本文選題：冷原子氣體 + 光晶格　； 參考：《中國科學(xué)技術(shù)大學(xué)》2016年博士論文

【摘要】：冷原子物理是利用磁光阱囚禁極低溫的堿金屬原子,并對其進(jìn)行測量、操控的新研究領(lǐng)域。其利用Feshbach共振技術(shù),可以人為調(diào)控冷原子系統(tǒng)的多體碰撞相互作用。因此冷原子氣體系統(tǒng)的實(shí)現(xiàn)和研究,可以用于量子模擬凝聚態(tài)系統(tǒng),實(shí)現(xiàn)可人為調(diào)控的強(qiáng)關(guān)聯(lián)體系,并對多體系統(tǒng)基本原理的研究,尋找強(qiáng)關(guān)聯(lián)體系中的新奇量子態(tài),提供了理想的實(shí)驗(yàn)平臺(tái)。1911年Onnes發(fā)現(xiàn)的超導(dǎo)現(xiàn)象,是凝聚態(tài)物理研究的熱點(diǎn)。1957年, Bardeen、 Cooper和Schrieffer提出BCS平均場理論,開啟了理論解釋超導(dǎo)／超流現(xiàn)象的先河。隨著重費(fèi)米子系統(tǒng)超導(dǎo)體(CeColn5)、有機(jī)物超導(dǎo)體((TMTSF)2PF2)、拓?fù)涑瑢?dǎo)體(Kitaev鏈)等新現(xiàn)象的發(fā)現(xiàn),BCS平均場理論已經(jīng)不足以解釋這些新奇的超導(dǎo)態(tài)。一方面,Fulde-Ferrell等奇異超流相的提出,為理論解釋這些新超導(dǎo)態(tài)提供了新思路。另一方面,Fulde-Ferrell等奇異超流相在真實(shí)的物理系統(tǒng)中的實(shí)現(xiàn),因?yàn)榧夹g(shù)上的困難而仍缺乏實(shí)驗(yàn)上的觀測。近年來拓?fù)洳牧霞巴負(fù)湎嘧兊难芯康玫綇V泛關(guān)注。所謂拓?fù)湫?是指系統(tǒng)依靠時(shí)間反演對稱性、粒子·空穴對稱性、和手性對稱性這三種對稱性的有無,使得系統(tǒng)的拓?fù)湫虬l(fā)生變化,其顯著特征是系統(tǒng)中存在空間分布局域在材料邊界的拓?fù)溥吘墤B(tài)。對拓?fù)湎嘧兊难芯磕軌蚪忉屩T如量子霍爾效應(yīng)、拓?fù)浣^緣體、拓?fù)涑瑢?dǎo)體等特殊量子態(tài)出現(xiàn)的物理機(jī)制。其中,拓?fù)涑瑢?dǎo)體因其支持以手性邊緣態(tài)形式存在的Majorana費(fèi)米子態(tài).而成為拓?fù)洳牧项I(lǐng)域的一個(gè)焦點(diǎn)。對拓?fù)涑瑢?dǎo)體的研究,能夠?yàn)橥負(fù)淞孔佑?jì)算和量子存儲(chǔ)提供理想的實(shí)驗(yàn)平臺(tái),在容錯(cuò)拓?fù)淞孔佑?jì)算上有著重要的應(yīng)用前景�；谝陨媳尘�,對奇異超流相出現(xiàn)的物理機(jī)制和拓?fù)湫再|(zhì)的研究,及其在冷原子系統(tǒng)中的制備、實(shí)現(xiàn),是這篇論文關(guān)注的焦點(diǎn)。我們展開的研究工作具體如下：1、利用自旋軌道耦合作用制備Fulde-Ferrell超流相。在近年來的冷原子實(shí)驗(yàn)工作中,人們利用Raman激光,將被囚禁的冷原子的兩個(gè)超精細(xì)能級耦合起來。由于在冷原子物理研究中,超精細(xì)能級通常被標(biāo)記為自旋量子數(shù),而Raman激光耦合的過程中原子能級的躍遷存在動(dòng)量傳遞。因此這個(gè)實(shí)驗(yàn)過程實(shí)際上模擬了凝聚態(tài)物理系統(tǒng)中的自旋軌道耦合作用。同時(shí),兩個(gè)超精細(xì)能級間的調(diào)諧模擬了作用在贗自旋空間的Zeeman場。我們的工作是利用自旋軌道耦合作用和Zeeman場,研究這兩個(gè)外場的同時(shí)存在對冷原子的超流態(tài)影響。我們展開的研究如下：(1)尋找奇異超流相Fulde-Ferrell超流相存在的可能性,并研究其出現(xiàn)的物理機(jī)制。(2)討論Fulde-Ferrell超流相在拓?fù)湎嘧冎斜憩F(xiàn)的拓?fù)湫再|(zhì),尋找奇異超流相中Majorana費(fèi)米子態(tài)存在的蹤跡,并討論拓?fù)湎嘧兂霈F(xiàn)的物理機(jī)制。(3)研究兩個(gè)外場作用對多體系統(tǒng)熱力學(xué)性質(zhì)影響。2、利用震蕩光晶格技術(shù)制備Fulde-Ferrell超流相。冷原子物理中的震蕩光晶格技術(shù)是近年來發(fā)展的實(shí)驗(yàn)方法,它的核心是利用激光,對原有的光晶格系統(tǒng)在某個(gè)維度上進(jìn)行光晶格震蕩。通過調(diào)節(jié)震蕩的頻率,使得系統(tǒng)不同軌道能帶間發(fā)生原子躍遷耦合,進(jìn)而改變系統(tǒng)的單粒子性質(zhì)。我們的工作就是利用震蕩光晶格所引入的不同軌道能帶耦合,誘導(dǎo)Fulde-FeI]rell超流相,并研究其出現(xiàn)的物理機(jī)制和拓?fù)湫再|(zhì)。3、利用驅(qū)動(dòng)光晶格技術(shù)制備Fulde-Ferrell超流相。受震蕩光晶格技術(shù)的啟發(fā),我們利用激光對原有的光晶格體系里,在某個(gè)維度上再加一套運(yùn)動(dòng)的光晶格勢場。通過調(diào)節(jié)驅(qū)動(dòng)的光晶格的運(yùn)動(dòng)速度,可以耦合不同軌道的能帶,從而改變系統(tǒng)單粒子性質(zhì)。由于單粒子能帶的空間對稱性被破壞,Fulde-Ferrell超流相應(yīng)運(yùn)而生。這個(gè)的方案構(gòu)造簡單,能夠規(guī)避自旋軌道耦合帶來的熱效應(yīng)等帶來的技術(shù)阻礙。另外,由于系統(tǒng)的自旋簡并沒有被破壞,這種方案誘導(dǎo)的Fulde-Ferrell超流相沒有自旋極化率,這一特性明顯區(qū)別于先前依靠破壞自旋簡并制備Fulde-Ferrell超流相的工作。因此、我們的工作對Fulde-Ferrell超流相出現(xiàn)的物理機(jī)制提供了新的思路。4、利用自旋依賴的光品格系統(tǒng)制備p波超流相。在冷原子物理中,自旋依賴的光晶格技術(shù)是通過不同的激光將兩種超精細(xì)態(tài)的原子囚禁在兩套光晶格里。我們的工作是將這兩套光晶格在空間上錯(cuò)位,使得一套光晶格囚禁的原子可以同時(shí)與另一套光晶格囚禁的原子發(fā)生關(guān)聯(lián)作用,進(jìn)而誘導(dǎo)出p波超流相。這里,p波超流相是一種具有拓?fù)浞瞧接剐再|(zhì)的超導(dǎo)態(tài),在p波超流相中可以尋找到在基本粒子物理、暗物質(zhì)等領(lǐng)域有重要作用的Majorana費(fèi)米子態(tài)。我們的工作提供了在冷原子系統(tǒng)中實(shí)現(xiàn)p波超流相的方案,相比先前研究文獻(xiàn)的結(jié)果.我們的方案構(gòu)造簡單,能夠規(guī)避先前實(shí)驗(yàn)上p波Feshbach共振的技術(shù)困難,具有更好的實(shí)驗(yàn)可行性。
