Albert Ryou

Synthetic Landau levels for photons

Synthetic photonic materials are an emerging platform for exploring the interface between microscopic quantum dynamics and macroscopic material properties. Photons experiencing a Lorentz force develop handedness, providing opportunities to study quantum Hall physics and topological quantum science. Here we present an experimental realization of a magnetic field for continuum photons. We trap optical photons in a multimode ring resonator to make a two-dimensional gas of massive bosons, and then employ a non-planar geometry to induce an image rotation on each round-trip. This results in photonic Coriolis/Lorentz and centrifugal forces and so realizes the Fock–Darwin Hamiltonian for photons in a magnetic field and harmonic trap. Using spatial- and energy-resolved spectroscopy, we track the resulting photonic eigenstates as radial trapping is reduced, finally observing a photonic Landau level at degeneracy. To circumvent the challenge of trap instability at the centrifugal limit, we constrain the photons to move on a cone. Spectroscopic probes demonstrate flat space (zero curvature) away from the cone tip. At the cone tip, we observe that spatial curvature increases the local density of states, and we measure fractional state number excess consistent with the Wen–Zee theory, providing an experimental test of this theory of electrons in both a magnetic field and curved space. This work opens the door to exploration of the interplay of geometry and topology, and in conjunction with Rydberg electromagnetically induced transparency, enables studies of photonic fractional quantum Hall fluids and direct detection of anyons.

Observation of Cavity Rydberg Polaritons

We demonstrate hybridization of optical cavity photons with atomic Rydberg excitations using electromagnetically induced transparency (EIT). The resulting dark state Rydberg polaritons exhibit a compressed frequency spectrum and enhanced lifetime indicating strong light-matter mixing. We study the coherence properties of cavity Rydberg polaritons and identify the generalized EIT linewidth for optical cavities. Strong collective coupling suppresses polariton losses due to inhomogeneous broadening, which we demonstrate by using different Rydberg levels with a range of polarizabilities. Our results point the way towards using cavity Rydberg polaritons as a platform for creating photonic quantum materials.

A strongly interacting polaritonic quantum dot

Polaritons are promising constituents of both synthetic quantum matter1 and quantum information processors2, whose properties emerge from their components: from light, polaritons draw fast dynamics and ease of transport; from matter, they inherit the ability to collide with one another. Cavity polaritons are particularly promising as they may be confined and subjected to synthetic magnetic fields controlled by cavity geometry3, and furthermore they benefit from increased robustness due to the cavity enhancement in light–matter coupling. Nonetheless, until now, cavity polaritons have operated only in a weakly interacting mean-field regime4,5. Here we demonstrate strong interactions between individual cavity polaritons enabled by employing highly excited Rydberg atoms as the matter component of the polaritons. We assemble a quantum dot composed of approximately 150 strongly interacting Rydberg-dressed 87Rb atoms in a cavity, and observe blockaded transport of photons through it. We further observe coherent photon tunnelling oscillations, demonstrating that the dot is zero-dimensional. This work establishes the cavity Rydberg polariton as a candidate qubit in a photonic information processor and, by employing multiple resonator modes as the spatial degrees of freedom of a photonic particle, the primary ingredient to form photonic quantum matter6.Cavity polaritons whose matter component is composed of highly excited Rydberg atoms are shown to act as a zero-dimensional quantum dot. Trapping 150 polaritons led to the observation of blockaded photon transport.

Photons and polaritons in a broken-time-reversal nonplanar resonator

The combination of twisted resonators with Rydberg polaritons is experimentally explored to simultaneously break inversion and time-reversal symmetries. Besides showing how to design a low-loss optical isolator, the work provides tools for the exploration of topological many-body physics from light.

Active cancellation of acoustical resonances with an FPGA FIR filter

We present a novel approach to enhancing the bandwidth of a feedback-controlled mechanical system by digitally canceling acoustical resonances (poles) and anti-resonances (zeros) in the open-loop response via an FPGA FIR filter. By performing a real-time convolution of the feedback error signal with an inverse filter, we can suppress arbitrarily many poles and zeros below 100 kHz, each with a linewidth down to 10 Hz. We demonstrate the efficacy of this technique by canceling the ten largest mechanical resonances and anti-resonances of a high-finesse optical resonator, thereby enhancing the unity gain frequency by more than an order of magnitude. This approach is applicable to a broad array of stabilization problems including optical resonators, external cavity diode lasers, and scanning tunneling microscopes and points the way to applying modern optimal control techniques to intricate linear acoustical systems.

Deterministic Positioning of Colloidal Quantum Dots on Silicon Nitride Nanobeam Cavities

We experimentally demonstrated deterministic positioning of solution processed colloidal quantum dots on a silicon nitride nanobeam resonator, with potential applications in nonlinear optics, multi-functional optical devices, and on-chip, solid-state quantum simulators.

Cavity integrated layered material devices

Layered materials have recently emerged as a promising class of optoelectronics material with high quantum efficiency of photo-emission, absorption and nonlinear optical properties. With significant progress in understanding the material science of these atomically thin materials, it is an opportune time to integrate these materials with existing optoelectronic platform to realize the full potential of the 2D materials. Integrating 2D material with nano-resonator could efficiently enhance the light-matter interaction and develop novel optoelectronics devices. Cavity-enhanced 2D material electro-optics modulation, nano-laser, and second order nonlinear devices has been demonstrated. In this paper, we report our recent progress on the cavity-integrated TMDC monolayer platform, including novel cavities for 2D material photonics and cavity nonlinear optics.