A cloud of laser cooled 40Ca+ in a linear ion trap

Abstract

A cloud of 40 Ca + is successfully trapped and cooled using the radiation of a red-detuned 397 nm laser beam and a resonant 866 nm laser beam in our prototype linear ion trap, which was designed and constructed for studying quantum information processing. We have characterized the size of the ion cloud, estimating the temperature to be in the order of milli-Kelvins.ion trap, laser cooling, quantum information processing Citation:Laser-cooled trapped ions are considered as promising candidates for the investigation and implementation of quantum information processing (QIP). There have been experimental demonstrations for simple quantum algorithms with trapped ions [1] and for entangling eight ultra-cold ions in a linear trap [2]. It is thought that scalable QIP with trapped ions could be carried out by moving the ions from one zone to another in a multi-trap device [3] or by entangling spatially separate ions by entangling the emitted photons [4]. There are approximately 25 research groups studying QIP with various trapped ion species. The leading groups at NIST and Innsbruck are employing 9 Be + [5] and 40 Ca + [6]. The Oxford groups are working with 40 Ca + [7], and other groups are exploring 111 Cd + [8], 171 Yb + [9], 43 Ca + [10], 138 Ba + [11] and 88 Sr + [12]. Since ion traps could potentially provide a very clean and isolated space for confinement, the ultra-cold ions trapped inside could be manipulated coherently, which favors storage and processing of quantum information [13]. We may encode qubits in the electronic levels of the ions and manipulate these qubits by lasers either individually or globally. Interactions between *These authors contributed equally to this work †Corresponding authors (email: hxueren@wipm.ac.cn; mangfeng@wipm.ac.cn) the qubits occur via the quantized vibrational modes of the ions.This paper describes recent work on the successful trapping of a cloud of 40 Ca + ions in our prototype linear ion trap. This is the first step toward the QIP with a line of trapped ions undertaken in China. The linear ion trap we built consists of four radio frequency (RF) blades, two end-cap tips and two compensation electrodes. In comparison with the traditional linear ion trap with four RF-rods and two ring end-caps, our trap could provide stronger trapping potential and cleaner trapping space due to the reduction in trap size and the minimization of the ceramic surface facing toward the trap.Our trap setup is described in Figure 1, the opposing RF blades are separated by 1.6 mm, and the spacing between the two end-cap tips is 5.0 mm. The ions are produced in the trap center by the electron bombardment on an atomic beam from the calcium oven. The linear trap is encapsulated in a vacuum chamber connected to a 40 L/s ion pump (Vacion plus 40 diode pump, Varian Inc) plus a titanium sublimation pump (Varian). Chamber pressures below 10 −9 mbar can be inferred from the measured current through the ion pump (≤0.1 μA). To trap ions, a prototype tunable RF drive running

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“…We are also aware that the influence of detuning in a linear ion trap has been studied. [30] Here, we set the MW detunings to δ f = 0, 1.1, 2.2, 3.3 MHz. Hyperfine structure plays an important role here as in the case δ f = 0 (see Fig.…”