Presentation on theme: "Engineering Atom Chips"— Presentation transcript:
1 Engineering Atom Chips Michael KraftNano-Scale Systems Integration GroupSchool of Electronics and Computer ScienceSouthampton University
2 Overview What are Atom Chips? Building Blocks of Atom Chips WiresCavitiesActuatorsAtom Chips ExamplesConclusions
3 What are Atom Chip? Control electrons using wires Control photons using optical fibresHow do you control atoms?ATOM CHIPS!Using electromagnetic fields and light to interact with clouds or single atomsAtoms (or clouds) can be trapped in magnetic fields and hover a few um above a chips surface
4 Atom Chips Fundamental research New devices – precise sensors Devices for trapping and manipulation of atoms on integrated microchips.Quantum laboratories on chip.Fundamental researchQuantum behaviourLow dimensional physicsEntanglement and couplingNew devices – precise sensorsAtom interferometersAtomic clocksAccelerometers/GyroscopesQuantum information processingQuantum computers
5 Atom Chip Electrostatic z parallel plate Tuneable optical cavity Electrostatic xy comb driveElectrostatic z parallel plateTuneable optical cavityBose-Einstein atom cloudHigh current density gold wiresSiliconFibre gold coated at the tip
6 Multi-Domain MEM System → INTEGRATION is a key issue! Electrostatics3D Actuator for optical cavity alignment & tuningElectromagneticConfinement field for atom cloudsOptical MEMSOptical cavity for single atom detection→ INTEGRATION is a key issue!
7 Processing Challenges Wet and Dry Etching of SiliconSmooth cavitiesDRIE for high aspect ratiosElectroplating and/or etching of GoldHigh current density, smooth edged gold wiresAssemblyMulti-level wafer bonding with good alignmentUltra high vacuum compatible→ Considerable process development necessary→ Applicable to other MEMS devices
8 Atom Guides - WiresHigh current density wires allow the creation, trapping and manipulation of cold atoms and BEC’s.Neutral atoms in a magnetic field feel a potential due their magnetic moment.V - potential,µ - magnetic moment of the atomB - magnetic field.It is this potential that is used to trap and manipulate the atoms. Atoms accumulate in areas of minimum potential.
9 Splitting Atom CloudsMinimum coalescesMinimum splits
10 Cold Atoms and Bose-Einstein Condensate High temperatureSolid ballsT = T(crit) =170nK for 87RbBose-Einstein condensationMatter waves overlapLow temperatureWave packetsT<T(crit)Pure BEC, Single matterwave
11 Du, PhD thesis, U. of Colorado, 2005 Laser CoolingDu, PhD thesis, U. of Colorado, 2005Setup three counter propagating laser beams and a magnetic fieldMOT on chip: use 3 lasers and a mirror
12 Wire Fabrication: Electroplating 5µm of gold is electroplating into the mouldThe resist is removed creating the finished chipAn electroplating mould is created using photoresistThe Cr/Au layer is patterned using a wet etchSilicon substrate with 100nm of oxide deposited100nm of gold is depositedSiliconSilicon oxideChromiumGoldPhotoresist12
17 Fabrication: Ion Beam Milling The Gold is ion beam milled or wet etchedSilicon substrate with 100nm of oxide depositedThe resist is removed creating the finished chip5µm of Gold is sputteredPhotoresist is spun and patternedSiliconSilicon oxideChromiumGoldPhotoresist17
18 Problems With Ion Beam Milling Variable etch rate across the wafer, leading to over etching
19 Fabrication Challenges Corrugation in these wires causes fluctuations in the magnetic field that leads to fragmentation in the atom cloud.Electrochemical deposition into a mouldIon beam millingGold and chromium wet etch
21 Wire Atom Chip Under Test In contrast to the videotape chip, here is a microfabricated, wire-based chip
22 Atom Interferometer on a Chip spectacular sensitivity too EM fieldso gravityo other feeble forces67 mm23 mmIn contrast to the videotape chip, here is a microfabricated, wire-based chip3.5 microns of gold
23 Pyramidal Micro-cavities Current cooling techniquesAtoms 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 chipPyramids on chip can be used to act as a MOTSimpler system, automatic alignment, arrays of MOTs possible.
