Quantum Information Processing at the Attosecond Timescale

Arxiv – Quantum Information Processing at the Attosecond

Coherent processing of quantum information and attosecond science had so far little in common. We here show that recent data in high harmonic emission reveal quantum information processing at the attosecond timescale. High harmonic generation in the strong-field regime is governed by tunneling ionization followed by the motion of the electron in the continuum and its re-collision in the atomic core. Before the actual photon detection the electron-photon state exhibits a high degree of quantum coherence and entanglement, that has so far remained elusive. By observing the interference pattern created by the spatiotemporal overlap of photons emitted by two interfering electron paths we generate a photon Hadamard gate and thus erase the electron-trajectory information. This allows the measurement of the relative phase in electron-trajectory quantum superpositions and establishes the era of electron-photon quantum coherence and entanglement at the attosecond timescale of high-field physics.

Concluding, by realizing a Hadamard gate for the photons before the actual photon detection we erase the electron-trajectory information imprinted in the harmonic photons and thus we access the relative phase of the electronic quantum superpositions created in the HHG process. The availability of the full quantum information physically retrievable in the process of HHG will certainly open new vistas in the investigation of strong-field light-matter interaction processes leading to coherent light emission, in particular HHG in all states of matter. Our findings establish a new era in high-field physics in the context of quantum coherence and entanglement in ultrafast electron-photon dynamics and thus bridge quantum information pro- cessing with attosecond science and high resolution spectroscopy studies in the EUV spectrum.

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