Download YbPosterweb

●Ytterbium has seven stable isotopes (A=168, 170, 171, 172, 173, 174,
176) and the parity-violating effects are expected to be different for each
isotope. This limits the dependence of the measurement upon atomic
structure calculations, which are currently less precise than experimental
measurements.
●The high charge of the ytterbium nucleus (Z = 70) is important since the
parity-violating effects scale as Z3. The parity violating effect is expected
to be ~10 and 100 times larger than those previously studied in thallium
and cesium, respectively.
●In ytterbium, the odd parity state 6s6p 1P1 state is near in energy to the
even parity 5d6s 3D1 state (see energy diagram). In perturbation theory, the
mixing of these states is enhanced by the small energy denominator.
Why ytterbium?
●An external electric field also mixes states of opposite parity. This
results in a Stark-induced transition amplitude. This much larger transition
amplitude can be interfered with the small parity-violating transition
amplitude allowing observation of the small parity-violating effects.
●Atomic selection rules forbid E1 transitions between states of the same
parity. However, the parity-violating weak interaction between the
nucleons and electrons can mix states of opposite parity, resulting in a
small parity-violating E1 transition amplitude.
The Forbidden Transition in Ytterbium
Parity Nonconservation In Atoms
●Within an atom there is an interaction due to the weak force. This
interaction occurs via the exchange of virtual Z-bosons between the
electrons and nucleons within an atom. Because this interaction does not
conserve parity the parity of atomic states, as defined by the
electromagnetic interaction, is not completely preserved.
●The presence of a parity-violating interaction mixes states of opposite
parity. This mixing is manifested in the optical properties of the atom.
●Because the Standard Model predicts the size of these parity-violating
effects, precision measurements of atomic parity violation provide a lowenergy test for the Standard Model and may be sensitive to physics beyond
the Standard Model.
●The M1 amplitude for the 6s2 1S0 → 5d6s 3D1 transition is estimated to
be highly suppressed, but a direct measurement of the M1 amplitude is
necessary do determine any effect its presence may have on the parity
nonconservation measurement.
●Determining the parity-violating amplitude by observing the interference
with the Stark-induced amplitude requires a small M1 amplitude so that
the parity-nonconserving amplitude is not masked by the M1 amplitude.
M1 Transition Amplitude
●Given the branching ratios of the decay of the 5d6s 3D1 state, we can
also use fluorescence to measure the Stark-induced amplitude. The atoms
in the excited 5d6s 3D1 state decay through the 6s6p 3P2, 1, 0 states to the
6s2 1S0 ground state. Comparing the fluorescence from the 6s6p 3P1→ 6s2
1S transition (556nm), after exciting with 408nm light, with the
0
fluorescence from the 6s6p 3P1→ 6s2 1S0 transition (556nm), after exciting
with 556nm light, allows for a second method of measurement of the
Stark-induced amplitude.
●To calibrate the density of the atomic beam we measure the absorption
of 556nm light on the 6s2 1S0 → 6s6p 3P1 transition. This absorption
coefficient is known from the lifetime of the 6s6p 3P1 state.
●In order to determine the parity-violating effects on an absolute scale we
are currently working on measuring the Stark-induced transition
amplitude. We use a c.w. laser to excite the 6s2 1S0 → 5d6s 3D1 transition
(408nm) in an effusive atomic beam (see diagram) within the presence of
an electric field and measure the absorption.
Stark-induced E1 Amplitude
Work In Progress
Current Experimental Apparatus
Observation of the Forbidden Transition
0.00
171 1/2 -> 1/2
170
173 5/2 -> 5/2
173 5/2 -> 7/2
Fluorescence
-0.05
173 5/2 -> 3/2
176
171 1/2 -> 3/2
-0.10
172
-0.15
174
8000
6000
4000
2000
0
Relative Frequency (in MHz)
This plot shows the fluorescence from the 6s6p 3P1 → 6s2 1S0 transition after exciting the 3D1
state. The fluorescence is observed with a photomultplier tube as the excitation-laser
frequency is scanned.
Low-Lying Energy Levels of Ytterbium
6s5d 3D3
6s5d 3D2
6s5d 3D1
6s6p 1P1
6s6p 3P2
6s6p 3P1
6s6p 3P0
408 nm
556 nm
6s2 1S0
Odd
Even
Investigation of the 6s2 1S0 → 5d6s 3D1 Transition in Atomic Ytterbium
C.J. Bowers, D. Budker, E. D. Commins, D. DeMille, S.J. Freedman, G. Gwinner, J.E. Stalnaker
Stark Shift Measurement
Fluorescence
-5
-10
-15
-20
-25x10
-3
400
300
200
Realative Frequency (in MHz)
100
0
This plot shows the effect of the electric field on both the amplitude and position of the transition
for the case of Yb171 1/2 → 1/2. The electric field is switched between 40kV and 25kV
throughout the scan. Points are connected to show time sequence. Each point corresponds to a
~2 second time period.
Results
Lifetime Measurements
●In order to determine the branching ratios the lifetimes of 21 excited states in atomic ytterbium
were measured using time-resolved fluorescence detection after pulsed laser excitation (C.J.
Bowers et.al. Phys. Rev. A 53, 3103(1995)).
Stark Shifts
●We have measured the Stark shifts of the 6s2 1S0 → 5d6s 3D1 transition (408nm). This is done
by exciting with laser light at 408nm and observing the cascade fluorescence at 556nm while
varying the electric field.
●In order to minimize the effects of temperature drifts of the laser frequency, we switch the
electric field between two values as we scan over the resonance (see Stark shift plot).
●The size of the shifts are ~20 MHz for the values of the electric field used (20-50kV).
Isotope Shifts and Hyperfine Structure
●Our experimental setup allows us to measure the isotope shifts and hyperfine structure for the
5d6s 3D1 states. This is done by exciting the 6s2 1S0 →5d6s 3D1 transition and observing the
fluorescence of the 6s6p 3P1→ 6s2 1S0 transition with the photomultiplier tube.
Chopping of the atomic beam allows lock-in detection of both
fluorescence and absorption signals
408 nm Transmission
Photodiode Detector
556 nm Transmission
Photodiode Detector
Normalization of laser power reduces noise in absorption signals
due to laser power fluctuations.
Low laser power avoids optical pumping and saturation effects.
Mirror
Fluorescence detection during a calibrated laser frequency scan
(with increased 408nm laser power) is used for measurement of
hyperfine structure, isotope shifts, and Stark shifts.
Atomic
Holes in Field Fluorescence
Beam
Plates to See Detection
Chopper
Fluorescence PMT
Wheel
Dichroic
Mirror
Electric Field Plates
(~45kV/cm)
Atomic Beam
556 nm
Atomic Oven
E
408 nm Normalization
Photodiode Detector
408nm Laser Beam
(~20mW)
Beamsplitter
Dichroic
Mirror
556 nm Normalization
Photodiode Detector
556nm Laser Beam
(~2nW)
Mirror
Beamsplitter