Progress in quantum computing: Researchers control rate of photon emission from luminescent imperfections in diamond

Engineers and physicists at Harvard have managed to capture light in tiny diamond pillars embedded in silver, releasing a stream of single photons at a controllable rate.

The advance represents a milestone on the road to quantum networks in which information can be encoded in spins of electrons and carried through a network via light, one photon at a time.

The finding was published in Nature Photonics, appearing online Oct. 9.

"We can make the emission of photons faster, which will allow us to do more processing per second -- for example, more computations -- in the future quantum network," explains principal investigator Marko Lončar, Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS).

The device Lončar's research team has built consists of parallel rows of tiny, nanofabricated diamond posts, embedded in a layer of silver, that can each act as a single photon source.

By removing the silver wrapping from their nanostructures, the team was also able to achieve a slower release of photons, which is of interest for probing the dynamics of the quantum system.

The breakthrough takes advantage of imperfections in the diamond's crystal lattice, where carbon atoms are replaced by other elements. To the naked eye, these imperfections can appear as discolorations in the diamond, turning it yellow in the case of nitrogen. Occasionally, there is also a vacancy (missing carbon atom) next to the nitrogen atom.

Each nitrogen-vacancy imperfection can serve as a nearly perfect quantum emitter, capable of emitting red photons one by one, even at room temperature. The technology is a promising candidate for realization of scalable, on-chip quantum networks.

"The color centers in diamond are very interesting as qubits for quantum information processing, where they can be used as memory to store information," says Lončar. "More importantly, they can be interrogated -- they can be written into and read out -- with light."

Lončar's team fabricates diamond posts that contain negatively charged nitrogen vacancy centers, which can absorb light and hold its energy for a given amount of time, finally releasing it in the form of photons.

"The rate at which photons are emitted can be controlled by carefully nano-engineering the center's surrounding," says co-author Irfan Bulu, a research associate in the Lončar group. Attaining fine control of that release, however, has been difficult.

"One of the main challenges has been the efficiency with which you can write information into the spin of these color centers, as well as the efficiency with which you can collect photons emitted from the color centers," explains co-author Jennifer Choy, a graduate student in Lončar's lab at SEAS. "The other challenge has been the rate -- how quickly you can perform these processes."

Previous work from Lončar's group solved the collection efficiency problem by using diamond nanowires to channel and direct the flow of photons. The new research manipulates the radius of diamond pillars and adds the silver coating. The diamond-silver construction acts as an optical nanoresonator, creating a strong electromagnetic field around the emitter and offering a new level of control over the rate of emission.

Moreover, the device functions at room temperature -- an essential requirement for practical computing applications -- and the nanostructured chips are fully scalable.

"We've designed everything in parallel in a massive system, which allows us to make thousands or millions of devices with more or less the same properties, and we use conventional microfabrication and nanofabrication techniques, unlike what has been done in this field before," says Birgit Hausmann, a graduate student in Lončar's lab at SEAS and one of the co-authors.

In addition to Lončar, Choy, Hausmann, and Bulu, co-authors included Tom Babinec, a graduate student at SEAS; Mughees Khan, a staff scientist at the Wyss Institute for Biologically Inspired Engineering at Harvard; Patrick Maletinsky, a fellow of the Department of Physics at Harvard; and Amir Jacoby, Professor of Physics in the Harvard Faculty of Arts and Sciences.

The work was supported by grants and fellowships from the U.S. Department of Defense, the Defense Advanced Research Projects Agency (DARPA) QuEST program, the National Science Foundation (NSF), the King Abdullah University of Science and Technology (KAUST), the Sloan Foundation, and the NSF-supported Nanoscale Science and Engineering Center (NSEC) at Harvard. Fabrication took place at the NSF-supported Center for Nanoscale Systems (CNS) at Harvard.

The above story is reprinted (with editorial adaptations) from materials provided by Harvard University.

