Double quantum dot turnstile as an electron spin entangler
量子阱中rashba自旋—轨道耦合的rabi劈裂效应
量子阱中rashba自旋—轨道耦合的rabi劈裂效应嘿，朋友！你知道量子阱中 rashba 自旋—轨道耦合的 rabi 劈裂效应吗？这玩意儿听起来是不是特别高深莫测，仿佛是来自遥远宇宙深处的神秘密码？咱先来说说这量子阱。
你就把它想象成一个特别神奇的小“坑”，里面的粒子就像调皮的小精灵，到处蹦跶。
而这个 rashba 自旋—轨道耦合呢，就像是小精灵们玩耍时的一种特殊规则。
想象一下，咱们平常玩游戏都有规则吧？比如跳皮筋得按特定的节奏跳，踢毽子不能用手碰。
这 rashba 自旋—轨道耦合也是类似的，它决定了粒子们在量子阱这个小“坑”里怎么运动，怎么相互作用。
那 rabi 劈裂效应又是啥呢？这就好比一场热闹的音乐会。
本来乐队演奏得好好的，声音很和谐。
可突然来了个特别的因素，就像有人在乐队里敲了一记特别响的鼓，整个音乐的节奏和声音就发生了变化。
rabi 劈裂效应就是这个突然出现的“特别响的鼓”，让量子阱里粒子的状态发生了显著的改变。
你说神奇不神奇？这量子阱里的世界，可比咱们肉眼看到的世界复杂多了，也有趣多了。
咱再深入聊聊这个 rabi 劈裂效应。
它可不是随随便便就出现的，得有特定的条件。
就像植物生长需要阳光、水分和土壤一样，rabi 劈裂效应的出现也得有合适的环境。
比如说，粒子的能量得达到一定的值，或者外部施加的电磁场强度得恰到好处。
你可能会问，研究这个有啥用呢？这用处可大了去啦！就好比咱们发明了指南针，能在茫茫大海中找到方向。
了解量子阱中 rashba 自旋—轨道耦合的rabi 劈裂效应，能让咱们在微观世界里找到新的“方向”，说不定就能开发出超级厉害的新技术呢！比如说更高效的电子设备，或者更精准的量子计算。
想想看，未来的电脑可能快得像闪电，手机的功能强大到超乎想象，这一切都可能源于对这个看似神秘的效应的研究。
所以啊，别小看这量子阱中 rashba 自旋—轨道耦合的 rabi 劈裂效应，它说不定就是打开未来科技大门的一把神奇钥匙呢！。
利用褶皱结构PEDOT_PSS空穴注入层构筑高性能QLED器件
利用褶皱结构PEDOT_PSS空穴注入层构筑高性能QLED器件利用褶皱结构PEDOT:PSS空穴注入层构筑高性能QLED器件量子点发光二极管（Quantum Dot Light Emitting Diodes，简称QLED）作为一种新型发光器件，具有高色彩饱和度、高亮度、宽色域、低功耗等优点，已经成为显示技术领域的研究热点。
其中，空穴注入层对于QLED器件的性能起着至关重要的作用。
近年来，研究人员发现通过引入褶皱结构PEDOT:PSS空穴注入层，可以进一步提高QLED器件的性能。
褶皱结构PEDOT:PSS空穴注入层的构筑方法主要包括两个步骤：薄膜形成和褶皱诱导。
首先，利用溶液法将PEDOT:PSS混合物均匀涂覆在透明导电玻璃上形成薄膜。
随后，通过力学或热诱导的方式在PEDOT:PSS薄膜上引入褶皱结构。
研究表明，褶皱结构PEDOT:PSS空穴注入层具有增加载流子迁移率、提高电流注入效率和增强光致发光效果等优势。
首先，褶皱结构PEDOT:PSS空穴注入层可以增加载流子迁移率。
由于PEDOT:PSS薄膜的柔软性和可延展性，褶皱结构的引入可以增大PEDOT:PSS薄膜表面积，从而增加载流子在空穴注入层内的传输通道，提高载流子迁移率，进而增强器件的电流注入效率。
其次，褶皱结构PEDOT:PSS空穴注入层可以提高电流注入效率。
褶皱结构PEDOT:PSS空穴注入层具有较大的表面粗糙度和较多的界面缺陷，这些特性可有效抑制不均匀电流分布和局部点状热效应，实现更均匀的电流注入，从而提高器件的亮度和稳定性。
另外，褶皱结构PEDOT:PSS空穴注入层可以增强光致发光效果。
由于褶皱结构PEDOT:PSS空穴注入层的较大表面积，光致发光效果更显著。
通过改变褶皱结构的形态和密度可以对光致发光效果进行调控，进而实现更高的亮度和更宽的色域。
值得注意的是，为了构筑高性能的褶皱结构PEDOT:PSS空穴注入层，需要对薄膜形成和褶皱诱导过程进行精确控制。
Evolution of Ge and SiGe Quantum Dots under Excimer Laser Annealing
CHIN.PHYS.LETT.Vol.25,No.1(2008)242 Evolution of Ge and SiGe Quantum Dots under Excimer Laser Annealing∗HAN Gen-Quan(韩根全)1∗∗,ZENG Yu-Gang(曾玉刚)1,YU Jin-Zhong(余金中)1,CHENG Bu-Wen(成步文)1,YANG Hai-Tao(杨海涛)21State Key Laboratory on Integrated Optoelectronics,Institute of Semiconductors,Chinese Academy of Sciences,Beijing1000832Tsinghua-Foxconn Nanotechnology Research Center,Department of Physics,Tsinghua University,Beijing100084(Received15September2007)We present different relaxation mechanisms of Ge and SiGe quantum dots under excimer laser annealing.Inves-tigation of the coarsening and relaxation of the dots shows that the strain in Ge dots on Gefilms is relaxed by dislocation since there is no interface between the Ge dots and the Ge layer,while the SiGe dots on Si0.77Ge0.23film relax by lattice distortion to coherent dots,which results from the obvious interface between the SiGe dots and the Si0.77Ge0.23film.The results are suggested and sustained by Vanderbilt and Wickham’s theory,and also demonstrate that no bulk diffusion occurs during the excimer laser annealing.PACS:68.65.Hb,68.35.Fx,68.35.Md,68.37.PsGe and SiGe self-assembled quantum dots (SAQDs)are widely studied for their promis-ing application in optoelectronics due to three-dimensional(3D)quantum confinement.