NOTE: End date changed to 9/30/2025 per D. Griffin/NASA-HQ (Ed., 1/20/25).

NOTE: Contract number changed to JPL 1699891 per J. Callas/JPL (Ed., 8/29/24).

NOTE: End date changed to 9/27/2024 per U. Israelsson/JPL (Ed., 10/20/21)

NOTE: End date changed to 3/31/2022 per B. Carpenter/NASA HQ (Ed., 1/4/2021)

NOTE: New end date is 10/30/2020 per JPL (Ed., 5/21/19)

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Modeling efforts focused on understanding the magnetic-field variation in the SM1 hardware and the effects on ultracold bubble formation. We have found the relevant radiofrequency (rf) resonances of multiple CAL traps and characterized their mechanical oscillation frequencies. Following resonance-finding we were able to demonstrate (in August 2024) that rf-dressing for bubble generation was feasible on SM1 hardware. Current efforts will focus on demonstrating adiabatic transport and radiofrequency dressing into a aspect-ratio ~2 bubble (in contrast to aspect ratio 3 or 4 bubbles of previous work). We have returned to calculations and discussions with Barry Garraway of Sussex University regarding techniques of compensating rf inhomogeneity using microwave radiation, in a process known as 'dual dressing'. Such a technique might be possible aboard CAL.

Dr. Lundblad was central planner of this work in this period, together with our partner at Jet Propulsion Laboratory (JPL), David Aveline, who, in addition to service as Co-Investigator, was our primary liaison to experimental operations aboard CAL. Postdoctoral scholars Gerent and Beregi at Bates College have supported the project through experimental planning and modeling. Theory Co-Investigators Smitha Vishveshwara and senior graduate student Brendan Rhyno provided regular insight and support, especially in regard to computational modeling of observed phenomena. Rhyno defended his PhD thesis in November 2024 (see bibliography), representing the culmination of many years of work investigating the physics of ultracold bubbles. The interesting phenomena that this project focuses on was dissemenated in many research-group seminars, department seminars, conference presentations, and posters.

NOTE: End date changed to 9/30/2025 per D. Griffin/NASA-HQ (Ed., 1/20/25).

NOTE: Contract number changed to JPL 1699891 per J. Callas/JPL (Ed., 8/29/24).

NOTE: End date changed to 9/27/2024 per U. Israelsson/JPL (Ed., 10/20/21)

NOTE: End date changed to 3/31/2022 per B. Carpenter/NASA HQ (Ed., 1/4/2021)

NOTE: New end date is 10/30/2020 per JPL (Ed., 5/21/19)

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Results of our research activities were presented at several conferences and international workshops, including the 2023 Bad Honnef ultracold atomic physics summer school ( https://www.dpg-physik.de/veranstaltungen/2023/ultracold_atoms_and_molecules ). [Ed. Note: See Bibliography.]

NOTE: End date changed to 9/27/2024 per U. Israelsson/JPL (Ed., 10/20/21)

NOTE: End date changed to 3/31/2022 per B. Carpenter/NASA HQ (Ed., 1/4/2021)

NOTE: New end date is 10/30/2020 per JPL (Ed., 5/21/19)

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Many years of effort from students and postdocs culminated in final analysis related to (and writing of a) paper presenting our first results from the CAL experiment. "Observation of ultracold atomic bubbles in orbital microgravity" was published in the journal Nature ( https://www.nature.com/articles/s41586-022-04639-8 ).

A review article of interest in bubble physics was published: "Perspective on quantum bubbles in microgravity." Quantum Sci Technology 8, 024003 (2023). https://iopscience.iop.org/article/10.1088/2058-9565/acb1cf/meta .

Results of our research activities were presented at several conferences and international workshops, including the 2022 American Physical Society (APS) Meeting of the Division of Atomic, Molecular, and Optical Physics (DAMOP), Sao Paolo Workshop on Low Dimensional Quantum Gases (March 2023), Heraeus 777 (Ultracold Matter and Applications, December 2022), and FINESS 2022 (Finite Temperature Non-equilibrium Superfluid Systems Conference - May 2022).

[Ed. Note: See Bibliography for complete citations.]

NOTE: End date changed to 9/27/2024 per U. Israelsson/JPL (Ed., 10/20/21)

NOTE: End date changed to 3/31/2022 per B. Carpenter/NASA HQ (Ed., 1/4/2021)

NOTE: New end date is 10/30/2020 per JPL (Ed., 5/21/19)

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Continued theoretical development occurred within the shell collaboration, leading to published work from Rhyno, et al. focusing on thermodynamics in ultracold shells ( https://doi.org/10.1103/PhysRevA.104.063310 ). Lundblad also continued collaborative discussion with Dr. Barry Garraway of Sussex regarding the potential to use microwave fields aboard CAL to enhance bubble quality; a document regarding this technique titled "Optimised shell potential for microgravity Bose-Einstein condensates" is in final preparation.

