Transcript ppt
Electron EDM search with PbO review: basic ideas, previous results work towards EDM data current status: reduction in anticipated sensitivity a new approach, thwarted hope for the future…. D. DeMille Yale Physics Department University Funding: NSF, Packard Found., CRDF, NIST, Sloan, Research Corp. General method to detect an EDM -2dE +2dE B E Energy level picture: S -2dE +2dE shift Figure of merit: resolution dE coh S / N 1 1 E coh C N Tint The problem(s) with polar molecules: Diluted signals due to thermal distribution over rotational levels (~10-4) Molecules with electron spin are thermodynamically disfavored (free radicals) high temperature chemistry, even smaller signals Addressing the problems with metastable PbO a(1)[3+] PbO is thermodynamically stable (routinely purchased and vaporized) a(1) populated via laser excitation (replaces chemistry) a(1) has very small -doublet splitting complete polarization with very small fields (~10 V/cm), equivalent to E 107 V/cm on an atom! can work in vapor cell (MUCH larger density and volume than beam) PbO Cell: Tl Beam: N = nV ~ 1016 N = nV ~ 108 Amplifying the electric field E with a polar molecule Eext Pb+ Eint O– Complete polarization of PbO* achieved with Eext ~ 10 V/cm Inside molecule, electron feels internal field Eint ~ 2Z3 e/a02 2.1(b) - 4.0(a) 1010 V/cm in PbO* (a)Semiempirical: M. Kozlov & D.D., PRL 89, 133001 (2002); (b)Ab initio: Petrov, Titov, Isaev, Mosyagin, D.D., PRA 72, 022505 (2005). Spin alignment & molecular polarization in PbO (no EDM) n - n S + + - - + -Brf z+ a(1) [3+] J=1- m = -1 S J=1+ - n + m = +1 S m=0 B E + + + ||-z n - + X, J=0+ EDM measurement in PbO* Novel state structure allows extra reversal of EDM signal n “Internal co-magnetometer”: most systematics cancel in comparison n - n + + B E + - n + - Proof-of-principle setup (top view) PMT Signal Data Processing Frequency E solid quartz light pipes PbO vapor cell B Larmor Precession ~ 100 kHz Vacuum chamber quartz oven structure Pulsed Laser Beam 5-40 mJ @ 100 Hz ~ 1 GHz B Vapor cell technology allows high count rate (but modest coherence time) Laser-only spin preparation for proof of principle rotational substructure vibrational substructure m = -1 S a(1) [3+] m=0 m = +1 S J=1J=1+ 570 nm || x 548 nm X, J=0+ Zeeman quantum beats in PbO: g-factors Gives info on: •Density limits •S/N in frequency extraction •g-factors •E-field effects Problems with fluorescence quantum beats: •Poor contrast C~10% •Backgrounds from blackbody, laser scatter reduced collection •Poor quantum efficiency for red wavelengths Verification of co-magnetometer concept Zeeman splitting ~ 450 kHz ~11 MHz RF E-field drives transitions ~1.6 ppt shift in Zeeman beat freq. Zeeman splitting slightly different in lower level g/g = 1.6(4) 10-3 -doublet will be near-ideal co-magnetometer Also: = 11.214(5) MHz; observed low-field DC Stark shift Status in 2004: a proof of principle [D. Kawall et al., PRL 92, 133007 (2004)] •PbO vapor cell technology in place •Collisional cross-sections as expected anticipated density OK •Signal size, background, contrast: Many improvements needed to reach target count rate & contrast •Shot-noise limited frequency measurement using quantum beats in fluorescence •g-factors of -doublet states match precisely: geff/g < 510-4 systematics rejection from state comparison very effective •E-fields OK: no apparent problems •EDM state preparation not demonstrated •EDM-generation cell & oven needed PbO vapor cell and oven Sapphire windows bonded to ceramic frame with gold foil “glue” Gold foil electrodes and “feedthroughs” Opaque quartz oven body: 800 C capability; wide optical access; non-inductive heater; fast eddy current decay w/shaped audio freq. drive State preparation: rotational Raman excitation J=2 28.2 GHz 28.2-.04 GHz J=1 40 MHz laser + wave preparation, as needed for EDM Doesn’t work!?! laser-prepared superposition, as in proof-of-principle (no good for EDM) Quasi-optical microwave delivery Laser beam overlaps with microwave beam “Dichroic” beamsplitter separates laser & microwave beams PbO cell Quartz lightpipes = multi-mode quasi-optical “fibers” for microwaves S/N enhancements—far less than anticipated Change Expected Actual Comments Pure 208PbO 2x S, 2x C 2x S, 1x C?? Contrast not understood Laser power 6x S ~3x S Ageing laser 2nd detector 2x S 2x S (est.) Trivial? Broad interference 20x S filter ~5x S (est.) Too much laser scatter, blackbody Vibrational level v”=0 vs. v”=1 1x S 1x C Too much laser scatter, blackbody 1x Too much laser scatter, signals too small 3x S 1.3x C Solid state detector 6x S (photodiode/APD) Bottom line: only ~2x improvement over Tl expected with current setup --taking data soon Laser double-resonance detection arbitrary units a Excite: X→a ( = 548 nm) Detect: X→a ( = 570 nm) X 20 arbitrary units 10 30 40 ms 50 60 70 C’ Excite: X→a→C’ ( = 548 +1114 nm) Detect: C’→a ( = 380-450 nm) 10 20 30 40 •~8x contrast •~2x quantum eff. 50 60 a 70 X •Dramatic reduction of blackbody, laser scatter A sad story: double-resonance detection DOESN’T WORK!*&%! Transition Probability C’ |+> |—> 1+cos(t) 1+cos(t) [+] + 1-cos(t) [-] =1!!! |—>-|+>/2 |—>+|+>/2 phase difference eit |—> |+> a Back to the future: absorption detection w/microwaves A •long cylindrical cell for increased absorption path P/P ~ 10-4 (cross-section & density well-known) •P ~ 100 W in cell for no saturation •Dominant noise from thermal carrier: cancellation via “bridge” (= dark fringe interferometer) •Shot noise limit with ~1015 wave /shot looks feasible •Enhanced absorption with resonant cavity: S/N Q Schematic of planned absorption detection scheme •Long cell minimal effect of leakage currents, easier heating & shielding Bottom line: de 10-29 ecm looks feasible! (50 cm long cell, Q = 100, shot-noise limited) “bridge” Magic Mixer/ detector tee horn cavity mirror lens Magic horn cavity mirror tee lens ~15 cm diam. 50 cm long alumina tube cell cos voltage on rod electrodes for transverse E-field J=2 J=1 First detection of microwave absorption in PbO (using current setup, no optimization) J=2 28.2 GHz J=1 Status of electron EDM search in PbO • Current version with fluorescence detection set to take data soon (~end of summer?) • All major parts in place, but projected sensitivity (statistical) now only ~2x beyond current Tl result •Major redesign for 2nd generation experiment based on long cell + microwave absorption underway •Projected 2nd generation sensitivity well beyond 10-29 ecm (better estimate to come soon…) The PbO EDM group Postdocs: (David Kawall) (Val Prasad) Grad students: (Frederik Bay) Sarah Bickman Yong Jiang Paul Hamilton Undergrads: Robert Horne Gabriel Billings Collaborators: Rich Paolino (USCGA) David Kawall (UMass)