SLIDE 1 Rydberg Atoms and Astrochemistry
- What are Rydberg Atoms?
- Why are they interesting?
- Why are they interesting?
- Examples of projects
- What is astrochemistry?
SLIDE 2 Rydberg atom-
- ne in a state of high principal quantum number n
2 3 The Rydberg levels are here n=1
2
n R W − =
Energy Very weakly bound
SLIDE 3
Rydberg Atom
An atom in a state of high principal quantum number n W= -R/n2 <r>=2n2 Large, weakly bound orbits V=-1/r Large, weakly bound orbits n=30 W=-14 meV <r>= 450 Ǻ
SLIDE 4 Properties of Rydberg Atoms
Property scaling n=20 value Binding energy
Energy Spacing 1/n3 27.3 cm-1 Orbital radius n2 400 Å Dipole matrix elements (∆n=0) n2 400 ea0 Geometric cross section n4 160,000 Å2 Geometric cross section n4 160,000 Å2 Radiative lifetime (low ℓ) n3 10 s Radiative lifetime (ℓ=n) n5 1 ms Stark avoided crossings 1/n4 1 cm-1 Polarizability n7 108 Å3 Van der Waals interaction n11
SLIDE 5
They have exaggerated properties and interact strongly with the environment. Display physics with clarity 300K black body radiation affecting clocks What is interesting about Rydberg Atoms? 300K black body radiation affecting clocks high intensity multiphoton processes Realization of otherwise impossible physical situations counting microwave photons in a cavity- Haroche gates for a quantum computer- Lukin, Grangier et al… time resolved collisions-Renn
SLIDE 6
Fluorescence detection of excited atoms and molecules Laser excitation Detect fluorescent photon
SLIDE 7
Detection by field Ionization
V=-1/r-Ez W=-1/2n2 W E=1/16n4 =2000 V/cm @ n=20
SLIDE 8 Atoms in Strong Radiation Fields The interaction between an atom and the radiation field Is given by
E H µ − =
int
Either the field can be strong (big laser) or the dipole Either the field can be strong (big laser) or the dipole can be big (Rydberg atom).
SLIDE 9 Photoionization Fermi’s Golden Rule for the rates
4 2 2 2 1
int int 2 2 E W f E E i f E i ∝ ∆ = Γ = Γ µ µ π µ π
SLIDE 10
Experiment Laser mw Field pulse time Detect atoms surviving the microwave pulse as the laser wavelength is scanned
SLIDE 11 Atomic beam apparatus/ field ionization detection Lower densities, 1010 cm-3 high detection sensitivity Kleppner et al
SLIDE 12 Atomic beam apparatus
SLIDE 13
Experiment Laser mw Field pulse time Detect atoms surviving the microwave pulse as the laser wavelength is scanned
SLIDE 14
SLIDE 15
SLIDE 16
Experiment with timing change Laser mw Field pulse time Detect atoms surviving the microwave pulse as the laser wavelength is scanned
SLIDE 17
Obvious structure separated by the photon energy. It takes the same field for ten photon ionization as one photon ionization.
SLIDE 18
The spectrum is continuous across the limit Microwaves take energy from the electron before it leaves the atom The eigenstates in the presence of the field are combined atom-microwave field states. Fermi’s Golden Rule does not work. Fermi’s Golden Rule does not work.
SLIDE 19 Interactions of Cold 300K Rydberg atoms with each other
3 2 1 2 1
) )( ( 3 r r r H dd
µ µ µ µ
The major interaction is the dipole-dipole interaction
r
r
SLIDE 20 Dipole Blockade-Lukin RR States with permanent moments in a static field Realization Walker & Saffman Grangier, Brouways
W
gR+Rg gg R Grangier, Brouways & Pillet
SLIDE 21 Magneto Optical Trap
- 85Rb
- T ~ 300µK
- d ~ 1 mm
- d ~ 1 mm
- N ~ 1010cm-3
- NT ~ 107
atoms
SLIDE 22
SLIDE 23
10-3cm Atoms in a MOT N=109cm-3 Rav= 10-3cm T=300 K v=20 cm/s n=30 diameter 10-5cm 1% of Rav On experimental time scale,1s, motion 2x10-5 cm The atoms are effectively frozen in place, like a solid. Dipole-dipole interaction 2/R3 =6 MHz. kT=20 MHz Many body interactions should be more important than binary interactions.
SLIDE 24
np Observe the broadening of the ns-np microwave transition as a function of density ns nsnp npns
SLIDE 25
Sweep the frequency of the microwaves through the ns-np transition and record the np signal
SLIDE 26 0.24 0.26 0.28 0.30
0.313X10
3
26.332X10
3
12.397X10
3
Microwave scan from 42s to 42p as function of 42s density
52388 52390 52392 52394 52396 52398 52400 52388 52390 52392 52394 52396 52398 52400 0.10 0.12 0.14 0.16 0.18 0.20 0.22 52388 52390 52392 52394 52396 52398 52400
42p1/2 [a. u.] frequency [X4 MHz]
SLIDE 27
Excitation and Timing
nd 480 nm laser field ramp ns 5s 5p 780 nm t (s) 0 1 2 Plasma n
SLIDE 28
Spontaneous Evolution to a Plasma
Rb 40d 2, 5, 12 s delays 2x 105 atoms Radiative lifetime 50s
SLIDE 29 Spontaneous Evolution to Plasma
- 1. Initial ionization
- 2. Electrons trapped
- 1. Initial ionization
- 2. Electrons trapped
- 3. Rapid ionization
- 4. Plasma
SLIDE 30
Dipole-Dipole Ionization
1/R3 1/R6 At RvdW the dipole-dipole interaction equals the detuning. For R <RvdW the good states are (dd±pf)/21/2. RvdW is comparable to the atomic spacing in the trap. Optical excitation is to the dd part (mostly attractive).
SLIDE 31
transition from 39s to 39p3/2
- Gated the free ion signal
- Sharp cutoff at resonance
frequency frequency
pairs on the repulsive (high frequency) interaction curve
SLIDE 32
What is astrochemistry? Over 140 molecular species have been observed in space, By their microwave rotational transitions. New radio telescopes will add enormous amounts of data. Laboratory measurements are required for identification. High frequency broadband spectrometer Brooks Pate, Kevin Lehmann, John Yates
SLIDE 33
Present students &post doctoral fellow Joshua Gurian Jirakan Nunkaew Hyunwook Park Richard Overstreet Richard Overstreet
