Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session J6: Spinor Gases |
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Chair: Han Pu, Rice University Room: 552AB |
Wednesday, May 25, 2016 2:00PM - 2:12PM |
J6.00001: Characterizing the "Higgs" amplitude mode in a Spin-1 Bose Einstein Condensate Bharath Hebbe Madhusudhana, Matthew Boguslawski, Martin Anquez, Bryce Robbins, Maryrose Barrios, Thai Hoang, Michael Chapman Spontaneous symmetry breaking in a physical system is often characterized by massless Nambu-Goldstone modes and massive Anderson-Higgs modes. It occurs when a system crosses a quantum critical point (QCP) reaching a state does not share the symmetry of the underlying Hamiltonian. In a spin-1 Bose Einstein condensate, the transverse spin component can be considered as an order parameter. A quantum phase transition (QPT) of this system results in breaking of the symmetry group $U(1)\times SO(2)$ shared by the Hamiltonian. As a result, two massless coupled phonon-magnon modes are produced along with a single massive mode or a Higgs-like mode, in the form of amplitude excitations of the order parameter. Here we characterize the amplitude excitations experimentally by inducing coherent oscillation in the spin population [1]. We further use the amplitude oscillations to measure the energy gap for different phases of the QPT. At the QCP, finite size effects lead to a non-zero gap, and our measurements are consistent with this prediction. \\ $^1$ T. M. Hoang et al, arXiv:1512.06766 [Preview Abstract] |
Wednesday, May 25, 2016 2:12PM - 2:24PM |
J6.00002: Universality of nonthermal behavior in spinor Bose condensates Yogesh Sharad Patil, Hil F. H. Cheung, Airlia Shaffer, Huiyao Y. Chen, Mukund Vengalattore Spinor Bose condensates exhibit a rich phase diagram with varied magnetic ordering and topological defects because of the close competition between their spin and charge dependent interactions. Quenching such a spinor condensate into a ferromagnetic state realizes robust non-equilibrium and prethermalized states whose macroscopic behavior differs from thermodynamic predictions. In previous work, we have identified the microscopic origin of prethermalization in Rubidium spinor gases as being the disparate energy scales of the phonon and magnon excitations in this gas [1]. This identification of the microscopic origin enables us to broaden the scope of our studies to address fundamental questions regarding the equilibration of isolated quantum systems. We will discuss our recent results that suggest the universality of this coarsening behavior and evidence that this system can be mapped on to a non-thermal fixed point studied in high energy field theories [2]. \\[4pt] [1] R. Barnett, A. Polkovnikov, and M. Vengalattore, Phys. Rev. A 84, 023606 (2011) \newline [2] J. Berges, arXiv:1503.02907 (2015) [Preview Abstract] |
Wednesday, May 25, 2016 2:24PM - 2:36PM |
J6.00003: Phase ordering dynamics in spin-1 ferromagnetic condensates Lewis Williamson, Peter Blakie Spinor Bose-Einstein condensates present rich phase diagrams for exploring phase transitions between states with different symmetry properties. In this work we simulate the approach to equilibrium of a spin-1 condensate quenched from an unmagnetised phase to three different ferromagnetic phases. The three ferromagnetic phases have Z$_2$, SO(2) and SO(3) symmetries respectively and possess different conservation laws. Following the quench, domains of magnetization form, with each domain making an independent choice of the symmetry breaking order parameter. These domains grow and compete for the global equilibrium state. We find that this growth follows universal scaling laws and identify the dynamic universality class for each of the three quenches. Polar-core spin-vortices play a crucial role in the phase ordering of the SO(2) system and we identify fractal structures in the domain patterns of the SO(2) and SO(3) systems. [Preview Abstract] |
Wednesday, May 25, 2016 2:36PM - 2:48PM |
J6.00004: Preparing a twin-Fock state of spinor atomic condensate Yiquan Zou, Xinyu Luo, Qi Liu, Ling-Na Wu, Meng Khoon Tey, Li You An even number $N$ of bosonic particles equally partitioned into two modes represents a twin-Fock state (TFS), which is manifestly entangled and can be used to approach Heisenberg limited sensing precision $1/N$. Small $N$ TFSs are routinely produced from parametric down conversion, for instance, the paired photons at $N=2$. Large $N$ TFSs, however, remain elusive although their presence have been inferred in spinor atomic condensates undergoing spin exchange collisions [1-4]. Such spin mixing process has been intensively studied in recent years, whereby a N-atom polar or non-magnetic condensate evolves into a mixture of TFSs with the number of paired atoms covering a broad range from $0$ to $N/2$. The present work reports our experimental observation of $N \simeq 20000$ condensed atoms almost completely and deterministically converted into a single component TFS at $\sim 10000$ pairs through adiabatic means.\\\\ 1. E. M. Bookjans, et al, Phys. Rev. Lett. \textbf{107}, 210406 (2011).\\ 2. C. Gross, et al, Nature \textbf{480}, 219 (2011).\\ 3. B. L\"ucke, et al., Science \textbf{334}, 773(2011).\\ 4. B. L\"ucke, et al, Phys. Rev. Lett. \textbf{112}, 155304 (2014). [Preview Abstract] |
Wednesday, May 25, 2016 2:48PM - 3:00PM |
