Population Transfer Resonance: A new Three-Photon Resonance for Small Scale Atomic Clocks

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Population Transfer Resonance A new Three-Photon
Resonance for Small Scale Atomic Clocks

• Ido Ben-Aroya, Gadi Eisenstein
• EE Department, Technion, Haifa, Israel.

FRISNO-11, Aussois, France, Mar. 2011
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The Synchronous World
The Quartz Crystal Oscillators (1920s?today)
NIST (NBS) Frequency Standard by Bell labs, 1929.
4 x 100 KHz crystal oscillators.
stability 10-7

• Resonance frequency shifted due to aging
• No two crystals with the same frequency.

Source NIST
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Frequency/Time Standard
Principle of Operation

• An oscillator with poor long-term stability
  (hours to years) is locked on a narrow filter
  around a fixed frequency ? improved long-term
  stability.

• High contrast
• Narrow width
• Fixed f0

Local Oscillator (Quartz Crystal)

• Stable during feedback

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Types of Reliable Frequency Standards

• CSAC
• Small dimension
• Low power consumption

Source Symmetricom
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CPT based CSAC

• CPT Two photon coherent process yielding narrow
  resonances with low contrast
• Clocks require complex locking schemes Multi
  field FM spectroscopy
• Large contrast resonances eliminate many of the
  locking problems

• D2 transition (780nm).
• Resonance width 186Hz
• Contrast 0.5 - 1.

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Types of Atomic Resonances
Electromagnetically Induced Transparency (EIT)
type
Electromagnetically Induced Absorption (EIA) type

• Important characteristics width and height (or
  contrast)
• ?EIA-type Population Transfer Resonance (PTR)
• Inspired by Zibrov and Walsworth group
  N-resonance demonstration.

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Population Transfer Resonance

• Three-level L-system interacts with three
  phase-locked fields in an N-type configuration
  scheme.

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Population Transfer Resonance

• The probe w3, is tuned on resonance and therefore
  is absorbed by the medium.
• w1 and w2 are highly one-photon detuned and
  sweep near the zero two-photon Raman detuning.

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Population Transfer Resonance

• w3 optically pumps the medium from g2gt to g1gt.
• The two-photon process induced by w1 and w2
  transfers the population back from g1gt to g2gt ?
  

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Population Transfer Resonance

• The absorption of w3 is enhanced due to the
  repopulation of g2gt
• Electromagnetically Induced Absorption
  (EIA)-type resonance.

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The Spectral Constellation

• The interacting frequency components originate
  from a laser which is locked to the 87Rb D2
  transition (F2gt?F2gt) and modulated by half
  the 87Rb hyperfine splitting frequency
  (fhfs/23.417 GHz).

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The Setup

• 3 main blocks Source, Medium, and Detection
  formation.
• Parameters Modulation frequency (w12), Total
  intensity (I), and Carrier to 1st side lobe
  intensity ratio (C1L).

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First Observation
Approx. 50 contrast.

• The probe (w3) intensity (normalized) is measured
  versus PM frequency sweeping near 3 417 345 KHz
  for various C1L ratios. I300 mW.

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First Observation

• EIA-type resonance for the probe (w3) and w1.
• EIT-type resonance for w2.

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The Model
Probing 2-ph process The Population Coupling
model
Two processes coupled by the population of their
states
A One, on resonance field interacting with a
three-level L-system with a g1gt?g2gt coupling
channel.
B Two highly one-photon detuned fields
interacting with a three-level L-system with a
g2gt?g1gt coupling channel.
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The Model (phase II)
The Coupling of Coherence

• The population coupling model is insufficient in
  describing the obtained resonance for moderate
  probe intensities.
• The coupling model neglects the existence of each
  process field(s) in the other process.
• The missing information the coherence in both
  processes.

Process B
Process A
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The Model
Process B
Process A

• The population of g2gt is given by a ratio
  between two polynomial terms of symmetric
  (Lorentzian) and anti-symmetric
  (dispersion-like) functions of the modulation
  frequency (d).
• The approximated anti-symmetric and symmetric
  functions

Fundamental Width
Anti-Symmetric
Symmetric
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The Model
Process B
Process A

• The absorption of the probe, under several
  assumptions, is an almost symmetric function of
  the modulation frequency
• Width (HWHM)
• Height
• Where s is the saturation parameter

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The Model
Process B
Process A
Results
Width (HWHM)
Height
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Model versus Measurements
Meas.
Model
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The Role of Temperature
Vapor Temperature, Beer Law, and PTR

• Higher temperatures ? more atoms and higher
  velocities.
• Assumption a change in temperature does not
  effect g12.
• w1 and w2 are not absorbed by the medium (due to
  the one-photon detuning).
• w3 obeys Beer-Lambert law
  namely, the probe (and only the probe) is
  absorbed by atoms in the medium which do not
  participate in the three-photon process.

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The Role of Temperature
Vapor Temperature, Beer Law, and PTR
Beer-Lambert

• At low intensities of the probe, the EIA effect
  is negligible.
• At higher temperatures the effect is shifted
  towards higher C1Ls.
• Stronger resonances are expected at higher
  temperatures.

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The Role of Temperature
Model Results
Higher resonances
Shift in the effect
No EIA
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The Role of Temperature
Experimental Observations
Higher resonances
Shift in the effect
No EIA
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Back to the Experimental Setup
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Back to the Experimental Setup
No Filters Before Cell
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Five Fields
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Experimental Results
Five Spectral Lines
EIT
Anti-Symmetric Resonance
EIA
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The Anti-Symmetric Resonance
A Novel Scheme for Atomic Clocks?

• The Local Oscillator should be stable during
  feedback.

• Employing symmetric resonances requires peak
  detection which delays the feedback
• Anti-symmetric resonances provides an almost
  instantaneous feedback, therefore other, less
  stable oscillators can be used
• Thin Film Resonators

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Summary

• A new type of EIA resonance was introduced.
• Resonant population transfer in a three-level
  L-system induced by three
  electromagnetic fields.
• A large contrast (50) was observed.
• A model describing the interaction was
  introduced.
• The role of vapor temperature was discussed.
• A first glance over the interaction of five
  fields with the same medium.
• A new scheme for atomic clocks?

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Acknowledgement

• This work is partially supported by the Technion
  Micro Satellite Program.
• Ramon fellowship of the Israeli ministry of
  science.

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Thank you