Single photon detection (SPD) has found increasingly important applications in many forefront areas of fundamental science and advanced engineering applications. The current SPD scheme has good sensitivity for photons in the high frequencies range (e.g., visible light). However, their sensitivity decreases drastically for low-frequency, low energy, microwave photons. As a result, the detection of single photons at this low frequency is highly prone to error from classical noise. In this talk we will present results from our recent studies of microwave response in a topological superconducting quantum interference device (SQUID) realized in Dirac semimetal Cd3As2. It is observed the effective temperature increases with the microwave power. This observation of large microwave response may pave the way for single photon detection at the microwave frequency in topological quantum materials.
The electromagnetic coupling of surface-plasmon-polariton (SPP) modes, which are localized around the surface of a conductive substrate, to quantum plasmons in a graphene sheet above the surface is investigated and their hybrid quantum-plasmon modes are analyzed. For a double-layer graphene structure, on the other hand, the interplay between the electromagnetic couplings of SPPs to each graphene sheet is explored. An effective- polarizability tensor for a combined system, including coupled double-layer graphene and conductive substrate, has been derived, which consists of the retarded nonlocal Coulomb interactions between electrons in different graphene sheets and the conductive substrate. Additionally, this calculated effective-scattering tensor can be used for constructing an effective-medium theory to study optical properties of inserted nanorods between the graphene sheets and metallic surface.
Properties of graphene can be tuned electrically and chemically, providing a promising system for application in
terahertz (THz) devices. Graphene response can be enhanced even further by means of coupling electromagnetic waves
into plasmon modes, frequency of which is controlled by geometrical parameters. To probe excitation of confined
plasmon modes and surface wave excitation, epitaxial graphene and its structures are investigated using THz near-field
microscopy. Detected near-field images suggest excitation of THz surface waves occurring at graphene edges, similar to
that observed at metallic edges, and excitation of confined plasmon modes. We will also discuss the impact of graphene
inhomogeneity on local THz transmission properties on the sub-wavelength scale.
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