Dynamics of Quantum Superposition States and Quantum Beating in Rubidium Vapor

Hiroki Nakatsuka, Jumpei Okada, Masahiro Matsuoka

Free precession beat of two-photon induced coherence was observed by the use of delayed probe pulses in atomic rubidium vapor. The two-photon coherence was created in the superposition state of the 5S 1/2 and 5D 5/2 levels of Rb by two-photon resonant excitation with a mode-locked dye laser pulse. The origin of the beat is attributed to the hyperfine splittings of the 5S 1/2 ground state of both Rb 85 and Rb 87 . The observed results are explained by a theory presented in this paper.

王晓晨 Wang Xiaochen, 蒋小军 Jiang Xiaojun, 赵子豪 Zhao Zihao +4 more

Thomas M. Spinka

Nonlinear optical processes, with a particular emphasis on parametric four-wave mixing (PFWM), are studied in rubidium vapor. A theoretical framework is introduced that enables accurate calculations of nonlinear light-matter interactions, and calculations of these interactions using this framework are performed for a broad range of excitation conditions. In particular, the effects of femtosecond pulse parameters such as pulse duration, pulse energy, center wavelength, and chirp are investigated. Simulation results provide insight into the light-matter interactions in rubidium vapor for these conditions. The effects of pump pulse parameters on the production and evolution of atomic wavepackets in the nonlinear medium are investigated. A number of femtosecond-scale phenomena that were elusive or previously unknown are observed, including the observation of quantum beating at pump-probe time delays exceeding 500 ps, quantum beating on the 7s1/2 - 5d3/2 energy defect at 611 cm-1, and the effects of pump pulse chirp on the amplitude and temporal dynamics of quantum beating. Toward the goal of using the nonlinear optical process of PFWM to interrogate the nearest neighbor distribution (NND), a new analytical derivation for the NND in the non-interacting particle approximation is presented, along with the results of molecular dynamics simulations of the NND in rubidium vapor for realistic pair interaction potentials.

N. N. Badalyan, V. A. Iradyan, M. E. Movsesyan

Matthew A. Morrison, Zhenhuan Yi, Chris O’Brien +4 more

Andrey A. Senin

Wavepackets are excited in rubidium vapor by intense ultrashort (∼100 fs) pulses centered at a wavelength of 620 nm or 770 nm. The generated atomic wavepackets are optically detected via a pump-probe experiment based on axially phase-matched parametric four-wave mixing (FWM). This nonlinear process results in coherent ultraviolet (UV) or violet emission that carries information about the relative number densities of the excited states. The frequency spectrum of the UV/violet signal intensity, recorded while varying the pump-probe time delay, shows the presence of quantum beats between energy levels involved in the FWM process. The time-frequency analysis of that temporal UV/violet data is done by means of the short-time Fourier transform that leads to retrieval of the temporal evolution of amplitude and phase of the quantum beats. The observed dynamics suggest that not only atomic but also molecular ( Rb*2 ) wavepackets are generated, and that the temporal history of the amplitude of the quantum beats reflects the production of the excited atomic fragments of Rb*2 dissociation. More precisely, changes in the Rb excited state number densities alter the third-order nonlinear susceptibility chi(3) of the Rb vapor, which affects generation of the output signal wave by FWM. Dissociation into several product states is detected, and their branching ratios are estimated. Thus, atomic wavepackets, combined with FWM, appear to be a sensitive new multichannel spectroscopic means to study the fundamental process of molecular dissociation.