Resolving the wave-vector in negative refractive media: The sign of Z\sqrt{Z}

We address the general issue of resolving the wave-vector in complex electromagnetic media including negative refractive media. This requires us to make a physical choice for the sign of a square-root imposed merely by conditions of causality. By considering the analytic behaviour of the wave-vector in the complex plane, it is shown that there are a total of eight physically distinct cases in the four quadrants of two Riemann sheets.Comment: 3 pages, 2 figures, RevTe

Sub-wavelength imaging with a left-handed material flat lens

We study numerically, by means of the pseudospectral time-domain method, the unique features of imaging by a flat lens made of a left-handed metamaterial that possesses the property of negative refraction. We confirm the earlier finding that a left-handed flat lens can provide near-perfect imaging of a point source and a pair of point sources with clear evidence of the sub-wavelength resolution. We illustrate the limitation of the resolution in the time-integrated image due to the presence of surface waves.Comment: 4 pages, RevTeX, 6 figures; added references and some discussio

Large Effects of Electric Fields on Atom-Molecule Collisions at Millikelvin Temperatures

Controlling interactions between cold molecules using external fields can elucidate the role of quantum mechanics in molecular collisions. We create a new experimental platform in which ultracold rubidium atoms and cold ammonia molecules are separately trapped by magnetic and electric fields and then combined to study collisions. We observe inelastic processes that are faster than expected from earlier field-free calculations. We use quantum scattering calculations to show that electric fields can have a major effect on collision outcomes, even in the absence of dipole-dipole interactions.Comment: 5 pages, 4 figure

High-energy-resolution molecular beams for cold collision studies

Stark deceleration allows for precise control over the velocity of a pulsed molecular beam and, by the nature of its limited phase-space acceptance, reduces the energy width of the decelerated packet. We describe an alternate method of operating a Stark decelerator that further reduces the energy spread over the standard method of operation. In this alternate mode of operation, we aggressively decelerate the molecular packet using a high phase angle. This technique brings the molecular packet to the desired velocity before it reaches the end of the decelerator; the remaining stages are then used to longitudinally and transversely guide the packet to the detection/interaction region. The result of the initial aggressive slowing is a reduction in the phase-space acceptance of the decelerator and thus a narrowing of the velocity spread of the molecular packet. In addition to the narrower energy spread, this method also results in a velocity spread that is nearly independent of the final velocity. Using the alternate deceleration technique, the energy resolution of molecular collision measurements can be improved considerably.Comment: 12 pages, 9 figure

Refraction of Electromagnetic Energy for Wave Packets Incident on a Negative Index Medium is Always Negative

We analyze refraction of electromagnetic wave packets on passing from an isotropic positive to an isotropic negative refractive index medium. We definitively show that in all cases the energy is always refracted negatively. For localized wave packets, the group refraction is also always negative.Comment: 5 pages, 3 figure

Observation of Quantum Effects in sub Kelvin Cold Reactions

There has been a long-standing quest to observe chemical reactions at low temperatures where reaction rates and pathways are governed by quantum mechanical effects. So far this field of Quantum Chemistry has been dominated by theory. The difficulty has been to realize in the laboratory low enough collisional velocities between neutral reactants, so that the quantum wave nature could be observed. We report here the first realization of merged neutral supersonic beams, and the observation of clear quantum effects in the resulting reactions. We observe orbiting resonances in the Penning ionization reaction of argon and molecular hydrogen with metastable helium leading to a sharp increase in the absolute reaction rate in the energy range corresponding to a few degrees kelvin down to 10 mK. Our method is widely applicable to many canonical chemical reactions, and will enable a breakthrough in the experimental study of Quantum Chemistry

Interferometry with Photon-Subtracted Thermal Light

We propose and implement a quantum procedure for enhancing the sensitivity with which one can determine the phase shift experienced by a weak light beam possessing thermal statistics in passing through an interferometer. Our procedure entails subtracting exactly one (which can be generalized to m) photons from the light field exiting an interferometer containing a phase-shifting element in one of its arms. As a consequence of the process of photon subtraction, and somewhat surprisingly, the mean photon number and signal-to-noise ratio of the resulting light field are thereby increased, leading to enhanced interferometry. This method can be used to increase measurement sensitivity in a variety of practical applications, including that of forming the image of an object illuminated only by weak thermal light

Nonlinear left-handed metamaterials

We analyze nonlinear properties of microstructured materials with negative refraction, the so-called left-handed metamaterials. We demonstrate that the hysteresis-type dependence of the magnetic permeability on the field intensity allows changing the material properties from left- to right-handed and back. Using the finite-difference time-domain simulations, we study wave transmission through the slab of nonlinear left-handed material, and predict existence of temporal solitons in such materials. We demonstrate also that nonlinear left-handed metamaterials can support both TE- and TM-polarized self-trapped localized beams, spatial electromagnetic solitons. Such solitons appear as single- and multi-hump beams, being either symmetric or antisymmetric, and they can exist due to the hysteresis-type magnetic nonlinearity and the effective domains of negative magnetic permeability.Comment: 7 pages, 8 figure

emiT: an apparatus to test time reversal invariance in polarized neutron decay

We describe an apparatus used to measure the triple-correlation term (\D \hat{\sigma}_n\cdot p_e\times p_\nu) in the beta-decay of polarized neutrons. The \D-coefficient is sensitive to possible violations of time reversal invariance. The detector has an octagonal symmetry that optimizes electron-proton coincidence rates and reduces systematic effects. A beam of longitudinally polarized cold neutrons passes through the detector chamber, where a small fraction beta-decay. The final-state protons are accelerated and focused onto arrays of cooled semiconductor diodes, while the coincident electrons are detected using panels of plastic scintillator. Details regarding the design and performance of the proton detectors, beta detectors and the electronics used in the data collection system are presented. The neutron beam characteristics, the spin-transport magnetic fields, and polarization measurements are also described.Comment: 15 pages, 13 figure