Exploring Quantum Coherence with Electron Beams
In the intricate dance of the quantum world, where the rules of classical physics no longer apply, scientists have found a powerful tool to probe the elusive phenomenon of quantum coherence – the electron beam. These charged matter waves, with their strong interactions and sensitivity to their environment, are shedding new light on the delicate nature of quantum systems.
Traditionally, scientists have employed superimposed, mutually coherent electron beams for holography and phase retrieval, allowing them to visualize the intricate wavefunctions of electron packets. But the latest research has delved deeper, exploring the dynamic interplay between these superposed electron beams and the matter they encounter.
Quantum coherence, the hallmark of quantum technologies, is a fragile state easily disrupted by the surrounding environment. Understanding the factors that influence this coherence is crucial for the practical implementation of quantum devices, from quantum computers to quantum sensors. Theoretically, quantum coherence is represented by the off-diagonal elements of a quantum system's density matrix, while experimentally, it is measured by the visibility of interference fringes resulting from the superposition of two quantum states.
Unlike the aloof photons, which typically exhibit minimal interaction with each other, charged particles like electrons display strong interactions, both with themselves and their environment. This unique characteristic makes electron beams superior probes, offering deeper insights into the complex dance of quantum decoherence.
In electron holography experiments, a beam is split into two paths, with one path passing through a material sample. The interference pattern formed when the two paths recombine on a detector screen can be analyzed to extract information about the sample, including its image intensity and phase. However, this interference can be degraded by the inelastic scattering of electrons due to their radiative coupling with the sample.
A groundbreaking study by Velasco et al. has delved into this phenomenon, providing a careful analysis of the decoherence experienced by electron-wave interferometry. They have demonstrated that the exchange of photons between the electron beam and the extended object it interacts with can lead to a significant loss of mutual coherence between the two paths of the electron beam, resulting in a reduction in the visibility of the interference fringes.
Remarkably, the researchers have found that the electron energy-loss probability function, which governs this photon exchange, diverges even faster at absolute zero temperature compared to non-zero temperatures. Furthermore, the rate of photon exchange, and thus the decoherence effect, increases as the distance between the electron beam and the object decreases.
This work not only introduces a new framework for understanding the decoherence of electron beams but also paves the way for the exploration of nonradiative decoherence channels and the role of different optical media in controlling the decoherence yield. By unraveling the intricate dynamics of electron-matter interactions, scientists are inching closer to a deeper comprehension of the quantum realm and the development of more robust quantum technologies.
Source: https://www.nature.com/articles/s41377-024-01430-4
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