[1]Many works have focused on the growth mechanism,[2,3] shape transition,[4,5]and the coarsening process under thermal annealing[6]of the SAQDs in S-K mode.Re-cently,we obtained SiGe quantum dots with small size and high density by excimer laser annealing(ELA).[7] The nanosecond pulse duration of the excimer,which induces rapid heating and cooling of the sample sur-face,ensuring that the laser induced quantum dots (LIQDs)are formed only by surface atoms diffusion.[8] We obtained Ge and SiGe laser induced quantum dots by ELA of the Ge and SiGefilms,respectively.In this Letter,we report that the laser-induced Ge and SiGe quantum dots undergo different relax-ation mechanisms.Atomic-force-microscopy(AFM) measurements indicate that the Ge LIQDs on the Ge film relax by formation of dislocation,while the SiGe LIQDs on the Si0.77Ge0.23film release the strain by the lattice tetragonal distortion and then form coher-ent dots.The theory developed by Vanderbilt and Wickham has shown[9]that the interface between the dots and the wetting layer plays a pivotal role in the relaxation process of the strained dots.For the SiGe LIQDs on the Si0.77Ge0.23film,our calculation shows that SiGe quantum dots with the Ge composition of about83%are formed on the Si0.77Ge0.23film,which indicates an obvious interface between the dots and the Si0.77Ge0.23film.The interface leads to the for-mation of the coherent SiGe relaxed dots.However, for the Ge LIQDs on the Gefilm,no interface between the dots and the wetting layer results in the formation of the dislocated dots.These are suggested and sus-tained by Vanderbilt and Wickham’s theory,and also demonstrates that no bulk diffusion occurs during the excimer laser annealing.The Ge and SiGefilms were grown by an ultra-high-vacuum chemical vapour deposition(UHV-CVD) system on(001)-oriented Si substrates at500◦C and 550◦C,respectively.The Gefilm is in thickness of about1nm(8monolayers),and the SiGefilm is about 20nm.The sources of Si and Ge are disilane and ger-mane,respectively.The Si substrates were cleaned in an ex-situ chemical etch process and loaded into an UHV growth chamber with basic pressure lower than 10−7Pa,and then heated up to950◦C to deoxidize. The thickness and Ge composition of the Si0.77Ge0.23film are determined by double-crystal x-ray diffraction (XRD).A193nm ArF excimer laser operating frequency in 40Hz,was used to ex-situ anneal the samples,which were annealed in argon ambient.A top-flat beam profile of10×10mm2with the energy density of about180mJ/cm2was obtained by using a homog-enizer.This was carried out to ensure uniform an-nealing of samples’surface.The surface morphology of the samples was measured by an SPA-300HV AFM, performed in tapping mode.Figure1shows the AFM images of Ge and SiGe LIQDs obtained by ELA of Ge and Si0.77Ge0.23films, respectively.The height profiles of the dots are also in Fig.1.The diameters of the Ge and SiGe LIQDs are20–25nm and15–20nm,respectively.The ther-mal process induced by the excimer laser pulse is only several tens nanoseconds,so during the ELA,only surface diffusion occurs.The dot energy can be ex-pressed by E=4ΓV2/3tan1/3θ−6AV tanθ,[2]where Γ=γd cscθ−γs cotθis the increase of surface energy,∗Supported by the National Natural Science Foundation of China under Grant No60576001.