APS Physics Tip Sheet – July 14, 2015
In this issue: Sending Quantum Messages Through Space; The Physics of Puddle Spreading; Terahertz-Controlled Chemistry; Perfect Absorbers of Light
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Sending Quantum Messages Through Space
Experiments demonstrate that qubits can be reliably transmitted from satellites to Earth, showing the feasibility of global quantum communications in space.
Quantum communication protocols such as quantum key distribution (QKD) transmit information with absolute security thanks to the laws of quantum mechanics. Demonstrated schemes are typically based on optical fibers but, according to a new study, quantum techniques may soon take advantage of the infrastructure of satellites orbiting the Earth. Researchers at the University of Padua and the Italian Space Agency have demonstrated that qubits encoded in photons can preserve their fragile quantum properties even after having bounced off satellites that are over a thousand kilometers away from Earth. The authors sent light pulses from Earth to five satellites, which reflected them back to Earth. The results showed that different qubit states could be faithfully distinguished after the long journey, achieving an error rate low enough for applications.
* G. Vallone, Paolo Villoresi (contact author) et al., “Experimental Satellite Quantum Communications,” Physical Review Letters (expected publication date: July 20)
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The Physics of Puddle Spreading
A new model explains how a puddle spreads by taking into account the forces between the liquid and the surface on which it lies.
Place a liquid drop on a surface, and it will spread out and then stop, leaving a puddle with sharp boundaries. But existing theories, based on the interplay between gravity, capillary and viscous forces, have not been able to fully explain the process. In particular, in contrast with everyday observations, they predict that the liquid never stops spreading. MIT researchers have now developed a new model that reproduces several experimental observations, including the spreading rate and the resulting shape of the puddle’s profile. The model’s success comes from its ability to account for intermolecular forces between the surface and the liquid, which become significant where the liquid is very thin, such as at the puddle’s edges. The authors plan to use the model to tackle a wide range of problems like flows over rough surfaces or though porous materials.
* A.A. Pahlavan, L. Cueto-Felgueroso, G.H. McKinley and Ruben Juanes (contact author), “Thin films in partial wetting: internal selection of contact-line dynamics,” Physical Review Letters (expected publication date: Jul 17)
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Terahertz-Controlled Chemistry
(Figure credit: H. Ogasawara/SLAC)
Pulses of Terahertz radiation have been used to selectively drive certain chemical reactions occurring on a metallic surface.
Many chemical reactions occur at a higher rate when the reactants are stuck to a surface, which acts as a catalyst. But sometimes other processes compete with the desired reaction, lowering its efficiency. Researchers from the U.S. and Sweden have demonstrated a new technique for controlling surface chemistry. The researchers used pulses of terahertz-frequency light—generated at Stanford’s Linac Coherent Light Source—to selectively drive the surface reaction by which carbon monoxide (CO) is oxidized, producing carbon dioxide (CO2). The pulses “kick” oxygen atoms adsorbed on the surface, so that they move along the surface and interact with CO molecules more often.
* J.L. LaRue, Hirohito Ogasawara (contact author) et al., “THz induced selective catalytic CO oxidation on Ru,” Physical Review Letters (expected publication date: Jul 15)
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Perfect Absorbers of Light
(Figure credit: Viktar Asadchy, Aalto University)
A metamaterial made of an array of helical elements absorbs radiation at certain frequencies while transmitting perfectly other frequencies.
Conventional devices used for absorbing light in a given frequency range often create an unwanted effect: they partly reflect frequencies outside the absorption frequency band. A team of researchers from Finland, Belarus and Japan has now designed and fabricated a thin metamaterial that absorbs electromagnetic waves over a narrow frequency band while producing no reflections at other frequencies. The device, made of an array of alternating right- and left-handed chromium–nickel helices embedded in a plastic-foam slab, could find applications ranging from optical filters to stealth technology.
* Viktar S. Asadchy (contact author) et al., “Broadband reflectionless metasheets:
Frequency-selective transmission and perfect absorption,” Physical Review X (published Jul 14)
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Journal articles and preprints are available to journalists on request.
