d) Spectroscopy with Trapped Ions
Ion
traps
are
promising
tools
for
ultrahigh
resolution
laser
spectroscopy
because
ions
can
be
ob
-
served
over
long
periods
without
perturbations.
Therefore,
transit
time
broadening
and
col
-
lisional
effects
can
largely
be
eliminated.
Because
of
these
properties
ion
traps
are
widely
dis
-
cussed as new frequency standards in the microwave and optical region.
For
such
applications
well
defined
atomic
transitions
are
of
interest,
which
in
the
microwave
range
can
be
found
between
hyperfine
levels
of
the
ionic
ground
state
and
in
the
optical
region
between long living excited states and the ground state.
Radio-Frequency Ion Trap
A
quadrupole
radio-frequency
ion
trap
(Paul-trap)
consists
of
a
ring
electrode
and
two
hyperboli
-
cally
shaped
endcap
electrodes.
When
these
electrodes
are
supplied
with
a
dc
and
ac
voltage,
under
appropriate
conditions
up
to
10
8
ions
are
trapped
in a pseudopotential determined by the applied voltages.
In
this
potential
the
ions
are
oscillating
on
a
lower
fre
-
quency,
the
macromotion,
which
is
additionally
modula
-
ted
by
the
mi
cromo
tion
originating
from
the
ac
driving
field.
The
ions
are
excited
by
a
continuous
wave
or
pulsed
laser
on
a
resonance
transition
or
even
on
a
‘forbidden’
optical
tran
sition
and
their
response
is
observed
as
fluorescence
radi
ation
through
one
of
the
endcap
electrodes
which
is
formed out of a mesh.
Our
experiments
with
trapped
ions
only
should
be
classified
as
some
first
steps
on
the
way
to
ultrahigh
resolution
frequency
measurements,
but
they
already
showed
two
surprising
dis
-
coveries.
Population Trapping in Excited Yb Ions
When
resonantly
exciting
ytterbium
(Yb)
ions
from
the
6s
2
S
1/2
to
the
6p
2
P
1/2
state
a
rapidly
de
-
creasing
fluorescence
signal
can
be
observed,
which
goes
down
to
zero
level.
A
further
analysis
shows
that
the
ions
can
still
be
found
in
the
trap
but
they
are
transferred
to
the
highly
meta
-
stable 4f
13
6s
2
2
F
7/2
state. Therefore, they are no longer available for a further direct excitation.
The
population
of
the
2
F
7/2
state
can
be
verified
by
selective
excitation
to
higher-lying
levels
with
wavelengths
in
the
vicinity
of
the
resonance
line.
In
this
way
all
ions
can
be
pumped
back
to
the
ground state and their presence in the trap checked.
A
trapping
effect
in
the
2
F
7/2
state
is
in
so
far
of
fundamental
importance,
as
the
Yb
ion
is
a
hot
candidate
for
the
realization
of
a
frequency
standard,
which
in
the
microwave
range
is
operating
on
the
ground-state
hyperfine
transition
of
one
of
the
odd
isotopes
or
in
the
optical
region
on
one of the well-defined transitions to the
2
D
3/2
or
2
D
5/2
-state.
The
lifetime
of
the
metastable
2
F
7/2
-state
could
be
measured
by
first
pumping
all
ions
into
the
metastable
state,
then
blocking
the
laser
and
after
longer
delay
probing
the
re-population
of
the
ground-state
and
thus
the
depopulation
of
the
metastable
state
by
a
second
excitation
on
the
resonance line while monitoring the fluorescence.
It
was
found
that
the
lifetime
of
the
2
F
7/2
-state
by
far
exceeds
the
ion-storage
time
of
about
7
h.
After
a
dark
period
of
4
h
less
than
2%
of
the
ions,
which
are
still
in
the
trap,
have
undergone
a
transition
into
the
ground-state.
From
this
a
radiative
lifetime
of
more
than
8
days
is
estimated,
which
is
by
far
the
longest
lifetime,
which
has
been
observed
for
an
optically
excited
atomic
state.
