We present the formalism of Time-dependent Exchange Perturbation Theory (TDEPT) built to all orders of perturbation, for the arbitrary time dependency of perturbation. The theory takes into account the rearrangement of electrons among centres. We show how the formalism can be reduced to the standard form of invariant perturbation theory by 'switching off' the re-arrangement of electrons among centres. The elements of the scattering S-matrix and transitions T-matrix and the formula for the electron scattering differential cross section are derived. The application of the theory to scattering and collision problems is discussed. As an example, we apply the theory to proton scattering on a Lithium atom, calculating the differential and total cross-sections.
Spin-exchange collisions in alkali or alkali/noble gas vapors are at the basis of quantum sensing, nucleon structure studies, tests of fundamental symmetries, and medical imaging. We here show that spin-exchange collisions in hot alkali vapors naturally produce strong bipartite entanglement, which we explicitly quantify using the tools of quantum information science. This entanglement is shown to have a lifetime at least as long as the spin-exchange relaxation time, and to directly affect measurable spin noise observables. This is a formal theoretical demonstration that a hot and dense atomic …
An ensemble of noble-gas nuclear spins is a unique quantum system that could maintain coherence for many hours at room temperature and above, owing to exceptional isolation from the environment. This isolation, however, is a mixed blessing, limiting the ability of these ensembles to interface with other quantum systems coherently. Here we show that spin-exchange collisions with alkali-metal atoms render a quantum interface for noble-gas spins without impeding their long coherence times. We formulate the many-body theory of the hybrid system and reveal a collective mechanism that strongly coupl…
Phase-locking between different partial-waves in atom-ion spin-exchange collisions
本文对单个$^{88}$ Sr $^+$离子与超冷Rb原子云碰撞的自旋动力学进行了实验和理论研究。虽然两种物质之间的自旋交换发生在平均9.1（6）次朗之万碰撞之后，但Sr $^+$离子塞曼量子位的自旋弛豫发生在48（7）次朗之万碰撞之后，由于小的二阶自旋-轨道耦合，这比先前研究的系统明显慢。此外，随着磁场的增加，吸热自旋交换速率降低。有趣的是，我们发现，虽然在自旋单重态和三重态势上碰撞时获得的相位在不同的分波之间变化很大，但决定自旋交换截面的单重态-三重态相位差在很宽的分波范围内保持锁定为单一值，这导致量子干涉效应。
We show that the cross sections for a broad range of resonant {\it inelastic} processes accompanied by excitation exchange (such as spin-exchange, Förster resonant, or angular momentum exchange) exhibit an unconventional near-threshold scaling $E^{Δm_{12}}$, where $E$ is the collision energy, $Δm_{12}=m_1'+m_2'-m_1-m_2$, and $m_i$ and $m_i'$ are the initial and final angular momentum projections of the colliding species ($i=1,\,2$). In particular, the inelastic cross sections for $Δm_{12}=0$ transitions display an unconventional $E^0$ scaling similar to that of elastic cross sections, and thei…
