Thick-film technology for ultra high vacuum interfaces of micro-structured traps

5.6 MB·

by  Delia Kaufmann

Noname manuscript No.
(will be inserted by the editor)
Thick-film technology for ultra high vacuum interfaces
of micro-structured traps
Delia Kaufmann, Thomas Collath, M. Tanveer Baig, Peter Kaufmann, Eman Asenwar,
Michael Johanning, Christof Wunderlich
Faculty IV: Science and Technology, Department of Physics, University of Siegen, 57068 Siegen, Germany
e-mail: [email protected]
2 Received: date / Revised version: date
1
0
2
Abstract We adopt thick-film technology to produce

n ultra high vacuum compatible interfaces for electrical
a
signals. These interfaces permit voltages of hundreds of
J
volts and currents of several amperes and allow for very
6
compactvacuumsetups,usefulinquantumopticsingen-
2
eral, and in particular for quantum information science

] using miniaturized traps for ions [1] or neutral atoms
h
[2,3,4]. Such printed circuits can also be useful as pure
p
- in-vacuum devices. We demonstrate a specific interface,
nt which provides eleven current feedthroughs, more than
a 70 dc feedthroughs and a feedthrough for radio frequen-
u cies. We achieve a pressure in the low 10−11mbar range
q
anddemonstratethefullfunctionalityoftheinterfaceby
[
trapping chains of cold ytterbium ions, which requires

2 the presence of all of the above mentioned signals. In
v Fig. 1 The wire bonded microtrap chip (the trap itself was
order to supply precise time-dependent voltages to the
2 developed in collaboration with the group of F. Schmidt-
ion trap, a versatile multi-channel device has been de-
8 Kaler[7,19]).Thewirebondsprovidedcandrfconnectivity,
0 veloped. a large number of wire bonds is dedicated to the current
4 carrying middle layer. Distributing the current over several
.
7 wire bonds allows to apply large currents.
0
1
1 Introduction
1 we introduce thick-film technology as a method to pro-
:
v Many experiments in atomic and molecular physics are duce custom made vacuum interfaces for a large num-
i conductedunderultrahighvacuum(UHV)conditionsto ber of signals (as dc and rf voltages and currents) with
X
obtain low collision rates with background gas. At the a small footprint and show that by sealing such parts
r
a same time, many of these experiments, especially those against simple custom made vacuum components UHV
related to quantum information science require versa- pressure can be attained.
tileanddetailedcontrol[3,4,5,6,7,8,9,10,11,12,13].For In the remainder of this article, we discuss thick-
a recent review of micro-structured ion traps, see [14]. film technology and its applicability to UHV setups and
Unlesscontrolisappliedusingopticalfieldsonly[15,16], presentthedesignanddescribethemanufacturingsteps
control is usually required in terms of a large number of of a specific interface. This interface is used to operate
controlvoltages[1,5,6,7,8,9,10,11,12,13]orcurrents[2, a micro-structured segmented linear ion trap for quan-
3], and rf or microwave fields [4,17,18]. tuminformationscienceexperiments(seefigure1).This
Scaling down such experiments is often desirable, ei- trap was designed to trap and laser cool tens of ions in
thertoimproveorsimplifytrapping,toincreasethelevel alocallytunableaxialpotential,anditallowstheappli-
of detail on the control of the trapping potential or to cation of a switchable magnetic field gradient to imple-
maketheminterestingandcompetitiveforindustrialap- ment MAgnetic Gradient Induced Coupling (MAGIC)
plications. In this case commercially available interfaces [20,21,22,23,24].MAGICprovidescouplingbetweenin-
imposeaseriouslimitforminiaturization.Asasolution, ternal and motional states and establishes coupling of
2 D. Kaufmann et. al.
Fig. 2 Steps of thick-film printing: as an example we show the top layer which provides rf and dc connectivity for the trap.