∗∗Email:hgquan@c 2008Chinese Physical Society and IOP Publishing LtdNo.1HANGen-Quan et al.243γs and γd are the surface energy per unit area of the wetting layer and dot facet,respectively,θis the facet angle with respect to the surface of the wetting layer,V is the volume of the dot,A =σ2(1−ν)/(2πG )where σis the in-plane misfit strain,and νand G are Poisson’s ratio and shear modulus,respectively.For the LIQDs,only surface energy should be stud-ied,and the second term on the right can be con-sidered as the effect of strain on the surface energy.From the formula,we can see that the slightly strained dots are not stable during the ELA.We speculate that the heavily strained LIQDs will grow,relax the strainin them with longer annealing time.To investigate the relaxation of the LIQDs,we prolong the anneal-ing time with the laser energy density of 180mJ/cm 2.As the ELA continues,We observe the relaxation and the shrinking of the LIQDs,while it is surprisingly found that Ge quantum dots on the Ge wetting layer and SiGe dots on the Si 0.77Ge 0.23layer underwent the different relaxation modes:the Ge dots relax through the formation of the dislocation,while the strain in the SiGe quantum dots on the Si 0.77Ge 0.23wetting layer is released by lattice tetragonal distortion.Fig.1.AFM images (500nm ×500nm)of LIQDs:(a)Ge LIQDs on the Ge film and the height profiles along the line marked,(b)SiGe LIQDs on the Si 0.77Ge 0.23film and the height profiles along the line marked.Figure 2shows a series of AFM images of the mor-phology of Ge LIQDs on the Ge film at different an-nealing times.When the annealing time is prolonged to 3.5hours,coarsening of the quantum dot,as shown in Fig.2(a),occurs.The contacting of the small and large dots in Fig.2(a)and 2(b)can be interpreted to be the losing materials of small dots to the near large dots,which is analogous to the anomalous coarsening in the SAQDs.[10]As the ELA proceeds,the density of the dots further decreases,and when the annealing time is up to 5hours,almost all the LIQDs disappear (shown in Fig.2(c)).After 7-h ELA,no new LIQDs are observed.We speculate that the relaxation of the laser induced Ge dots is by the dislocations and the strained film is also relaxed by the dislocations.Fig-ure 3shows the schematic of the relaxation process ofthe Ge quantum dots on the Ge film.Figure 4(a)shows the coarsening and the growth of the SiGe dots on the Si 0.77Ge 0.23film.After 4-h an-nealing,the SiGe dots become larger and the density decreases.As the annealing continues (5h),some new LIQDs appear.This indicates that the growth and disappearing of the SiGe dots give rise to the restora-tion of the strain in the Si 0.77Ge 0.23film.This will decrease the surface energy and increase the strain en-ergy.The recovered stress in the film drives the new LIQDs under ELA.This reveals that the SiGe dots grow and relax to be the coherent dots,i.e.,the strain in the SiGe dots is relaxed by the lattice distortion.Figure 5shows the schematic of the relaxation process of the SiGe quantum dots on the Si 0.77Ge 0.23film.244HAN Gen-Quan et al.Vol.25Fig.2.AFM images (1µm ×1µm)of the Ge LIQDs on the Ge film with different annealing times:(a)annealed for 3.5h,(b)annealed for 4h,(c)annealed for 