115 research outputs found
Conditions for spin squeezing in a cold 87Rb ensemble
We study the conditions for generating spin squeezing via a quantum
non-demolition measurement in an ensemble of cold 87Rb atoms. By considering
the interaction of atoms in the 5S_{1/2}(F=1) ground state with probe light
tuned near the D2 transition, we show that, for large detunings, this system is
equivalent to a spin-1/2 system when suitable Zeeman substates and quantum
operators are used to define a pseudo-spin. The degree of squeezing is derived
for the rubidium system in the presence of scattering causing decoherence and
loss. We describe how the system can decohere and lose atoms, and predict as
much as 75% spin squeezing for atomic densities typical of optical dipole
traps.Comment: 9 pages, 3 figures, submitted to J. Opt. B: Quantum Semiclass. Opt.
Proceedings of ICSSUR'0
Entangled light pulses from single cold atoms
The coherent interaction between a laser-driven single trapped atom and an
optical high-finesse resonator allows to produce entangled multi-photon light
pulses on demand. The mechanism is based on the mechanical effect of light. The
degree of entanglement can be controlled through the parameters of the laser
excitation. Experimental realization of the scheme is within reach of current
technology. A variation of the technique allows for controlled generation of
entangled subsequent pulses, with the atomic motion serving as intermediate
memory of the quantum state.Comment: 4 pages, 3 figures, revised version (new scheme for generation of
subsequent pairs of entangled pulses included). Accepted for publication in
Phys. Rev. Let
Experiments towards quantum information with trapped Calcium ions
Ground state cooling and coherent manipulation of ions in an rf-(Paul) trap
is the prerequisite for quantum information experiments with trapped ions. With
resolved sideband cooling on the optical S1/2 - D5/2 quadrupole transition we
have cooled one and two 40Ca+ ions to the ground state of vibration with up to
99.9% probability. With a novel cooling scheme utilizing electromagnetically
induced transparency on the S1/2 - P1/2 manifold we have achieved simultaneous
ground state cooling of two motional sidebands 1.7 MHz apart. Starting from the
motional ground state we have demonstrated coherent quantum state manipulation
on the S1/2 - D5/2 quadrupole transition at 729 nm. Up to 30 Rabi oscillations
within 1.4 ms have been observed in the motional ground state and in the n=1
Fock state. In the linear quadrupole rf-trap with 700 kHz trap frequency along
the symmetry axis (2 MHz in radial direction) the minimum ion spacing is more
than 5 micron for up to 4 ions. We are able to cool two ions to the ground
state in the trap and individually address the ions with laser pulses through a
special optical addressing channel.Comment: Proceedings of the ICAP 2000, Firenz
Vacuum-field level shifts in a single trapped ion mediated by a single distant mirror
A distant mirror leads to a vacuum-induced level shift in a laser-excited
atom. This effect has been measured with a single mirror 25 cm away from a
single, trapped barium ion. This dispersive action is the counterpart to the
mirror's dissipative effect, which has been shown earlier to effect a change in
the ion's spontaneous decay [J. Eschner et al., Nature 413, 495-498 (2001)].
The experimental data are well described by 8-level optical Bloch equations
which are amended to take into account the presence of the mirror according to
the model in [U. Dorner and P. Zoller, Phys. Rev. A 66, 023816 (2002)].
Observed deviations from simple dispersive behavior are attributed to
multi-level effects.Comment: version accepted by PR
Quantum interference from remotely trapped ions
We observe quantum interference of photons emitted by two continuously
laser-excited single ions, independently trapped in distinct vacuum vessels.
High contrast two-photon interference is observed in two experiments with
different ion species, calcium and barium. Our experimental findings are
quantitatively reproduced by Bloch equation calculations. In particular, we
show that the coherence of the individual resonance fluorescence light field is
determined from the observed interference
A diode laser stabilization scheme for 40Ca+ single ion spectroscopy
We present a scheme for stabilizing multiple lasers at wavelengths between
795 and 866 nm to the same atomic reference line. A reference laser at 852 nm
is stabilized to the Cs D2 line using a Doppler-free frequency modulation
technique. Through transfer cavities, four lasers are stabilized to the
relevant atomic transitions in 40Ca+. The rms linewidth of a transfer-locked
laser is measured to be 123 kHz with respect to an independent atomic
reference, the Rb D1 line. This stability is confirmed by the comparison of an
excitation spectrum of a single 40Ca+ ion to an eight-level Bloch equation
model. The measured Allan variance of 10^(-22) at 10 s demonstrates a high
degree of stability for time scales up to 100 s.Comment: 8 pages, 11 figure
Coupling a single atomic quantum bit to a high finesse optical cavity
The quadrupole S -- D optical transition of a single trapped
Ca ion, well suited for encoding a quantum bit of information, is
coherently coupled to the standing wave field of a high finesse cavity. The
coupling is verified by observing the ion's response to both spatial and
temporal variations of the intracavity field. We also achieve deterministic
coupling of the cavity mode to the ion's vibrational state by selectively
exciting vibrational state-changing transitions and by controlling the position
of the ion in the standing wave field with nanometer-precision
Precision measurement and compensation of optical Stark shifts for an ion-trap quantum processor
Using optical Ramsey interferometry, we precisely measure the laser-induced
AC-stark shift on the -- "quantum bit" transition near 729
nm in a single trapped Ca ion. We cancel this shift using an
additional laser field. This technique is of particular importance for the
implementation of quantum information processing with cold trapped ions. As a
simple application we measure the atomic phase evolution during a rotation of the quantum bit.Comment: 4 pages, 4 figure
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