Chihhui Wu

Adiabatic elimination-based coupling control in densely packed subwavelength waveguides

The ability to control light propagation in photonic integrated circuits is at the foundation of modern light-based communication. However, the inherent crosstalk in densely packed waveguides and the lack of robust control of the coupling are a major roadblock toward ultra-high density photonic integrated circuits. As a result, the diffraction limit is often considered as the lower bound for ultra-dense silicon photonics circuits. Here we experimentally demonstrate an active control of the coupling between two closely packed waveguides via the interaction with a decoupled waveguide. This control scheme is analogous to the adiabatic elimination, a well-known procedure in atomic physics. This approach offers an attractive solution for ultra-dense integrated nanophotonics for light-based communications and integrated quantum computing.

Coherence-Driven Topological Transition in Quantum Metamaterials

We introduce and theoretically demonstrate a quantum metamaterial made of dense ultracold neutral atoms loaded into an inherently defect-free artificial crystal of light, immune to well-known critical challenges inevitable in conventional solid-state platforms. We demonstrate an all-optical control, on ultrafast time scales, over the photonic topological transition of the isofrequency contour from an open to closed topology at the same frequency. This atomic lattice quantum metamaterial enables a dynamic manipulation of the decay rate branching ratio of a probe quantum emitter by more than an order of magnitude. Our proposal may lead to practically lossless, tunable, and topologically reconfigurable quantum metamaterials, for single or few-photon-level applications as varied as quantum sensing, quantum information processing, and quantum simulations using metamaterials.

Metasurface-enabled quantum vacuum effects over macroscopic distances (Presentation Recording)

Quantum vacuum engineering is an active field of research. Here we use recent advances in the field of metasurface (2D-array of sub-wavelength scale nano-antennas) to construct an anisotropic quantum vacuum (AQV) in the vicinity of a quantum emitter located at some macroscopic distance from the metasurface. Such AQV can induce quantum interference among several atomic transitions, even when the transition dipole moment corresponding to the decay channels are orthogonal. Recently, there have been few theoretical proposal to use metamaterials to engineer the back-action. All these approaches, which works in the near field (few tens of nanometers from the surface), suffers from trapping an atom at these distance, surface interactions like quenching, Casimir force etc. Hence it’s pivotal to construct the back-action over macroscopic distance. We harness the polarization dependent response of a metasurface to engineer the back-action of the spontaneous emission from the atom to itself. We show strong anisotropy in the decay rate of a quantum emitter which is a manifestation of AQV. Engineering light-matter interaction over macroscopic distances opens new possibilities for long-range interaction between quantum emitters for quantum information processing, spin-optics/spintronics etc.

Interacting dark resonances with metallic nano-antennas

We theoretically investigate interacting dark resonances in a plasmonic meta-molecule comprising a bright nano-antenna coupled to cascaded dark elements. This structure enables efficient energy transfer and exhibits sub-natural spectral response analogous to the atomic counterpart.

Interacting Dark Resonance Physics with MetaMolecules

We investigate interacting dark resonance type physics with plasmonic metamolecule consisting of a multi-layered radiative atom coupled to cascaded subradiant atoms. In addition to sub-natural spectral response, these metamolecules also exhibits efficient intramolecular excitation transfer.

Sub-wavelength critical coupling for densely integrated nano-photonics

We experimentally demonstrate a novel approach for densely packed coupled waveguides, based on adiabatic elimination scheme, allowing control of the inherent coupling between waveguides. At the nano-scale, zero coupling between the waveguides can be achieved.