**Overview**

Our group is generally interested in analog quantum simulation by which quantum systems would be especially apt at simulating actual physical quantum behavior in material. This requires sophistcated Hamiltonian engineering in the quantum system that consists of ultracold atoms. Various engineered Hamiltonians have been developed and implemented in our apparatus, which allows us to explore the synthetic quantum systems and material including but not limited to:

- Spin-orbit-coupeld fermionic system
- Topolgical matter in lattices
- SU(N) Fermi liuqid
- Dipolar bosonic fluid
- Non-Hermitian Quantum system (Open quantum system)

**Yb | quantum simulator**

Design, Synthesize and Simulate Topological Matter with ultracold fermions The driving force of this project is the curiosity and desire to quantum simulate exotic quantum phases beyond the natural conditions in an artificial system. Using ultracold ytterbium fermions trapped in engineered optical lattices, we aim to engineer the band structure and its topological nature by which topological phases in different dimensions can be experimentally explored.

Ultracold Fermions To mimic electron's behaviour in solids, we first prepare a gas of fermion in ultracold regime around 50nK above the absolute zero. This sample allows us to explore numerous quantum phenomena likewise exotic quantum materials.

**Reference**

[1] Bo Song, Long Zhang, Chengdong He, Ting Fung Jeffrey Poon,Elnur Hajiyev,Shanchao Zhang, Xiong-Jun Liu and Gyu-Boong Jo Observation of a symmetry-protected topological phase with ultracold fermions

[2] Bo Song, Chengdong He, Shanchao Zhang, Elnur Hajiyev, Wei Huang, Xiong-Jun Liu, Gyu-Boong Jo Spin-orbit-coupled two-electron Fermi gases of ytterbium atoms

[3] Bo Song, Yueyang Zou, Shanchao Zhang, Chang-woo Cho, Gyu-Boong Jo A cost-effective high-flux source of cold ytterbium atoms Applied Physics B, 122:250 (2016)

**Science Advances 4**, eaao4748 (2018)[2] Bo Song, Chengdong He, Shanchao Zhang, Elnur Hajiyev, Wei Huang, Xiong-Jun Liu, Gyu-Boong Jo Spin-orbit-coupled two-electron Fermi gases of ytterbium atoms

**Physical Review A Rapid Communications 94**, 061604(R) (2016)[3] Bo Song, Yueyang Zou, Shanchao Zhang, Chang-woo Cho, Gyu-Boong Jo A cost-effective high-flux source of cold ytterbium atoms Applied Physics B, 122:250 (2016)

**Previous Research Projects at UC Berkeley**

Optical Kagome superlattice

In this project, the optical version of kagome lattice was realized for the first time by trapping rubidium-87 atoms in a

bichromatic superlattice. The kagome optical lattice is expected to pave the way for characterizing and manipulating a new frustrated quantum material with ultracold atoms. The team examined phase transitions in a structure-dependent superfluid-Mott by employing the tunable triangular–kago me geometry. In parallel, the team investigated the magnetic properties of the spinor Bose gas by employing spin-sensitive spin-echo imaging with high optical resolution.

Geometry-driven Mott insulator transition

** **** ****The mean-field treatment of the Bose-Hubbard model predicts properties of lattice-trapped gases to be insensitive to the specific lattice geometry once system energies are scaled by the lattice coordination number z. We test this scaling directly by comparing coherence properties of 87Rb gases that are driven across the superfluid to Mott insulator transition within optical lattices of either the kagome (z 1⁄4 4) or the triangular (z 1⁄4 6) geometries. The coherent fraction measured for atoms in the kagome lattice is lower than for those in a triangular lattice with the same interaction and tunneling energies. A comparison of measurements from both lattices agrees quantitatively with the scaling prediction. **

Magnetism in a spin Bose-Einstein condensate

** **** **observing domain coarsening and a strong dependence of the equilibration dynamics on the quadratic Zeeman shift q. For small values of |q|, the textures arrive at a configuration independent of the initial spin-state composition, characterized by large length-scale spin domains and the establishment of easy-axis (negative q) or easy-plane (positive q) magnetic anisotropy. For larger |q|, equilibration is delayed as the spin-state composition of the degenerate spinor gas remains close to its initial value. These observations support the mean-field equilibrium phase diagram predicted for a ferromagnetic spinor Bose-Einstein condensate and also illustrate that equilibration is achieved under a narrow range of experimental settings, making the F=1 87Rb gas more suitable for studies of nonequilibrium quantum dynamics.