[Abstract]:Cold atom physics is a new field of research, which uses a magnetic optical trap to imprism extremely low temperature alkali metal atoms, and is a new field of control. By using Feshbach resonance technology, it can artificially regulate the interaction of multibody collisions between cold atomic systems. Therefore, the realization and research of cold atomic gas system can be used in quantum simulation condensed state system, and it can be realized. The strong association system which can be controlled, and the study of the basic principle of the multibody system, search for the novel quantum state in the strong association system, provide the superconducting phenomenon found in the ideal experimental platform.1911 Onnes, which is a hot.1957 year in condensed matter physics. Bardeen, Cooper and Schrieffer put forward the theory of BCS mean field, which opens the theoretical explanation. Superconductor / supercurrent phenomenon. With the discovery of new phenomena such as heavy fermion system superconductor (CeColn5), organic superconductor ((TMTSF) 2PF2), topological superconductor (Kitaev chain) and other new phenomena, BCS mean field theory is not enough to explain these new superconducting states. On the one hand, the new supercurrent of Fulde-Ferrell and other singular superfluid phase is put forward to explain these new superconductors in theory. State of state provides new ideas. On the other hand, the realization of Fulde-Ferrell and other singular superfluid phases in real physical systems, because of technical difficulties, still lacks experimental observation. In recent years, the research of topological materials and topological phase transition has been widely concerned. The so-called topology, which refers to the inversion of symmetry by time, and particle cavity symmetry. Whether there are three kinds of symmetry, such as sex, and chiral symmetry, make the topological order of the system change. Its remarkable feature is that there is a topological edge state of the spatial distribution in the material boundary in the system. The study of the topological phase transition can explain the physics of special quantum states such as the quantum Holzer effect, the topological insulator, the topological superconductor and so on. The topological superconductor is a focal point in the field of topological materials because of its support for the Majorana fermion states in the form of chiral edge states. The study of topological superconductors can provide an ideal experimental platform for topological quantum computation and quantum storage. It has an important application prospect in fault-tolerant quantum computing. In the above background, the research on the physical mechanism and topological properties of the singular superfluid phase and its preparation and implementation in the cold atomic system are the focus of this paper. 1, 1, using spin orbit coupling to prepare the superfluid phase. In the cold atom experiment in recent years, The Raman laser is used to combine the two ultra fine energy levels of the trapped cold atoms. Because in the cold atom physics, the hyperfine level is usually labeled as the spin quantum number, while the transition of the atomic energy level in the Raman laser coupling exists in the momentum transfer. So this experimental process actually simulates the condensed matter physics. The spin orbit coupling in the system. At the same time, the tuning between two hyperfine energy levels simulates the Zeeman field acting in the pseudo spin space. Our work is to study the effect of the two external fields on the superflow state of the cold atoms by using the spin orbit coupling action and the Zeeman field. The