Thefirstprintingstep(a)establishestheradialwiresfordc(thin)andrf(thick)connections,visibleasgreywires.Iffiltering
is not required, already one additional isolation layer (printed in blue in step (b)) suffices to complete the interface as this
avoids shortcuts induced by indium seals (see vacuum setup in section 4). The third step (c) adds a large conductive area
(again in dark grey) which acts as a filter capacitor. In picture (d) two more prints have been added: the circular blue ring
of isolating paste separates the filter capacitor from any indium seal, printed gold pads (displayed as yellow) improve the
adhesion for wire bonding. Also indicated in figure (a) are holes for the trap (blue) and for pumping (red).
all spins, mediated by the ions common vibrational mo- apatternofdcandrfelectrodesthatprovidestheentire
tion. MAGIC recently received attention, as it allows to trappingfunctionality.Thetrapoffersawideloadingre-
manipulate quantum information with rf [25] and mi- gion with nine segments, a narrow region for tight con-
crowave fields and allows for fast laserless conditional finement with nineteen segments and a three segment
gates [26]. Furthermore microwave gates were demon- taper to connect the two regions (see figure 1).
strated with high fidelity [27], robust states using mi- The photo in figure 1 shows the mounted microtrap.
crowavedressingfieldswereimplemented[28],aswellas The trapping potential is generated within the slit in
gates which are largely insensitive to detuning and am- the middle of the quadratic trap chip structure. Inside
plitude errors [29], the entanglement of non-neighboring the loading region the slit is 500µm wide and narrows
ions was shown [30], and it has been discussed as a down to 250µm in the narrower trapping region. The
promising approach to implement quantum simulations total length of the slit is 7.4mm, the edge length of the
[31,32]. whole trap chip is 11mm. The micro-structured design
of the trap allows for trapping ions in different trap re-
gions,movingthemalongtheslitandapplyingmagnetic
2 Micro-structured ion trap
gradients to the trapped ions.
Here, we describe the operation of a micro-structured The middle layer (stacked between the outer layers)
segmented linear ion trap. Such traps allow the tuning wasspecificallydevelopedtoprovideanadjustablemag-
of trapping parameters globally and locally. They thus netic field gradient. This layer is made of gold coated,
facilitate the splitting and merging of ion strings to im- electroplated alumina. We use the conductivity of this
plement scalable quantum computing based on simul- layer to apply a current for generating magnetic fields
taneous operations on only two ions [1], as well as the and gradients in the proximity of the trapped ions, in
tailoring of interaction Hamiltonians [33,34]. Providing ordertoaddressandcoupletrappedionsintheMAGIC-
this amount and detail of control, such traps require a scheme. To boost the coupling induced by the magnetic
large number of electrical signals. Among these are rf field gradient, it is desirable to attain as large gradients
signals with amplitudes of hundreds of volts to achieve as possible and this design was optimized for low dissi-
trapping of ions, a large number of dc voltages (here, patedheatpergradient,asthecurrentlimitthroughthe
up to ±10 volts) to shape the axial trapping potentials, coil is given by the damage threshold of the coil struc-
andcurrentsuptoafewamperesforatomovensand(in tureanditsconnections.Inapreliminarytest,wefound
case of employing MAGIC) for the creation of magnetic thatseveralamperescouldbeappliedwithoutanydam-
fields and gradients. age.Asthispreliminarytestwasdoneonateststructure
Our trap is based on a segmented 3-d linear trap de- withhighohmicresistancesandnocooling,weexpectto
sign developed in the group of F. Schmidt-Kaler [7,19], beabletoapplymorethan10Aofcurrentonthesetup.
other three dimensional microstructured traps are de- To avoid the wire bonds being a bottleneck, the current
scribed, for instance, in [5,6,8,13]. Ions are trapped in is distributed over many bonding wires when feeding it
the slit of a linear Paul trap composed of three laser- to the chip. The large number of additional wire bonds
machined layers made of alumina (Al O ). The outer required cropping of the top layer, to provide sufficient
2 3
gold-coated layers (in the following called top and bot- space for large bond pads on the middle layer (see fig-
tomlayer)featureelectricallyseparatedareaswhichform ure1).LasercutPolyimidfoilsinsertedbetweenalltrap
Thick-film technology for ultra high vacuum interfaces of micro-structured traps 3
layers isolate the entirely gold coated middle layer from
the outer trap layers electrically. Details on the design
and functionality of the magnetic field generating ele-
ments will be published elsewhere. In order to provide
allnecessaryconnections,acompactsolutionwasdevel-
oped and is described in what follows.
