Atoms as quantum probes of near field thermal emission

Transcription

1 Atoms as quantum probes of near field thermal emission A. Laliotis, J. C d Aquinho Carvalho, I. Maurin, T. Passerat de Silans, M. Ducloy, D. Bloch Laboratoire de Physique des Lasers, CNRS - Université Paris13 Villetaneuse

2 Atom-Surface Interaction An interaction between the dipole and his image reflector vacuum - + Image F z + - Atom Image coefficient V vw ~ ε 1 ε + 1 D 2 + D z 2 z 3 Force always attractive Van der Waals Shift ΔF i = C 3 z 3 Experiments: Yale, Orsay, Villetaneuse

3 Atom-Surface Interaction Interaction between the atom and the fluctuating vacuum Atomic polarisability Linear susceptibility of reflected field Near Field Casimir-Polder interaction of atom with fluctuating field Far Field modification of Lamb shift due to the presence Of the reflective boundary ground state alkalis λ~1µm

4 Beam of ground state Na atoms through cavity of variable size 0.7-7µm Measurement of transmitted atoms vs cavity width via ionization and channeltron detection Opacity ~ 1/transmission Van der Waals interaction Casimir-Polder interaction 3s3p wavelength λ~589nm

5 Cavity QED shifts For excited state atoms Spontaneous emission excited state dipole antenna interacting with its own field ground state In the far field shift ~ 1 z cos (2kz) NO experimental observation

6 Temperature dependence The influence of thermal fluctuations ΔF i = k B T a αβ iξ p p=0 Matsubara frequencies: G αβ z, iξ p p = 2k B T/ħ for distances greater than the thermal wavelength only the first term survives z > ħc k B T ΔF i ~ ε 0 1 ε T z 3 Lifshitz room temperature: T=300 K thermal wavelength : λ~7µm

7 Thermal equilibrium Temperature effects too small Out of thermal equilibrium Pitaevskii Stringari Antezza

8 Black-Body-Radiation : Near field vs far field Planck spectrum Black-Body Radiation Broadband radiation Energy per excitation ħω n ω, T N ω Number of excitations/mode-state density of states-modes ε ω For a real material : = ε ω + i ε ω In the near field : evanescent modes (surface polariton modes) z = 1000 z µm z = z 2 µm z = 0.1 µm z J.J Greffet PRL 1999, Nature 2002 from PRL (2000) ω p SiC

9 ε ω 1 ε ω + 1 Im Near field thermal emission and thermal effects on atoms Near field density of states-modes if ω p < ω o red detuned N ev ω ~ 1 ε ω 1 Im z3 ε ω + 1 j > i > ω o Intense monochromatic thermal fields stronger attraction C 3 ωp elevated T to excite the polaritons ħω p k B T ω if ω p > ω o blue detuned j > i > ω o Near field thermal emission, Near field heat transfer repulsion C 3

10 Temperature dependent vdw C 3 T = C m 3 r ω, T Resonant term Non-resonant term ( na ) 1 e r ab( na, ) 2Re ( na ) 1 1 e Absorption na K B na K ( an ) 1 1 r em( an, ) 2Re ( an ) 1 1 e KB Emission B an 4k (i ) 1 r (, ) ' p na QF na 2 2 p (i p) 1na p Matsubara frequency Re ε ω 1 ε ω + 1 with p = 2k B T/ħ ωp Im ε ω 1 ε ω + 1 In thermal equilibrium M-P Gorza & M Ducloy, Eur Phys J D (2006) Other authors: Barton, Scheel, Buhmann

11 Goal of our group : Demonstrating a T dependent C3 Near field effects due to thermally excited surface waves ω p ω o Atomic dipole transitions close to polaritons Only Excited Atoms Selective Reflection Spectroscopy Difficult Initial Experiments : CaF 2, BaF 2 surfaces Successful Experiments : sapphire surfaces, high T Future Experiments

12 Selective reflection Interface Window-Vapour reflection depends on vapour resonances R n n w w n n v v R+ΔR(ω) Resolution < 100 nm ω window vapour Sensitive to slow atoms close to surface Sub Doppler signal 2 ikz ESR p z e dz 0 Spectroscopic Measurement: Scan lasers around i> j> transition Fit spectrum (of vapour close to the surface) with a theoretical model Measurement of C3 (more precisely C3(j)-C3(j))

