily generalizable to higher dimensions and different geometries, allowing, for example, nearly perfect box traps, narrow tunnel junctions for atomtronics applications, and dynamically generated lattices with subwavelength spacings.

We theoretically study an extension of the Dicke model, where the single-particle Hamiltonian has three energy levels in Lambda configuration (i.e., the excited state is coupled to two nondegenerate ground states via two independent quantized light fields). The corresponding many-body Hamiltonian can be diagonalized in the thermodynamic limit with the help of a generalized Holstein-Primakoff transformation. Analyzing the ground-state energy and the excitation energies, we identify one normal and two superradiant phases, separated by phase transitions of both first and second oder. A phase with both superradiant states coexisting is not stable. In addition, in the limit of two degenerate ground states a dark state emerges, which seems to be analogous to the dark state appearing in the well-known stimulated Raman adiabatic passage scheme.