Source: https://www.osapublishing.org/optica/abstract.cfm?uri=optica-2-4-353
Timestamp: 2019-04-22 01:05:24+00:00

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Tapered optical fibers with a nanofiber waist are versatile light–matter interfaces. Of particular interest are laser-cooled atoms trapped in the evanescent field surrounding the optical nanofiber: they exhibit both long ground-state coherence times and efficient coupling to fiber-guided fields. Here, we demonstrate electromagnetically induced transparency, slow light, and the storage of fiber-guided optical pulses in an ensemble of cold atoms trapped in a nanofiber-based optical lattice. We measure group velocities of 50 m/s. Moreover, we store optical pulses at the single-photon level and retrieve them on demand in the fiber after 2 μs with an overall efficiency of (3.0±0.4)%. Our results show that nanofiber-based interfaces for cold atoms have great potential for the realization of building blocks for future optical quantum information networks.
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Fig. 1. (a) Schematic of the setup including the tapered optical fiber, the laser fields, and the single-photon counting module. The polarization of the probe field above and below the nanofiber is indicated by the dashed circular arrows. A homogeneous magnetic field B off is applied. (b) Cross-sectional view of the nanofiber, illustrating the orientations of the principal axes of quasi-linear polarizations of the nanofiber-guided fields. (c) Relevant Zeeman sublevels of the trapped cesium atoms. The transitions driven by the laser fields are indicated. The quantization axis is in the direction of B off .
Fig. 2. Transmission spectrum of the guided probe field under EIT conditions. (a) A narrow transmission window with a width clearly smaller than the natural linewidth is observed on an optically dense background. The control power is P c = 26 pW , and the probe power is P p = 2.9 pW . The orange line is a fit to the data (see text). The spectrum is averaged over 300 measurements. (b) For P c = 0.33 pW , we observe a transmission window that is about 10 times narrower. The orange line is a Lorentzian fit. Here, P p = 1.7 pW . Each data point is an average over 60 measurements. The error bars in (a) and (b) correspond to one standard deviation based on counting statistics.
Fig. 3. Slow fiber-guided light. (a) Time traces of probe pulses transmitted through the TOF under EIT conditions. A delay of the pulses with respect to a reference pulse (dark green) is clearly visible. The solid lines are Gaussian fits to the data. Each point is the result of the average over 5 pulses per atomic ensemble and over 800 experimental runs. The bin size is 1 μs. The error bars are as in Fig. 2. (b) Pulse delay, (c) pulse duration, and (d) pulse transmission as a function of the control power, P c . The orange lines are the results of a global fit of the data sets in (b)–(d); see text. The error bars are the standard errors of the Gaussian fits.
Fig. 4. Storage of light in a nanofiber-trapped ensemble of cold atoms. A pulse of duration τ = 0.2 μs that contains 0.8 photons on average is launched into the TOF and stopped inside the atomic medium. This is achieved by reducing P c ( t ) to zero (blue line). After 1 μs, P c ( t ) is increased to its initial value, and the pulse is retrieved and recorded by the SPCM (orange data). Here, B off = 15 G , the bin size is 100 ns, and the data are averaged over 55 pulses per atomic ensemble and 1600 experimental runs (2400 for reference). Green data, reference, recorded without atoms; black line, simulated time trace (see text).
(1) χ ˜ ( δ p ) = [ 2 δ p γ 21 ( 4 δ p 2 − | Ω c | 2 γ 21 γ 31 ) + 2 δ p γ 31 ] + i [ 1 + 4 δ p 2 γ 21 2 + | Ω c | 2 γ 21 γ 31 ] | | Ω c | 2 γ 21 γ 31 + ( 1 − 2 i δ p γ 21 ) ( 1 − 2 i δ p γ 31 ) | 2 .

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