Interaction of half-quantized vortices in two-component Bose-Einstein condensates

Eto, Minoru; Kasamatsu, Kenichi; Nitta, Muneto; Takeuchi, Hiromitsu; Tsubota, Makoto

doi:10.1103/physreva.83.063603

Cited by 111 publications

(137 citation statements)

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“…The separation distance of the pair and the magnitude of the core magnetization gradually increase, and the growth ceases after t h ∼ 1.3 s when the separation distance reaches about s 0 = 17.6 µm. This saturation behavior seems to be consistent with the short-range repulsive interactions between HQVs with opposite core magnetization [21,22]. Taking into account the imaging resolution of ≈ 4 µm, we estimate the FWHM of a fully developed, magnetized HQV core to be ≈ 8.4 µm that corresponds to ∼ 1.7ξ s , whereξ s is the average value of the spin healing lengths at the positions of the HQV pairs.…”

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confidence: 70%

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Half-Quantum Vortices in an Antiferromagnetic Spinor Bose-Einstein Condensate

et al. 2015

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We report on the observation of half-quantum vortices (HQVs) in the easy-plane polar phase of an antiferromagnetic spinor Bose-Einstein condensate. Using in situ magnetization-sensitive imaging, we observe that pairs of HQVs with opposite core magnetization are generated when singly charged quantum vortices are injected into the condensate. The dynamics of HQV pair formation is characterized by measuring the temporal evolutions of the pair separation distance and the core magnetization, which reveals the short-range nature of the repulsive interactions between the HQVs. We find that spin fluctuations arising from thermal population of axial magnon excitations do not significantly affect the HQV pair formation dynamics. Our results demonstrate the instability of a singly charged vortex in the antiferromagnetic spinor condensate. In a scalar superfluid, the supercurrent circulation around quantum vortices is quantized in units of h/m due to U (1) gauge symmetry [1], where h is the Planck constant and m is particle mass. However, when a superfluid possesses an internal spin degree of freedom, there is an intriguing possibility for the superfluid to host quantum vortices of a fractional circulation of h/m. The superfluid phase interwinds with the spin orientation and a new relation is imposed on the supercurrent circulation in connection with spin texture [2]. Fractional quantum vortices are of particular interest in two-dimensional (2D) superfluidity. In the absence of long-range order in two dimensions [3], the superfluid phase transition in 2D is associated with vortex-antivortex pairing as described by the Berezinskii-Kosterlitz-Thouless (BKT) theory [4,5]. Hence fractional quantum vortices, introduced as new point defects, represent an interesting opportunity to explore for exotic superfluid phases, possibly beyond the BKT physics.Quantum vortices having h/2m circulation, so-called half-quantum vortices (HQVs) have been experimentally observed in spinor superfluid systems such as excitonpolariton condensates [6][7][8] and triplet superconductors [9]. In previous cold atom experiments, HQV states were created with an optical method in two-component Bose-Einstein condensates (BECs) [10], where the two components are not symmetric in terms of interactions. Recently, a spin-1 BEC with antiferromagnetic interactions has been considered with great interest because HQVs are topologically allowed in the polar phase of the system [11][12][13]. Theoretical studies predicted an anomalous superfluid density jump at the phase transition in two dimensions [14][15][16] as well as a new superfluid state that has completely broken spin ordering [17,18].In this Letter, we report on the observation of HQVs in the easy-plane polar phase of an antiferromagnetic spinor BEC of 23 Na atoms. Using magnetization-sensitive imaging, we observe that pairs of HQVs with opposite core magnetization are generated when singly charged quantum vortices are injected into the condensate. The temporal evolutions of the pair separation distance and t...

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confidence: 70%

“…It was predicted in mean-field calculations that in the AF phase a singly charged vortex state is energetically unstable to decay into two HQVs [21][22][23]. Note that the two HQVs have opposite core magnetization.…”

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confidence: 99%

Half-Quantum Vortices in an Antiferromagnetic Spinor Bose-Einstein Condensate

et al. 2015

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“…Subsequently, their stability [34,40] and dynamics [34,35] have been examined theoretically. It was shown that these states feature intriguing interactions that decay with the distance r between them as 1/r 3 [35]. Pairs of VB soliton complexes can form bound states in atomic BECs, as shown in detail in Ref.…”

Section: Introductionmentioning

confidence: 99%

“…In the two-dimensional (2D) setting, such patterns are well-known stable vortices [32] (vortices were studied in multi-component systems too [33]). A vortex in one component generates an effective axisymmetric potential well in the other, which may trap a bright 2D solitary wave, producing a complex that was given different names -in particular, a vortex-bright (VB) soliton [34], a half-quantum vortex [35], a filledcore vortex [36], as well as a baby Skyrmion [37]. Similar stable two-component modes are "semi-vortices" in the free 2D [38] and 3D [39] space with the attractive SPM and XPM terms, which are made stable by the spin-orbit coupling; they are composed of a bright vortex soliton in one component, and a bright fundamental one in the other.…”

