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A Pyramidal Magneto-Optical Trap for a Compact Source of Cold Atoms

Florian Sander

Published Jan 1, 2025• 0 citations
OpenAlex

Abstract

In order to scale up quantum computing, a scalable experimental architecture is needed, with the trapped-ion quantum computing platform; this has led to the implementation of surface ion traps. Despite being more performant than the older linear Paul trap design, they suffer from a lower trap depth. This reduces not only the probability of ion capture but also increases the dependency on the vacuum quality. Therefore, clean, cold, compact and robust atom sources are needed for the next generation of ion-trap-based quantum computers. Within the scope of this thesis, a repumped 3D magneto-optical trap (MOT) for the 40Ca species with a loading time of 1 s was demonstrated. Furthermore, we have also shown the ability to measure the performance of cold atom sources by resolving different Calcium isotopes via photoionisation detection. Finally, we demonstrate a novel and compact pyramid MOT design, which was tested and verified for 40Ca. The presented magneto-optical trap design can be integrated into other quantum computing experiments.

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A three-dimensional magneto-optical trap (MOT), acting as an efficient method for producing cold atoms from room-temperature atomic vapor, has been widely used to develop atomic sensors. Various compact MOTs using a single laser beam have been reported, simplifying apparatuses and leading to miniaturized devices. Here, we propose single-beam MOTs based on back-to-back pyramidal and conical mirrors. In such back-to-back mirrors, a MOT trapping volume is formed by an incident laser beam, a retroreflected beam, and multiple reflections from the mirror surfaces. We present the design of back-to-back mirrors and a series of compact MOT configurations, with the potential of increasing access to the MOT and simultaneously creating multiple MOTs. We demonstrate a MOT in a back-to-back conical mirror, loading \ensuremath{\sim}1 \ifmmode\times\else\texttimes\fi{} ${10}^{7}$ ${}^{87}\mathrm{Rb}$ atoms from background vapor and cooling the atoms to \ensuremath{\sim}7 \textmu{}K using polarization gradients. Single-beam MOTs based on back-to-back mirrors contribute to building compact and scalable cold-atom-based sensors.

