For many practical applications involving lasers, it’s important to be able to control the direction of the laser beams. Just ask Han Solo, or the captain of the Death Star. Researchers from North Carolina State University have come up with a very energy-efficient way of steering laser beams that is precise and relatively inexpensive.
“In many cases, it is much easier to redirect a laser beam at a target than to steer the laser itself. We intended to develop a way to do this efficiently and without moving anything,” says Dr. Michael Escuti, an associate professor of electrical engineering at NC State and co-author of a paper on the research. “We also wanted to be able to steer the beams over a wide range of angles, which is important for practical applications.”
The key to the Escuti team’s success was the use of “polarization gratings,” which consist of a thin layer of liquid crystal material on a glass plate. The researchers created a device that allows a laser beam to pass through a stack of these polarization gratings. Researchers manipulated the optical properties of each grating, and were able to steer the laser beams by controlling how each individual grating redirects the light. “Because each individual grating is very good at redirecting light in the desired directions with almost no absorption, the stack of gratings do not significantly weaken the laser power,” Escuti says.
Another advantage of the system, Escuti explains, is that “every grating that we add to the stack increases the number of steerable angles exponentially. So, not only can we steer lasers efficiently, but we can do it with fewer components in a more compact system.
“Compared to other laser steering technologies, this is extremely cost-effective. We’re taking advantage of materials and techniques that are already in widespread use in the liquid crystal display sector.”
The technology has a variety of potential applications. For example, free space communication uses lasers to transfer data between platforms – such as between satellites or between an aircraft and soldiers on the battlefield. This sort of communication relies on accurate and efficient laser-beam steering. Other technologies that could make use of the research include laser weapons and LIDAR, or laser radar, which uses light for optical scanning applications – such as mapping terrain.
Escuti’s team has already delivered prototypes of the technology to the U.S. Air Force, and is currently engaged in additional research projects to determine the technology’s viability for a number of other applications.
The paper, “Wide-angle, nonmechanical beam steering with high-throughput utilizing polarization gratings,” was co-authored by Escuti; NC State Ph.D. student Jihwan Kim; former NC State Ph.D. student Chulwoo Oh; and Steve Serati of Boulder Nonlinear Systems, Inc. The paper is published in the journal Applied Optics. The research was funded by the U.S. Air Force Research Laboratory.
NC State’s Department of Electrical and Computer Engineering is part of the university’s College of Engineering.
Source North Carolina State University
Notable events, developements and publications in science and technology this week. Updated daily.
Monday, May 2, 2011
New protein regulates water in the brain to control inflammation
New research in the FASEB Journal suggests that aquaporin-4, a water transporting protein, plays a role in brain inflammation via a mechanism involving astrocyte swelling and cytokine release.
A new protein, called aquaporin-4, is making waves and found to play a key role in brain inflammation, or encephalitis. This discovery is important as the first to identify a role for this protein in inflammation, opening doors for the development of new drugs that treat brain inflammation and other conditions at the cellular level rather than just treating the symptoms. This discovery was published in the May 2011 issue of The FASEB Journal (http://www.faseb.org).
"Our study establishes a novel role for a water channel, aquaporin-4, in neuroinflammation, as well as a cell-level mechanism," said Alan S. Verkman, M.D., Ph.D., a senior researcher involved in the work from the Department of Medicine and the Department of Physiology at the University of California, San Francisco. "Our data suggest that inhibition or down-regulation of aquaporin-4 expression in brain and spinal cord may offer a new therapeutic option in diseases such as multiple sclerosis, neuromyelitis optica and other conditions associated with neuroinflammation."
Scientists compared normal mice and mice without genes for producing aquaporin-4 using a model of brain inflammation. These experiments showed significantly reduced brain inflammation in the mice that did not produce aquaporin-4. Researchers then systematically investigated the various possible causes of this reduced neuroinflammation and surprisingly found that aquaporin-4 deletion causes the brain to be less susceptible to inflammation, involving differences in astrocyte reaction to stress. The involvement of aquaporin-4 in brain inflammation provides a new determinant and better understanding of how the brain responses to inflammatory stresses. This suggests that using drugs or other agents that target this protein may be effective for treating a variety of conditions associated with brain or spinal cord inflammation.
"This a new lead in our efforts to stem inflammation in the brain," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. "The importance of water movement in and out of cells cannot be understated, and this paper helps to clarify what has otherwise been a muddy view of aquaporins."
Source EurekaAlert!
A new protein, called aquaporin-4, is making waves and found to play a key role in brain inflammation, or encephalitis. This discovery is important as the first to identify a role for this protein in inflammation, opening doors for the development of new drugs that treat brain inflammation and other conditions at the cellular level rather than just treating the symptoms. This discovery was published in the May 2011 issue of The FASEB Journal (http://www.faseb.org).
