## SCL Seminar by Ivana Vasic

SCL seminar of the Center for the Study of Complex Systems, will be held on Friday, 17 March 2017 at 14:00 in the library reading room “Dr. Dragan Popović" of the Institute of Physics Belgrade. The talk entitled

will be given by Dr. Ivana Vasić (Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade).

Due to highly controllable properties, systems of ultracold atoms are promising platforms for quantum simulations. One of the early successes in this direction was the observation of a superfluid-Mott insulator transition in a lattice Bose gas, as a prototype of a quantum phase transition. With the development of experimental techniques, present-day cold atom setups feature artificial gauge potentials that mimic magnetic fields, as well as finite-range interactions, for example in Rydberg dressed systems. In this talk, we will review several recent theoretical results [1-4] motivated by these latest experimental advances.

Dynamical response of a Bose-Einstein condensate to an external perturbation is used to probe such systems experimentally. At first, we will discuss the dynamics of a Bose-Einstein condensate induced by a widely used experimental protocol where the ground state of a one-component condensate is perturbed by transferring half of the atoms into another hyperfine state. We will establish the necessary conditions for the onset of dynamical instability in this setup [1]. Next, we will address the response of lattice bosons to controlled local dissipation, which is an alternative way to probe such systems [2]. Our results show that in the regime of weak dissipation, atomic losses are proportional to the initial atomic density and are enhanced by the local dissipation. More interesting is a regime of strong dissipation, where measurement process suppresses unitary time evolution of the system, and in a roundabout way reveals the properties of the underlying microscopic Hamiltonian.

In the second part of the talk, we will study bosonic phases in the presence of artificial gauge fields [3, 4]. Following up on the recent experimental realization of the celebrated Haldane model in an ultracold atom setup, we map out the ground state phase diagram and excitations of the bosonic Haldane-Hubbard model. Finally, we will discuss excitation spectra of a Bose-Einstein condensate with a newly proposed coupling of spin and angular momentum, as a way to experimentally identify different phases expected in this setup.

[1] I. Vidanović, N. J. van Druten, and M. Haque, New J. Phys. 15, 035008 (2013).

[2] I. Vidanović, D. Cocks, and W. Hofstetter, Phys. Rev. A 89, 053614 (2014).

[3] I. Vasić, A. Petrescu, K. Le Hur, and W. Hofstetter, Phys. Rev. B 91, 094502 (2015).

[4] I. Vasić and A. Balaž, Phys. Rev. A 94, 033627 (2016).

**"Bosonic Phases of Ultracold Atomic Gases"**will be given by Dr. Ivana Vasić (Scientific Computing Laboratory, Center for the Study of Complex Systems, Institute of Physics Belgrade).

**Abstract of the talk:**Due to highly controllable properties, systems of ultracold atoms are promising platforms for quantum simulations. One of the early successes in this direction was the observation of a superfluid-Mott insulator transition in a lattice Bose gas, as a prototype of a quantum phase transition. With the development of experimental techniques, present-day cold atom setups feature artificial gauge potentials that mimic magnetic fields, as well as finite-range interactions, for example in Rydberg dressed systems. In this talk, we will review several recent theoretical results [1-4] motivated by these latest experimental advances.

Dynamical response of a Bose-Einstein condensate to an external perturbation is used to probe such systems experimentally. At first, we will discuss the dynamics of a Bose-Einstein condensate induced by a widely used experimental protocol where the ground state of a one-component condensate is perturbed by transferring half of the atoms into another hyperfine state. We will establish the necessary conditions for the onset of dynamical instability in this setup [1]. Next, we will address the response of lattice bosons to controlled local dissipation, which is an alternative way to probe such systems [2]. Our results show that in the regime of weak dissipation, atomic losses are proportional to the initial atomic density and are enhanced by the local dissipation. More interesting is a regime of strong dissipation, where measurement process suppresses unitary time evolution of the system, and in a roundabout way reveals the properties of the underlying microscopic Hamiltonian.

In the second part of the talk, we will study bosonic phases in the presence of artificial gauge fields [3, 4]. Following up on the recent experimental realization of the celebrated Haldane model in an ultracold atom setup, we map out the ground state phase diagram and excitations of the bosonic Haldane-Hubbard model. Finally, we will discuss excitation spectra of a Bose-Einstein condensate with a newly proposed coupling of spin and angular momentum, as a way to experimentally identify different phases expected in this setup.

[1] I. Vidanović, N. J. van Druten, and M. Haque, New J. Phys. 15, 035008 (2013).

[2] I. Vidanović, D. Cocks, and W. Hofstetter, Phys. Rev. A 89, 053614 (2014).

[3] I. Vasić, A. Petrescu, K. Le Hur, and W. Hofstetter, Phys. Rev. B 91, 094502 (2015).

[4] I. Vasić and A. Balaž, Phys. Rev. A 94, 033627 (2016).