[time-nuts] 88Sr+ ion-clock live stream

[Bob kb8tq]

Cool !!!

> On Dec 6, 2019, at 10:39 AM, Anders Wallin <anders.e.e.wallin at gmail.com> wrote:
> 
> Hi all, you may find our live-stream from the lab amusing:
> https://www.youtube.com/watch?v=z9VFbs4FogY
> 
> The central bright dot is fluorescence at 422nm from laser cooling a single
> trapped 88Sr+ ion. The ion emits about 1e7 photons/s at most and we
> currently detect about 500 of those in a 20ms detection window (using a
> Hamamatsu PMT module).
> The bar-chart shows the clock-transition spectrum at 445 THz (674nm). The
> X-axis is a drive-frequency to the last AOM that shifts the clock-laser
> frequency to coincide with the ion frequency. The frequency around 75.9MHz
> should be doubled to get the real optical frequency-shift (double-pass AOM).
> We 'shoot' 100 pulses at each clock-laser frequency towards the ion, and
> detect how many times we are able to drive the ion into the 'dark'
> clock-state. The clock state is long-lived (400ms or so), and detection is
> by turning on the cooling and noticing that the ion is dark. In theory the
> ion should blink in the camera-view also, but the exposure-time is now long
> enough that there is not much visible blinking.
> 
> The height of the bars show that we are able to excite the clock-transition
> with about 20-30% probability at the moment.
> 
> The clock-transition splits into five symmetric Zeeman pairs, four of which
> are observed in this scan range. We have two magnetic shields and
> compensating electromagnets to reduce the DC magnetic field to 0.4 uT or
> so. This splits the outermost components by about 20kHz (10kHz AOM-range in
> the figure, doubled). The line-center is around 75.945 MHz on the AOM. This
> corresponds to the clock-transition center, 444 779 044 095 486.5 Hz. Maybe
> we should make this more obvious, an AOM number like 75 MHz is not so
> impressive...
> 
> The peaks are now around 500Hz wide. This is about 1e-12 fractional. There
> is room for improvement as the 88Sr+ clock-state natural lifetime of 400ms
> only limits linewidth to 4Hz or so... Line-center (the middle of all zeeman
> peaks) can be determined more precisely than linewidth.
> 
> The control system (ARTIQ) is now just repeating the same scan over and
> over, takes around 1h per scan (12kHz range with 25Hz resolution IIRC), and
> each new spectrum is plotted with a new color.
> 
> Enjoy it while it lasts - this is a live stream and anything may happen
> (cooling laser unlocks from Rb-cell, clock-laser unlocks from ULE-cavity,
> ion disappears, whatever....). Ion storage times have been in the ~4 days
> range previously - so I am hoping it will run nice now for 24h or so.
> 
> Final clock-operation will not scan this thoroughly over all the peaks,
> just three of them, and just one frequency on the left/right side of each
> peak - and then a numerical servo locks on to the center of each peak.
> 
> If you run an optical clock I hereby challenge you to live-stream it and
> post here!
> 
> cheerio,
> Anders
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