Ultracold Atoms Group | University of Toronto
We are an experimental atomic physics group studying trapped ultracold atomic gases. We use ultracold fermionic potassium to study a variety of quantum mechanical condensed matter and atomic physics problems. Research interests include non-equilibrium phenomena, Fermi gases near unitarity, novel laser cooling techniques, quantum simulation, and quantum information.
Located in the physics department of the University of Toronto, we are part of the vibrant scientific community here in Toronto. Other exciting research in physics at the university may be found here.
Observation of unitary p-wave interactions between fermions in an optical lattice
The realisation of exchange-antisymmetric pair wavefunctions in controllable quantum systems, such as ultracold gases, could enable new types of quantum simulations, topological quantum gates, and exotic few-body states. However, p-wave and other antisymmetric interactions are weak in naturally occurring systems, and their enhancement via Feshbach resonances in ultracold systems has been limited by three-body loss. Here we create isolated pairs of spin-polarised fermionic atoms in a multi-orbital three-dimensional optical lattice. We spectroscopically measure elastic p-wave interaction energies of strongly interacting pairs of atoms near a magnetic Feshbach resonance and find pair lifetimes to be up to fifty times larger than in free space. We demonstrate that on-site interaction strengths can be widely tuned by the magnetic field and confinement strength but collapse onto a universal single-parameter curve when rescaled by the harmonic energy and length scales of a single lattice site. Since three-body processes are absent within our approach, we are able to observe elastic unitary p-wave interactions for the first time. We take the first steps towards coherent temporal control via Rabi oscillations between free-atom and interacting-pair states. All experimental observations are compared both to an exact solution for two harmonically confined atoms interacting via a p-wave pseudopotential, and to numerical solutions using an ab-initio interaction potential. The understanding and control of on-site p-wave interactions provides a necessary component for the assembly of multi-orbital lattice models, and a starting point for investigations of how to protect such a system from three-body recombination even in the presence of tunnelling.
V. Venu, P. Xu, M. Mamaev, F. Corapi, T. Bilitewski, J. P. D'Incao, C. J. Fujiwara, A. M. Rey, J. H. Thywissen
Probing open and closed channel p-wave resonances
We study the interplay between a p-wave Feshbach resonance and an open channel shape resonance using a variety of theoretical techniques and experimental measurements. Good agreement between our rf spectra (above in blue) and theoretical lineshape theory (red lines) allow us to precisely characterize this resonance. The cartoons (b,d,f,h) show the levels involved in resonant association (RA) and spin flip association (SFA) spectroscopy for both bound and quasi-bound states. We find excellent agreement with coupled-channels calculations and develop a simplified two-channel model that takes into account the open channel shape resonance, the Feshbach resonance, and weak dipole-dipole interactions.
Ahmed-Braun et al., Physical Review Research 3, 033269 (2021)
Transition between dynamical phases
We have observed a phase transition between two dynamical phases in a harmonically trapped ultracold Fermi gas. This transition is between a paramagnet like state (A), in which the total magnetization of the trapped atoms decreases quickly, and a dynamical ferromagnet state (C-E) where the magnetization is protected by the opening of an energy gap. The agreement between our data and theory (red lines) validates the mapping between our harmonically trapped atoms and the collective Heisenberg spin model on a lattice composed of the harmonic oscillator modes.
Smale et al., Science Advances, 5, eaax1568 (2019)
[doi:10.1126/sciadv.aax1568] [journal link]
Measuring a.c. conductivity in an optical lattice
Using a.c. conductivity spectra for ultracold potassium 40 in a cubic lattice, we find the spectral weight at low frequency. For variable number (N), deposited heat (Q), scattering length (as), and lattice depth (V), the data collapses onto the expected response of a single-band Hubbard model. At hight T/t (temperature divided by tunnelling energy), the data approaches a 1/T regime (dashed black line). Inset: Scattering does not "destroy" conductivity, but only moves it from one part of the spectrum to another, leaving spectral weight and band mass relatively unchanged.
Anderson et al., Physical Review Letters, 122, 153602 (2019)
[doi: 10.1103/PhysRevLett.122.153602] [journal link]
Quantum-limited spin transport
We have observed quantum-limited spin transport in strongly interacting two-dimensional Fermi gases. We measure the rate of demagnetization of polarized samples in the presence of a magnetic field gradient, which drives coherence-eroding spin currents. We found that a lower bound on spin diffusivity, of roughly hbar/m, is respected for all interaction strengths, temperatures, and applied gradients accessible in our setup.
Luciuk et al., Physical Review Letters, 118, 130405 (2017)
[doi: 10.1103/PhysRevLett.118.130405] [journal link]
January.2020: Cora Fujiwara joins the lab as a Postdoctoral Fellow. Welcome!
