Coherent spin control in a SU(N) quantum gas of strontium 87
Abstract:
Ensembles of large-spin S > 1/2 atoms offer richer potential applications in areas like quantum computing, quantum simulations, and quantum magnetism as compared to what is possible with effective spin-half S = 1/2 atoms. For instance, in quantum simulations, large-spin atoms can be used to simulate high-spin models in optical lattices or traps which are crucial for exploring strongly correlated systems and high Tc superconductivity. Moreover, in quantum computing, atoms with large spins enable more complex forms of quantum entanglement because of the multiple spin degrees of freedom that can be simultaneously entangled. These systems can serve as qubits with higher dimensions (qudits) and enable more complex quantum gate operations. Furthermore, in quantum magnetism, atoms with large spins can exhibit SU(N) symmetry in their interactions (N being 2S + 1). In such systems, instead of traditional spin-1/2 particles interacting through simple spin-exchange mechanisms, there can be higher-rank spin interactions that can lead to richer quantum magnetism.
In this thesis, firstly, I present experimental results for manipulating the nuclear spins of ultracold atoms of 87Sr. To achieve spin state selectivity, a tensor light shift is introduced into the ground state manifold. Then a two-photon Raman transition between two spin states enables us to control the final spin state deterministically. We can drive adiabatic Raman passages between the selected two spin states with a one-way efficiency of 80%. These passages are efforts towards realizing the super-exchange interactions when done inside optical lattices. In the future, this work will lead us closer to investigating quantum magnetism.
Secondly, I show that we can perform Ramsey interferometry between the chosen two spin states. Taking advantage of a large spin manifold of 87Sr, we developed two interferometers that utilize a series of unitary rotations between the two chosen spin states. These interferometers are run with four spin states. The first interferometer measures the tensor light shift and the combination of vector light shift and linear Zeeman splitting in one shot. The second interferometer is capable of measuring the two collective atomic variables simultaneously. This interferometer can be used to measure quantum correlations in one shot. In general, these interferometric ideas can be applied to quantum computing and metrology.
At last, I present our first result on the measurement of SU(N) symmetry within the ground state of 87Sr with the help of Ramsey interferometry. There are two measurements: one in the 1D lattice and the other in bulk gas. I observe the SU(N) asymmetry to be smaller than the relative uncertainty 10−2, where the theoretical prediction is about 10−9. Subsequently, I outline the immediate objectives to lower this uncertainty by an order of magnitude. This measurement leads us towards a better understanding of atoms with large spins that can exhibit SU(N) symmetry.
Soutenance de thèse de Husain Ahmed
Date: Mardi 10 décembre 2024 – 14H15
Location: Amphi D
Laboratoire de Physique des Lasers, 99 av. J.B. Clément 93430 Villetaneuse France
Jury:
- Alexandre Gauguet (Referee)
- Patrick Cheinet (Referee)
- Mathilde Hugbart (Examiner)
- Sebastien Bize (Examiner)
- Gabriel Dutier (Examiner)
- Bruno Laburthe-Tolra (Co-supervisor)
- Martin Robert-de-Saint-Vincent (Co-supervisor)