55 research outputs found
Quantum State Engineering using Single Nuclear Spin Qubit of Optically Manipulated Ytterbium Atom
A single Yb atom is loaded into a high-finesse optical cavity with a moving
lattice, and its nuclear spin state is manipulated using a nuclear magnetic
resonance technique. A highly reliable quantum state control with fidelity and
purity greater than 0.98 and 0.96, respectively, is confirmed by the full
quantum state tomography; a projective measurement with high speed (500us) and
high efficiency (0.98) is accomplished using the cavity QED technique. Because
a hyperfine coupling is induced only when the projective measurement is
operational, the long coherence times (T_1 = 0.49 s and T_2 = 0.10 s) are
maintained. Our technique can be applied for implementing a scalable one-way
quantum computation with a cluster state in an optical lattice.Comment: 4 figure
How to Measure the Quantum State of Collective Atomic Spin Excitation
The spin state of an atomic ensemble can be viewed as two bosonic modes,
i.e., a quantum signal mode and a -numbered ``local oscillator'' mode when
large numbers of spin-1/2 atoms are spin-polarized along a certain axis and
collectively manipulated within the vicinity of the axis. We present a concrete
procedure which determines the spin-excitation-number distribution, i.e., the
diagonal elements of the density matrix in the Dicke basis for the collective
spin state. By seeing the collective spin state as a statistical mixture of the
inherently-entangled Dicke states, the physical picture of its multi-particle
entanglement is made clear.Comment: 6 pages, to appear in Phys. Rev.
Single Nuclear Spin Cavity QED
We constructed a cavity QED system with a diamagnetic atom of 171Yb and
performed projective measurements on a single nuclear spin. Since Yb has no
electronic spin and has 1/2 nuclear spin, the procedure of spin polarization
and state verification can be dramatically simplified compared with the pseudo
spin-1/2 system. By enhancing the photon emission rate of the 1S0-3P1
transition, projective measurement is implemented for an atom with the
measurement time of T_meas = 30us. Unwanted spin flip as well as dark counts of
the detector lead to systematic error when the present technique is applied for
the determination of diagonal elements of an unknown spin state, which is
delta|beta|^2 < 2 * 10^-2. Fast measurement on a long-lived qubit is key to the
realization of large-scale one-way quantum computing.Comment: 5 pages, 5 figure
Quantum memory of a squeezed vacuum for arbitrary frequency sidebands
We have developed a quantum memory technique that is completely compatible
with current quantum information processing for continuous variables of light,
where arbitrary frequency sidebands of a squeezed vacuum can be stored and
retrieved using bichromatic electromagnetic induced transparency. 2MHz
sidebands of squeezed vacuum pulses with temporal widths of 470ns and a
squeezing level of -1.78 +- 0.02dB were stored for 3us in the laser-cooled 87Rb
atoms. -0.44 +- 0.02dB of squeezing was retrieved, which is the highest
squeezing ever reported for a retrieved pulse.Comment: 4pages, 5figure
Bose-Einstein Condensation of Europium
We report the realization of a Bose-Einstein condensate of europium atoms,
which is a strongly dipolar species with unique properties, a highly symmetric
electronic ground state and a
hyperfine structure. By means of evaporative cooling in a crossed optical
dipole trap, we produced a condensate of Eu containing up to atoms. The scattering length of Eu was estimated to be by comparing the velocities of expansion of condensates
with different orientations of the atomic magnetic moments. We observed
deformation of the condensate in the vicinity of the Feshbach resonance at
with a width of .Comment: 5 pages, 4 figure
Faraday Rotation with Single Nuclear Spin Qubit in a High-Finesse Optical Cavity
When an off-resonant light field is coupled with atomic spins, its
polarization can rotate depending on the direction of the spins via a Faraday
rotation which has been used for monitoring and controlling the atomic spins.
We observed Faraday rotation by an angle of more than 10 degrees for a single
1/2 nuclear spin of 171Yb atom in a high-finesse optical cavity. By employing
the coupling between the single nuclear spin and a photon, we have also
demonstrated that the spin can be projected or weakly measured through the
projection of the transmitted single ancillary photon.Comment: 6 pages, 6 figure
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