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Narrow Line Cooling of 84Sr

Roger Ding

Published Dec 12, 2016• 0 citations
OpenAlex

Abstract

Laser cooling has become a powerful tool for producing quantum gases and has enabled the study of a wide range of phenomena only accessible at ultracold temperatures. This thesis will describe the implementation and characterization of a magneto-optical trap (MOT) for laser cooling strontium to microkelvin temperatures operating on the narrow 689nm transition (the “red” MOT). The red MOT is the second cooling stage required to create quantum degenerate gases of strontium, bridging the temperatures and densities produced by the first cooling stage (the 461 nm “blue” MOT) and the shallow conservative traps for evaporation to quantum degeneracy.

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We report on a narrow-line laser cooling and trapping of strontium atoms near quantum degeneracy. Employing a magneto-optical trap (MOT) on the spin-forbidden transition 1S0−3P1 at 689 nm, we have laser-cooled an atomic sample down to the photon recoil temperature of 400 nK with a phase space density of 10−2. The atoms were then compressed into a new type of far-off resonance optical dipole trap that was designed to allow simultaneous Doppler cooling, resulting in a phase space density of 10% to that required for quantum degeneracy. It is shown that this value is finally limited by light-assisted collisions occurring in the optical cooling. To reduce these inelastic losses, we applied evaporative cooling and demonstrated a creation of two-dimensional atomic gases.

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Chinese Physics Letters•Mar 1, 2011•10 citations
Laser cooling has become a powerful tool for producing quantum gases and has enabled the study of a wide range of phenomena only accessible at ultracold temperatures. This thesis will describe the implementation and characterization of a magneto-optical trap (MOT) for laser cooling strontium to microkelvin temperatures operating on the narrow 689nm transition (the “red” MOT). The red MOT is the second cooling stage required to create quantum degenerate gases of strontium, bridging the temperatures and densities produced by the first cooling stage (the 461 nm “blue” MOT) and the shallow conservative traps for evaporation to quantum degeneracy.
We report on a narrow-line laser cooling and trapping of strontium atoms near quantum degeneracy. Employing a magneto-optical trap (MOT) on the spin-forbidden transition 1S0−3P1 at 689 nm, we have laser-cooled an atomic sample down to the photon recoil temperature of 400 nK with a phase space density of 10−2. The atoms were then compressed into a new type of far-off resonance optical dipole trap that was designed to allow simultaneous Doppler cooling, resulting in a phase space density of 10% to that required for quantum degeneracy. It is shown that this value is finally limited by light-assisted collisions occurring in the optical cooling. To reduce these inelastic losses, we applied evaporative cooling and demonstrated a creation of two-dimensional atomic gases.
Laser cooling 88^{88}88Sr to microkelvin temperature with an integrated-photonics system
We report on experiments generating a magneto-optical trap (MOT) of 88-strontium (88^{88}88Sr) atoms at microkelvin temperature, using integrated-photonics devices. With metasurface optics integrated on a fused-silica substrate, we generate six-beam, circularly polarized, counter-propagating MOTs on the blue broad-line, 461 nm, and red narrow-line, 689 nm, Sr cooling transitions without bulk optics. By use of a diverging beam configuration, we create up to 10 mm diameter MOT beams at the trapping location. To frequency stabilize and linewidth narrow the cooling lasers, we use fiber-packaged, integrated nonlinear waveguides to spectrally broaden a frequency comb. The ultra-coherent supercontinuum of the waveguides covers 650 nm to 2500 nm, enabling phase locks of the cooling lasers to hertz level linewidth. Our work highlights the possibility to simplify the preparation of an ultracold 88Sr gas for an optical-lattice clock with photonic devices. By implementing a timing sequence for control of the MOT lasers and the quadrupole magnetic-field gradient, we collect atoms directly from a thermal beam into the blue MOT and continuously cool into a red MOT with dynamic detuning and intensity control. There, the red MOT temperature is as low as 2 μ2~μ2 μK and the overall transfer efficiency up to 16%. We characterize this sequence, including an intermediate red MOT with modulated detuning. Our experiments demonstrate an integrated photonics system capable of cooling alkaline-earth gases to microkelvin temperature with sufficient transfer efficiencies for adoption in scalable optical clocks and quantum sensors.
Summary form only given. All-optical production of quantum degenerate atomic gases has been one of the long-standing targets in laser cooling. We report a novel approach towards this direction based on a narrow-line laser cooling for strontium atoms. By employing two transitions with markedly different dipole moments, i.e., the allowed /sup 1/S/sub 0/-/sup 1/P/sub 1/ (/spl lambda/=461 nm, /spl gamma/=2/spl pi//spl times/32 MHz) and the spin-forbidden /sup 1/S/sub 0/-/sup 3/P/sub 1/ (/spl lambda/=689 nm, /spl gamma/=2/spl pi//spl times/7.6 kHz) transition, thermal strontium atoms were Doppler-cooled down to 400 nK or the photon recoil temperature, in a magneto-optical trap (MOT). Presents the corresponding energy levels for cooling and trapping. The use of a narrow spin-forbidden transition successfully reduced the radiation trapping effects at a high atom density over 10/sup 12//cm/sup 3/, thus enabling us to attain the hitherto high phase space density of 0.01 in a MOT.
We have used the narrow 2 S 1/2 [arrow right] 3 P 3/2 transition in the ultraviolet (UV) to laser cool and magneto-optically trap (MOT) 6 Li atoms. Laser cooling of lithium atoms is usually performed on the 2 S 1/2 [arrow right] 2 P 3/2 (D2) transition, where temperatures of twice the Doppler limit, or ∼300 μ K for lithium, are achieved. The linewidth of the UV transition is seven times narrower than the D2 line, resulting in a lower Doppler limit. We show that a MOT operating on the UV transition reaches temperatures as low as 59 μ K. We load 6 million atoms from this UV MOT into a 1070 nm optical dipole trap (ODT). We show that the light shift of the UV transition in the ODT is small and blue-shifted, facilitating efficient loading. Evaporative cooling of a two spin-state mixture of 6 Li in the ODT produces a quantum degenerate Fermi gas with 3 million atoms in only 11 seconds.
performance of our broad-line (461 nm, 30.5 MHz), narrow-line (689 nm, 7.5 kHz) magneto-optical traps, and examine evaporative cooling for all four isotopes. The new apparatus will be used to create and study tunable long-range interactions by dressing with strongly-interacting Rydberg states. The ability to trap the four different isotopes allows a measure of control of these interactions through access to a range of attractive and repulsive interactions. Simultaneous trapping of different isotopes provides opportunities for novel laser cooling schemes for studying Bose-Bose and Bose-Fermi mixtures.
We report the experimental realization of strontium magneto-optical trap (MOT) operating on the intercombination transition 1 S 0 − 3 P 1 at 689 nm, namely red MOT. A 689 nm laser used for cooling and trapping is injection locked to a master laser, whose linewidth is narrowed to 150 Hz by locking to a high finesse optical reference cavity. 88 Sr atoms pre-cooled and trapped by the broad 1 S 0 − 1 P 1 transition at 461 nm are transferred to the red MOT with the help of a time sequence controller. The transfer ratio is about 20% and the red MOT's temperature is estimated to be less than 20 μK by the time-of-flight (TOF) image analysis.