Spectral Magnetization Ratchets with Discrete Time Quantum Walks

Quantum ratchet in disordered quantum walk

Symmetrically evolving discrete quantum walk results in dynamic localization with zero mean displacement when the standard evolution operations are replaced by a temporal disorder evolution operation. In this work we show that the quantum ratchet action, that is, a directed transport in standard or disordered discrete-time quantum walk can be realized by introducing a pawl like effect realized by using a fixed coin operation at marked positions that is, different from the ones used for evolution at other positions. We also show that the combination of standard and disordered evolution operatio…

原子光学踢转子量子行走中自发辐射诱导的棘轮

Spontaneous-emission induced ratchet in atom-optics kicked rotor quantum walks

本文研究了原子光学踢转子量子行走中的自发辐射现象，发现其能在原本对称的量子行走中诱发不对称性，可用于构建量子行走棘轮或类Parrondo量子博弈，展示了将不利效应转化为有利应用的潜力。

量子棘轮与Lindblad速率方程

Quantum ratchet with Lindblad rate equations

该研究在一维周期晶格上建立量子随机行走模型，利用Lindblad速率方程和系统对称性推导出长时间极限下的速度解析式，发现速度可多次反转，且需非零跃迁速率以实现定向运动。

Hamiltonian ratchets with ultra-cold atoms

Quantum-resonance ratchets have been realized over the last ten years for the production of directed currents of atoms. These non-dissipative systems are based on the interaction of a Bose-Einstein condensate with an optical standing wave potential to produce a current of atoms in momentum space. In this paper we provide a review of the important features of these ratchets with a particular emphasis on their optimization using more complex initial states. We also examine their stability close to resonance conditions of the kicking. Finally we discuss the way in which these ratchets may pave th…

A quantum random walk of a Bose-Einstein condensate in momentum space

Each step in a quantum random walk is typically understood to have two basic components; a `coin-toss' which produces a random superposition of two states, and a displacement which moves each component of the superposition by different amounts. Here we suggest the realization of a walk in momentum space with a spinor Bose-Einstein condensate subject to a quantum ratchet realized with a pulsed, off-resonant optical lattice. By an appropriate choice of the lattice detuning, we show how the atomic momentum can be entangled with the internal spin states of the atoms. For the coin-toss, we propose …

Implementing Parrondo's paradox with two coin quantum walks

Parrondo's paradox is ubiquitous in games, ratchets and random walks.The apparent paradox, devised by J.~M.~R.~Parrondo, that two losing games $A$ and $B$ can produce an winning outcome has been adapted in many physical and biological systems to explain their working. However, proposals on demonstrating Parrondo's paradox using quantum walks failed {for large number of steps}. In this work, we show that instead of a single coin if we consider a two coin initial state which may or may not be entangled, we can observe a genuine Parrondo's paradox with quantum walks. Further we focus on reasons f…