arXiv subjects

Hon-Lam Lai

Publications and source records attributed to Hon-Lam Lai.

5 recordsLinked to original sources

arXiv2024

Two-mode Open Quantum Systems: Decoherence and Localized Bound State Dynamics

Dissipationless localized bound states of open quantum systems are significantly robust to decoherence and have potential applications in quantum technologies. In this work, the decoherence dynamics and dissipationless localized bound states of a two-mode open quantum system are investigated. The conditions for the emergence of dissipationless localized bound states are analytically solved, and the corresponding critical system-environment couplings under different values of the inter-mode coupling and the detuning are determined. The decoherence dynamics of the system under such conditions are analyzed and dissipationless coherence between the different localized bound states against decoherence is clearly shown. This may provide a new avenue to develop dissipationless quantum technology for quantum operations.

quant-ph↗

arXiv2023

Quantum transport theory of hybrid superconducting systems

We present a quantum transport theory for hybrid superconducting systems based on our exact master equation approach. The total transient transport current is decomposed into components that describe coherent transports through different paths of particle and hole channels. We show that the coherent transports are resultant interferences of numerous repeated tunneling processes and cannot be rendered as a simple normal transmission or Andreev reflection as usually described quantum transport involving superconductivity. As a practical application, we find that the coherent transport currents passing through a pair of well-separated Majorana zero modes vanish due to the totally destructive interference between the particle and hole channels.

cond-mat.mes-hall↗

arXiv2021

Generating Majorana qubit coherence in Majorana Aharonov-Bohm interferometer

We propose an Aharonov-Bohm interferometer consisted of two topological superconducting chains (TSCs) to generate coherence of Majorana qubits, each qubit is made of two Majorana zero modes (MZMs) with the definite fermion parity. We obtain the generalized exact master equation as well as its solution and study the real-time dynamics of the MZM qubit states under various operations. We demonstrate that by tuning the magnetic flux, the decoherence rates can be modified significantly, and dissipationless MZMs can be generated. By applying the bias voltage to the leads, one can manipulate MZM qubit coherence and generate a nearly pure superposition state of Majorana qubit. Moreover, parity flipping between MZM qubits with different fermion parities can be realized by controlling the coupling between the leads and the TSCs through gate voltages.

cond-mat.mes-hall↗

arXiv2019

Decoherence dynamics of Majorana qubits under braiding operations

We study the decoherence dynamics of Majorana qubit braiding operations in a topological superconducting chain (TSC) system, in which the braiding is performed by controlling the electron-chemical potentials of the TSCs and the couplings between them. By solving rigorously the Majorana qubit dynamics, we show how the Majorana qubit coherence is generated through bogoliubon correlations formed by exchanging Majorana zero modes (MZMs) between two TSCs in braiding operations. Using the exact master equation, we demonstrate how MZMs and also the bogoliubon correlations dissipate due to charge fluctuations of the controlling gates at both the zero and finite temperatures. As a result, Majorana qubit coherence and the fermion parity conservation cannot be immune from local perturbations during braiding operations.

cond-mat.mes-hall↗

arXiv2018

Exact master equation and decoherence dynamics of Majorana zero modes under the gate-induced charge fluctuation

In this paper, we derive the exact master equation to investigate the decoherence dynamics of Majorana zero modes in the Kitaev model, a 1D $p\,$-wave spinless topological superconducting chain (TSC), that is disturbed by charge fluctuations through gate controls. The exact master equation is derived by extending Feynman-Vernon influence functional approach to fermionic open systems involving pairing excitations. We obtain the exact master equations for the zero-energy bogoliubon in the TSC, and then transfer it into the master equation for Majorana zero modes. Within this exact master equation formalism, we can describe in detail the non-Markovian decoherence dynamics of zero-energy bogolibons as well as the Majorana zero modes under local perturbations. We find that at zero temperature, there is a zero-energy localized bound state which is not the original zero-energy bogoliubon or the original Majorana zero mode but a localized bound state of Majorana zero mode after the charge fluctuation is taken into account. It is this zero-energy localized bound state that protects Majorana zero modes from decoherence, as a long-time non-Markovain memory effect. However, for the environment at finite temperature, the zero-energy localized bound state cannot be formed when Majorana zero modes are locally perturbed, and decoherence is inevitable.

cond-mat.mes-hall↗