Asymmetric EPR entanglement in continuous variable systems

TL;DR

This paper explores asymmetric continuous variable entanglement, demonstrating how asymmetries affect entanglement strength and optimal measurement configurations through theoretical analysis and experimental validation.

Contribution

It introduces a method to visualize and quantify asymmetric entanglement, showing that the optimal beamsplitter ratio depends on asymmetries and may differ from 50/50.

Findings

Optimal beamsplitter ratio depends on asymmetries

Asymmetric entanglement can be effectively visualized

Experimental validation of asymmetric entanglement with a 0.78/0.22 beamsplitter

Abstract

Continuous variable entanglement can be produced in nonlinear systems or via interference of squeezed states. In many of optical systems, such as parametric down conversion or interference of optical squeezed states, production of two perfectly symmetric subsystems is usually used for demonstrating the existence of entanglement. This symmetry simplifies the description of the concept of entanglement. However, asymmetry in entanglement may arise naturally in a real experiment, or be intentionally introduced in a given quantum information protocol. These asymmetries can emerge from having the output beams experience different losses and environmental contamination, or from the availability of non-identical input quantum states in quantum communication protocols. In this paper, we present a visualisation of entanglement using quadrature amplitude plots of the twin beams. We quantitatively discuss the strength of asymmetric entanglement using EPR and inseparability criteria and theoretically show that the optimal beamsplitter ratio for entanglement is dependent on the asymmetries and may not be 50/50. To support this theory, we present experimental results showing one particular asymmetric entanglement where a 0.78/0.22 beamsplitter is optimal for observing entanglement.