Comment on “Indications of energetic consequences of decoherence at short times for scattering from open quantum systems” [AIP Advances 1, 022118 (2011)]
The paper by Chatzidimitriou-Dreismann, Gray and Blach in the title reports measurements on gaseous hydrogen, performed on the VESUVIO electron volt neutron spectrometer at the ISIS neutron source. It was claimed in this paper that the VESUVIO measurements show that, if the energy transfer is sufficiently large that the bond in the H2 molecule is broken, then a larger energy transfer than that predicted by conventional neutron scattering theory occurs. It was also claimed that this is the first evidence for an increase in the energies of the proton and its environment due to quantum disentanglement. It is shown here that this evidence is almost certainly a spurious consequence of errors in the data analysis of Chatzidimitriou-Dreismann et al. When the standard VESUVIO instrument programs are used to analyse the same data on gaseous hydrogen the results obtained are in very good agreement with conventional theory.
The paper by Chatzidimitriou-Dreismann, Gray and Blach in the title reports measurements on gaseous hydrogen, performed on the VESUVIO electron volt neutron spectrometer at the ISIS neutron source. It was claimed in this paper that the VESUVIO measurements show that, if the energy transfer is sufficiently large that the bond in the H2 molecule is broken, then a larger energy transfer than that predicted by conventional neutron scattering theory occurs. It was also claimed that this is the first evidence for an increase in the energies of the proton and its environment due to quantum disentanglement. It is shown here that this evidence is almost certainly a spurious consequence of errors in the data analysis of Chatzidimitriou-Dreismann et al. When the standard VESUVIO instrument programs are used to analyse the same data on gaseous hydrogen the results obtained are in very good agreement with conventional theory.
Dreismann, Gray and Blach (DGB) have claimed that neutron scattering from molecular hydrogen at energy transfers E sufficiently large to break the H-H bond, gives E ∼3% larger than predicted by conventional quantum theory. DGB presented this claim as the first experimental evidence for energetic consequences of decoherence of quantum entangled particles due to interactions with the environment. It is shown here this claim is entirely spurious. DGB obtained disagreement with conventional theory by changing the geometrical description of the Vesuvio instrument at ISIS, they used to collect their data. Instead of using the default scattering angles obtained from neutron diffraction, DGB used scattering angles obtained using a steel rule and protractor. DGB then manufactured apparent but in fact completely spurious evidence for quantum decoherence effects from the large measurement errors in the scattering angles they used. These give shifts to both higher and lower E than predicted by conventional quantum theory. DGB simply ignored detectors giving shifts to lower values of E. DGB also ignored previously published H2 data that clearly contradict their claim.
The Comment by Mayers and Reiter criticizes our work on two counts. Firstly, it is claimed that the quantum decoherence effects that we report in consequence of our experimental analysis of neutron Compton scattering from H in gaseous H2 are not, as we maintain, outside the framework of conventional neutron scattering theory. Secondly, it is claimed that we did not really observe such effects, owing to a faulty analysis of the experimental data, which are claimed to be in agreement with conventional theory. We focus in this response on the critical issue of the reliability of our experimental results and analysis. Using the same standard Vesuvio instrument programs used by Mayers et al., we show that, if the experimental results for H in gaseous H2 are in agreement with conventional theory, then those for D in gaseous D2 obtained in the same way cannot be, and vice-versa. We expose a flaw in the calibration methodology used by Mayers et al. that leads to the present disagreement over the behaviour of H, namely the ad hoc adjustment of the measured H peak positions in TOF during the calibration of Vesuvio so that agreement is obtained with the expectation of conventional theory. We briefly address the question of the necessity to apply the theory of open quantum systems.
Decoherence of quantum entangled particles is observed in most systems, and is usually caused by system-environment interactions. Disentangling two subsystems A and B of a quantum system AB is tantamount to erasure of quantum phase relations between A and B. It is widely believed that this erasure is an innocuous process, which e.g. does not affect the energies of A and B. Surprisingly, recent theoretical investigations by different groups showed that disentangling two systems, i.e. their decoherence, can cause an increase of their energies. Applying this result to the context of neutron Compton scattering from H2 molecules, we provide for the first time experimental evidence which supports this prediction. The results reveal that the neutron-proton collision leading to the cleavage of the H-H bond in the sub-femtosecond timescale is accompanied by larger energy transfer (by about 3%) than conventional theory predicts. It is proposed to interpreted the results by considering the neutron-proton collisional system as an entangled open quantum system being subject to decoherence owing to the interactions with the “environment” (i.e., two electrons plus second proton of H2).
