Free-space Propagation of Stationary Light

R. Loudon

Murat Yessenov, Ayman F. Abouraddy

It is typically assumed that the fluctuations associated with a stationary broadband incoherent field propagate in free space at the speed of light in vacuum c. Here we introduce the concept of "coherence group velocity" which, in analogy to the group velocity of coherent pulses, is the speed of the peak of the coherence function. We confirm experimentally that incorporating a judicious spatio-temporal spectral structure into a field allows tuning its coherence group velocity in free space. Utilizing light from a superluminescent diode, we interferometrically measure the group delay encountered by the cross-correlation of a structured field synthesized from this source with the unstructured diode field. By tracking the propagation of this cross-correlation function, we measure coherence group velocities in the range of 12c to -6c.

Samina Masood, Iram Saleem

U-Shin Kim, Yong Sup Ihn, Chung-Hyun Lee +1 more

We report the first experimental demonstration of trapping a free-propagating single-photon into a cold atomic ensemble. Also, we observe that the quantum properties of the single-photon state are preserved during the trapping process. © 2024 The Author(s)

B. V. Ermakov, Yu A Il'inskiĭ

Matias Koivurova, Chaoliang Ding, Jari P. Turunen +1 more

The concept of cross-spectral purity of light, established by Mandel for stationary optical fields, is extended to nonstationary fields. Separability conditions that ensure the cross-spectral purity of nonstationary light are derived in the space-frequency and space-time domains. It is also shown that the property of cross-spectral purity is not strictly preserved on propagation of fields with any appreciable spectral bandwidth. Further, we introduce a method for generating cross-spectrally pure (stationary and nonstationary) fields from spatially incoherent light sources by means of achromatic Fourier-transform systems.