Cold Atoms, Cold Molecules and Optics On Chips (AMO Chips) N. P. Bigelow University of Rochester

Transcription

1 Cold Atoms, Cold Molecules and Optics On Chips (AMO Chips) N. P. Bigelow University of Rochester

2 Cold Atoms, Cold Molecules and Optics On Chips (AMO Chips) N. P. Bigelow University of Rochester + =?

3 How do we cool something without touching it with something cold? HOT Fast Atoms COLD Slow atoms refrigerator REALLY COLD Condensed Gas refrigerator Use radiation pressure to push on the atoms and make them slow down.

4 Light Pressure!

5 Atomic Motion: The Doppler effect Thermal atomic velocities produce optical Doppler shifts larger than atomic absorption bandwidths.!"=k v

6 ATOMIC RESONANCE + DOPPLER EFFECTS Laser Cooling: Idea of Wineland/Dehmelt and Haensch/Schawlow 1975 }!" " o " LASER Laser below Resonance!"<0!"~k v Atoms moving towards the laser beam scatter (absorb and emit) More photons per unit time and are preferentially slowed

7 Laser Cooling: Idea of Wineland/Dehmelt and Haensch/Schawlow 1975 Laser below resonance The Doppler shift guarantees that atoms are slowed by oncoming laser beams--doppler Cooling.

8 The Doppler-Cooling Limit : in 1978 Wineland and Itano worked out the theory of heating and cooling, calculating the lowest possible temperature. T Dopp = 240 µk for Na The randomness of absorbing and emitting photons heats the atoms, competing with Doppler-Cooling.

9 Laser Cooling and Trapping techniques have enabled key technologies and revolutionized AMO physics Clocks Precision measurement Matter wave sensors for navigation and metrology (GPS) more.

10 What happens to atoms at low temperatures? The size of the atomic wavepacket grows the thermal debroglie wavelength increases motion becomes increasingly wave-like!x!p#h/2 600 mph (300 m/sec) 1 mm/sec

11 What happens to atoms at low temperatures? The size of the atomic wavepacket grows the thermal debroglie wavelength increases motion becomes increasingly wave-like!x!p#h/2 600 mph (300 m/sec) 1 mm/sec When the atoms are cold enough, they phase-lock

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13 BEC $ Matter Wave Overlap de Broglie Wavelength increases as temperature decreases 10 2 K Billiard Balls 10-7 K Pure BEC

14 Cornell & Wieman

15 The BEC wave function % = &e i' has an amplitude and a phase

16 Water waves

17 Two condensates µm Ketterle MIT group

18 ... interfere Interference pattern Ketterle - MIT group

19 AN EXAMPLE OF APPLIED LASER COOLING debroglie Wave - atom - gyroscope the Sagnac interferometer The atom version is more sensitive (all things being equal) by Mc 2 /h(

20 The real challenge in deploying these techniques in usable devices

21 The Solution

22 What is an Atom Chip? Schmeidmeyer group Libbrecht group Mesoscopic wire-chip lithography is being use to manipulate atoms hovering over the surface using B fields. Combining atoms with nanostructures realizes an atom chip.

23 The starting point: surface magneto-optical trap +! +!! " SiO 2 (80nm) Ag(60nm) Si(300µm)! " R(%) > 95% d N cloud! chip MOT 7 ~ 10 ~ 1mm atoms

24 Atom Chip ) + -) - polarization Y I S ~1-3 A x SiO 2 (250nm) Z Ag(50nm) Cu(1mm) I B ~15-20 A Si(1mm) Small wire chip lithography is useful in manipulating atoms. Chip surface also acts an a mirror.

25 Magnetic Trapping (and Evaporative Cooling) PE µ r B r Spin Flip Frequency ~ MHz z µ r B r

26 Nothing Exotic

27 Magnetic Trapping (and Evaporative Cooling) PE µ r B r Spin Flip Frequency ~ MHz z µ r B r

28 Chip Traps z 2-d trap or guide y z 0 U(x) = µ B(x) B=B 0 y Fields cancelled at a particular point above the chip Constant bias & wire current are optimized

29 Loading Onto the Chip Imaging of sample Schmeidmeyer group

30 Atom-chip Beam Splitter Folman & Schmeidmeyer

31 BEC on a Chip! Cornell & Wieman J. Reichel and T. Hänsch

32 Atomic Conveyor Belt Reichel

33 g

34 NIST workers (and others) have Also realized chip-scale atom cells and clocks!

35 Atom Chips are REAL and at a Vacuum Tube -like stage of development..so what next? Dana Anderson group

36 Some new AMO Chip directions

37 Some new AMO Chip directions Optics integrated on the chip

38 Initial Idea laser field guiding conductor Optical fiber/waveguide Chip-substrate

39 OPTICS ON THE CHIP: IMPLEMENTATION We have fibers with waists as small as 6 µm provided by Corning

40 Atomic electric-eye chip P. Quinto-Su, M. Tschernek, M. Holmes and N. P. Bigelow, On-chip detection of laser-cooled atoms, Optics Express, 12, 5098 <100 atom sensitivity Lineshape for different intensities

