A research team led by Associate Professor J. F. Chen have achieved an important advance in single-photon manipulation: the team has experimentally realized spatiotemporal (2+1)D Airy bullets at the single-photon level for the first time. The work, titled “Spatiotemporal single-photon Airy bullets,” is published in Physical Review Letters as an Editors’ Suggestion and is featured as Viewpoint by Physics Magazine, published by the American Physical Society. The article is also highlighted as PRL 2024 selection.

Single photons are a perfect carrier of quantum information for long-distance transmission, supporting both efficient state transfer between network nodes and enhanced information security. Photons are fast, resilient to many environmental disturbances, and offer multiple degrees of freedom for encoding—such as polarization, momentum, orbital angular momentum, frequency and time-bin. However, as in classical optics, dispersion and diffraction can still affect the propagation of photons over distance. Airy beams are known for their propagation-invariant behavior (including nondiffraction and self-healing) and for their characteristic self-accelerating, curved trajectories. While modern laser techniques have produced Airy “bullets” in classical light fields, Airy control of nonclassical light—especially simultaneously in space and time—has remained limited. The Chen group addressed this challenge by combining cutting-edge quantum optical control techniques to achieve full manipulation of a single photon in both spatial and temporal degree of freedom.

The team operated a cold atomic ensemble platform with advanced quantum-optics techniques to bring nondiffracting optics into the quantum domain. Using the electromagnetically induced transparency (EIT) slow-light effect in an elongated atomic ensemble, a spatially structured excitation can be mapped into the temporal waveform of emitted single photons. In parallel, the researchers applied spatial single-photon shaping to sculpt the transverse mode. Together, these capabilities enabled the generation of a spatiotemporal (2+1)D Airy single-photon bullet that is resistant to both diffraction and dispersion. A key breakthrough of the work is that the team exploited nonclassical correlations between paired photons generated in a nonlinear optical process, allowing the nondiffracting Airy photon bullet to remain detectable even in the presence of strong classical light noise. This unique quantum light field opens up new possibilities for applications in quantum communication, quantum information processing, single-photon microscopy, and nondestructive biological imaging.

Fig.1: The experimental observation of spatial-temporal single-photon Airy bullet.

In the experiment, the researchers generated a pair of entangled photons by laser-pumping a cold atomic ensemble at a temperature of approximately 100 μK. As shown in Fig. 1(a), one of the pump laser beams was spatially modulated by a spatial light modulator (SLM) to carry the characteristic Airy waveform, while, under the coupling of another strong laser beam, the electromagnetically induced transparency (EIT) effect resulted in the spatial modulation of the atomic ensemble by the Airy light waveform. This spatial modulation was then transferred into the temporal waveform of the photon pair, reshaping the temporal profile of the photons. When one photon served as a heralding trigger for the presence of its partner photon, the paired photon was prepared as a single photon and spatially shaped by the SLM, resulting in the Airy waveform in both time and space. As a result, the researchers successfully reshaped the spatial and temporal dimensions of the single photon into the standard Airy waveform, as shown in Fig. 1(b), where the temporal spatiotemporal waveform of the single photon was measured using photon counting techniques. Fig. 1(c) shows the Airy waveform of the single photon measured directly in the time domain. The second-order autocorrelation function of the single photon within the 1 μs coherence time remained below the classical lower bound of g(2) = 1. A characteristic feature of Airy beams is that their propagation path in space is not straight, but follows a parabolic trajectory, demonstrating the self-accelerating property. Fig. 1(d) illustrates the propagation path of the single-photon Airy bullet. Despite significant classical light noise interference, the single-photon Airy bullet still exhibited a self-accelerating parabolic trajectory, which was preserved through the nonclassical correlation between photon pairs.

This work exploits a cold atomic ensemble as the medium to achieve, for the first time, full spatiotemporal control of a single-photon Airy bullet. In the construction of quantum computing and communication networks, the modal distributions of light in the time, frequency, or spatial domains can be engineered into Airy waveforms, thereby enabling Airy bullets to mitigate dispersion, diffraction, and related propagation effects during transmission. Single-photon Airy bullets are expected to find further applications in experimental studies of quantum communication and quantum information processing.

Southern University of Science and Technology (SUSTech) is the first affiliation on the paper. Associate Professor J. F. Chen and Researcher Georgios A. Siviloglou are corresponding authors, and Jianmin Wang (Ph.D. student) is the first author. The work is also contributed by team members Ying Zuo and Xingchang Wang, and the collaborator Professor Demetrios N. Christodoulides (University of Southern California). The research was supported by the National Natural Science Foundation of China and other provincial and institutional programs.