3 Microtrap Chip Carrier
3.1 Thick-film technology
(a) (b)
Weadoptthick-filmtechnologytodesignacompactcar-
rierformicro-structuredtrapswhichsimultaneouslyacts Fig.3 Themicrotrapchipcarrierafterallprintingstepsare
as a vacuum interface. Thick-film technology is a well- applied, before mounting and wire bonding of the trap chip
knowntechniqueforthefabricationofelectroniccircuits (a) top view: The thick-film printing procedure was detailed
for this side in figure 2. This side features a large number of
[35,36]. With a screen printing process, wire structures
dcchannelswithasmallfootprintandtherfsupply.(b)bot-
are printed onto ceramics or other suitable insulating
tomview:thissidewasoptimizedforcurrents(forovensand
materials. After the printing process, e.g. on alumina,
solenoids) and features wide conductors and large contact
the printed conducting paste has to be fired at 850◦C.
areas.
Small glass particles inside the conducting paste fuse,
and the printed structures reliably cling to the ceramic
surface.Afterthefirstprintinghasbeenfired,morecom-
electrode should be located close to the trap (in our de-
plex structures and circuits can be generated by suc-
sign we achieve less than 10cm).
cessively adding more layers on top of an already fixed
structure. All these requirements were implemented with a sin-
The paste used in the process is not limited to con- gle thick-film printed ceramic block forming the micro-
ducting paste (which can contain e.g. silver and palla- trap chip carrier. This chip carrier consists of a 15mm
dium, or gold), but also isolating pastes as well as resis- thick block of alumina with outer dimensions of 65mm
tor pastes and pastes to create specific dielectric layers × 75mm.
(e. g. to create printed capacitors) are available. Thick- Thedesignofthethick-filmprintedstructureforthe
film technology can be used to produce wire structures upper side of the chip carrier is illustrated in figure 2.
withaminimumwidthoflessthan0.1mm.Usingalaser Fromlefttoright,thesequenceoftheprintingprocessis
to trim the printed circuits, even smaller structures can indicated to allow a detailed view of the complex struc-
befabricated.Withthesametechnique,thick-filmresis- ture. Figure 2a shows the blueprint of silver-palladium
tors can be adjusted to accuracies of better than 0.1%. wires connecting to the 70 dc electrodes, and the ta-
The wire bonding technique, conducting glue and even pered rf electrode’s connection with two shielding wires
common soldering can be used to connect the printed printed next to it. To fabricate low pass filters close to
structures to certain setups. the microtrap, the next two printing steps provide a ca-
We found that thick-film printed ceramics can be pacitance overlaying all wires, which connects to all dc
usedinUHVenvironments(seeSec.4).Forourpurpose, electrodes.Inordertoformthiscapacitor,blueisolation
aluminaisadvantageousasabasematerial,becausethe paste was printed upon the wire structure in a first step
heat conductivity of this ceramic is comparatively high (seefigure2b).Figure2cshowsthestructureofthecon-
(about 25W/(K·m)) and allows to remove any thermal ducting capacitance layer. In the last two printing steps
intake from ohmic heating. (shown in figure 2d), a ring of blue isolation paste for
the vacuum interface, and golden pads for wire bond-
ing were fabricated. The isolation layer of the capacitor
3.2 Design and implementation was printed twice in order to prevent shortcuts. For the
ring,threeisolatinglayersprovideathicknessofatleast
In order to conduct experiments with the microtrap, a 20µm to apply polishing (see section 4). Although we
radio frequency voltage, 70 dc-voltages, and currents of gainedpositiveexperiencewithresistivepastes,wekeep
several amperes have to be applied to the trap. Fur- all resistors for filtering outside vacuum on nearby ex-
thermore, heat generated from ohmic losses needs to be changable filter boards to keep them fully flexible (see
removed. As ion trapping can only be performed in an section 6). The thickness of the chip carrier is 15mm
UHVenvironment,allsignalshavetobefedthroughvac- and thus provides good mechanical stability and allows
uum interfaces. In order to reduce noise and rf crosstalk toaddstudholesforheatpipestocoolthewholecarrier
on dc electrodes, low pass filters connected to every dc from the air side.
