Bonn 2025 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 45: Mechanical, Macroscopic, and Continuous-variable Quantum Systems (joint session QI/Q)
Q 45.5: Talk
Wednesday, March 12, 2025, 15:45–16:00, HS IX
Entanglement detection in continuous-variable systems using two states — •Elena Callus1, Tobias Haas2, and Martin Gärttner1 — 1Institute of Condensed Matter Theory and Optics, Friedrich-Schiller-Universität Jena, Germany — 2Centre for Quantum Information and Communication, Université Libre de Bruxelles, Belgium
The Shchukin-Vogel hierarchy gives necessary conditions for the separability of continuous-variable systems in terms of moments of the mode operators. However, higher-order moments, which are essential for non-Gaussian entanglement detection, are hard to extract efficiently. While recent work has shown the general usefulness of multiple state copies for entanglement witnessing in this regard, the therein proposed measurement schemes require at least three copies that would need to be phase-matched and interfered simultaneously. In this work, we demonstrate the capabilities from using only two states that are interfered on a beam-splitter with variable phase and photon-number detectors. This allows us to access certain classes of moments of the mode operators up to arbitrarily high orders. With their associated separability criteria, we witness entanglement in non-Gaussian classes of N00N states, with arbitrarily large N, and two-mode Schrödinger cat states.
Keywords: Entanglement; Continuous variables; Witness; Shchukin-Vogel hierarchy