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Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them

22/11/2017

Researchers have discovered that dense ensembles of quantum spins can be created in diamond with high resolution using an electron microscopes, paving the way for enhanced sensors and resources for quantum technologies.

Diamonds are made of carbon atoms in a crystalline structure, but if a carbon atom is replaced with another type of atom, this will result in a lattice defect. One such defect is the Nitrogen-Vacancy (NV), where one carbon atom is replaced by a nitrogen atom, and its neighbor is missing (an empty space remains in its place).

If this defect is illuminated with a green laser, in response it will emit red light (fluoresce) with an interesting feature: its intensity varies depending on the magnetic properties in the environment. This unique feature makes the NV center particularly useful for measuring magnetic fields, magnetic imaging (MRI), and quantum computing and information.

In order to produce optimal magnetic detectors, the density of these defects should be increased without increasing environmental noise and damaging the diamond properties.

Now, scientists from the research group of Nir Bar-Gill at the Hebrew University of Jerusalem’s Racah Institute of Physics and Department of Applied Physics, in cooperation with Prof. Eyal Buks of the Technion – Israel Institute of Technology, have shown that ultra-high densities of NV centers can be obtained by a simple process of using electron beams to kick carbon atoms out of the lattice.

This work, published in the scientific journal Applied Physics Letters, is a continuation of previous work in the field, and demonstrates an improvement in the densities of NV centers in a variety of diamond types. The irradiation is performed using an electron beam microscope (Transmission Electron Microscope or TEM), which has been specifically converted for this purpose. The availability of this device in nanotechnology centers in many universities in Israel and around the world enables this process with high spatial accuracy, quickly and simply.

The enhanced densities of the NV color centers obtained, while maintaining their unique quantum properties, foreshadow future improvements in the sensitivity of diamond magnetic measurements, as well as promising directions in the study of solid state physics and quantum information theory.

Nitrogen Vacancy (NV) color centers exhibit remarkable and unique properties, including long coherence times at room temperature (~ ms), optical initialization and readout, and coherent microwave control.

“This work is an important stepping stone toward utilizing NV centers in diamond as resources for quantum technologies, such as enhanced sensing, quantum simulation and potentially quantum information processing”, said Bar-Gill, an Assistant Professor in the Dept. of Applied Physics and Racah Institute of Physics at the Hebrew University, where he founded the Quantum Information, Simulation and Sensing lab.

"What is special about our approach is that it's very simple and straightforward," said Hebrew University researcher Dima Farfurnik. "You get sufficiently high NV concentrations that are appropriate for many applications with a simple procedure that can be done in-house."

CITATION: Farfurnik, D., et al. Enhanced concentrations of nitrogen-vacancy centers in diamond through TEM irradiationAppl. Phys. Lett. 111, 123101 (2017). Publisher's Version

SUPPORT: This work was supported in part by the Minerva ARCHES award, the CIFAR-Azrieli global scholars program, the Israel Science Foundation (Grant No. 750/14), the Ministry of Science and Technology, Israel, the Technion security research foundation, and the CAMBR fellowship for Nanoscience and Nanotechnology.

PHOTO 1: http://media.huji.ac.il/new/photos/hu171114_bar-gill.jpg - Diamond sample illuminated by green light in our home-built microscope. Sample is placed on a special mount, within a printed circuit board, used to deliver microwaves which allow quantum manipulations and magnetic sensing with the NVs. (Credit: Yoav Romach)

PHOTO 2: http://media.huji.ac.il/new/photos/hu171114_bar-gill-cryo.jpg - Cryogenic sample chamber, with diamond sample mounted on copper cold plate. (Credit: Yoav Romach)

PHOTO 3: https://drive.google.com/file/d/1TsGTAKrw1l_dw2X2tUDlbBluwnP_LoGf/view - Hebrew University researchers Nir Bar-Gill and Dima Farfurnik with a diamond magnetic microscope. (Credit: Nir Bar-Gill)

Enhancing the quantum sensing capabilities of diamond: Shooting electrons at diamonds can introduce quantum sensors into them
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HU Researchers: Simple Method Measures How Long Bacteria Can Wait Out Antibiotics

21/06/2017

The efficient classification of bacterial strains as tolerant, resistant, or persistent could help to guide treatment decisions, and could ultimately reduce the ever-growing risk of resistance

A growing number of pathogens are developing resistance to one or more antibiotics, threatening our ability to treat infectious diseases. Now, according to a study published in Biophysical Journal, a simple new method for measuring the time it takes to kill a bacterial population could improve the ability of clinicians to effectively treat antimicrobial-tolerant strains that are on the path to becoming resistant.

