Single-Photon Transistor Mediated by Interstate Rydberg Interactions

We report on the realization of an all-optical transistor by mapping gate and source photons into strongly interacting Rydberg excitations with different principal quantum numbers in an ultracold atomic ensemble. We obtain a record switch contrast of 40% for a coherent gate input with mean photon number one and demonstrate attenuation of source transmission by over ten photons with a single gate photon. We use our optical transistor to demonstrate the nondestructive detection of a single Rydberg atom with a fidelity of 0.72(4).

Figure 1

(a) Level scheme, (b) simplified schematic, and (c) pulse sequence of our all-optical transistor. (d) The absorption spectrum for the source field (dots) over the full intermediate state absorption valley shows the EIT window on resonance; the gate field spectrum (circles) is taken around the two-photon resonance at ${\delta }_g=40\mathrm{MHz}$. The solid lines are fits to the EIT spectra. The linewidth of the source EIT window $\mathrm{\Delta }\nu =2\mathrm{MHz}$ and the optical depth $\mathrm{OD}=25$ of our system are extracted from the brown curve.

Figure 2

Switch contrast (red) as function of (a) mean number of incident gate photons and (b) mean number of stored photons according to Eq. (2). The dashed line indicates the fundamental limit set by the photon statistics of the coherent gate input. Black data points represent the calculated switch contrast expected for (a) one-, two- and three-photon Fock input states or (b) deterministic single and two stored gate excitations.

Figure 3

(a) Optical gain of our transistor, measured for coherent gate input ${\overline{N}}_{\mathrm{g},\text{in}}=0.75(3)$ (blue data) and extrapolated to single photon Fock state input (green line) and single stored excitation (black line). (b) Source photon transfer function without (red) and with coherent gate input ${\overline{N}}_{\mathrm{g},\text{in}}=0.75(3)$ (blue). We observe a constant switch contrast between the two data sets over the whole source input range. The green (black) solid line are again the estimated behavior of the system for a single-photon Fock input state (a single stored excitation). Shaded regions are error estimates.

Figure 4

(a) Histograms of single shot detection events with and without stored gate excitation (red bars and blue bars, respectively). The strong shift of the red histogram originates from the switch effect of single or two gate Rydberg excitations in the medium. (b) Accounting for the Poissonian statistics of gate Rydberg excitations, we decompose the red histogram in (a) into gated and not-gated contributions. The dashed green line is the discrimination level which predicts the presence of a Rydberg atom in a single shot with the highest fidelity of 0.72(4).