Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:0906.2174 · Physical Review A

Angular collapse of dipolar Bose-Einstein condensates

Ryan Wilson, Shai Ronen, John L. Bohn

Published Aug 20, 2009• 69 citations
arXivHTMLPDF

Abstract

We explore the structure and dynamics of dipolar Bose-Einstein condensates (DBECs) near their threshold for instability. Near this threshold a DBEC may exhibit nontrivial biconcave density distributions, which are associated with instability against collapse into ``angular roton'' modes. Here we discuss experimental signatures of these features. In the first, we infer local collapse of the DBEC from the experimental stability diagram. In the second, we explore the dynamics of collapse and find that a nontrivial angular distribution is a signature of the DBEC possessing a biconcave structure.

DOI
10.1103/physreva.80.023614

Related papers

Stability and structure of an anisotropically trapped dipolar Bose-Einstein condensate: Angular and linear rotons

A. D. Martin, P. B. Blakie

We study theoretically Bose-Einstein condensates with polarized dipolar interactions in anisotropic traps. We map the parameter space by varying the trap frequencies and dipolar interaction strengths and find an irregular-shaped region of parameter space in which density-oscillating condensate states occur, with maximum density away from the trap center. These density-oscillating states may be biconcave (red-blood-cell-shaped), or have two or four peaks. For all trap frequencies, the condensate becomes unstable to collapse for sufficiently large dipole interaction strength. The collapse coincides with the softening of an elementary excitation. When the condensate mode is density oscillating, the character of the softening excitation is related to the structure of the condensate. We classify these excitations by linear and angular characteristics. We also find excited solutions to the Gross-Pitaevskii equation, which are always unstable.

arXiv:1209.3839•Physical Review A•Nov 26, 2012•36 citations

Radial and Angular Rotons in Trapped Dipolar Gases

Shai Ronen, Daniele C. E. Bortolotti, John L. Bohn

We study Bose-Einstein condensates with purely dipolar interactions in oblate traps. We find that the condensate always becomes unstable to collapse when the number of particles is sufficiently large. We analyze the instability, and find that it is the trapped-gas analogue of the "roton-maxon" instability previously reported for a gas that is unconfined in 2D. In addition, we find that under certain circumstances the condensate wave function attains a biconcave shape, with its maximum density away from the center of the gas. These biconcave condensates become unstable due to azimuthal excitation--an angular roton.

arXiv:cond-mat/0607704•Physical Review Letters•Jan 19, 2007•244 citations

Emergent structure in a dipolar Bose gas in a one-dimensional lattice

Ryan Wilson, John L. Bohn

We consider an ultracold dipolar Bose gas in a one-dimensional lattice. For a sufficiently large lattice recoil energy, such a system becomes a series of nonoverlapping Bose-Einstein condensates that interact via the long-range dipole-dipole interaction (ddi). We model this system via a coupled set of nonlocal Gross-Pitaevskii equations (GPEs) for lattices of both infinite and finite extent. We find significantly modified stability properties in the lattice due to the softening of a discrete roton-like mode, as well as ``islands'' in parameter space where biconcave densities are predicted to exist and that only exist in the presence of the other condensates on the lattice. We solve for the elementary excitations of the system to check the dynamical stability of these solutions and to uncover the nature of their collapse. By solving a coupled set of GPEs exactly on a full numeric grid, we show that this emergent biconcave structure can be realized in a finite lattice with atomic $^{52}\mathrm{Cr}$.