Nuclei and electrons in condensed matter and/or molecules are usually entangled, due to the prevailing (mainly electromagnetic) interactions. However, the "environment" of a microscopic scattering system (e.g. a proton) causes ultrafast decoherence, thus making atomic and/or nuclear entanglement effects not directly accessible to experiments. However, our neutron Compton scattering experiments from protons (H-atoms) in condensed systems and molecules have a characteristic collisional time about 100–1000 attoseconds. The quantum dynamics of an atom in this ultrashort, but finite, time window is governed by non-unitary time evolution due to the aforementioned decoherence. Unexpectedly, recent theoretical investigations have shown that decoherence can also have the following energetic consequences. Disentangling two subsystems A and B of a quantum system AB is tantamount to erasure of quantum phase relations between A and B. This erasure is widely believed to be an innocuous process, which e.g. does not affect the energies of A and B . However, two independent groups proved recently that disentangling two systems, within a sufficiently short time interval, causes increase of their energies. This is also derivable by the simplest Lindblad-type master equation of one particle being subject to pure decoherence. Our neutron-proton scattering experiments with H 2 molecules provide for the first time experimental evidence of this effect. Our results reveal that the neutron-proton collision, leading to the cleavage of the H-H bond in the attosecond timescale, is accompanied by larger energy transfer (by about 2–3%) than conventional theory predicts. Preliminary results from current investigations show qualitatively the same effect in the neutron-deuteron Compton scattering from D 2 molecules. We interpret the experimental findings by treating the neutron-proton (or neutron-deuteron) collisional system as an entangled open quantum system being subject to fast decoherence caused by its "environment" (i.e., two electrons plus second nucleus of H 2 or D 2 ). The presented results seem to be of generic nature, and may have considerable consequences for various processes in condensed matter and molecules, e.g. in elementary chemical reactions.
In general, nuclei and electrons in condensed matter and/or molecules are entangled, due to the prevailing (electromagnetic) interactions. As a matter of fact, the "environment" interacting with a microscopic system of interest (e.g. a proton) causes the destruction of the entanglement. This process, called decoherence, has until now prevented experimenters from directly accessing atomic and/or nuclear entanglement effects in real experiments. However, our neutron and electron Compton scattering experiments from protons (H-atoms) in several condensed systems and molecules at ambient conditions demonstrated a new striking effect, i.e. an "anomalous" decrease of scattering intensity from protons, which seem to become partially "invisible" to the neutrons. This effect, which has no interpretation within conventional neutron scattering theory, is proposed to be caused by the non-unitary time evolution (due to decoherence) during the ultrashort, but finite, time-window of the neutron-proton scattering process. Due to the large energy (several eV) and momentum (20-200 Å −1 ) transfers of these experiments the collisional time between the probe particle and a struck proton is 100–1000 attoseconds long. It is shown that, due to this short timescale, the scattering process must be theoretically treated within quantum dynamics of open quantum systems. New experimental neutron Compton scattering results from a single crystal KHCO 3 are presented. They provide the first direct evidence for a connection between the momentum distribution and the "anomalous" scattering intensity of H. Additionally, recent experiments with electron-atom Compton scattering at momentum transfers are mentioned, which reveal the presence of this effect even in scattering from single H 2 molecules in the gas phase. Theoretical discussions "from first principles" are presented, also in relation to the quantum Zeno effect, which underline the crucial role of decoherence in the considered experiments. The experimental results and their qualitative interpretation show that epithermal neutrons being available at spallation sources (e.g. ISIS/UK, SNS/USA or ESS/Sweden), and electron spectrometers with large scattering angles, provide tools for investigating new physical and chemical phenomena in the sub-femtosecond timescale.
Several recent experiments have shown that protons, and to some extent also deuterons, show anomalous cross sections when the neutrons have energies in the range 10-100 eV (this results in a Compton scattering process where an essential part of the energy is transferred to one of the scattering particles). Here, an experiment on partially deuterated water, carried out by Chatzidimitriou-Dreismann et al., is analyzed in terms of a theory, which assumes that during the short duration (<10(-15) s) of this scattering process, protons are exchange correlated and cannot be considered as independent scattering objects. The quantum decoherence time for protons in liquid water is estimated from a simple model for the interaction of the water protons with hydrogen bonds.