Interfacing of an optical nanofiber with tunably spaced atoms in an optical lattice

TL;DR

The paper addresses efficient, scalable interfacing of a large 1D atomic array with an optical nanofiber to study photon-mediated collective interactions. It introduces a tunable optical lattice with spacing $d_\mathrm{lat}$ in the range $0.88-1.5~\mu$m, projected onto the nanofiber via a stationary $4f$ imaging system, combining evanescent trapping with optical-tweezer-like control. The authors demonstrate trapping of $N \approx 1270 \pm 35$ atoms at a depth $U_0 \approx k_\mathrm{B} \times 0.5$ mK, with a trap lifetime $t_\mathrm{trap} \approx 14.7$ ms and a nearest-site coupling of roughly $1.8\%$ into the guided mode, plus parametric-heating measurements validating axial-frequency tunability with lattice spacing. The work offers a versatile platform for exploring long-range collective radiative dynamics and quantum networking with nanophotonic waveguides, including potential Bragg/Chiral regimes and compatibility with optical tweezers for scalable addressability.

Abstract

We experimentally demonstrate efficient interfacing of a large number of atoms to an optical nanofiber using an optical lattice with tunable spacing ($0.88-1.5~μ$m) projected onto the nanofiber. The lattice beam and reflections from the nanofiber yield trap potentials that provide tight confinement in all motional degrees of freedom $\approx 220$ nm above the nanofiber surface, enabling efficient atom-photon coupling. We achieve trapping of $\approx1300$ atoms in periodic trap sites with a trap lifetime of $\approx15$ ms. We also observe the effect of varied lattice periods on the atomic motional frequencies. Our new scheme is adaptable to other nanophotonic cold-atom systems and provides a versatile and scalable platform for studying photon-mediated long-range collective interactions.

Figures (4)

• Figure 1: Schematic diagram of the experiment: The optical lattice is formed by illuminating the grating plate with the lattice beam (see upper-right inset), which is projected onto the nanofiber via the $4f$ imaging system composed of two aspherical lenses (ALs). The probe and heating beams co-propagate through the nanofiber with orthogonal polarizations. The avalanche photodiode (APD) measures the transmission of the probe beam. SMF: single-mode fiber, CL: cylindrical lens, GP: grating plate, PBS: polarizing beam splitter, HWF: half-wave plate, VBG: volume Bragg grating.
• Figure 2: Simulated intensity of the lattice light interfaced with the nanofiber rendered in the (a) $x-z$ and (b) $y-z$ plane, residing at $y=0$ and $x=0$, respectively. The geometric convention follows that of Fig. \ref{['fig:schematic']}. The shaded rectangle in (a) and the circle in (b) represent the cross-section of the nanofiber in the respective plane. The color-map scale is displayed in arbitrary units. The local intensity maximum nearest to the nanofiber surface is marked with "$\times$". (c) The estimated radial trapping potentials along the $z$ axis (dashed lines in (a) and (b)), corresponding to the van der Waals (vdW) potential (solid black line), lattice (solid red line), and total potential (solid blue line) are plotted against the distance from the nanofiber surface $z-R$, where $R=240$ nm is the radiaus of the nanofiber.
• Figure 3: (a) Transmission data with a 5-ms holding time while the lattice beams are on (blue circles) and off (red squares), fitted by Eq. \ref{['eq:T_spectrum']}. (b) The optical depth is plotted against various lattice holding times. The solid line represents an exponentially decaying function that fits the data, with a time constant of 14.7 ms. (c) The absorbed probe power $P_\mathrm{abs}$ is plotted for the range of incident power $P_\mathrm{in}$. The solid line represents the data fit according to Eq. \ref{['eq:saturation']}, and the horizontal dashed line represents the asymptotic limit of the absorption, $P^\mathrm{max}_\mathrm{abs}$, obtained from the fit.
• Figure 4: (a) The results of the atom loss spectroscopy induced by the intensity modulation are presented for various lattice periods ($d_\mathrm{lat}$). The solid curves fit the data with double Gaussian curves to estimate the axial trap frequency $f_\mathrm{ax}$. (b) The axial trap frequencies $f_\mathrm{ax}$ from the fittings from (a) are plotted against the varied lattice periods. The solid line fits the data by Eq. \ref{['eq:vib_freq']}.