Bloch-Wave Engineering of Quantum Dot Micropillars for Cavity Quantum Electrodynamics Experiments

We have employed Bloch-wave engineering to realize submicron diameter high quality factor $\mathrm{GaAs}/\mathrm{AlAs}$ micropillars (MPs). The design features a tapered cavity in which the fundamental Bloch mode is subject to an adiabatic transition to match the Bragg mirror Bloch mode. The resulting reduced scattering loss leads to record-high vacuum Rabi splitting of the strong coupling in MPs with modest oscillator strength quantum dots. A quality factor of 13 600 and a splitting of $85\mu \mathrm{eV}$ with an estimated visibility $v$ of 0.41 are observed for a small mode volume MP with a diameter $d_c$ of 850 nm.

Figure 1

(a) Schematic sketch of the layer sequence of the adiabatic cavity design illustrating the bottom/top DBR with $30/25$ mirror pairs and a 3 taper cavity region. Inset: Zoom-in view of the cavity region. (b) The position of the photonic band gap as the function of $z$ is schematically illustrated. The resonance wavelength of the cavity mode is represented by the dashed line. (c), (d) Electric field amplitude profiles in a MP with $d_c=750\mathrm{nm}$ for the reference (c) and the adiabatic (d) design, respectively.

Figure 2

(a) Computed $Q$ factor and $V_{\mathrm{mode}}$ as a function of $d_c$ for the reference and the adiabatic cavity designs. (b) Computed $Q$ factor for reference designs with $25/30$, $28/33$, and $31/36$ DBR mirror layer pairs. (c) Experimentally measured maximum values of the $Q$ factor for the reference ($25/30$ and $28/33$ mirror pairs) and the adiabatic cavity designs ($25/30$ mirror pairs). (d) The visibility as a function of diameter $d_c$ is illustrated for the adiabatic (dashed curve) and reference design (full curve) for an oscillator strength of $f=10$. The onset of SC at $v=1/4$ is depicted using the dotted line.

Figure 3

(a) Strong QD ($X$)—cavity ($C$) coupling of a MP with $d_c=850\mathrm{nm}$ and $Q=13600$ via temperature tuning. Temperature dependent (b) linewidth and (c) peak position determined from (a).