In our case γ 1D ≈ 0.13 γ 0, so sub-radiance from infinite-range interactions is limited to γ 0 − γ 1D ≈ 0.87 γ 0. However, these events are obscured by the dominant signal of slower decays produced from free space interactions. Infinite-range interactions also produce sub-radiant decay rates. 2a) corresponds to an average of sub-radiant decays due to pairs of atoms located within a wavelength, i.e., free space interaction (Fig. The slow decay (green dashed line in Fig. Its time dependence can be described by two distinct exponential decays.
Observation of super- and sub-radianceįigure 2 shows a typical signal of the atomic decay as measured through the ONF. Both effects can provide quantitative experimental evidence of collective states. Super-radiance can be measured as an enhanced decay rate at short times. Sub-radiant states have lifetimes much longer than most other processes, favoring their observation. Their random positioning leads to probabilistic super- or sub-radiant states on each experimental realization. However, collective states are still observed when atoms from a MOT are free to go near the ONF. This kind of control has been challenging to implement for atoms trapped close enough to the ONF (tens of nanometers) to ensure significant mode coupling.
After the probe turns off (extinction ratio better than 1:2 × 10 3 in one atomic natural lifetime), we collect photons spontaneously emitted into the ONF mode to measure the decay time using time-correlated single photon counting.Ĭollective states can be tailored by positioning the atoms in a particular arrangement. A weak free space probe pulse, propagating perpendicular to the fiber, excites atoms for 50 ns using the F = 2 → F′ = 3 transition. By detuning the repumper below resonance, we address atoms near the nanofiber (whose levels have been shifted by van der Waals interactions) such that the atomic density distribution peaks at ~30 nm away from the surface. A repumper beam driving the F = 1 → F = 2 transition propagates through the nanofiber, leaving in the F = 2 ground state-only atoms that interact with the ONF-guided mode. They are prepared in the F = 1 ground level by an external free propagating beam.
After the MOT is turned off, the atoms form a cold thermal gas around the ONF.
This ONF is single mode at the D2 resonant wavelength of 780 nm. We overlap a cold atomic cloud of 87Rb atoms from a magneto-optical trap (MOT) with a 240 nm radius ONF. With σ i \(\left( \phi )\) (with β 0 being the propagation constant of the resonant-guided mode and Δ ϕ the angle difference in cylindrical coordinates).
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