arXiv:1012.6029•Physical Review A•Feb 28, 2011•29 citations

Manifestations of the Roton in Dipolar Bose-Einstein Condensates

Ryan Wilson

Today, sixteen years after the realization of the first Bose-Einstein condensate (BEC), the field of ultracold many-body physics is booming. In particular, much excitement has been generated by the prospect of creating a degenerate quantum gas of dipolar atoms or molecules. Already, some experimental groups have succeeded in Bose-condensing atomic 52Cr and 164Dy, while other groups have made significant progress towards achieving degeneracy of heteronuclear molecules, such as fermionic 40K87Rb and bosonic 87Rb133Cs, where the strength of the dipolar interaction promises to be much greater than that of the already rich 52Cr condensate. Just as the creation of BEC launched a whole new field of research, dipolar BECs are likely to do the same. However, such systems present a theoretical challenge due to the long-range, anisotropic nature of the dipolar interaction. In this thesis, I present a theoretical investigation of ultracold Bose gases with dipolar interactions.\nThe first part of this thesis is dedicated to the field theoretical treatment of a quantum Bose fluid with dipolar interactions in the ultracold, dilute regime, where the system is well-described by a classical condensate field with quasiparticle excitations. The set of nonlinear integrodifferential equations that describe these objects are derived and novel methods for solving them are presented that, in general, require intricate numerical treatment. Of particular importance is the emergence of a roton mode, reminiscent of that in superfluid 4He. In the second part of this thesis, I show how the roton plays a critical role in the ground state structure and dynamics of a dipolar BEC. Full numerical simulations show that the roton can, for example, be seen in the radial density profile of a quantized vortex state or in the angular collapse and explosion of a dipolar BEC. Additionally, I show the crucial role that this roton plays in determining the transition to superfluidity in these systems. Thus, a set of novel phenomena in ultracold dipolar Bose gases is explained by the presence of the roton, and experimental signatures of these phenomena are made clear.

•Jan 1, 2011•0 citations

Vortex to Rotons Transition in Dipolar Bose-Einstein Condensates

Alberto Villois, Miguel Onorato, Davide Proment

Dipolar Bose-Einstein condensates (dBECs) exhibit a plethora of physics phenomena, from supersolidity to the rotonlike minimum in the elementary excitation spectrum. In this work we first demonstrate the existence of axis-symmetric solitary waves in (quasi-)two-dimensional dBECs: these localized excitations are characterized by quantized vortex dipoles that continuously transit to vortex-free density depletions. We then show how the presence of the roton minimum fundamentally alters the fate of such solutions when approaching Landau's critical speed: when propagating along the polarization direction where the roton minimum occurs, the solitary wave transits into roton excitations rather than into phonons as for standard contact-interaction BECs. This finding suggests that Feynman's hypothesis, conjectured for 3D superfluid liquid helium regarding the creation of rotons as fading vortex excitations, is valid in the context of 2D dBECs.

arXiv:2407.18412•Physical Review Letters•May 30, 2025•3 citations

Roton Excitations in an Oblate Dipolar Quantum Gas

Jan-Niklas Schmidt, Jens Hertkorn, Mingyang Guo +7 more

We observe signatures of radial and angular roton excitations around a droplet crystallization transition in dipolar Bose-Einstein condensates. In situ measurements are used to characterize the density fluctuations near this transition. The static structure factor is extracted and used to identify the radial and angular roton excitations by their characteristic symmetries. These fluctuations peak as a function of the interaction strength indicating the crystallization transition of the system. We compare our observations to a theoretically calculated excitation spectrum allowing us to connect the crystallization mechanism with the softening of the angular roton modes.

