Measurement of the van der Waals interaction by atom trajectory imaging

Abstract

We study the repulsive van der Waals interaction of cold rubidium 70S 1/2 Rydberg atoms by analysis of time-delayed pair correlation functions. After excitation, Rydberg atoms are allowed to accelerate under the influence of the van der Waals force. Their positions are then measured using a single-atom imaging technique. From the average pair correlation function of the atom positions we obtain the initial atom-pair separation and the terminal velocity, which yield the van der Waals interaction coefficient C6. The measured C6 value agrees well with calculations. The experimental method has been validated by simulations. The data hint at anisotropy in the overall expansion, caused by the shape of the excitation volume. Our measurement implies that the interacting entities are individual Rydberg atoms, not groups of atoms that coherently share a Rydberg excitation. The van der Waals interaction is important in the description and control of interactions in few-and manybody dynamics studies. This interaction has been critical in the observation of Rydberg excitation blockades and collective excitations [1][2][3][4], Rydberg crystals [5,6], and Rydberg aggregates [7,8]. Rydberg interactions have been used in quantum information processsing [9][10][11][12]. The van der Waals interaction between two Rydberg atoms has been measured using spectroscopic methods [13,14]. Several measurements have been performed near surfaces to observe radiative Rydberg-level shifts caused by image charge interaction near metal surfaces [15,16]. The van der Waals interaction between excited cesium atoms and a dielectric surface has been measured using selective reflection spectroscopy [17].Here, we develop a method to study the van der Waals interaction between Rydberg atoms using direct spatial imaging of their trajectories [18][19][20][21]. Pairs of 70S 1/2 rubidium Rydberg atoms are prepared with a well-defined initial separation by detuning an excitation laser and utilizing the r −6 dependence of the van der Waals interaction [21,22]. After preparation, the atoms are subject to van der Waals forces (which are repulsive in this case). The effect of the forces is observed by tracking the interatomic distance between the Rydberg atoms, after they have been allowed to move for selected wait times (see Fig. 1). The atom trajectories and thereby the van der Waals interaction coefficient C 6 are extracted from the pair correlation functions of the Rydberg atom positions.The experimental setup is shown in Fig. 1(a). 85 Rb ground-state atoms are prepared in a magneto-optical trap (MOT) at a density of 10 10 cm −3 . The twophoton Rydberg excitation to 70S 1/2 is driven by simultaneous 780 nm and 480 nm laser pulses with a 5 µs duration and ≈1 GHz red-detuning from the 5P 3/2 intermediate state. Both beams propagate in the xy plane and are linearly polarized alongẑ. The 780 nm beam has a Gaussian beam parameter w 0 of 0.75 mm and the 480 nm beam is focused to w 0 = 8 µm. The Rydberg atoms are ionized by applying a high voltage to a tip imaging p...

Enhanced Chiral Discriminatory van der Waals Interactions Mediated by Chiral Surfaces

“…The interactions with the gas molecules will lead to a separation of the trajectories of the molecules in the beam, depending on their handedness. This trajectory imaging technique has been already used for Rubidium Rydberg atoms [38]. Conclusions.…”

Control of Rydberg-atom blockade by dc electric-field orientation in a quasi-one-dimensional sample

“…Such works explore different aspects of condensed matter physics: i) transition to the crystalline phase [19,20]; ii) energy transport [21]; iii) spatial correlations [22]; iv) Rydberg aggregates [23]; v) van der Waals interaction and Rydberg blockade effect [24][25][26]. Clearly, Rydberg atoms can be used as a prototype for the study of such complex properties because they are a simpler system and easier to control.…”

Population transfer driven by far-off-resonant fields

“…In addition, the scheme can be used to realize population inversion for Rydberg states, e.g., from the ground state |g ≡ 5S 1/2 |F = 2, m = 2 to the Rydberg state |r ≡ 60S 1/2 of the cold 87 Rb atom. Since this atomic transition frequency is in the ultraviolet region, it conventionally employs 780-nm and 480-nm lasers via the intermediate state |e ≡ 5P 3/2 |F = 3, m = 3 under two-photon resonance condition [39]. In our scheme, only 780-nm lasers can work.…”