A
laser
which
is
stabilized
on
the
2
S
1/2
-->
2
F
7/2
transition
would
be
the
ultimate
frequency
standard
with
a
Q-value
of
better
than
10
21
.
Such
an
optical
atomic
clock
has
unprecedented
uses
ranging
from
technological
applications
like
GPS
or
gravity
sensing
up
to
examining
pos
-
sible variations of fundamental physical constants.
Self-Induced Zeeman-Coherences
The
macro-
and
micro-motion
of
ions
in
a
Paul-trap
can
limit
the
ultimate
frequency
resolution
for
using
these
traps
as
frequency
standards.
While
Doppler
broadening
of
an
atomic
transition
can
be
avoided
by
confining
the
ions
within
a
cloud
smaller
than
the
transition
wavelength,
systematic
line shifts caused by the second-order Doppler effect still have to be considered.
Storage of single ions, which can efficiently be cooled by optical sideband cooling, would be the
most consequent solution, but such experiments suffer from poor signal-to-noise ratios.
Therefore,
particularly
the
development
of
better
cooling
techniques
requires
a
deeper
under
-
stan
ding of the ion motion and distribution of the ions in the trap.
For
a
sensitive
detection
of
these
motions
in
frequency
and
amplitude
we
use
a
phenomenon
which
we
termed
Self-Induced
Zeeman
Coherences
.
Ions
oscillating
in
the
trap
potential
and
addi
-
tionally
subjected
to
a
small
magnetic
field,
undergo
sub-level
transitions
between
adjacent
Zeeman
states
when
their
motional
frequency
is
identical
with
the
Larmor
frequency,
i.e.,
the
splitting frequency of these state in the applied magnetic field.
These
transitions
are
related
to
a
coherent
superposition
of
adjacent
states
and
originate
from
the
inherent
motion
of
the
ions
in
a
slightly
inhomogeneous
magnetic
field.
These
self-induced
transi
tions
are
sensitively
detected
by
means
of
an
optical
pumping
scheme.
They
allow
to
quan
-
tify
the
distribution
of
the
ions
in
the
trap,
their
exact
oscillation
frequencies
and
amplitudes
as
well as a moderate cooling of the ions.
Doctoral Theses
H. Lehmitz
Kohärenzspektroskopie mit ultrakurzen Lichtimpulsen – Zeit- und frequenzaufgelöste Messungen am Beispiel von
Cäsium sowie Voruntersuchungen zu Messungen an gespeicherten Ytterbiumionen
School of Electrical Engineering, Helmut-Schmidt-Uiversity, Hamburg 1989
G. A. Newburgh
Self Induced Zeeman Coherence and Optical Pulse Train Spectroscopies performed on Paul Trapped Ytterbium
Ions
School of Electrical Engineering, Helmut-Schmidt-Uiversity, Hamburg 1995
H. Ebensing
Untersuchungen zur Ionenbewegung durch selbstinduzierte Kohärenzen an Ca-Ionen in einer Paul-Falle
School of Electrical Engineering, Helmut-Schmidt-Uiversity, Hamburg 1998
T. Baier
Kohärenzspektroskopie und Untersuchungen zur Dichteverteilung an Kalzium-Ionen in einer Paulfalle
School of Electrical Engineering, Helmut-Schmidt-Uiversity, Hamburg 2004
Refereed Publications in Journals and Conference Digests
H. Lehmitz, J. Hattendorf, R. Blatt, H. Harde
Observation of Complete Population Trapping in an Excited State of Yb Ions
Technical Digest of International Quantum Electronics Conference (Japan
Society of Applied Physics, Tokio, 1988), p. 592 (1988)
H. Lehmitz, J. Hattendorf, R. Blatt, H. Harde
