Two-photon excitation of ultracold atoms to Rydberg states

Abstract

Abstract. In this work, we discuss two-photon excitation and diagnostic of ultracold Rydberg atoms in a magneto-optical trap. Lithium atoms were excited by using ultraviolet cw laser. For identification of Rydberg transitions, we recorded resonance fluorescence of ultracold atoms. Spectra of transitions 2P-nS, 2p-nD were measured. Our results are in good agreement with calculations and experimental data available in literature. Presented work is a part of our project focused on preparation and study of Rydberg matter and ultracold plasma.Our research project is focused on study of a Rydberg matter and non-ideal plasma [1,2]. Results of the research can be useful for fundamental physics and for some applications as quantum computers. Atoms can be optically transferred to definite Rydberg states by twophoton or multi-photon excitation processes [3,4]. The problem is to diagnose highly-excited states. In addition to the traditional approach, induced ionization of Rydberg atoms by applied electric field [2], recently EIT [5] and FWM [6] techniques have been used for identification of the Rydberg transitions. As the first step in our research project we have performed cw two-step excitation of ultracold lithium atoms from the ground state to a highly-excited state. In the current paper we describe our experimental setup and observation of the Rydberg transitions in lithium atoms in magneto-optical trap (MOT). A basic description of the MOT for lithium atoms is presented in [7]. Our vacuum system is similar to an experimental apparatus which used in laboratory of A. Turlapov for investigation of the Fermi gas of 6 Li atoms [8]. The atomic transitions, which participated in excitation of Rydberg states, are shown in figure 1.Optical transitions in D 2 line are used for optical cooling and trapping of lithium atoms. Optical transitions in D 1 line are used for absorption measurements of an atomic cloud in MOT by using a weak probe laser. In figure 1 a blue arrow shows an ultraviolet transition (350 nm) from the excited state 2P 3/2 to highly excited states.In our laboratory an experimental setup for trapping and ultraviolet excitation of 7 Li atoms is assembled. Our setup is described in [9][10][11]. It consists of vacuum and optical systems. The vacuum system includes an oven (the source of a thermal atomic beam), a Zeeman slower, and a main vacuum chamber (residual air pressure < 10 −9 mbar), where 7 Li atoms are trapped.In the optical part of the setup we use two amplified external cavity diode lasers (ECDL) for the cooling and trapping of 7 Li atoms. One of them is the cooling laser, which is slightly detuned from the cycling transition 2S 1/2 (F = 2)-2P 3/2 (F ′ = 3). This laser is locked to the thermally stabilized reference cavity with tunable transmission resonances. The other laser is repump laser ELBRUS 2015