Quantum-dot-induced phase shift in a pillar microcavity

We perform high-resolution reflection spectroscopy of a quantum dot resonantly coupled to a pillar microcavity. We show the change in reflectivity as the quantum dot is tuned through the cavity resonance and measure the quantum-dot-induced phase shift using an ultrastable interferometer. The macroscopic phase shift we measure could be extended to the study of charged quantum dot pillar microcavity systems, where it could be exploited to realize a high-efficiency spin photon interface for hybrid quantum information schemes.

Figure 1

(a) A schematic diagram of a 2.5-$\mu$m-diameter pillar with 33 (26) bottom (top) mirror pairs, containing a single QD. (b) Scanning electron microscope (SEM) image of a pillar microcavity etched using electron beam lithography. (c) Schematic diagram of the setup used to measure the phase shift caused by a single QD coupled to a pillar microcavity. BS1 and BS2 are both 50:50 nonpolarizing beam splitters; the Soleil-Babinet compensator allows us to initialize the setup with $\sin \varphi =0$.

Figure 2

(a) PL data for the micropillar sample. The QD can be seen on the higher-energy side (right) of the cavity mode at low temperatures. As the temperature is increased the QD tunes through the cavity; when the two are resonantly coupled (21 K) the spectra are unclear. (b) The reflectivity of the QD micropillar around 21 K where the PL signal is unresolved. There appears to be a double peak structure when the QD and cavity are resonantly coupled. The red lines represent fits to Eq. (1). The dashed lines represent the predicted positions of the QD and cavity mode based on the PL data. There is in general a good agreement between the predicted and measured positions of the features; however, at lower temperatures (below 21 K) the QD signal is weak and another QD near the cavity seems to interfere with the signal. (c) The corresponding phase features from Eq. (1), with solid lines representing fits using the values obtained from the reflectivity measurement.

Figure 3

(a) The reflected amplitude for a nonresonantly coupled QD cavity $r_c=|r(\omega )|{}_c^2$ at 22 K (QD detuning ${\omega }_d-{\omega }_c\approx 25\pm 2\hspace{0.5em}\mu$eV), and a cavity with a resonantly coupled QD $r_d=|r(\omega )|{}_2^d$ at 21 K. (b) The corresponding phase shifts for an (effectively) empty cavity ${\varphi }_c$ and a cavity with a resonantly coupled QD ${\varphi }_d$, and the conditional phase shift ${\varphi }_d-{\varphi }_c$. The dashed lines represent the line of 0 phase shift for each plot.

Figure 4

(a) Scan of the bare cavity mode using a $100\times$ objective lens with $\text{NA}=0.7$. The red line represents a fit to Eq. (1), where ${\kappa }_s=22\pm 2\hspace{0.5em}\mu$eV and $\kappa =3\pm 0.2\hspace{0.5em}\mu$eV. (b) Simulated data for the phase shift that would be obtained from an empty cavity ${\varphi }_c$, a resonantly coupled QD-cavity ${\varphi }_d$, and the conditional phase shift ${\varphi }_d-{\varphi }_c$, based on the improved mode matching seen in (a).