Michael Rosenblit

Single-atom detection using whispering-gallery modes of microdisk resonators

We investigate the possibility of using dielectric microdisk resonators for the optical detection of single atoms trapped and cooled in magnetic microtraps near the surface of a substrate. The bound and evanescent fields of optical whispering-gallery modes are calculated and the coupling to straight waveguides is investigated using finite-difference time domain solutions of Maxwells equations. Results are compared with semianalytical solutions based on coupled mode theory. We discuss atom detection efficiencies and the feasibility of nondestructive measurements in such a system depending on key parameters such as disk size, disk-waveguide coupling, and scattering losses.

Electron bubbles in helium clusters. I. Structure and energetics

In this paper we present a theoretical study of the structure, energetics, potential energy surfaces, and energetic stability of excess electron bubbles in ((4)He)(N) (N=6500-10(6)) clusters. The subsystem of the helium atoms was treated by the density functional method. The density profile was specified by a void (i.e., an empty bubble) at the cluster center, a rising profile towards a constant interior value (described by a power exponential), and a decreasing profile near the cluster surface (described in terms of a Gudermannian function). The cluster surface density profile width (approximately 6 A) weakly depends on the bubble radius R(b), while the interior surface profile widths (approximately 4-8 A) increase with increasing R(b). The cluster deformation energy E(d) accompanying the bubble formation originates from the bubble surface energy, the exterior cluster surface energy change, and the energy increase due to intracluster density changes, with the latter term providing the dominant contribution for N=6500-2 x 10(5). The excess electron energy E(e) was calculated at a fixed nuclear configuration using a pseudopotential method, with an effective (nonlocal) potential, which incorporates repulsion and polarization effects. Concurrently, the energy V(0) of the quasi-free-electron within the deformed cluster was calculated. The total electron bubble energies E(t)=E(e)+E(d), which represent the energetic configurational diagrams of E(t) vs R(b) (at fixed N), provide the equilibrium bubble radii R(b) (c) and the corresponding total equilibrium energies E(t) (e), with E(t) (e)(R(e)) decreasing (increasing) with increasing N (i.e., at N=6500, R(e)=13.5 A and E(t) (e)=0.86 eV, while at N=1.8 x 10(5), R(e)=16.6 A and E(t) (e)=0.39 eV). The cluster size dependence of the energy gap (V(0)-E(t) (e)) allows for the estimate of the minimal ((4)He)(N) cluster size of N approximately 5200 for which the electron bubble is energetically stable.

Simultaneous optical trapping and detection of atoms by microdisk resonators

We propose a scheme for simultaneously trapping and detecting single atoms near the surface of a substrate using whispering gallery modes of a microdisk resonator. For efficient atom-mode coupling, the atom should be placed within approximately 150nm from the disk. We show that a combination of red and blue detuned modes can form an optical trap at such distances while the backaction of the atom on the field modes can simultaneously be used for atom detection. We investigate these trapping potentials including van-der-Waals and Casimir-Polder forces and discuss corresponding atom detection efficiencies, depending on a variety of system parameters. Finally, we analyze the feasibility of nondestructive detection.

Electron bubbles in helium clusters. II. Probing superfluidity

In this paper we present calculations of electron tunneling times from the ground electronic state of excess electron bubbles in ((4)He)(N) clusters (N=6500-10(7), cluster radius R=41.5-478 A), where the equilibrium bubble radius varies in the range R(b)=13.5-17.0 A. For the bubble center located at a radial distance d from the cluster surface, the tunneling transition probability was expressed as A(0)phi(d,R)exp(-betad), where beta approximately 1 A(-1) is the exponential parameter, A(0) is the preexponential factor for the bubble located at the cluster center, and phi(d,R) is a correction factor which accounts for cluster curvature effects. Electron tunneling dynamics is grossly affected by the distinct mode of motion of the electron bubble in the image potential within the cluster, which is dissipative (i.e., tau(D)>tau(0)) in superfluid ((4)He)(N) clusters, where tau(D) is the bubble motional damping time (tau(D) approximately 4 x 10(-12) s for normal fluid clusters and tau(D) approximately 10 s for superfluid clusters), while tau(0) approximately 10(-9)-10(-10) s is the bubble oscillatory time. Exceedingly long tunneling lifetimes, which cannot be experimentally observed, are manifested from bubbles damped to the center of the normal fluid cluster, while for superfluid clusters electron tunneling occurs from bubbles located in the vicinity of the initial distance d near the cluster boundary. Model calculations of the cluster size dependence of the electron tunneling time (for a fixed value of d=38-39 A), with lifetimes increasing in the range of 10(-3)-0.3 s for N=10(4)-10(7), account well for the experimental data [M. Farnik and J. P. Toennies, J. Chem. Phys. 118, 4176 (2003)], manifesting cluster curvature effects on electron tunneling dynamics. The minimal cluster size for the dynamic stability of the bubble was estimated to be N=3800, which represents the threshold cluster size for which the excess electron bubble in ((4)He)(N) (-) clusters is amenable to experimental observation.