Journal Reference:

Jennifer T. Choy, Birgit J. M. Hausmann, Thomas M. Babinec, Irfan Bulu, Mughees Khan, Patrick Maletinsky, Amir Yacoby, Marko Lončar. Enhanced single-photon emission from a diamond–silver aperture. Nature Photonics, 2011; DOI: 10.1038/nphoton.2011.249

Progress toward smell television: Targeted release of various scents from individually addressable chambers

 3-D movies, Dolby surround for a more realistic audio experience -- virtual reality is on the march. And how much more realistic would a film be if a barbecue actually smelled of grilled meat or if you could smell a sea breeze when the protagonist takes his love for an evening stroll on the beach? This type of smell experience may become reality for the home television viewer in the not-too-distant future.

In the journal Angewandte Chemie, a team led by Jongmin Kim at Samsung Electronics in Korea and Sungho Jin at the University of California, San Diego, USA, have now introduced a new approach for making a compact device that could fit on the back of a television to produce thousands of different scents.

Previous technologies for the controlled release of scents were not simple enough and were much too crude for the sensitive electronics of our televisions and video players. An odor module needs to be small and robust and deliver results that are reproducible over multiple cycles; the response should be rapid and the user should be able to regulate the strength of the odor. Kim, Jin, and their co-workers aim to overcome these challenges with their new concept.

Their method is based on an array of individual cells that are filled with scent-containing solutions. The miniature containers are made from a cross-linked silicone polymer. Except for a tiny hole in the top, they are completely sealed. A needle can be sued to inject a different scent solution into each cell. In the “off” state the tiny hole stays closed. The scent containers are switched on by heating. This causes the silicone to expand and the pressure on the inside to increase, forcing a small amount of gas-phase scent out of the tiny hole.

A two-dimensional lattice of heating wires, known as an X-Y matrix, can be used to specifically address individual containers. The scientists prepared a prototype, which they successfully tested with two different perfumes, “Live by Jenifer Lopez” and “Passion by Elizabeth Taylor”. Testers could detect both scents and differentiate between them.

“Our new concept is not only of interest for the entertainment industry,” state Kim and Jin, “it could also be used for combinatorial studies of gas-phase reactions and the development of vapor-based pharmaceuticals.”

More information: Sungho Jin, An X–Y Addressable Matrix Odor-Releasing System Using an On–Off Switchable Device, Angewandte Chemie International Edition, http://dx.doi.org/ … ie.201102759

Provided by Wiley (news : web)

Antibiotic progress for disease that causes half a million deaths a year

Scientists are making progress in their quest to find an improved antibiotic for a strain of meningitis that results in over half a million deaths a year worldwide. The fungal disease Cryptococcal Meningitis is especially rife in AIDS patients and there are fears that if new drugs cannot be found, it could become untreatable. The results are published in one of the most respected journals in the field of membrane biology - Biochimica et Biophysica Acta – Biomembranes. Further experiments will be carried out at STFC’s ISIS neutron source this week.

Cryptococcal Meningitis is diagnosed in nearly a million people a year worldwide, mainly in AIDS patients but also in others with defects in their cell mediated-immunity. More than 600,000 of these cases lead to fatalities. Currently, there is no vaccine for Cryptococcal Meningitis. Unlike most other strains of the disease, it is not passed from person to person, but is actually acquired from the environment, possibly by exposure to birds. The disease is most prominent in Sub-Saharan Africa but is also known to be on the increase in areas such as Thailand and India.

With funding from the Engineering and Physical Sciences Research Council, scientists from King’s College London have been using neutrons to look at the effects of the antibiotic Amphotericin which is currently used to treat Cryptococcal Meningitis. They hope this will help them devise new and more effective treatments, in particular for the disease-causing fungi that have developed a resistance to the drug.

“Such an approach, of course, requires that we fully understand how Amphotericin works, and unfortunately this is not the case”, said David Barlow – the lead researcher from King’s College London.

“We do know that the drug has little effect on the cells in a human because these cells are surrounded by membranes containing cholesterol. We also know that the drug exerts its effects on fungi because their cells do not contain cholesterol, but instead have a related steroid, ergosterol. However it is quite unclear how this difference between human and fungal cell membranes matters to the workings of Amphotericin.”

