34 research outputs found
Direct frequency-comb-driven Raman transitions in the terahertz range
We demonstrate the use of a femtosecond frequency comb to coherently drive
stimulated Raman transitions between terahertz-spaced atomic energy levels.
More specifically, we address the and fine
structure levels of a single trapped Ca ion and spectroscopically
resolve the transition frequency to be Hz. The achieved accuracy is nearly a factor of five better than the
previous best Raman spectroscopy, and is currently limited by the stability of
our atomic clock reference. Furthermore, the population dynamics of
frequency-comb-driven Raman transitions can be fully predicted from the
spectral properties of the frequency comb, and Rabi oscillations with a
contrast of 99.3(6)\% and millisecond coherence time has been achieved.
Importantly, the technique can be easily generalized to transitions in the
sub-kHz to tens of THz range and should be applicable for driving, e.g.,
spin-resolved rovibrational transitions in molecules and hyperfine transitions
in highly charged ions.Comment: 9 pages, 8 figure
Modes of Oscillation in Radiofrequency Paul Traps
We examine the time-dependent dynamics of ion crystals in radiofrequency
traps. The problem of stable trapping of general three-dimensional crystals is
considered and the validity of the pseudopotential approximation is discussed.
We derive analytically the micromotion amplitude of the ions, rigorously
proving well-known experimental observations. We use a method of infinite
determinants to find the modes which diagonalize the linearized time-dependent
dynamical problem. This allows obtaining explicitly the ('Floquet-Lyapunov')
transformation to coordinates of decoupled linear oscillators. We demonstrate
the utility of the method by analyzing the modes of a small `peculiar' crystal
in a linear Paul trap. The calculations can be readily generalized to
multispecies ion crystals in general multipole traps, and time-dependent
quantum wavefunctions of ion oscillations in such traps can be obtained.Comment: 24 pages, 3 figures, v2 adds citations and small correction
Blackbody-radiation-assisted molecular laser cooling
The translational motion of molecular ions can be effectively cooled
sympathetically to temperatures below 100 mK in ion traps through Coulomb
interactions with laser-cooled atomic ions. The distribution of internal
rovibrational states, however, gets in thermal equilibrium with the typically
much higher temperature of the environment within tens of seconds. We consider
a concept for rotational cooling of such internally hot, but translationally
cold heteronuclear diatomic molecular ions. The scheme relies on a combination
of optical pumping from a few specific rotational levels into a ``dark state''
with redistribution of rotational populations mediated by blackbody radiation.Comment: 4 pages, 5 figure
Lifetime measurement of the metastable 3d 2D5/2 state in the 40Ca+ ion using the shelving technique on a few-ion string
We present a measurement of the lifetime of the metastable 3d 2D5/2 state in
the 40Ca+ ion, using the so-called shelving technique on a string of five
Doppler laser-cooled ions in a linear Paul trap. A detailed account of the data
analysis is given, and systematic effects due to unwanted excitation processes
and collisions with background gas atoms are discussed and estimated. From a
total of 6805 shelving events, we obtain a lifetime
tau=1149+/-14(stat.)+/-4(sys.)ms, a result which is in agreement with the most
recent measurements.Comment: 10 pages, 7 figures. Submitted for publicatio
Matter-wave diffraction in time with a linear potential
Diffraction in time of matter waves incident on a shutter which is removed at
time is studied in the presence of a linear potential. The solution is
also discussed in phase space in terms of the Wigner function. An alternative
configuration relevant to current experiments where particles are released from
a hard wall trap is also analyzed for single-particle states and for a
Tonks-Girardeau gas.Comment: 11 pages, 6 figure
Matter wave pulses characteristics
We study the properties of quantum single-particle wave pulses created by
sharp-edged or apodized shutters with single or periodic openings. In
particular, we examine the visibility of diffraction fringes depending on
evolution time and temperature; the purity of the state depending on the
opening-time window; the accuracy of a simplified description which uses
``source'' boundary conditions instead of solving an initial value problem; and
the effects of apodization on the energy width.Comment: 11 pages, 11 figure
Laser Cooling of two trapped ions: Sideband cooling beyond the Lamb-Dicke limit
We study laser cooling of two ions that are trapped in a harmonic potential
and interact by Coulomb repulsion. Sideband cooling in the Lamb-Dicke regime is
shown to work analogously to sideband cooling of a single ion. Outside the
Lamb-Dicke regime, the incommensurable frequencies of the two vibrational modes
result in a quasi-continuous energy spectrum that significantly alters the
cooling dynamics. The cooling time decreases nonlinearly with the linewidth of
the cooling transition, and the effect of trapping states which may slow down
the cooling is considerably reduced. We show that cooling to the ground state
is possible also outside the Lamb-Dicke regime. We develop the model and use
Quantum Monte Carlo calculations for specific examples. We show that a rate
equation treatment is a good approximation in all cases.Comment: 13 pages, 10 figure