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arXiv:1202.3526

Quaternary-singlet State of Spin-1 Bosons in Optical Lattice

Zhang, Jie

Published Feb 16, 2012• 0 citations
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Abstract

We present the quantum ground state properties of $^{23}$Na spinor condensates, which is confined in a periodic or double-well potential and subject to a magnetic dipole-dipole interaction between nearby wells. A novel singlet state arise in the system and can be discussed in explicit form. Caused by the competition between the intra-site spin exchange interactions and the inter-site dipole-dipole interactions, this quaternary-singlet\ state is a entangled state formed by at lest four particles and vanish the total spin. This is distinct from the direct product of the two conventional singlet pairs.

DOI
10.48550/arxiv.1202.3526

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We present the quantum ground state properties of 23^{23}23Na spinor condensates, which is confined in a periodic or double-well potential and subject to a magnetic dipole-dipole interaction between nearby wells. A novel singlet state arise in the system and can be discussed in explicit form. Caused by the competition between the intra-site spin exchange interactions and the inter-site dipole-dipole interactions, this quaternary-singlet\ state is a entangled state formed by at lest four particles and vanish the total spin. This is distinct from the direct product of the two conventional singlet pairs.
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We examine spinor Bose-Einstein condensates in optical superlattices theoretically using a Bose-Hubbard Hamiltonian that takes spin effects into account. Assuming that a small number of spin-1 bosons is loaded in an optical potential, we study single-particle tunneling that occurs when one lattice site is ramped up relative to a neighboring site. Spin-dependent effects modify the tunneling events in a qualitative and quantitative way. Depending on the asymmetry of the double well, different types of magnetic order occur, making the system of spin-1 bosons in an optical superlattice a model for mesoscopic magnetism. We use a double-well potential as a unit cell for a one-dimensional superlattice. Homogeneous and inhomogeneous magnetic fields are applied, and the effects of the linear and the quadratic Zeeman shifts are examined. We also investigate the bipartite entanglement between the sites and construct states of maximal entanglement. The entanglement in our system is due to both orbital and spin degrees of freedom. We calculate the contribution of orbital and spin entanglements and show that the sum of these two terms gives a lower bound for the total entanglement.
We consider insulating phases of cold spin-1 bosonic particles with antiferromagnetic interactions, such as 23Na,{}^{23}\mathrm{Na},23Na, in optical lattices. We show that spin-exchange interactions give rise to several distinct phases, which differ in their spin correlations. In two- and three-dimensional lattices, insulating phases with an odd number of particles per site are always nematic. For insulating states with an even number of particles per site, there is always a spin-singlet phase, and there may also be a first-order transition into the nematic phase. The nematic phase breaks spin rotational symmetry but preserves time reversal symmetry, and has gapless spin-wave excitations. The spin-singlet phase does not break spin symmetry and has a gap to all excitations. In one-dimensional lattices, insulating phases with an odd number of particles per site always have a regime where translational symmetry is broken and the ground state is dimerized. We discuss signatures of various phases in Bragg scattering and time-of-flight measurements.
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