J6.00005: Core structure and dynamics of non-Abelian vortices in a biaxial nematic spinor Bose-Einstein condensate Magnus O. Borgh, Janne Ruostekoski We demonstrate that multiple interaction-dependent defect core structures as well as dynamics of \emph{non-Abelian} vortices can be realized in the biaxial nematic (BN) phase of a spin-2 atomic Bose-Einstein condensate (BEC). An experimentally simple protocol may be used to break degeneracy with the uniaxial nematic phase. We show that a discrete \emph{spin-space symmetry} in the core may be reflected in a breaking of its \emph{spatial symmetry.} The discrete symmetry of the BN order parameter leads to non-commuting vortex charges. We numerically simulate reconnection of non-Abelian vortices, demonstrating formation of the obligatory \emph{rung vortex.} In addition to atomic BECs, non-Abelian vortices are theorized in, e.g., liquid crystals and cosmic strings. Our results suggest the BN spin-2 BEC as a prime candidate for their realization. [Preview Abstract] |
Wednesday, May 25, 2016 3:00PM - 3:12PM |
J6.00006: Magnetic solitons in a binary Bose-Einstein condensate Chunlei Qu, Lev Pitaevskii, Sandro Stringari Solitons, the fascinating topological excitations of nonlinear systems, have drawn a considerable research interest in many physical branches. Here I will talk about a magnetic soliton solution to a two-component repulsive Bose gas. The properties of the soliton, including the wave function, the energy and the effective mass, will be presented. I will also discuss the oscillation behaviour of the magnetic solitons in a harmonic trap. [Preview Abstract] |
Wednesday, May 25, 2016 3:12PM - 3:24PM |
J6.00007: Collision of Half-Quantum Vortices in a Spinor Bose-Einstein Condensate Sang Won Seo, Woo Jin Kwon, seji Kang, Yong-il Shin We report on the experimental observation of the collision dynamics of half quantum vortices (HQVs) in the easy-plane polar phase of antiferromagnetic spin-1 Bose-Einstein condensates [1].~Using a deterministic vortex dipole generation method, we perform collision experiment between two HQV pairs. The scattering patterns of the HQVs reveal their short range interactions that arise from their ferromagnetic cores. In addition, we investigate the relaxation of turbulent superflow containing many HQVs, providing a new type of quantum turbulence. In the relaxation dynamics, we observe that spin waves are generated and maintained by the HQV collisions. [1] S.W. Seo, W.J. Kwon, S. Kang and Y. Shin, arXiv:1512.07696 [Preview Abstract] |
Wednesday, May 25, 2016 3:24PM - 3:36PM |
J6.00008: Thermodynamic properties of Fermi gases in states with defined many-body spins Vladimir Yurovsky Zero-range interactions in cold spin-$1/2$ Fermi gases can be described by single interaction strength, since collisions of atoms in the same spin state are forbidden by the Pauli principle. In a spin-independent trap potential (even in the presence of a homogeneous spin-dependent external field), the gas can persist in a state with the given many-body spin, since the spin operator commutes with the Hamiltonian. Spin and spatial degrees of freedom in such systems are separated, and the spin and spatial wavefunctions form non-Abelian irreducible representations of the symmetric group, unless the total spin is $S=N/2$ for $N$ atoms (see {[}1{]}). Although the total wavefunction, being a linear combination of products of the spin and spatial functions, is permutation-antisymmetric, the non-Abelian permutation symmetry is disclosed in the matrix elements and, as demonstrated here, in thermodynamic properties. The effects include modification of the specific heat and compressibility of the gas. 1.V. A. Yurovsky, Phys. Rev. Lett. \textbf{113}, 200406 (2014); Phys. Rev. A \textbf{91}, 053601 (2015). [Preview Abstract] |
Wednesday, May 25, 2016 3:36PM - 3:48PM |
J6.00009: The Operator Product Expansion Beyond Leading Order for Spin-1/2 Fermions Samuel Emmons, Daekyoung Kang, Lucas Platter Strongly interacting systems of ultracold, two-component fermions have been studied using various techniques for many years. One technique that has been applied is a quantum field theoretical formulation of the zero-range model. In this framework, the Operator Product Expansion was used to derive universal relations for systems with a large scattering length[1]. This corroborated and extended the work of Tan[2-4]. We calculate finite range corrections to the momentum distribution using the OPE framework and demonstrate the utility of including the $1/k^6$ tail from the OPE for the momentum distribution. Corrections to the universal relations for the system are calculated and expressed in terms of the S-wave effective range and an additional quantity D similar to Tan's contact which, in addition to the contact, relates various physical observables. We compare our results with quantum Monte Carlo calculations for the two-component Fermi gas with large scattering length. \\References: \\1. E. Braaten and L. Platter, Phys. Rev. Lett. 100, 205301 (2008) \\2. S. Tan, Annals of Physics 323, 2971 (2008), ISSN 0003-4916 \\3. S. Tan, Annals of Physics 323, 2952 (2008), ISSN 0003-4916 \\4. S. Tan, Annals of Physics 323, 2987 (2008), ISSN 0003-4916 [Preview Abstract] |
Wednesday, May 25, 2016 3:48PM - 4:00PM |
J6.00010: Fermi spin current contribution in spin wave spectrum of spin-1/2 fermions. Pavel Andreev, Leonid Kuzmenkov General theory predicts the presence of the thermal part of the spin current in the spin evolution equation for bosons and fermions. For bosons in Bose-Einstein condensate state, it is equal to zero. However, for degenerate fermions it is non zero and it can give a considerable contribution since it describes the Pauli blocking. In this work, we consider spin-1/2 partially polarized fermions. We derive an equation of state for the thermal part of the spin current of degenerate fermions and call it Fermi spin current. We present the spin evolution equation with the Fermi spin current as a part of applied hydrodynamic model. We consider spectrum of collective excitation and describe contribution of the Fermi spin current in the spin wave spectrum. [Preview Abstract] |
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