4 D. Kaufmann et. al.
Fig. 4 Schematics of the chip carrier embedded into the vacuum and optical system, as seen from top: fluorescence light is
detected via light gathering optics with a numerical aperture of 0.4 (left); the rest of the vacuum setup, containing an ion
getterpump,atitaniumsublimationpumpandaniongauge(connectedtotheright)containsnofurtherfeedthroughsforthe
microtrap.
The microtrap chip carrier, completely fabricated, components (pumps and a gauge) with ISO-CF flanges
is displayed in figure 3a and 3b. Figure 3a shows the to the right. The contact surfaces of the glass cap and
top view of the carrier, designed as illustrated in the the steel chamber are polished, but no optical surface
blueprints of figure 2. This final thick-film printed de- quality is required. The counterparts of these surfaces
sign provides a capacitance of (44 ± 3)pF for each dc on the chip carrier (the rings of isolating paste, visible
connecting wire. Several holes in the ceramic block (in- as blue rings in figure 3) were polished as well.
dicated in red in figure 2a) are pumping holes to pro- Indium wires with a diameter of 0.5mm were placed
vide good pumping through the carrier. The rectangu- between the polished surfaces and the stack was com-
lar hole in the middle of the carrier (indicated in blue pressedwithfourM4screwsapplyingatorqueof0.5Nm
in figure 2a) is located where the trap is mounted. All (see setup shown in figure 6). Indium will create a com-
other holes are feedthroughs for screws in order to con- pressionsealduetoitslowelasticitymodulus(10.5GPa
nectelectricallytheupperandthelowersideofthechip [37]). We proved the tightness of the indium seals with
carrier and to fix the atomic ovens (see overview in fig- helium leak tests using a quadrupole mass spectrometer
ure4).Figure3bshowsthebottomviewofthechipcar- and found the signal to be dominated by the slow rise
rier, which is used to provide high current supplies for duetodiffusionthroughthechamberwalls.Adiminutive
the atomic ovens and the coil structure providing the amount of vacuum grease is used on all surfaces to be
magnetic gradient. Furthermore, it contains a thick-film abletoseparatethepieceswithoutexcessiveapplication
printed isolation ring similar to the one on the top side offorcebecauseindiumisstickyandwouldotherwisebe
of the carrier. difficult to remove when reopening the chamber.
The trap is glued to the carrier and electrically con-
nectedwithwirebonds(seefigure1).Areliableconnec-
tionisensuredbyconnectingeachdcelectrodewithtwo 4.2 Vacuum system
bonding wires.
