Polariton condensation in an optically induced two-dimensional potential

We demonstrate experimentally the condensation of exciton polaritons through optical trapping. The nonresonant pump profile is shaped into a ring and projected to a high quality factor microcavity where it forms a two-dimensional repulsive optical potential originating from the interactions of polaritons with the excitonic reservoir. Increasing the population of particles in the trap eventually leads to the emergence of a confined polariton condensate that is spatially decoupled from the decoherence inducing reservoir, before any buildup of coherence on the excitation region. In a reference experiment, where the trapping mechanism is switched off by changing the excitation intensity profile, polariton condensation takes place for excitation densities more than two times higher and the resulting condensate is subject to much stronger dephasing and depletion processes.

Figure 1

Polariton trap over real-space excitation spot, displaying the trapping mechanism. Polaritons scattered to high-energy states leave the trap, while those scattered to low energy and momentum remain confined.

Figure 2

Single-mode exciton-polariton condensate in a ring-shaped trap. Emission images in real space below (a), at (b), and above threshold (c). The inset in (c) shows the interference fringes of the condensate. Red line in (c) is the condensate profile along the $x$ axis. Polariton condensation is clearly visible in the center of the ring and is separate from the excitation spot outlined by the emission in (a). (d)–(f) Dispersion images below (d), at (e), and above (f) threshold. (g) Same as (c) but with a logarithmic color scale showing that the condensate propagation beyond the trap is minimal.

Figure 3

Trapping potential and spatially resolved dispersions. (a), (b) Dispersion images below threshold ($P=0.2P_{th}$) from a $5-\mu \text{m}$-diameter spatially filtered region from the center of the ring (a) and from the rim (b). Energy profile of the central slice of the ring at threshold (c) and the extracted maxima of intensity along the $x$ axis for visualization of the trap profile (d). Points a and b correspond to (a) and (b) respectively.

Figure 4

Integrated intensity with increasing power density from the trapped condensate (open black circles) and from a Gaussian excitation (red circles) measured at $k=0\mu {\text{m}}^{-1}$ of the spatially filtered dispersions.

Figure 5

Linewidth and blueshift of polaritons from the center of the ring excitation (open black circles) and from a Gaussian excitation (red circles), measured at $k=0\mu {\text{m}}^{-1}$ of the spatially filtered dispersions. (a) Linewidth vs excitation power for polaritons at the center of the ring and a Gaussian excitation. (b) Energy shift of the two condensates vs threshold power. Lines are guides for the eyes.