柴田 康介

We demonstrated high-sensitivity optical spectral imaging of a single layer of a quantum gas of ytterbium atoms in a two-dimensional optical lattice using the ultranarrow S-1(0)-P-3(2) transition. We successfully obtained a set of excitation-frequency-dependent fluorescence images with an excitation laser of the linewidth of 1 kHz (FWHM), and the overall features were well explained by considering the inhomogeneous light shift originating from the Gaussian beam shape of the optical lattice potential which provided the steepest potential gradient of 3.6 kHz/mu m. This result is also the successful demonstration of the tunable local atom addressing along the equipotential contour depending on the excitation laser frequency with the frequency resolution of 8 kHz and the spatial resolution of approximately 2 mu m. The demonstrated technique will be useful for many purposes including the measurement of interaction shift in the study of a quantum gas and quantum information processing.

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 S-1(0)-P-1(1) transition which provides high-resolution in the in situ fluorescence imaging and the other using the S-1(0)-P-3(1) transition for cooling the atoms in the optical lattice. We performed in situ imaging of Yb-174 atoms and could observe a Moire pattern with a period of about 6 mu m 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.

We demonstrate optical magnetic resonance imaging (OMRI) of a Bose-Einstein condensate of ytterbium atoms trapped in a one-dimensional (1D) optical lattice using an ultra-narrow optical transition (1)S(0)a dagger"P-3(2) (m=-2). We developed a vacuum chamber equipped with a thin glass cell, which provides high optical access and allows a compact design of magnetic coils. A line shape of a measured spectrum of the OMRI is well described by a spatial distribution of the atoms in a 1D optical lattice with the Thomas-Fermi approximation and an applied magnetic field gradient. The observed spectrum exhibits a periodic structure corresponding to the optical lattice periodicity.

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.