The vacuum parts visible in figure 4 connect to further
standardstainlesssteelUHVcomponents.Themaincom-
4 Vacuum ponents are an ion getter pump, a titanium sublimation
pumpandaniongauge,allconnectedviastandardCF40
4.1 Indium seals parts.
All steel parts were baked on air at approximately
To achieve a pressure in the UHV range required for 300◦C for three days, to reduce the achievable vacuum
this experiment we found that placing rings of indium pressure [38]. In a second step, we connected the setup
betweenpolishedsurfacesofthevacuumcomponentsof- showninfigure6toaturbomolecularpumpandapplied
fersareliablesealingmethod.Theessentialvacuumsys- a second clean bake at approximately 120◦C (compati-
tem can be seen in figure 4. The chip carrier is placed ble with all components built in and below the melting
betweenaglasscapwithaninterferometricqualitywin- temperature of indium at 156.4◦C [37]) for three days
dow towards the left, which ensures good optical access toremoveanyexcessamountofvacuumgreasefromthe
and a steel chamber which connects to standard UHV system. After this cleaning bake, the ion getter pump,
Thick-film technology for ultra high vacuum interfaces of micro-structured traps 5
the titanium sublimation pump and the ion gauge were pad with via Top PCB
assembled and the final bake at approximately 120◦C
was applied for four days.
chip carrier conductive
After four months of daily ion trapping the pressure
epoxy
is in the low 10−11mbar range. We can observe 172Yb-
ionsoveratimespanofapproximatelysevenhours.This
was estimated from trapping of larger samples and ob- Fig. 5 Glueingofthemicrotrapcarrierandthetop-PCB:a
serving the lifetime of the complete chain. firstdropletofconductiveepoxyisappliedthroughtheviain
thepadusingasyringeaftercheckingforcorrectalignment.
Aseconddropletappliedonthesidestrengthensthemechan-
icalconnectionandimprovestheresistanceofthecontact.A
5 Electrical Interconnect
gapof0.3mmallowstocontrolthespreadingofgluebetween
the chip carrier and the top-PCB.
All control voltages and currents are supplied to the
microtrap carrier via two double-layer printed circuit
6 Trapping potentials
boards(PCB)whichprovidequickandconvenientmulti-
pin connectors to connect to any signal source (see fig- TherfpotentialrequiredforthePaultrapisprovidedto
ure6).Thehighthermalconductivityandthelargemass the microtrap using a frequency generator which can be
of the chip carrier (compared to the PCBs) exclude the amplified before feeding the signal to a helical resonator
use of conventional soldering techniques (soldering and (for design details, see [39,40,41,42]). Apart from de-
reflow soldering). As an alternative, conductive epoxy is signing the trap for low capacitance, we tried to keep
used to connect the chip carrier to the PCBs. the load capacitance small (about 30pF) by connecting
The upper PCB (in the following called top-PCB) the helix to the microtrap with a short (5cm) co-axial
is connected to the chip carrier as indicated in figure 5. cableandshortconnectionsonthetop-PCBandthechip
The large number of pads on this board requires small carrier. The rf feedthrough introduces a capacitance of
sizes and increases the risk of accidental shortcuts from about 1-3pF. The Q-factor of the helix with connected
spreading glue. To resolve this problem, each pad on microtrap system exceeds 500, which is comparable to
the top-PCB has a 0.95mm-hole, which can be used to the Q-factor obtained with a conventionally connected
check the alignment (to the corresponding pad on the trap.
chip carrier) and to insert the correct amount of glue All dc potentials for the segmented electrodes are
using a syringe. To allow for controlled spreading of the provided by computer-controlled DAC channels via a
glue we found that a gap of approximately 0.3mm be- routing device which allows each signal to be connected
tween chip carrier and PCB is essential. An additional to any number or pattern of electrodes.
drop of epoxy at the side of the carrier (see figure 5) in- WealsodevelopedanElectricFieldGenerator(EFG)
creases the mechanical strength and conductivity of the [43] which provides versatile dc potentials required for a
connection. This technique ensures fault free connectiv- fast and detailed control of the axial trapping potential,
ity for all connections of top-PCB by providing the pos- e.g. for shuttling of ions between trapping and process-
sibilitytocheckandrepair(ifrequired)anybadcontact ing zones. The EFG in its present version provides 20
or short cut between neighbouring pads before proceed- channels and is planned to be extended to 100 chan-
ingtocuring.Theresistancebetweenbondpadsandthe nels in the future. Potentials up to 15V can be con-
pp
top-PCB after curing was found to be below 15Ω for all trolled with an update rate up to 20MHz, a precision of
connections. approximately 1mV, and a noise level below ±0.5mV.
