标题： 与环境模式纠缠导致马约拉纳量子比特的保真度和可见度降低 显示英文标题

标题： Fidelity and visibility reduction in Majorana qubits by entanglement with environmental modes

摘要： 我们研究拓扑超导体中由零能马约拉纳束缚态编码的拓扑量子比特的动力学和读出。 我们考虑由于电磁环境引起的玻色子模式，这些模式将马约拉纳流形与高于能隙的连续准粒子耦合。 这种耦合导致拓扑超导体的简并基态通过准粒子态和玻色子以类似极化子的方式被修饰，并使系统变得无能隙。 只有在修饰态的低能谱范围内操作和读出量子比特时，拓扑保护和完整的相干性才能得到维持。 如果量子点读出耦合到未修饰的马约拉纳模态，从而违反这一条件，我们将讨论保真度和/或可见度的降低。 对于未修饰的马约拉纳基的投影测量，我们提出了一种适用于弱马约拉纳-环境耦合的布洛赫-雷德菲尔德方法，并考虑了费米子数奇偶性守恒施加的约束。 在马尔可夫近似下，我们的结果基本上确认了基于费米黄金规则的有限温度退相干的早期理论。 然而，完整的非马尔可夫动力学还揭示了投影测量导致的保真度降低。 使用具有$p$-波配对的无自旋纳米线模型，我们提供了描述这些效应的定量结果。 显示英文摘要

摘要： We study the dynamics and readout of topological qubits encoded by zero-energy Majorana bound states in a topological superconductor. We take into account bosonic modes due to the electromagnetic environment which couple the Majorana manifold to above-gap continuum quasi-particles. This coupling causes the degenerate ground state of the topological superconductor to be dressed in a polaron-like manner by quasi-particle states and bosons, and the system to become gapless. Topological protection and hence full coherence is only maintained if the qubit is operated and read out within the low-energy spectrum of the dressed states. We discuss reduction of fidelity and/or visibility if this condition is violated by a quantum-dot readout that couples to the bare (undressed) Majorana modes. For a projective measurement of the bare Majorana basis, we formulate a Bloch-Redfield approach that is valid for weak Majorana-environment coupling and takes into account constraints imposed by fermion-number-parity conservation. Within the Markovian approximation, our results essentially confirm earlier theories of finite-temperature decoherence based on Fermi's golden rule. However, the full non-Markovian dynamics reveals, in addition, the fidelity reduction by a projective measurement. Using a spinless nanowire model with $p$-wave pairing, we provide quantitative results characterizing these effects.