Minutes-scale Schr{ö}dinger-cat state of spin-5/2 atoms (2410.09331v1)

Abstract: Quantum metrology with nonclassical states offers a promising route to improved precision in physical measurements. The quantum effects of Schr{\"o}dinger-cat superpositions or entanglements allow measurement uncertainties to reach below the standard quantum limit. However, the challenge in keeping a long coherence time for such nonclassical states often prevents full exploitation of the quantum advantage in metrology. Here we demonstrate a long-lived Schr{\"o}dinger-cat state of optically trapped $^{173}$Yb (\textit{I}\ =\ 5/2) atoms. The cat state, a superposition of two oppositely-directed and furthest-apart spin states, is generated by a non-linear spin rotation. Protected in a decoherence-free subspace against inhomogeneous light shifts of an optical lattice, the cat state achieves a coherence time of $1.4(1)\times 10^3$ s. A magnetic field is measured with Ramsey interferometry, demonstrating a scheme of Heisenberg-limited metrology for atomic magnetometry, quantum information processing, and searching for new physics beyond the Standard Model.

• The paper introduces a method to create minute-scale Schrödinger-cat states in spin-5/2 173Yb atoms with a coherence time of 1.4×10³ seconds.
• It employs an optical lattice and decoherence-free subspace strategy to precisely control spin states and achieve sensitivity near the Heisenberg limit.
• The experimental advances offer promising applications in quantum metrology, computing, and probing physics beyond the Standard Model.

Minutes-Scale Schrödinger-Cat State of Spin-5/2 Atoms

This paper presents a significant advancement in the creation of long-lived Schrödinger-cat states using spin-5/2 nuclei of $^{173}$Yb atoms. These cat states are quantum superpositions of the $m = +5/2$ and $m = -5/2$ nuclear-spin projection states, and are realized by nonlinear spin rotation. The robust methodology provides a coherence time notably extended to $1.4(1) \times 10^3$ seconds, a substantial achievement for quantum systems susceptible to decoherence.

Methodology and Experimental Setup

The experiment employs a well-controlled optical setup where $^{173}$Yb atoms are trapped in an optical lattice with precision manipulations mediated by laser fields. The crucial intervention involves protecting the cat states in a decoherence-free subspace. Herein, the spin-light interaction Hamiltonian is meticulously configured to balance noise and coherence, achieving collective decoherence immunity. The apparatus for optical measurement, coherent spin control, and state-selective probing is intricately designed to handle the spin states without inducing additional decoherence pathways.

Results and Key Findings

A central result is the demonstration of Ramsey interferometry using the cat state, evidencing sensitivity close to the Heisenberg limit. The cat state shows maximum sensitivity to perturbations such as magnetic fields and vector shifts, which are of relevance in probing physics beyond the Standard Model. The reported robustness of the cat states against decoherence – manifested in an enduring phase coherence over extended periods – contrasts markedly with typical states suffering rapid decoherence.

The specificity of the interaction model and the precision applied in laser control denote substantial improvements over previous quantum state manipulation techniques. By using optimal light polarizations and leveraging the decoherence-free subspace, the paper describes experimentally viable routes to achieving long-term coherence without isolating environmental interactions completely.

Future Implications

Brownian explorations of quantum metrology, quantum information processing, and fundamental physics can derive considerable utility from such long-lived quantum states. This research foreshadows diverse potential applications such as qubit implementation for quantum computing architectures, advanced metrology including time-keeping devices, and even speculative exploration for evidence of new physics phenomena.

Moreover, the conceptualization of exploiting high-spin states to contribute to quantum memory and error correction paradigms in quantum information theory marks a promising direction forward. The strategic utility of coupling cat states with multi-particle entanglement schemes to further refine measurement precision and fidelity stands well-positioned for future explorations.

Finally, prospective developments could envisage scaling of these techniques to larger arrays or new atomic species, facilitating complex quantum interactions while minimizing decoherence, thereby harnessing quantum mechanical advantages over classical systems.

In conclusion, this research delineates significant pathways toward practical quantum applications, broadening vistas in quantum engineering and fundamental scientific inquiry.