Loop-structure stability of a double-well-lattice Bose-Einstein condensate

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We study experimentally the stability of excited, interacting states of bosons in a double-well optical lattice in regimes where the nonlinear interactions are expected to induce "swallowtail" looped band structure. By carefully preparing different initial coherent states and observing their subsequent decay, we observe distinct decay rates that provide direct evidence for multivalued, looped band structure. The double well lattice both stabilizes the looped band structure and allows for dynamic preparation of different initial states, including states within the loop structure. We confirm our state preparation procedure with dynamic Gross-Pitaevskii calculations. The excited loop states are found to be more stable than dynamically unstable ground states, but decay faster than expected based on a mean-field stability calculation, indicating the importance of correlations beyond a mean field description.Interactions in Bose-Einstein condensates (BECs) can give rise to qualitatively new nonlinear phenomena [1][2][3][4][5]. For example, superfluids in optical lattices can exhibit additional, interaction-stabilized states arising from the so-called "swallowtail catastrophe" in which the band structure becomes multi-valued [6][7][8][9]. As the interaction increases, the collective band structure at the edge of the Brilloiun zone (BZ) develops a cusp (a discontinuity in the derivative), and subsequently a loop with multiple energy states that can be occupied at the same quasimomentum. The existence of loop states is related to dynamical asymmetry in Landau-Zener tunneling between coupled states of the many-body system [10], which has been used to indirectly observe nonlinear loop structure [4,11]. Despite the fact that ultracold atoms in optical lattices are an ideal system to realize nonlinear wave dynamics, the interaction strengths needed to generate such interesting band structure in a simple lattice are prohibitively large.In addition to multi-valued band structure at the edge of the BZ, period doubled solutions are also expected to occur halfway to the edge of the BZ [12]. Adding a weak lattice at half the main lattice period expands the parameter regime where band structure loops are expected [8], making them more experimentally feasable. The states associated with the loop are collective excited states, and an essential consideration in their observation is their stability. Even in the weakly interacting, mean-field limit, dynamical instabilities [13][14][15] can arise that quickly destroy the excited superfluid state. Dynamically stable mean-field solutions exist [16], and in particular there are accessible regimes where mean field calculations predict different stability for the multi-valued bands. An example of such looped band structure is shown in Fig. 1a. Correlations outside of a mean field description of the system, however, can cause additional instability in the excited states [4,17]. Using ultra cold atoms to study unconventional excited states [18][19][20][21][22] requires understanding such relaxa...

supporting

confidence: 86%

contrasting

confidence: 60%

mentioning

confidence: 99%

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Nonlinear looped band structure of Bose-Einstein condensates in an optical lattice

Koller¹,

Goldschmidt²,

Brown³

et al. 2016

Self Cite

“…In particular, the lowest branch can be dynamically stable in the whole Brillouin zone (BZ) in the limit of strong coherent coupling. We also find that this system can show a hysteretic behavior with a loop-like structure in the Bloch band which resembles the so-called "swallowtail" loop [20][21][22][23][24][25][26][27][28][29][30].…”

mentioning

confidence: 71%

Stabilization of nonlinear lattices: A route to superfluidity and hysteresis

Watanabe

Zhang

2018

The Bloch states of a Bose-Einstein condensates (BECs) in pure nonlinear lattices (NLs) are dynamically unstable, so that they cannot show superfluidity. We overcome this problem by finding that the two-component BECs in NLs can be stabilized by the coherent linear coupling. Furthermore, in the limit of the strong coherent coupling, the lowest Bloch band in the whole Brillouin zone can be dynamically stable. We also find a hysteretic behavior with loop-like structure in the Bloch band resembling the so-called "swallowtail" loop. The dynamical stabilization and hysteretic behavior can be observed in experiments by current technology.

“…With a certain lattice geometry, a spin-orbital like coupling can naturally appear in an orbital gas with s and p-orbitals without Raman transitions [22]. Theoretical studies of orbital physics largely focusing on two or three dimensions suggest exotic orbital phases [3][4][5][6][23][24][25][26][27][28][29][30][31] beyond the scope of spin physics.…”

Section: Introductionmentioning

confidence: 99%

Orbital coupled dipolar fermions in an asymmetric optical ladder

Liu

2013

We study a quantum ladder of interacting fermions with coupled s and p orbitals. Such a model describes dipolar molecules or atoms loaded into a double-well optical lattice, dipole moments being aligned by an external field. The two orbital components have distinct hoppings. The tunneling between them is equivalent to a partial Rashba spin-orbital coupling when the orbital space (s, p) is identified as spanned by pseudo-spin 1/2 states. A rich phase diagram, including incommensurate orbital density wave, pair density wave and other exotic superconducting phases, is proposed with bosonization analysis. In particular, superconductivity is found in the repulsive regime.