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

[Bob kb8tq]

Hi

Very cool !!!

Sort of sounds like we will not be doing this in a basement lab any time soon :(

Bob

> On Apr 23, 2020, at 11:27 AM, Anders Wallin <anders.e.e.wallin at gmail.com> wrote:
> 
> Today (a mere 4-and-a-half months since my post below) we managed to lock
> the ultra-stable laser to 3 pairs of Zeeman-components of the ion.
> As previously, this is a complex experiment so it may fail at any time,
> enjoy it while it lasts: https://www.youtube.com/watch?v=hZQtlHXECQ4
> 
> The servo that steers the clock-laser onto the clock-transition of the ion
> measures quantum jumps on the red and blue side of each Zeeman-peak, and
> strives for the same amount of jumps on both sides.
> 
> The overlay image cycles between a few different images:
> - The clock-transition line-center estimates, based on the mid-point
> between a Zeeman pair. Unfortunately this is still in units of the final
> double-pass AOM that shifts the clock-laser frequency before the ion. I'll
> try to improve this so it relates to the actual optical frequency at 445
> THz in the future.
> - an estimate of the magnetic field (1.2 uT or so), again three separate
> estimates based on the Zeeman-pairs.
> - The 'quantum-jumps' observed on the red and blue side of each transition.
> The servo strives for equal amount of jumps on the blue and red side - then
> we know we are centered on the peak. You can note how noisy the data is
> (with Poisson statistics) when we only have one atom to work with! (Compare
> to a Ceasium clock with a SNR of 1e6 (or so I hear))
> 
> We roughly checked the observed line-center against the drift-model for one
> of our active Hydrogen-masers and so far they agree to about 3e-15. The
> BIPM SRS recommended frequency is given with an (conservative?) uncertainty
> of 1.5e-15 [1]
> 
> regards,
> Anders
> 
> [1] https://www.bipm.org/utils/common/pdf/mep/88Sr+_445THz_2017.pdf
> 
> On Fri, Dec 6, 2019 at 5:39 PM 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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