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Photonics Letters of Poland

Optical system for Doppler cooling of trapped calcium ions

Łukasz Kłosowski, Katarzyna Pleskacz, Szymon Wójtewicz, Daniel Lisak, Mariusz Piwiński

Published Dec 31, 2017• 7 citations
Publisher

Abstract

In the experiments involving trapped ions, application of a cooling procedure is required. The optical Doppler scheme is one of the most commonly used methods for slowing down the ions motion. In this paper we present an optical system sufficient for cooling calcium ions in such scheme. The system allows also for optical detection of the trapped ions. Full Text: PDF ReferencesF. Major, V. Gheorghe, and G. Werth, Charged Particle traps, Physics and Techniques of Charged Particle Field Confinement (Springer 2005). DirectLink Ł. Kłosowski, M. Piwiński, and M. Drewsen, "Integral electron impact ionization cross section of molecules through Coulomb crystallization of the product ions", J. Phys. Conf. Ser. 635, 072003 (2015) CrossRef D. J. Wineland and Wayne M. Itano, "Laser cooling of atoms", Phys. Rev. A 20, 1521 (1979) CrossRef R. Drever et al., "Laser phase and frequency stabilization using an optical resonator", Appl. Phys. B 31, 97 (1983) CrossRef P. W. Smith, "Mode-locking of lasers", Proceedings of the IEEE 58, 1342 (1970) CrossRef S. Stenholm, "The semiclassical theory of laser cooling", Rev. Mod. Phys. 58, 699 (1986) CrossRef

