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

1. Technion 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

2. 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 Ido B – Technion, Israel.

3. Frequency/Time Standard Reference Δf f0 Error Principle of Operation • An oscillator with poor long-term stability (hours to years) is locked on a narrow filteraround a fixed frequency improved long-term stability. • High contrast • Narrow width • Fixed f0 Local Oscillator (Quartz Crystal) • Stable during feedback Ido B – Technion, Israel.

4. Types of Reliable Frequency Standards 2’’ • CSAC: • Small dimension • Low power consumption Source: Symmetricom Ido B – Technion, Israel.

5. 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%. Ido B – Technion, Israel.

6. Types of Atomic Resonances Electromagnetically Induced Absorption (EIA) type: Electromagnetically Induced Transparency (EIT) type: • Important characteristics: width and height (or contrast) EIA-type: Population Transfer Resonance (PTR) Inspired by Zibrov and Walsworth group “N-resonance” demonstration. Ido B – Technion, Israel.

7. Population Transfer Resonance • Three-level L-system interacts with three phase-locked fields in an N-type configuration scheme. Ido B – Technion, Israel.

8. 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. Ido B – Technion, Israel.

9. Population Transfer Resonance • w3 optically pumps the medium from |g2> to |g1>. • The two-photon process induced by w1 and w2 transfers the population back from |g1> to |g2>  … Ido B – Technion, Israel.

10. Population Transfer Resonance • The absorption of w3 is enhanced due to the repopulation of |g2> • Electromagnetically Induced Absorption (EIA)-type resonance. Ido B – Technion, Israel.

11. The Spectral Constellation • The interacting frequency components originate from a laser which is locked to the 87Rb D2 transition (|F=2>|F’=2>) and modulated by half the 87Rb hyperfine splitting frequency (fhfs/2=3.417 GHz). Ido B – Technion, Israel.

12. 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). Ido B – Technion, Israel.

13. First Observation • The probe (w3) intensity (normalized) is measured versus PM frequency sweeping near 3 417 345 KHz for various C1L ratios. I=300 mW. Approx. 50 % contrast. Ido B – Technion, Israel.

14. First Observation • EIA-type resonance for the probe (w3) and w1. • EIT-type resonance for w2. Ido B – Technion, Israel.

15. 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 |g1>|g2> coupling channel. B: Two highly one-photon detuned fields interacting with a three-level L-system with a |g2>|g1> coupling channel. Ido B – Technion, Israel.

16. 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 A Process B Ido B – Technion, Israel.

17. The Model probe atom 2-ph Process A Process B • The population of |g2> 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 Ido B – Technion, Israel.

18. The Model Process A Process B • 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: Ido B – Technion, Israel.

19. The Model Process A Process B Results Width (HWHM) Height Ido B – Technion, Israel.

20. Model versus Measurements Meas. Model Ido B – Technion, Israel.

21. 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. Ido B – Technion, Israel.

22. The Role of Temperature Vapor Temperature, Beer Law, and PTR • 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. Beer-Lambert : Ido B – Technion, Israel.

23. The Role of Temperature Model Results Higher resonances Shift in the effect No EIA Ido B – Technion, Israel.

24. The Role of Temperature Experimental Observations Higher resonances Shift in the effect No EIA Ido B – Technion, Israel.

25. Back to the Experimental Setup Ido B – Technion, Israel.

26. Back to the Experimental Setup No Filters Before Cell Ido B – Technion, Israel.

27. Five Fields Ido B – Technion, Israel.

28. Experimental Results Five Spectral Lines EIT Anti-Symmetric Resonance EIA Ido B – Technion, Israel.

29. The Anti-Symmetric Resonance Reference ATOM RES. LO feedback 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 Ido B – Technion, Israel.

30. 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? Ido B – Technion, Israel.

31. Acknowledgement • This work is partially supported by the Technion Micro Satellite Program. • Ramon fellowship of the Israeli ministry of science. Ido B – Technion, Israel.

32. Thank you