ResearchPod Summary
Understanding whether gravity possesses an intrinsic quantum nature remains a central challenge in theoretical physics. This paper investigates a bipartite system of massive particles confined in a one-dimensional double-well potential and coupled through mutual Newtonian gravity, known as gravitational cat (gravcat) states. The authors examine how quantum correlations and quantum coherence behave under the combined influence of gravitational coupling, single-particle energy scales, and thermal fluctuations.
Rather than relying on conventional basis-dependent coherence measures, the study employs the square root of the quantum Jensen-Shannon divergence (QJSD) from the maximally mixed state. This approach yields a basis-independent measure of total coherence that splits operationally into two distinct parts: collective coherence, which captures quantum correlations between the two particles, and localized coherence, which measures the intrinsic quantum superposition within each individual particle. The researchers analyze thermal density operators across varying temperatures, gravitational coupling strengths, and single-particle energy scales to map out the distribution and robustness of these quantum resources.
Evaluating non-classical correlations via the Bures distance of entanglement and quantum discord reveals a delicate interplay between local energy splitting and gravitational interaction. At zero temperature, entanglement increases significantly with stronger gravitational coupling, as the interaction term drives the system toward a Bell-like state. However, excessive single-particle energy splitting diminishes this entanglement by making the local Hamiltonian terms dominant over the gravitational interaction.
As thermal energy increases, entanglement degrades monotonically and vanishes entirely at threshold temperatures that depend strongly on the system parameters. Quantum discord exhibits a similar qualitative dependence on temperature and coupling strength, but decays smoothly without the abrupt finite-temperature sudden death observed for entanglement. The results confirm that generating robust thermal entanglement and non-classical correlations requires careful tuning between the single-particle energy scale and the gravitational coupling.
Decomposing the total coherence into localized and collective components uncovers distinct operational characteristics under thermal noise. Localized coherence, which reflects the single-particle superposition across the double-well potential minima, proves significantly more robust against thermal fluctuations than collective coherence. While thermal mixing rapidly disrupts the inter-particle correlations responsible for collective coherence, the individual subsystems retain their local coherence up to much higher temperatures.
Increasing the gravitational coupling strength preferentially enhances collective coherence by strengthening the correlations established between the two particles. Consequently, the balance between localized and collective coherence serves as a sensitive indicator of how environmental temperature and gravitational interaction redistribute quantum resources in macroscopic superposition states.
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