Kosuke Shibata

Control of Resonant Interaction between Electronic Ground and Excited States

We observe a magnetic Feshbach resonance in a collision between the ground and metastable states of two-electron atoms of ytterbium (Yb). We measure the on-site interaction of doublyoccupied sites of an atomic Mott insulator state in a three-dimensional optical lattice as a collisional frequency shift in a high-resolution laser spectroscopy. The observed spectra are well fitted by a simple theoretical formula, in which two particles with an s-wave contact interaction are confined in a harmonic trap. This analysis reveals a wide variation of the interaction with a resonance behavior around a magnetic field of about 1.1 Gauss for the energetically lowest magnetic sublevel of Yb, as well as around 360 mG for the energetically highest magnetic sublevel of Yb. The observed Feshbach resonance can only be induced by an anisotropic interatomic interaction. This novel scheme will open the door to a variety of study using two-electron atoms with tunable interaction.

A scalable quantum computer with ultranarrow optical transition of ultracold neutral atoms in an optical lattice

We propose a new quantum-computing scheme using ultracold neutral ytterbium atoms in an optical lattice, especially in a monolayer of three-dimensional optical lattice. The nuclear Zeeman sublevels define a qubit. This choice avoids the natural phase evolution due to the magnetic dipole interaction between qubits. The Zeeman sublevels with large magnetic moments in the long-lived metastable state are also exploited to address individual atoms and to construct a controlled-multiqubit gate. Estimated parameters required for this scheme show that this proposal is scalable and experimentally feasible.

Fictitious magnetic resonance by quasielectrostatic field

We propose a new kind of spin manipulation method using a fictitious magnetic field generated by a quasielectrostatic field. The method can be applicable to every atom with electron spins and has distinct advantages of small photon scattering rate and local addressability. By using a CO2 laser as a quasielectrostatic field, we have experimentally demonstrated the proposed method by observing the Rabi oscillation of the ground state hyperfine spin F=1 of the cold 87Rb atoms and the Bose–Einstein condensate.

Laser spectroscopic probing of coexisting superfluid and insulating states of an atomic Bose-Hubbard system

A system of ultracold atoms in an optical lattice has been regarded as an ideal quantum simulator for a Hubbard model with extremely high controllability of the system parameters. While making use of the controllability, a comprehensive measurement across the weakly to strongly interacting regimes in the Hubbard model to discuss the quantum many-body state is still limited. Here we observe a great change in the excitation energy spectra across the two regimes in an atomic Bose–Hubbard system by using a spectroscopic technique, which can resolve the site occupancy in the lattice. By quantitatively comparing the observed spectra and numerical simulations based on sum rule relations and a binary fluid treatment under a finite temperature Gutzwiller approximation, we show that the spectra reflect the coexistence of a delocalized superfluid state and a localized insulating state across the two regimes.

High-Sensitivity In situ Fluorescence Imaging of Ytterbium Atoms in a Two-Dimensional Optical Lattice with Dual Optical Molasses

We developed a dual molasses technique which enabled us to perform high-sensitivity in situ fluorescence imaging of ytterbium (Yb) atoms in a two-dimensional optical lattice prepared in a thin glass cell. This technique successfully combines two different kinds of optical molasses for Yb atoms, that is, the one using the 1S0–1P1 transition which provides high-resolution in the in situ fluorescence imaging and the other using the 1S0–3P1 transition for cooling the atoms in the optical lattice. We performed in situ imaging of 174Yb atoms and could observe a Moire pattern with a period of about 6 µm produced by the molasses beam with 556 nm and the optical lattice with 532 nm, which implies that the temperature was kept below the lattice depth during the fluorescence imaging. The number of photons per atom is estimated to be enough for single atom detection with our imaging system. This result is quite promising for the realization of an Yb quantum gas microscope.

Loading of atoms into an optical trap with high initial phase-space density

We report a method for loading cold atoms into an optical trap with high initial phase-space density (PSD). When the trap beam is overlapped with atoms in optical molasses of optimized parameters including large cooling beam detuning compared with conventional detuning used for a magneto-optical trap (MOT), more than

Excitation enhancement in electric multipole transitions near a nanoedge

3\ifmmode\times\else\texttimes\fi{}{10}^{6}

Formability of ultrafine-grained interstitial-free steel fabricated by accumulative roll-bonding and subsequent annealing

rubidium atoms with an initial temperature less than 20

Observation of long-lived van der Waals molecules in an optical lattice

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Optical magnetic resonance imaging with an ultra-narrow optical transition

are loaded into a single beam trap. The obtained maximum initial PSD is estimated to be