88Sr+ clock transition in a low magnetic field

Live-stream from the VTT MIKES ion-clock lab

We've completed a second magnetic shielding layer, based on the same plywood+METGLAS concept as the first shield. This should further shield the 88Sr+ ion from unwanted magnetic field fluctuations. To further reduce the DC-field we've now applied a counter-field using a few milliAmps of current through three coils that surround the ion trap.

When the Zeeman components are this close together (the field is <0.4 uT) it is fairly quick to scan over the components. Here we see the four innermost pairs of peaks +/-C1 through +/-C4 of the clock-transition at 445 THz (674nm red light!). One scan runs in about one hour - and will be plotted on top of the older scans. We shoot 100 pulses of the laser-light at the ion and the height of the bar shows how many times we successfully drove the ion into the dark clock-state.

Multiplexer S/N 4

Slight design changes to the RF Multiplexer design.

Front panel buttons B1 and B2 now extend out of the front-panel and are easily accessible. Pressing the buttons advances the state of the MUX1 and MUX2 boards.

Transmission bandwidth. This MUX has 50-Ohm impedance relays, and the 3dB bandwidth is around 1.0-1.2 GHz.
Inside of MUX-box. Two 1:8 boards with BNC connectors side-by-side. Arduino MKRZERO and Ethernet Shield on the right. A simple carrier board distributes SPI-signals from the Arduino to the MUX-boards and provides front-panel pushbuttons and LEDs. Top center is a 230VAC to 5VDC powersupply. Top left 230VAC input.

Torsion-box workbench with parfguide hole-pattern

(Built a few months ago, but better blog late than never..)

Here's a 1600mm-by-930 mm workbench built from two sheets (1220mm x 2440mm, 4-by-8 metric feet) of 15mm plywood. It's a torsion-box design with the top and bottom sheets separated by 240mm. The sides have rounded openings that create storage-bays for tools etc. The top has 20mm diameter holes drilled using the parfguide-system (it uses pythagoras 3-4-5 triangles to get the holes reasonably accurately positioned). The hole-grid is 10x17 so there are 170 holes in total. Assembled using pocket-hole screws.

  • Parts cut and pocket holes drilled.
  • The middle dividers don't have rounded openings. For more stiffness maybe lengthwise dividers would be good also?
  • Assembled torsion-box, without top
  • Gluing 2x4s for the legs
  • Stand from 2x4s
  • Torsion-box on stand, before drilling holes.
  • Storage-bay opening.
  • UJK parfguide system jig and 20mm forstner-bit
  • 170 holes drilled! Two parf-dogs show how the holes are used.

Here's a rough sketch of the dimensions. The dimensions were chosen to fit my workshop, so that it could be built from two 1220mm-by-2440mm sheets, and the dimensions rounded to fit the 96mm-by-96mm parfguide hole pattern nicely.

Sketch of dimensions.

The pieces needed can be cut from two sheets of plywood, resulting in two top/bottom pieces, two long-sides, two short-sides, and four internal dividers. I only used two of the dividers.

sketch of how to cut the pieces from a sheet of plywood.

There are a lot of torsion-box or "Paulk workbench" builds out there, here are some links:

Laser cutting

First try at using the 50W CO2 laser cutter at the Iso Omena library. Material is 4mm Birch ply (K-rauta). I didn't have time to optimize the speed/power settings, so the edge-finish is quite burned, and a flame appears from time to time. There was a 3M tape-film (?model?) available, which when taped over the plywood-to-be-cut should reduce burning and flaming - but I didn't have time to try it.

Workflow: DXF files exported from CAD, the into Adobe Illustrator, set all linewidths to 0.01mm, then save as PDF, then print from Adobe Acrobat to the Epilog printer-driver, set speed/power for the material, send to the machine, set the (0,0) coordinate (top left) for the job, and press Go!

~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...