**Reference**

[1] C.K. Thomas, T.H. Barter, T. Leung, M. Okano, G.-B. Jo, J. Guzman, I. Kimchi, A. Vishwanath, D.M. Stamper-Kurn Mean-field scaling of the superfluid to Mott insulator transition in a 2D optical superlattice

**Physical Review Letters 119**, 100402 (2017)

[2] Gyu-Boong Jo, Jennie Guzman, Claire K. Thomas, Pavan Hosur, Ashvin Viswanath, and Dan M. Stamper-Kurn .Ultracold Atoms in a Tunable Optical Kagome Lattice

**Physical Review Letters 108**045305 (2012)

[3] J.Guzman, G.-B.Jo, A.N. Wenz, K.W. Murch, C.K. Thomas, D.M. Stamper-Kurn Long Time scale dynamics in a degenerate F=1 Rb spinor condensate

**Physical Review A 84**063625 (2011)

**Previous Research Projects at MIT**

Many-body-enhanced Atom Interferometry In this project, we addressed how many- body phenomena can enhance the quantum coherence of Bose-Einstein condensates in a double-well Josephson junction realized in an micro-fabricated atom chip. One example is a non-classical number-squeezed state of BECs induced from mean-field interaction effects, confirmed by matter-wave interferometry. This seminal work has been regarded as a proof of principle experiment for confined matter-wave interferometry with phase coherence times up to 200ms. With a controllable Josephson junction filled with bosonic superfluid, it was also demonstrated the generation of dark solitons by merging two condensates leads to phase-sensitive dissipation.

**Reference**

[1] G.-B. Jo, J.H. Choi, C.A. Christensen, Y.R. Lee, T.A. Pasquini, W. Ketterle, and D.E. Pritchard Matter-Wave Interferometry with Phase Fluctuating Bose-Einstein Condensates

**Physical Review Letters 99**, 240406 (2007)[2] G.-B. Jo, J.-H. Choi , C.A. Christensen, T.A. Pasquini, Y.-R. Lee, W. Ketterle, and D.E. Pritchard Phase Sensitive Recombination of Two Bose-Einstein Condensates on an Atom Chip

**Physical Review Letters 98**, 180401 (2007)[3] G.-B. Jo, Y. Shin, S. Will, T. A. Pasquini, M. Saba, W. Ketterle , D. E. Pritchard, M. Vengalattore, and M. PrentissLong Phase Coherence Time and Number Squeezing of two Bose-Einstein Condensates on an Atom Chip

**Physical Review Letters 98**, 030407 (2007) Atom optics in a hollow-core Photonics crystal fiber Ultracold sodium atoms have been trapped inside a hollow-core optical fiber. The atoms are transferred from a free-space optical dipole trap into a trap formed by a red-detuned Gaussian light mode confined to the core of the fiber. We show that at least 5% of the atoms held initially in the free-space trap can be loaded into the core of the fiber and retrieved outside. Trapped atoms in a fiver can serve as a confined atom interferometer, which can tremendously enhance the interrogation time. Furthermore, the high-density atomic ensemble allows for us to explore non-linear quantum optics in the presence of strong coupling between atoms and photons inside the finer

**Reference**

[1] C.A. Christensen, S. Will, M. Saba, G.-B. Jo, Y.Shin, W. Ketterle, and D.E. Pritchard Trapping of Ultracold Atoms in a Hollow-core Photonic Crystal Fiber

**Physical Review A 78**033429 (2008)Atom optics : Quantum reflection With ultracold atoms, we address how quantum reflection of
BECs differs from the reflection of single atoms and understand the role of interatomic interactions before, during, and
after reflection. Using atom optics technique we found a
saturation of the reflection probability at low incident
velocity, suggesting that the description of quantum reflection is incomplete. We propose a simple theoretical extension incorporating a mean-field potential which is found to
dramatically suppress the reflection probability near zero
velocity. Further, we observe that interactions between the
incident and reflected condensate lead to predicted collective excitations of the reflected condensate and incoherent scattering.

**Reference**

[1] T. A. Pasquini, M. Saba, G.-B. Jo, Y. Shin, W. Ketterle, D. E. Pritchard, T. A. Savas, N. Mulders

**Physical Review Letters****97**, 260402 (2006)