We experimentally and theoretically investigate collective radiative effects in an ensemble of cold atoms coupled to a single-mode optical nanofiber. Our analysis unveils the microscopic dynamics of the system, showing that collective interactions between the atoms and a single guided photon gradually build up along the atomic array in the direction of propagation of light. These results are supported by time-resolved measurements of the light transmitted and reflected by the ensemble after excitation via nanofiber-guided laser pulses, whose rise and fall times are shorter than the atomic lifetime. Superradiant decays more than 1 order of magnitude faster than the single-atom free-space decay rate are observed for emission in the forward-propagating guided mode, while at the same time, no speed-up of the decay rate is measured in the backward direction. In addition, position-resolved measurements of the light that is transmitted past the atoms are performed by inserting the nanofiber-coupled atomic array in a 45-m-long fiber ring resonator, which allow us to experimentally reveal the progressive growth of the collective response of the atomic ensemble. Our results highlight the unique opportunities offered by nanophotonic cold atom systems for the experimental investigation of collective light-matter interaction.
In this work we considered light interaction with two-level quantum systems chirally coupled to a single guided mode with account for a spin-locking effect. The chiral coupling allows achieving asymmetric interaction between the two-level systems, which strongly affects the light scattering of a guided mode of an optical nanofiber by one-dimensional atomic chain. We have also build an analytical model of unidirectional transport of quantum excitation and verified it with modelling of atoms coupled with surface plasmon polariton mode of a metallic nanowire. In particularly, we showed the tolerance of the unidirectionally coupled systems over the positional disorder of the two-level systems.
We study the propagation of nanofiber-guided light through an array of atomic cesium, taking into account the transitions between the hyperfine levels
6S1/2F=4 and $6{P}_{3/2}{F}^{\ensuremath{'}}=5$ of the
D2 line. We derive the coupled-mode propagation equation, the input-output equation, the scattering matrix, the transfer matrix, and the reflection and transmission coefficients for the guided field in the linear, quasistationary, weak-excitation regime. We show that, when the initial distribution of populations of atomic ground-state sublevels is independent of the magnetic quantum number, the quasilinear polarizations along the principal axes
x and
y, which are parallel and perpendicular, respectively, to the radial direction of the atomic position, are not coupled to each other in the linear coherent scattering process. When the guided probe field is quasilinearly polarized along the major principal axis
x, forward and backward scattering have different characteristics. We find that, when the array period is far from the Bragg resonance, the backward scattering is weak. Under the Bragg resonance, most of the guided probe light can be reflected back in a broad region of field detunings even though there is an irreversible decay channel into radiation modes. When the atom number is large enough, two different band gaps may be formed, whose properties depend on the polarization of the guided probe field.
Scattering is a general process in both fundamental and applied physics. In this paper, we investigate Rayleigh scattering of a solid-state-emitter coupled to a nanofiber, by
S-matrix-like theory in
k-space description. Under this model, both Rayleigh scattering and dipole interaction are studied between a two-level artificial atom embedded in a nanocrystal and fiber modes (guided and radiation modes). It is found that Rayleigh scattering plays a critical role in the transport properties and quantum statistics of photons. On the one hand, Rayleigh scattering produces the transparency in the optical transmitted field of the nanofiber, accompanied by the change of atomic phase, population, and frequency shift. On the other hand, the interference between two kinds of scattering fields by Rayleigh scattering and dipole transition modifies the photon statistics (second-order autocorrelation function) of output fields, showing a strong wavelength dependence. This study provides guidance for the solid-state emitter acting as a single-photon source and can be extended to explore the scattering effect in many-body physics.
We study the subradiant collective states of a periodic chain of two-level atoms with either transversal or longitudinal transition dipole moments with respect to the chain axis. We show that long-lived subradiant states can be obtained for the transversal polarization by properly choosing the chain period for a given number of atoms in the case of no open diffraction channels. While not being robust against the positional disorder along the chain, these highly subradiant states have a linewidth that decreases with the number of atoms much faster than it was shown previously. In addition, our paper shows that similar states are present even if there are additional interaction channels between the atoms, i.e., they interact via the waveguide mode of an optical nanofiber, for instance. We develop a theoretical framework allowing us to describe the spectral properties of the system in terms of contributions from each collective eigenstate and we show that subradiant states manifest themselves in the transmission and reflection spectra, allowing us to observe interaction-induced transparency in a very narrow spectral range. Such long-lived collective states may find potential applications in nanophotonics and quantum optics.
Abstract We propose two experimental schemes for nanofiber-based compensated optical dipole traps that optimize the collective coupling of a one-dimensional array of atoms. The created array satisfies the second-order Bragg condition ( d = λ ), facilitating constructive interference of atomic radiation into the nanofiber and generating coherent back reflections of guided modes. Both schemes use far-off resonance light to minimize light scattering and atomic heating. Our numerical study focuses on the D2 line for 87 Rb atoms. The results are generalizable to different atomic species and could improve the study of collective and nonlinear atomic effects.