All dc electrodes require currents only in the mA- The device allows to program, store and quickly recall
regime, whereas higher currents are necessary to drive up to 16 different output waveform patterns for each
our atom ovens (up to 2.5A, see section 8) or to gen- channel. High bandwidth and update rates, as possible
erate magnetic fields gradients. All higher currents are with this device, are interesting for ultra-fast transport
providedthroughthelowerboard(calledbottom-PCB). betweentrapsegments[19],or,providedtheupdaterate
We achieved substantially lower resistivity compared to substantially exceeds the trap drive frequency, even to
the upper side using tapered wires on the chip carrier compensate micromotion where this is impossible with
and large pad areas (65mm2 – 121mm2) for large cross dc (e.g. due to rf field components along the trap axis).
sections of the conductive epoxy connections, accompa- For quantum simulations in surface traps, such a device
niedbythick,shortandwidetracesonthebottom-PCB. could provide arbitrary superpositions of dc and rf on
On the other hand, scaling up the width per connec- each pixel electrode, giving full freedom for the lattice
tion results in a much lower number of connections on geometry of the trapped ions. Details on the EFG will
this board (11 total). The resistance between chip car- be published elsewhere.
rier and the bottom-PCB after curing was found to be It is desirable to remove stray fields and rf crosstalk
below 90mΩ for all connections. on all dc electrodes to obtain clean trapping potentials.
6 D. Kaufmann et. al.
Weachievethisusingtheprintedcapacitanceonthechip
carrier (explained in section 3, and shown in figure 2),
and an additional low-pass filter for each dc electrode.
Each of these filters is similar to a π-filter with two ca-
pacitors (1µF each) but with a resistor (15kΩ) instead
of an inductor. The filters are implemented on an ex-
changable 4-layer PCB. This filter is plugged into the
Top-PCB from the air side, and can easily be replaced,
ifdesired,byanotherfilter-PCBwithadifferentcharac-
teristics such as a notch filter.
7 Lasers and detection
The fine structure of ytterbium requires two lasers for
laser cooling [44]: one laser at 369nm drives the 2S
1/2
-2P -transition for cooling and detection, a second
1/2
laser at 935nm drives the 2D -3[3/2] -transition to
3/2 1/2
avoid optical pumping into the metastable 2D state.
3/2
Another laser at 638nm is useful to pump back atoms
from the 2F state which is occasionally populated by
7/2
collisions. A fourth laser at 399nm drives the 1S -1P
0 1
-transition in neutral ytterbium and is used for isotope
selective photoionization [45]. A feature of ytterbium is
Fig. 6 Essential vacuum setup: a simple and compact cus-
theavailabilityofallthesewavelengthsfromlaserdiodes.
tom made steel chamber with a CF 50 flange provides the
AlllasersaresetupasexternalcavitydiodelasersinLit-
basis for the chip holder, and provides an exit port for the
trowconfigurationandlockedtopressuresealedtemper-
laser beams through a CF 16 flange view port. On the pol-
ature stabilized Fabry-Perot cavities by a side of fringe
ished surface of the tube the ceramic chip carrier is placed,
lock. The 369nm laser diode needs to be cooled down and on top of that a cylindrical glass cap with an interfero-
to −5◦C to reduce the free-running wavelength [46] by metricqualitywindow,anti-reflectioncoatedforallourlaser
1.9nm and requires an air tight housing to avoid con- wavelengths. The chip carrier is connected to printed cir-
densation of water on the cold surface. The lasers are cuit boards (see section 5). The multipin connectors are not
coupled into single mode fibres and are combined with shown. The whole stack is compressed with a steel frame by
dichroic mirrors into a single beam which is focused by threaded rods.
