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.
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]
Fluorescence microscopy of individual atoms in an optical lattice
We demonstrate fluorescence microscopy of individual fermionic potassium atoms in a 527-nm-period optical lattice. Using electromagnetically induced transparency (EIT) cooling on the 770.1-nm D1 transition of 40K, we find that atoms remain at individual sites of a 0.3-mK-deep lattice, with a 1/e pinning lifetime of 67(9)s, while scattering ~1000 photons per second. The plane to be imaged is isolated using microwave spectroscopy in a magnetic field gradient, and can be chosen at any depth within the three-dimensional lattice. With a similar protocol, we also demonstrate patterned selection within a single lattice plane. High resolution images are acquired using a microscope objective with 0.8 numerical aperture, from which we determine the occupation of lattice sites in the imaging plane with 94(2)% fidelity per atom. Imaging with single-atom sensitivity and addressing with single-site accuracy are key steps towards the search for unconventional superfluidity of fermions in optical lattices, the initialization and characterization of transport and non-equilibrium dynamics, and the observation of magnetic domains.
Edge et al., Physical Review A 92, 063406 (2015) as ''Editors' Suggestion''
[doi: 10.1103/PhysRevA.92.063406][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!