Spectroscopic Studies on Trapped Yb Ions
Digest of Technical Papers of the European Conference on Quantum Electronics, (University Hannover,
Hannover, 1988), p. MoCB2 (1988)
H. Lehmitz, J. Hattendorf, R. Blatt, H. Harde
Observation of an Extremely Long Living Metastable State in Yb II
Europhysics Conference Abstracts of 20th EGAS-Conference 12 F (European Physical Society, Graz, 1988),
p. 140 (1988)
H. Lehmitz, J. Hattendorf, R. Blatt, H. Harde
Self-Induced Zeeman Coherences in Trapped Ions
Europhysics Conference Abstracts of 20th EGAS-Conference 12 F (European Physical Society, Graz, 1988),
p. 143 (1988)
H. Lehmitz, J. Hattendorf, R. Blatt, H. Harde
Population Trapping in Excited Yb-Ions
Physical Review Letters 62, 2108 (1989)
H. Harde
Optical Cooling of Trapped Ions by Means of Self-Induced Zeeman Coherences
in International Conference on Quantum Electronics Technical Digest Series 1990, Vol. 8, (Optical Society of
America, Washington,DC 1990), p. 278 (1990)
H. Harde, H. Lehmitz, J. Hattendorf-Ledwoch, R. Blatt
Self-Induced Zeeman-Coherences in a Paul Trap
Applied Physics B 53, 131 (1991)
H. Ebensing, A. Newburgh, H. Harde
Systematic Studies of the Ion Motion in a Paul Trap by Means of Self-Induced Coherences
in: ''Quantum Electronics and Laser Science Conference'', 1993 OSA Technical Digest Series, Vol. 3
(Optical Society of America, Washington, DC, 1993), p. 194 (1993)
H. Ebensing, T. Baier, G. A. Newburgh, H. Harde
Measurement and Interpretation of Motional Frequencies and their Harmonics of Paul Trapped Ions
Proceedings of the 1996 European Quantum Electronics Conference, IEEE Catalog No. 96TH8162,
ISBN: 0-7803-3171-0, p. 113 (1996)
T. Baier, H. Ebensing, H. Harde
Measurement and Interpretation of Motional Frequencies and their Harmonics of Paul Trapped Ions
Proceedings of the 29th EGAS-Conference, ed. by H.-D. Kronfeldt (Optisches Institut, TU Berlin, Berlin 1997),
p. 530 (1997)
T. Baier, H. Ebensing, H. Harde
Observation of Motion-Induced Coherences with Trapped Ions
Proceedings of the 1998 European Quantum Electronics Conference, IEEE
Catalog No. 98TH8326, ISBN: O-7803-4233, P. 123 (1998)
T. Baier, I. Malchartzek, H. Ebensing, H. Harde
Motion-Induced Coherences and Density Distributions in a Paul-Trap
Quantum Electronics and Laser Science Conference, OSA Technical Digest (Optical Society of America,
Washington DC, 2000), p. 66, QTuA32 (2000)
T. Baier, I. Malchartzek, H. Ebensing, H. Harde
Motion-Induced Dark Resonances and Density Distribution in a Paul-Trap
International Quantum Electronics Conference 2000, IEEE Conference Digest, San Francisco, 7.-12. Mai 2000,
Catalog Number 00TH8504, QTuA7, ISBN: 0-7803-6318-3 (2000)
T. Baier, I. Malchartzek, H. Ebensing, H. Harde
Motion-Induced Dark Resonances and Density Distribution in a Paul-Trap
International Quantum Electronics Conference, Nice, 10.-15. September 2000, QTuA7 (2000)
Contributions on National Conferences and Meetings
J. Hattendorf, H. Lehmitz, R. Blatt, H. Harde
Nachweis der Mikro- und Makrobewegung von Ionen in einer RF-Ionenfalle über selbstinduzierte Zeeman-
Kohärenzen
Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Fachausschuss Atomphysik, Bonn, 23. März 1988,
