Strongly Interacting Quantum gases using spin-Coherent state Representation

Lennart Sobirey, Jonas Siegl, Niclas Luick +3 more

Muhammad Nadzim Zamri, Ainul Zaim Zakaria, Bahari Iskandar

We studied the interacting system of qubit with a collection of N qubits or known as spin coherent state. From the interaction of the qubit – spin coherent state system, we can observe many interesting phenomena such as ‘collapse and revival’ in the time evolution of the qubit state, the qubit of attractor state, the qubit – spin coherent state entanglement, and the occurrence of the Schrӧdinger’s cat state. The event of ‘collapse and revival’ will be mainly focused in this study. Prior studies had shown the Bloch Sphere and Majorana Sphere representations for the interaction system between qubit and a coherent state. Therefore, in this research, we will analyze the time evolution of the qubit state in the qubit – spin coherent state interacting system for the one qubit case, and represent the dynamics of the qubit state using the Majorana Sphere representation.

Herman C. W. Beijerinck, S. J. J. M. F. Kokkelmans, Bout Marcelis

Kévin Roux, Hideki Konishi, Victor Helson +1 more

Strong quantum correlations in matter are responsible for some of the most extraordinary properties of materials, from magnetism to high-temperature superconductivity, but their integration in quantum devices requires a strong, coherent coupling with photons, which still represents a formidable technical challenge in solid state systems. In cavity quantum electrodynamics, quantum gases such as Bose-Einstein condensates or lattice gases have been strongly coupled with light. However, neither Fermionic quantum matter, comparable to electrons in solids, nor atomic systems with controlled interactions, have thus far been strongly coupled with photons. Here we report on the strong coupling of a quantum-degenerate unitary Fermi gas with light in a high finesse cavity. We map out the spectrum of the coupled system and observe well resolved dressed states, resulting from the strong coupling of cavity photons with each spin component of the gas. We investigate spin-balanced and spin-polarized gases and find quantitative agreement with ab initio calculation describing light-matter interaction. Our system offers complete and simultaneous control of atom-atom and atom-photon interactions in the quantum degenerate regime, opening a wide range of perspectives for quantum simulation.

Hui Zhai

Vladimir Yurovsky

Second-order phase transitions have no latent heat and are characterized by a change in symmetry. In addition to the conventional symmetric and antisymmetric states under permutations of bosons and fermions, mathematical group-representation theory allows for non-Abelian permutation symmetry. Such symmetry can be hidden in states with defined total spins of spinor gases, which can be formed in optical cavities. The present work shows that the symmetry reveals itself in spin-independent or coordinate-independent properties of these gases, namely as non-Abelian entropy in thermodynamic properties. In weakly interacting Fermi gases, two phases appear associated with fermionic and non-Abelian symmetry under permutations of particle states, respectively. The second-order transitions between the phases are characterized by discontinuities in specific heat. Unlike other phase transitions, the present ones are not caused by interactions and can appear even in ideal gases. Similar effects in Bose gases and strong interactions are discussed.