24 Pyramidal Micro-cavities KOH etched inverted pyramids with current carrying wires24
26 SEM Biggest pyramid in the mask design = 1.2 mm Atomically smooth side walls
27 Pyramid PatterningReflected gold coating needs to be removed at the edges to avoid disturbing light reflectionsPyramid created by process shown previously leaving it with a gold coatingElectrophoritic resist is deposited in the pyramids and patternedThe gold and chromium is wet etchedThe resist is removed leaving the flower patterned pyramids
29 Pyramid Atom Chip Fabrication 170nm of TEOS oxide is deposited along with 50 nm of chromium and 100nm of goldThe gold wires are electroplated, the resist removed and the chips completedOpenings are etched into the fronts for the pyramidal etchThe back alignments are protected with a PECVD nitride layerThe chromium/gold layer is patternedThe pyramids are etched in KOHThe front nitride and oxide are strippedAn electroplating mould is created from AZ9260 resist(100) Silicon wafer, 170nm of oxide is deposited followed by 50 nm of Nitride and the alignments etched into the backThe alignment marks are etched into the oxideSiliconChromiumSilicon oxidePhotoresistGoldSilicon nitride
32 Spherical Micro-cavities 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.
33 Spherical Micro-cavities Focal spots clearly visible under microscope
34 Spherical Cavities Fabrication A silicon substrate with 100nm of oxide deposited and patterned100nm of silicon nitride is deposited and patternedThe silicon nitride is stripped using orthophosphoric acidThe silicon is etched using a HF based solutionThe resist is removed creating the finished chip3µm of Gold is sputteredPhotoresist is spun and patterned and the gold is ion beam milledThe silicon is etched using an ASE isotropic etchA 50nm Chromium and 100nm Gold layer is sputteredPhotoresist is spun and patternedSiliconChromiumSilicon oxidePhotoresistGoldSilicon nitride
35 High Finesse Optical Cavity optical fibre74 pmreflection390 nm0.9999bragg stackdielectric coatedmicro-mirror0.9999100 mm
36 Spherical Micro-cavities Various etch rates can be used to make any radius of curvatureLonger etch rates gives smoother mirrors
38 Actuation Design Guidelines xy actuationAlignment of optical cavityMisalignment between fibre and spherical mirror during fabricationxy translation of 5-10 mmxy actuation accuracy of mmz actuationStable and tunable optical cavityz translation of 4-5 mm (coarse tuning)z actuation accuracy of a few nm (fine tuning)
39 Translation in +xy direction (xy-actuator) At 117 V a maximum coverage area of 17.5 by 17.5 mm is achieved.
40 Resonance Frequencies Mode 1: Resonance frequency (fzres=581Hz) in z motionMode 2: Resonance frequency (fxres=820Hz) in x motionMode 3: Resonance frequency (fyres=820Hz) in y motion
44 In Plane Atom Chip Design Tuneable optical cavity(spherical cavity and plane mirror )Bose Einstein atom cloudFibre with spherical gold coated cavity tip fitted in v-grooveElectrostatic x comb driveSiliconHigh current densitygold wires
45 ConclusionMicrofabrication is a very suitable approach for manipulating clouds of or single atomsEstablished a modular ‘toolbox’ for atom chips, including wires, optical cavities and actuatorsThe near futureAtom arraysControl over single atomsFurther forwardMiniaturised atom devices and sensorsFar futureQuantum computing with neutral atoms?
46 People Involved University of Southampton Imperial College London Michael KraftGareth LewisZak MoktadirCarsten GollaschImperial College LondonE.A.HindsPyramidsJonathan AshmoreFernando Ramirez MartinezSam PollockAthanasios LaliotisCavitiesMichael TrupkeJon GoldwinJoanna KhunnerAtom guidesStefan ErikssonRob SewelJoss DingjanNanoscale SystemsIntegration Group