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Related Experiment Video
Updated: Jan 23, 2026

Gradient Echo Quantum Memory in Warm Atomic Vapor
Published on: November 11, 2013
Quantum liquids.
1Department of Physics and Astronomy, University of Delaware, Newark, DE 19716-2593, United States of America.
Pioneering neutron scattering experiments revealed key insights into quantum liquids like liquid helium-4 and helium-3. These studies observed the Bose-Einstein condensate fraction and detailed density excitations, advancing our understanding of quantum fluid dynamics.
Area of Science:
- Condensed Matter Physics
- Quantum Fluids
- Neutron Scattering
Background:
- Roger A Cowley's research significantly advanced the understanding of quantum liquids, specifically liquid helium-4 and helium-3.
- Previous theories by Feynman and Cohen predicted different behaviors for the phonon-roton mode in liquid helium-4.
Purpose of the Study:
- To investigate the collective and independent particle response of liquid helium-4 using neutron scattering.
- To explore the density excitations and dynamic response of liquid helium-3 under varying conditions.
- To compare experimental findings with theoretical predictions for quantum liquids.
Main Methods:
- Neutron scattering measurements were conducted at Chalk River Laboratories and the Institut Laue Langevin.
- Detailed measurements of energy, intensity, and width of the phonon-roton mode in liquid helium-4.
- Investigation of density response in liquid helium-3, a challenging material due to high neutron absorption.
Main Results:
- Observed the termination of the phonon-roton mode at finite energy, supporting Pitaevskii's predictions.
- First-ever observation of the Bose-Einstein condensate (BEC) fraction in liquid helium-4.
- Successfully documented the density response of liquid helium-3, stimulating further research.
Conclusions:
- Cowley's experiments provided crucial data on quantum liquid dynamics, validating specific theoretical models.
- The observation of BEC in liquid helium-4 was a landmark achievement in quantum physics.
- Pioneering work on liquid helium-3 opened new avenues for studying dense quantum systems.

