New Frontiers in Spin Squeezing

Baochen Wu, Kevin C. Cox, Graham P. Greve +1 more

Yoo Kyung Lee

The dynamics of many interacting spins is an active frontier of research; not only can they explain magnetic phenomena, but they also provide paradigmatic models with deep connections to high-T_c superconductivity, optimization problems, neural networks, and more. Experiments with ultracold alkali atoms in optical lattices have realized spin models with great success. In particular, the isotropic Heisenberg model---the XXX model---was realized more than a decade ago. The ⁷Li apparatus described here was the first to realize a tunable, anisotropic Heisenberg model, also known as the XXZ model. In this thesis, I will describe how the capabilities of this apparatus were harnessed to characterize the spin models we realize, employ them to observe new resonances, and to contribute to studies in spin squeezing and fundamental physics. First, I will discuss how we prepared and observed phantom helix states: eigenstates of the XXZ Hamiltonian. Our understanding of the contact interactions and the phantom helix states enabled us to observe long-predicted lattice-induced resonances, whose effects can be leveraged as another knob to tune the XXZ Hamiltonian. Furthermore, our control over the spin system allowed us to generate spin-squeezed states, a paradigmatic form of entanglement for spin ensembles. This is the first time squeezed states were realized with nearest-neighbor contact interactions in a lattice. Finally, our control over the spin degree of freedom and defects in our state preparation allowed us to create pristine periodic lattices with which to study gedankenexperiments in light scattering.

Jian Ma, Xiaoguang Wang, C. P. Sun +1 more

Yutong Yang, Maya Miklos, Yee Ming Tso +3 more

Optical atomic clocks with unrivaled precision and accuracy have advanced the frontier of precision measurement science and opened new avenues for exploring fundamental physics. A fundamental limitation on clock precision is the standard quantum limit (SQL), which stems from the uncorrelated projection noise of each atom. State-of-the-art optical lattice clocks interrogate large ensembles to minimize the SQL, but density-dependent frequency shifts pose challenges to scaling the atom number. The SQL can be surpassed, however, by leveraging entanglement, though it remains an open problem to achieve quantum advantage from spin squeezing at state-of-the-art stability levels. Here, we demonstrate clock performance beyond the SQL, achieving a fractional frequency precision of 1.1×10^{-18} for a single spin-squeezed clock. With cavity-based quantum nondemolition measurements, we prepare two spin-squeezed ensembles of ∼30 000 strontium atoms confined in a two-dimensional optical lattice. A synchronous clock comparison with an interrogation time of 61 ms achieves a metrological improvement of 2.0(2) dB beyond the SQL, after correcting for state preparation and measurement errors. These results establish the most precise entanglement-enhanced clock to date and offer a powerful platform for exploring the interplay of gravity and quantum entanglement.

Barış Öztop, Alexander A. Klyachko, A.S. Shumovsky

We reformulate definition of spin squeezing and spin coherence in terms of the total variance in spin operators. We propose a new measure of spin squeezing. We show equivalence of spin squeezing and spin entanglement.