Many years of effort from students and postdocs culminated in final analysis related to (and writing of a) paper presenting our first results from the CAL experiment. "Observation of ultracold atomic bubbles in orbital microgravity" is in press in the journal Nature, and is also available on the arXiv preprint server ( https://arxiv.org/abs/2108.05880).

Results of our research activities were presented at several conferences, including the 2021 American Physical Society (APS) Meeting of the Division of Atomic, Molecular, and Optical Physics (DAMOP). Additionally, Lundblad presented these results at the 2021 Marcel Grossman meetings.

NOTE: End date changed to 9/27/2024 per U. Israelsson/JPL (Ed., 10/20/21)

NOTE: End date changed to 3/31/2022 per B. Carpenter/NASA HQ (Ed., 1/4/2021)

NOTE: New end date is 10/30/2020 per JPL (Ed., 5/21/19)

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Phase 1 ("SM2") of the operation continued until the end of calendar 2019. Our datasets from this period focus on the generation of ultracold shell systems, confirming theoretical predictions that microgravity would enable their occurrence. We performed thermometry on the resulting shells as a function of size, and also explored the wide variety of shell sizes that could be created with this protocol. Reduction and analysis of this data is in process. A key conclusion of this work appears to be that while ultracold shells are possible in microgravity, maintaining the BEC state across the inflation process is difficult, due to nonadiabiaticity and low initial condensate fraction. Nevertheless, these observations represent physics impossible (or prohibitively difficult) to observe in a terrestrial setting, and have opened a new pathway in ultracold atomic physics research enabled by CAL and the International Space Station (ISS).

Phase 2 ("SM3") of the CAL operation commenced soon after and is ongoing. With a new atom chip geometry, SM3 permits us to explore shells with more spherical aspect ratios and possessing reduced inhomogeneity due to a larger rf coil. We have explored the parameter space of shell geometry and temperature with several different trap configurations, and we have also initiated an effort to use CAL's atom-interferometer Bragg beam to probe the nature of these ultracold shells. Looking ahead to upcoming upgrades, we hope to apply a second rf/microwave field in order to evaporatively cool the samples in the shell, thereby avoiding the heating associated with shell inflation; we also hope to use an additional signal associated with an upcoming upgrade to perform rf/microwave spectroscopy of the shell state in order to better understand the nature of Bose–Einstein condensation in a shell geometry.

Continued theoretical development occurred within the shell collaboration, leading to published work from Padavic et al. focusing on potential vortex physics in ultracold shells. Lundblad also continued collaborative discussions with Dr. Barry Garraway of Sussex regarding the potential to use microwave fields aboard CAL to enhance bubble quality.

Many years of modeling effort from students and postdocs culminated in a paper presenting the idea of the shell project and realistic modeling of its experimental sequences ( https://doi.org/10.1038/s41526-019-0087-y ; see also Bibliography section). This paper is proving to be a useful resource for theorists around the world seeking to obtain a sense of the capabilities of CAL in the shell-physics context.

Results of our research activities were presented at several conferences, including the 2019 and 2020 American Physical Society (APS) Meetings of the Division of Atomic, Molecular, and Optical Physics (DAMOP). Additionally, Lundblad traveled to the December 2019 workshop in Ulm, Germany, focusing on the development of a successor instrument to CAL (Bose-Einstein Condensate and Cold Atom Laboratory (BECCAL)), and presented preliminary data.

NOTE: New end date is 10/30/2020 per JPL (Ed., 5/21/19)

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Data focused on understanding residual micromotion in the expanded atom traps (‘sloshing’) and validation of trap models--preliminary results largely show agreement at the few-percent level in trap frequencies.

Initial attempts at generating shell-trapped ultracold clouds-- the central goal of this project-- were made, and showed preliminary positive signs, although anticipated inhomogeneities appear to play expected roles.

Further communication took place between Co-Investigator (Co-I) Aveline and Principal Investigator (PI) Lundblad regarding flight hardware, and detailed communication took place between Co-I Lannert and PI Lundblad regarding numerical simulation of these CAL experiments.

Lundblad also extended collaborative work with other theorists in the field regarding specific modeling issues, particularly Barry Garraway of Sussex. Progress on the construction of CAL-like prototype hardware at Bates was begun using a newly-arrived atom chip apparatus from ColdQuanta. Lundblad’s work continued to focused mostly on understanding potential issues with trap inhomogeneity aboard CAL that could result in incomplete shell-BEC population or asymmetric shells, as well as beginning to model adiabaticity in these systems.

