Josephson ladders as a model system for 1D quantum phase transitions
Josephson ladders as a model system for 1D quantum phase transitions
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约瑟夫森梯子作为一维量子相变的模型系统
DOI：
10.1016/j.crhy.2018.09.002
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发表时间：
2018
影响因子：
1.4
通讯作者：
Petković, Aleksandra
中科院分区：
文献类型：
--
作者：
Bell, Matthew T.;Douçot, Benoît;Gershenson, Michael E.;Ioffe, Lev B.;Petković, Aleksandra
量子模拟的想法出现于 20 世纪 80 年代初，是由于认识到使用经典计算机模拟复杂量子系统的根本困难。随着时间的推移，这个想法已经演变成量子计算的一个子领域[1]。与量子计算机类似，量子模拟器基于量子位（qubit）网络，但与成熟的量子计算机相比，量子模拟器不采用离散门操作和纠错码。具有可调参数的量子模拟器旨在仅模拟某些类型的哈密顿量。然而，有可能表明，一个非常通用的哈密顿量可以通过具有 XX 和 YY 相互作用的一类看似受限的自旋链来模拟 [2, 3]。人们希望这样的模拟器将有助于设计新颖的量子系统并探索过去无法实现的现象和机制。此外，量子模拟器可以在绝热量子计算的背景下进行量子退火的实验研究。现代量子模拟器基于多个平台，包括冷原子 [4, 5]、冷离子 [6] 和超导量子位 [7]。我们的研究重点是设计模拟量子一维模型的人工自旋系统——具有受控相互作用的可调谐一维约瑟夫森阵列。横向磁场中一维伊辛自旋链的可积模型是非平衡热力学和量子临界现象背景下的范例 [8, 9]。横向场 Ising 和 XY 模型都与广泛的物理系统相关，在理解量子相变中发挥着至关重要的作用 [9]。在过去的五十年里，这些模型产生了大量的理论活动。最近，这些模型在量子退火技术和绝热量子算法的发展中发挥了至关重要的作用[10]。过去，一维量子自旋动力学的实验研究很大程度上局限于凝聚态系统中的微观自旋。已经证明，LiHoF4 和 CoNb2O6 等准一维自旋材料可以在量子相变（QPT）范围内连续调谐[11-13]。尽管这些工作为横向场伊辛模型的研究开辟了新的前景，但在可控和可调系统中实验实现一维量子自旋模型仍然是一个挑战。事实上，作为一种实验工具，固体中的准一维自旋系统在几个方面受到限制：（i）链间相互作用不是微弱的，因此，这些系统不可避免地是准一维的，（ii）最近邻自旋之间的交换相互作用不能改变，（iii）所有自旋对的交换相互作用都是相同的，这不允许在不添加大量杂质的情况下探索无序和相边界的影响，以及（iv）这些系统可用的实验工具——中子散射——仅与一小类激发相互作用。人工自旋系统设计的灵活性不受这些限制，有助于弥合理想自旋链的理论研究与块状磁性样品的实验研究之间的差距。特别是，这种灵活性允许人们解决无序对横向场自旋模型的静力学和动力学影响的重要问题。最近，横向场伊辛模型在人工和完全可控的自旋链中实现——具有可调谐自旋-自旋耦合的八个通量量子位[10]。我们使用专门设计的一维约瑟夫森梯子寻求类似的方法......
The idea of quantum simulations emerged in the early 1980s out of the realization of the fundamental difficulty of emulating complex quantum system using classical computers. Over time, this idea has evolved into a sub-field of quantum computing [1]. Similar to the quantum computers, quantum simulators are based on the networks of quantum bits (qubits), but, in contrast to the fully-fledged quantum computers, quantum simulators do not employ discrete gate operations and error correction codes. The quantum simulators with tunable parameters are designed to emulate only certain types of Hamiltonians. However, it is possible to show that a very general Hamiltonian can be simulated by a seemingly restricted class of spin chains with XX and YY interactions [2, 3]. One hopes that such simulators will facilitate designing novel quantum systems and exploring phenomena and regimes inaccessible in the past. Furthermore, quantum simulators enable the experimental study of quantum annealing in the context of adiabatic quantum computation. Modern quantum simulators are based on several platforms, which include cold atoms [4, 5], cold ions [6], and superconducting qubits [7]. Our research focuses on designing artificial spin systems–tunable 1D Josephson arrays with controlled interactions–that emulate the quantum 1D models. The integrable model of a 1D Ising spin chain in the transverse magnetic field serves as a paradigm in the context of nonequilibrium thermodynamics and quantum critical phenomena [8, 9]. Both the transverse field Ising and XY models, being relevant to a broad range of physical systems, played a crucial role in the understanding of quantum phase transitions [9]. These models have generated a formidable body of theoretical activity over the past fifty years. Recently, these models played a crucial role in the development of quantum annealing techniques and adiabatic quantum algorithms [10].In the past, the experimental study of quantum spin dynamics in 1D has been largely limited to microscopic spins in condensed-matter systems. It has been demonstrated that such quasi-1D spin materials as LiHoF4 and CoNb2O6 can be continuously tuned across the quantum phase transition (QPT)[11–13]. Though these works opened up new vistas in the studies of transverse field Ising model, the experimental realization of 1D quantum spin models in well-controllable and tunable systems remains a challenge. Indeed, as an experimental tool, the quasi-1D spin systems in solids are limited in several respects:(i) the inter-chain interactions are not negligibly weak, and, thus, these systems are inevitably quasi-1D,(ii) the exchange interactions between the nearest-neighbor spins cannot be varied,(iii) the exchange interactions are the same for all pair of spins, which does not allow for exploring the effect of disorder and phase boundaries without adding a significant amount of impurities, and (iv) the available experimental tool for these systems–scattering of neutrons–interacts only with a narrow class of excitations. Flexibility in the design of artificial spin systems, which are free from these limitations, facilitates bridging the gap between the theoretical study of ideal spin chains and the experimental investigation of bulk magnetic samples. In particular, this flexibility allows one to address an important issue of the effects of disorder on the statics and dynamics of transverse field spin models. Recently, the transverse-field Ising model was realized in the chain of artificial and fully-controllable spins–eight flux qubits with tunable spin–spin couplings [10]. We pursue a similar approach using specially designed one-dimensional Josephson ladders …
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