arXiv:2102.01461•Physical Review Letters•May 12, 2021•72 citations
We explore the structure and dynamics of dipolar Bose-Einstein condensates (DBECs) near their threshold for instability. Near this threshold a DBEC may exhibit nontrivial biconcave density distributions, which are associated with instability against collapse into ``angular roton'' modes. Here we discuss experimental signatures of these features. In the first, we infer local collapse of the DBEC from the experimental stability diagram. In the second, we explore the dynamics of collapse and find that a nontrivial angular distribution is a signature of the DBEC possessing a biconcave structure.
We study theoretically Bose-Einstein condensates with polarized dipolar interactions in anisotropic traps. We map the parameter space by varying the trap frequencies and dipolar interaction strengths and find an irregular-shaped region of parameter space in which density-oscillating condensate states occur, with maximum density away from the trap center. These density-oscillating states may be biconcave (red-blood-cell-shaped), or have two or four peaks. For all trap frequencies, the condensate becomes unstable to collapse for sufficiently large dipole interaction strength. The collapse coincides with the softening of an elementary excitation. When the condensate mode is density oscillating, the character of the softening excitation is related to the structure of the condensate. We classify these excitations by linear and angular characteristics. We also find excited solutions to the Gross-Pitaevskii equation, which are always unstable.
We study Bose-Einstein condensates with purely dipolar interactions in oblate traps. We find that the condensate always becomes unstable to collapse when the number of particles is sufficiently large. We analyze the instability, and find that it is the trapped-gas analogue of the "roton-maxon" instability previously reported for a gas that is unconfined in 2D. In addition, we find that under certain circumstances the condensate wave function attains a biconcave shape, with its maximum density away from the center of the gas. These biconcave condensates become unstable due to azimuthal excitation--an angular roton.
We consider an ultracold dipolar Bose gas in a one-dimensional lattice. For a sufficiently large lattice recoil energy, such a system becomes a series of nonoverlapping Bose-Einstein condensates that interact via the long-range dipole-dipole interaction (ddi). We model this system via a coupled set of nonlocal Gross-Pitaevskii equations (GPEs) for lattices of both infinite and finite extent. We find significantly modified stability properties in the lattice due to the softening of a discrete roton-like mode, as well as ``islands'' in parameter space where biconcave densities are predicted to exist and that only exist in the presence of the other condensates on the lattice. We solve for the elementary excitations of the system to check the dynamical stability of these solutions and to uncover the nature of their collapse. By solving a coupled set of GPEs exactly on a full numeric grid, we show that this emergent biconcave structure can be realized in a finite lattice with atomic 52Cr^{52}\mathrm{Cr}52Cr.
Today, sixteen years after the realization of the first Bose-Einstein condensate (BEC), the field of ultracold many-body physics is booming. In particular, much excitement has been generated by the prospect of creating a degenerate quantum gas of dipolar atoms or molecules. Already, some experimental groups have succeeded in Bose-condensing atomic 52Cr and 164Dy, while other groups have made significant progress towards achieving degeneracy of heteronuclear molecules, such as fermionic 40K87Rb and bosonic 87Rb133Cs, where the strength of the dipolar interaction promises to be much greater than that of the already rich 52Cr condensate. Just as the creation of BEC launched a whole new field of research, dipolar BECs are likely to do the same. However, such systems present a theoretical challenge due to the long-range, anisotropic nature of the dipolar interaction. In this thesis, I present a theoretical investigation of ultracold Bose gases with dipolar interactions.\nThe first part of this thesis is dedicated to the field theoretical treatment of a quantum Bose fluid with dipolar interactions in the ultracold, dilute regime, where the system is well-described by a classical condensate field with quasiparticle excitations. The set of nonlinear integrodifferential equations that describe these objects are derived and novel methods for solving them are presented that, in general, require intricate numerical treatment. Of particular importance is the emergence of a roton mode, reminiscent of that in superfluid 4He. In the second part of this thesis, I show how the roton plays a critical role in the ground state structure and dynamics of a dipolar BEC. Full numerical simulations show that the roton can, for example, be seen in the radial density profile of a quantized vortex state or in the angular collapse and explosion of a dipolar BEC. Additionally, I show the crucial role that this roton plays in determining the transition to superfluidity in these systems. Thus, a set of novel phenomena in ultracold dipolar Bose gases is explained by the presence of the roton, and experimental signatures of these phenomena are made clear.
Dipolar Bose-Einstein condensates (dBECs) exhibit a plethora of physics phenomena, from supersolidity to the rotonlike minimum in the elementary excitation spectrum. In this work we first demonstrate the existence of axis-symmetric solitary waves in (quasi-)two-dimensional dBECs: these localized excitations are characterized by quantized vortex dipoles that continuously transit to vortex-free density depletions. We then show how the presence of the roton minimum fundamentally alters the fate of such solutions when approaching Landau's critical speed: when propagating along the polarization direction where the roton minimum occurs, the solitary wave transits into roton excitations rather than into phonons as for standard contact-interaction BECs. This finding suggests that Feynman's hypothesis, conjectured for 3D superfluid liquid helium regarding the creation of rotons as fading vortex excitations, is valid in the context of 2D dBECs.
We observe signatures of radial and angular roton excitations around a droplet crystallization transition in dipolar Bose-Einstein condensates. In situ measurements are used to characterize the density fluctuations near this transition. The static structure factor is extracted and used to identify the radial and angular roton excitations by their characteristic symmetries. These fluctuations peak as a function of the interaction strength indicating the crystallization transition of the system. We compare our observations to a theoretically calculated excitation spectrum allowing us to connect the crystallization mechanism with the softening of the angular roton modes.