Towards coherent polaritonic circuits operating at room temperature

TL;DR

The paper tackles the challenge of realizing coherent polaritonic circuits that operate at room temperature by enabling flexible, on-demand fabrication of polaritonic devices through Focused Ion Beam milling of a Rhodamine 3B SMILES organic microcavity. It demonstrates room-temperature polariton condensation and propagation in arbitrarily shaped waveguides, including rectangular and trapezoidal geometries, and validates the results with open-dissipative Gross-Pitaevskii simulations. The work reports device-level demonstrations such as a ring, Y-splitter, and Mach-Zehnder interferometer, illustrating the potential for integrated, room-temperature polaritonic circuits and highlighting avenues to overcome lifetime and heating-related limitations. Overall, this approach offers a versatile platform for designing complex coherent polariton devices on demand, paving the way for scalable room-temperature polaritonic circuitry.

Abstract

Polariton condensation is a potential system state for performing analog computations, given that it exhibits quantum behavior at macroscopic scales readily probed with low-cost optical methods. Current methods of fabricating devices in polariton microcavities largely involve patterning the devices via e-beam lithography before the cavity is completed, which offers less flexibility in device creation and reduces the maximum possible refractive index contrast. Moreover, the momentum and spatial distributions of the condensate are highly dependent on the host platform, and it has been difficult to preserve the desired behavior when modifying a given cavity. Here we introduce a method that addresses both of these challenges with the creation of polaritonic circuits of arbitrary forms etched via Focused Ion Beam into an organic microcavity based on Rhodamine 3B Perchlorate within a Small Molecule Ionic Isolation Lattices complex. We demonstrate room temperature condensation and propagation of polaritons in rectangular and trapezoidal waveguides by analyzing spatial and angle-resolved photoluminescence. We also discuss the blue-shifting and non-zero momentum of the condensate and show that it is strongly confined up to several higher energy levels. As an example, we report the spatial profiles of condensation in custom devices, such as a ring waveguide, a Y-splitter, and a Mach-Zehnder interferometer. This work represents a first step towards the realization of more complex, fully integrated, coherent polaritonic circuits operating at room temperature.

Figures (5)

• Figure 1: Cavity schematic and condensation profile. (a) Organic microcavity with active dye layer R3B-SMILES ($\sim$45 nm), bottom TiO$_2$-SiO$_2$ DBR, and top Ag mirror ($\sim$100 nm). Angle-resolved PL is shown before (b), at (c), and above (d) the condensation threshold. Corresponding real-space PL is shown in (e, f, g).
• Figure 2: Finite-$\vec{k}$ condensation in rectangular and trapezoidal waveguides. The FIB-patterned rectangular wire is depicted in (a) with SEM image inset. Angle-resolved PL along the short and long axes is shown in (b) and (c), respectively. Real-space PL is shown in (d). Corresponding images for the trapezoidal case are shown in (e) through (h). Both devices were excited at the center.
• Figure 3: Numerical simulations. The GPE in Eq. \ref{['eq:gpe']} is evolved until steady state is reached, then the wavefunction is time-integrated and plotted in real space and Fourier-transformed to momentum space. The transformation is taken along the long axis where applicable. Results are shown for the planar (row 1), rectangular waveguide (row 2), and trapezoidal waveguide (row 3) cases, where the two leftmost columns are excited below condensation threshold and the two rightmost columns are excited above. The dashed white parabolas in momentum-space simulations correspond to the geometric structure (free energy dispersion). The dashed white outlines in in real-space simulations correspond to device boundaries.
• Figure 4: Experimental real-space emission above threshold from several fabricated devices: ring (a), Y-splitter (b), and Mach-Zehnder interferometer (MZI) (c). The ring is excited with a broad ($\sim 10$ µm) laser spot, the Y-splitter with a tight ($\sim$ 2 µm) spot at the left node, and the MZI with a tight ($\sim 10$ µm) spot at the left arm.
• Figure 5: Schematic of experimental optical setup.