arXiv:cond-mat/0504010v1 [cond-mat.other] 1 Apr 2005
Bose-Einstein condensation in a mm-scale Ioffe-Pritchard trap
Kevin L. Moore,∗Thomas P. Purdy, Kater W. Murch, Kenneth R.
Brown, Keshav Dani, Subhadeep Gupta, and Dan M. Stamper-Kurn
Department of Physics, University of California, 366 LeConte Hall #7300, Berkeley, CA 94720
(Dated: February 2, 2008)
We have constructed a mm-scale Ioffe-Pritchard trap capable of providing axial field curvature
of 7800 G/cm2with only 10.5 Amperes of driving current. Our novel fabrication method involving
electromagnetic coils formed of hard anodized aluminum strips is compatible with ultra-high vacuum
conditions, as demonstrated by our using the trap to produce Bose-Einstein condensates of 106
87Rb atoms. The strong axial curvature gives access to a number of experimentally interesting
configurations such as tightly confining prolate, nearly isotropic, and oblate spheroidal traps, as
well as traps with variable tilt angles with respect to the nominal axial direction.
PACS numbers: 03.75.Nt, 32.80.Pj, 05.30.Jp
Magnetic traps have become a staple of ultracold
atomic physics. As such, innovations in magnetic trap-
ping techniques have consistently led to new experi-
mental breakthroughs.For example, the invention of
the time-orbiting-potential (TOP) trap to stem Majo-
rana losses in spherical quadrupole traps led to the
first gaseous Bose-Einstein condensates (BECs) . The
cloverleaf trap , the QUIC trap , and other electro-
and permanent magnet configurations allowed for stable
confinement of large BECs with DC fields and variable
aspect ratios; these capabilities led, for example, to pre-
cise tests of mean-field theories , observations of quasi-
condensates in reduced dimensions , and studies of
long-lived hyperfine coherences in two-component gases
. The rapidly-developing magnetic-trapping technol-
ogy of atom chips now provides new capabilities for ma-
nipulating ultracold atoms and studying their properties
(e.g. coherence of condensates in a waveguide , the de-
cay of doubly-charged vortices in a BEC , etc.).
A typical configuation for magnetic trapping with DC
magnetic fields is the Ioffe-Pritchard (IP) trap . Near
the trap center — at distances small compared to the
size of or distance to the magnets used to generate the
trapping fields — an IP trap is characterized by three
quantities: the axial bias magnetic field B0, the radial
quadrupole field gradient B′
ρ, and the axial field curva-
z. The magnitudes of these parameters scale as
I/d, I/d2and I/d3, respectively, where I is the total
current carried in the wire(s) (or magnetization of fer-
romagnets), and d is their characteristic length scale or
distance from the location of the magnetic trap center.
Both because of this scaling, and because the effective
radial curvature can be greatly increased by lowering the
bias field B0, the limitation to the confinement strength
of an IP trap comes typically from the maximum axial
curvature which can be attained.
As indicated by the I/d3scaling of the axial curvature,
strategies for increasing the confinement of an IP trap in-
∗Electronic address: firstname.lastname@example.org
volve both increasing the current in the coils and decreas-
ing the characteristic size scale of the trap. Magnetic
traps used in most ultracold atom experiments have been
constructed on one of two different length scales. Cen-
timeter (inch) scale traps, which provide superior optical
access, utilize currents of 1000’s of Amperes, typically
distributed as smaller currents in each of several turns
of wire. The highest currents sustainable in such traps,
limited by resistive heating, restrict axial field curvatures
to the neighborhood of 100 G/cm2.
Alternatively, magnetic confinement can be provided
with modest currents by reducing the field-producing
wires and their distance to the ultracold atoms to mi-
croscopic sizes. This strategy has been carried out effec-
tively with surface microtraps [10, 11, 12], resulting in
versatile ultracold atomic experiments. The typical size
scale for these microfabricated magnetic traps is ∼100
µm, and typically only 1 A of current is required to
produce IP traps with field curvatures in excess of 104
G/cm2[11, 13]. Microtraps are not ideally suited for all
experimental endeavors, however, as the atomic cloud is
trapped ∼100 µm or less from the planar surface.
In this article we describe the design, construction, op-
eration, and performance of a millimeter-scale, ∼10 A (or
∼ 100 Ampere-turns) magnetic trap which bridges the
two aforementioned regimes. This “millitrap” utilizes a
novel fabrication scheme which allows for the production
of axial field curvatures of over 7800 G/cm2and is shown
to be compatible with experimental requirements for the
creation of large BECs. We demonstrate that this trap,
owing to its high axial field curvature, allows for a wide
range of trapping geometries, ranging from the typical
prolate spheroidal to the more unusual oblate spheroidal
configuration. Further, we describe a modification of the
IP trapping fields which allows for traps with a variable
tilt angle with respect to the nominal axial direction,
a capability which is compatible with excitation of the
“scissors mode” , the creation of vortices [15, 16] or
other studies of superfluid flow [17, 18] in a BEC. The
trap is also suitable for loading and trapping an ultra-
cold atomic gas inside a high-finesse cavity formed by
conventional mm-scale mirrors [19, 20, 21](or near other
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