T. Takano

Spin squeezing of a cold atomic ensemble with the nuclear spin of one-half.

In order to establish an applicable system for advanced quantum information processing based on the interaction between light and atoms, we have demonstrated a quantum nondemolition measurement with a collective spin of cold ytterbium atoms (171Yb), and have observed 1.8(-1.5)+2.4 dB spin squeezing. Since 171Yb atoms have only a nuclear spin of one-half in the ground state, the system constitutes the simplest spin ensemble and is thus robust against decoherence. We used very short pulses with a width of 100 ns, and as a result the interaction time became much shorter than the decoherence time, which is important for multistep quantum information processing.

Spin squeezing via one-axis twisting with coherent light.

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 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 S^{-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.

Manipulation of Nonclassical Atomic Spin States

We report successful manipulation of nonclassical atomic spin states. We apply an off-resonant noncircularly-polarized light pulse to a measurement-induced squeezed spin state of a cold atomic ensemble. By changing the pulse duration, we clearly observe a rotation of the anisotropic quantum-noise distribution in good contrast with the case of manipulation of a coherent spin state where the quantum-noise distribution is always isotropic. This is an important step for quantum state tomography, quantum swapping, and precision spectroscopic measurement.

Fast polarimetry system for the application to spin quantum non-demolition measurement

We report the development of a fast pulse polarimeter for the application to quantum non-demolition measurement of atomic spin (spin QND). The developed system was tunable to the atomic resonance of a ytterbium atom and has narrow laser line width suitable for spin QND. Using the developed polarimeter, we successfully demonstrated the measurement of the vacuum noise, with 106 to 107 photon number per pulse.

Paramagnetic Faraday rotation with spin-polarized ytterbium atoms

We report the observation of paramagnetic Faraday rotation of spin-polarized ytterbium (Yb) atoms. As the atomic samples, we used an atomic beam, released atoms from a magneto-optical trap (MOT), and trapped atoms in a far-off-resonant trap (FORT). Since Yb is diamagnetic and includes a spin-1/2 isotope, it is an ideal sample for spin physics, such as quantum non-demolition measurement of spin (spin QND), for example. From the results of the rotation angle, we confirmed that the atoms were almost perfectly polarized.

Measurement schemes for the spin quadratures on an ensemble of atoms

We consider how to measure collective spin states of an atomic ensemble based on the multi-pass approaches for quantum interface between light and atoms. We find that a scheme with two passages of a light pulse through the atomic ensemble is efficient to implement the homodyne tomography of the spin state. Thereby, we propose to utilize optical pulses as a phase shifter that rotates the quadrature of the spins. This method substantially simplifies the geometry of experimental schemes.

Atomic Spin Squeezing Towards Sub‐Shot‐Noise Measurement Of Permanent Electric Dipole Moment

We have been studying laser‐cooled and trapped atoms towards the detection of the permanent electric dipole moment (p‐EDM). The existence of the p‐EDM shows the CP‐violation and its detection has significant implications for the test of the proposed elementary particle models. However, the current experimental accuracy has not yet reached the range of the predicted value of the standard model. Especially, a measurement error due to a shot noise is one of the important factors. To overcome the shot‐noise limit, we are now trying to generate the atomic squeezed spin state.

Realization of quantum non‐demolition measurement of nuclear spin 1/2 of cold ytterbium atom

We have demonstrated a quantum non‐demolition (QND) measurement with a collective spin of cold ytterbium atoms (171Yb) via Faraday rotation interaction, and have observed 1.8−1.5+2.4 dB spin squeezing. Since 171Yb atoms have only a nuclear spin of one‐half in the ground state, the system constitutes the simplest spin ensemble and is thus robust against decoherence. Furthermore, we have considered the atomic quantum swapping gate as a quantum information device using multiple Faraday rotation interactions, and have found that we can realize the quantum‐domain performance for a realistic experimental condition.

Bose‐Einstein Condensation of Yb atoms

We could recently achieve the Bose Einstein condensation (BEC) of Yb atoms. Yb differs from most of the elements that have previously been condensed, because it is a two‐electron atom with the singlet S ground state. Furthermore the Bosonic isotopes of Yb, like 174Yb which we succeeded to condensate, has no nuclear spin, so that the ground state is completely spin‐less state and hence insensitive to magnetic fields. Thus a new type of atom could join the group of atoms for BEC studies. We would like to report how we could achieve the BEC of Yb atoms.

BOSE-EINSTEIN CONDENSATION OF YTTERBIUM ATOMS

We report the achievement of Bose-Einstein condensation of ytterbium (Yb) atoms by the all-optical method. The Yb atomic beam from an oven is first decelerated by the Zeeman slowing technique using the singlet transition and then captured by a magnetooptical trap using an intercombination transition. The evaporative cooling is performed in a novel crossed optical trap, which results in the formation of condensates of about 5 x 10 3 atoms of 174 Yb. We determine the scattering length of 174 Yb to be between 1 and 3 nm by combining the behavior of the condensate and the result of measuring photoassociation. The prospect of Yb condensates is also discussed.