5h,(d)annealed for 7h.Fig.3.Schematic diagram of the relaxation mode of the Ge quantum dots on the Ge film.Fig.4.AFM images (1µm ×1µm)of the SiGe LIQDs on the Si 0.77Ge 0.23film for different annealing times:(a)annealed for 4h,(b)annealed for 5h.These results reveal the existence of two different relaxation mechanisms:generation dislocation in the dots and formation coherent relaxed dots.When the quantum dots grow,the relaxation of quantum dots is the competing of the lattice distortion (coherent re-laxed dots)with the formation of the dislocation (dis-located relaxed dots).The theory developed by Van-derbilt and Wickham [9]compares the two mechanisms of elastic relaxation and yields a phase diagram of a lattice mismatched system in which all possible mor-phologies are present,i.e.,uniform films,dislocated dots,and coherent dots.No.1HAN Gen-Quan et al.245It was shown by Vanderbilt and Wickham that morphology of the mismatched system is determined by the ratio of the energy of interface between dots and the wetting layer (E interface )to the change of the sur-face energy (∆E surf ).[9]The deposited material wets the substrate firstly,and then the 2D strained film transforms to the 3D quantum dots.If ∆E surf is posi-tive and large,or if the energy of the interface between the dots and the wetting layer is relatively small,the formation of coherently strained dots is not favoured.With an increase in the amount of deposited material,a transition occurs from uniform film to dislocated dots,and the coherently strained dots are not formed.If ∆E surf is positive and small,or if the energy of the dislocated interface is relatively large,with an increase in the amount of deposited material,a transition oc-curs from a uniform film to coherent dots.Further de-position may cause the onset of dislocations.The de-tailed calculation and the phase diagram can be found in Ref.[9].Fig.5.Schematic diagram of the relaxation process of the SiGe quantum dots on the Si 0.77Ge 0.23film.This theory can be used to interpret the differ-ent relaxation modes of the Ge and SiGe dots.It is sure that the pyramidal laser induced Ge dots,with the diameter of about 20–25nm and density of about 6×1010cm −2,do not exhaust the Ge film with the thickness more than 1nm (8monolayers).Because no bulk diffusion occurs during the annealing,atoms intermixing between the dots and the wetting layer need not be considered.We think that the pure Ge LIQDs are formed on the Ge film,i.e.,there is no in-terface between the dots and the wetting layer.For the SiGe LIQDs on the Si 0.77Ge 0.23film,based on the surface chemical potential calculation,we show that the heavily strained SiGe quantum dots must have a misfit above 0.035corresponding to a Ge composi-tion of about 83%,to promise E surf <0(the dots stable under ELA).[7]This indicates the SiGe dots are Ge richer than the Si 0.77Ge 0.23film,which also results from that the surface diffusion coefficient of Ge is 102–103times greater than that of Si.