Fujio Shimizu

Persistent Supercurrent Atom Chip

Rubidium-87 atoms are trapped in an Ioffe-Pritchard potential generated with a persistent supercurrent that flows in a loop circuit patterned on a sapphire surface. The superconducting circuit is a closed loop made of a 100 microm wide molecular-beam epitaxy-grown MgB2 stripe carrying a supercurrent of 2.5 A. To control the supercurrent in the stripe, an on-chip thermal switch operated by a focused argon-ion laser is developed. The switch operates as an on/off switch of the supercurrent or as a device to set the current to a specific value with the aid of an external magnetic field. The current can be set even without an external source if the change is in the decreasing direction.

Giant Quantum Reflection of Neon Atoms from a Ridged Silicon Surface

The specular reflectivity of slow, metastable neon atoms from a silicon surface was found to increase markedly when the flat surface was replaced by a grating structure with parallel narrow ridges. For a surface with ridges that have a sufficiently narrow top, the reflectivity was found to increase more than two orders of magnitude at the incident angle θ of 10 mRad from the surface. The slope of the reflectivity vs θ near zero was found to be nearly an order of magnitude smaller than that of a flat surface. A grating with 6.5% efficiency for the first-order diffraction was fabricated by using the ridged surface structure.

Study of the Intensity Dependent Refractive Index in Liquids

The susceptibilities for the optical Kerr effect which was induced by the Q -switched laser field were measured in several liquids. When the laser beam is linearly polarized, little dispersion is observed in the difference n // - n ⊥ of the refractive indexes between parallel and perpendicular polarizations for the wave length range of 5200 A∼4200 A. When the laser beam is circularly polarized, the difference between right and left circular polarizations is about 1/400 of n // - n ⊥ for CS 2 . Those values for C 6 H 6 , CCl 4 and acetone are found to be smaller than the present limits of experimental accuracies. Theoretical considerations for the susceptibility of fourth rank tensor which contributes to the change in the complex refractive index induced by the strong optical field are also presented.

Atomic-matter-wave scanner

We report on the experimental realization of an atom optical device that allows scanning of an atomic beam with a controllable diffraction grating for atomic waves. We used a time-modulated evanescent wave field above a glass surface to diffract a continuous beam of metastable neon atoms at grazing incidence. The diffraction angles and efficiencies were controlled by the frequency and form of modulation, respectively. With an optimized shape, obtained from a numerical simulation, we were able to transfer more than 50% of the atoms into the first order beam, which we were able to move over a range of 8 mrad.

Atom manipulation using atomic de Broglie waves

We demonstrated several techniques to manipulate laser-cooled Ne atoms interferometrically by using a silicon nitride film with holes and electrodes. Laser-cooled neon atoms passed through a computer-generated through-hole binary hologram and generated an atomic image on a substrate. The hologram can be designed to provide a spherical phase correction, where the reconstructed pattern is focused on the substrate at a finite distance from the hologram. A resolving power over 150 was achieved. This type of holographic manipulation can be further developed extended to reconstruct gray-scale patterns, which can be used to deposit a relief-like 3D atomic pattern on surfaces. Unlike photons, atoms interact with electric, magnetic, and optical fields. This enables a holographic atomic-wave manipulation to perform functions that are difficult for a light wave. We also demonstrated using a Stark shift induced by an external electric field to switch and modify atomic patterns in real time. We also discuss how to develop reflective interferometric devices by using quantum reflection.

Quantum reflection of cold atoms

The coherent reflection of ultra-cold neon and helium atoms from silicon surfaces and surface structures is measured and analyzed. When the silicon surface is flat, the reflection is explained by the quantum reflection due to van der Waals attractive potential near the silicon surface. When the silicon surface is modified to form a grating structure, the reflectivity increases dramatically. For certain ranges of surface structure parameters, the reflection may be interpreted as a coherent summation of Fresnel diffraction of the atomic wave at the ridges of the grating structure.

Atom optics using solid surfaces and surface structures

A cold beam of metastable helium atoms is used to study the quantum reflection on solid surfaces and surface structures. The results are applied to construct reflection-type atom optical devices, such as diffraction gratings. Simple solid surfaces and surface structures offer several advantages as precision reflectors for atomic waves: They are inherently stable, accurate and nearly dispersionless, and in addition they can be made very large. The reflection is coherent as long as the de Broglie wavelength is large compared to the surface roughness, which is easily realized with polished surfaces and laser-cooled atoms. We report here on new experiments with laser-cooled He* atoms to investigate atom-surface interactions and to construct atom optical components based on micro-scale surface structures. A cross-sectional view of the experimental setup is shown in Fig. 1. Metastable helium atoms in the 2S1 state are trapped and cooled in a magneto-optical trap using the transition at 1083 nm. The atoms are release from the trap by illuminating the cloud of trapped atoms from the top with short pulses of a focused, resonant laser beam. The sample surfaces are placed in the atomic beam line below the trap at grazing incident angle. The pattern of scattered atoms is detected on a micro-channel plate detector, which provides a spatial resolution below 100μm. The velocity of the atoms is adjusted with the length and intensity of the releasing pulses, and the detector is gated to detect only atoms that arrive within a short, chosen interval. A measurement of the reflectivity of He* on a flat, polished silicon surface as a function of the normal incident velocity component between 3 and 30 cm/s is shown in Fig. 2. On a flat solid surface the reflection can be explained as the quantum reflection at the steep slope of the van der Waals attraction near the surface. We compare our result to a calculation of the van der Waals surface potential using the frequencydependent dipole polarizability of He* and the dielectric properties of silicon, and analyze the influence of doping and of an oxide surface layer on the potential shape. The dashed line represents the reflectivity expected on a perfect conductor, the solid line on undoped silicon and the dashed line on undoped silicon covered with a 100nm-thick oxide layer. Although the silicon sample is doped and has an electrical conductivity of 0.02 (Ωm), the experimental data clearly deviate from the reflectivity expected on a conductor. For a conductivity below about 100 (Ωm) and a distance of several hundred nm, the presence of free charges has almost no influence on the potential shape. An oxide layer has an appreciable effect on the reflectivity only when the layer thickness exceeds about 20 nm. QTuG2-2

Reflective Double Slit Atom Interferometer

A double slit atom interferometer with a reflective double slit that is formed on a flat silicon surface is demonstrated. The result shows that quantum reflection is a promising mechanism to construct stable highly accurate atom-optical devices.

Imaging of atomic beam with the electrostatic atom lens

In the field of atom optics, there has been much interests in developing components such as lenses, mirrors, beam splitters and waveguides to manipulate neutral atoms. Especially many clever methods to focus neutral atoms have been developed. The lenses have been constructed using the static electrical and magnetic fields, Fresnel zone plates, and radiation pressure forces. Before the laser cooling and trapping techniques were invented, the electrostatic fields could not be used for manipulating neutral atoms because of its weak interaction energy with atoms. After the cold atoms were available, it has been possible to manipulate atoms with weak electrostatic interaction energy. We developed an atom lens system using electrostatic fields.

Atom interferometers and atom holography

Various techniques of atom manipulation with a binary hologram are discussed and demonstrated experimentally. An atomic beam of metastable neon in the 1s3 state and a SiN thin film with holes that expresses the transmission function of the hologram are used to demonstrate this technique. The gray-scale holography of atoms is demonstrated for the first time. Other possibilities of holographic manipulation of atoms are also discussed.