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We demonstrate a quantum gas microscope based on the Faraday effect that does not require a stochastic spontaneous emission process. We reveal the dispersive feature of this Faraday-imaging method by comparing the detuning depende...
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We demonstrate a quantum gas microscope based on the Faraday effect that does not require a stochastic spontaneous emission process. We reveal the dispersive feature of this Faraday-imaging method by comparing the detuning dependence of the Faraday signal with that of the photon scattering rate. In addition, we determine the atom distribution through a deconvolution analysis, demonstrate absorption and dark-field Faraday imaging, and reveal the various shapes of the point spread functions for these methods, which are fully explained by a theoretical analysis. The results constitute an important first step toward ultimate quantum nondemolition site-resolved imaging and open the way to quantum feedback control of a quantum many-body system with single-site resolution.
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One of the remaining issues concerning the spin-triplet superconductivity of Sr_2RuO_4 is the strong limit of the in-plane upper critical field H_(c2) at low temperatures. In this study, we clarified the dependence of H_(c2) on th...
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One of the remaining issues concerning the spin-triplet superconductivity of Sr_2RuO_4 is the strong limit of the in-plane upper critical field H_(c2) at low temperatures. In this study, we clarified the dependence of H_(c2) on the angle θ between the magnetic field and the ab plane at various temperatures, by precisely and accurately controlling the magnetic field direction. We revealed that, although the temperature dependence of H_(c2) for |θ|≥5° is well explained by the orbital pair-breaking effect, H_(c2)(T) for |θ|<5° is clearly limited at low temperatures. We also revealed that the H_(c2) limit for |θ|<5° is present not only at low temperatures but also at temperatures close to T_c. These features may provide additional hints for clarifying the origin of the H_(c2) limit. Interestingly, if the anisotropic ratio in Sr_2RuO_4 is assumed to depend on temperature, the observed angular dependence of H_(c2) is reproduced better at lower temperature with an effective-mass model for an anisotropic three-dimensional superconductor. We discuss the observed behavior of H_(c2) based on existing theories.
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We observe long-lived tightly bound van der Waals molecules of ytterbium in a three-dimensional optical lattice with a lifetime of 8.0 s. The molecules, state-selectively produced by a photoassociation technique from a Bose-Einste...
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We observe long-lived tightly bound van der Waals molecules of ytterbium in a three-dimensional optical lattice with a lifetime of 8.0 s. The molecules, state-selectively produced by a photoassociation technique from a Bose-Einstein condensate or an atomic Mott insulator, are successfully detected with a photodissociation method where the molecules are photodissociated into two atoms and the atoms are captured by a magneto-optical trap or optical molasses, for the fluorescence detection. This work will open up various possibilities of research with van der Waals molecules in an optical lattice.
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The superconducting gap structure of LaFePO (T_c=7.4 K) is studied by thermal conductivity (k) at low temperatures in fields H parallel and perpendicular to the c axis. A clear two-step field dependence of k(H) with a characterist...
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The superconducting gap structure of LaFePO (T_c=7.4 K) is studied by thermal conductivity (k) at low temperatures in fields H parallel and perpendicular to the c axis. A clear two-step field dependence of k(H) with a characteristic field H_s(～350 Oe) much lower than the upper critical field H_(c2) is observed. In spite of the large anisotropy of H_(c2), k(H) in both H directions is nearly identical below H_s. Above H_s, k(H) grows gradually with H with a convex curvature, followed by a steep increase with strong upward curvature near H_(c2). These results indicate multigap superconductivity with active two-dimensional (2D) and passive three-dimensional bands having contrasting gap values. Together with the recent penetration depth results, we suggest that the 2D bands consist of nodal and nodeless ones, consistent with extended s-wave symmetry.
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We develop an optical lattice system for an ultracold atomic gas mixture of ytterbium (~(174)Yb) and lithium (~6Li), which is an ideal system for studying disorder and impurity problems. We load a Bose-Einstein condensate of ~(174...
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We develop an optical lattice system for an ultracold atomic gas mixture of ytterbium (~(174)Yb) and lithium (~6Li), which is an ideal system for studying disorder and impurity problems. We load a Bose-Einstein condensate of ~(174)Yb into a three-dimensional optical lattice and observe its interference patterns in time-of-flight (TOF) images. Furthermore, we perform laser spectroscopy of ~(174)Yb in an optical lattice using the ultranarrow optical transition ~1S_0-~3P_2 in both cases with and without ~6Li. Owing to the weak interspecies interaction, we do not observe clear effects of ~6Li in the obtained interference patterns or excitation spectra. However, this is an important first step in the optical control of atomic impurity in ultracold fermions. We also measure the polarizabilities of the ~3P_2 state of ~(174)Yb atoms in an optical trap with a wavelength of 1070 nm. We reveal that the polarizability can be tuned to be positive, zero, or the same as the ground state, which is useful for certain applications.
