In this issue: Distributing Entanglement on the Cheap, Asking Photons Where They Have Been, Why Swimming Particles Aggregate
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Distributing Entanglement on the Cheap
Three new experiments demonstrate how entanglement can be shared between two distant parties without the need of sending an entangled carrier.
Entangled states lie at the heart of quantum physics and can be used as a powerful resource in emerging quantum technologies such as quantum key cryptography. The disruption of entanglement, which can be caused by any interaction with the environment, poses the hardest challenge to practical applications. But three different international research teams have now demonstrated experiments that distribute entanglement between two distant parties by sending a non-entangled carrier. Their arrangements place this carrier in a "cheaper," so-called separable state, which is still tied, or “correlated,” to the two parties, but in a way that is less fragile to environmental disturbance than entanglement is. The scheme may thus help realize communication schemes that are more robust to noise.
* Christian Peuntinger (contact author) et al, “Distributing entanglement with separable states”, Physical Review Letters (expected publication date: Dec 4)
* CE Vollmer, Roman Schnabel (contact author) et al, “Experimental entanglement distribution by separable states”, Physical Review Letters (expected publication date: Dec 4)
* A Fedrizzi, Tomasz Paterek (contact author) et al, “Experimental distribution of entanglement with separable carriers”, Physical Review Letters (expected publication date: Dec 4)
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Asking Photons Where They Have Been
A new experiment exposes the path taken by photons in an optical setup, revealing an unconventional quantum phenomenon.
A research team at the Tel-Aviv University has demonstrated a technique that is able to find out what path – among a few possible ones – photons have taken in an optical apparatus. The experiment allowed them to reveal a bizarre quantum mechanical phenomenon: photons pass through a section of the setup that they neither enter nor exit. The authors explain the effect by invoking an alternative interpretation of quantum mechanics called a “two-state vector formalism”, in which any quantum state in the present is described through a relationship between quantum states in the future and quantum states in the past.
* A Danan, D Farfurnik, S Bar-Ad, Lev Vaidman (contact author), “Asking photons where they have been”, Physical Review Letters (expected publication date: Dec 9)
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Why Swimming Particles Aggregate
Simulations explain why ensembles of swimming particles in solution sometimes aggregate in clusters.
Particles that move of their own accord, such as bacteria or beads propelled by chemical reactions, can organize themselves into diverse arrangements, such as coherently moving swarms or ordered arrays. A commonly observed behavior is the formation of a number of clusters, which may achieve a stable size or aggregate into a single dense phase. The reasons for the diverse behaviors are clarified by the work of a team of researchers from Europe (UK, Spain, Germany) and the US. The authors’ simulations explain why clustering may occur, depending on a fine balance of different forces: the attractive or repulsive forces between particles and the swimming intensity of the self-propelled particles. The model could be used to describe the behavior of biologically relevant systems or to design new ways of assembling tiny particles into well-defined structures.
* BM Mognetti, Chantal Valeriani (contact author) et al, “Living clusters and crystals from low-density suspensions of active colloids”, Physical Review Letters (expected publication date: Dec 6)
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Journal articles and preprints are available to journalists on request.
