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Complex Light and Optical Forces

Local and remote synthesis of single-photon space-time wave packets

Bryan L. Turo, Bahaa E. A. Saleh, Ayman F. Abouraddy

Published Mar 5, 2026• 0 citations

Abstract

Space-time wave packets (STWPs) are a new class of spatiotemporally structured light fields that are endowed with a host of unique properties, including diffraction-free propagation at controllable group velocity, self-healing, and dispersion-free propagation in dispersive media. These characteristics make STWPs useful candidates for free-space optical communications, particularly for quantum communications. We demonstrate here the first single-photon STWP produced in two different configurations from entangled-photon pairs produced through spontaneous parametric downconversion. In the first configuration, a spatiotemporal spectral modulator is placed in the path of the signal photon, whose arrival is heralded by detection of the idler photon, which we refer to as local STWP synthesis. In the second configuration, the signal photon after the modulator is detected to herald the arrival of the idler photon, which we refer to as remote STWP preparation. In both configurations, we observe the predicted diffraction-free propagation of single-photon STWPs. These results pave the way for quantum communications using spatiotemporally structured quantum states of light.

DOI: 10.1117/12.3081448

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We experimentally demonstrate temporal shaping of a heralded single-photon wave packet, prepared by conditional measurement of the idler photon of the entangled photon pair in the process of spontaneous parametric down-conversion. The heralded single-photon wave packet for the signal photon, after being tailored with the help of chirp broadening and interference effects, was observed directly by measuring the time-correlated single-photon-counting histogram. We also demonstrate remote control of the temporal shaping effect by spectral filtering of the idler photon.

Space-Time Wave Packets (STWPs) have enabled numerous nontrivial properties, such as tunable group velocities, nondiffraction and nonlocal spin textures in optical fields. However, this has not been properly studied in matter waves. Here, we investigate free-electron STWPs, which are propagation-invariant and group-velocity-tunable matter wave packets, constructed by constraining the spatiotemporal spectrum of the electron wavefunction in momentum space. Due to the unique dispersion of free-electrons, the electron STWP can carry two different topologies, and host both meron and skyrmion topological textures in momentum space. We demonstrate the topological phase transitions and tunable skyrmion numbers by spectral geometry tuning. We also show the topologically robust propagation of the electron pulses and corresponding real-space skyrmionic expectation value textures encoded within each single electron wavefunction. Our results open a platform for topological free-electron wavepackets uses in sensing and information transfer.

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