possibility of the existence of the flow phase Fulde-Ferrell supercurrent and its physical mechanism. (2) the topological properties of the Fulde-Ferrell superfluid phase in the topological phase transition are discussed, the trace of the Majorana fermion state in the singular superfluid phase is found, and the physical mechanism of the appearance of the topological phase transition is discussed. (3) the study of two external fields to the multibody system The thermodynamic properties affect.2, using the concussion optical lattice technology to prepare the Fulde-Ferrell superfluid phase. The shock optical lattice technology in cold atom physics is an experimental method developed in recent years. Its core is to use laser to shake the original optical lattice system in a certain dimension. By adjusting the frequency of the shock, the system is different. The coupling of atomic transition between the orbital energy bands will change the single particle properties of the system. Our work is to use the different orbital energy bands introduced by the oscillating light lattice to induce the Fulde-FeI]rell superfluid phase, and to study the physical and topological properties of the.3, and to prepare the Fulde-Ferrell superfluid phase by the drive optical lattice technology. Inspired by the optical lattice technology, we use the laser to add a set of light lattice potential fields to a certain dimension in the original optical lattice system. By adjusting the velocity of the driven optical lattice, we can coupling the energy bands of different orbits, thus changing the single particle properties of the system. Because the spatial symmetry of the single particle energy band is destroyed, Fuld This scheme is simple and can avoid the technical impediments caused by the thermal effect of spin orbit coupling. In addition, because the spin degeneracy of the system is not destroyed, the Fulde-Ferrell superflow phase induced by this scheme has no spin polarization, which is obviously different from the previous reliance on spins. Degenerate and prepare the Fulde-Ferrell superfluid phase. Therefore, our work provides a new idea for the physical mechanism of the Fulde-Ferrell superfluid phase,.4, using the spin dependent optical character system to prepare the P wave superfluid phase. In cold atom physics, the spin dependent optical lattice technology is the two hyperfine atoms by different lasers. It is imprisoned in two sets of optical lattices. Our work is to mislocate the two sets of optical lattices in space, so that a set of atoms trapped by a set of optical lattices can be associated with another set of atoms trapped in a set of optical lattices, and then the P wave superfluid phase is induced. Here, the P wave superfluid phase is a superconducting state with a topological non mediocre property, in the P wave superstructure. We can find the Majorana fermion states that have important roles in the fields of elementary particle physics, dark matter and other fields. Our work provides a scheme for the realization of the P wave superfluid phase in the cold atomic system. Compared with the previous research literature, our scheme is simple and can avoid the technical difficulties of the P wave Feshbach resonance in previous experiments. It has better experimental feasibility.
【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O469

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