Coherent Magnon Optics in a Ferromagnetic Spinor Bose-Einstein Condensate

Marti, G. Edward; MacRae, Andrew; Olf, Ryan; Lourette, Sean; Fang, Fang; Stamper-Kurn, Dan

doi:10.1103/physrevlett.113.155302

Cited by 62 publications

(78 citation statements)

References 24 publications

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“…Recent theoretical work [2][3][4][5][6][7][8][9] has explored the Bose polaron case, and the ability to use a Feshbach resonance to tune [10] the impurity-boson scattering length a IB opens the possibility of exploring the Bose polaron in the strongly interacting regime [11][12][13][14]. Experiments to date [15][16][17][18][19][20] have focused on the weak Bose polaron limit. The Bose polaron in the strongly interacting regime is interesting in part because it represents step towards understanding a fully strongly interacting Bose system.…”

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confidence: 99%

Bose Polarons in the Strongly Interacting Regime

Hu¹,

Graaff²,

Kedar³

et al. 2016

Phys. Rev. Lett.

446

507

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When an impurity is immersed in a Bose-Einstein condensate, impurity-boson interactions are expected to dress the impurity into a quasiparticle, the Bose polaron. We superimpose an ultracold atomic gas of 87 Rb with a much lower density gas of fermionic 40 K impurities. Through the use of a Feshbach resonance and RF spectroscopy, we characterize the energy, spectral width and lifetime of the resultant polaron on both the attractive and the repulsive branches in the strongly interacting regime. The width of the polaron in the attractive branch is narrow compared to its binding energy, even as the two-body scattering length formally diverges.The behavior of a dilute impurity interacting with quantum bath is a simplified yet nontrivial many-body model system with wide relevance to material systems. For example, an electron moving in an ionic crystal lattice is dressed by coupling to phonons and forms a quasiparticle known as a Bose polaron (see Fig. 1a) that is an important paradigm in quantum many-body physics [1]. Impurity atoms immersed in a degenerate bosonic or fermionic atomic gas are a convenient experimental realization for Bose or Fermi polaron physics, respectively. Recent theoretical work [2-9] has explored the Bose polaron case, and the ability to use a Feshbach resonance to tune [10] the impurity-boson scattering length a IB opens the possibility of exploring the Bose polaron in the strongly interacting regime [11][12][13][14]. Experiments to date [15][16][17][18][19][20] have focused on the weak Bose polaron limit. The Bose polaron in the strongly interacting regime is interesting in part because it represents step towards understanding a fully strongly interacting Bose system. While a IB can be tuned to approach infinity, the boson-boson scattering length a BB can still correspond to the meanfield limit. A dilute impurity interacting very strongly with a Bose gas that is otherwise in the mean-field regime is, on the one hand, something more difficult to model and to measure than a weakly interacting system. On the other hand it is theoretically more tractable, and empirically more stable than a single-component "unitary" Bose gas in which a BB diverges and thus every pair of atoms is strongly coupled [21].Our experiment employs techniques similar to those used in recent Fermi polaron measurements [22][23][24][25]. However, there are important differences between the Bose polaron and the Fermi polaron. From a theory point of view, the Bose polaron problem involves an interacting superfluid environment and also has the possibility of three-body interactions [14], both of which are not present for the Fermi polaron. And on the experimental side, both three-body inelastic collisions and the relatively small spatial extent of a BEC (compared to that of the impurity gas) create challenges for measurements of the Bose polaron. This work, in parallel with work done at Aarhus [26], describes the first experiments performed on Bose polarons in the strongly interacting regime. In our case, the impurity is fermi...

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mentioning

confidence: 99%

Bose Polarons in the Strongly Interacting Regime

Hu¹,

Graaff²,

Kedar³

et al. 2016

Phys. Rev. Lett.

446

507

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“…The upper bound of the lattice systems is given by the same expression as the continuous systems (17).…”

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confidence: 99%

“…This indicates that the effective mass of the magnon is the same as the atomic mass at the meanfield level. However, the observed effective mass of the magnon is heavier than that of the atomic mass [17].…”

Section: Introductionmentioning

confidence: 89%

Upper bound of one-magnon excitation and lower bound of effective mass for ferromagnetic spinor Bose and Fermi gases

Kunimi

Saito

2015

Phys. Rev. A

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Using a variational method, we derive an exact upper bound for one-magnon excitation energy in ferromagnetic spinor gases, which limits the quantum corrections to the effective mass of a magnon to be positive. We also derive an upper bound for one-magnon excitation energy in lattice systems. The results hold for both Bose and Fermi systems in d dimensions as long as the interaction is local and invariant under spin rotation.

