CategoryTime and Frequency

~800Hz wide clock-transition in 88Sr+

Here's the latest preliminary result from the VTT MIKES 88Sr+ ion clock (in case you missed the live-stream!):

-C2 component of the clock transition at 445 THz in 88Sr+

This shows a ~2 kHz slice (left axis, double the 1 kHz shown, because we plot the input frequency of a double-pass AOM) of the optical spectrum around 445 THz, where we expect to find the -C2 Zeeman component of the clock-transition in 88Sr+ (a secondary representation of the SI second). The right axis shows the probe-pulse length in seconds, where we see only a few percent excitation (z-axis) at short pulse lengths, but a clearer signal up to >10% at longer probe pulse lengths of 40 and 50 ms.

It ain't pretty, but considering the carrier is at 445 THz, this noisy and broad looking 800 Hz wide peak is still a measurement to a relative level of 2e-12. When fully operational a line-width of <10 Hz (2e-14) is expected.

Our experiment now has one metglas magnetic shield. This particular Zeeman component (-C2) has a sensitivity of 11 kHz/uT, so the observed linewidth of 800 Hz could be caused by a low-frequency AC magnetic field with an amplitude of 30-40 nT or so. We think the remaining DC-field is around 1.6 uT (down from 66 uT without the metglas shield).

Among other improvements, next is building a second metglas shield, to reduce AC fluctuations in the magnetic shield even further. Stay tuned...

Trapping again

Since about July 15th our single-ion experiment has been in maintenance-mode, but today again some trapping!

The central 'pale blue dot' is a single 88Sr+ ion trapped between the inner electrodes (cylindrical) which are driven with a ~400 Vpp ~16 MHz sine-wave to create a Paul trap. The outer conical electrodes are grounded. The window-reflections of the 422nm cooling laser create the larger circular spots in the top half of the picture. A single laser-cooled 88Sr+ ion emits around 10 million photons per second, making it easily visible on 1s or longer exposures with a DSLR. Sigma 105mm/F2.8 macro objective with a short (13mm?) extension-tube.

Live stream:

uBlox F9T qErr correction

Here's a test of how to correct the 1PPS signal out of an F9T with the qErr-value from the UBX-TIM-TP message.

When the time-interval-counter is configured with start=reference-clock, stop=uBlox, the qErr is applied with a + sign to the measured time-interval - resulting in much smoother data for averaging times up to tau=1000s.

uBlox F9T test

Test of the 1PPS stability of an uBlox F9T dev-kit RCB-F9T

AllanTools 2019.07

A new release of AllanTools is now available on PyPi.

Faster mtotdev() and htotdev()

The AllanTools functions mtotdev() and htotdev() are now almost 10-times faster, after an update to the code that more efficiently calculates moving averages.

The old code used numpy.mean() for each iteration of a loop:

However this can be computed much faster by noticing that the new mean differs from the old (already computed!) mean by just two points, one at the start is dropped, and a new one at the end is added:

Lab live-stream: Trapped 88Sr+ ion

Live-stream from the VTT MIKES ion clock lab.

We started trapping in this 2nd-generation VTT MIKES ion trap in early May and we are now working with characterizing the trap and laser cooling. Hopefully the ion stays in the trap for several days!

Thursday Trapping

Single-ion Sr+ trap.

Tuesday Trapping

This is not Stable32

Recently merged plotting-functions for allantools with a look and feel of Stable32 - thanks to yxie.

I should probably run python3 to get special characters like tau and sigma to work..

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