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We present experimental results on the inelastic and elastic interspecies interactions between ytterbium (Yb) in the metastable ~3P_2 state loaded into a deep optical lattice and spin polarized lithium (Li) in its ground state. Fo...
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We present experimental results on the inelastic and elastic interspecies interactions between ytterbium (Yb) in the metastable ~3P_2 state loaded into a deep optical lattice and spin polarized lithium (Li) in its ground state. Focusing on the m_J = 0 magnetic sublevel of Yb(~3P_2), bias magnetic fields between 20 and 800 G are investigated and significantly enhanced inelastic collision rates with high magnetic fields are found. In addition, by direct spectroscopy of the Yb Mott insulator immersed in the Li Fermi gas an upper boundary of the background scattering length of the Yb(~3P_2,m_J = 0)-Li(~2S_(1/2),F = 1/2,m_F = +1/2) system is estimated, revealing the absence of useful Feshbach resonances. These observations are qualitatively consistent with the theoretical calculations.
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We measured crystal growth and melting rate of nuclear-ordered solid ~3He in a rectangular sample cell. The melting rate was much faster than the growth rate at all temperatures in the low field phase (U2D2) and strongly depended ...
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We measured crystal growth and melting rate of nuclear-ordered solid ~3He in a rectangular sample cell. The melting rate was much faster than the growth rate at all temperatures in the low field phase (U2D2) and strongly depended on temperature. The melting occurred on a rough surface and the dissipation mechanism of the melting was compared with the surface magnon scattering mechanism. The crystal growth rate did not depend on temperature and was compared with the spiral growth model associated with screw-dislocations. We found that a large chemical potential difference started to develop when the crystal grew large enough so that the sample became almost single domain at the upper part of the sample cell. We attributed this saturation to the pinning of the screw dislocation on the sample wall. This chemical potential difference decreased rapidly when the crystal was in the high field phase and the crystal grew as it did before the saturation. The crystal continued to grow even after the crystal returned to the U2D2 phase from the high field phase.
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Optical reflectivity experiments on fluid mercury against a sapphire surface under high pressure and temperature reveal the existence of a prewetting transition of mercury on sapphire substrate. In the present work, we preformed n...
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Optical reflectivity experiments on fluid mercury against a sapphire surface under high pressure and temperature reveal the existence of a prewetting transition of mercury on sapphire substrate. In the present work, we preformed not only normal reflection measurements but also ellipsometric measurements with 45 deg reflection geometry to make a quantitative analysis. By using this technique, we determined the bulk complex refractive index, and then, the properties of the wetting layer were determined.
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Coherent manipulation of quasiparticles is a crucial method to realize ultrafast switching of the relating macroscopic order. In this paper, we studied coherent phonon generation under strong light field which allows one to induce...
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Coherent manipulation of quasiparticles is a crucial method to realize ultrafast switching of the relating macroscopic order. In this paper, we studied coherent phonon generation under strong light field which allows one to induce nonperturbative nonlinear optical phenomena in solids. The efficiency of coherent phonon generation starts to saturate and deviate from the pronounced linear power dependence when the light intensity goes into the nonperturbative regime. It is clarified that the deviation is not originated from the absorption saturation due to the real incoherent carrier generation. We propose a theoretical model based on the Floquet picture and show that the saturation is due to a limitation of the driving force inherent in nonresonant driving of the electronic system in the nonperturbative regime.
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Recently we developed a new microwave spectroscopy technique in the frequency range up to 40 GHz, and measured the static dielectric constant and the dielectric relaxation time for supercritical water. In the present work we repor...
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Recently we developed a new microwave spectroscopy technique in the frequency range up to 40 GHz, and measured the static dielectric constant and the dielectric relaxation time for supercritical water. In the present work we report the dielectric properties of heavy water at temperatures and pressures up to 770 K and 59 MPa, respectively. The static dielectric constant of D_2O as well as H_2O are well described by the Uematsu-Franck formula when the number density instead of the mass density is used as the input parameter. The dielectric relaxation time decreases rapidly with increasing temperature in liquid H_2O and D_2O and jumps to a large value at the liquid-gas transition. The relaxation time of D_2O is longer than that of H_2O in the liquid state, and the difference becomes smaller with decreasing density in the gaseous state. For both H_2O and D_2O the most relevant parameter determining the relaxation time is the temperature at high densities or at low temperatures, and it is the density at low densities or at high temperatures. Based upon the observation that the dielectric relaxation time becomes fairly long in the dilute limit, we have concluded that the dielectric relaxation in the gaseous state is governed by the binary collision of water molecules and explained the relaxation time quantitatively by the collision time. We have extended the interpretation of the dielectric relaxation to the liquid state by taking into account the contribution of bound water molecules that are incorporated in the hydrogen-bond network. Anomalous relaxation at low temperatures is also discussed.
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