Quantum Light Improves Atomic Ionisation Control

Scientists at the Peking University, led by Haodong Liu, have demonstrated that manipulating the quantum characteristics of light can significantly improve the precision of attosecond physics experiments. Their work centres on strong-field ionization of xenon atoms, achieved using bright squeezed vacuum (BSV) light, with average pulse energies reaching 10 J. This non-classical light source selectively enhances specific structures within the photoelectron momentum distributions, offering a novel pathway towards understanding and controlling ultrafast atomic dynamics. A quantum-trajectory Monte Carlo model attributes this enhancement to increased coherence between correlated electron paths, effectively mitigating the effects of noise and opening new avenues for investigation in the field.

Squeezed vacuum light reveals coherent electron pathways in xenon ionization

A tenfold increase over previous limits in strong-field ionization of xenon atoms has been achieved utilising bright squeezed vacuum (BSV) light, with pulse energies reaching 10 J. Strong-field ionization, a fundamental process in attosecond physics, occurs when an intense laser field is sufficient to remove electrons from atoms, even from tightly bound orbitals. Traditionally, these experiments have been conducted using coherent-state driving lasers, treating light as a classical electromagnetic wave. However, the quantum nature of light, its inherent fluctuations and correlations, has remained largely unexplored due to experimental limitations. The observed BSV selectively enhances ‘spider-like’ structures, holographic patterns within the photoelectron momentum distributions, due to enhanced coherence between correlated electron trajectories. These spider-like structures arise from the interference of direct photoelectrons with those that have undergone rescattering, where the liberated electron is pulled back towards the ionising atom by the strong laser field before being ejected again. Analysis revealed that the 10 J pulse energies from the bright squeezed vacuum selectively amplify these spider-like holographic structures, patterns indicative of forward electron rescattering, by 1.6 times compared to conventional laser sources. This amplification is not simply an increase in signal strength, but a genuine enhancement of the coherence between the contributing electron pathways. A quantum-light-corrected quantum-trajectory Monte Carlo model demonstrated that field noise effectively filters out asynchronous electron paths, strengthening the signal and confirming the enhanced coherence. The model incorporates the quantum properties of the BSV, accurately simulating the observed photoelectron momentum distributions and validating the experimental findings. The quantum-trajectory method tracks the evolution of individual electron trajectories in the laser field, accounting for the complex interplay between the laser and the atomic potential. Maintaining the necessary BSV intensity for more complex atomic targets remains a key technical hurdle, precluding immediate practical applications such as quantum electron sources, but the principle is demonstrably sound.

Holographic imaging benefits from quantum light’s enhanced electron pattern definition

Attosecond physics, the study of phenomena occurring on the timescale of attoseconds (10^-18 seconds), relies on understanding how light liberates electrons from atoms, a process known as strong-field ionization, and forms the basis of rapidly advancing technologies such as ultrafast spectroscopy and imaging. Most experiments, however, treat light as a simple wave, overlooking its quantum properties, and this investigation deliberately challenges that assumption. Bright squeezed vacuum, a type of non-classical light, exhibits reduced quantum noise in one quadrature of the electromagnetic field at the expense of increased noise in the other. This ‘squeezing’ of the quantum fluctuations can be harnessed to improve the precision of measurements. Bright squeezed vacuum selectively sharpens the patterns created by ejected electrons, enhancing the ‘spider-like’ holographic structures. These structures provide information about the potential energy landscape experienced by the electron during its interaction with the atom and the laser field, effectively acting as a holographic image of the atomic potential. Demonstrating strong-field ionization with this non-classical light source, exhibiting both predictable and erratic wave behaviours, reveals a new method for enhancing coherence in attosecond physics experiments. Coherence, in this context, refers to the well-defined phase relationship between the different electron pathways contributing to the observed photoelectron momentum distribution. The quantum-light-corrected model confirmed that these active paths maintain stability against disruptive noise, establishing a mechanism where quantum fluctuations actively protect coherence, and selectively amplifies spider-like structures by reinforcing the synchronicity of correlated electron paths. This coherence protection is crucial for achieving high-resolution imaging and precise control over ultrafast processes. The observed effect suggests that BSV can be used to suppress decoherence, a process that degrades the quality of quantum information and limits the performance of quantum devices. Further research will focus on extending these techniques to more complex atomic systems and exploring the potential for developing novel quantum-enhanced spectroscopic methods.

The research demonstrated strong-field ionization of xenon atoms using bright squeezed vacuum, a type of light with unique quantum properties. This process selectively enhances spider-like holographic structures in the resulting electron patterns, providing a clearer image of the atomic potential. Researchers found that these quantum fluctuations actively protect the coherence of electron pathways, making the process more stable and robust against noise. The study establishes bright squeezed vacuum as an effective coherence filter and reveals a new understanding of quantum-enabled dynamics in ultrafast physics.