a beam shaping telescope into the trap region. The fi-
bre collimators are adjusted to compensate chromatic 8 Loading and trapping
aberrations of the focussing telescope. The beam is di-
rected with two mirrors through the trap slit. One of To start trapping ions, all lasers are locked to temper-
these mirrors is a piezo motor controlled mount with an ature stabilized cavities and set to the correct wave-
alignmentprecisionofsubmicrometeranditdetermines length [12]. The reproducibility of our home-built scan-
the position where the laser beams cross the trap. ning Michelson lambdameter and all lasers is on the or-
The fluorescent light from the trapped ions is col- der of a few tens of Megahertz and sufficient to ensure
limated by a custom made lens system [47] (see also successful loading, once the correct wavelengths are set.
figure 4), optimized for a large numerical aperture of Wecreatecollimatedbeamsofneutralytterbiumat-
0.4, whilst maintaining a diffraction limited spot over a oms by ohmic heating of a small sample of granular yt-
field of view of 500µm. The collimated resonance flu- terbium in a miniature tube-shaped steel oven (for de-
orescence can be directed either to a photo multiplier sign,modellingandoperation,see[45,48]).Twoidentical
tube (PMT) or to an EMCCD Camera. Simultaneous ovens,mountedtotheovenholder(seefigure4)approx-
observation of resonance fluorescence from ions on the imatelyalignedinaplanenormaltothelaserbeam,are
cameraandfromneutralatomsonthePMTisalsopos- filled with isotopically enriched samples of 171Yb and
sible using a dichroic mirror. We use a single-band pass 172Yb, respectively. Deposition of ytterbium atoms on
filter with a transmission peak at 370nm and a width electrodes in the regions relevant for high fidelity ex-
(FWHM) of 6nm in front of the camera to detect fluo- periments is avoided by skimming the atomic beams by
rescence light from the ion. Additional adjustable aper- apertures. Further reduction of neutral atom deposition
tures are placed in auxiliary focal planes to further dis- ontrapelectrodesisaccomplishedbyaligningtheatomic
criminate against unavoidable stray-light from the trap beamsuchthatitintersectsthetrapaxisapproximately
electrodes at the cooling wavelength of 369nm. in the middle of the wide loading region. At this po-
Thick-film technology for ultra high vacuum interfaces of micro-structured traps 7
and microwave-fields. Such interfaces are useful in gen-
eralatomicandmolecularphysics,especiallywhenwork-
ingwithmicro-structuredcomponents,suchastrapsfor
neutral atoms or ions. The vacuum compatibility was
found to be satisfying and matches usual requirements
in atomic and molecular physics, as we regularly attain
pressures in the low 10−11mbar range.
Fig. 7 Loading of an ion chain: above we show a sequence We also used similar multi-layered thick-film based
ofspatialresolvedresonancefluorescenceimagesrecordedby
chip carriers as pure in-vacuum devices as they allow
the EMCCD camera (false color coded). Each picture (from
for complex structures, as, for example, solder free fil-
left to right) with a string of ions represents a time-step,
ter boards in the immediate vicinity of the trap to pas-
whereoneadditionalionwasloaded.Allpicturesweretaken
sively remove noise from dc electrodes. For this purpose
inasingleloadingrun.Theseparationbetweentwoionswas
determinedtoapproximately17µm,correspondingtoanax- not only conductive and isolating pastes are available
ial trap frequency of ν ≈2π· 95kHz. (which alone are sufficient to create capacitors) but also
z
resistivepastesforprintedresistorsanddedicateddielec-
tric pastes to create compact capacitors. The properties
sition, due to the separation of approximately 500µm of such circuits can be fine-tuned precisely by changing
fromthetaperregion,theinfluenceofunwantedaxialrf the area of printed structures using laser trimming [36].
fieldcomponentsissufficientlyscreenedtobenegligible. Evenmoreapplicationsarepossiblebythick-filmhybrid
Atomic ions are produced using a two-step photo- technology, which combines thick-film technology with
ionizationprocess,witharesonantfirststep(see[45]for conventional (glued or soldered) SMD elements.
