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 Sadler 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 1P11P1 1S01S0 λ = 461 nm Γ = 2π x 32 MHz 3P03P0 3P13P1 3P23P2 λ = 689 nm Γ = 2π x 7.5 kHz 2 nd stage cooling Introduce a second stage of cooling Blue MOT: ~ 5 mK ~ 1 x 10 9 atoms/cm 3 Red MOT: ~ 400 nK ~ 1 x atoms/cm 3 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 CCD PD Detect transition via fluorescence Frequency modulate double pass AOM Lock-in amplifier extracts the signal Group Meeting 10/10/11

Improving error signal: Zeeman splitting 3P13P S01S0 B ≠ 0 B = 0 Degenerate energy levels Magnetic field removes (2j+1)-fold degeneracy → isotropy destroyed is the Landé g-factor Group Meeting 10/10/11 Energy, E 0 1

Improving error signal: Magnetic coils atomic beam CCD PD coils 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 → 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 τ circuit >> τ lock-in → τ circuit ~ 3 s

689 nm light on the main experiment MOT & Zeeman On-resonant probe 8 μs 689 nm laser either constantly on/off during this cycle Time → Repeat Simple electron shelving experiment 1P11P1 1S01S0 τ strong 3P13P1 τ weak τ weak >> τ strong Gaussian width ~ 4.5 MHz Group Meeting 10/10/ nm laser is locked to the hot atoms using slow lock

What next? Group Meeting 10/10/11 Master 689 Hot atoms Fast lock feedback Slow lock feedback Cavity Slave 689 Cold atoms 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