3.Spektroskopische Methoden und Präzisionsmessungen

Transkript

1 Inhalt WPF FortgeschritteneAtomphysik I Literatur Budker, Kimball, demille Atomic Physics, Oxford Woodgate Elementary atomic Structure,Oxford Foot Atomic Physics, Oxford Friedrich Theoretische Atomphysik, Springer Demtröder Laserspektroskopie, Springer 1. Atomstruktur 1.1 Diracgleichung, Elektronenspin und Feinstruktur 1.2 Lamb Shift 1.3 Hyperfeinstruktur und Zeeman Effekt 1.4 Übergänge und Auswahlregeln 1.5 Helium 1.6 Mehrelektronensysteme und Zentralfeldnäherung 1.7 Alkali Atome 1.8 Hund sche Regeln 1.9 Rydberg Atome und Stark Effekt 1.10 Geonium 2. Atom-Licht Wechselwirkung 2.1 Zwei Niveauatom 2.2 Lichtkräfte und Laserkühlung 2.3 Drei Niveauatome und elektromagnetisch induzierte Transparenz 3.Spektroskopische Methoden und Präzisionsmessungen 4. Atom-Atom Kollisionen Streutheorie Feshbach Resonanzen 5. Ultrakalte Atome

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3 Lamb Shift in the optical spectrum 300 K Feinstruktur ~10 GHz Williams, R. C. The fine structure of H and D under varying discharge conditions," Phys. Rev. 54, 558 (1938). 100 K

4 Doppler free spectroscopy Hänsch, T. W., I. S. Shahin, A. L. Schawlow, Optical resolution of the Lamb shift in atomichydrogen by laser saturation spectroscopy Nature 235, 63 (1972)

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6 Microwave Experiment by Lamb and Retherford Lamb, W. E., and R. C. Retherford Fine structure of the hydrogen atom by a microwave method Phys. Rev. 72, 241 (1947).

7 Milchstrasse bei 21 cm Linie im H Atom Lebensdauer des Angeregten Zustands ~ einige Mio Jahre Anregung thermisch ABER 80% d. Universums sind H Atome 21cm Linie wird nicht durch Staub absorbiert

8 The Hydrogen Maser GHz. H. M. Goldenberg, D. Kleppner, and N. F. Ramsey PRL, 8, 361 (1960)

9 H Spektroskopie Hänsch MPQ, Garching

10 experimentelle Ergebnisse (Spektren)

11 Messung der 1S-2S 2S-Absolutfrequenz Vergleich mit Cs-Fontänen- Atomuhr Salomon (Paris) Differenz zu 1999: 29 (57) Hz

12 Lambshift L und Rydbergkonstante R Spektroskopie an H und D auf Übergängen 1S-2S, 2S-2P, 2S-8S/8D und 2S-12D L = (22)kHz R = (84) cm 1 mit relativer Genauigkeit von !!! Marc Christian Fischer, Dissertation der Fakultät für Physik der Ludwig-Maximilians-Universität München: Höchstauflösende Laserspektroskopie an atomarem Wasserstoff

13 Zeitabhängigkeit fundamentaler Konstanten α und µ Cs /µ B =g Cs m e /m p Messung von f 1S-2S (d. h. Vergleich H optisch mit Cs HFS) über längere l Zeit (1999,2003). Messung der Absolutfrequenz des Übergangs 5d 10 6s 2 S 1/2 (F = 0) 5d 9 6s 2 2 D 5/2 (F = 2,m F = 0) eines Hg + -Ions in einer Falle (d. h. Vergleich Hg + optisch (el.-quadr.) mit Cs-HFS) am NIST Boulder, Colorado USA, 2 Jahre lang S. Bize et al., PRL 90, (2003)

14 Zeitabhängigkeit fundamentaler Konstanten setzt man: und :

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18 Reminder: Stark map of Rubidium 40F 43S 41D 42P 39F 42S 40D 41P BEC exp. n=40,l>f n=39,l>f electrical field (V/cm) laser frequency with respect to 5 P3/2-level (THz) Dn (MHz) D n= D 5/2 41 D 3/2 laser frequency with respect to 5 P3/2-level (Thz) electrical field (V/cm) electrical field (V/cm)

19 Circular Rydberg atoms for quantum optics experiments Haroche, Raimond, ENS very high electric dipole matrix element on a transition between neighboring states (scales as n squared, 1250 atomic units for the 51 to 50 transition Very long lifetimes (30 ms): The acceleration of the electron is minimal, and hence the radiative losses as low as possible Millimeter-wave transitions between neighboring states ( GHz for the transition between 51 and 50) Perfect implementation of a two level system in a weak directing electric field. No fine or hyperfine structures. Sensitive and selective detection (field ionization method): detect single atoms and determine quantum number

20 Preparation Three diode lasers excite the transitions from the 5S ground state of 85Rb. Through 5P and 5D levels, the 52F level is finally reached. Lasers polarizations are chosen so that only the m=2 substate is populated. The last laser step is resonant only in zero electric field, during 2µs. An electric field is the switched on, and the population transferred to a low lying level in the Stark manifold. A radiofrequency source excites the degenerate transitions to the circular state in an adiabatic rapid passage process.

