Overview of the complete vacuum system. The octagonal MOT chamber is connected via a differential pumping stage to the glass science cell. The length of the system from the center of the MOT chamber to the center of the glass cell is 51 cm. Atoms are transported within the vacuum system in a magnetic quadrupole trap which is mounted on a motorized translation stage. The line of sight between the MOT chamber and the science cell is blocked by a glass prism inserted into the transport path. In order to transport the atoms over the glass prism, a pair of shift coils is attached to the vacuum system. The glass cell houses a super-polished prism and is surrounded by a coil assembly (not shown for clarity) used for generating a static quadrupole potential and a magnetic bias field.
Drawing of the MOT chamber (all dimensions are in mm). (a) Side view along the transport axis. The height of the MOT chamber body is 57 mm. The small central hole is a 6 mm diameter exit hole for the transported atoms. (b) View from above of the octagonal shaped MOT chamber. Viewports are attached to the four DN40 CF-flanges to allow optical access for the horizontal MOT beams as indicated. Similarly, viewports on the DN16 CF-flange and two further DN40 CF-flanges provide optical access for the optical pumping beam and fluorescence detection as shown. (c) Cross sectional view of the MOT chamber along the transport axis. The overall height of the system is minimized by using counterbored view ports on the top and bottom of the chamber (not shown in (a) and (b)).
Measurements of the lifetime of a cold atomic cloud for four positions along the transport axis of the vacuum system. Atoms were loaded into a 180 G cm−1 transport trap and then moved to one of the four positions along the transport axis and held for a variable time. The atomic cloud was then transported back to the initial start position and the number of atoms recaptured in the MOT was recorded using fluorescence detection. Fitting the data with a single exponential decay returned lifetimes of: 10(1) s (blue, open squares) in the MOT chamber, 9(1) s (green, open circles) at the start of the 6 mm tube section, 72(5) s (red, full circles) in the bellows section just before the gate valve, and 186(9) s (black, full squares) in the science cell.
Setup of the obstacle prism in the vacuum system. A glass prism, embedded in a macro mount is mounted into the transport path. The mount is held with two rounded down screws in the steel vacuum tube. The prism blocks the line of sight between MOT chamber and glass cell and allows injection of further beams by total internal reflection at its back face.
(a) Schematic of the science cell setup showing the glass cell, the Dove prism, and a set of quadrupole coils. A dipole trapping beam enters the glass cell through the rear face of the prism and subsequently exits the vacuum chamber via the obstacle viewport. (b) Photograph of the Dove prism in the glass cell. The super-polished glass prism sits in a ceramic mount which rests in the corner of the glass cell.
Atom number as a function of the peak vertical displacement of the trap transporting the atoms. On the left hand side (blue solid line) of the graph atoms are lost as they hit the prism, on the right hand side atoms are lost due to hitting the walls of the vacuum tube (red dashed line). Inset shows a drawing of the obstacle prism and mount looking along the transport path. The red ellipse shows the vertical displacement of the atom cloud as it passes over the obstacle.
Displacement of trap center during the transport over the obstacle. (a) Vertical (z) trap displacement as a function of distance between the coil centers. The shaded rectangle shows the size of the obstacle and the arrow shows the typical rms vertical diameter of a 200 μK cloud. (b) Horizontal (x) position of the trap center (red solid line) compared to the position of the transport coil center (black dashed line). The inset shows the trap displacement from the transport coil center as a function of distance between the coil axes.
Transported atom number (a) and temperature (b) as a function of the transport time. For these measurements the acceleration and deceleration were kept constant at 1.0 m s−2 and the velocity of the trapezoidal profile was varied [see inset of (b)]. The solid lines through the data are to guide the eye only.
Measurement of the temperature as a function of transport velocity over the obstacle. (a) Example of a two-part transport profile: the transport before the obstacle is kept the same, and only the velocity over the obstacle in the second part of the profile is changed (as indicated). (b) For transport velocities above 0.3 m s−1 there is a sudden increase in the temperature of the cloud.
Accelerations during the transport over the obstacle. (a) Acceleration in z-direction (black dashed line) and x-direction (red solid line) of the trap center as a function of distance between the coil axes calculated for a transport velocity of 0.26 m s−1. (b) Maximum acceleration in z-direction (black dashed line) and x-direction (red solid line) for various transport velocities. The dotted red line marks the native radial acceleration of the atoms in a quadrupole trap with a 180 G cm−1 vertical field gradient.
The trajectory to BEC in a hybrid trap starting from N ∼2 × 108, PSD ∼10−7 in the bottom right and progressing to N ∼106, PSD >1 in the top left. The inset shows false color images of the transition to BEC from a thermal cloud (L) to a bimodal distribution to a pure condensate (R). Right hand side: Absorption images of cold atoms which are brought up to the surface.
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