[11]If the atoms interdiffusion is neglected,there should be an obvious interface between the SiGe quantum dots and the Si 0.77Ge 0.23wetting layer.It is suggested theoret-ically by Vanderbilt and Wickham and supported by our experiments that the interface between the quan-tum dots and the wetting layer plays a pivotal role in the competition between the lattice distortion and the formation of dislocation.Vanderbilt and Wickham’s theory is proven by our results and also confirms and enforces our previous conclusion that the pure Ge dots and an abrupt inter-face between the dots and wetting layer are availablewhich is attributed to no bulk atoms diffusion under ELA.In conclusion,we have studied the different relax-ation mechanisms of the Ge and SiGe quantum dots on Ge and Si 0.77Ge 0.23films,respectively,under ELA.We recover the pivotal role of the interface between the dots and the wetting layer.The relaxation of Ge dots by dislocation is attributed to no interface between Ge dots and the Ge layer,and that of SiGe dots by lattice tetragonal distortion results from the obvious interface between SiGe dots and the Si 0.77Ge 0.23film.This is sustained by Vanderbilt and Wickham’s theory.References[1]Baribeau J M,Wu X,Rowell N L and Lockwood D J 2006J.Phys.:Condens.Matter 18R139[2]TersoffJ and LeGoues F K 1994Phys.Rev.Lett.723570[3]Sutter P,Schick I,Ernst W and Sutter E 2003Phys.Rev.Lett.91176102[4]Rastelli A,Stoffel M,TersoffJ,Kar G S and Schimidt O G2005Phys.Rev.Lett.95026103[5]Montalenti F,Raiteri P,Migas D B,von K¨a nel H,RastelliA,Manzano C,Costantini G,Denker U,Schimidt O G,Kern K and Miglio L 2004Phys.Rev.Lett.93216102[6]Kamins T I,Medeiros-Ribeiro G,Ohlberg D A A andWilliams R S 1999J.Appl.Phys.851159[7]Han G Q,Zeng Y G,Yu J Z,Cheng B W and Yang H T2007J.Cryst.Growth (submitted)[8]Misra N,Xu L,Pan Y L,Cheung N and Grigoropoulos CP 2007Appl.Phys.Lett.90111111[9]Vanderbilt D and Wickham L K 1991Mater.Res.Soc.Symp.Proc.202555[10]Rastelli A,Stoffel M,TersoffJ,Kar G S and Schmidt O G2005Phys.Rev.Lett.95026103[11]Huang L,Liu F,Lu G-H and Gong X G 2000Phys.Rev.Lett.96016103。
道明光学超导概念
道明光学超导概念
道明光学超导（Demonmetiou optic superconductivity）是一种
在光学材料中观察到的现象，它类似于超导体中的电子对的库伦耦合。
它是由斯蒂尔和鲁卡以及道赛父子的研究团队发现的。
道明光学超导的基本概念是在介质中通过光的相互作用形成光子对，这些光子对在材料中传递，并表现出类似超导体中电子对的特性。
这些光子对可以通过相干的相互作用来传输能量和信息，而且它们之间有一种强相互作用。
这种相互作用类似于超导体中的库伦相互作用，它使得光子对能够在材料中几乎无阻碍地传递。
与传统的光学材料不同，道明光学超导体具有较低的折射率，这是由于光子对的强耦合导致的。
这种强耦合可以在一定的温度和光强度下产生，并具有与超导体相似的零电阻和非局域性等特性。
道明光学超导具有许多潜在的应用领域，包括高速光通信、量子计算、光量子存储等。
然而，目前对于道明光学超导的研究还处于起步阶段，需要进一步的实验和理论研究来深入了解和应用这种现象。
磁通量子比特
磁通量子比特
磁通量子比特（flux qubit）是一种基于超导量子比特的量子比特实现方式之一。
它利用超导线圈中的磁通量量子化现象来储存和操作量子信息。
磁通量量子化是指当磁通通过一个超导环路时，磁通的取值只能是一个固定的量子化值。
这个量子化值由磁通量子数Φ0决定，Φ0 = h/2e，其中h是普朗克常数，e是元电荷。
磁通量子化意味着磁通的取值是离散的，而不是连续的。
在磁通量子比特中，超导线圈形成一个环路，其中通过一个超导隧道结（Josephson junction），隧道结的超导层之间存在一个超导隧穿电流。
这个超导隧穿电流可以通过调节外部磁场来改变，从而改变磁通通过环路的大小。
当磁通通过环路的大小等于Φ0的整数倍时，系统的能量最低，可以作为量子比特的基态。
而当磁通通过环路的大小不等于Φ0的整数倍时，系统的能量变高，可以作为量子比特的激发态。
通过对磁场的控制，可以在磁通量子比特之间实现量子态的操作，包括量子叠加态的制备、量子门操作等。
磁通量子比特具有长的相干时间和较高的准确性，因此被认为是一种很有潜力的量子比特实现方式。
第一讲 台面型电子加速器——激光尾波场加速器
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FIB介绍
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sample 為 Si
表面濺擊(Sputtering):
指 Ga+直接撞擊表面原子將其擊出,有下列幾項要點: Sputtering Rate: 對不同物質會有不同的濺擊速率(下表). 結晶方向不同有不同的濺擊速率.若同一平面有不同的晶粒(Grain)方向,會造成無 法平坦蝕刻(例:Cu). 無法選擇性蝕刻. 被移除的物質回積(redeposition): 無法開高視比的孔洞(high aspect hole),因為被擊出的物質撞到側壁又填回,到一 定深度後就不易再加深. 若回填物為導體,在電路修正時將會造成漏電或短路.
下圖分別顯示:Deflector 工作原理,Scanning Pattern, Rotate Image.