September.2019: Colin Dale, Darby Bates, and Frank Corapi officialy join the lab officially. Welcome!
August.2019: Our dynamical phase transition paper has been published in Science Advances.
June.2019: Rongzi Zhou joins the lab as a visiting undergrad. Welcome!
May.2019: Colin Dale and Frank Corapi join the lab on pre-PhD placements. Welcome!
May.2019: Hanzhen Lin and Daniel Venn join the lab for NSERC USRAs. Welcome!
April.2019: Our conductivity paper appears in PRL.
March.2019: Kenneth is officially Qualified!
March.2019: Alena Nierhauve starts working in the lab. Welcome!
Oct.2018: Lennard Miller (on exchange from Strathclyde) joins the lab for the year. Welcome!
Sept.2018: Haille and Matt both earn their M.Sc. Congratulations!
July.2018: Ben leaves to start a new lab with a faculty position at YaleNUS in Singnapore. Congratulations, and best of luck!
May.2018: Michael Morris, Bernie Hsu, and Wentao Cui start NSERC summer terms. Welcome!
Sept.2017: Graham Edge is awarded the Dimitris N. Chorafas Foundation award for outstanding doctoral work. Congratulations!
Sept.2017: Kenneth Jackson and Matthew Taylor join the group. Welcome!
Jun.2017: Vijin passes qualifying exam
Jun.2017: Chris is now Dr. Luciuk
Jun.2017: Stefan moves to Metamaterials Technologies (Halifax) as Senior Optical Engineer
May.2017: Peihang passes qualifying exam
May.2017: Chris passes departmental PhD exam
Apr.2017: Tristan Gauti arrives for a summer internship. Welcome!
Mar.2017: 2D spin transport paper appears in PRL.
Dec.2016: Graham Edge passes final Ph.D. defence! Next up: postdoc in the Vutha group.
Dec.2016: Preprint available describing our observations of quantum-limited spin transport in 2D Fermi gases.
Sept.2016: Ben Olsen and Fudong Wang arrive and join the lab as new post-docs. Welcome!
Sept.2016: Vijin passes MSc exam!
Aug.2016: Joseph presenting at Quantum Gases 2016 in Beijing.
July.2016: Geyue (Frank) Cai arrives from HKUST for a 10-week internship
2015-16: Five group alum have recently started faculty positions: Brian Shuve (at Harvey Mudd), Swati Singh (at Williams), David Shirokoff (at NJIT), John Simpson (at Waterloo), and Hyun Youk (at TU Delft). Congratulations all !
June.2016: Joseph presenting p-wave results at EQM2016 in St. Andrews, Scotland
Apr.2016:Masahito Ueda writes Fermi gases: anisotropic universality in Nature News & Views, on our p-wave contact observation.
Feb.2016: Fabian Böttcher arrives from Stuttgart for a 3-month visit
Feb.2016: Our p-wave contact discovery appears online in Nature Physics!
Dec.2015: Fermi gas microscope paper chosen as ``Editor's Suggestion'' in PRA
Oct.2015: Preprint available on our imaging of individual fermionic atoms in an optical lattice
Sept.2015: Marcius joins XPRIZE as Director of Technical Operations for the Carbon XPRIZE
Sep.2015: Joseph presenting at the BEC conference in Sant Feliu, Spain
Sep.2015: Vijin, Peihang, and Haille join the group. Welcome!
Aug.2015: Rhys passes qualifying exam
Aug.2015: Daniel passes M.Sc exam!
Jun.2015: Joseph presenting at Gordon conference
Jun.2015: Joseph, Rhys, and Chris presenting at DAMOP in Columbus
June.2015: Alma joins Morgan Solar, Inc. !
Apr.2015: Graham presenting at YAO in Zurich
Jan.2015: David McKay starts Research Staff position at IBM Watson Labs. Congratulations!
Mar.2015: First images of individual 40K atoms in a lattice!
Dec.2014: Scott passes M.Sc. exam!
Dec.2014: Leggett-Rice paper accepted to PRL!
Oct.2014:Preprint available on our observation of the Leggett-Rice effect in a unitary Fermi gas
Oct.2014: Nicolas Zuber arrives from Stuttgart for an 18-week research training visit
Aug.2014: Ryan becomes "Master Day"
Jul.2014: Dylan starts new job at Aerodyne Research; Alma starts postdoc at Sunnybrook.
Jun.2014: Dylan defends Ph.D. Congratulations!
May.2014: Alma defends Ph.D. Congratulations!
May.2014: Our article out in Science!
May.2014: Chris passes qualifying exam: now ABD...all-but-dissertation.
Mar.2014: Scott Beattie accepts position at NRC in Ottawa. Congratulations!