Trap loss of spin-polarized 4He*&
He* Feshbach resonances
Joe Borbely(19-03-2012)
Rob van Rooij, Steven Knoop, Wim Vassen
• Trap loss equation
• Experimental details:– Setup– Procedure
• Results with 4He*– magnetic-field dependent trap loss rates
• Present work– Feshbach resonance: 3He*-4He* Bose-Fermi quantum gas
Outline
• Trap loss equation
• Experimental details:– Setup– Procedure
• Results with 4He*– magnetic-field dependent trap loss rates
• Present work– Feshbach resonance: 3He*-4He* Bose-Fermi quantum gas
Outline
Trap loss equation
He*: 19.82 eV
In a spin-polarized gas, Penning ionization is forbidden due to spin conservation.
)12( 13* mSHe
Total spin of the colliding particles in the final state cannot exceed 1, whereas initially the total spin is 2
g
5
33
221 nLnLnLn
In an unpolarized gas two-body losses yield,
Time evolution of trapped density,
L1: background (one-body) collisionsL2: two-body collisions
In spin-polarized He* PI suppressed by 104 → one reason for achieving BEC
L3: three-body collisions: very large release energy Dominant
However, our detection signal (the MCP) is a measure of atom number, not density
We are interested in solving
c2 and c3 are constants that depend on trap geometry
33
221 nLnLnLn
5933
57221 NLcNLcNLN
Trap loss equation
Axial frequency Radial frequency
time (ms) time (ms)
1. Collisions with background gas
5933
57221 NLcNLcNLN Trap loss equation
eXHeXHe*
metastable helium can ionize all atoms (through collisions)- except neon (and ground state helium) atoms
Calculated two-body loss rate for 4He* atoms at 1nK
RIPISRTotal
2. The spin-dipole interaction induces two inelastic two-body (L2) collision processes: - Relaxation Induced Penning Ionization (RIPI) - Spin Relaxation (SR)
g
5
g
1
GV Shylapnikov et al, PRL 73, 3247 (1994)PO Fedichev et al, PRA 53, 1447 (1996)V Venturi et al, PRA 60, 4635 (1999)
couples
iBs SgM i
21 BM
Dominate loss mechanism
5933
57221 NLcNLcNLN Trap loss equation
3. Recombination can occur due to interaction between spin-polarized 4He* in the course of three-body collisions (L3)
Two-body Penning Ionization
spin-polarized helium molecule
two-body PI
4 mK >> 1K
5933
57221 NLcNLcNLN Trap loss equation
• Trap loss equation
• Experimental details:– Setup– Procedure
• Results with 4He*– magnetic-field dependent trap loss rates
• Present work– Feshbach resonance: 3He*-4He* Bose-Fermi quantum gas
Outline
electron bombardment19.82 eV
1557 nm
2059 nm
1083 nm
2x ~120 nm
1557 nm laser light
1083 nm laser light
MCP
Same laser but different frequency detunings for:• collimation• slowing• cooling• trapping• detection
Experimental setup
magnetic field
~100% tranfer
magnetic field
atom
+pho
ton
ener
gy
RFhB 0
+1
-1
0
-1
+1
0
Dressed picture of 4He* in an RF field
Experimental Procedure
Atoms are confined in the dipole trap
Both m=+1 and m=-1 magnetic substates are trappable
• Trap loss equation
• Experimental details:– Setup– Procedure
• Results with 4He*– magnetic-field dependent trap loss rates
• Present work– Feshbach resonance: 3He*-4He* Bose-Fermi quantum gas
Outline
One-body loss: L1
Atomic transfer: BEC thermal
• assumption: thermal equilibrium holds during one-body decay of a condensate
• loss of a thermal atom (i.e. collisions with background gas) cause a free place in the otherwise saturated thermal distribution
• a BEC atom fills the thermal hole (keeps thermal equilibrium)
3
4
whole
thermal
Theory:
Experiment:(a)
(b)
1.7(2)
1.5(2)
80% - 20%
50% - 50%
BEC% - Thermal%
5933
57221 cccc NLcNLcNLN long times (> 15 sec)
Three-body loss: L3
Fix: 25
Magnetic-field independent
Identical for m=+1 and m=-1 atoms
s
5933
57221 cccc NLcNLcNLN
Use only m=-1 atoms (since L2=0)
scmL sysstat
6273 10)6.0()4.0(5.6
scmL
6273 10)3(9
scmL
6274.15.03 108.0
AS Tychkov et al, PRA 73, 031603(R) (2006)
Present result:
VU previous result:
Seidelin result (modified):S Seidelin et al, PRL 93, 090409 (2004)
Two-body loss rate: L2
11 251 sL 1627
3 105.6 scmLFix:
5933
57221 cccc NLcNLcNLN
Two-body loss rate: L2
5933
57221 cccc NLcNLcNLN
N0 @10 ms
N1 @ 2 s
Two-body loss rate: L2 (Comparison with Theory)59
3357
221 cccc NLcNLcNLN
• Trap loss equation
• Experimental details:– Setup– Procedure
• Results with 4He*– magnetic-field dependent trap loss rates
• Present work– Feshbach resonance: 3He*-4He* Bose-Fermi quantum gas
Outline
Ener
gy
Atomic separation, R
Feshbach resonance
0two free atoms
entrance channel
Ubg(R)
Ubg(R) asymptotically connects to two free atoms in the ultracold gasUb(R) can support molecular bound states near the threshold of the entrance channel
a
0
1)(BB
aBa bg
Feshbach resonances are a tool to control the interaction strength between atoms(ultracold chemistry - He*Rb Efimov physics - Steven Knoop)
In the ultracold domain, collisions take place with atoms that have nearly zero energy
scatt
erin
g le
ngth
B
0
quintet
molecular bound channel
singletUb(R)
Zeeman energy of the atomic scattering state becomes equal to that of a molecular bound state because of the difference in magnetic moments
coupling
Ec B
What is a Feshbach resonance?
Feshbach resonances in He*
g
5~1sB0 = 99 GB=2 mG
g
11 << 5
21
Feshbach resonance in 3He*- 4He*
s ms
magnetic trap
3He*(23S f=3/2, mf=-1/2) 4He*(23S f=1, mf=-1)
b A3He*(23S f=3/2, mf=-3/2)
a
Dipole trap
RF spectroscopy 3He*-4He* Feshbach resonance
Feshbach resonance in 3He*- 4He*
3He*(23S f=3/2, mf=-1/2) + 4He*(23S f=1, mf=-1)
b: 3He* mf=-1/2A: 4He* mf=-1
a: 3He* mf=-3/2
Ene
rgy
diff
eren
ce:
A+
b -
A
b Threshold = A+b energy
•Enhanced trap loss at FR •Get information of triplet molecular state
RFA+b
AbA+a
no collisions between identical fermions
limited by three-bodyloss rate
Questions?
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