Observation of the supersolid stripe phase in spin-orbit coupled Bose-Einstein condensates
Observation of the supersolid stripe phase in spin-orbit coupled Bose-Einstein condensates
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发表时间：
2017-06
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通讯作者：
Jun-Ru Li;Jeongwon Lee;Wujie Huang;Sean Burchesky;B. Shteynas;F. C. Top;A. Jamison;W. Ketterle
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作者：
Jun-Ru Li;Jeongwon Lee;Wujie Huang;Sean Burchesky;B. Shteynas;F. C. Top;A. Jamison;W. Ketterle
超固体是一个耐人寻味的概念。它结合了超流体流动的特性和固体1的长程空间周期性，这两个特性通常是相互排斥的。最初对量子晶体2和超固体度的讨论集中在固体氦-4上，在那里预测空位可以形成稀薄的弱相互作用玻色-爱因斯坦凝聚体1，3。在这个系统中，直接观察超固体度一直是难以捉摸的†。然后，超固体的概念被推广到包括其他打破空间平移对称性的超流体系统。其中一个系统是具有自旋-轨道耦合的玻色-爱因斯坦凝聚体，它具有超固态条纹相5-8。尽管最近对该系统进行了几项研究9，10，但尚未观察到条纹相。在这里，我们报道了利用布拉格反射直接观测到预测的条纹相位的密度调制。我们的工作建立了一个具有独特对称破缺性质的系统。未来感兴趣的是通过引入涡旋11、12、孤子13、杂质14或无序来进一步突破空间对称性。†虽然最初对超固态3的观察结果证明是由不寻常的弹性性质引起的，但实验仍然揭示了量子可塑性和质量超输运，可能是由超流流经相互连接的位错1、4的核心产生的。2超固态被定义为自发打破两个连续的U(1)对称的系统：通过选择超流的相来实现内部规范对称性，通过形成密度波1来实现空间的平移对称性。对于超冷原子，理想化的哈密顿量可以通过实验来实现和研究。从超流体玻色-爱因斯坦凝聚体(BEC)出发，通过添加偶极相互作用15、16、里德堡相互作用17、超辐射瑞利散射18、晶格中最近邻相互作用19和自旋-轨道相互作用5-8等形式的相互作用，预测了几种形式的超固体。其中几个建议导致了沿单一空间方向的稳固。仅为一个自由度破坏平移对称性类似于液晶。BEC中的超固体是一种不寻常的物质形式，因为它结合了气体、超流体和固体的行为。在自旋-轨道耦合的玻色-爱因斯坦凝聚体中，超固体条纹相自然地出现在描述中，其中自旋-轨道耦合起着带有动量转移的自旋翻转过程的作用，如图1a所示。在固体材料中，由于电磁场的相对论变换，以v速度通过电场E的电子经历塞曼能量项-B(vE)。…
Supersolidity is an intriguing concept. It combines the property of superfluid flow with the long-range spatial periodicity of solids 1 , two properties which are often mutually exclusive. The original discussion of quantum crystals 2 and supersolidity focuses on solid Helium-4 where it was predicted that vacancies could form dilute weakly interacting Bose-Einstein condensates 1,3. In this system, direct observation of supersolidity has been elusive †. The concept of supersolidity was then generalized to include other superfluid systems which break the translational symmetry of space. One of such systems is a Bose-Einstein condensate with spin-orbit coupling which has a supersolid stripe phase 5-8. Despite several recent studies of this system 9,10 , the stripe phase has not been observed. Here we report the direct observation of the predicted density modulation of the stripe phase using Bragg reflection. Our work establishes a system with unique symmetry breaking properties. Of future interest is further spatial symmetry breaking through the introduction of vortices 11,12 , solitons 13 , impurities 14 or disorder. † Although the original observation of supersolidity 3 turned out to be caused by unusual elastic properties, experiments still revealed quantum plasticity and mass supertransport, probably created by superfluid flow through the cores of interconnected dislocations 1, 4 2 Supersolids are defined as systems which spontaneously break two continuous, U(1), symmetries: the internal gauge symmetry by choosing the phase of the superfluid, and the translational symmetry of space by forming a density wave 1. With ultracold atoms, idealized Hamiltonians can be experimentally realized and studied. Starting from superfluid Bose-Einstein condensates (BECs), several forms of supersolids have been predicted by adding interactions in the form of dipolar interactions 15, 16 , Rydberg interactions 17 , superradiant Rayleigh scattering 18 , nearest-neighbour interaction in lattices 19 and spin-orbit interactions 5-8. Several of these proposals lead to solidity along a single spatial direction. Breaking the translational symmetry for only one degree of freedom is analogous to liquid crystals. Supersolidity in BEC is an unusual form of matter as it combines gaseous, superfluid, and solid behaviours. In a spin-orbit coupled Bose-Einstein condensate, the supersolid stripe phase emerges naturally in a description where spin-orbit coupling acts as a spin flip process with momentum transfer as shown in Fig. 1a. In solid-state materials, an electron moving at velocity v through an electric field E experiences a Zeeman energy term-B(vE) due to the relativistic transformation of electromagnetic fields. …