Zhiyuan Fan

Quantum entanglement in the motion of macroscopic objects is of significance to both fundamental studies and quantum technologies. Here we show how to entangle the mechanical vibration modes of two massive ferrimagnets that are placed in the same microwave cavity. Each ferrimagnet supports a magnon mode and a low-frequency vibration mode coupled by the magnetostrictive force. The two magnon modes are, respectively, coupled to the microwave cavity by the magnetic dipole interaction. We first generate a stationary nonlocal entangled state between the vibration mode of the ferrimagnet-1 and the magnon mode of the ferrimagnet-2. This is realized by continuously driving the ferrimagnet-1 with a strong red-detuned microwave field and the entanglement is achieved by exploiting the magnomechanical parametric down-conversion and the cavity-magnon state-swap interaction. We then switch off the pump on the ferrimagnet-1 and, simultaneously, turn on a red-detuned pulsed drive on the ferrimagnet-2. The latter drive is used to activate the magnomechanical beamsplitter interaction, which swaps the magnonic and mechanical states of the ferrimagnet-2. Consequently, the previously generated phonon-magnon entanglement is transferred to the mechanical modes of two ferrimagnets. The work provides a scheme to prepare entangled states of mechanical motion of two massive objects, which may find applications in various studies exploiting macroscopic entangled states.

Organic-inorganic hybrid metal halide perovskites (MHPs) have attracted tremendous attention for optoelectronic applications. The long photocarrier lifetime and moderate carrier mobility have been proposed as results of the large polaron formation in MHPs. However, it is challenging to measure the effective mass and carrier scattering parameters of the photogenerated large polarons in the ultrafast carrier recombination dynamics. Here, we show, in a one-step spectroscopic method, that the optical-pump and terahertz-electromagnetic probe (OPTP) technique allows us to access the nature of interplay of photoexcited unbound charge carriers and optical phonons in polycrystalline CH₃NH₃PbI₃ (MAPbI₃) of about 10 μm grain size. Firstly, we demonstrate a direct spectral evidence of the large polarons in polycrystalline MAPbI₃. Using the Drude–Smith–Lorentz model along with the Frӧhlich-type electron-phonon (e-ph) coupling, we determine the effective mass and scattering parameters of photogenerated polaronic carriers. We discover that the resulting moderate polaronic carrier mobility is mainly influenced by the enhanced carrier scattering, rather than the polaron mass enhancement. While, the formation of large polarons in MAPbI₃ polycrystalline grains results in a long charge carrier lifetime at room temperature. Our results provide crucial information about the photo-physics of MAPbI₃ and are indispensable for optoelectronic device development with better performance.

A tunable polarization state converter/synthesizer based on an anisotropic resonant metasurface (ARM) is demonstrated. The semiconductor-based metasurface is designed to have a thermo-optically actuated optical mode excited by an incident free-space optical field. A diversity of output polarization states is reversibly generated and controlled by the temperature-dependent phase retardance between the two principal linear polarization states. The effect of metasurface inhomogeneity on the range of achievable polarization states is discussed and quantified, and the potential routes to “perfect” efficiency are suggested. By virtue of having a thickness of a fraction of the operating wavelength, ARMs represent a novel class of tunable polarization states’ generating devices poised to find use in free-space communications and other applications.

The metasurface under study was engineered to enhance the local fields, which is crucial for the efficiency of the nonlinear photon conversion. In our design of the metasurface, we make use of high-Q collective resonances common to regular arrays of semiconductor particles, as verified by MIR FTIR spectroscopy. We facricate 600-nm-thick silicon rectangles situated on a sapphire substrate. In order to demonstrate power- dependent blue-shifting of THG, we focused a 200 ± 30 fs MIR laser pulses centered at λ = 3.62 μm, with a variable non-destructive fluence in the 1

A periodic metagate is designed on top of a boron nitride‐graphene heterostructure to modulate the local carrier density distribution on the monolayer graphene. This causes the bandgaps of graphene surface plasmon polaritons to emerge because of either the interaction between the plasmon modes, which are mediated by the varying local carrier densities, or their interaction with the metal gates. Using the example of a double‐gate graphene device, we discuss the tunable band properties of graphene plasmons due to the competition between these two mechanisms. Because of this, a bandgap inversion, which results in a Zak phase switching, can be realized through electrostatic gating. Here we also show that an anisotropic plasmonic topological edge state exists at the interface between two graphene gratings of different Zak phases. While the orientation of the dipole moments can differentiate the band topologies of each graphene grating, the angle of radiation remains a tunable property. This may serve as a stepping stone toward active control of the band structures of surface plasmons for potential applications in optical communication, wave steering, or sensing.

We propose a electrically tunable plasmonic platform for valleytronics—a mono-layer graphene with its chemical potential controlled by a periodically structured metagate. Topologically protected edge states show reflection-free propagation around sharp corners.

We design and experimentally demonstrate a bianisotropic all-silicon metasurface that shows a near unity diffraction efficiency by implementing a 4-mode interference in the far field. Resonant and non-resonant properties of these modes and respective interaction can be mediated by sculpting meta-atoms of the metasurface.

We report an experimental observation of photon acceleration in mid-infrared semiconductor metasurfaces manifested as blue-shifted third harmonic generation at carrier frequencies of up to 3.1ω.

A large number of inorganic materials form crystals with chiral symmetry groups. Enantioselectively synthesizing nanostructures of such materials should lead to interesting optical activity effects. Here we report the synthesis of colloidal tellurium and selenium nanostructures using thiolated chiral biomolecules. The synthesis conditions are tuned to obtain tellurium nanostructures with chiral shapes and large optical activity. These nanostructures exhibit visible optical and chiroptical responses that shift with size and are successfully simulated by an electromagnetic model. The model shows that they behave as chiral optical resonators. The chiral tellurium nanostructures are transformed into chiral gold and silver telluride nanostructures with very large chiroptical activity, demonstrating a simple colloidal chemistry path to chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to interactions of chiral (bio)molecules with chiral inorganic surfaces, with relevance to asymmetric catalysis, chiral crystallization and the evolution of homochirality in biomolecules.