- Sylvain Capponi (LPT, Toulouse): Numerical study of one-dimensional SU(N) cold atomic Fermi gases — from molecular Luttinger liquids to topological phases
Alkaline-earth and ytterbium cold atomic gases make it possible to simulate SU(N)-symmetric fermionic systems in a very controlled fashion. Such a high symmetry is expected to give rise to a variety of novel phenomena ranging from molecular Luttinger liquids to (symmetry- protected) topological phases. We review some of the phases that can be stabilized in a one dimensional lattice. The physics of this multicomponent Fermi gas turns out to be much richer and more exotic than in the standard SU(2) case. For N > 2, the phase diagram is quite rich already in the case of the single-band model, including a molecular Luttinger liquid (with dominant superfluid instability in the N-particle channel) for incommensurate fillings, as well as various Mott-insulating phases occurring at commensurate fillings. Particular attention will be paid to the cases with additional orbital degree of freedom (which is accessible experimentally either by taking into account two atomic states or by putting atoms in the p-band levels). We introduce two microscopic models which are relevant for these cases and discuss their symmetries and strong coupling limits. More intriguing phase diagrams are then presented including, for instance, symmetry protected topological phases characterized by non-trivial edge states.
- Ivan Shelykh (NTU, Singapore): Aharonov- Bohm effect induced by circularly polarized light
In our talk we will demonstrate theoretically that strong electron coupling to circularly polarized photons in non-singly-connected nanostructures results in the appearance of an artificial gauge field that changes the electron phase. The effect arises from the breaking of time-reversal symmetry and is analogous to the well-known Aharonov-Bohm phase effect. It can manifest itself in the oscillations of conductance as a function of the intensity and frequency of the illumination. The theory of the effect is elaborated for mesoscopic rings in both ballistic and diffusive regimes, for both charged particles and neutral excitons.
- Dario Poletti (SUTD, Singapore): Artificial gauge fields in Hamiltonian and in dissipative systems
- Philippe Lecheminant (LPTM, Cergy-Pontoise): Ultracold Fermi gases with an SU(N) symmetry: an overview
In this talk, we will review recent experimental and theoretical progress on ultracold alkaline-earth and ytterbium Fermi gases loaded into optical lattices. One remarquable property of these atoms is the existence of an SU(N) symmetry, N being the number of nuclear spin states, which stems from the large decoupling between electronic and nuclear spin degrees of freedom for states with zero total electronic angular momentum. It paves the way of the investigation of SU(N) many-body physics with the stabilization of many exotic phases such as SU(N) chiral spin liquid with Non-Abelian statistics, or SU(N) symmetry-protected topological phases. We will provide an overview of some important results on this SU(N) fermionic systems, together with some interesting perspectives.
- Benoît Grémaud (MajuLab, Singapore): Mean field approach to SU(2) and SU(4) fermions
- Ulrike Bornheimer (CQT, Singapore): SU(3) Non-Abelian Gauge Fields in a Bosonic 2D Honeycomb Lattice
We investigate the single-particle spectrum of spin-1 bosons propagating in a 2D honeycomb optical lattice and subjected to a SU(3) spin-orbit coupling. This physical situation is equivalently obtained from a gauge transformation of the Harper model and can be realized experimentally. We focus on the analysis of the edge states obtained when open boundary conditions are imposed in one direction. Indeed, their very existence reflects the topology of the bulk system through the bulk-edge correspondence. We also examine the localization properties of these edge states, stability and dependence on symmetries of the Hamiltonian.
- David Wilkowski (MajuLab, Singapore): A SU(N) non-Abelian gauge transformation in an atomic system dressed with laser light
In 1984, M. Berry showed that the adiabatic transportation of a single quantum state give rise to a phase factor of purely geometrical origin. The same year, F. Wilczek and A. Zee generalized the concept to degenerated quantum states. In particular it may lead to the appearance of a non trivial non-Abelian gauge transformation on a subsystem embedded into a more trivial system having a U(1) symmetry. This mechanism is at the origin of some fascinating physical properties of topological and/or geometrical based systems such as quantum hall effect, spin hall effect, spin orbit coupling. It is also envisioned for robust quantum information processing. Despite its importance in many areas in physic, few test bed experiments, showing non-Abelian gauge transformation, have been performed so far. In this talk, I will present our experimental approach which consists in an atomic cold ensemble dressed with laser light. Here the non-Abelian gauge transformation is performed on the subsystem composed of states which are not coupled to the vacuum field.
- Frédéric Chevy (LKB, Paris): From ultracold to ultrafast, two examples of analogue simulation using cold atoms
Over the past few years, ultracold atoms have emerged as priviledged platfoms for the experimental exploration of quantum many-body physics. To demonstrate the versatility of ultracold atomic techniques, I will discuss during my talk two experiments performed recently at ENS addressing widely different physical situations. In the first part, I will show how the possibility of tuning interatomic interactions have paved the road to the observation of the first double Bose-Fermi superfluids. In liquid 3H/4He mixtures where a similar system has been looked for over the past forty years, the critical temperature is strongly reduced by repulsive inter-isotope interactions. Using Feshbach resonances, we were able to stabilize the mixture and cool it to the superfluid regime. By putting the two clouds into relative motion, we have also explored the properties of superfluid counterflows and we have unveiled a novel mechanism for the breakdown of superfluidity that extends Landau’s celebrated argument.
