Reconstruction of attosecond beating by interference of two-photon transitions is a cornerstone technique of attosecond chronoscopy, routinely used to extract photoemission delays from the phase of sideband oscillations. Here, we theoretically investigate the reconstruction of attosecond beating by interference of two-photon transitions protocol driven by quantum light and demonstrate that it is intrinsically sensitive to the quantum nature of the driving field. When the probe field is prepared in a nonclassical state, its photon statistics are imprinted onto photoelectrons via continuum-continuum transitions, giving rise to an additional time delay of several tens of attoseconds. We trace this delay to the phase associated with the second-order anomalous moment ⟨a[over ^]^{2}⟩ of the probe field. Extending the framework to a three-sideband configuration, which enables retrieval of the fourth-order anomalous moment ⟨a[over ^]^{4}⟩, we show that the interferometer exhibits significantly enhanced sensitivity to quantum fluctuations. Our work illustrates quantum attosecond photoelectron interferometry as a phase-sensitive probe of quantum light, offering a promising route for time-resolved quantum metrology at the attosecond scale.
Reconstruction of attosecond beating by interference of two-photon transitions is a cornerstone technique of attosecond chronoscopy, routinely used to extract photoemission delays from the phase of sideband oscillations. Here, we theoretically investigate the reconstruction of attosecond beating by interference of two-photon transitions protocol driven by quantum light and demonstrate that it is intrinsically sensitive to the quantum nature of the driving field. When the probe field is prepared in a nonclassical state, its photon statistics are imprinted onto photoelectrons via continuum-continuum transitions, giving rise to an additional time delay of several tens of attoseconds. We trace this delay to the phase associated with the second-order anomalous moment ⟨a[over ^]^{2}⟩ of the probe field. Extending the framework to a three-sideband configuration, which enables retrieval of the fourth-order anomalous moment ⟨a[over ^]^{4}⟩, we show that the interferometer exhibits significantly enhanced sensitivity to quantum fluctuations. Our work illustrates quantum attosecond photoelectron interferometry as a phase-sensitive probe of quantum light, offering a promising route for time-resolved quantum metrology at the attosecond scale.
We present a general theoretical framework for multiphoton processes driven by quantum light fields, establishing a direct link between photon statistics and photoelectron observables. Our results show that the autocorrelation and cross-correlation functions, which quantify the underlying photon statistics, are directly mapped onto the resulting photoelectron spectra. Although our framework is broadly applicable, we demonstrate specifically in the example of reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) the influence of the light statistical properties. In this approach, the amplitude, contrast and phase of the oscillations of the sideband signal as a function of pump-probe delay reveal the quantum nature of light. We analyze these observables across several quantum configurations, including correlated infrared and harmonic modes, as well as the uncorrelated case with non-classical harmonic statistics, thereby establishing a general framework for quantum-light RABBIT spectroscopy. We compare the analytical theory with numerical simulations for the case of classical harmonics and an infrared field in a squeezed coherent state, obtaining excellent agreement. Our results reveal how the interplay between classical and quantum correlations dictates the coherence of the photoemission process, providing a new window into the quantum-optical foundations of attosecond science.
Attosecond chronoscopy enables the exploration of correlated electron dynamics in real time. One key observable of attosecond physics is the determination of "time zero" of photoionization, the time delay with which the wave packet of the ionized electron departs from the ionic core. This observable has become accessible by experimental advances in attosecond streaking and reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) techniques. In this Letter, we explore photoionization time delays by strong extreme ultraviolet fields beyond the linear-response limit. We identify novel signatures in time delays signifying strong coupling between atoms and light fields and the light-field dressing of the ion. As a prototypical case, we study the interelectronic coherence and entanglement in helium driven by a strong extreme ultraviolet field. By the numerical solution of the time-dependent Schrödinger equation in its full dimensionality, we show that the time delay of the photoionized electron allows one to monitor the ultrafast variations of coherence dynamics and entanglement in real time.
