Title: Reducing phonon-induced decoherence in solid-state single-photon sources with cavity quantum electrodynamics
Semiconductor quantum dots (QDs) are good candidates for developing integrated sources of single-photons as fundamental flying qubits for optical quantum networks [1]. Yet, developing QD-based devices demands reducing decoherence processesto generate indistinguishable single photons without post-selection. The interaction of the QD with the acoustic phonon bathis responsible for two decoherence phenomena: (i) a non-Markovian dephasing process, consisting in the phonon-assistedemission of photons in the phonon sidebands (PSBs), and (ii) a Markovian pure dephasing in the zero-phonon line (ZPL),resulting from virtual transitions towards higher energy levels. In this work we demonstrate both theoretically andexperimentally that the use of a strong Purcell effect in narrowband cavities limits both phonon decoherence effects andenables the emission of highly indistinguishable non-postselected single-photons [2].
We study the indistinguishability of two photons generated by the same QD-cavity device delayed by 12.2 ns as functionof temperature. Our devices are composed of a QD deterministically coupled in position and energy to a micropillar-cavity. The devices are electrically contacted to tune the QD in resonance with the cavity mode with the applied voltageat each temperature [3,4]. First, the ZPL indistinguishability is studied by filtering out the emission in the PSBs, it slightly decreases from 99.3% at 9 K to 97.3% at 18 K. This is in striking contrast with measurementsobtained in other systems (see open symbols in Fig. 1(b) [5-9]) where no Purcell effect was implemented: the acceleration ofspontaneous emission by a nominal Purcell factor of ~24 strongly limits the effect of pure dephasing.
We also show that the use of a strong Purcell effect also efficiently suppresses the fraction of emission in thePSB: the calculated and measured spectra of a QD in the cavity shows astrong suppression of the PSB emission as compared to the case of a QD in bulk (dashed line), the emission being efficientlyredirected toward the ZPL. Since the maximum indistinguishability is related to the fraction of emission in the ZPL, sucheffect results in a strong increase of the indistinguishability of the full emission spectrum: it is brought from 87% (resp.25%) without Purcell effect to more than 99% (resp ≈ 75%) at 0 K (resp. 20 K).
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