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A Universal Atomic and Molecular Detector for Atom Interferometry
Maxwell Gregoire
Cronin LabUniversity of Arizona
Polarizability
E
d
p = Qd = α E
p: dipole moment Q: electron charged: displacement
E: electric field
valence electron cloud
nucleus
DiffractionP
Mach-Zehnder Atom InterferometerP
Mach-Zehnder Atom Interferometer
P
bars blocktransmission
P
bars allowtransmission
P
Mach-Zehnder Atom Interferometer
Mach-Zehnder Atom Interferometer
-
+
● Creates phase shift in atom waves:
Φ proportional to α
The Problem: Current Detector
Langmuir-Taylor “hot wire” detector● Thermal/surface ionization: atoms
contacting a filament ionize as they boil off
● Efficient only if atom's ionization potential is comparable to filament's work function
atoms ionsDiscriminator
&Pulse
Counter
filament
CEM
ptable.com
ptable.com
The Solution: Universal Detector
● We want to be able to detect atoms from the entire periodic table
● We want to be able to detect molecules
ptable.com
Motivations: Test Atomic Theory
● Test atomic theory:
polarizability, van der Waals coeff's, state lifetime, branching ratio, and index of refraction calculations
all rely on knowing the
atomic dipole transition matrix elements
● Measuring one of those things tests the theory
ptable.com
Motivations: Parity Non-Conservation
● PNC research tests for beyond-the-standard-model physics
● Observing the rate of parity-violating transitions requires knowing the atomic dipole transition matrix elements
ptable.com
Motivations: Atomic Clocks
● Atomic clocks use trapped atoms to keep time● Limitation on accuracy is due to lack of knowledge
of blackbody radiation shift, which depends on polarizability
ptable.com
Electron Impact Ionization Detector
IonizationRegionatoms ions
MassFilter filtered
ions
Discriminator&
PulseCounter
CEM
Electron Impact Ionization Detector
IonizationRegionatoms
MassFilter filtered
ions
Discriminator&
PulseCounter
SRS RGA 200 contains
● Quadrupole Mass Analyzer
● Channel Electron Multiplier
CEM
Build our own Discriminator
● AMPTEK A111, variable level
Use LabJack as pulse counter
ions
http://www.thomasnet.com/articles/instruments-controls/analyzers-residual-gas
Electron Impact Ionization Detector
IonizationRegionatoms
MassFilter filtered
ions
Discriminator&
PulseCounter
Design considerations:
● Ionization cross section
● Phase-space density
● Phase-space density limit/ beam divergence
● Filament heat/resulting noise
CEM
ions
Farland, Kinney, Phys. Rev. 137, A1058 (1964)
Electron Impact Ionization Detector
IonizationRegionatoms
MassFilter filtered
ions
Discriminator&
PulseCounter
CEM
atom beam being ionized
electron beam
Ideas:
● 1) shaped beam ● 2) almost-tangential beam(s)
ions
Electron Impact Ionization Detector
IonizationRegionatoms
MassFilter filtered
ions
Discriminator&
PulseCounter
CEM
Ideas:
● 3) pinching magnet along with beam or filament source
ions
DeKieviet et al, Rev. Sci. Instrum. 71, 2015 (2000)
Acknowledgements
People
● Professor Alex Cronin
● PhD students: Will Holmgren (~2013) Ivan Hromada (~2014) Raisa Trubko (~2015), Me (~2016), You (?)
● Undergraduates: Adam deBolt (2013), James Greenberg (2014)
Organizations
● University of Arizona Dept. of Physics
● National Science Foundation
● National Institute of Standards and Technology
Questions?