"Our study establishes a novel role for a water channel, aquaporin-4, in neuroinflammation, as well as a cell-level mechanism," said Alan S. Verkman, M.D., Ph.D., a senior researcher involved in the work from the Department of Medicine and the Department of Physiology at the University of California, San Francisco. "Our data suggest that inhibition or down-regulation of aquaporin-4 expression in brain and spinal cord may offer a new therapeutic option in diseases such as multiple sclerosis, neuromyelitis optica and other conditions associated with neuroinflammation."
Scientists compared normal mice and mice without genes for producing aquaporin-4 using a model of brain inflammation. These experiments showed significantly reduced brain inflammation in the mice that did not produce aquaporin-4. Researchers then systematically investigated the various possible causes of this reduced neuroinflammation and surprisingly found that aquaporin-4 deletion causes the brain to be less susceptible to inflammation, involving differences in astrocyte reaction to stress. The involvement of aquaporin-4 in brain inflammation provides a new determinant and better understanding of how the brain responses to inflammatory stresses. This suggests that using drugs or other agents that target this protein may be effective for treating a variety of conditions associated with brain or spinal cord inflammation.
"This a new lead in our efforts to stem inflammation in the brain," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. "The importance of water movement in and out of cells cannot be understated, and this paper helps to clarify what has otherwise been a muddy view of aquaporins."
Source EurekaAlert!
Single Atom Stores Quantum Information
A powerful quantum computer could be designed with an incredibly tiny memory
A data memory can hardly be any smaller: researchers working with Gerhard Rempe at the Max Planck Institute of Quantum Optics in Garching have stored quantum information in a single atom. The researchers wrote the quantum state of single photons, i.e. particles of light, into a rubidium atom and read it out again after a certain storage time. This technique can be used in principle to design powerful quantum computers and to network them with each other across large distances.
Quantum computers will one day be able to cope with computational tasks in no time where current computers would take years. They will take their enormous computing power from their ability to simultaneously process the diverse pieces of information which are stored in the quantum state of microscopic physical systems, such as single atoms and photons. In order to be able to operate, the quantum computers must exchange these pieces of information between their individual components. Photons are particularly suitable for this, as no matter needs to be transported with them. Particles of matter however will be used for the information storage and processing. Researchers are therefore looking for methods whereby quantum information can be exchanged between photons and matter. Although this has already been done with ensembles of many thousands of atoms, physicists at the Max Planck Institute of Quantum Optics in Garching have now proved that quantum information can also be exchanged between single atoms and photons in a controlled way.
Using a single atom as a storage unit has several advantages - the extreme miniaturization being only one, says Holger Specht from the Garching-based Max Planck Institute, who was involved in the experiment. The stored information can be processed by direct manipulation on the atom, which is important for the execution of logical operations in a quantum computer. “In addition, it offers the chance to check whether the quantum information stored in the photon has been successfully written into the atom without destroying the quantum state,” says Specht. It is thus possible to ascertain at an early stage that a computing process must be repeated because of a storage error.
The fact that no one had succeeded until very recently in exchanging quantum information between photons and single atoms was because the interaction between the particles of light and the atoms is very weak. Atom and photon do not take much notice of each other, as it were, like two party guests who hardly talk to each other, and can therefore exchange only a little information. The researchers in Garching have enhanced the interaction with a trick. They placed a rubidium atom between the mirrors of an optical resonator, and then used very weak laser pulses to introduce single photons into the resonator. The mirrors of the resonator reflected the photons to and fro several times, which strongly enhanced the interaction between photons and atom. Figuratively speaking, the party guests thus meet more often and the chance that they talk to each other increases.
The photons carried the quantum information in the form of their polarization. This can be left-handed (the direction of rotation of the electric field is anti-clockwise) or right-handed (clock-wise). The quantum state of the photon can contain both polarizations simultaneously as a so-called superposition state. In the interaction with the photon the rubidium atom is usually excited and then loses the excitation again by means of the probabilistic emission of a further photon. The Garching-based researchers did not want this to happen. On the contrary, the absorption of the photon was to bring the rubidium atom into a definite, stable quantum state. The researchers achieved this with the aid of a further laser beam, the so-called control laser, which they directed onto the rubidium atom at the same time as it interacted with the photon.
Source Max-Planck-Gesellschaft
The fact that no one had succeeded until very recently in exchanging quantum information between photons and single atoms was because the interaction between the particles of light and the atoms is very weak. Atom and photon do not take much notice of each other, as it were, like two party guests who hardly talk to each other, and can therefore exchange only a little information. The researchers in Garching have enhanced the interaction with a trick. They placed a rubidium atom between the mirrors of an optical resonator, and then used very weak laser pulses to introduce single photons into the resonator. The mirrors of the resonator reflected the photons to and fro several times, which strongly enhanced the interaction between photons and atom. Figuratively speaking, the party guests thus meet more often and the chance that they talk to each other increases.
