Research

"Cavity-Quantum-Electrodynamical Toolbox for Quantum Magnetism", Mivehvar, Ritsch, and Piazza, Phys. Rev. Lett. 122, 113603 (2019); 

“Disorder-Driven Density and Spin Self-Ordering of a Bose-Einstein Condensate in a Cavity”, Mivehvar, Piazza, and Ritsch, Phys. Rev. Lett. 119, 063602 (2017): 

In these two papers, we proposed for the first time a model which realizes a generalized self-ordering transition in bosonic atoms, with both internal and external degrees of freedom, via a cavity-induced order-by-disorder mechanism. Beyond the critical pump strength, the atomic system with a trivial spin orientation begins to spatially self-order toward a crystalline structure with spin-wave texture, reminiscent of formation of crystalline magnetic materials in nature. The spin texture depends on the cavity-mediated spin-spin interactions, which in turn depend on the interference among different electromagnetic modes. Our proposals basically implement various long-range quantum spin Hamiltonians. First experimental steps toward realizing these proposals have produced intriguing results at the ETH Zurich [Landini et al., Phys. Rev. Lett. 120, 223602 (2018)] and at the Stanford University [Kroeze et al., Phys. Rev. Lett. 121, 163601 (2018)]. 

“Driven-Dissipative Supersolid in a Ring Cavity”, Mivehvar, Ostermann, Piazza, and Ritsch, Phys. Rev. Lett. 120, 123601 (2018):

In this article, we put forward a simple model to realize a supersolid state in an open atom-cavity quantum system. Supersolid is a crystalline state which can flow like a superfluid without a friction, an enigmatic and seemingly paradoxical phase of matter. It had been elusive for almost half a century since its prediction up until recently, where clear signatures of supersolidity have been observed in weakly interacting ultracold atomic systems. However, these atomic systems comprise intrinsically driven-dissipative open quantum systems, a situation which lies outside the thermal equilibrium condition considered so far in theory. We studied for the first time the effect of dissipations on main features of a supersolid and showed that fundamental characteristics of a supersolid are robust against drives and dissipations, provided that the latter preserve spatial translation invariance. Our proposal may also have a potential application in quantum metrology as a precise gravimeter. 

“Superradiant Topological Peierls Insulator inside an Optical Cavity”, Mivehvar, Ritsch, and Piazza, Phys. Rev. Lett. 118, 073602 (2017):

In this work, we proposed a model which realizes a novel topological self-ordering transition, where both matter, in the form of ultracold fermionic atoms, and light, composed of photons trapped inside an optical cavity, play equally important roles. Topological states of matter are new phases of matter with exotic characteristics, such as robust conducting edge states at their physical edges. Due to light-mediated interactions, fermionic atoms spontaneously self-order into a spatially dimerized pattern which corresponds to a topological insulating state. Remarkably, the key topological features of the system, i.e., the bulk topological invariant and the presence of edge states, can be non-destructively extracted via the cavity output. This may open a new avenue in the quantum-gas field as a new technique for a non-destructive measurement of topological properties.