“These findings allow measurement of tolerance, which has previously been largely overlooked in the clinical setting,” says senior study author Prof. Nathalie Balaban, the Joseph and Sadie Danciger Professor of Physics at the Hebrew University of Jerusalem. “Routinely measuring tolerance could supply valuable information about the duration of antibiotic treatments, reducing the chance of both under- and over-treatment. Furthermore, data compiled from such measurements could give an estimate of how widespread the phenomenon of tolerance really is, which is currently a complete unknown.”

According to the World Health Organization, antibiotic resistance is one of the biggest threats to global health and is putting the achievements of modern medicine at risk. Due to selective pressure, pathogens acquire resistance through mutations that make the antibiotic less effective, for example, by interfering with the ability of a drug to bind to its target. Currently, clinicians determine which antibiotic and dose to prescribe by assessing resistance levels using a routine metric called minimum inhibitory concentration (MIC)—the minimal drug concentration required to prevent bacterial growth.

Although resistant strains continue to grow despite exposure to high drug concentrations, tolerant strains can survive lethal concentrations of an antibiotic for a long period of time before succumbing to its effects. Tolerance is often associated with treatment failure and relapse, and it is considered a stepping stone toward the evolution of antibiotic resistance. But unlike resistance, tolerance is poorly understood and is currently not evaluated in healthcare settings.

“The lack of a quantitative measure means that this aspect of the treatment relies largely on the experience of the individual physician or the community,” says first author Asher Brauner, a PhD student in Balaban’s lab at the Hebrew University’s Racah Institute of Physics. “This can lead to treatment being either too short, increasing the risk of relapse and evolution of resistance, or much too long, unnecessarily causing side effects, release of antibiotic waste into the environment, and additional costs.”

To address this problem, Balaban and her team developed a tolerance metric called the minimum duration for killing 99% of the population (MDK99). The protocol, which can be performed manually or using an automated robotic system, involves exposing populations of approximately 100 bacteria in separate microwell plates to different concentrations of antibiotics for varied time periods, while determining the presence or lack of survivors.

The researchers applied MDK99 to six Escherichia coli strains, which showed tolerance levels ranging from 2 to 23 hr under ampicillin treatment. MDK99 also facilitates measurements of a special case of tolerance known as time-dependent persistence—the presence of transiently dormant subpopulations of bacteria that are killed more slowly than the majority of the fast-growing population. Like other forms of tolerance, time-dependent persistence can lead to recurrent infections because the few surviving bacteria can quickly grow to replenish the entire population once antibiotic treatment stops.

“A take-home message from this is that it is important to complete a course of antibiotic treatment as prescribed, even after the disappearance of the symptoms,” Balaban says. “Partial treatment gives tolerance and persistence mutations a selective advantage, and these, in turn, hasten the development of resistance.”

In future studies, Balaban and her team will use MDK99 to study the evolution of tolerance in patients. Moreover, the ability to systematically determine the tolerance level of strains in the lab could facilitate research in the field. “If implemented in hospital clinical microbiology labs, MDK99 could enable the efficient classification of bacterial strains as tolerant, resistant, or persistent, helping to guide treatment decisions,” Balaban says. “In the end, understanding tolerance and finding a way to combat it could significantly reduce the ever-growing risk of resistance.”

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Scientists involved with this research are affiliated with The Racah Institute of Physics and The Center for NanoScience and NanoTechnology at The Hebrew University of Jerusalem, and The Broad Institute of Harvard University and Massachusetts Institute of Technology (MIT).

FUNDING: This work was supported by the European Research Council (ERC) (grant 681819) and the Israel Science Foundation (ISF) (grant 492/15).

CITATION: Biophysical Journal. Asher Brauner, Noam Shoresh, Ofer Fridman, Nathalie Q. Balaban.: “An Experimental Framework for Quantifying Bacterial Tolerance” http://www.cell.com/biophysj/fulltext/S0006-3495(17)30551-9 / doi: 10.1016/j.bpj.2017.05.014

HU Researchers: Simple Method Measures How Long Bacteria Can Wait Out Antibiotics
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