Population Transfer Resonance: A new Three-Photon Resonance for Small Scale Atomic Clocks Ido Ben-Aroya, Gadi Eisenstein EE Department, Technion, Haifa, Israel. Technion FRISNO-11, Aussois, France, Mar. 2011

FRISNO-11Ido B – Technion, Israel. 2 The Synchronous World The Quartz Crystal Oscillators (1920s  today) NIST (NBS) Frequency Standard by Bell labs, x 100 KHz crystal oscillators. stability: Source: NIST Resonance frequency shifted due to aging No two crystals with the same frequency.

FRISNO-11Ido B – Technion, Israel. 3 Frequency/Time Standard An oscillator with poor long-term stability ( hours to years ) is locked on a narrow filter around a fixed frequency  improved long-term stability. Local Oscillator (Quartz Crystal) f0f0 ΔfΔf High contrast Narrow width Fixed f 0 Stable during feedback Principle of Operation

FRISNO-11Ido B – Technion, Israel. 4 Types of Reliable Frequency Standards Source: Symmetricom CSAC: Small dimension Low power consumption 2’’

FRISNO-11Ido 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%.

FRISNO-11Ido B – Technion, Israel. 6 Types of Atomic Resonances Important characteristics: width and height (or contrast)  EIA-type: Population Transfer Resonance (PTR) Inspired by Zibrov and Walsworth group “N-resonance” demonstration. Electromagnetically Induced Transparency (EIT) type: Electromagnetically Induced Absorption (EIA) type:

FRISNO-11Ido B – Technion, Israel. 7 Population Transfer Resonance Three-level  -system interacts with three phase-locked fields in an N-type configuration scheme.

FRISNO-11Ido B – Technion, Israel. 8 Population Transfer Resonance The probe  3, is tuned on resonance and therefore is absorbed by the medium.  1 and  2 are highly one-photon detuned and sweep near the zero two-photon Raman detuning.

FRISNO-11Ido B – Technion, Israel. 9 Population Transfer Resonance  3 optically pumps the medium from |g2> to |g1>. The two-photon process induced by  1 and  2 transfers the population back from |g1> to |g2>  …

FRISNO-11Ido B – Technion, Israel. 10 Population Transfer Resonance  The absorption of  3 is enhanced due to the repopulation of |g2>  Electromagnetically Induced Absorption (EIA)-type resonance.

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

FRISNO-11Ido B – Technion, Israel. 12 The Setup 3 main blocks: Source, Medium, and Detection formation. Parameters: Modulation frequency (  12 ), Total intensity (I), and Carrier to 1 st side lobe intensity ratio (C1L).

FRISNO-11Ido B – Technion, Israel. 13 First Observation The probe (  3 ) intensity (normalized) is measured versus PM frequency sweeping near KHz for various C1L ratios. I=300  W. Approx. 50 % contrast.

FRISNO-11Ido B – Technion, Israel. 14 First Observation EIA-type resonance for the probe (  3 ) and  1. EIT-type resonance for  2.

FRISNO-11Ido B – Technion, Israel. 15 The Model Probing 2-ph process: The Population Coupling model B: Two highly one- photon detuned fields interacting with a three-level  -system with a |g 2 >  |g 1 > coupling channel. A: One, “on resonance” field interacting with a three-level  - system with a |g 1 >  |g 2 > coupling channel. Two processes coupled by the population of their states

FRISNO-11Ido B – Technion, Israel. 16 The Model (phase II) 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. The Coupling of Coherence Process BProcess A

FRISNO-11Ido B – Technion, Israel. 17 The population of |g 2 > is given by a ratio between two polynomial terms of symmetric (Lorentzian) and anti- symmetric (“dispersion-like”) functions of the modulation frequency (  ). The approximated anti-symmetric and symmetric functions: Process B Process A Symmetric Anti- Symmetric Fundamental Width: probe atom 2-ph The Model

FRISNO-11Ido B – Technion, Israel. 18 The Model 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: Process B Process A

FRISNO-11Ido B – Technion, Israel. 19 The Model Results Process B Process A Width (HWHM) Height

FRISNO-11Ido B – Technion, Israel. 20 Model versus Measurements Model Meas.

FRISNO-11Ido B – Technion, Israel. 21 The Role of Temperature Higher temperatures  more atoms and higher velocities. Assumption: a change in temperature does not effect  12.  1 and  2 are not absorbed by the medium (due to the one-photon detuning).  3 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. Vapor Temperature, Beer Law, and PTR

FRISNO-11Ido B – Technion, Israel. 22 The Role of Temperature 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. Vapor Temperature, Beer Law, and PTR Beer-Lambert :

FRISNO-11Ido B – Technion, Israel. 23 The Role of Temperature Model Results No EIA Shift in the effect Higher resonances

FRISNO-11Ido B – Technion, Israel. 24 The Role of Temperature Experimental Observations No EIA Higher resonances Shift in the effect

FRISNO-11Ido B – Technion, Israel. 25 Back to the Experimental Setup

FRISNO-11Ido B – Technion, Israel. 26 Back to the Experimental Setup No Filters Before Cell

FRISNO-11Ido B – Technion, Israel. 27 Five Fields

FRISNO-11Ido B – Technion, Israel. 28 Experimental Results Five Spectral Lines EIT EIA Anti- Symmetric Resonance

FRISNO-11Ido B – Technion, Israel. 29 The Anti-Symmetric Resonance The Local Oscillator should be stable during feedback. A Novel Scheme for Atomic Clocks? ATOM RES. LO 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

FRISNO-11Ido B – Technion, Israel. 30 Summary A new type of EIA resonance was introduced. –Resonant population transfer in a three-level  -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?

FRISNO-11Ido B – Technion, Israel. 31 Acknowledgement This work is partially supported by the Technion Micro Satellite Program. Ramon fellowship of the Israeli ministry of science.

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