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Close encounters with a BEC Robust spatial coherence 5 µm from a room-temperature atom chip

Close encounters with a BEC Robust spatial coherence 5 µm from a room-temperature atom chip (and prospects for precision measurements of surface effects) Shuyu Zhou, David Groswasser , Mark Keil , Yonathan Japha , Ron Folman * Ben-Gurion University of the Negev, Be’er Sheva , Israel.

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Close encounters with a BEC Robust spatial coherence 5 µm from a room-temperature atom chip

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  1. Close encounters with a BEC Robust spatial coherence 5 µm from a room-temperature atom chip (and prospects for precision measurements of surface effects) Shuyu Zhou, David Groswasser, Mark Keil , YonathanJapha, Ron Folman* Ben-Gurion University of the Negev, Be’erSheva, Israel Atom Chip Group http://www.bgu.ac.il/atomchip/ Ilse Katz Institute for Nanoscale Science and Technology http://www.bgu.ac.il/en/iki Precision Physics of Simple Atomic Systems – PSAS 2016 Jerusalem, May 22-27/2016 1/28

  2. Close encounters with a BEC Robust spatial coherence 5 µm from a room-temperature atom chip (and prospects for precision measurements of surface effects) • what can we do with atoms at µm and sub-µm distances from surfaces? • probe atom-surface forces (e.g., gravitational and Casimir-Polder force) • map electron transport in microscopic curcuits • guided matter-wave interferometry (λ ≈1 µm for ultracold atoms) • investigate coherence length (e.g., Johnson noise) • engineer atomic circuits (“atomtronics”) • … • how do we bring atoms close to the surface? • atomic beam fly-by experiments • controlled-approach experiments using the “atom chip” • attaining robust spatial coherence (phase correlation throughout a BEC) • experiment: long coherence lifetime and coherence length • experiment: retaining coherence even below a tunneling barrier • theory: decoherence due to noise and atom loss • challenges and applications Atom Chip Group http://www.bgu.ac.il/atomchip/ Ilse Katz Institute for Nanoscale Science and Technology http://www.bgu.ac.il/en/iki Precision Physics of Simple Atomic Systems – PSAS 2016 Jerusalem, May 22-27/2016 1/28

  3. Close encounters with a BEC a brief history … Spielberg et al. (1977) Precision Physics of Simple Atomic Systems – PSAS 2016/Jerusalem 2/28

  4. Close encounters with a BEC a brief history … Spielberg et al. (1977) Precision Physics of Simple Atomic Systems – PSAS 2016/Jerusalem 2/28

  5. Close encounters with a BEC a brief history … • realizations of long-lived spin coherence, but spatial coherence is more fragile • spatial coherence of trapped atoms observed only when ≥40 μm from the surface • permanent-magnet lattices with atoms trapped close to a surface (but no diffraction) • atoms reflected from surfaces (diffraction observed but atoms not held in the lattice) • atomic beam fly-by (not coherent – atom loss due to Casimir-Polder force) Precision Physics of Simple Atomic Systems – PSAS 2016/Jerusalem 2/28

  6. spatial coherence at 5 µm: apparatus magnetic micro-trap for ultracold atoms: the “atom chip” IZ Iw Bext smooth harmonic potential R. Folman, P. Krüger, J. Schmiedmayer, J. Denschlag, and C. Henkel , Adv. At. Mol. Opt. Phys. 48, 263 (2002) 3/28

  7. spatial coherence at 5 µm: apparatus turning on the magnetic lattice potential IZ Iw Bext adjustable potential barriers 5μm period S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 4/28

  8. spatial coherence at 5 µm: apparatus experimental configuration 10-11 – 10-12 torr Iw IZ CCD laser S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 5/28

  9. spatial coherence at 5 µm: apparatus experimental configuration • Experimental parameters • ≈4000 atoms in a BEC of 87Rb in the |F = 2, mF = 2> state. • for d > 9 μm, the potential is purely harmonic (ωǁ=2π x 45 Hz). • for d ≈ 5 μm, the potential is a magnetic lattice with a 5 μm periodicity along x axis. • Experimental procedures • atoms are trapped in the magnetic lattice for periods t = 30-500 ms and then released. • atoms are imaged after 12 ms of free expansion under gravity, alllowing expansion. • observed atom density measures the momentum distribution of the trapped cloud. d = 5µm S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 6/28

  10. spatial coherence at 5 µm: results short holding time High-contrast fringes Diffraction pattern observed after t= 100 ms: (a) average of 30 consecutive images. (b) optical density profile, observed contrast ≈0.6. spatial coherence observed at 5 µm (~10x closer) S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 7/28

  11. spatial coherence at 5 µm: results short holding time High-contrast fringes Gross-Pitaevskisimulations, include holding and release – comparison to experiment: (a) interference peaks after release and expansion. (b) optical density profile. S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 7/28

  12. spatial coherence at 5 µm: results holding times up to 500 ms Robust spatial coherence Diffraction patterns observed after t = 30-500 ms: (a) all data, all holding times (>1000 cycles). (b) side-peak amplitudes are 2-5σ outside a band for random (simulated) phases for each experimental realization. spatial coherence over most of the length of the BEC. S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 8/28

  13. spatial coherence at 5 µm: results holding times up to 500 ms Persistent spatial coherence contrast vs. holding time: (a) no loss of contrast for at least 500 ms (average of the two first-order fringes with 1100 < N < 1900 atoms) (b) dependence of the contrast on atom number no dephasing for t <500 ms 0.6 0.4 0.2 0 (b) contrast 1000 3000 average number of atoms, <N> S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 9/28

  14. spatial coherence at 5 µm: results holding times up to 500 ms Persistent spatial coherence contrast vs. holding time: (a) no loss of contrast for at least 500 ms (average of the two first-order fringes with 1100 < N < 1900 atoms) (b) dependence of the contrast on atom number 0.6 0.4 0.2 0 (b) contrast • greatest contrast observed for: • fewest number of atoms • (lowest chemical potential µ) • longest holding time 1000 3000 average number of atoms, <N> S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 10/28

  15. spatial coherence at 5 µm: results 500 ms holding time Spatial coherence for low μ Diffraction pattern observed after t = 500 ms and with N = 400±130 atoms. S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 12/28

  16. spatial coherence at 5 µm: perspective 500 ms holding time Spatial coherence for low μ Diffraction pattern observed after t = 500 ms and with N = 400±130 atoms. classical surface at 300 K while BEC is at 100 nK surface BEC S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 32/28

  17. spatial coherence at 5 µm: perspective 500 ms holding time Spatial coherence for low μ Diffraction pattern observed after t = 500 ms and with N = 400±130 atoms. classical surface at 300 K while BEC is at 100 nK and yet: long-lived coherence is maintained only 5 µm away! surface BEC spatial coherence: achieved one order of magnitude closer to a surface opens the field for magnetic tunneling barriers S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 32/28

  18. spatial coherence at 5 µm: perspective low chemical potential Spatial coherence for low μ Diffraction pattern observed after t = 500 ms and with N = 400±130 atoms. fewest N Þ lowest chemical potential, likely below the potential barrier. S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 13/28

  19. spatial coherence at 5 µm: perspective low chemical potential Spatial coherence for low μ Diffraction pattern observed after t = 500 ms and with N = 400±130 atoms. • the chemical potential is most likely below the potential barrier. • how is coherence • maintained in this case? • rapid tunneling? • atom-atom interactions? • atom loss? S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) 33/28

  20. spatial coherence at 5 µm: perspective low chemical potential Spatial coherence for low μ Diffraction pattern observed after t = 500 ms and with N = 400±130 atoms. • the chemical potential is most likely below the potential barrier. • how is coherence • maintained in this case? • rapid tunneling? • atom-atom interactions? • atom loss? we consider a model double-well system: the dynamics of a BEC in a double-well potential is equivalent to a Josephson junction of two superconductors joined by a tunneling barrier. Y. Japha, S. Zhou, M. Keil, R. Folman, C. Henkel, and A. Vardi, New J. Phys. 18, 055008 (2016) 13/28

  21. suppression and enhancement of decoherence model double-well system BEC dynamics: squeezing Non-interacting case: each atom is in an equal superposition of the two wells. Interacting case: the ground state is a partially localized state; in the phase- number plane this is a number- squeezed state, where the phase distribution is stretched and the number distribution is squeezed by a factor ξ. Y. Japha, S. Zhou, M. Keil, R. Folman, C. Henkel, and A. Vardi, New J. Phys. 18, 055008 (2016) 14/28

  22. suppression and enhancement of decoherence model double-well system BEC dynamics: atom loss Non-interacting case: atom loss is simultaneous between the two wells. Interacting case: atom loss can be partially localized, creating number fluctuations (localized loss). Y. Japha, S. Zhou, M. Keil, R. Folman, C. Henkel, and A. Vardi, New J. Phys. 18, 055008 (2016) 15/28

  23. suppression and enhancement of decoherence model double-well system BEC dynamics: evolution Non-interacting case: steady state, no evolution (losses do not induce number fluctuations). Interacting case: number fluctuations are translated into phase fluctuations, which are much larger than in the case of a non-interacting system. • enhanced decoherence: Y. Japha, S. Zhou, M. Keil, R. Folman, C. Henkel, and A. Vardi, New J. Phys. 18, 055008 (2016) video 16/28

  24. suppression and enhancement of decoherence model double-well system BEC dynamics: evolution Non-interacting case: steady state, no evolution (losses do not induce number fluctuations). Interacting case: number fluctuations are translated into phase fluctuations, which are much larger than in the case of a non-interacting system. • enhanced decoherence: Y. Japha, S. Zhou, M. Keil, R. Folman, C. Henkel, and A. Vardi, New J. Phys. 18, 055008 (2016) 17/28

  25. spatial coherence at 5 µm summary of results Summary of experimental results • Robust spatial coherence achieved for a BEC ≈5μm from a room temperature surface. • Coherence length of at least ℓ≈ 15μm for >500ms (possibly lifetime-limited). • Corrugations due to impurities and imperfections do not destroy the coherence. • Significant milestone for atom chip applications and for interferometric probing of surface effects. S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) Y. Japha, S. Zhou, M. Keil, R. Folman, C. Henkel, and A. Vardi, New J. Phys. 18, 055008 (2016) 18/28

  26. spatial coherence at 5 µm summary of results Summary of experimental results • Robust spatial coherence achieved for a BEC ≈5μm from a room temperature surface. • Coherence length of at least ℓ≈ 15μm for >500ms (possibly lifetime-limited). • Corrugations due to impurities and imperfections do not destroy the coherence. • Significant milestone for atom chip applications and for interferometric probing of surface effects. Summary of theoretical investigations • Elucidate the interplay between spatial dephasing, inter-atomic interactions, and external noise. • Suppression or enhancement of decoherence due to interactions (squeezing). S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) Y. Japha, S. Zhou, M. Keil, R. Folman, C. Henkel, and A. Vardi, New J. Phys. 18, 055008 (2016) 18/28

  27. spatial coherence at 5 µm summary of results Summary of experimental results • Robust spatial coherence achieved for a BEC ≈5μm from a room temperature surface. • Coherence length of at least ℓ≈ 15μm for >500ms (possibly lifetime-limited). • Corrugations due to impurities and imperfections do not destroy the coherence. • Significant milestone for atom chip applications and for interferometric probing of surface effects. Summary of theoretical investigations • Elucidate the interplay between spatial dephasing, inter-atomic interactions, and external noise. • Suppression or enhancement of decoherence due to interactions (squeezing). Future prospects: challenges and applications • Spatial coherence near a classical environment now in the range of just a few μm from a surface, thereby approaching the threshold for realistic atomic circuits. • Enable a range of applications, e.g., advanced surface probes, guided acceleration sensors, atomtronics ... S. Zhou, D. Groswasser, M. Keil, Y. Japha, and R. Folman, Phys. Rev. A (2016, in press; arXiv: 1505.02654v2) Y. Japha, S. Zhou, M. Keil, R. Folman, C. Henkel, and A. Vardi, New J. Phys. 18, 055008 (2016) 18/28

  28. challenges and applications improving tunneling barriers engineering the potential (a) multi-layer chip (b) µm-size wires (c) use more wire pairs to make thinner barriers S. Machluf, Ph.D. Thesis, Ben-Gurion University (Be’erSheva, Israel, 2013) M. Keil, O. Amit, S. Zhou, D. Groswasser, Y. Japha, and R. Folman, J. Mod. Optics (2016, in press; arXiv: 1605.04939) 19/28

  29. challenges and applications improving tunneling barriers nanowires and nanotubes nm-size wires give tighter traps than µm-size wires (a) gold nanowires (b) carbon nanotubes (a) (b) nanowires also get less noise by using less material CNTs also get smoother potentials due to ballistic currents R. Salem, Y. Japha, J. Chabé, B. Hadad, M. Keil, K.A. Milton, and R. Folman, New J. Phys. 12, 023039 (2010) P.G. Petrov, S. Machluf, S. Younis, R. Macaluso, T. David, B. Hadad, Y. Japha, M. Keil, E. Joselevich, and R. Folman, Phys. Rev. A79, 043403 (2009) 20/28

  30. challenges and applications reducing “technical” noise • Based on direct conversion of amplitude-squeezed light to photocurrent. • Optical squeezing allows measurements below the fundamental shot noise limit (impossible in the domain of classical optics). • An amplitude-squeezed light source and a high-efficiency linear photodiode are used to generate photocurrent with sub-Poissonian electron statistics. D.V. Strekalov, N. Yu, and K. Mansour NASA Tech Brief NPO-47949 (Pasadena, 2011) 21/28

  31. challenges and applications coherence length Johnson noise anisotropic conductivity: spin-flips due to random magnetic noise in the conductors would cause number fluctuations. measure coherence length? BEC T. David, Ph.D. Thesis, Ben-Gurion University (Be’erSheva, Israel, 2009) T. David, Y. Japha, V. Dikovsky, R. Salem, C. Henkel, and R. Folman, Eur. Phys. J. D 48, 321 (2008) 22/28

  32. challenges and applications near-surface forces alternating potentials gravitational (or CP) force: potential differences due to varying density would cause phase and number jumps, modifying the decoherence. F. Sorrentino, A. Alberti, G. Ferrari, V.V. Ivanov, N. Poli, M. Schioppo, and G.M. Tino. Phys. Rev. A 79, 013409 (2009) 23/28

  33. challenges and applications near-surface probes matter-wave homodyning: one wavepacket is sent close to the surface for interaction with a system of interest, while the other wavepacket is maintained further away as a reference (Mach-Zehnder interferometry) (Dimopoulos and Geraci, PRD 68 124021 2003) biophysical systems: a “pancake”-shaped BEC is brought close to an in vivo neural network to detect magnetic fields due to electrical activity (BEC isolated using a µm-thick UHV-compatible membrane). non-Newtonian gravity: atomic beam fly-by experiments probing Casimir-Polder forces at ≈2-10 nm (Lepoutreet al., EPL 88 200002 2009) 24/28

  34. challenges and applications “atomtronics” 25/28

  35. challenges and applications triple-well transistor-like potential BEC transport dynamics (a)magnetic+optical potential (b) calculated potential energy (c) measured atomic density (slightly above Tc) 4.8 μm (a) (b) (c) S.C. Caliga, C.J.E. Straatsma and D.Z. Anderson, New J. Phys. 18, 025010 (2016) 26/28

  36. spatially coherent BECs 5µm from a room-temperature surface 27/28

  37. spatially coherent BECs 5µm from a room-temperature surface “A self-interfering clock as a ‘which path’ witness” Stern-Gerlach type matter-wave interferometer on an atom chip YairMargalit today, 12:00 PM 27/28

  38. spatially coherent BECs 5µm from a room-temperature surface Shuyu Zhou, David Groswasser, Mark Keil , YonathanJapha, Ron Folman* Ben-Gurion University of the Negev, Be’erSheva, Israel Acknowledgements Co-authors: JulienChabé, Ron Salem, Tal David, Benny Hadad PlamenPetrov, Roberto Macaluso, Shimon Machluf, SaeedYounis Kim Milton, Ernesto Joselevich, AmichayVardi, Carsten Henkel Technical: ZinaBinstock, BGU nanofabrication facility Discussions: Marko Burghard BGU AtomChip Group Financing: Israel Science Foundation EC “MatterWave” consortium German-Israeli Project Cooperation (DIP) Council for Higher Education (PBC) Ministry of Immigrant Absorption Atom Chip Group http://www.bgu.ac.il/atomchip/ Ilse Katz Institute for Nanoscale Science and Technology http://www.bgu.ac.il/en/iki Precision Physics of Simple Atomic Systems – PSAS 2016 Jerusalem, May 22-27/2016 28/28

  39. spatially coherent BECs 5µm from a room-temperature surface Shuyu Zhou, David Groswasser, Mark Keil , YonathanJapha, Ron Folman* Ben-Gurion University of the Negev, Be’erSheva, Israel Atom Chip Group http://www.bgu.ac.il/atomchip/ Ilse Katz Institute for Nanoscale Science and Technology http://www.bgu.ac.il/en/iki Precision Physics of Simple Atomic Systems – PSAS 2016 Jerusalem, May 22-27/2016 28/28

  40. spatially coherent BECs 5µm from a room-temperature surface Shuyu Zhou, David Groswasser, Mark Keil , YonathanJapha, Ron Folman* Ben-Gurion University of the Negev, Be’erSheva, Israel and thank you ... for your attention! Atom Chip Group http://www.bgu.ac.il/atomchip/ Ilse Katz Institute for Nanoscale Science and Technology http://www.bgu.ac.il/en/iki Precision Physics of Simple Atomic Systems – PSAS 2016 Jerusalem, May 22-27/2016 28/28

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