Mainz 2026 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 34: Quantum Technologies – Sensing I
Q 34.7: Talk
Wednesday, March 4, 2026, 16:15–16:30, P 5
Understanding the disorder robustness of Over-Un-Twisting echo protocols — •Vineesha Srivastava1,2 and Klemens Hammerer1,2 — 1Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, Innsbruck 6020, Austria — 2Institute for Theoretical Physics, University of Innsbruck, Innsbruck 6020, Austria
Precision in phase estimation using Ramsey interferometry is limited by quantum projection noise, constraining classical-spin protocols to the standard quantum limit. Entanglement generated through one-axis twisting (OAT) can overcome this limitation, and, in principle, enable sensitivities up to the Heisenberg limit, motivating enhanced Ramsey-echo protocols that apply OAT interactions before and after the phase imprint to surpass simple squeezing schemes.
In earlier work, a variational framework for such echo protocols revealed a previously unknown over-un-twisting (OUT) protocol, in which the initial squeezing is reversed using twice the interaction time. Remarkably, recent experiments on dense room-temperature nitrogen - vacancy ensembles have demonstrated a doubly inverting echo analogous to the OUT protocol, exhibiting disorder-robust signal amplification, which is an effect not fully explained by current theory.
In this work, we investigate the microscopic origins and limits of this robustness. Using cumulant-expansion techniques, we analyze how inhomogeneous spin - spin couplings modify the nonlinear echo dynamics and identify regimes in which OUT-like protocols preserve their metrological advantage.
Keywords: Echo protocols; Quantum sensing; Signal amplification; Disordered spins