Post on 03-Jan-2016
description
D. Jin
JILA, NIST and the University of Colorado
$ NSF, NIST
An atomic Fermi gas near a
p-wave Feshbach resonance
1. Motivation
2. A p-wave Feshbach resonance
3. Molecule energies and lifetimes
4. Future
Outline
Fermi condensate
Fermionic superfluidityCooper pairing: two correlated fermions act like a boson
Examples
Superconductivity: Cooper pairs of electrons
Superfluid 3He: 3He atom pairs
Superfluidity in nuclear matter:Nucleon pairs
P-wave pairing?Fermi condensates with non-s-wave pairing?
• Examples: • superfluid 3He (p-wave)• high Tc superconductors (d-wave)
• Novel features:• anistropic gap• multiple superfluid phases,• narrow resonance
s-waveL=0
p-waveL=1
m l= -1,0,+1
• This is the first step toward making molecule condensates and fermion pair condensates.
• New possibilities: non-s-wave molecules, heteronuclear molecules, fermionic molecules, ground-state molecules, and polar molecules.
Making molecules
other non-s-wave Feshbach molecule studies:
Grimm (s- to g- wave), Salomon (p-wave)
Molecules can be very efficiently created using a Feshbach resonance.
• magnetic-field sweep across resonance• three-body collisions near a Feshbach resonance• rf association
• magnetic-field modulation
Making molecules
A magnetic-field tunable atomic scattering resonance
Channels are coupled by the hyperfine interaction.
Feshbach resonance
→ ←colliding atoms in channel 1
molecule state in channel 2
P-wave resonance
0
V(R)
R
centrifugal barrier
S
0
V(R)
R
22
)1(
rm
ll
300 K
300 K
0.5 K
Collisions and Fermions
one spin-state
two spin-states
ela
stic
co
llisi
on
cro
ss s
ect
ion
B. DeMarco et al., PRL 82, 4208 (1999)
40K
P-wave resonance
180 200 22010-13
10-12
10-11
10-10
10-9
(cm
2)
B (gauss)
C.A. Regal, C. Ticknor, J.L. Bohn, & D.S. Jin, PRL 90, 053201 (2003)
40K
spin-polarized gas|f=9/2, mf=-7/2>
ela
stic
colli
sion
cro
ss
sect
ion
198 199 2000
2x105
4x105
6x105
8x105
Num
ber
B (Gauss)
Multiplet structure
ml = ±1 ml = 0B0 = 198.3 G B0 = 198.8 G
C. Ticknor, C.A. Regal, D.S. Jin, and J.L. Bohn, PRA 69, 042712 (2004).
ml = ±1ml = 0B
198.8 199.0 199.20
1
20
5
100
10
20
0
20
40
B (G)
EF = 4.4 kHz
EF = 7.7 kHz
EF = 10.4 kHz
Ato
m n
umbe
r (x
104 )
EF = 13.3 kHz
Width of loss feature
ml = 0resonance
Feature of a narrow resonance
B-field modulation
0 20 40 60 80 1000
2x104
4x104
6x104
Ato
m n
umb
er
frequency (kHz)
B below both resonances
dissociation M. Greiner, C.A. Regal, & D.S. Jin, PRL 94, 070403 (2005)association S.T. Thompson, E. Hodby, & C.E. Wieman, PRL 94, 190404 (2005)
Near a Feshbach resonance, a resonant oscillating B-field can create molecules.
0
V(R)
R
centrifugal barrier
Quasi-bound molecules
0
V(R)
R
centrifugal barrier
0 20 40 60 80 1000
2x104
4x104
Nu
mb
er
frequency (kHz)
B above theresonance
-1.0 -0.5 0 0.5 1.0 1.5-300
-200
-100
0
100
200
En
erg
y (k
Hz)
B (Gauss)
P-wave molecule energy
ml = ±1
ml = 0
B
J.P. Gaebler, J.T. Stewart, J.L. Bohn, & D.S. Jin, PRL 98, 200403 (2007)
A way to “see” molecules
0
V(R)
R
Create molecules
Look for energetic atoms created by tunneling
A way to “see” molecules
ml = 0ml = ±1
B
A way to “see” molecules
ml = 0ml = ±1
B
0 0.5 1.0 1.5 2.00
1x104
2x104
Mo
lecu
le N
um
be
r
Hold time (ms)
Molecule lifetime
ml = ±1
B
time
resonance
=1.2 ms
hold time
molecule creation
Quasi-bound molecule lifetime
B
time
resonance
hold time
molecule creation
-200 -100 010-3
10-2
10-1
100
10 100
Energy (kHz)
Life
time
(ms)
Molecule Lifetimes
E32
J.P. Gaebler, J.T. Stewart, J.L. Bohn, & D.S. Jin, PRL 98, 200403 (2007)
ml = 0ml = ±1
Dipolar relaxationSince our atoms are not in the lowest energy spin state, the molecules can undergo “one-body” decay.
2
9,
2
9
2
9,
2
9
2
7,
2
9
2
7,
2
9
2
9,
2
9
2
7,
2
9
This decay process would not exist for atoms in the lowest energy spin state. (6Li has such a p-wave resonance).
bound free
Collisional decayAfter removing atoms (blasting with resonant light)
0 5 10 15 200
5000
10000
15000
N m
olec
ules
time (ms)
= 7 ± 1 msml = 0
-200 -100 010-3
10-2
10-1
100
10 100
Energy (kHz)
Life
time
(ms)
What’s next?
ml = 0ml = ±1 E32
0 2 4 6 80
1x104
2x104
Mol
ecul
e N
umbe
r
Hold time at resonance (ms)0 2 4 6 8
0
1x104
2x104
Mol
ecul
e N
umbe
r
Hold time at resonance (ms)
Molecule CreationB
timeresonance
ml = 0
ml = ±1
Molecule Creation
198.7 198.8 198.9 199.00
5000
10000
15000
N m
olec
ules
B (G)
Molecule Creation
-50 0 50 100 150 2000
4000
8000
12000 Fermi Energy 13.0 kHz 9.8 kHz 6.4 kHz
Nm
olec
ules
B (mG)
Conclusion:
We can create and detect p-wave Feshbach molecules in a Fermi gas of atoms.
Novel aspects include:
• Centrifugal barrier• Quasi-bound state• Narrow resonance
The molecule lifetime is short.
0
V(R)
R
Group MembersJ. Goldwin
M. Olsen
P-wave molecule work: Jayson Stewart, John Gaebler