41 Shortly thereafter: another big breakthrough

42 Molecule Chips? A primer on cold molecule sources Building cold molecules our debut of molecule chips

43 Making cold molecules is not as easy as making cold atoms Laser cooling (in general) does not work

44 An old idea:ground state diatomic molecule formation from atom pairs? Y e (R) 2 energy V e (R) S+P laser Y g (R) 2 Bind colliding pairs into excited-state molecules (PA) then they decay in to bound (electronic) ground-states E S+S K Photoassociation (PA) - make excited-state V g (R) Condon radius R C Internuclear distance R Spontaneous decay to Electronic ground-state

45 An old idea:ground state diatomic molecule formation from atom pairs? Y e (R) 2 energy V e (R) S+P laser Y g (R) 2 Lousy FC factors! won t work! E S+S K V g (R) Condon radius R C Internuclear distance R

46 BUT In 1997 Pierre Pillet and co-workers startled the community by showing the Cs 2 ground-state molecules were produced in a conventional MOT

47 Formation Detection

48 R-transfer method Frank-Condon Matching

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51 What about more complex molecules??? What about POLAR molecules? (hetero-nuclear)

52 Recall: Origin of molecular electric dipoles No E-field: no dipole! J = 1, m J = 0 = p> + - Wavefunctions of polar molecules z, E With E-field: induced dipole ,> + s>+ p> polarized molecules act like permanent dipoles - + J = 0 = s> *> + s>- p> + - Small splitting (~10-4 ev) between states of opposite parity (rotation) leads to large polarizability (vs. atoms, ~ few ev)

53 Samples of Polar Molecules Are Interesting The dipole-dipole coupling of the quantum particles can be harnessed for quantum information applications (Ions [Zoller], Quantum Dots [Barenco], Rydbergs [Lukin]) There are novel quantum fluids expected for polar molecules There are applications to symmetry tests (EDM, etc.) Novel collision properties Why Not!!! Low temperatures are enabling or enhancing

54 Why Cold (Polar) Molecules? More Reasons Later.

55 Doyle approach - Thermalization with cold helium gas & magnetic trapping Dilution Refrigerator ~mk Paramagnetic molecules Large samples

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58 Making Cold Polar Molecules! At Harvard, Doyle has pioneered cryogenic techniques! Several groups are now cooling molecules using electrostatic/dynamic techniques (Meijer, Hinds, Rempe )

59 Meijer - time and spatially varying E fields decelerator (à la high-energy in reverse; H. Gould) accelerate

60 Meijer - decelerator (à la high-energy; H. Gould) decelerate

61 Meijer approach: Starting with a molecular beam Cooling of internal degrees of freedom in a pulsed supersonic expansion High initial phase-space density But: high velocity in the lab frame, typically in the m/s range and exploiting the interaction of (polar) molecules with an electric field U W F pot Stark Stark = = = W Stark " µ # "! W! z E Stark

62 Operation principle of the Stark-decelerator PRL 83 (1999) 1558 PRL 84 (2000) 5744

63 The 1 meter long Stark-decelerator

64 Making Cold Polar Molecules! Using judiciously selected laser light cold molecules in their electronic ground states have been created by several groups (Sao Carlos, Yale, Connecticut, Rochester..) Count Na+Cs Cs Na v = Time (µs)!using magnetic and optically controlled Feshbach resonances very cold heteronuclear molecules have been created (JILA, MIT..) B-dependent resonance

65 Making Cold Polar Molecules the Frank-Condon factors may be better ( 2 (1 Count Na+Cs Cs Na v = Time (µs) B-dependent resonance

66 (transition rate)+ (collision rate& pair distribution)* (excitation rate)* (survival rate)*(process probability-fc factors)* (density 2 )*(volume) These factors determine molecular production rates

67 We might be CLOBBERED by the pair distribution function R homo /R hetero = 950/76 ~ 13 (R homo /R hetero = 950/76 ~ 1/10) 2 ~ 100! The interaction time is also smaller by a factor of ~ 13!