其他:
典型 FIB 系統 [2] : Column 長度 15 cm 2 µA(離子流)從 Source 流出 經過 spray aperture 後約 20 nA 經 limiting aperture 選擇使用 20nA - 1pA Beam Current 離子束與物質作用 離子轟擊
超晶格第四章半导体超晶格
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第四章 半导体超晶格
§1 引言 §2 异质结 §3 超晶格量子阱中的新现象 §4 超晶格电子态理论 §5 超晶格晶格振动 §6 超晶格量子阱的光学性质 §7 超晶格量子阱的垂直输运性质 §8 超晶格量子阱应用例举 §9 量子Hall效应 *§10 低维超晶格和微结构
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异质结 - 超晶格的基本单元
“半导体异质结物理”, 虞丽生,科学出版社.
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宁波材料所在新型双电层薄膜晶体管领域取得新进展
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超导量子干涉器及应用_钟青
现代计量测试1998年第3期超导量子干涉器及应用钟 青 乔蔚川(中国计量科学研究院,北京 100013)摘要:作为灵敏度极高的磁传感器,超导量子干涉器的制作工艺日臻完善,它的应用也愈来愈接近现实。
本文简要介绍它的原理及应用。
一、引言超导量子干涉器,简称SQUID(Superco nducting Quantum Interfer ence Device),是一种灵敏度极高的磁通-电压传感器。
它通常含有一个或更多的约瑟夫逊结。
约瑟夫逊结是两个超导体之间的弱连接,可以通过小于临界电流的超导电流。
按器件工作时偏置方式不同,SQUID可分为直流(DC-)和射频(RF-)两种,如图1。
DC-SQU ID 是在一个超导环路中插入两个约瑟夫逊结。
当偏置的直流电流略大于两个结的临界电流之和时,器件的阻抗和器件两端的电压是穿过环路的外磁通量的周期函数,其周期为一个磁通量子 0( 0= 2.07×10-15Wb)。
RF-SQU ID是在一个超导环路中插入一个约瑟夫逊结。
射频电流通过谐振槽路的电感耦合到超导环路中。
槽路的阻抗和输出电压随穿过超导环的磁通而周期变化。
环中磁通每增加或减少一个磁通量子,输出电压变化一个周期。
图1 (a)DC-SQ U ID (b)R F-SQ U I D在偏置电流上加一个调制信号,用锁相放大器测量输出电压,并线性化电压与磁通的关系,如图2。
最后,SQUID输出一个与穿过超导环路的磁通呈线性关系的电压。
SQUID的优点主要表现在:(1)极高的灵敏度。
在低温方面,DC-SQUID磁场灵敏度最好的是2fT/Hz1/2[1];在高温方面,RF-SQ UID最好的磁场灵敏度为15fT/Hz1/2[2];磁通灵敏度为10×10-6 0/Hz1/2[2]。
(2)极大的动态范围,高温仪器可达到±400 0[3]。
(3)极好的线性度,通常的磁测量仪器都是非线性或局部线性的,而SQUID是线性的。
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arXiv:cond-mat/0307024v2 [cond-mat.mes-hall] 26 Nov 2004DoublequantumdotturnstileasanelectronspinentanglerXuedongHu1,2andS.DasSarma21DepartmentofPhysics,UniversityatBuffalo,SUNY,Buffalo,NY14260-1500
2CondensedMatterTheoryCenter,DepartmentofPhysics,
UniversityofMaryland,CollegePark,MD20742-4111(Dated:February2,2008)
Westudytheconditionsforadoublequantumdotsystemtoworkasareliableelectronspinentangler,andtheefficiencyofabeamsplitterasadetectorfortheresultingentangledelectronpairs.Inparticular,wefocusontherelativestrengthsofthetunnelingmatrixelements,theappliedbiasandgatevoltage,thenecessityoftime-dependentinput/outputbarriers,andtheconsequenceofconsideringwavepacketstatesfortheelectronsastheyleavethedoubledottoenterthebeamsplitter.Weshowthatadoublequantumdotturnstileis,inprinciple,anefficientelectronspinentanglerorentanglementfilterbecauseoftheexchangecouplingbetweenthedotsandthetunableinput/outputpotentialbarriers,providedcertainconditionsaresatisfiedintheexperimentalset-up.