The photons carried the quantum information in the form of their polarization. This can be left-handed (the direction of rotation of the electric field is anti-clockwise) or right-handed (clock-wise). The quantum state of the photon can contain both polarizations simultaneously as a so-called superposition state. In the interaction with the photon the rubidium atom is usually excited and then loses the excitation again by means of the probabilistic emission of a further photon. The Garching-based researchers did not want this to happen. On the contrary, the absorption of the photon was to bring the rubidium atom into a definite, stable quantum state. The researchers achieved this with the aid of a further laser beam, the so-called control laser, which they directed onto the rubidium atom at the same time as it interacted with the photon.
The spin orientation of the atom contributes decisively to the stable quantum state generated by control laser and photon. Spin gives the atom a magnetic moment. The stable quantum state, which the researchers use for the storage, is thus determined by the orientation of the magnetic moment. The state is characterized by the fact that it reflects the photon’s polarization state: the direction of the magnetic moment corresponds to the rotational direction of the photon’s polarization, a mixture of both rotational directions being stored by a corresponding mixture of the magnetic moments.
This state is read out by the reverse process: irradiating the rubidium atom with the control laser again causes it to re-emit the photon which was originally incident. In the vast majority of cases, the quantum information in the read-out photon agrees with the information originally stored, as the physicists in Garching discovered. The quantity that describes this relationship, the so-called fidelity, was more than 90 percent. This is significantly higher than the 67 percent fidelity that can be achieved with classical methods, i.e. those not based on quantum effects. The method developed in Garching is therefore a real quantum memory.
The physicists measured the storage time, i.e. the time the quantum information in the rubidium can be retained, as around 180 microseconds. “This is comparable with the storage times of all previous quantum memories based on ensembles of atoms,” says Stephan Ritter, another researcher involved in the experiment. Nevertheless, a significantly longer storage time is necessary for the method to be used in a quantum computer or a quantum network. There is also a further quality characteristic of the single-atom quantum memory from Garching which could be improved: the so-called efficiency. It is a measure of how many of the irradiated photons are stored and then read out again. This was just under 10 percent.
The storage time is mainly limited by magnetic field fluctuations from the laboratory surroundings, says Ritter. “It can therefore be increased by storing the quantum information in quantum states of the atoms which are insensitive to magnetic fields.” The efficiency is limited by the fact that the atom does not sit still in the centre of the resonator, but moves. This causes the strength of the interaction between atom and photon to decrease. The researchers can thus also improve the efficiency: by greater cooling of the atom, i.e. by further reducing its kinetic energy.
This state is read out by the reverse process: irradiating the rubidium atom with the control laser again causes it to re-emit the photon which was originally incident. In the vast majority of cases, the quantum information in the read-out photon agrees with the information originally stored, as the physicists in Garching discovered. The quantity that describes this relationship, the so-called fidelity, was more than 90 percent. This is significantly higher than the 67 percent fidelity that can be achieved with classical methods, i.e. those not based on quantum effects. The method developed in Garching is therefore a real quantum memory.
The physicists measured the storage time, i.e. the time the quantum information in the rubidium can be retained, as around 180 microseconds. “This is comparable with the storage times of all previous quantum memories based on ensembles of atoms,” says Stephan Ritter, another researcher involved in the experiment. Nevertheless, a significantly longer storage time is necessary for the method to be used in a quantum computer or a quantum network. There is also a further quality characteristic of the single-atom quantum memory from Garching which could be improved: the so-called efficiency. It is a measure of how many of the irradiated photons are stored and then read out again. This was just under 10 percent.
The storage time is mainly limited by magnetic field fluctuations from the laboratory surroundings, says Ritter. “It can therefore be increased by storing the quantum information in quantum states of the atoms which are insensitive to magnetic fields.” The efficiency is limited by the fact that the atom does not sit still in the centre of the resonator, but moves. This causes the strength of the interaction between atom and photon to decrease. The researchers can thus also improve the efficiency: by greater cooling of the atom, i.e. by further reducing its kinetic energy.
The researchers at the Max Planck Institute in Garching now want to work on these two improvements. “If this is successful, the prospects for the single-atom quantum memory would be excellent,” says Stephan Ritter. The interface between light and individual atoms would make it possible to network more atoms in a quantum computer with each other than would be possible without such an interface; a fact that would make such a computer more powerful. Moreover, the exchange of photons would make it possible to quantum mechanically entangle atoms across large distances. The entanglement is a kind of quantum mechanical link between particles which is necessary to transport quantum information across large distances. The technique now being developed at the Max Planck Institute of Quantum Optics could some day thus become an essential component of a future “quantum Internet”.
Christian Meier
Source Max-Planck-Gesellschaft
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