Section: Introductionmentioning

confidence: 99%

Vortex-soliton complexes in coupled nonlinear Schrödinger equations with unequal dispersion coefficients

et al. 2016

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We consider a two-component, two-dimensional nonlinear Schrödinger system with unequal dispersion coefficients and self-defocusing nonlinearities, chiefly with equal strengths of the self-and cross-interactions. In this setting, a natural waveform with a nonvanishing background in one component is a vortex, which induces an effective potential well in the second component, via the nonlinear coupling of the two components. We show that the potential well may support not only the fundamental bound state, but also multi-ring excited radial state complexes for suitable ranges of values of the dispersion coefficient of the second component. We systematically explore the existence, stability, and nonlinear dynamics of these states. The complexes involving the excited radial states are weakly unstable, with a growth rate depending on the dispersion of the second component. Their evolution leads to transformation of the multi-ring complexes into stable VB solitons ones with the fundamental state in the second component. The excited states may be stabilized by a harmonic-oscillator trapping potential, as well as by unequal strengths of the self-and cross-repulsive nonlinearities.

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“…CONFINEMENT a. Liberated vortices The static intervortex forces between the well-separated unconfined HQVs (ω = 0) at distance R were found [24] as Uuu U * = − 2 π log ρ and…”

Section: Introductionmentioning

confidence: 99%

Confinement of half-quantized vortices in coherently coupled Bose-Einstein condensates: Simulating quark confinement in a QCD-like theory

Eto

Nitta

2018

Phys. Rev. A

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We demonstrate that the confinement of half-quantized vortices (HQVs) in coherently coupled Bose-Einstein condensates (BECs) simulates certain aspects of the confinement in SU (2) quantum chromodynamics (QCD) in 2+1 space-time dimensions. By identifying the circulation of superfluid velocity as the baryon number and the relative phase between two components as a dual gluon, we identify HQVs in a single component as electrically charged particles with a half baryon number. Further, we show that only singlet states of the relative phase of two components can stably exist as bound states of vortices, that is, a pair of vortices in each component (a baryon) and a pair of a vortex and an antivortex in the same component (a meson). We then study the dynamics of a baryon and meson; baryon is static at the equilibrium and rotates once it deviates from the equilibrium, while a meson moves with constant velocity. For both baryon and meson we verify a linear confinement and determine that they are broken, thus creating other baryons or mesons in the middle when two constituent vortices are separated by more than some critical distance, resembling QCD. I. INTRODUCTIONIn modern elementary particle physics, one of the most important and difficult problems is the confinement of quarks (and gluons) in quantum chromodynamics (QCD). What we daily observe in nature at low energy are not elementary constituents, that is, quarks and gluons but they are strongly confined to form hadrons. There are two types of hadrons: baryons, consisting of only quarks, and mesons, consisting of quarks and antiquarks. Various baryons and mesons can exist because there are several species (called as flavors) of quarks, such as up (u) and down (d). The widely accepted explanation of the confinement is that chromo-electric flux from a quark is squeezed to form a flux tube in a dual superconductor, in which magnetic monopoles are condensed [1][2][3]. Thus, the interaction energy between (anti-)quarks is proportional to the distance between them; this is a salient signal of the confinement. Although the explanation is quite plausible, it is difficult to prove it. Therefore, many studies have been conducted for QCD-like theories.From among these studies, Polyakov [4] made an important remark using a duality about a U (1) gauge theory in 2+1 space-time dimensions; this can be obtained as the low-energy limit of an SU (2) gauge theory with a triplet scalar field. The duality mentioned here is the one between the XY and Abelian-Higgs models in 2 + 1 dimensions [5,6], providing insights for understanding the fractional quantum Hall effect [7], Mott transitions [8], etc. As a photon has only one polarization in three spece-time dimensions, it can be dualized to the so-called dual photon (a periodic scalar field) θ ∈ [0, 2π) defined throughUnder the duality relation, electrically charged bosons in the original theory are interchanged by vortices in θ. The dual photon is massless in the perturbation theory but it gets mass m dp through nonperturbative monopole e...

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Interaction of half-quantized vortices in two-component Bose-Einstein condensates

Cited by 111 publications

References 57 publications

Half-Quantum Vortices in an Antiferromagnetic Spinor Bose-Einstein Condensate

Half-Quantum Vortices in an Antiferromagnetic Spinor Bose-Einstein Condensate

Vortex-soliton complexes in coupled nonlinear Schrödinger equations with unequal dispersion coefficients

Confinement of half-quantized vortices in coherently coupled Bose-Einstein condensates: Simulating quark confinement in a QCD-like theory

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