PACSnumbers:03.67.Lx,03.67.-a,73.20.Dx,85.30.Vw,
I.INTRODUCTIONExperimentalandtheoreticalstudiesinquantumcomputingandquantuminformationprocessinghaveshownthatthereexistnaturalresourcesinthequantumregime1suchasquantumsuperpositionandentanglementthatcanbeexploitedtoprovideadditionalcomputingpower.Inparticular,thestudyofquantumentanglementhasattractedwidespreadattentionbecauseofitsdirectrelevancetoquantumcomputationanditsimplicationstothefoundationsofquantummechanics.1,2Manyphysicalsystemsrangingfromatomicandopticaltosolidstatehavebeenproposedaspotentialcandidatesforquantuminformationprocessingandforprovidinginsightstotheirinherentquantummechanicalproperties.Specifically,localizedspins(electronornuclear)trappedinsolidstatehostmaterials(particularlysemiconductors)havebeenconsideredasgoodcandidatesforthesepurposesbecauseoftheirrelativelyisolated(fromtheirenvironment)nature.3,4,5,6,7Inthiscontext,thecreationandthedetectionofelectronspinentanglementbecomecriticallyimportanttasks,andarethesubjectmatterofinteresttousinthispaper.Quantumentanglementisamanifestlynon-classicalpropertyofthequantumstateofacompositesystem(e.g.twoormoreparticles)wheretheentangledcompositestatecannotbedecomposedintoaproductoftheindividualstatesoflocalconstituents,andassuchtheconstituentsare“entangled”nomatterhowfartheyareseparatedspatially.Theclassicexampleisthespinsinglet“EPR”stateoftwospin-1/2fermions,where,nomatterhowfarapartthetwoparticlesarespatially,ameasurementofthespinofoneparticlecompletelydeterminesthequantumspinstateoftheother(provided,ofcourse,thespinsingletstateofthetwo-particlestateispreservedcoherentlyuptothemeasurementprocess,i.e.nodecoherencetakesplaceuntilmeasurement).Entanglementleadstospecificnonlocal(andnontriviallynonclassical)correlationsinthemeasuredpropertiesoftheindividualconstituents,whicharetypicallyexpressedintermsofthecelebratedBell’sinequalities.AviolationofBell’sinequalitiesincorrelationmeasurementsoftheconstituentsindicatesthepresenceofentanglementinthetechnicalsense(i.e.showsthatthestateofoneconstituentisinextricablyandnonlocallyquantum-mechanicallyen-tangledwiththestateoftheotherconstituentnomatterhowfarspatiallyaparttheymaybe).Directdemonstrationofentanglement(asmanifestedintheviolationofBell’sinequalities)havesofarbeenlimitedmostlytoexperimentsinvolvingphotons8,9,10becauseentangledphotonsareeasytoproduceinlaboratoriesusingtheparametricdownconversionprocessesinopticalnonlinearcrystals,andphotonshaveverylongcoherencelengthssincetheyareex-tremelyweaklyinteractingobjects.However,fromaclassicalperspectiveatleast(i.e.whenconsideringlightasanallpervadingwaveratherthanacollectionofquantizedphotons),nonlocalentanglementmanifestationoflightwavesisnotaparticularlyshockingsituationasitwouldbewithclassicallymassiveobjectssuchasatoms11andelectrons,whichareclassicallypurelyparticle-like,makinganynonlocalclassicalcorrelationimpossible.Entanglement(inthetechnicalBell’sinequalitiesorEPRsense)hasneverbeenexperimentallydemonstratedinanycondensedmattersystems.Becauseofstronginteractionsinherentlypresentinallsolidstatesystems,thegroundstateisoftenaninteractingmany-bodystate(e.g.thestronglycorrelatedLaughlinstateforthefractionalquantumHallsystem,theBetheansatzsingletgroundstateforone-dimensionalspinchains,theBCSsuperconductinggroundstate)wherethecollectivestateishighly’entangled’inthesensethatitcannotbewrittenasameanfieldproductstateofoneelectronHartreewavefunctions.12,13Whilesuchstronglycoupledstates(theLaughlinstateinthefractionalquantumHallsystembeingaclassicexample)areintrinsicallyentangledbydefinition,ingeneraltheyareunsuitablefortheobservationofentanglementinthetechnicalsenseofEPR/Bell’sinequalities,sinceturningofftheinteractions