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In order to scale up quantum computing, a scalable experimental architecture is needed, with the trapped-ion quantum computing platform; this has led to the implementation of surface ion traps. Despite being more performant than the older linear Paul trap design, they suffer from a lower trap depth. This reduces not only the probability of ion capture but also increases the dependency on the vacuum quality. Therefore, clean, cold, compact and robust atom sources are needed for the next generation of ion-trap-based quantum computers. Within the scope of this thesis, a repumped 3D magneto-optical trap (MOT) for the 40Ca species with a loading time of 1 s was demonstrated. Furthermore, we have also shown the ability to measure the performance of cold atom sources by resolving different Calcium isotopes via photoionisation detection. Finally, we demonstrate a novel and compact pyramid MOT design, which was tested and verified for 40Ca. The presented magneto-optical trap design can be integrated into other quantum computing experiments.
The ongoing drive to transfer quantum technologies from research laboratories to practical, portable devices requires the development of multiple key enabling technologies. The field of cold atoms, which includes high-precision metrology and quantum simulation, has various real-world applications including time-keeping and navigation. A crucial component in these systems is a cold-atom source that generates a flux of low-velocity atoms suitable for subsequent capture. A large flux enables fast repetition rates, high duty cycles, long measurement times, and resistance to long-term performance degradation with a good signal-to-noise ratio, all of which are essential to produce cold-atom devices and technologies that are capable of out-performing the classical alternatives. This thesis presents the design, fabrication and characterisation of a novel cold-atom source using a compact pyramidal magneto-optical trap (MOT) with a unique adjustable-aperture mechanism. This allowed an investigation of the dependence of the flux characteristics on the aperture size, a parameter space that has not previously been explored. The measurements showed a strong dependence of the flux on the aperture size, with a negligible flux below 0.4mm, then an approximately linear increase up to 1.0mm, at which point the relationship showed possible signs of saturation. Using 87Rb, a flux of 1.18×1010 atoms/s was produced using a 1.27mm aperture, for which the mean velocity of the atoms was 21.6(3) m/s with a FWHM of 11.2(2) m/s, and the FWHM divergence of the beam was 86(2) mrad. This is the highest recorded flux from a pyramid or 2D+-MOT source, and amongst the highest reported fluxes from any MOT sources, and avenues for improvement still remain. This work fulfils the aim of demonstrating a compact and robust cold-atom source generating a high flux of laser-cooled atoms for real-world quantum technology applications.
We demonstrate fast loading of our trapped ion quantum computer using a compact 2D Magneto-Optical Trap (MOT). We characterize the MOT loading system by direct measurements of the cold atomic beam produced thereby. We load both ytterbium and barium ions two orders of magnitude faster than using a conventional oven loading method with negligible impact on vacuum performance in the trapped ion region. These improvements to loading address one of the concerns in scaling our QCCD architecture up to large Qubit numbers.
Abstract We realize a two-stage, hexagonal pyramid magneto-optical trap (MOT) with strontium, and demonstrate loading of cold atoms into cavity-enhanced 1D and 2D optical lattice traps, all within a single compact assembly of in-vacuum optics. We show that the device is suitable for high-performance quantum technologies, focusing especially on its intended application as a strontium optical lattice clock. We prepare 2 × 10 4 spin-polarized atoms of 87 Sr in the optical lattice within 500 ms; we observe a vacuum-limited lifetime of atoms in the lattice of 27 s; and we measure a background DC electric field of 12 V m −1 from stray charges, corresponding to a fractional frequency shift of (−1.2 ± 0.8) × 10 −18 to the strontium clock transition. When used in combination with careful management of the blackbody radiation environment, the device shows potential as a platform for realizing a compact, robust, transportable optical lattice clock with systematic uncertainty at the 10 −18 level.
Magneto-optical traps (MOTs) are widely used for laser cooling of atoms. We have developed a high-flux compact cold-atom source based on a pyramid MOT with a unique adjustable aperture that is highly suitable for portable quantum technology devices, including space-based experiments. The adjustability enabled an investigation into the previously unexplored impact of aperture size on the atomic flux, and optimisation of the aperture size allowed us to demonstrate a higher flux than any reported cold-atom sources that use a pyramid, LVIS, 3D-MOT or grating MOT. We achieved 2.1(1) × 1010 atoms/s of 87Rb with a mean velocity of 32(1) m/s, FWHM of 27.6(9) m/s and divergence of 59(4) mrad. Halving the total optical power to 195 mW caused only a 20% reduction of the flux, and a 30% decrease in mean velocity. Methods to further decrease the velocity as required have been identified. The low power consumption and small size make this design suitable for a wide range of cold-atom technologies.
Magneto-optical traps (MOTs), indispensable to cold-atom-based quantum computing and quantum precision measurement, are increasingly desired in compact and stable form. Particularly, the six-beam 3D-MOT, distinguished by symmetric geometry and superior trapping performance, finds particularly broad applications. Conventional implementations, however, rely on complex and bulky free-space optics, hindering miniaturization, practical assembly, and long-term stability. Here, we demonstrate a compact six-beam 3D-MOT system that employs two multifunctional optical metasurface chips to implement the optical-field functionalities required for cooling and trapping atoms. By combining two metasurface chips and a vacuum cell, a photonic-integrated cell module (PICM) is implemented as the core assembly and the volume is only" 73*73*107 mm^3" . In success, 1.3 * 10^3 Rb atoms are trapped and cooled to the temperature of ~183 μK. It should be noticed that the laser beam is guided to the metasurface through optical fiber, thus such fully fiber-coupled architecture enables straightforward and stable operations. We believe that this work would pave a practical route toward compact and portable 3D-MOT.
A three-dimensional magneto-optical trap (MOT), acting as an efficient method for producing cold atoms from room-temperature atomic vapor, has been widely used to develop atomic sensors. Various compact MOTs using a single laser beam have been reported, simplifying apparatuses and leading to miniaturized devices. Here, we propose single-beam MOTs based on back-to-back pyramidal and conical mirrors. In such back-to-back mirrors, a MOT trapping volume is formed by an incident laser beam, a retroreflected beam, and multiple reflections from the mirror surfaces. We present the design of back-to-back mirrors and a series of compact MOT configurations, with the potential of increasing access to the MOT and simultaneously creating multiple MOTs. We demonstrate a MOT in a back-to-back conical mirror, loading \ensuremath{\sim}1 \ifmmode\times\else\texttimes\fi{} 107{10}^{7}107 87Rb{}^{87}\mathrm{Rb}87Rb atoms from background vapor and cooling the atoms to \ensuremath{\sim}7 \textmu{}K using polarization gradients. Single-beam MOTs based on back-to-back mirrors contribute to building compact and scalable cold-atom-based sensors.