Quantum entanglement and decoherence due to electrons-protons coupling

Tyno Abdul‐Redah, M. Krzystyniak, C. A. Chatzidimitriou‐Dreismann

Smail B. Bougouffa, K. Berrada

C. A. Chatzidimitriou‐Dreismann

Abstract. The “anomalous ” scattering of neutrons and electrons from protons in the electron-volt energy range is described, and related experimental results are presented. Due to the very short characteristic scattering time, there is no well defined separation of time scales of electronic and protonic motions. An outline of a proposed theoretical interpretation is presented, which is based on the fact that scattering protons represent open quantum systems. PACS number: 03.65.Ud 1 Introductory Remarks The counter-intuitive phenomenon of entanglement [1] between two or more quantum systems has emerged as the most emblematic feature of quantum me-chanics. Experiments investigating entanglement, however, are mainly focused on collections of few simple (two- or three-level) quantum systems thoroughly isolated from their environment (e.g., atoms in high-Q cavities and optical lat-tices). These experimental conditions are necessary due to the decoherence of entangled states [2, 3]. In short, decoherence refers to the suppression of quan-tum superpositions caused by the environment. By contrast, quantum entanglement (QE) in condensed and/or molecular mat-ter at ambient conditions is usually assumed to be inaccessible experimentally. However, applying two new scattering techniques (NCS and ECS, see below) which operate in the sub-femtosecond time scale, we provided results indicating that short-lived entangled states may affect measurements in condensed matter even at room temperature [4–6]. The first direct experimental evidence of short-lived (that is, attosecond) QE involving protons in condensed matter was provided by means of the novel neu-tron Compton scattering (NCS) method. Starting in 1995, our experiments on 1310–0157 c © 2006 Heron Press Ltd. 193

N. Chandra, R. Ghosh

C. A. Chatzidimitriou‐Dreismann, M. Krzystyniak

Nuclei and electrons in condensed matter and/or molecules are usually entangled, due to the prevailing electromagnetic interactions. Usually, the “environment” of a microscopic scattering system (e.g., a proton) causes an ultrafast decoherence, thus making atomic and/or nuclear entanglement effects not directly accessible to experiments. However, neutron Compton scattering (NCS) and electron Compton scattering represent ultrafast techniques operating in the sub-femtosecond timescale, thus opening a way for investigation of such dehoherence and short-lived entanglement phenomena of atoms in molecules and condensed matter. The experimental context of NCS and a new striking scattering effect from protons (H-atoms) in several condensed systems and molecules are described. In short, one observes an “anomalous” decrease of scattering intensity from protons, which seem to become partially “invisible” to the neutrons. The experiments apply large energy (several electronvolts) and momentum (10–200 Å −1 transfers, and the collisional (or scattering) time between the neutron and a struck proton is only 100–1000 attoseconds long. Similar results are also obtained with electron-atom Compton scattering at large momentum transfers. As an example, we present new NCS experimental results from a single crystal, which also provide new physical insights into the attosecond quantum dynamics of protons in molecules and condensed matter. Theoretical discussions and models are presented which show that the effect under consideration is caused by the non-unitary time evolution (due to decoherence) of open quantum systems during the ultrashort, but finite, time-window of the neutron-proton scattering process. The conceptual connection with the well known Quantum Zeno Effect is pointed out. The experimental results, together with their qualitative interpretation “from first principles,” show that epithermal neutrons being available at spallation sources, and electron spectrometers providing large momentum transfers, may represent novel tools for investigation of thus far unknown physical and chemical attosecond phenomena.