We address the validity of the single-mode approximation that is commonly invoked in the analysis of entanglement in non-inertial frames and in other relativistic quantum information scenarios. We show that the single-mode approximation is not valid for arbitrary states, finding corrections to previous studies beyond such approximation in the bosonic and fermionic cases. We also exhibit a class of wave packets for which the single-mode approximation is justified subject to the peaking constraints set by an appropriate Fourier transform.
We investigate the effects of relative motion on entanglement harvesting by considering a pair of Unruh-Dewitt detectors moving at arbitrary, but independent and constant velocities, both linearly interacting with the vacuum scalar field. Working within the weak coupling approximation, we find that the Negativity is a (non-elementary) function of the relative velocity of the detectors, as well as their energy gaps and minimal separation. We find parameter regions where Negativity increases with velocity up to a maximum and then decreases, reaching zero at some sublight velocity. At any given r…
Probing Lorentz-invariance-violation with quantum coherence of Unruh-DeWitt detector
School of Physics, Hangzhou Normal University（杭州师范大学物理学院）；Department of physics and electrical engineering, Liupanshui Normal University（六盘水师范学院物理与电气工程系）
Tunable-Size Unruh-DeWitt Detector in a Multimode Cavity
Institut für Theoretische Physik, Universität Innsbruck（因斯布鲁克大学理论物理研究所）；Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences（奥地利科学院量子光学与量子信息研究所）；Okinawa Institute of Science and Technology Graduate University（冲绳科学技术大学院大学）；Institute of Physics, Maria Curie-Skłodowska University（玛丽亚·居里-斯克沃多夫斯卡大学物理研究所）
We ask whether quantum teleportation from the outside to the inside of a horizon is possible, using entanglement extracted from a vacuum. We first calculate analytically, within the perturbation theory, entanglement extracted from the Minkowski vacuum into a pair of an inertial and an accelerated Unruh-DeWitt detectors, which are initially in the ground states and interact with a neutral massless scalar field for an infinitely long time. We find that entanglement can be extracted, but is "fragile", depending on adiabaticity of switching of the detectors at the infinite past and future. We then…
Can a relativistic quantum field theory be consistently described as a theory of localizable particles? There are many known issues with such a description, indicating an answer in the negative. In this paper, we examine these obstructions by tracing how they (partially) subside in passing to an approximation of ordinary quantum mechanics in the non-relativistic regime. We undertake a recovery of the characteristic features of non-relativistic quantum mechanics beyond simply the Schrödinger equation. We find that once this is achieved, there are persisting issues in the localizability of parti…
We study the quantum coherence in de Sitter space for the bipartite system of Alice and Bob who initially share an entangled state between the two modes of a free massive scalar field. It is shown that the space-curvature effect can produce both local coherence and correlated coherence, leading to the increase of the total coherence of the bipartite system. These results are sharp different from the Unruh effect or Hawking effect, which, in the single mode approximation, cannot produce local coherence and at the same time destroy correlated coherence, leading to the decrease of the total coher…
We revisit the problem involving two constantly accelerating Unruh-DeWitt detectors using Open Effective Field Theory methods. We study the time evolution of the joint detector state using a Markovian approximation which differs from the standard one taken in the literature. We show that this Markovian limit already implies the complete positivity of the dynamical evolution map without invoking the rotating wave approximation (RWA), in contrast to standard derivations of open system master equations. By calculating explicitly the domain of validity of this Markovian approximation, we argue tha…
We revisit the interaction of a first-quantized atomic system (consisting of two charged quantum particles) with the quantum electromagnetic field, pointing out the subtleties related to the gauge nature of electromagnetism and the effect of multipole approximations. We connect the full minimal-coupling model with the typical effective models used in quantum optics and relativistic quantum information such as the Unruh-DeWitt (UDW) model and the dipole coupling approximation. We point out in what regimes different degrees of approximation are reasonable and in what cases effective models need …
Sudden death and birth of entanglement beyond the Markovian approximation
在马尔可夫近似下，研究了两个初始纠缠的量子比特与两个不相关的库相互作用的纠缠动力学。这与马尔可夫水库的情况完全不同[C. E. Lopez等人，物理修订信函101（2008）080503]，我们发现两个库的纠缠突然诞生（ESB）相对于两个量子比特的纠缠突然死亡（ESD）没有一定的对称性。最后给出了纠缠复兴的唯象解释。
Envelope induced ionization dynamics beyond the dipole approximation
当原子和分子被有限持续时间和越来越高强度的激光脉冲电离时，经常使用的偶极子近似的有效性，其中忽略了外场的空间依赖性和磁分量，最终被打破。我们报告说，当超越偶极近似的描述暴露于紫外光的原子，脉冲形状的空间依赖性，包络线，提供了主导的校正，而载体的空间依赖性可以忽略不计。我们提出了一个一阶超越偶极校正的哈密顿量，占专门的非偶极效应所产生的载波包络的脉冲。我们证明了氢的{ \it ab initio}计算，这种近似，我们将被称为{ \it包络近似}，再现了完全的相互作用，绝对和微分观测量的偶极子近似，并证明是有效的，为广泛的高频领域。对于薛定谔方程和狄拉克方程都是这样做的。此外，它表明，包络近似提供了一个相互作用项，从而产生更快的数值收敛的部分波相比，其确切的对应。
The method of many-body Green's functions is developed for arbitrary systems of electrons and nuclei starting from the full (beyond Born-Oppenheimer) Hamiltonian of Coulomb interactions and kinetic energies. The theory presented here resolves the problems arising from the translational and rotational invariance of this Hamiltonian that afflict the existing many-body Green's function theories. We derive a coupled set of exact equations for the electronic and nuclear Green's functions and provide a systematic way to approximately compute the properties of arbitrary many-body systems of electrons…
