Transcript Nonlinear Spectroscopy of Cold Atoms, Preparations for the

Nonlinear Spectroscopy of Cold Atoms,
Preparations for the BEC
Experiments
Jerzy Zachorowski
M. Smoluchowski Institute of Physics,
Jagiellonian University
The Group
Tomasz Brzozowski
Maria Mączyńska
Jerzy Zachorowski
Michał Zawada
Wojciech Gawlik
IF UJ
Magneto-Optical Trap
I
85Rb
N  108
T  100 K
I
Spectroscopy of Cold Atoms
I = 22.4 ·I
0
-50
-40 -20
0
-40
-30
-20
-10
0
10
Detuning from the 3 -4 resonance [MHz]
20
-2
-1
0
1
2
trap -
-2 -1
probe [MHz]
0
1
2
20
Laser system
Frequency
stabilization
Laser
monitoring
Trap beam
Probe beam
PD
AOM
Rb
AOM
AOM
OI
AOM
OI

OI

Master
laser
Laser
amplifier
Probe
laser
Central Structure
• Raman transitions between light-shifted
Zeeman sublevels
• Raman transitions between vibrational
levels in the optical lattice
absorption signal [arb. units]
Zeeman sublevels
a
d
 1-2
3, -2
b
-3
-2
-1
0
 0-1 3,1
3,-1
0-1 0-1
-4
1-2
c
1
3,0
2
3
4
p - L [MHz]
3,2
Vibrational levels
•Electric field in the trap: 6 beams of different polarizations.
•Relative phases not fixed, but relatively stable.
•Interference: intensity and/or polarization modulation.
•Additional optical forces (dipole forces).
•Atoms cooled and localized in the lattice nodes.
•Atomic movement quantized: vibrational energy levels.
Difference absorption-wave mixing
four-wave mixing [a.u.]
FWM signal [arb. units]
absor ption [a.u.]
Ultra-narrow central resonance
absorption signal [arb. units]
Remarks
-2
-2
-1
0
1
2
-2
-1
0
prob e-pump beam detuning [MHz]
1
2
New experiments: trap modulation
-1
0
1
2
3
p - L [MHz]
Bose-Einstein
Condensation
2  2
dB 
mk BT
de Broglie wavelength:
density n, distance n1/3,
n 1/ 3  dB (T )
condensation when:
Ketterle,
PRL 77,
416 (1996)
Lower temperatures
• Spontaneous emission: temperatures limited to 10 – 1K
• „Dark traps”: optical dipole or magnetic forces
• Cooling by evaporation
100 K
300 K
MOT
100 nK
MT
Three steps to BEC
1. Magneto-Optical Trap:
temperature 10 mK, density 1010 cm-3
limit – interaction with light.
2. Magnetic Trap:
trap in field minimum - only „low-field-seeking” states
losses at B = 0.
3. Evaporation cooling:
forced evaporation of hot atoms,
thermalisation by collisions.
1995 - E. Cornell & C. Wieman Rb87
50 nK
200 nK
400 nK
Evidence:
• narrow peak in velocity distribution
• peak’s amplitude  when T
• cloud shape same as that of the potential well
Now
Over 30 laboratories produce BEC
87Rb, 23Na, 7Li, ↑H , He*, ...
Experiments with BEC
•Matter-wave optics: condensate interference, atom laser
•Nonlinear atom optics
•Superfluidity, vortices
•Ultra-low density condensed-matter: Mott insulator
Cold fermions
Matter-wave Optics – Atom Optics
coherent waves
 interference
a)
”atom laser”
b)
NIST
c)
MPQ
MIT
Nonlinear atom-optics
a) light waves
(material medium nonlinearity)
 kin = kout
 in = out
b) matter waves (always nonlinear)
BEC
1999 NIST (W. Phillips)
& Marek Trippenbach (UW)
Superfluidity, Vortices
MIT
LENS, Florence
Ultra-low density
condensed-matter
Mott transition
MPQ – Garching
Micro-BEC
6000 87Rb atoms
loading time 8 s
cooling time 2,1 s
current 2A
Garching
Micro-BEC 2
Tubingen
87Rb
Number of atoms in BEC: 106
Condensation at T=1K
Cooling time 27s
Cold fermions
Do not thermalize (Pauli exclusion)
Sympathetic cooling
e.g. fermion 40K & boson 87Rb, fermion 6Li & boson 7Li
1999 D. Jin (JILA) 40K
2001 R. Hulet (Rice)
Li7
Li6
Our way towards BEC
Element 87Rb
Magneto-optical trapping
T  30 K, N  108
MOT
Transfer to magnetic trap by radiation pressure,
recapture in a MOT
separated vacuum regions
differential pumping (10-8 mbar 10-11 mbar)
Magnetic trapping:
forced evaporation of hottest atoms,
thermalization by collisions
T  100 nK, N  105 - 106
MT
Transfer of atoms
•
•
•
repetitive pushing by resonant light beam, recapture
in lower MOT
collection speed: 108–1010 s-1
loading of lower MOT: 107–109 s-1
constant pushing by narrow light beam (Dalibard)
flux: ~108 s-1
magnetic transfer directly into magnetic trap
(Hänsch)
30% efficiency, complicated.
Magnetic traps
QUIC = Quadrupole + Joffe configuration:
B ≠ 0 at trap center
Dalibard
Hänsch
September 2002
• Laser system prepared
• Upper MOT ready & operating
• Next steps: transfer & recapture
magnetic trapping