The second part of my talk will be devoted to the study of Weyl fermions. These massless particles were first thought to describe neutrinos, until the discovery of their oscillations, and have recently been observed in TaAs compunds. Their interest stems form their peculiar topological properties associated with their spin orbit coupling. I will show that after a phase-space rotation, their dynamics is equivalent to that of magnetically confined atoms and I will present a study of the dynamics of Weyl particles in a harmonic trap. Contrary to massive atoms, the oscillation frequency of massless particles is energy dependent, a peculiar feature leading to a blurring of the center-of-mass motion of the cloud and to a quasi-thermalization of the system driven by the non-linearities of the single-particle hamiltonian.
- Manas Mukherjee (CQT, Singapore): Precision tests for fundamental physics
Trapped ion provide pristine environment to perform precision tests while precision tests are door towards understanding the behaviour of natural forces. Here we will discuss how a single trapped heavy atom can be used to explore the weak force of nature with the possibility of observing violation of spatial symmetry [1]. Our recent measurements [2] along with other measurements [3] on the electronic wavefunctions for two dipole transitions of one such heavy atom allowed a precision test of many body (in this case many electron system) theories below one percent precision. An overview of the future prospect in this context will be further elaborated.
[1] C. S. Wood, S. C. Bennett, D. Cho, B. P. Masterson, J. L. Roberts, C. E. Tanner, and C. E. Wieman, Science 275, 1759 (1997); N. Fortson, Phys. Rev. Lett. 70, 2383 (1993); P. Mandal and M. Mukherjee Phys. Rev. A (Rapid Comm.) 82, 050101(R) (2010); B. K. Sahoo, P. Mandal, and M. Mukherjee, Phys. Rev. A 83, 030502(R) (2011).
[2] D. De Munshi, T. Dutta, R. Rebhi, M. Mukherjee Phys. Rev. A 91, 040501(R) (2015)
[3] ] J. A. Sherman, A. Andalkar, W. Nagourney, and E. N. Fortson, Phys. Rev. A 78, 052514 (2008).
- Frédéric Hébert (INLN, Nice): QMC study of the Rabi-Hubbard model
The Rabi model is a simple model for light matter interaction, describing the interaction of a two level atom/spin with one light mode. When several such models are coupled, many new phenomenons have been predicted such as photons Mott phases in what is called the Rabi-Hubbard model.
However, those predictions depend on neglecting the effects of terms that do not conserve the total number of excitations (the so-called counter rotating terms), in a simplified model known as the Jayne-Cummings model. Mean field study by Schiro et al. of the full model suggested that the physics is rather different when these terms are taken into account in the full model.
We studied this model with QMC, which provides unbiased and exact results, and showed that the physics seems largely modified by the inclusion of these terms, as envisionned by Schiro et al. We discuss more generally under which conditions the Jayne-Cummings can be a good approximation of the full Rabi-Hubbard model.
- Luigi Amico (University of Catania): Atomtronics flux qubits
I will discuss the effective quantum dynamics of Bose-Einstein condensates trapped in ring shaped potentials. Interrupting the ring with weak links, atomic analogs of SQUIDs are realized. I will demonstrate how the cases of single and three weak links provide a feasible atomtronics physical implementations of flux qubits.
- Dimitris Angelakis (CQT, Singapore and TUC Crete): Many-body physics with light
In this talk, I will try to review in a pedagogic way the works in the area of many-body physics and quantum simulation with light starting from the early theoretical proposals for realising equilibrium models all the way to the more recent works in driven dissipative platforms. I will start by describing the founding works on the Jaynes-Cummings lattice or Jaynes-Cummings-Hubbard model and the corresponding photon-blockade induced Mott transition. I will continue by briefly discussing how to realize effective spin models and Fractional Hall states in coupled nonlinear resonator arrays (CRAs) and then discuss the recent efforts to study out-of-equilibrium many-body effects using driven CRAs, including the predictions for photon fermionization and crystallization. I will also try to summarize the work in realizing strongly correlated Tonks gases, Luttinger liquids, and topological models with photons in slow light set ups. I will review the major theory results and also briefly outline recent developments in ongoing experimental efforts involving different platforms in circuit QED, Rydberg polaritons and nanophotonic platforms.
- Ewan Munro (CQT, Singapore):Optical properties of atoms with photonic crystal-induced long-range interactions
In recent years there has been significant interest in the fusion of quantum optics and nanophotonics, where quantum emitters (‘atoms’) are coupled to structures such as cavities and waveguides whose characteristic dimensions are comparable to the resonant wavelength of the atom. Primarily conceived as a route to more efficient atom-photon coupling and improved scalability compared to traditional quantum optics setups, such systems also allow for the exploration of qualitatively new classes of light-matter interactions. One example of this is to couple atoms to photonic band-gap materials, where it is possible to engineer long-range coherent interactions between the atoms. Motivated by recent advances in experimental capabilities along such lines, we study the fundamental optical properties of such a system in both the linear and several-photon regimes. In particular, we show how a modification is required of the basic characterisation tools of standard atomic ensemble physics, and consider how the system may be used to produce non-classical states of light.
- Matthias Troyer (ETH, Zürich):Topological Charge Pumping and Hofstadter-Hubbard Model
Topological charge pumping plays a role in design and detection of topological phases in ultracold atomic gases and condensed matter systems. We have proposed an experimental setup to realize a topological Thouless pump in a 1D optical superlattice, which is a dynamical analog of the integer quantum Hall effect. This protocol has been implemented by the Kyoto group and topological pumping was observed from a quantized center-of-mass shift of the atomic cloud. I will then explain how to use the topological pumping effect to identify interaction induced topological phase transitions in the Hofstadter-Hubbard model and end with some new insights into the fermion sign problem in quantum Monte Carlo simulations.