details). When there is no filter in the detection chan- The scope of the experiment described in this article
nel discriminating light at 399nm, the effectiveness of is to utilize switchable and tunable magnetic field gra-
photoionization can be deduced from the neutral atom dients to use MAGIC. Together with the flexibility of
fluorescence.Visibleresonancefluorescencefromneutral the axial trapping potential [33,34,19] this should allow
atoms can serve as a first frequency reference and cali- for interesting experiments rooted in quantum informa-
bration of the lambdameter with an atomic standard. It tion science and to generate tailored Hamiltonians for
alsoindicatesexcessiveneutralatomflux,whichisdetri- quantum simulations.
mental for our vacuum and causes undesirable coating Thestrongmagneticfieldgradientextendsoverafew
of the electrodes with ytterbium. hundreds of micrometers and ions need to be shuttled
We usually set the oven current, such that the ion intotheexperimentregion(locatedapproximatelyinthe
loading rate is small enough (less than one per second) middleofthenarrowtrapslit,seefigure1)toexperience
toloadionsonebyone.Thefirstionisloadedduringthe itseffect.ThereuponMAGICcanbeutilizedusingradio
warm-up of the oven after approximately two minutes, frequency fields operating on Zeeman levels of the 2S
1/2
startingfromacoldoven.Theloadingrateisthenslowly ground state or, for an easier shelving on Zeeman levels
acceleratedandlongerchainscanbeloadedwithinafew of the 2D manifold [25]. Another possibility is to use
3/2
minutes (see figure 7). Applying an rf power of 125mW the isotope 171Yb+which provides a nuclear spin of I =
results in a radial trapping frequency of 888kHz, cor- 1/2 and is thus more difficult to laser cool, since the
responding to an rf amplitude of approximately 200Vpp hyperfinestructurerequiresadditionalrepumpingfields.
and a stability parameter of q ≈ 0.22. The rf drive fre- MAGIC provides the potential to perform quantum
quencyis7.7MHz.Thepressurerisesduringtheloading information science experiments using Doppler cooled
process up to the mid-10−11mbar range. ions,removingtheobstacle(ornuisance)ofgroundstate
cooling, associated with many implementations of ion
trap based quantum logic. But on the other hand, as
9 Outlook the gradient couples internal and motional states, it al-
lows for sideband cooling using microwaves, simultane-
We showed that thick-film technology allows to gener- ous cooling of many vibrational modes [49] and allows
ate customized vacuum feedthroughs for electrical sig- to improve laser cooling altogether [50].
nals. These feedthroughs were shown to be suitable for
dc and rf signals with voltages up to a few hundreds of
volts and for currents up to a few amperes. Gold pastes Appendix A: Technical Details
are available with up to eight times higher conductivity
and should allow for even smaller current interfaces or The microtrap chip carrier consists of a 15mm thick
larger currents. Moreover, it should be possible, using a block of alumina with outer dimensions of 65mm ×
properdesign,toextendthefrequencyrangeintothemi- 75mm. It was milled by MicroCeram GmbH Meissen.
crowave regime. Thick-film interfaces allow for compact The thick film printing of the block was carried out by
designs with very good access for lasers, detection, rf- the Hybrid Laboratory of the University of Siegen.
8 D. Kaufmann et. al.
Forthethickfilmprints,isolatingpasteDuPont5704, thank Andr´es F. Var´on for fruitful discussions. We ac-
goldpasteDuPont5722Landsilver-palladiumpasteDu- knowledgefinancialsupportbytheEuropeanUnion(STREP
Pont LF 121 were used. As the thickness of the alumina Microtrap and PICC), by the Deutsche Forschungsge-
block is about 15 times higher than typical thick-film meinschaft and by secunet AG.
printed ceramics, the firing process had to be adjusted.
Insteadofastandard50K/minslopeamaximumveloc-
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