Verhandl. DPG (VI) 23, A 41 (1988)
H. Lehmitz, J. Hattendorf, R. Blatt, H. Harde
Beobachtung des ''Shelving'' an Yb Ionen
Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Fachausschuss Atomphysik, Bonn, 24. März 1988,
Verhandl. DPG (VI) 23, A 67 (1988)
H. Lehmitz, H. Harde
Interpretation von selbstinduzierten Zeeman-Kohärenzen an gespeicherten Ionen
Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Arbeitsgemeinschaft Quantenoptik, Essen,
6. März 1989, Verhandl. DPG (VI) 24, Q 5.5 (1989)
H. Ebensing, A. Newburgh, H. Harde
Untersuchungen zu selbstinduzierten Zeeman-Kohärenzen in einer Paul-Falle
Frähjahrstagung der Deutschen Physikalischen Gesellschaft, Arbeitsgemeinschaft Quantenoptik, Hannover,
24. März 1992, Verhandl. DPG (VI) 27, Q 12.10, 1415 (1992)
H. Ebensing, A. Newburgh, H. Harde
Messungen der Bewegungsfrequenzen von gespeicherten Yb-Ionen mittels selbstinduzierter Kohärenzen
Poster Lasertag 1992, Hannover, 2. Dezember 1992
H. Ebensing, A. Newburgh, H. Harde
Bewegungsfrequenzen von gespeicherten Yb-Ionen mittels selbstinduzierter Kohärenzen
Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Arbeitsgemeinschaft Quantenoptik, Berlin,
16. März 1993, Verhandl. DPG (VI) 28, 440 (1993), Q 38.2
H. Ebensing, A. Newburgh, H. Harde
Bewegungsfrequenzen und -amplituden von Ionen in einer Paulfalle
Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Arbeitsgemeinschaft Quantenoptik, Hamburg,
15. März 1994, Verhandl. DPG (VI) 29, Q 5A.5, 665 (1994)
A. G. Newburgh, H. Harde
Coherent Population Trapping: Generalization of Two-Field Dark Resonance and Optical Pulse Train Interference
Spectroscopy
Poster Lasertag 1995, Hannover, 6. Dezember 1995
H. Ebensing, T. Baier, H. Harde
Messungen der Ionenbewegung von Ca
+
in einer Paul-Falle
Poster Lasertag 1995, Hannover, 6. Dezember 1995
H. Ebensing, G. A. Newburgh, H. Harde
Messung und Interpretation von Harmonischen der Bewegungsfrequenz gespeicherter Ionen in einer Paul-Falle
Frühjahrstagung der DPG, Sektion Quantenoptik, Jena, 12. März 1996,
Verhandl. DPG (VI) 31, Q 23.3, 241 (1996)
G. A. Newburgh, H. Harde
Coherent Population Trapping: Generalization of Two-Field Dark Resonance and Optical Pulse Train Interference
Spectroscopy
Frühjahrstagung der DPG, Sektion Quantenoptik, Jena, 14. März 1996,
Verhandl. DPG (VI) 31, Q 34.13, 277 (1996)
H. Ebensing, T. Baier, H. Harde
Bewegungsspektrum von gespeicherten Ca
+
-Ionen
Poster Lasertag 1996, Hannover, 11. Dezember 1996
T. Baier, H. Ebensing, H. Harde
Bewegungsfrequenzen und -amplituden von Ca-Ionen in einer Paul-Falle
Frühjahrstagung der DPG, Arbeitsgemeinschaft Quantenoptik, Mainz, 5. März 1997,
Verhandl. DPG (VI) 32, A 17.3, 203 (1997)
T. Baier, H. Ebensing, H. Harde
Bewegungs- und Dunkelresonanzen gespeicherter Ca-Ionen
Frühjahrstagung der DPG, Fachverband Atomphysik, Heidelberg, 15. März 1999,
Verhandl. DPG (VI) 34, A 1.3, 235 (1999)
T. Baier, H. Harde
Messung der Bewegungsfrequenzen gespeicherter Ca-Ionen in einer Paul-Falle mittels Zeeman-Kohärenzen und
Dunkelresonanzen
Poster Norddeutsches Laserkolloquium 1998, Hannover, 9. Dezember 1999
Physics & Climate