Fig. 1: Realisation of up to three cascaded single-photon absorbers using Rydberg superatoms.
From: Controlled multi-photon subtraction with cascaded Rydberg superatoms as single-photon absorbers
a To create nsub saturable superatom absorbers, we place nsub ensembles of cold 87Rb atoms in the path of a tightly focussed probe beam. Using an acousto-optical deflector (AOD), we can control the number and position of the optical traps that tightly confine the ensembles below the Rydberg blockade radius rB along the probe direction. b Within rB strong van der Waals interactions restrict each ensemble to a single Rydberg excitation as the probe photons and a control field couple \(|g\rangle =|5{S}_{1/2},F=2,{m}_{F}=2\rangle\) to a Rydberg state \(|r\rangle =|121{S}_{1/2},{m}_{J}=1/2\rangle\) via \(|e\rangle =|5{P}_{3/2},F=3,{m}_{F}=3\rangle\) in a Raman scheme with detuning Δ/2π ≈ 100 MHz and thus to the absorption of a single photon at a time for a two-photon detuning of δ = 0. The transmitted probe pulses are coupled into a single-mode optical fibre (not shown) and detected on four single-photon counters in a Hanbury-Brown-Twiss configuration. c Representation of the absorber as an effective three-level system in terms of singly excited collective states following adiabatic elimination of \(|e\rangle\). Strong dephasing γD from the bright excited state \(|W\rangle\), with strong coupling \(\sqrt{\kappa {R}_{{\rm{in}}}}\) from the ground state \(|G\rangle\), into dark excited states \(|D\rangle\) prevents stimulated re-emission of the absorbed photon and the absorption of further photons until it is subject to Raman decay Γ ≪ γD, κ.
