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?