68 Nevertheless, several groups built multispecies MOTs - including Rochester and Sao Carlos and

69 Kasevich Arimondo Ingusio Weidemuller Windholz DeMille Stwalley/Gould Wang/Buell Ruff others NaCs NaK NaRb RbCs KRb LiCs LiNa? Most reactive Bose-Fermi&Isotopic: Jin, Salomon, Ertmer, Ketterle, Hulet, Sengstock Sukenik

70 We started with Na + Cs

71 Our system NaCs NaCs PA and PI Spectroscopy Korek et al., Can. J. Phys. 78, 977 (2000)

72 NaCs PA and PI Spectroscopy PA

73 NaCs PA and PI Spectroscopy Spontaneous Relaxation

74 NaCs PA and PI Spectroscopy Spectroscopic probe via REMPI using pulsed dye laser

75 Electronic Ground State Polar Molecules At ~ 260 µ- have been created in two-species MOT 2500 photons 2000 cold Na Cold Cs Count Thermal Na Na 2 Cold NaCs Cs 2 Na+Cs Cs Na Time (µs)

76 What if we choose the PA tuning to couple to states with better FC overlap? PA

77 By photoassociating (PA) on a particular transition with strong F-C factors we can massively enhance NaCs production Na + Cs + NaCs + Cs 2 +! PA = -950 GHz. PI = nm 60 ions/shot >100 khz production

78 Photoionization Energetics - there is another knob - the PI probe laser wavelength

79 Sample Photoionization Spectrum down into ground-state well! PA = -950 GHz Photoassociation laser fixed in frequency Photoionization laser scanned in frequency A scan of the population distribution of molecules created in the electronic ground state

80 Sample Photoionization Spectrum! PA = -950 GHz. PI as low as 570 nm A scan of the population distribution of molecules created in the electronic ground state

81 Sample Photoionization Spectrum! PA = -950 GHz. PI as low as 570 nm Ground state molecules bound by as much as 3000 cm -1 Singlets and Triplets Quadratic PI energy dependence verified A scan of the population distribution of molecules created in the electronic ground state

82 Photoassociation Spectrum Zero is Cesium 6s 1/2 (F=4)!6p 3/2 (F=5) PA laser (molecule-maker) tuning

83 Photoassociation Spectroscopy Zero is Cesium 6s 1/2 (F=4)!6p 3/2 (F=5) PA laser (molecule-maker) tuning

84 Zooming-in reveals clear rotational structure!j(j+1)

85 Full Energy Level Diagram Which states are we probing?

86 PA Analysis Start with diabatic potentials Add spin-orbit Diagonalize matrix for Hund s case (c) potentials Energy (cm -1 ) R (Angstrom)

87 PA Analysis Calculate bound states using LEVEL Can identify largest detunings as /=2 Preliminarily assign vibrational quantum numbers Detuning (cm -1 ) Vibrational Quantum Number Calculated Omega=2 Levels Observed

88 Franck-Condon Factors

89 Verification of polar molecules: RbCs behavior in E-field - demille group Fitted electric dipole moment for this (/=0 + ) state: µ= 1.3 Debye From Dave DeMille at Yale and Tom Bergeman At SB

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91 Some new AMO Chip directions Realizing Molecule Chips

92 Molecules and Chips

93 Atom Chip ) + -) - polarization Y I S ~1-3 A x SiO 2 (250nm) Z Ag(50nm) Cu(1mm) I B ~15-20 A Si(1mm) z y z 0 B=B 0 y

94 Single-species molecule chips Cs 2 Appl. Phys. B, 80, 639

95 Creating and manipulating cold atomic mixtures-on-a-chip Trap Image of Trap Atom chip surface Holmes, Tscherneck, Quinto-Su and Bigelow, Phys. Rev. A, 69, Rb-Cs

96 Cold (Polar) Molecules and Quantum Information Count Na+Cs Cs Na Time (µs)

97 Polar Molecules Allow Coupling Enabling Quantum Information Applications Heteronuclear molecules are highly polarizable The dipole-dipole coupling of the molecules can be harnessed for quantum information applications (see protocols for EDMs in Quantum Dots - e.g. Barenco, et al PRL )

98 A specific qubit platform Each atom sees a local field that couples it to its neighbors and permits selective addressing r E a = r E ext (x a ) + r E int (x a ) The coupling cannot be switched off but instead can be compensated using echo-type refocussing techniques of NMR. What is needed is a source of cold molecules D. DeMille, PRL 88,

99 The real workers C. Haimberger, J. Kleinert, M. Holmes M. Tscherneck, P. Quinto-Su A. Wakim New Theory Team T. Bergeman and O. Dulieu Thanks to NSF And to W. D. Phillips, W. Ketterle, D. DeMille for sharing some very nice slides with me that used are in this talk!