Gael Reinaudi. Invited speaker at "Quantum Engineering based on Atoms and Photons", Hannover 2007

Manipulation of ultra-cold atom packets.
Towards a new setup to produce a continuous atomic beam in
the degenerate regime
Gaël Reinaudi
Laboratoire Kastler Brossel
Previous members

Séminaire à Hannovre le 27 fevrier 2007
Par Gaël Reinaudi

Thierry Zhaoying
Lahaye Wang

Post-Doc Post-Doc
G.R. Tomasz David Antoine
Kawalec Guéry-Odelin Couvert

PhD Post-Doc Team leader PhD

Reminder , How to… Moving mirror Train of traps Dipolar beam

Experimental Setup
7 · 109 atoms/s @ 1 m/s
Step 1: Step 3:
Production of cold Cooling by forced
atomic packets evaporation

PRA 73, 035402 (2006)
Step 2:
Injection, and
magnetic guiding (4.5 m)

2 · 109 atoms
in 100 ms


Evaporation on a magnetically guided beam

RF

Tini = 574µK Tf = 164µK
Flux ~ 7 · 109/s Flux ~ 9 · 108/s
nλ3 = 2 · 10-8 nλ3 = 2 · 10-7
Gain of one order of
magnitude in phase space
density

PRA 72, 033411 (2005)


How far are we from the Bose-Einstein condensation ?

The maximal gain in phase space density one can expect is
limited by the number Nc of collisions undergone on average
by each atom during its propagation in the guide

Up to now, we have had at best : Nc ~ 25

With Nc ~ 200,
We could gain the 8 orders of magnitude that we need in
phase space density.
EPJD 33, 67 (2005) PRA 73, 063622 (2006)


What makes it difficult ? 

 1. Our way to produce a continuous beam implies a
longitudinal dilution of a single packet, resulting
in a reduction of the collision rate by a factor ~ 6.

 2. The duration available for evaporative cooling is
limited by the injection velocity.

 3. The efficiency of evaporation is reduced for a
two dimensional implementation with respect to
its three dimensional counterpart.


Outline of the talk
Improving the evaporation conditions:
1. Slowing the packets of atoms with a moving magnetic mirror

2. Maintaining a 3D confinement in the guide with a train of magnetic traps

Improving the packets preparation and injection:
3. Confining the atoms for the entrance in the magnetic guide using a
dipolar Beam
1070 nm
300 Watts


• The moving mirror: the idea
…and the results

• The train of Ioffe-Pritchard traps: the idea
…and the results

• The dipolar trap: the idea
…and preliminary results


Moving Mirror, the idea :

Lab frame Mirror frame
mirror mirror

Before atom atom
collision vi vm vi - vm
= 1.4 m/s = 80 cm/s

mirror mirror

After atom atom
collision vm -(vi - vm)
2·vm-vi

= 20 cm/s ! !!
Ec reduced by 98% !!!


Moving Mirror

= 1.7m


The magnetic Mirror

magnets

on the axis of the magnetic guide
Glass
tube
magnetic guide

magnets
160G 1m/s
For 87Rb (F=1;mF=-1)


The magnetic Mirror

magnets

Glass
tube
magnetic guide

magnets


Measures

zp = 1.7m


Measures

zp = 1.7m

Deduce vz = 142 cm/s
and Δvz = 12 cm/s


Measures

zp = 1.7m

vm = 86 cm/s

and Δvz = 12 cm/s


Measures

zp = 1.7m

vm = 86 cm/s

and Δvz = 12 cm/s

vz ~ 35 cm/s
Δvz ~ 12 cm/s
Ec reduced by 94%


Periodic slowing of packets
zp 1.7m
zp = 2.25m

vm = 85cm/s

Injection @ vi = 120cm/s
with no mirror
Probe @ 1.7m

Same conditions, but with
the mirror @ vm = 85cm/s
Probe @ 1.7m

Same conditions, but with
the mirror @ vm = 85cm/s
Probe @ 2.25m

EPJD 40, 405 (2006)


The Conveyor Belt =   

50 magnets on a conveyor belt

 3D Trapping  Maintain a high collision rate

 Slow motion of the train  More time to perform evaporation

 Evaporation in 3D trap  Optimal gain in phase space density


Potential experienced by the atoms

Copper
tubes
I=400A

5 cm Magnets

Guide

Train of quadrupolar 3D traps


Quadrupolar Ioffe-Pritchard

Ioffe-Pritchard

Bsol

|Bz| Quadrupolar
Bsol

z

Magnets


Influence of the relative velocity
Vi = 80cm/s
d = 1.7m

MOT
probe

Trapped atoms
Slowed atoms
Vi ~
Fast atoms

-Spreading is frozen out

-Large capture range of velocity


Different classes of atom
vi = vc = 50 cm/s B0 = 20 G

Cloud 100% trapped

vi = vc = 50 cm/s B0 = 50 G

Cloud partially reflected

vi = 80 cm/s vc = 50 cm/s B0 = 40 G


Periodic injection

probe

|Bz| at the level of the probe

vi = vc = 88 cm/s ; B0 = 32 G Atomic density


Parallelization of evaporation

+ evaporation T : 520 µK 280 µK

|Bz| at the level of the probe PRA 74, 033622 (2006)

vi = vc = 88 cm/s ; B0 = 32 G Atomic density


Dipolar beam
Yb fibered laser
P = 300W, λ = 1070nm

M² = 1.02

Δλ = 1nm
 photo-association losses?

typical trap (Waist x Rayleigh length)
Magnetic guide
100µm x 3cm with Imax = 2 MW/cm² 3 mK
I

50µm x 8mm with Imax = 8 MW/cm² 12 mK
I

20µm x 1mm with Imax = 50 MW/cm² 75 mK
MOT chamber


Dipolar beam
Yb fibered laser
P = 300W, λ = 1070nm

M² = 1.02

Δλ = 1nm
 photo-association losses?

Clouds of ~108 atoms @ 200µK
Density : 5·1013/cm3
Collision rate : 5·103/s

MOT chamber


Dipolar beam: the idea

Coupling packets of atoms into a magnetic guide

Coupling packets of atoms into a train of Ioffe-Pritchard traps


Currently studied: Transport of atoms
MOT chamber Science chamber


Currently studied: Transport of atoms
MOT chamber Science chamber

Preliminary experiments:

Loading 4·107 atoms @ 80W
Power T ~ 200µK (w=35µm)

Starting transportation @ 3W
with 6·106 atoms @ 30µK
2cm
time
1s 100ms Round trip in 1.5s


Conclusion
– Moving mirror
Perspective:
generation of a continuous,
intense and very slow beam of
guided atoms.

EPJD 40, 405 (2006)

– Train of Ioffe-Pritchard Traps
Perspective:
Parallel production of condensates

PRA 74, 033622 (2006)

– Transport In dipolar beam
Perspective:
Coupling those packets in
– The magnetic guide
– The conveyor belt

Gael Reinaudi. Invited speaker at "Quantum Engineering based on Atoms and Photons", Hannover 2007

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