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arXiv:2610.26901

Symmetry and Quantum Interference in the Attosecond Domain

C. Figueira de Morisson Faria, S. Hashim, J. Rivera-Dean, T. Rook

physics.atom-phquant-phSubmitted Oct 16, 2026• Announced Oct 20, 2026• 0 citations
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Abstract

In this review, we examine the interplay of symmetry and quantum interference in the attosecond domain primarily through one- and two-electron photoelectron momentum distributions. Using our own work, we discuss how tailored laser fields provide control over dynamical symmetries, and how quantum-orbit methods make it possible to connect the resulting momentum-space structures to specific ionisation, propagation, and rescattering pathways. Particular emphasis is placed on ultrafast photoelectron holography and nonsequential double ionisation through recollision excitation with subsequent ionisation, where several distinct forms of quantum interference can be identified and manipulated. We also discuss how target properties, including the binding potential, orbital symmetry and parity, modify this mapping. Finally, we consider emerging opportunities offered by non-classical states of light, for which photon statistics and quantum fluctuations provide additional degrees of freedom for controlling symmetry and strong-field electron dynamics.

Comments
Review article; 38 pages excluding references

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In this review, we examine the interplay of symmetry and quantum interference in the attosecond domain primarily through one- and two-electron photoelectron momentum distributions. Using our own work, we discuss how tailored laser fields provide control over dynamical symmetries, and how quantum-orbit methods make it possible to connect the resulting momentum-space structures to specific ionisation, propagation, and rescattering pathways. Particular emphasis is placed on ultrafast photoelectron holography and nonsequential double ionisation through recollision excitation with subsequent ionisation, where several distinct forms of quantum interference can be identified and manipulated. We also discuss how target properties, including the binding potential, orbital symmetry and parity, modify this mapping. Finally, we consider emerging opportunities offered by non-classical states of light, for which photon statistics and quantum fluctuations provide additional degrees of freedom for controlling symmetry and strong-field electron dynamics.
When small quantum systems, atoms or molecules, absorb a high-energy photon, electrons are emitted with a well-defined energy and a highly symmetric angular distribution, ruled by energy quantization and parity conservation. These rules are based on approximations and symmetries which may break down when atoms are exposed to ultrashort and intense optical pulses. This raises the question of their universality for the simplest case of the photoelectric effect. Here we investigate photoionization of helium by a sequence of attosecond pulses in the presence of a weak infrared laser field. We continuously control the energy of the photoelectrons and introduce an asymmetry in their emission direction, at variance with the idealized rules mentioned above. This control, made possible by the extreme temporal confinement of the light-matter interaction, opens a road in attosecond science, namely, the manipulation of ultrafast processes with a tailored sequence of attosecond pulses.
We study the two-dimensional photoelectron momentum distribution in a synthesized field of an attosecond pulse and a weak infrared femtosecond pulse by solving the time-dependent Schr\"odinger equation of He atoms. The photoelectron momentum spectra reveal fruitful interference structures. With a semiclassical model, we show that some of the photoelectron interference structures come from the interference between the direct and backward-scattering electron trajectories. Those backward-scattering electrons are freed by the attosecond pulse and then are hard rescattered with parent ions by the streaking infrared field. By changing the phase delay between the attosecond pulse and the infrared laser field, we find that two kinds of backward-scattering electron trajectories will contribute to the holographic pattern. We show that backward-scattering holography can be explored with attosecond streaking experiments.
This thesis investigates quantum dynamics induced in atoms by ultrashort pulses of light. The work is motivated by recent developments in free-electron lasers, which generate ultrashort pulses of intense, coherent light and enable coherent control of quantum dynamics. We develop theoretical models to study the processes of absorption and emission in laser-atom interactions. Additionally, we study photoionisation, which creates an ion and an electron, and the entanglement that can be generated between these particles. Finally, we have investigated how the spontaneous decay of the ion induces entanglement transfer from the ion-electron pair to the electron-photon pair.This thesis compiles seven papers. Paper I investigates the absorption of light from an attosecond pulse by an atom in a prepared coherent superposition of states. We show how the evolution of the phase of the superposition wave packet influences the attosecond transient absorption spectra. Paper II predicts the existence of Mollow-like triplets in the absorption spectra of strongly coupled atoms. We establish the conditions for the pulse envelope under which this