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confidence: 99%

“…New features of quantum gases emerged with the first realizations of spinor Bose-Einstein condensates (SBEC) [4,5], thanks to the many degrees of freedomboth internal and external -and to the excellent control of the experimental parameters. SBECs are extremely rich and versatile systems to study complex quantum vacuua [6], for example to test the validity of universal phenomena like the Kibble-Zurek mechanism [7-9], or to study Goldstone modes such as gapless magnons [10].The coupling of SBECs to magnetic fields has been exploited to study quantum phase transitions in SBECs [11][12][13], and to realize point-like topological defects such as Dirac monopoles [14-16] and 2D skyrmions [17]. In these works, spin symmetries and topology were induced by strong gradients, e.g.…”

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Spontaneous $\mathcal{PT}$ symmetry breaking of a ferromagnetic superfluid in a gradient field

Vanderbruggen¹,

Palacios²,

Coop³

et al. 2015

EPL

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We consider the interaction of a ferromagnetic spinor Bose-Einstein condensate with a magnetic field gradient. The magnetic field gradient realizes a spin-position coupling that explicitly breaks time-reversal symmetry T and space parity P, but preserves the combined PT symmetry. We observe using numerical simulations, a phase transition spontaneously breaking this remaining symmetry. The transition to a low-gradient phase, in which gradient effects are frozen out by the ferromagnetic interaction, suggests the possibility of high-coherence magnetic sensors unaffected by gradient dephasing.PACS numbers: 67.85. Fg, 64.60.Ej Introduction -The discovery of the very complex vacuum in superfluid 3 He proved to be highly stimulating to the theory of symmetry breaking [1] and topological defects [2,3]. New features of quantum gases emerged with the first realizations of spinor Bose-Einstein condensates (SBEC) [4,5], thanks to the many degrees of freedomboth internal and external -and to the excellent control of the experimental parameters. SBECs are extremely rich and versatile systems to study complex quantum vacuua [6], for example to test the validity of universal phenomena like the Kibble-Zurek mechanism [7-9], or to study Goldstone modes such as gapless magnons [10].The coupling of SBECs to magnetic fields has been exploited to study quantum phase transitions in SBECs [11][12][13], and to realize point-like topological defects such as Dirac monopoles [14-16] and 2D skyrmions [17]. In these works, spin symmetries and topology were induced by strong gradients, e.g. 37 mT/m in Ref. [14]. Here we show that via a quantum phase transition at lower gradients ∼ 0.5 mT/m, the ferromagnetic interaction can "freeze out" the gradient effect. This suggests the possibility of magnetic sensors free from gradient dephasing, a practical limitation in coherent magnetometry [18][19][20][21][22][23][24].We use group theoretical methods that have proven fruitful in the analysis and classification of SBEC phases [1,25]. The interaction with the gradient realizes an interesting spin-position coupling that explicitly breaks the parity P and time-reversal T symmetries, only preserving the combined PT symmetry. Numerically solving the Gross-Pitaevskii equations of the system, we observe that below a critical value of the magnetic field gradient, the PT symmetry is spontaneously broken and a nonzero overall magnetization appears. This occurs when the ferromagnetic interactions dominate the coupling energy between the gradient field and the spins, resulting in a globally polarized condensate. Moreover, we observe that this effect is associated with a phase transition. Interestingly, discrete, and in particular PT , symmetry breaking is also observed in Bose gases with spin-orbit coupling [26][27][28].

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Coherent Magnon Optics in a Ferromagnetic Spinor Bose-Einstein Condensate

Cited by 62 publications

References 24 publications

Bose Polarons in the Strongly Interacting Regime

Bose Polarons in the Strongly Interacting Regime

Upper bound of one-magnon excitation and lower bound of effective mass for ferromagnetic spinor Bose and Fermi gases

Spontaneous $\mathcal{PT}$ symmetry breaking of a ferromagnetic superfluid in a gradient field

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