Nano-trampoline developed to probe quantum behavior

May 28, 2017 04:13

Bar Ilan University collaborates with French counterparts at CNRS Grenoble to develop experiment detecting quantum events in ultra-thin films.

A scientist prepares protein samples for analysis in a lab

A scientist prepares protein samples for analysis in a lab at the Institute of Cancer Research in Sutton. (photo credit:REUTERS)

A unique experiment to detect quantum events in ultra-thin films has been developed by a research group from Bar-Ilan University, in collaboration with French colleagues at CNRS Grenoble. It was carried out by Prof. Aviad Frydman of BIU’s physics department and the Institute of Nanotechnology and Advanced Materials and his student Shachaf Poran, together with Dr. Olivier Bourgeois of CNRS Grenoble.

They have for the first time provided a method for such ultra-delicate detection.

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The measurement performed by Frydman’s group – published in the scientific journal Nature Communications – is the first of its kind. They said that their novel research enhances the understanding of basic phenomena that occur in nano-sized systems close to absolute zero temperature.

This work is expected to be a milestone in the understanding of physical processes that govern the behavior of ultrathin systems at ultralow temperatures.

The theoretical prediction of such quantum criticality was provided a few decades ago, but how to measure this experimentally has remained a mystery. A phase transition is a general term for physical phenomena in which a system moves from one state to another after changing the temperature. Routine examples of this are the transition from ice to water (solid to liquid) at zero degrees centigrade and from water to vapor (liquid to gas) at 100 degrees.

The temperature at which transition takes place is called the critical point. Near it, interesting physical phenomena occur. For example, as water is heated, small gas regions start forming and the water bubbles.

As the temperature of the liquid is raised toward the critical point, the size of the gas bubbles grows.

As the size of the bubble becomes comparable to the wavelength of light, the light is scattered and causes the normally transparent liquid to appear “milky” – a phenomenon known as critical opalescence.

Scientists have been increasingly interested in quantum phase transitions, in which a system transits between two states at absolute zero temperature (-273º C) by manipulating a physical parameter such as magnetic field, pressure or chemical composition instead of temperature. In these transitions the change occurs not due the thermal energy provided to the system by heating but rather by quantum fluctuations. Although it is not possible to reach absolute zero, characteristics of the transition can be detected in the system’s very low-temperature behavior near the quantum critical point. Such characteristics include “quantum bubbles” of one phase in the other. The size and lifetime of these quantum bubbles increase as the system is tuned toward the critical point, giving rise to a quantum equivalent of critical opalescence.

In normal phase transitions there is a unique measurable quantity that is used to detect a critical point. This is the specific heat that measures the amount of heat energy that should be supplied to a system in order to raise its temperature by one degree. Increasing the temperature of a system by two degrees requires twice the energy that is needed for increasing it by one degree, but close to a phase transition, this is no longer the case. Much of the energy is invested in creating the bubbles and, therefore, more energy must be invested to generate a similar change in temperature.

Measurements of a quantum critical point pose a greater challenge, as they must be carried out at low temperatures, and nano-thin layers need very sensitive measurements.

Frydman’s group overcame these obstacles by developing a unique experimental design based on a thin membrane suspended in air by very narrow bridges, thereby forming a nano-trampoline.

NEW AMOEBA NAMED FOR LORD OF THE RINGS CHARACTER Researchers in Brazil have identified a microorganism with a carapace that resembles the wizard’s hat worn by Gandalf in Lord of the Rings, a series of novels by J.R.R.

Tolkien. They decided to name the ameba species Arcella gandalfi as a tribute to Tolkien’s wizard. The new species is described in a recent article published by the journal Acta Protozoologica.

The camoebians are among the 30 to 45 lineages of amoebae known to exist worldwide. During their evolution, they have developed the ability to produce a varyingly shaped outer carapace, or shell, to protect themselves.

The group headed by researchers at the University of Sao Paulo’s Bioscience Institute said that new amoeba species are very rarely discovered because they’re so tiny and not widely studied. In addition, there are very few taxonomists who specialize in this group in Brazil,” said Prof. Daniel J. G. Lahr, a zoologist and the principal investigator. In recent years, Lahr began receiving reports of the existence of this species of freshwater microorganism from various parts of Brazil. The number of specimens collected in these regions was so small, however, that it was impossible to perform a laboratory analysis to make sure that they genuinely represented a new species.

Then he received a tip from Jordana de Carvalho e Féres, a biologist who works for a firm of environmental consultants specializing in taxonomic identification and population analysis of zooplankton. She found 180 specimens of the shelled amoeba in two samples collected from Amapa and Rio de Janeiro. The team isolated the organism from the samples, performed all the necessary measurements and produced images to make sure it really was a new species, Lahr said.

The color of A. gandalfi ranges from light yellow to brown, and the diameter and height of its conical shell average 81 and 71 micrometers, (.01 millimeter).

Although A. gandalfi is microscopic, it is considered large for a single- celled organism.

“It’s just one cell, and yet it’s capable of building this funnel-shaped carapace,” Lahr said. They are not sure why it has a bony shield. It may protect the amoebae from the dryness that is abundant among plankton in shallow lakes and ponds, streams and reservoirs, or, they suggest, against ultraviolet radiation.

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