21 State dependent detection Rydberg atoms

22 Prepare single photon in cavity

23 Photon exchange with empty cavity

24 Interaction with classical field n = 0.85 photons

25 Copy quantum state R1,R2: prepare atomic state e.g. π/2 pulses Copy atom state to photon state

26 Entanglement π/2 pulse with cavity send 2nd atom in g with π pulse atom photon entanglement atom atom entanglement

27 Bohr s Gedanken experiment

28 Modern version of Bohr s proposal

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32 Bohr experiment with circular Rydberg atoms

33 First beam splitter

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35 Cryogenic experiment!

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37 Mesoskopische Quantenphysik Tilman Pfau University of Stuttgart

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39 Interactions make life interesting critical behaviour density ideal Bose-gas Interacting gas superfluidity L. Hau et al., Phys. Rev. A 58, R54 (1998). Bose Nova MIT JILA

40 Outline van der Waals blockade in frozen Rydberg matter Rydberg excitation of a BEC

41 Reminder: Stark map of Rubidium 40F 43S 41D 42P 39F 42S 40D 41P BEC exp. n=40,l>f n=39,l>f electrical field (V/cm) laser frequency with respect to 5 P3/2-level (THz) D n= Dn (MHz) S 1/ elektrisches Feld (V/cm) D 5/2 41 D 3/2 laser frequency with respect to 5 P3/2-level (Thz) relative Frequenz (MHz) electrical field (V/cm) electrical field (V/cm)

42 Rydberg Rydberg interaction Simplest case: van der Waals V() r C = r n energy r(x'),r(x) blockade condition C6 h Max( ΓΩ, ) 6 r c r > fewµ m c g,r g,g Ω r c r=x-x

43 Rydberg Rydberg interaction blockade condition C6 h Max( ΓΩ, ) 6 r c r c 5µ m energy r(x'),r(x) N BEC 10 5 g,r 2 rkepler n a0 100nm N BEC 1 g,g Ω r=x-x r c MOT work: Storrs, Michigan, Freiburg, Paris,

44 Mesoscopic quantum dynamics g g ryd g g g g << r c E Ω? g g g g g g g G collective states 1 E = gg g+ g g g+ + ggg N G= ggg,,..., g { ryd,,,...,, ryd,,...,...,,..., ryd } Ω = NΩ Collective coherent time scale 0

45 Related mesoscopic systems: excitons in quantum dots E F C V 2X X

46 Related mesoscopic systems: excitons in quantum dots E F C V 1 E = v v v + v v v + + N G = v, v, v,..., v { c,,,...,, c,,...,... vvv,,..., c } Ω = NΩ Collective coherent time scale 0

47 Mesoscopic quantum dynamics >r c ryd ryd ryd ryd ryd sat n ryd n ryd ryd ryd t n Ω = N Ω Ω blockade g 0 0 nryd Collective coherent time scale

48 vdw blockade in thermal cloud Change density by microwave Change Ω 0

49 Coherent collective excitation Blockade time scale: Ω Ω0 ng

50 Strong blockade regime Saturation value: N sat ( n ) Ω 0 g,0 0

51 Simplyfied model nryd = 710 cm 9 3 π Assume dense packing : r = 6 18 c µ m

52 Scaling behaviour of r c?? C 6 # nn h N 6 meso rc Ω 0

53 What about the BEC?

54 Rydberg excitation of a BEC BEC T>T c T c

55 Rydberg excitation in a BEC Rydberg atoms survive in BEC BEC survives Rydberg excitation τ~100 µsec Rydberg lifetime in BEC Note: sofar BEC just serves as a dense small well defined mesoscopic sample! but in the future exp. it can serve as a phase reference

56 Rydberg conclusion & outlook strongly interacting Rydberg Matter scalable mesoscopic quantum system measured blockade radius & collective coherent scaling behaviour first Rydberg excitation of a BEC general technique for all quantum gases! n=40 Next steps: Decoherence & Coherent manybody physics Phase sensitive measurements Rydberg molecules? biexcitons? Control interactions by Förster resonance Gate operations? 480,5 nm 5P 3/2 780 nm 5S 1/2 F=2 1> 87 Rb qubit D. Jaksch et al., PRL 85, 2208; Lukin et al., PRL 87, F=1 0>

57 Hans G. Dehmelt * 9 September 1922 in Görlitz

58 Boiling electrons by RF

59 Detecting Spin flips by magnetically induced shift of axial frequency

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