Figure 1

(a) Sketch of the experimental setup: two photons with different energies enter a Michelson interferometer that consists of a 50:50 beamsplitter and two retroreflectors. The two interferometer output ports are each coupled to an optical fiber, delayed relative to each other with half of the excitation laser repetition time and recombined again at another beamsplitter. (b) Schematics of the intensity interference pattern at one interferometer output for two example wavelengths versus the path difference between the two interferometer arms.Reuse & Permissions

Figure 2

(a) Unfiltered spectrum of the quantum dot emission. (b) Spectrum of the light emerging from one Michelson output port. (c) The same as in (b) but taken at the other output port. Insets show correlation measurements of exciton and biexciton emission taken after each output port. The gray curves have been obtained after filtering with a bandpass filter.Reuse & Permissions

Figure 3

Intensity correlation of the excitonic (a) and biexcitonic (b) spectral line after coupling to a fiber. Both single-line correlations were obtained by blocking one of the interferometer arms. (c) Intensity correlation function of the multiplexed signal.Reuse & Permissions

Figure 4

Results obtained from a Monte Carlo simulation: (a) for a combination of differently and (b) equally charged exciton and biexciton states.Reuse & Permissions

Figure 5

Possible implementations of the multiplexer into the BB84 protocol. In both schemes the polarization is modulated between straight and circular polarization using an polarizer P with an electro-optical modulator (EOM). Bob’s detection side is realized by another EOM, a polarizing beamsplitter PBS, and detectors D. ${\omega }_1$ and ${\omega }_2$ indicate the two energies of the photons and M is the Michelson arrangement. In (a) the two photons are recombined without time delay, in (b) a time delay is introduced and the two beams are then recombined with a beamsplitter BS, like it is done in the experiment.Reuse & Permissions