13 Interaction between Cs and CaF 2 /BaF 2 atom-surface 8P 3/2 36 μm 39 μm 7D 5/2 7D 3/2 CaF 2 polariton 24 μm T~600 K 8P 1/2 ω p > ω o 387 nm 6S 1/2 Cs Laser excitation C 3 dielectrics with : BaF 2 polariton 35 μm T~400 K surface resonances close to atomic transitions surface waves thermally excited at low temperatures

14 Theoretical predictions for 8P 3/2 Sapphire CaF 2 BaF 2

15 Temperature dependent ε(ω) BaF 2 CaF 2 Dielectric constant and surfaces resonances measured for different temperatures T. Passerat de Silans et al. J. Phys.: Condens. Matter 21 (2009)

16 Making and testing a vacuum cell Huge technical difficulties, impossible for BaF 2 A cell is made with CaF 2 Promising results for D1 line T 2 temp control T 3 temp control CaF 2 Sapphire Window Cs reservoir T 1 temp control 30MHz vdw interaction measured for D1 transition A. Laliotis et al. Appl. Phys. B 2008 After extended use at high temperature CaF2 quality clearly degrades

17 SR experiments on Cs(8P) - CaF 2 T. Passerat de Silans et al. Laser Physics 24 (2014) Quality of the surface has deteriorated Experiments do not agree with theory

18 Interaction sapphire and Cs(7D) Dipole couplings from Cs(7D) Dominant contribution of 7D 5F at 10.8 µm sapphire polariton at ~12 µm

19 Theoretical predictions : sapphire and Cs(7D 3/2 ) Higher temperatures required T~ 1200 K

20 High temperature all sapphire cell Super polished sapphire windows (roughness 0.3 nm) Maximum temperature 1200 K Temperature gradient is required Oven 3 Oven 2 Oven 1 Cs drop Shim coils Shim coils to compensate the magnetic field of the oven

21 Lock-in detection Experimental set-up FM modulation AM modulation

22 The Cs hyperfine structure and its importance for our measurements Collisions redistribute the excitation among all velocity classes 7D 3/2 F=5 F=4 F=3 F=2 672 nm x F=4 6P 1/2 F=3 894 nm 6S 1/2 Cs F=4 F=3 Pump and probe are tuned to hyperfine levels

23 Experimental spectrum F=4 F =3,4,5 Fitting C 3 and Γ ± C3 = 51 khz μm 3 C3 = 67 khz μm 3

24 Extracting the C 3 coefficient Varying the Cs density changes Γ and therefore the shape of the spectra Changing hyperfine transitions also changes radically the obtained spectrum Window temperature Tw = 630 K C3 = 63.5 khz μm 3 Γ = 16 MHz C3 = 63.7 khz μm 3 Γ = 16 MHz

25 Spectra for different window temperatures Γ = 17 MHz Γ = 17.2 MHz Γ = 24.2 MHz

26 The ultimate test C3 = 85.8 khz μm 3 Γ = 19.3 MHz C3 = 54.8 khz μm 3 Γ = 18.8 MHz

27 Summary of our experimental results A. Laliotis et al. Nature Communications 5:4364 (2014)

28 Future/preliminary experiments Cs(7P 1/2 ) and Cs(7P 3/2 ) close to sapphire 7P 3/2 7P 1/2 6D 3/2 15μm 12.1μm Excitation lasers 0,455 μm 0,459 μm 6S 1/2 Cs(7P 1/2 ) very resonant experiment with difficult predictions Change of the Cs(7P 1/2 ) lifetime? Possible repulsion for Cs(7P 3/2 )?

29 Acknowledgements Joao Carlos d Aquinho Carvalho Thierry Passerat de Silans Isabelle Maurin Philippe Ballin, Martial Ducloy, Daniel Bloch External collaborators: David Sarkisyan Goran Pichler Rios Leite Horacio Failache Arturo Lezama Pedro Chaves de Souza Segundo Thanks for your attention

30 Casimir-Polder Surface Repulsion forces in Experiments the presence of surface polaritons at T=0 6D 3/2 876μm 12μm 15μm 7P 3/2 Selective reflection experiments 6P 1/2 894μm 7P 1/2 atomic de-excitation (emission) excitation of surface mode 6S 1/2 Cs Sapphire 12.1μm Van der Waals interaction measured on vapour-sapphire interface C 3 is -150 KHz µm 3 (vdw repulsion)

31 C 3 (khz μm 3 ) C 3 vs Cs vapor pressure T=330 C T=520 C T=630 C Γ (MHz)

32 Summary of our experimental results