Reducing Phonon-Induced Decoherence in Solid-State Single-Photon Sources with Cavity Quantum Electrodynamics

Abstract

Solid-state emitters are excellent candidates for developing integrated sources of single photons. Yet, phonons degrade the photon indistinguishability both through pure dephasing of the zerophonon line and through phonon-assisted emission. Here, we study theoretically and experimentally the indistinguishability of photons emitted by a semiconductor quantum dot in a microcavity as a function of temperature. We show that a large coupling to a high quality factor cavity can simultaneously reduces the effect of both phonon-induced sources of decoherence. It first limits the effect of pure dephasing on the zero phonon line with indistinguishabilities above 97% up to 18K. Moreover, it efficiently redirects the phonon sidebands into the zero-phonon line and brings the indistinguishability of the full emission spectrum from 87% (resp. 24%) without cavity effect to more than 99% (resp 76%) at 0 K (resp. 20 K). We provide guidelines for optimal cavity designs that further minimize the phonon-induced decoherence.Indistinguishable single photons are the building blocks of optical quantum computation protocols and quantum networks [1][2][3]. This has motivated great efforts to develop devices generating on-demand indistinguishable single photons, using solid-state emitters such as diamond color centres [4, 5], molecules [6] or semiconductor quantum dots (QDs) [7][8][9][10][11][12]. In QDs, understanding the extrinsic sources of decoherence such as spin and charge noise [13] has recently enabled impressive progresses in the performances of these sources [11,12]. Yet, acoustic phonons generally remain an intrinsic and limiting source of dephasing.Indeed acoustic phonons are responsible for two kinds of dephasing processes. First, acoustic phonons induce a rapid and partial decay of coherence [14][15][16]. This non-Markovian dephasing dynamics is the time-domain counterpart of the emitter spectrum consisting of a sharp zero-phonon line (ZPL) sitting on top of a broad phonon sideband (PSB) [17][18][19]. Second, acoustic phonons can assist virtual transitions towards higher energy levels, resulting in a Markovian pure dephasing of the ZPL [3]. Such effects impose two severe limitations to obtain indistinguishable photons: (i) to work at low temperatures, typically below 10 K for QDs and (ii) to use spectral postselection of the ZPL. Indeed, even at zero temperature, phonon emission processes result in the presence of a PSB on the low energy side, fundamentally limiting the indistinguishability. In practice, the indistinguishability has been measured to rapidly drop with temperature even with spectral selection [21], and without it remains further away from unity [22].In typical self-assembled QDs, the emission fraction into the ZPL, η ZPL , represents typically 90% of the emission at 4K, a fraction that rapidly drops with temperature. Moreover, the photons emitted in the PSB are essentially incoherent, due to their broadband nature with respect to the natural linewidth. In a Hong-Ou-Mandel (HOM) experiment, only the fraction η ...

Efficient Pulse‐Excitation Techniques for Single Photon Sources from Quantum Dots in Optical Cavities

“…The criteria for suppression of two‐photon emission is usually , although this criterion can be relaxed to due to the dynamical decoupling between the cavity and exciton that occurs during a short pulse. Furthermore, high Purcell factor, high Q cavities increase photon indisinguishability by filtering the phonon sidebands . For these parameters, simultaneous indistinguishabilities of and emitted cavity photon numbers of can be achieved for a short pulse of ps.…”

“…Although only strictly accurate in a long‐time limit and with weak cavity coupling (), this metric is given by (on resonance), which is slightly reduced by phonon coupling . High Purcell factors can, even for a short pulse, simultaneously increase SPS efficiency and indistinguishability by increasing the proportion of photons emitted into the desired cavity mode, while filtering out phonon sidebands that degrade the coherence of emitted photons …”

Limitations on the indistinguishability of photons from remote solid state sources

“…Additionally, active stabilization schemes can be employed to minimize long time drifts of the emission frequency [63,64]. Interesting perspectives are introduced by emitters coupled to a cavity in two different regimes [65]: enhancing the spontaneous emission rate by means of the Purcell-effect broadens the natural linewidth of an emitter, thereby bringing it closer to the Fourier-limit for constant PD and SD. If in contrast an emitter is weakly coupled to a high-quality cavity, it incoherently populates the cavity mode with a single photon.…”

Reproducibility of High-Performance Quantum Dot Single-Photon Sources

“…Quantum dots behave like artifical atoms that can emit single photons on demand. By fabricating a microcavity * niccolo.somaschi@quandela.com † pascale.senellart-mardon@c2n.upsaclay.fr around a QD, these single photons can be efficiently collected while simultaneously mitigating pure dephasing [14][15][16].…”