DOI
10.4302/plp.v9i4.764

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In the experiments involving trapped ions, application of a cooling procedure is required. The optical Doppler scheme is one of the most commonly used methods for slowing down the ions motion. In this paper we present an optical system sufficient for cooling calcium ions in such scheme. The system allows also for optical detection of the trapped ions. Full Text: PDF ReferencesF. Major, V. Gheorghe, and G. Werth, Charged Particle traps, Physics and Techniques of Charged Particle Field Confinement (Springer 2005). DirectLink Ł. Kłosowski, M. Piwiński, and M. Drewsen, "Integral electron impact ionization cross section of molecules through Coulomb crystallization of the product ions", J. Phys. Conf. Ser. 635, 072003 (2015) CrossRef D. J. Wineland and Wayne M. Itano, "Laser cooling of atoms", Phys. Rev. A 20, 1521 (1979) CrossRef R. Drever et al., "Laser phase and frequency stabilization using an optical resonator", Appl. Phys. B 31, 97 (1983) CrossRef P. W. Smith, "Mode-locking of lasers", Proceedings of the IEEE 58, 1342 (1970) CrossRef S. Stenholm, "The semiclassical theory of laser cooling", Rev. Mod. Phys. 58, 699 (1986) CrossRef
Trapped atomic ions are a multifaceted platform that can serve as a quantum information processor, precision measurement tool and sensor. However, in order to perform these experiments, the trapped ions need to be cooled substantially below room temperature. Doppler cooling has been a tremendous work horse in the ion trapping community. Hydrogen-like ions are good candidates because they have typically have a simple closed cycling transition that requires only a few lasers to Doppler cool. The \\textsuperscript{2}S to \\textsuperscript{2}P transition for these ions however typically lies in the UV to deep UV regime which makes buying a standard CW laser difficult as optical power here is hard to come by. Rather using a CW laser, which requires frequency stabilization and produces low optical power, this thesis explores how a mode-locked laser in the comb regime Doppler cools Yb ions. This thesis explores how a mode-locked laser is able to laser cool trapped ions and the consequences of using a broad spectrum light source. I will first give an overview of the architecture of our oblate Paul trap. Then I will discuss how a 10 picosecond optical pulse with a repetition rate of 80 MHz interacts with a 20 MHz linewidth \\textsuperscript{2}S\\(_{1/2}\\) to \\textsuperscript{2}P\\(_{1/2}\\) transition. Next I will go over our experiment involving ultrafast Ramsey experiment between the \\textsuperscript{2}S\\(_{1/2}\\) and \\textsuperscript{2}P\\(_{1/2}\\) states. Finally, I will present the results of these experiments.
A range of experimental techniques for application in reaction studies between ionic and neutral atoms/molecules and high resolution spectroscopy experiments with sympathetically cooled molecular ions are presented. A novel ion trap loading scheme using the photo-ionisation of atoms generated by the pulsed laser ablation of a solid calcium target has been characterised. We have identified the range of ablation laser fluences that must be used in order to produce a flux of neutral calcium atoms, which is a prerequisite for isotope selective ion trap loading. Calcium ions are trapped and laser cooled in a linear radio-frequency ion trap. We have developed a spectroscopy scheme that allows the entire fluorescence spectrum of trapped ions to be rapidly collected with high precision while maintaining a low ion temperature and good ion localisation throughout interrogation. The scheme has been demonstrated by measuring the saturation intensity of the calcium ion 4S1/2?4P1/2 transition. We have developed a novel scheme to measure the secular motion of trapped ions and demonstrated the application of the technique to ion-neutral collision reaction experiments. Employing pulsed excitation and Doppler velocimetry, we have measured the centre-of-mass mode frequency of single ions as well as large ion crystals with a frequency precision better than 2x10-3 within an interrogation time on the order of seconds. This method has been used to measure the mass of ions and observe charge exchange collisions between trapped calcium isotopes. In particular, we have measured the 44Ca++40Ca!40Ca++44Ca reaction cross section and demonstrated the single-event resolution of the technique. Finally, we have developed a novel all-optical broadband scheme for exciting, amplifying and measuring the secular motion of ions in the trap. Oscillation induced by optical excitation has been coherently amplified to control and measure the ion's secular motion. Requiring only a single interrogation laser, the ion's oscillation amplitude can be precisely controlled. The application of this technique to non-destructive spectroscopy of trapped molecular ions is discussed.
Beams of atoms and molecules (N.F. Ramsey). Momentum exchange between matter and light (S. Stenholm). Quantum effects in atomic optics (D.F. Walls). New laser cooling mechanisms (C. Cohen-Tannoudji). Laser cooling configurations (G. Nienhuis). Velocity-selective coherent population trapping in one and two dimensions (E. Arimondo). Coupled-pendulum model of the forces on three-level atoms (M. Prentiss et al.). Laser cooling and manipulation of atoms and selected applications (S. Chu). Laser cooling and trapping of neutral atoms (W.D. Phillips). Search for montional quantization of laser-cooled atoms (R. Gupta, S. Padua, T. Bergeman, H. Metcalf). The low (temperature) road toward Bose-Einstein condensation in optically and magnetically trapped cesium atoms (Ch. Monroe, E. Comell, C. Wieman). Manipulation of atoms by laser light (W. Ertmer). Laser manipulation of helium: the limits of the semi-classical description (A. Aspect et al.). Light manipulation of atoms (V.1. Balykin). Atom traps and atom optics (D.E. Pritchard and W. Ketterle). Electromagnetic traps for, charged and neutral particles (W. Paul). Laser cooling of trapped ions (W.M. Itano et al.). High-resolution atomic spectroscopy of laser-cooled ions (D.J. Wineland et al.).
Laser cooling is fundamental to quantum computing and metrology using atomic systems. Precise control often requires cooling atoms' motional degrees of freedom to the quantum ground state, imposing operation time and architectural limitations particularly in large-scale systems. Here we demonstrate how the integrated optical control of interest for scaling trapped-ion systems additionally enables laser cooling that bypasses limitations of conventional schemes. Leveraging multi-channel integrated delivery of ultraviolet to infrared wavelengths for calcium ion control including in passively phase-stable ultraviolet standing waves (SWs), we experimentally verify a long-standing prediction by Cirac et al., realizing Doppler cooling to below the conventional Doppler limit at a SW node. We also present the first realization of ground-state cooling via electromagnetically induced transparency (EIT) using a ``probe" beam delivered as a SW with atoms positioned at a node, predicted to enable multi-mode sub-recoil-limit laser cooling. We demonstrate cooling of motional modes spanning an approximately 5 MHz bandwidth from the Doppler temperature to near the ground state within 150~\textmu s, reaching nˉ≈0.05\bar n \approx 0.05nˉ≈0.05 phonon number occupancies for the target mode. Direct evaluation against the comparable running-wave (RW) scheme shows the SW implementation's simultaneous advantage in cooling rate, motional mode bandwidth, and final phonon number, as previously theoretically predicted. Our work leverages capabilities enabled by integrated optical delivery to demonstrate fast cooling of multiple modes to the quantum ground state, and more broadly how scalable approaches to optical control can enable enhancements in fundamental atomic functionalities.
The interaction of laser radiation with matter is widely used to cool atomic and molecular gases to extremely low temperatures. In connection with this, a considerable number of works on quantum optics have recently been devoted to laser cooling of matter. The principle of Doppler cooling for neutral atoms was proposed by T. Nanch and A. Shavlov, and for trapped ions by D. Wineland and H. Dehmelt. The chapter shows the scheme of the principle of Doppler cooling. The atomic beam is slowed by transmission of a pulse that occurs at the time when the atom absorbs a quantum of light. When laser cooling of atoms in a certain volume, a problem arises with optical pumping. The scheme of cooling an atomic beam by laser radiation in a magnetic field, called the Zeeman slowing, is most often used to obtain slow atomic beams.
Abstract One of the most remarkable achievements of laser control is the manipulation of atomic particles, their velocities, positions, etc., which is referred to as laser cooling and laser trapping . These two effects are interrelated and usually prove effective when used jointly. That this is so one can see by considering as an example the laser cooling of trapped ions and the laser trapping of laser-cooled neutral atoms (Fig. 5.1). The sequences of processes in these two situations are directly opposite. Ions can easily be trapped in an electromagnetic trap of large depth (Paul 1990) and then be cooled for a long time by laser radiation (sideband cooling) (Wineland and Dehmelt 1975; Dehmelt 1990). Neutral atoms are first slowed down and cooled by laser radiation down to millikelvin temperatures, and only then confined in an optical trap. Trapped atoms can further be cooled to microkelvin temperatures. The present chapter and Chapter 6 consider the cooling and trapping of neutral atoms, the present chapter concentrating on their cooling, and Chapter 6 on trapping. But it would be reasonable first to familiarize the reader with the history of the early ideas in this field that eventually led to the advent of a new domain of physics—the physics of ultracold atoms and molecules (Chapters 7 and 8).