Lannert and Vishveshwara’s work continued to focus on simulation of collective modes, and led to a paper published (Sun, K., Padavic, K., Yang, F., Vishveshwara, S. & Lannert, C. Static and dynamic properties of shell-shaped condensates. Phys Rev A 98, 013609 (2018).)

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Lannert and Vishveshwara’s work continued to focus on simulation of collective modes, and led to a paper published and another in review ("Static and Dynamic Properties of Shell-shaped Condensates" https://arxiv.org/abs/1712.04428 ).

Work with Aveline continued to address validation issues remaining after the 2015 SCR (science concept review), and led to a successful CAL ORT in April 2018.

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Lundblad’s work continued to focused mostly on understanding potential issues with trap inhomogeneity aboard CAL that could result in incomplete shell-BEC population or asymmetric shells. A significant insight was gained regarding potential correction of antenna-coupling inhomogeneity which should be implemented on future versions of CAL.

Lannert and Vishveshwara’s work continued to focus on simulation of collective modes, and led to a paper currently in review ("Physics of hollow Bose-Einstein condensates." https://arxiv.org/abs/1612.05809 ).

Work with Aveline continued to address validation issues remaining after the 2015 Science Concept Review (SCR).

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Lundblad’s work focused mostly on understanding potential issues with trap inhomogeneity aboard CAL that could result in incomplete shell-BEC population or asymmetric shells. The significant insights here were that the asymmetric anharmonicity of the atom-chip trap, as well as the impossibility of unity aspect ratio, are prime sources of inhomogeneity. Additionally, the rf antenna results in an inhomogeneous rf coupling which we continue to model. The model outputs are potential-energy surfaces for various chip-current configurations.

Lannert’s work focused on numerical simulations (Gross-Pitaevskii) of collective excitations and ballistic-flight interference of shell BECs. They were guided by model potential-energy surfaces provided by Lundblad. This work has led to a publication in preparation, and resulted in a new collaboration with Prof. Smitha Vishveshwara of the University of Illinois.

Together with JPL testbed work performed by Aveline allowing validation of the general proposed concepts, this collaboration passed the NASA Science Concept Review in August 2015.

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e., a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the Cold Atom Laboratory (CAL) “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.

Lundblad at Bates College and Aveline at Jet Propulsion Laboratory (JPL) focused on the details of how precisely a bubble-geometry Bose-Einstein condensate will be formed given the particular nature of the magnetic trap that will lie at the heart of CAL. In particular, they focused on trap symmetry, requisite trap homogeneity, and studied requirements for the actual apparatus. Aveline and Lundblad convened at Bates College for a workshop on this material in the summer of 2014.

Lannert at Smith College/UMass performed theoretical calculations of a Bose-Einstein condensate trapped in a shell/bubble potential, in particular characterizing how such gas shakes or quivers when excited. These calculations will inform our plans to do experiments related to this shaking or quivering on the CAL flight experiment. Since bubble-geometry Bose-Einstein condensates do not exist terrestrially this will be a novel experiment. Lannert and Lundblad convened at Bates College for a workshop on this material in August 2014.

In summary, considerable progress was made in the understanding of how one might be able to use the CAL apparatus to generate bubble/shell geometries for Bose-Einstein condensates. Further work this coming year will focus on specific implementation of various concept and calibration experiments using the CAL testbed, exploring theoretical modeling of the shell condensate at a more sophisticated level, and beginning construction on a CAL-like machine at Bates College, under the supervision of a postdoctoral fellow.

We propose a specific program to explore a trapping geometry for quantum gases that is both tantalizing theoretically and prohibitively difficult to attain terrestrially: a quantum gas in a bubble geometry, i.e. a trap formed by a spherical or ellipsoidal shell structure, confining a 2D quantum gas to the surface of an experimentally-controlled topologically-connected “bubble.” The physics of a quantum gas confined to such a surface has not been explored terrestrially due to the limitations of gravitational sag; interesting work has certainly been done with gases confined to the lower regions of bubble potentials, but the fully symmetric situation has yet to be explored. The low-energy excitations of such a system are unexplored, and notions of vortex creation and behavior as well as Kosterlitz-Thouless physics are tantalizing aims as well. The solid-state modeling goals of the optical-lattice physics community are also fundamentally connected to the system, as the canonical Mott-insulator/superfluid transition features superfluid shells isolated between insulating regions.

The central method to reach the sought-after bubble-geometry BEC or DFG is that of rf or microwave dressing of the bare trapping potentials provided by the CAL “chip trap.” Radiofrequency dressing has been used conceptually through "rf-knife" evaporative cooling, but more recently through explicit construction of adiabatic potentials for interferometry, and shell-trap construction for both thermal and quantum gases. The proposed work is a window into a physical regime that is quite difficult to achieve terrestrially due to trap distortion; given the advantages of a microgravity environment, NASA CAL is uniquely positioned to realize the physics goals of this proposal.