Anna Korver, Dan Thrasher, and Thad Walker Northrop-Grumman Review September

Experimental implementation Spin exchange field broadening – Review from last time – Refining the theory Alkali field shift measurement Preliminary dual species results (Dan) Feedback (Dan)

3 Dressing Field Coils Dual Sided-Dual Frequency pumping RF Heating

Bias field for NMR: – Sequence of short 2π pulses for Rb – A 2π pulse is the same as a 0π pulse Equivalent to zero field optical pumping Freedom in alkali polarization direction – f p = γ s B bias A. Korver, R. Wyllie, B. Lancor, T. Walker, Physical Review Letters 111 (4), (2013) DAMOP 20155Spin Exchange Narrowing

NMR Drive: – Rb polarization modulated at the NMR frequency Liquid crystals flip pump polarization – Xe resonance is driven through spin exchange collisions with the oscillating Rb On resonance the Rb and Xe spins are in phase DAMOP 20156Spin Exchange Narrowing On ResonanceOff Resonance

Angle random walk: – Figure of merit: B Xe 7Spin Exchange Narrowing

Quadrature: DAMOP 20159Spin Exchange Narrowing

Add a modulating B x 180° out of phase with the alkali polarization modulation DAMOP Spin Exchange Narrowing

Turn “off” the Xe field by pumping a sub- harmonic of its resonance frequency – How does the “fudge” factor depend on the harmonic? Broadening decreases Fudge factor approaches 1

Model’s assumption: – Longitudinal and transverse relaxation rates are the same – What if they aren’t? » Our “fudge” factor enters the theory

which doesn’t make sense Large Xe and Rb fields – Back action of the Xe z polarization on the Rb – Sub-harmonic pumping helps to mitigate it, but doesn’t eliminate it – Might change our plans to use lower density Xe

Synchronous spin exchange turned what was a frequency shift into a broadening of the line width that is compensable. At high density figure of merit improved a factor of 75. Spin exchange broadening mechanism discovered, understood, and compensated 17Spin Exchange Narrowing

At 2x10 13 /cm 3 density, the alkali field is measured to be ~ 300μG which translates to a 0.1Hz frequency shift How much has Synchronous Spin Exchange Optical Pumping suppressed the alkali field shift?

Switch bias field direction – 2π pulse polarity Density dependence of Xe resonance frequency Indirectly: measure S z

131-Xe – Δf = 0.063Hz 129-Xe – Δf = 0.205Hz

The two polarities are different Suggest only factor of 9 suppression of z alkali polarization

Any DC offset of S z corresponds to a residual alkali field shift – DC offset = 0.038% Rb polarization » Corresponds to 60uHz shift

Simultaneously pump 129-Xe and 131-Xe Detection frequency not at pump modulation frequency – Eliminate noise at pump modulation frequency Sub-harmonic pumping of both isotopes: – ω: pump modulation frequency – ω 1 : bias modulation frequency

Pure field modulation would requires 8mG of z field modulation Modulate 2π pulse frequency  modulate bias field

Proven we can couple to each isotope individually Dual species coupling: