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Engineering Atom Chips Michael Kraft Nano-Scale Systems Integration Group School of Electronics and Computer Science Southampton University.

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Presentation on theme: "Engineering Atom Chips Michael Kraft Nano-Scale Systems Integration Group School of Electronics and Computer Science Southampton University."— Presentation transcript:

1 Engineering Atom Chips Michael Kraft Nano-Scale Systems Integration Group School of Electronics and Computer Science Southampton University

2 Michael KraftEngineering Atom Chips2 Overview What are Atom Chips? Building Blocks of Atom Chips Wires Cavities Actuators Atom Chips Examples Conclusions

3 Michael KraftEngineering Atom Chips3 Control electrons using wires Control photons using optical fibres How do you control atoms? ATOM CHIPS! Using electromagnetic fields and light to interact with clouds or single atoms Atoms (or clouds) can be trapped in magnetic fields and hover a few um above a chips surface What are Atom Chip?

4 Michael KraftEngineering Atom Chips4 Devices for trapping and manipulation of atoms on integrated microchips. Quantum laboratories on chip. Fundamental research Quantum behaviour Low dimensional physics Entanglement and coupling Atom Chips New devices – precise sensors Atom interferometers Atomic clocks Accelerometers/Gyroscopes Quantum information processing Quantum computers

5 Michael KraftEngineering Atom Chips5 High current density gold wires Electrostatic xy comb drive Electrostatic z parallel plate Fibre gold coated at the tip Silicon Bose-Einstein atom cloud Tuneable optical cavity Atom Chip

6 Michael KraftEngineering Atom Chips6 Multi-Domain MEM System Electrostatics –3D Actuator for optical cavity alignment & tuning Electromagnetic –Confinement field for atom clouds Optical MEMS –Optical cavity for single atom detection INTEGRATION is a key issue!

7 Michael KraftEngineering Atom Chips7 Processing Challenges Wet and Dry Etching of Silicon –Smooth cavities –DRIE for high aspect ratios Electroplating and/or etching of Gold –High current density, smooth edged gold wires Assembly –Multi-level wafer bonding with good alignment Ultra high vacuum compatible Considerable process development necessary Applicable to other MEMS devices

8 Michael KraftEngineering Atom Chips8 High current density wires allow the creation, trapping and manipulation of cold atoms and BECs. Neutral atoms in a magnetic field feel a potential due their magnetic moment. V - potential, µ - magnetic moment of the atom B - magnetic field. It is this potential that is used to trap and manipulate the atoms. Atoms accumulate in areas of minimum potential. Atom Guides - Wires

9 Michael KraftEngineering Atom Chips9 Splitting Atom Clouds Minimum coalesces Minimum splits

10 Michael KraftEngineering Atom Chips10 Cold Atoms and Bose-Einstein Condensate High temperature Solid balls Low temperature Wave packets T = T(crit) =170nK for 87 Rb Bose-Einstein condensation Matter waves overlap T

11 Michael KraftEngineering Atom Chips11 Laser Cooling Setup three counter propagating laser beams and a magnetic field Du, PhD thesis, U. of Colorado, 2005 MOT on chip: use 3 lasers and a mirror

12 Michael KraftEngineering Atom Chips12 Wire Fabrication: Electroplating Silicon substrate with 100nm of oxide deposited100nm of gold is depositedThe Cr/Au layer is patterned using a wet etch An electroplating mould is created using photoresist 5µm of gold is electroplating into the mouldThe resist is removed creating the finished chip Silicon Silicon oxide Chromium Gold Photoresist

13 Michael KraftEngineering Atom Chips13 Four Wire Trap

14 Michael KraftEngineering Atom Chips14 Problems With Electroplating Resist reflow

15 Michael KraftEngineering Atom Chips15 Problems With Electroplating Mushrooming

16 Michael KraftEngineering Atom Chips16 Problems With Electroplating Current density

17 Michael KraftEngineering Atom Chips17 Fabrication: Ion Beam Milling Silicon Silicon oxide Chromium Gold Photoresist Silicon substrate with 100nm of oxide deposited 5µm of Gold is sputtered Photoresist is spun and patterned The Gold is ion beam milled or wet etched The resist is removed creating the finished chip

18 Michael KraftEngineering Atom Chips18 Problems With Ion Beam Milling Variable etch rate across the wafer, leading to over etching

19 Michael KraftEngineering Atom Chips19 Fabrication Challenges Electrochemical deposition into a mould Ion beam milling Gold and chromium wet etch Corrugation in these wires causes fluctuations in the magnetic field that leads to fragmentation in the atom cloud.

20 Michael KraftEngineering Atom Chips20 Gold Wires 2cm Atom Chip Layout

21 Wire Atom Chip Under Test

22 23 mm 3.5 microns of gold 67 m Atom Interferometer on a Chip spectacular sensitivity to o EM fields o gravity o other feeble forces

23 Michael KraftEngineering Atom Chips23 Current cooling techniques Atoms are cooled in a macroscopic magneto- optical trap (MOT). Clouds are then transferred from the macroscopic MOT cloud to the microscopic Atom Chip. Inverted Pyramid: MOT on a chip Pyramids on chip can be used to act as a MOT Simpler system, automatic alignment, arrays of MOTs possible. Pyramidal Micro-cavities

24 Michael KraftEngineering Atom Chips24 Pyramidal Micro-cavities KOH etched inverted pyramids with current carrying wires

25 Michael KraftEngineering Atom Chips25 Pyramidal Cavities

26 Michael KraftEngineering Atom Chips26 Biggest pyramid in the mask design = 1.2 mm Atomically smooth side walls SEM

27 Michael KraftEngineering Atom Chips27 Electrophoritic resist is deposited in the pyramids and patterned The gold and chromium is wet etched The resist is removed leaving the flower patterned pyramids Pyramid created by process shown previously leaving it with a gold coating Pyramid Patterning Reflected gold coating needs to be removed at the edges to avoid disturbing light reflections

28 Michael KraftEngineering Atom Chips28 Patterned Pyramid With Wires

29 Michael KraftEngineering Atom Chips29 (100) Silicon wafer, 170nm of oxide is deposited followed by 50 nm of Nitride and the alignments etched into the back The alignment marks are etched into the oxide Openings are etched into the fronts for the pyramidal etch The back alignments are protected with a PECVD nitride layer The pyramids are etched in KOH The front nitride and oxide are stripped 170nm of TEOS oxide is deposited along with 50 nm of chromium and 100nm of gold The chromium/gold layer is patterned An electroplating mould is created from AZ9260 resist The gold wires are electroplated, the resist removed and the chips completed Silicon Silicon oxide Chromium Gold Photoresist Silicon nitride Pyramid Atom Chip Fabrication

30 Michael KraftEngineering Atom Chips30 Patterned Pyramid Atom Chip

31 Michael KraftEngineering Atom Chips31 Pyramid Atom Chip in the Lab

32 Michael KraftEngineering Atom Chips32 Spherical microfabricated cavities are ideal for making high finesse optical resonators. The aim is to achieve single atom – photon interaction. Light couples directly in and out of the resonator through an optical fibre. Spherical Micro-cavities

33 Michael KraftEngineering Atom Chips33 Spherical Micro-cavities Focal spots clearly visible under microscope

34 Michael KraftEngineering Atom Chips34 A silicon substrate with 100nm of oxide deposited and patterned 100nm of silicon nitride is deposited and patterned The silicon is etched using a HF based solution The silicon nitride is stripped using orthophosphoric acid The silicon is etched using an ASE isotropic etch A 50nm Chromium and 100nm Gold layer is sputtered Photoresist is spun and patterned 3µm of Gold is sputtered Photoresist is spun and patterned and the gold is ion beam milled The resist is removed creating the finished chip Silicon Silicon oxide Chromium Gold Photoresist Silicon nitride Spherical Cavities Fabrication

35 Michael KraftEngineering Atom Chips35 optical fibre bragg stack dielectric coated micro-mirror reflection finesse = pm 390 nm 100 m High Finesse Optical Cavity

36 Michael KraftEngineering Atom Chips36 Spherical Micro-cavities Various etch rates can be used to make any radius of curvature Longer etch rates gives smoother mirrors

37 Michael KraftEngineering Atom Chips37 Atom Chip

38 Michael KraftEngineering Atom Chips38 Actuation Design Guidelines xy actuation –Alignment of optical cavity –Misalignment between fibre and spherical mirror during fabrication –xy translation of 5-10 m –xy actuation accuracy of m z actuation –Stable and tunable optical cavity –z translation of 4-5 m (coarse tuning) –z actuation accuracy of a few nm (fine tuning)

39 Michael KraftEngineering Atom Chips39 Translation in +xy direction (xy-actuator) At 117 V a maximum coverage area of 17.5 by 17.5 m is achieved.

40 Michael KraftEngineering Atom Chips40 Resonance Frequencies Mode 1: Resonance frequency (f z res =581Hz) in z motionMode 2: Resonance frequency (f x res =820Hz) in x motion Mode 3: Resonance frequency (f y res =820Hz) in y motion

41 Michael KraftEngineering Atom Chips41 Actuator Chip Prototype

42 Michael KraftEngineering Atom Chips42 Actuator Chip Prototype

43 Michael KraftEngineering Atom Chips43 Fabrication Process XY Actuator Silicon substrate (380 um) 1 st dry-etch (320 um) Glass substrate (500 um) Anodic bonding 2 nd dry-etch (60 um)

44 Michael KraftEngineering Atom Chips44 Electrostatic x comb drive Tuneable optical cavity (spherical cavity and plane mirror ) Bose Einstein atom cloud Fibre with spherical gold coated cavity tip fitted in v-groove High current density gold wires Silicon In Plane Atom Chip Design

45 Michael KraftEngineering Atom Chips45 Microfabrication is a very suitable approach for manipulating clouds of or single atoms Established a modular toolbox for atom chips, including wires, optical cavities and actuators The near future Atom arrays Control over single atoms Further forward Miniaturised atom devices and sensors Far future Quantum computing with neutral atoms? Conclusion

46 Michael KraftEngineering Atom Chips46 Imperial College London E.A.Hinds Pyramids Jonathan Ashmore Fernando Ramirez Martinez Sam Pollock Athanasios Laliotis Cavities Michael Trupke Jon Goldwin Joanna Khunner Athanasios Laliotis Atom guides Stefan Eriksson Rob Sewel Joss Dingjan University of Southampton Michael Kraft Gareth Lewis Zak Moktadir Carsten Gollasch Nanoscale Systems Integration Group People Involved


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