The high-order Bragg spectroscopy of interacting boson gases was used to test the universality of the Feynman-Tantan

Universal physics in strongly interacting boson gases

The interaction between particles is the core of the strongly correlated quantum many-body physical effect, and the discovery of universal relationships can simplify the microscopic characterization of the interaction and help to better understand the physical laws existing in complex quantum many-body systems. Ultracold atomic quantum gases have superior controllability, which provides an ideal experimental platform for studying and testing universal relationships. According to Bogoliubov’s theory, in the collective excitation spectrum of weakly interacting ultracold bose atomic gases, the frequency shift of the resonance frequency is linearly dependent on the scattering length of the atoms. Subsequently, Feshbach resonance was used to enhance the interaction of ultracold atoms, but the experimental results were seriously different from Bogoliubov’s theoretical predictions.

In 2017, the research group at the University of Cambridge in the United Kingdom proposed the Feynman-sandalwood relationship by combining the Feynman energy relationship and the sandalwood coefficient describing the collision of the two bodies, and the frequency shift of resonance excitation is proportional to the scattering length of ultracold atoms at the weak interaction limit. However, in the region of strong interaction, this frequency shift decreases with the increase of scattering length, and even signs are inverted. Experimentally, the excitation spectrum of ultracold 39K atomic gas was measured by two-photon Bragg spectroscopy, and the Feynman-Tan relation was verified in a large interaction range. Since the frequency shift in the Feynman-Tan relation is inversely proportional to the atomic mass, it is of great significance to test the universality of this relationship in other kinds of ultracold atomic systems for the study of strongly correlated ultracold bose atomic quantum gases.

Figure 1 (a) experimental setup for interacting ultracold atom Bragg spectra, (b) schematic diagram of six-photon Bragg scattering, (c) Four-photon and six-photon high-order Bragg spectroscopy to test the universality of the Feynman-Tan relation.

Examine the universality of the Feynman-Tan relation

Recently, the research team of Professor Jia Suotang, Professor Ma Jie and Associate Professor Li Yuqing of Shanxi University used high-order Bragg spectroscopy to test the universality of the Feynman-Tantantra relation in ultra-cold 133Cs atomic gas. In particular, the 133Cs atom used here has a large mass, which provides an ideal experimental platform for testing the universality of the Feynman-Tan relation containing atomic mass. The research team used hybrid evaporative cooling technology to prepare quasi-one-dimensional ultracold 133Cs atomic quantum gas, applied two laser beams that were far out of tune and with precise control of relative frequency to the atomic sample, and developed high-order Bragg spectroscopy technology of four-photon and six-photon on the basis of two-photon Bragg spectroscopy. The interaction of ultracold atoms was adjusted over a wide range under a low magnetic field (< 150 G), and the change of frequency shift of the gas resonance excitation frequency of ultracold atoms with scattering length was studied by measuring the Bragg spectrum under different interactions. When the interaction between atoms increases, the frequency shift of the resonant frequency first increases and then decreases to a negative value, which is consistent with the curve predicted by the Feynman-Tan relation. Compared to two-photon Bragg spectra, the higher-order Bragg spectra of four- and six-photons have greater momentum shifts, allowing shifts in frequency shift symbols to be observed with smaller interactions. This study verifies the universality of the Feynman-Tan relation in different ultracold atomic systems, which is important for describing and understanding the collective excitation of Bose quantum gases under strong interactions.


Ultracold 133Cs atomic gas has a large atomic mass and the interaction can be controlled in a wide range, which provides a very ideal experimental platform for testing the universality of the physical relationship containing atomic mass, which is of great significance for understanding complex strongly correlated many-body physics. In addition, the study of high-order Bragg spectroscopy of strongly interacting ultracold atomic gases will provide deeper insights into inelastic scattering in quantum many-body systems.

The article was published in Light: Science & Applications in the top international academic journal “Testing universality of Feynman-Tan relation in interacting Bose gases using high-order Bragg spectra”, Yunfei Wang and Huiying Du is the co-first author of the paper, and Yuqing Li and Jie Ma are the corresponding authors of the paper.

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(Source: LightScienceApplications)
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