RIS-Assisted Integrated Sensing and Backscatter Communications for Future IoT Networks

Reconfigurable intelligent surface (RIS), by intelligently manipulating the incident waveform, offers a spectral and energy efficient capability for improving sensing and communication performance. In this article, we introduce a novel concept of RIS-assisted integrated sensing and backscatter communication (ISABC) system, by introducing RIS as either helper or transceiver to resolve the energy constraint of devices in internet of things (IoT) network and enable non line-of-sight (NLoS) sensing. We first introduce the RIS-assisted ISABC framework, including the system architecture and realization of RIS. Three potential applications are then discussed, with the analysis on their requirements. The research on several critical techniques for the RIS-assisted ISABC system is then discussed. Finally, we provide our vision of the challenges and future research directions to facilitate the development of the RIS-assisted ISABC systems

Temporal Quantum Control with Graphene

We introduce a novel strategy for controlling the temporal evolution of a quantum system at the nanoscale. Our method relies on the use of graphene plasmons, which can be electrically tuned in frequency by external gates. Quantum emitters (e.g., quantum dots) placed in the vicinity of a graphene nanostructure are subject to the strong interaction with the plasmons of this material, thus undergoing time variations in their mutual interaction and quantum evolution that are dictated by the externally applied gating voltages. This scheme opens a new path towards the realization of quantum-optics devices in the robust solid-state environment of graphene.Comment: 5 pages, 2 figure

Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators

Plasmons in graphene nanoresonators have many potential applications in photonics and optoelectronics, including room-temperature infrared and terahertz photodetectors, sensors, reflect arrays or modulators1, 2, 3, 4, 5, 6, 7. The development of efficient devices will critically depend on precise knowledge and control of the plasmonic modes. Here, we use near-field microscopy8, 9, 10, 11 between λ0 = 10–12 μm to excite and image plasmons in tailored disk and rectangular graphene nanoresonators, and observe a rich variety of coexisting Fabry–Perot modes. Disentangling them by a theoretical analysis allows the identification of sheet and edge plasmons, the latter exhibiting mode volumes as small as 10−8λ03. By measuring the dispersion of the edge plasmons we corroborate their superior confinement compared with sheet plasmons, which among others could be applied for efficient 1D coupling of quantum emitters12. Our understanding of graphene plasmon images is a key to unprecedented in-depth analysis and verification of plasmonic functionalities in future flatland technologies.Peer ReviewedPostprint (author's final draft

Imbalanced superfluid state in an annular disk

The imbalanced superfluid state of spin-1/2 fermions with s-wave pairing is numerically studied by solving the Bogoliubov-de-Gennes equation at zero temperature in an annular disk geometry with narrow radial width. Two distinct types of systems are considered. The first case may be relevant to heavy fermion superconductors, where magnetic field causes spin imbalance via Zeeman interaction and the system is studied in a grand canonical ensemble. As the magnetic field increases, the system is transformed from the uniform superfluid state to the Fulde-Ferrell-Larkin-Ovchinnikov state, and finally to the spin polarized normal state. The second case may be relevant to cold fermionic systems, where the numbers of fermions of each species are fixed as in a canonical ensemble. In this case, the groundstate depends on the pairing strength. For weak pairing, the order parameter exhibits a periodic domain wall lattice pattern with a localized spin distribution at low spin imbalance, and a sinusoidally modulated pattern with extended spin distribution at high spin imbalance. For strong pairing, the phase separation between superfluid state and polarized normal state is found to be more preferable, while the increase of spin imbalance simply changes the ratio between them.Comment: 8 pages, 10 figures. Final version with references added and discussion on Sarma state remove

Poincar\'e gauge theory with even and odd parity dynamic connection modes: isotropic Bianchi cosmological models

The Poincar\'e gauge theory of gravity has a metric compatible connection with independent dynamics that is reflected in the torsion and curvature. The theory allows two good propagating spin-0 modes. Dynamical investigations using a simple expanding cosmological model found that the oscillation of the 0$^+$ mode could account for an accelerating expansion similar to that presently observed. The model has been extended to include a $0^{-}$ mode and more recently cross parity couplings. We investigate the dynamics of this model in a situation which is simple, non-trivial, and yet may give physically interesting results that might be observable. We consider homogeneous cosmologies, more specifically, isotropic Bianchi class A models. We find an effective Lagrangian for our dynamical system, a system of first order equations, and present some typical dynamical evolution.Comment: 8 pages, 1 figures, submitted to IARD 2010 Conference Proceedings in {\em Journal of Physics: Conference Series}, eds. L. Horwitz and M. Land (2011

Subdiffractional focusing and guiding of polaritonic rays in a natural hyperbolic material

Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. In such materials light propagation is unusual, leading to novel and often non-intuitive optical phenomena. Here we report infrared nano-imaging experiments demonstrating that crystals of hexagonal boron nitride (hBN), a natural mid-infrared hyperbolic material, can act as a "hyper-focusing lens" and as a multi-mode waveguide. The lensing is manifested by subdiffractional focusing of phonon-polaritons launched by metallic disks underneath the hBN crystal. The waveguiding is revealed through the modal analysis of the periodic patterns observed around such launchers and near the sample edges. Our work opens new opportunities for anisotropic layered insulators in infrared nanophotonics complementing and potentially surpassing concurrent artificial hyperbolic materials with lower losses and higher optical localization.Comment: 25 pages, 5 figure

Resonant Visible Light Modulation with Graphene

Fast modulation and switching of light at visible and near-infrared (vis-NIR) frequencies is of utmost importance for optical signal processing and sensing technologies. No fundamental limit appears to prevent us from designing wavelength-sized devices capable of controlling the light phase and intensity at gigaherts (and even terahertz) speeds in those spectral ranges. However, this problem remains largely unsolved, despite recent advances in the use of quantum wells and phase-change materials for that purpose. Here, we explore an alternative solution based upon the remarkable electro-optical properties of graphene. In particular, we predict unity-order changes in the transmission and absorption of vis-NIR light produced upon electrical doping of graphene sheets coupled to realistically engineered optical cavities. The light intensity is enhanced at the graphene plane, and so is its absorption, which can be switched and modulated via Pauli blocking through varying the level of doping. Specifically, we explore dielectric planar cavities operating under either tunneling or Fabry-Perot resonant transmission conditions, as well as Mie modes in silicon nanospheres and lattice resonances in metal particle arrays. Our simulations reveal absolute variations in transmission exceeding 90% as well as an extinction ratio >15 dB with small insertion losses using feasible material parameters, thus supporting the application of graphene in fast electro-optics at vis-NIR frequencies.Comment: 17 pages, 13 figures, 54 reference

The Origin of Separable States and Separability Criteria from Entanglement-breaking Channels

In this paper, we show that an arbitrary separable state can be the output of a certain entanglement-breaking channel corresponding exactly to the input of a maximally entangled state. A necessary and sufficient separability criterion and some sufficient separability criteria from entanglement-breaking channels are given.Comment: EBCs with trace-preserving and EBCs without trace-preserving are separately discusse