Electromechanics of Suspended Spiral Capacitors and Inductors

Most electromechanical devices are in two-dimensional metallic drums under high tensile stress, which causes increased mechanical frequency and quality factor. However, high mechanical frequencies lead to small zero-point displacements $x_{\rm zp}$, which limits the single-photon interaction rate $g_0$. For applications which demand large $g_0$, any design with increased $x_{\rm zp}$ is desirable. It is shown that a patterned drum by spiral shape can resolve this difficulty, which is obtained by a reduction of mechanical frequency while the motion mass is kept almost constant. An order of magnitude increase in $g_0$, and agreement between simulations and interferometric measurements is observed

CUBIT: Capacitive qUantum BIT

In this letter, it is proposed that cryogenic quantum bits can operate based on the nonlinearity due to the quantum capacitance of two-dimensional Dirac materials, and in particular graphene. The anharmonicity of a typical superconducting quantum bit is calculated, and the sensitivity of quantum bit frequency and anharmonicity with respect to temperature are found. Reasonable estimates reveal that a careful fabrication process can reveal expected properties, putting the context of quantum computing hardware into new perspectives.Comment: Published: 2 July 201

Third-order Optical Nonlinearity in Two-dimensional Transition Metal Dichalcogenides

We present a detailed calculation of the linear and nonlinear optical response of four types of monolayer Two-Dimensional (2D) Transition-Metal Dichalcogenides (TMDCs), having the formula $\textrm{MX}_2$ with M=Mo,W and X=S,Se. The calculations are based on 6-band tight-binding model of TMDCs, and then performing a semiclassical perturbation analysis of response functions. We numerically calculate the linear $\chi_{\mu\nu}^{(1)}(-\omega;\omega)$ and nonlinear surface susceptibility tensors $\chi_{\mu\nu\zeta\eta}^{(3)} (-\omega_\Sigma;\omega_r,\omega_s,\omega_t)$ with $\omega_\Sigma=\omega_r+\omega_s+\omega_t$. Both non-degenerate and degenerate cases are studied for third-harmonic generation and nonlinear refractive index, respectively. Computational results obtained \textit{with no external fitting parameters} are discussed regarding two recent reported experiments on ${\rm MoS}_2$, and thus we can confirm the extraordinarily strong optical nonlinearity of TMDCs. As a possible application, we demonstrate generation of a $\frac{\pi}{4}-$rotated squeezed state by means of nonlinear response of TMDCs, in a silica micro-disk resonator covered with the 2D material. Our proposed method will enable accurate calculations of nonlinear optical response, such as four-wave mixing and high-harmonic generation in 2D materials and their heterostructures, thus enabling study of novel functionalities of 2D photonic integrated circuits

Community-level Monitoring of HIV Spread

Health departments are using HIV data to monitor HIV growth in real time. The main purpose of this monitoring is to come up with policies for efficient allocation of medical resources. In order to achieve the efficient medical resources allocation, a method should be established for predicting where future transmissions of HIV will occur using the partial information of the transmission history. Validity of these predictions are of paramount importance as it affects the policy for allocation of medical resources. Indeed, the more accurate the prediction is, the more efficiently preventive care or other resources can be allocated to the network.The focus of this work is on community-level monitoring of HIV spread prevention. We have modeled the sexual network as communities of individuals and proposed community-level methods for prediction. Then, we have compared predictive power of the proposed methods in different settings of the network