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LASSP -  Laboratory of Atomic and Solid State Physics

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Cohen group reveals the secret of the Oobleck

Neil Lin and Itai Cohen, along with researchers from the University of Edinburgh, have come up with a unique experiment to explain why shear thickening happens.

Read more in the Chronicle or the Synopsis or the full article in Physical Review Letters.

Shear thickening

Vengalattore group demonstrates "Weeping Angel" effect

The act of observation has profound consequences on a quantum system. In this work, we experimentally demonstrate the famous 'Heisenberg microscope' and show the dramatic effect of continuous position measurements on the evolution of a quantum system. In particular, we confine nanoKelvin temperature atoms within an optical lattice and show that the act of imaging these atoms induces their localization, i.e. suppresses tunneling. In other words, we freeze the quantum motion of these atoms simply by the act of gazing at them. This phenomenon, a manifestation of the quantum Zeno effect, has no classical equivalent. 

The nature of measurement and its influence on a quantum system presents one of the foremost puzzles in our current understanding of quantum physics. Its ramifications include the intrinsic obstacles to 'ideal' measurements, the origin of the so-called standard quantum limit to measurement precision and the incongruity of such concepts when extended to the macroscopic domain (as encapsulated, for instance, in Schrodinger's famous cat paradox). Our experiments distil the essence of a position measurement by observing the effect of single photon scattering events on the spatial evolution of an atom. Furthermore, the tunability and simplicity of our measurement technique potentially allows it to be used as a valuable resource for the control of interacting quantum many-body systems.

Our two-photon imaging technique also allows us to tune the 'strength of the measurement', i.e. the rate at which the atoms scatter photons, over a wide dynamic range. As we gradually increase this measurement strength, we observe the continuous crossover from the regime of weak measurements, where the act of observation has negligible influence on the atoms, to the regime of strong measurements, where the act of observation causes a dramatic suppression of tunneling. This crossover behavior is an instance of emergent classicality in a quantum system due to continuous measurement. 

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QZE figure

Cohen group unravel root cause of plant twists and turns

To feed the world’s burgeoning population, producers must grow crops in more challenging terrain – where plant roots must cope with barriers. To that end, Tzer Han Tan, the Itai Cohen group and Boyce Thompson Institute plant biologists have uncovered a valuable plant root action, in that roots – when their downward path is blocked, as often occurs in rocky soil – display a “grow and switch” behavior, now reported in the latest Proceedings of the National Academy of Sciences. Prof Chris Henley, who passed away last June, also contributed to the research.

Read more in the Chronicle



plant root growth

Vinay Ambegaokar Receives 2015 John Bardeen Prize

Last week in Geneva Switzerland Vinay Ambegaokar received the 2015 John Bardeen Prize for his contributions to the statics, dynamics and kinetics of Josephson junctions and nanowires.

More on the prize at:

Also see the award announcement in the Chronicle.

Photo credit: Lionel Windels

Vinay Ambegaokar receives 2015 Bardeen Prize

Uyen Nguyen's Origami Art Featured in VOGEL Fashions

UPDATE Aug 5, 2015

Check out the article in the Chronicle and the new video...


Uyen Nguyen's origami art is part of a VOGEL collection that features creased textiles. For info on the collection see Nguyen works in the Cohen group studying the mechanical properties of Origami and designing materials with tailored mechanical properties.

Origami Fashion

Vengalattore group develop novel quantum resonators

Mukund Vengalattore's group has developed a novel method of manipulating mechanical resonators to be sensitive enough to work at the quantum scale.

Read more in the Chronicle and in The Times of India and the article in Physics Review Letters.