triplet pattern can be supported.Paper III studies two-photon Rabi oscillations, establishing which systems can sustain such dynamics. We find that a two-photon Rabi oscillating system can induce giant counter-rotating oscillations in the population dynamics, enabling investigations of physical effects beyond the rotating-wave approximation.Paper IV studies ionisation from an atom strongly coupled by a dichromatic field, where interference between the two frequency components shapes the temporal symmetry of the atomic dynamics, allowing for coherent control of the photoelectron distribution.Paper V considers an experiment performed at a Free-Electron Laser facility where a helium atom is ionised and the resulting ion is subsequently strongly coupled. The photoelectron spectra are theoretically reproduced and the entanglement between the ion and photoelectron is studied. Paper VI investigates how the entanglement in the ion--electron pair, generated via photoionisation followed by strong coupling, can be coherently controlled by harnessing the time symmetry of the pulse. We find that the observable manifestation of the entanglement can be altered in such a way that the electron energy becomes associated with the ionic state, allowing the entanglement to be detected via coincidence measurements. Paper VII investigates how quantum correlations between the ion and the electron can be coherently controlled by sequential strong coupling of the ion. We find that both the build-up of entanglement and its manifestation can be controlled, and we establish a quantitative measure of the amplitude entanglement that explains the dynamics in an intuitive way. Paper VIII studies the process of entanglement transfer induced by the spontaneous decay of the ion. We find that the ion--electron entanglement generated during the ultrashort interaction with the laser field is transferred to the electron--photon system over the much longer timescale of fluorescence.
This perspective introduces attosecond qubits: coherent two-level subsystems that arise naturally in strong-field physics from the interference of experimentally distinguishable quantum pathways. These attosecond qubits are dynamical superposition states formed during strong-field evolution and appear in diverse settings: short-long trajectories in HHG, early-late ionization bursts, polarization-selective recombination channels, and momentum- or energy-bin structures in ATI. Attosecond qubits can be prepared, rotated, and measured using existing attosecond techniques, providing a Hilbert-space description of sub-cycle electronic dynamics. Coulomb interaction, tunneling fluctuations, soft-photon dressing, and macroscopic propagation define ultrafast decoherence channels. This framework links attosecond physics with quantum information science and identifies new opportunities for coherence metrology, temporal quantum tests, ultrafast decoherence studies, and the exploration of quantum speed limits in strongly driven, time-dependent Hamiltonians.
The generation and control of extreme ultraviolet (XUV) radiation by high harmonic generation (HHG) have advanced ultrafast science, providing direct insights into electron dynamics on their natural time scale. Attosecond science has established the capability to resolve ultrafast quantum phenomena in matter by characterizing and controlling the classical properties of the high harmonics. Recent theoretical proposals have introduced novel schemes for generating and manipulating XUV HHG with distinct quantum features, paving the way to attosecond quantum optics. In this work, we transfer fundamental concepts in quantum optics into attosecond science. By driving the HHG process with a combination of an infrared bright squeezed vacuum (BSV, a non-classical state of light), and a strong coherent field, we imprint the quantum correlations of the input BSV onto both the ultrafast electron wavefunction and the harmonics' field. Performing in-situ HHG interferometry provides an insight into the underlying sub-cycle dynamics, revealing squeezing in the statistical properties of one of the most fundamental strong-field phenomena -- field induced tunneling. Our measurement allows the reconstruction of the quantum state of the harmonics through homodyne-like tomography, resolving correlated fluctuations in the harmonic field that mirror those of the input BSV. By controlling the delay between the two driving fields, we manipulate the photon statistics of the emitted attosecond pulses with sub-cycle accuracy. The ability to measure and control quantum correlations in both electrons and XUV attosecond pulses establishes a foundation for attosecond electrodynamics, manipulating the quantum state of electrons and photons with sub-cycle precision.
Ultrafast high harmonic beams provide new opportunities for coherently controlling excitation and ionization processes in atoms, molecules, and materials on attosecond time scales by employing multiphoton two-pathway electron-wave-packet quantum interferences. Here we use spectrally tailored and frequency tuned vacuum and extreme ultraviolet harmonic combs, together with two phase-locked infrared laser fields, to show how the total single and double photoionization yields of argon can be coherently modulated by controlling the relative phases of both optical and electronic-wave-packet quantum interferences. This Letter is the first to apply quantum control techniques to double photoionization, which is a fundamental process where a single, high-energy photon ionizes two electrons simultaneously from an atom.