Sketches of different cascades of the biexciton-exciton decay. The sketches on the left side show the different states involved in the XX-X decay: biexciton (top panel), exciton (middle panel), and the QD-ground state (bottom panel). (a) All four possible transitions have different energies; no entanglement is possible. (b) The energies of XX and X are tuned into resonance (same colors-same energy): it is proposed that the time reordering allows restoring entanglement . The transitions of the i-th generation in (a) and (b) emit linear (Hi, Vi) polarized light. (c) FSS (Δ1 ≈ 0) tuned to values smaller than the respective linewidth; the so-called which-path information encoded in the FSS is erased, and entanglement is achieved. The transitions in (c) emit circularly (σ + , σ−) polarized light.
Plumhof et al. Nanoscale Research Letters 2012 7:336 doi:10.1186/1556-276X-7-336