本文選題：量子比特　切入點(diǎn)：退相干　出處：《江西師范大學(xué)》2012年碩士論文

【摘要】：隨著量子計(jì)算和量子通信技術(shù)的發(fā)展，超導(dǎo)量子比特在量子信息技術(shù)中已顯示出了巨大的潛能。固態(tài)量子比特更是因?yàn)樗目杉尚远蔀閷?shí)現(xiàn)量子計(jì)算機(jī)最具有潛力的元件之一。但由于環(huán)境對(duì)量子比特的耗散作用過(guò)強(qiáng)，在量子調(diào)控過(guò)程中，量子比特與環(huán)境的相互作用或者其他的原因，會(huì)導(dǎo)致量子相干性的消失，從而使量子信息散失在無(wú)法控制的環(huán)境中，出現(xiàn)退相干現(xiàn)象。量子關(guān)聯(lián)被認(rèn)為是研究量子信息過(guò)程中必不可少的一種資源，為此，我們研究了初始糾纏的量子比特在不同的環(huán)境下糾纏度和量子失協(xié)的動(dòng)力學(xué)演化。 1.基于電路理論與Bloch-Redfield方程，研究了超導(dǎo)磁通量子比特電路的動(dòng)力學(xué)演化。在二能級(jí)近似下，我們比較分析了歐姆、亞歐姆、以及超歐姆熱庫(kù)環(huán)境對(duì)超導(dǎo)磁通量子比特退相干的影響。研究結(jié)果表明：(1)一般來(lái)說(shuō)可以通過(guò)選取弱耦合系數(shù)，盡量降低與環(huán)境的耦合，獲得相對(duì)長(zhǎng)的退相干時(shí)間；(2)相比較來(lái)說(shuō),在其他條件不變時(shí)，構(gòu)建一個(gè)亞歐姆熱庫(kù)環(huán)境或超歐姆熱庫(kù)環(huán)境更有利于提高退相干時(shí)間；(3)超歐姆熱庫(kù)環(huán)境下，提高環(huán)境指標(biāo)系數(shù)有利于延長(zhǎng)超導(dǎo)磁通量子比特的退相干時(shí)間。因此，在一定的條件下，我們可以通過(guò)優(yōu)化電路的設(shè)計(jì)，利用電感線圈間的耦合效應(yīng)，降低系統(tǒng)的退相干。 2．我們?cè)诓煌h(huán)境耗散模型下，給出了耦合量子比特量子關(guān)聯(lián)的動(dòng)力學(xué)演化，比較研究了共生糾纏度和量子失協(xié)的變化特點(diǎn)。研究發(fā)現(xiàn)糾纏度強(qiáng)烈地依賴于初始環(huán)境，并在演化過(guò)程中不可避免地發(fā)生糾纏死亡(ESD)現(xiàn)象；在一定的初始條件下，糾纏的演化會(huì)出現(xiàn)坍塌和復(fù)蘇效應(yīng)(dark and bright periods)，，但最終糾纏度仍會(huì)等于零。由于退相干的影響，盡管量子失協(xié)也會(huì)最終減小到零，但與糾纏的演化不同，量子失協(xié)一般不會(huì)發(fā)生糾纏突然死亡現(xiàn)象，而且量子失協(xié)生存時(shí)間更長(zhǎng)，也就是說(shuō)利用量子失協(xié)更有利于量子信息處理。
[Abstract]:With the development of quantum computing and quantum communication technology, superconducting quantum bits have shown great potential in quantum information technology.Solid-state quantum bits have become one of the most promising components for quantum computers because of their integrability.However, due to the excessive dissipation of the environment to the quantum bits, the interaction between the quantum bits and the environment or other reasons will lead to the disappearance of quantum coherence in the process of quantum regulation.Thus, quantum information is lost in an uncontrollable environment and decoherence occurs.Quantum correlation is considered to be an essential resource in the study of quantum information. Therefore, we study the degree of entanglement and the dynamical evolution of quantum disconnection in different environments.1.Based on circuit theory and Bloch-Redfield equation, the dynamical evolution of superconducting magnetic flux subbit circuits is studied.In the two-level approximation, we compare and analyze the effects of ohmic, sub-ohmic, and ultra-ohmic heat pool environments on superconducting magnetic flux bit decoherence.The results show that in general, the weak coupling coefficient can be selected to minimize the coupling with the environment and obtain a relatively long time of decoherence.The construction of a sub-ohm heat reservoir environment or a super-ohmic heat reservoir environment is more conducive to increasing the decoherence time and increasing the environmental index coefficient to prolong the decoherence time of superconducting magnetic fluxons.Therefore, under certain conditions, we can reduce the system decoherence by optimizing the circuit design and utilizing the coupling effect between inductance coils.2.Under different environment dissipation models, we give the dynamics evolution of quantum correlation of coupled quantum bits, and compare the characteristics of the degree of symbiotic entanglement and quantum disconnection.It is found that the degree of entanglement is strongly dependent on the initial environment, and the phenomenon of entanglement death (ESDs) inevitably occurs in the evolution process, and under certain initial conditions,The evolution of entanglement will result in collapse and resuscitation effect, but the degree of entanglement will be equal to zero in the end.Because of the effect of decoherence, quantum disassociation will eventually be reduced to zero, but unlike the evolution of entanglement, quantum decoupling usually does not occur entanglement sudden death phenomenon, and quantum disassociation survival time is longer.That is to say, it is more advantageous to process quantum information by using quantum disconnection.
【學(xué)位授予單位】：江西師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2012
【分類號(hào)】：O413.1;TP38

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本文編號(hào)：1709398