Description

The laboratory at the UGR was completed in 2016 and has been recently named as Singular Lab at the UGR. The existing setups are described in the following:

Laser system

img2447 The main laser system is placed on an optical table with dimensions 2.5 m x 1.5 m, and it comprises eight tunable diode lasers (DL Pro TOPTICA Photonics) with external-cavity resonator in Littrow configuration. The diode lasers are classified in terms of their center wavelength as follows:

  • 2 UV lasers at 397 nm needed for laser cooling of 40Ca+ by driving the S1/2 - P1/2 electric-dipole transition.
  • 4 IR lasers at 866 nm required to restore the cooling when it is interrupted via the decay from P1/2 to the dark state D3/2, which can occur with a probability of 7%.
  • 2 IR lasers at 854 nm to drive the D5/2 - P3/2 transition, since the probability of populating the D5/2 dark state from the P1/2 state scales with the magnetic field strength. The branching ratio relative to the main decay is proportional to the square of B, as measured by the group of Prof. Richard Thompson at Imperial College London (link). In this scenario, we need 4 additional 854 nm beams to address all D5/2 - P3/2 pumping transitions that arise in the 7-T magnetic field regime. The additional 854 nm beams are generated by feeding an electro-optical modulator (EOSPACE) with the two existing 854 nm laser beams. A microwave signal generator with frequency range from 9 kHz to 40 GHz along with an amplifier is used to electrically feed the EOM.

On the other hand, an additional optical table holds three diode lasers, a frequency doubler, an optical frequency comb and a continuous-wave Titanium:Sapphire laser (CW Ti:Sa laser). The laser setup is described as follows:

  • An UV tunable diode laser at 423 nm (DL Pro TOPTICA Photonics) and a free-running diode laser at 375 nm (iBeam TOPTICA Photonics), both needed for accomplishing the photoionization of the neutral Ca atoms injected to the ion traps. An additional high-power (<100 mW) 397 nm diode laser has been installed for maximizing the output laser power in the Penning trap setup.
  • A CW Ti:Sa laser (Sirah Matisse TX) that provides very wide tunability (700 to 1000 nm) and high output power (>0.5 W). Before the completion of the diode lasers setup in 2016, the Ti:Sa laser served as a 423 nm laser source by means of the frequency doubler (SHG Pro TOPTICA Photonics).

The wavelength of the lasers is measured and stabilized using a Fizeau-based wavelength meter (HighFinesse WSU-10) with an absolute accuracy of 10 MHz (3 sigma). A stabilized HeNe laser (632.9909463 nm) with high frequency stability provides the reference value to calibrate the wavemeter. The setup to couple all 12 laser beams needed for the Penning trap experiment has been completed in January 2016, and further preparations of the imaging system have been made to study the fluorescence of 40Ca+ ions stored in Penning traps at 7 T.

Optical Frequency Comb

comb In December 2015, an optical frequency comb (Menlo Systems FC1500-250-WG) was installed in the laboratory. This device provides absolute frequency measurements with very high precision, and therefore provides an accurate frequency stabilization of laser sources. At present time, the whole apparatus is operative and ready to start with the tests of the Ti:Sa laser locking to the frequency comb in order to improve the frequency stabilization.

Penning traps beamline

preparation_trap penning The Penning traps beamline comprises a laser-desorption ion source, a transfer section, a Penning traps system and a time-of-flight (TOF) section for identification. The laser desorption ion source for injecting ions in the traps is in operation since 2013. First trapping was already accomplished in 2014 and, by the end of 2014, it was possible to obtain the so-called cooling resonance for 40Ca+ ions and other ion species. The Penning trap system consists of two traps: a preparation trap and a measurement trap. The preparation trap is made of stack of cylinders for cooling and separation of the incoming ions and the measurement trap exhibits a novel geometry to study the laser cooling of 40Ca+ ions in the 7 T magnetic field.

Open-ring Paul trap test bench

paul_trap

In 2015, a Paul trap experiment with a single ion laser-cooled to the Doppler limit was reached. This trap has a non-conventional geometry, which was taken as reference for the design and construction of the double-microtrap system. The trap is made of two sets of three concentric rings centered on the z-axis. A description of the setup can be found here.

The experiments performed in this setup have provided us the characterization of a single laser-cooled 40Ca+ ion as an optical detector of electric signals. In 2017, a manuscript reporting these measurements has been published in Scientific Reports (link to the Open Access manuscript). Further characterization measurements were realized with two 40Ca+ ions in order to extend the method to Penning traps. These results have been reported on a special issue of Journal of Modern Optics (link to the manuscript)

Double-microtrap system

microtraps_assembled

In 2016, we received and installed the double-microtrap system. The setup is comprised of two identical microfabricated traps, where the ion-ion coupling takes place through a common electrode. The traps electrodes have been designed in our group and then fabricated by TRANSLUME. In the final stage of the experiment, the measurement Penning trap will be substituted by the double-Penning-(micro)trap system.

Cryogenic system

straps

In the final stage of the experiment, the traps have to run at cryogenic temperatures in order to reduce the Johnson thermal noise existing in the setup. For that reason, a two-stage pulsed tube cryocooler (Sumitomo Heavy Industries RP-082B) was installed in the laboratory. The use of the cryocooler implies that the associated electronics must be compatible with cryogenic temperatures. For this purpose, we have developed and tested new electronic circuits for cryogenic use in collaboration with the local company SEVEN SOLUTIONS, S.L., where tests of the electronics in the cryocooler at 4 K have been already carried out. This link at the company website reports on this collaboration and shows the specs of the electronics.

Furthermore, efforts have been focused on designing the shielding structure needed to cool down the setup to cryogenic temperatures. The cooling is accomplished by means of a set of thermal copper straps manufactured by Technology Applications, Inc. This link at the company website reports on the successful implementation of the thermal straps in the cryocooler setup.