Research published in the journal Biochimica et Biophysica Acta – Biomembranes shows that Amphotericin can insert itself into cell membranes regardless of whether they contain cholesterol, ergosterol, or no sterol at all, and the resulting changes in the structure of the membrane seem to be the same for all three systems. This means the reason for the drug having less impact on human cells than fungal cells cannot purely be down to the fact that human cells contain cholesterol – other factors must be at play.

What seems more likely is that the drug interacts more rapidly with fungal cells than human cells, or that the structures it forms after inserting in to their membranes are different for the two types of cell.

“We're now going on to investigate the first of these possibilities, and during our next experiments at ISIS, we plan to look for differences in the speed with which the drug enters human and fungal cell membranes”, said David Barlow. “The more information we can gather about how this complex system works, the more likely we are to be able to develop a new antibiotic that will be as effective as Amphotericin has been until recently”.

In addition to Cryptococcal Meningitis, Amphotericin is also used to treat infections such as the tropical disease Visceral Leishmaniasis.

More information: Download the full scientific paper.

Provided by Science & Technology Facilities Council

First non-trivial atom circuit: Progress toward an atom SQUID

Researchers from the National Institute of Standards and Technology (NIST) and the University of Maryland (UM) have created the first nontrivial "atom circuit," a donut-shaped loop of ultracold gas atoms circulating in a current analogous to a ring of electrons in a superconducting wire. The circuit is "nontrivial" because it includes a circuit element -- an adjustable barrier that controls the flow of atom current to specific allowed values.

The newly published work was done at the Joint Quantum Institute, a NIST/UM collaboration.

Ultracold gases, such as the Bose-Einstein condensate of sodium atoms in this experiment, are fluids that exhibit the unusual rules of the quantum world. Atomic quantum fluids show promise for constructing ultraprecise versions of sensors and other devices such as gyroscopes (which stabilize objects and aid in navigation). Superfuid helium circuits have already been used to detect rotation. Superconducting quantum interference devices (SQUIDs) use superconducting electrons in a loop to make highly sensitive measurements of magnetic fields. Researchers are striving to create an ultracold-gas version of a SQUID, which could detect rotation. Combined with ultracold atomic-gas analogs of other electronic devices and circuits, or "atomtronics" that have been envisioned, such as diodes and transistors, this work could set the stage for a new generation of ultracold-gas-based precision sensors.

To make their atom circuit, researchers created a long-lived persistent current -- a frictionless flow of particles -- in a Bose-Einstein condensate of sodium atoms held by an arrangement of lasers in a so-called optical trap that confines them to a toroidal, or donut, shape. Persistent flow -- occurring for a record-high 40 seconds in this experiment -- is a hallmark of superfluidity, the fluid analog of superconductivity.

The atom current does not circle the ring at just any velocity, but only at specified values, corresponding in this experiment to just a single quantum of angular momentum. A focused laser beam creates the circuit element -- a barrier across one side of the ring. The barrier constitutes a tunable "weak link" that can turn off the current around the loop.

Superflow stops abruptly when the strength of the barrier is sufficiently high. Like water in a pinched garden hose, the atoms speed up in the vicinity of the barrier. But when the velocity reaches a critical value, the atoms encounter resistance to flow (viscosity) and the circulation stops, as there are no external forces to sustain it.

In atomic Bose-Einstein condensates, researchers have previously created Josephson junctions, a thin barrier separating two superfluid regions, in a single atomic trap. SQUIDs require a Josephson junction in a circuit. This present work represents the implementation of a complete atom circuit, containing a superfluid ring of current and a tunable weak link barrier. This is an important step toward realizing an atomic SQUID analog.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

A. Ramanathan, K. Wright, S. Muniz, M. Zelan, W. Hill, C. Lobb, K. Helmerson, W. Phillips, G. Campbell. Superflow in a Toroidal Bose-Einstein Condensate: An Atom Circuit with a Tunable Weak Link. Physical Review Letters, 2011; 106 (13) DOI: 10.1103/PhysRevLett.106.130401