Recently, it was reported the observation of acoustically induced transparency (AIT) of stainless-steel foil for resonant gamma-ray photons with an energy of 14.4 keV emitted from a radioactive Mossbauer source ⁵⁷Co [1]. Similar to the electromagnetically induced transparency (EIT) and Autler–Townes splitting (ATS), AIT constitutes the appearance of a spectral domain of very weak absorption of radiation, located at the place of a nuclear resonant spectral line (Fig.1). However, in contrast to EIT and ATS, AIT doesn’t require a strong coherent electromagnetic driving field and can occur already in a two-level system. AIT is caused by coherent uniform oscillations of nuclei with ultrasonic frequency, which can be implemented by piston-like vibration of a solid absorbing medium. Similar to EIT and ATS, the material dispersion in the AIT spectral window has a sharp slope (Fig.1), which corresponds to a decrease in the group velocity of propagating radiation. In this paper, we show that under the same experimental conditions as in [1], single 14.4 keV photons emitted by the ⁵⁷Co source can be slowed down below 6 m/s at room temperature in a stainless-steel foil of a certain thickness, enriched with ⁵⁷Fe nuclide, oscillating at an optimal frequency. The corresponding single-photon wave packet of gamma radiation having a duration of about 80 ns can be delayed by about 100 ns.

Fig. 1. Absorption (red curve, right axis) and dispersion (blue curve, left axis) of the vibrating resonant absorber ⁵⁷Fe in the case of AIT in the laboratory reference frame, at the vibration amplitude of 0.38 $\lambda $ (where $\lambda $ is the radiation wavelength) and frequency of 3$\gamma_{21}$ (where $\gamma_{21}$ is the halfwidth of the nuclear absorption line). The black dashed curve (right axis) is the absorption line of the motionless absorber. In the case of the incident wave packet with Lorentz spectrum of the halfwidth $\gamma_{21}$ , the black dashed curve also represents the incident field spectrum.

[1] Radeonychev, Y.V., Khairulin, I.R., Vagizov, F.G., Scully, M. & Kocharovskaya, O. Observation of acoustically induced transparency for $\gamma $-ray photons. Phys. Rev. Lett. 124, 163602 (2020).

Y. V. Radeonychev, I. R. Khairulin, and Olga Kocharovskaya
JETP Letters 114, issue 12 (2021)