Selective population of Core Nonpenetrating Rydberg states David Grimes, Yan Zhou, Timothy J Barnum, Ethan Klein, Robert Field Department of Chemistry,

Selective population of Core Nonpenetrating Rydberg statesDavid Grimes, Yan Zhou, Timothy J Barnum, Ethan Klein, Robert FieldDepartment of Chemistry, MIT

Outline

• Introduction to core nonpenetrating (CNP) Rydberg states

• Why CNP states are useful• Using chirped pulse millimeter wave

(CPmmW) spectroscopy to access and identify these states

• The difficulties in accessing these states in most molecules

• Using CPmmW spectroscopy to overcome the obstacles 2

What are Core Nonpenetrating States?

3

N+N

Λ

( )ℓ

N+

N

ℓ

• Centrifugal barrier prevents overlap with the core• Nonradiative decay mechanisms (autoionization,

predissociation) scale as overlap with the core (n-3, exponentially decreasing with ℓ).

• Electron decouples from molecular axis as n, , N ℓ increase.• The majority of electronic states of every molecule are CNP

states.

𝑟𝑚𝑖𝑛∝ ℓ (ℓ+1) ℓR

Uses for Core Nonpenetrating States

4

State selective ion generation Molecular deceleration

Molecular Ion Structure Quantum Information

Hudson, Odom Lundeen (atoms), Field

Merkt, Meijer, Lewandowski,,Ubachs, Hinds

Field

Ladder climbing

5

57d–54f

56g–54f

56g–54h

artifact

57d54f

56g 54

h

Laser

1.8455 1.846 1.8465 1.847 1.8475 1.848 1.8485 1.849 1.8495

x 104

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

Probe laser/cm-1

Inte

grat

ed F

IDStark Demolition via chirped pulse millimeter wave spectroscopy

6

CNPCP

CP or CNP

1V/cm

CNP l>4

FIDno

FID

CP32.96 33.96 35.02 36.04 37.07 38.08

33.3733.67

35.24 36.58

• Different field intensities can discriminate between quantum defects.

The Zone of Death

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ABAB

+

hν

e- (n ≈ 30)

A B+

AB+

e-

R

Energy

R

Energy

A+ + B-

A + B

• Core nonpenetrating states are both scientifically interesting and protect themselves from nonradiative decay.

• Difficult to access with many photons when fighting fast decay processes.

• Can access nearly nonpenetrating states with laser through perturbations located near integer n*, and/or at high N when ℓ uncoupling becomes strong.

Simple ways to deal with the Zone of Death

8

generator

detector

TOF

LIF

pump lasers

5% NO in He

• Transitions to higher- ℓstates observed in ion channel

• No FID yet detected in the general expansion (needs ~1 μs)

• May require pulse sequence to excite to even higher ℓ

Avoiding the Zone of Death altogether

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τ <1ns

τ >1µs

τ ~100ns

(f) State

h Stateg State

(d) State τ ~100 ns

• STImulated Rapid Adiabatic Passage (STIRAP) is a three state, two photon coherent population transfer technique.

• Capable of full population transfer.

• Intermediate state never populated.

• Robust against changes in experimental conditions.

ωL

ωmm

Ɛmm ƐL

Technological Hurdles

10

Modifiable chirp shape

Short time phase

stability

Tunable chirp rate

Long time phase

stability

• Similar requirements for the laser – current plan is to pulse amplify a CW laser for phase stability, with a 100 ns pump laser if possible

Conclusions• Core nonpenetrating states are a fertile ground

for future experiments in a variety of fields.• Access to high-ℓ states demonstrated in Ca

through ladder climbing.• Determination of core nonpenetrating states in

BaF demonstrated through Stark Demolition measurements.

• More general techniques, in particular STIRAP, are needed for access to core nonpenetrating states in other molecules.

• Our CPmmW system is ideally suited to both identify and access (via STIRAP) core nonpenetrating states.

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Acknowledgements• Prof. Robert Field

• Yan Zhou• Tim Barnum• Dr. Steve Coy• Ethan Klein• Dr. Tony Colombo• Dr. Jeff Kay• Dr. Carrie

Womack• Barratt Park• Jun Jiang• Dr. Josh Baraban• Bryan Changala

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• Prof. John Doyle• Dr. Dave

Patterson

• Prof. Dave DeMille• Dr. John Berry

• Prof. Brooks Pate• Dr. Justin Neill

• Prof. John Muenter