Correlations between optical modes, ranging from classical fluctuations to quantum entanglement, are a cornerstone of modern optics and emerging quantum technologies. However, probing these correlations on the natural timescale of electronic motion - the attosecond regime - remains a major challenge. Here, we generate and characterize correlated attosecond extreme-ultraviolet (XUV) emission by perturbing gas-phase high-harmonic generation with two-mode bright squeezed vacuum. The signal and idler fields imprint their correlated amplitude and phase fluctuations onto two families of harmonics, thereby transferring these correlations from the infrared to broadband XUV modes. Even harmonics serve as an intrinsic attosecond phase-sensitive probe of these correlations through interference between indistinguishable XUV pathways. Shot-resolved covariance measurements reveal the amplitude correlations, while even-harmonics resolve the phase correlations with sub-cycle precision. Time-domain reconstruction of the correlated emission reveals a transition from maximal fluctuations to near-silence within only 30 as. Whereas the signal and idler driven attosecond pulse trains exhibit excess fluctuations individually, their joint reconstruction shows strongly suppressed fluctuations, reflecting their shared correlations. These results establish a framework for generating and probing quantum correlations on attosecond timescales, opening the door to quantum attosecond science.
Combining attosecond science with semiconductor physics provides a promising interdisciplinary platform for the attosecond control of semiconducting properties. In each field, the reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) and the time-resolved and angle-resolved photoemission spectroscopy (tr-ARPES) have been central experimental techniques for probing microscopic dynamics of electrons. However, the integration of the two techniques, bridging the two fields, has been missing so far although they have many technical similarities. Here, we develop a theoretical framework that integrates the two techniques based on the second-order time-dependent perturbation theory. Within this framework, we investigate the RABBIT spectroscopy in semiconductors focusing on the recent hallmark of tr-ARPES, namely quantum path interference between Floquet and Volkov states. Moreover, we theoretically identify a novel quantum path incorporating the virtual excitation, which substantially interferes with the Floquet and Volkov states in both the RABBIT spectroscopy and tr-ARPES of semiconductors. Importantly, we find that such virtual excitation channel induces an attosecond topological interference with the Floquet-Volkov paths, encoding topological quantities such as the local Berry curvature into the time shift of RABBIT sidebands, which is directly related to the photoelectron emission delay. Our findings establish a theoretical framework connecting attosecond spectroscopy to tr-ARPES, paving the way for future applications of attosecond science in semiconductors.
Abstract Correlations between optical modes, ranging from classical fluctuations to quantum entanglement, are a cornerstone of modern optics and emerging quantum technologies. However, probing these correlations on the natural timescale of electronic motion - the attosecond regime - remains a major challenge. Here, we generate and characterize correlated attosecond extreme-ultraviolet (XUV) emission by perturbing gas-phase high-harmonic generation with two-mode bright squeezed vacuum. The signal and idler fields imprint their correlated amplitude and phase fluctuations onto two families of harmonics, thereby transferring these correlations from the infrared to broadband XUV modes. Even harmonics serve as an intrinsic attosecond phase-sensitive probe of these correlations through interference between indistinguishable XUV pathways. Shot-resolved covariance measurements reveal the amplitude correlations, while even-harmonics resolve the phase correlations with sub-cycle precision. Time-domain reconstruction of the correlated emission reveals a transition from maximal fluctuations to near-silence within only 30 as. Whereas the signal and idler driven attosecond pulse trains exhibit excess fluctuations individually, their joint reconstruction shows strongly suppressed fluctuations, reflecting their shared correlations. These results establish a framework for generating and probing quantum correlations on attosecond timescales, opening the door to quantum attosecond science.
Until recently, attosecond optical spectroscopy and quantum optics evolved along non-overlapping directions. In attosecond science, attosecond pulses have been regarded as classical waves, applied to probe electron dynamics on their natural time scale. Here, we transfer fundamental concepts of quantum optics into attosecond physics, enabling control of both the properties of the XUV attosecond pulses and the quantum fluctuations of matter on attosecond time scales. By combining bright squeezed vacuum (BSV) with a strong laser field to drive high-harmonic generation, we transfer the quantum properties of the BSV onto the resulting XUV attosecond pulses. Applying advanced attosecond interferometry, we reconstruct the quantum state of the XUV high harmonics and their associated attosecond pulses with attosecond precision. Finally, we resolve the squeezing of the electron's wavepacket during one of the most fundamental strong-field phenomena - field induced tunneling. The ability to measure and control quantum correlations in both electrons and XUV attosecond pulses establishes a foundation for attosecond quantum electrodynamics, manipulating the quantum state of electrons and photons with sub-cycle precision.