Danielle Boddy

Durham University – Atomic & Molecular Physics group

Red MOT is on its way to save the day!

The team

Group Meeting 10/10/11

Matt Jones

Charles Adams

Graham Lochead

Dan Sadle

r

Christophe Vaillant

Me

Motivation: Rydberg physics

Rydberg physics:

Atoms in states with high principle quantum number, n

Strong, tunable interactions

Applications include quantum computation

Group Meeting 10/10/11

Motivation: Are we blockaded yet?

At present

Where we

want to be

Group Meeting 10/10/11

Motivation: Entering van der Waals blockade

1P1

1S0

λ = 461 nmΓ = 2π x 32

MHz

3P0

3P1

3P2

λ = 689 nmΓ = 2π x 7.5 kHz2nd stage cooling

Introduce a second stage of cooling

Blue MOT: ~ 5 mK

~ 1 x 109 atoms/cm3

Red MOT: ~ 400 nK

~ 1 x 1012

atoms/cm3

Limited by linewidth of laser (initially)

Group Meeting 10/10/11

Limited by linewidth of transition

Outline

Improving the error signal

Slow lock circuit

689 nm laser on cold atoms

Last time….

Group Meeting 10/10/11

What next?

Summary

Last time…..

atomic beam

CCDPD

Detect transition via fluorescence

Frequency modulate double pass AOMLock-in amplifier extracts the signal

Group Meeting 10/10/11

Improving error signal: Zeeman splitting

3P1-1

0+1

1S0

BmgE JBJ

EE

B ≠ 0B = 0

Degenerate energy levels

Magnetic field removes (2j+1)-fold degeneracy → isotropy destroyed

is the Landé g-factorJg

Group Meeting 10/10/11

Energy, E

-1 0 1

Improving error signal: Magnetic coils

atomic beam

CCDPDcoils

We can define a quantization axis by applying a magnetic field

Dipole aligns in the direction of the field → photon emitted with linear polarisation

-component observed in all directions except along field

Calibrated coils → 0.064 G/A/turn

Group Meeting 10/10/11

Slow lock circuit

Group Meeting 10/10/11

After coils

Before coils

Lock cavity to hot atoms

Circuit MUST have a slow bandwidth

But how slow is slow?

Use lock-in amplifier to remove higher frequency noise from signal

Time constant set to 100 ms

Need τcircuit >> τlock-in → τcircuit ~ 3 s

689 nm light on the main experiment

MOT & Zeeman

MOT & Zeeman

On-resonant probe 8 μs

689 nm laser either constantly on/off during this cycle

Time →

Repeat

Simple electron shelving experiment 1P1

1S0

τstrong

3P1

τweak

τweak >> τstrong

Gaussian width ~ 4.5 MHz

Group Meeting 10/10/11

689 nm laser is locked to the hot atoms using slow lock

What next?

Group Meeting 10/10/11

Master 689

Hot atom

s

Fast lock feedback Slow lock feedbackCavity

Slave 689

Cold atom

s

Slave is injection locked to the Master laser

Summary

Group Meeting 10/10/11

Added coils around hot atomic beam to define a quantization axis

Error signal has improved!

Slow lock circuit is built and works

First ever experiment of 689 nm laser on (our) cold atoms

Slave laser is built