EXCESS ELECTRON SURFACE STATES ON HELIUM CLUSTERS

In this paper we report on quantum mechanical calculations for the ground and the excited electronic surface states of an excess electron on (He)N clusters (N=3.5×105–6×1023), exploring the cluster size dependence of the excess electron localization and the bridging between the properties of the electron on cluster microsurfaces and on flat macrosurfaces. Representing the e‐(He)N potential by a short‐range repulsive model potential or by a pseudopotential, together with a long‐range attractive dielectric image potential, we have shown that the electronic energies are relatively insensitive (i.e., within 20% for N=106 and within 6% for N≥107) to the details of the short‐range repulsive interactions. The model potential results in a ‘‘critical’’ radius R(1,0)c=148 A with a number of constituents N(1,0)c=3.0×105 for electron localization in the ground n=1, l=0 electronic state, while with a further increase of the cluster radius R above R(1,0)c, higher n,l states become localized at cluster radii R(n,l)c, wi...

Excess electron states on the microsurfaces of Ne and H2 clusters

In this paper we report on the ground and excited electronic states of localized excess electron surface states of (Ne)−N (N=1.1×104–6×1023) and (H2)−N (N=4.6×103–6×1023) clusters. We used an electron‐cluster model potential, which consists of a short‐range repulsive interaction with a strength V0 [with a lower limit V0 (≳0) corresponding to the energy of the quasifree electron in the macroscopic condensed material], and a long‐range attractive polarization potential, to explore cluster size effects on the energetics and on the charge distribution of these excess electron clusters. The onset of the cluster size for excess electron localization in the ground (n=1, l=0) electronic state was inferred from a near‐threshold scaling analysis, being characterized by a ‘‘critical’’ cluster radius R(1,0)c≂2(1−Q)a0/Q, where Q=(e−1)/4(e+1) is the effective cluster charge (for the cluster dielectric constant e), R(1,0)c=39 A for Ne(s), R(1,0)c=46 A for Ne(l), R(1,0)c=35 A for H2(s) and R(1,0)c=41 A for H2(l), where...

Optical solver of combinatorial problems: nanotechnological approach

We present an optical computing system to solve NP-hard problems. As nano-optical computing is a promising venue for the next generation of computers performing parallel computations, we investigate the application of submicron, or even subwavelength, computing device designs. The system utilizes a setup of exponential sized masks with exponential space complexity produced in polynomial time preprocessing. The masks are later used to solve the problem in polynomial time. The size of the masks is reduced to nanoscaled density. Simulations were done to choose a proper design, and actual implementations show the feasibility of such a system.

In-vivo energy harvesting nano robots

Biological collaborative systems behavior is fascinating, urging researchers to mimic their behavior through programmable matters. These matters constitute a particle system, wherein the particles bind with their neighbors to swarm and navigate. Caterpillar swarm inspired particle system involves layered architecture with a predefined number of layers. Through this work, a coordinated layered particle system inspired by caterpillar swarms is discussed. We first propose a novel design for producible nano-particles that uses electrodes to harvest electricity from the blood serum, energy that can be later used for swarming, inter/outer communication, coordination, sensing and acting according to an instructing program. The benefit of moving and acting in a swarm is demonstrated by a design of telescopic movement in pipes (e.g., blood vessels), wherein each layer uses the accumulated speed of all layers below and moves faster, thus mimicking the faster motion of a caterpillar swarm.

Nanotechnology based optical solution for NP-hard problems

We present a design for a micro optical architecture for solving instances of NP-hard problems, using nano-technology. The architecture is using pre-processed masks to block some of the light propagating through them. We demonstrate how such a device could be used to solve instances of Hamiltoniancycle and the Permanent problems.

Design of microcavity resonators for single-atom detection

Whispering gallery modes of a microdisk resonator are useful for the optical detection of single rubidium and cesium atoms near the surface of a substrate. Light is coupled into two high-Q whispering-gallery modes of the disk which can provide attractive and/or repulsive potentials, respectively, via their evanescent fields. The sum potential, including van der Waals/Casimir-Polder surface forces, may be tuned to exhibit a minimum at distances on the order of 100 nm from the disk surface. Simultaneously optically trapping and detecting is possible, with the back-action of an atom held in this trap on the light fields being suffciently strong to provide a measurable effect. Atom trapping and detection depend on a variety of system parameters and experimental realizations differ for different atoms.