自旋量子位元與自旋環境交互作用的相消干現象--與時間相關的密度矩陣重整化群的研究

Spin Qubit Decoherence by Spin Bath -- a Time-Dependent DMRG Study

賴承彥(Chen-Yen Lai)

指導教授 ： 陳柏中

國立清華大學/理學院/物理學系/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00412

摘要

In this thesis, we use the new numerical method – density matrix renormalization group – to study the decoherence of spin qubit. Because of diverging Hilbert space in quantum system, the linear growth and effective truncation make us can simulate quantum system accurately. Also, time-dependent DMRG was developed to simulate the real-time dynamics of quantum system. We use this method to study the non-equilibrium properties.
Spin decoherence induced by a spin bath has recently been the subject of interest in the field of quantum computation and spintronics. Unlike the spin-boson model, the resulting decoherence depends crucially on the nature of the spin bath and its coupling to the central spin. In this work we investigate the decoherence of a central spin which is coupled non-uniformly to a spin chain by means of the time-dependent density matrix renormalization group technique. Using this technique the coupling between the central spin and the spin chain can take any form, in contrast to the typical uniform or on-site coupling taken in the literature. Two qubit decoherence is also an interesting subject in this thesis. The distance between
qubits affect the decoherence of qubits. We have studied the resulting spin
decoherence induced by spin chains in the Ising, XY, XXZ, and Heisenberg universality classes. Connection between the decoherence the quantum phase transition of the spin chain is discussed.
An exotic interaction, which can’t be realized in semiconductor wire, exist in a system : double wire loaded by fermionic polar molecules. Different interaction can be tuned by external electric field. We study the phase diagram of this system by means of static DMRG. An interesting phase – spontaneous interwire coherence -- is found.

關鍵字

密度矩陣重整化群 ； 量子資訊

並列摘要

In this thesis, we use the new numerical method – density matrix renormalization group – to study the decoherence of spin qubit. Because of diverging Hilbert space in quantum system, the linear growth and effective truncation make us can simulate quantum system accurately. Also, time-dependent DMRG was developed to simulate the real-time dynamics of quantum system. We use this method to study the non-equilibrium properties.
Spin decoherence induced by a spin bath has recently been the subject of interest in the field of quantum computation and spintronics. Unlike the spin-boson model, the resulting decoherence depends crucially on the nature of the spin bath and its coupling to the central spin. In this work we investigate the decoherence of a central spin which is coupled non-uniformly to a spin chain by means of the time-dependent density matrix renormalization group technique. Using this technique the coupling between the central spin and the spin chain can take any form, in contrast to the typical uniform or on-site coupling taken in the literature. Two qubit decoherence is also an interesting subject in this thesis. The distance between
qubits affect the decoherence of qubits. We have studied the resulting spin
decoherence induced by spin chains in the Ising, XY, XXZ, and Heisenberg universality classes. Connection between the decoherence the quantum phase transition of the spin chain is discussed.
An exotic interaction, which can’t be realized in semiconductor wire, exist in a system : double wire loaded by fermionic polar molecules. Different interaction can be tuned by external electric field. We study the phase diagram of this system by means of static DMRG. An interesting phase – spontaneous interwire coherence -- is found.

並列關鍵字

density matrix renormalization group ； spin decoherence ； two spin decoherence ； non-Makovian ； quantum information ； td dmrg

參考文獻

[1] K. G. Wilson, Rev. Mod. Phys. 77. 259 (2005).

[2] Steven R. White, Phys. Rev. B, 48, 10345 (1993).

[3] Steven R. White, Phys. Rev. Lett. 77. 3633 (1996).

[4] S. Ostlund and S. Rommer, Phys. Rev. Lett. 75, 3537 (1995).

and K. Hallberg (Editors), Density Matrix Renormalization: A New