We report the observation of a Bose-Einstein condensation of ytterbium atoms by evaporative cooling in a novel crossed optical trap. Unlike the previously observed condensates, a ytterbium condensate is a two-electron system in a singlet state and has distinct features such as the extremely narrow intercombination transitions which are ideal for future optical frequency standard and the insensitivity to external magnetic field which is important for precision coherent atom optics, and the existence of the novel metastable triplet states generated by optical excitation from the singlet state.

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To establish an applicable system for advanced quantum information processing between light and atoms, we have demonstrated the quantum non-demolition (QND) measurement with a collective spin of cold ytterbium atoms ( 171 Yb), and observed 1.8 +2.4 −1.5 dB spin squeezing. Since a 171 Yb atom has only a nuclear spin of 1/2 in the ground state, the system is the simplest spin ensemble and robust against decoherence. We used very short pulses with the width of 100 ns, so the interaction time became much shorter than the decoherence time, which is important for multi-step quantum information processing.PACS numbers: 42.50.Ct, 42.50.Dv Quantum non-demolition (QND) measurements are measurements in which the strategy is chosen to evade the undesirable effect of back action [1,2]. They have been developed to manage the quantum noise, and are also useful for a quantum-state preparation device and producing a quantum entanglement [3] as well as a feasible model to capture basic features of a quantum measurement process [1,2]. Previously, the QND measurement of the photon number and the amplitude quadrature of light have been realized [4,5,6,7]. The QND measurement of the collective spin is also considerably interesting, and in fact the QND interaction of collective spin of an atomic ensemble (spin-QND interaction) via the Faraday-rotation interaction with linearly-polarized off-resonant light has been proposed [8,9]. An implication is the spin squeezed state [10], which could improve the measurement precision of the atomic clock transition [11,12] and of the permanent electric dipole moment to test the violation of time reversal symmetry [13]. The spin-QND interaction is also useful for implementing continuous-variable quantum information devices, such as quantum memory and quantum teleportation [3,14,15,16,17]. The variety of the interactions and tunability of their strength are useful characteristics of atoms whereas the property of the interaction is rather fixed by the parameter of the non-linear crystal for the case of the QND measurement in optics [1].Previous experimental approaches for the spin-QND interaction [3,18] used thermal alkali atoms and continuous-wave light or long pulsed light of typically 1 ms width, which is comparable with the decoherence time of the atomic spin [3,18]. Hence, it is essential to implement the interaction with shorter pulses and more controllable cold atoms for composing the quantum interface where more-than-twice interactions between the atoms and light beam are required [17]. In addition, it should be noted that the description of the spin-QND interaction is based on the standard model of the collective spin composed of the spin one-half atoms [19,20]. However, the cesium atoms used in the previous experiments have more complicated multi-level structures, which causes serious difficulties as is pointed out in Ref. [19,20]. Therefore, it is widely valuable to demonstrate the spin-QND interaction with cold spin one-half atoms and short pulses.In this Letter, we report the success...

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Unlike photons, which are conveniently handled by mirrors and optical fibres without loss of coherence, atoms lose their coherence via atom–atom and atom–wall interactions. This decoherence of atoms deteriorates the performance of atomic clocks and magnetometers, and also hinders their miniaturization. Here we report a novel platform for precision spectroscopy. Ultracold strontium atoms inside a kagome-lattice hollow-core photonic crystal fibre are transversely confined by an optical lattice to prevent atoms from interacting with the fibre wall. By confining at most one atom in each lattice site, to avoid atom–atom interactions and Doppler effect, a 7.8-kHz-wide spectrum is observed for the 1S0−3P1(m=0) transition. Atoms singly trapped in a magic lattice in hollow-core photonic crystal fibres improve the optical depth while preserving atomic coherence time.

We propose a new method of spin squeezing of atomic spin, based on the interactions between atoms and off-resonant light which are known as paramagnetic Faraday rotation and the fictitious magnetic field of light. Since the projection process, squeezed light, or special interactions among the atoms are not required in this method, it can be widely applied to many systems. The attainable range of the squeezing parameter is zeta greater, similarS(-2/5), where S is the total spin, which is limited by additional fluctuations imposed by coherent light and the spherical nature of the spin distribution.

This article describes the recent progress of optical lattice clocks with neutral strontium ( 87 Sr), ytterbium ( 171 Yb) and mercury ( 199 Hg) atoms. In particular, we present frequency comparison between the clocks locally via an optical frequency comb and between two Sr clocks at remote sites using a phase-stabilized fibre link. We first review cryogenic Sr optical lattice clocks that reduce the room-temperature blackbody radiation shift by two orders of magnitude and serve as a reference in the following clock comparisons. Similar physical properties of Sr and Yb atoms, such as transition wavelengths and vapour pressure, have allowed our development of a compatible clock for both species. A cryogenic Yb clock is evaluated by referencing a Sr clock. We also report on a Hg clock, which shows one order of magnitude less sensitivity to blackbody radiation, while its large nuclear charge makes the clock sensitive to the variation of fine-structure constant. Connecting all three types of clocks by an optical frequency comb, the ratios of the clock frequencies are determined with uncertainties smaller than possible through absolute frequency measurements. Finally, we describe a synchronous frequency comparison between two Sr-based remote clocks over a distance of 15 km between RIKEN and the University of Tokyo, as a step towards relativistic geodesy.

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