Graduate University

Hayama, Japan

Graduate University

Hayama, Japan
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News Article | May 5, 2017
Site: www.materialstoday.com

Stress sensors are important tools when it comes to evaluating the robustness of a material exposed to strong mechanical forces. In a paper in Advanced Materials, researchers at Okinawa Institute of Science and Technology Graduate University (OIST) in Japan report a new kind of sensor molecule that brightens when the material it is incorporated into comes under heavy mechanical stress. Such light-based sensing molecules, known as photoluminescent mechanophores, are not new, but current applications of them are single-use only. They typically involve a strong force – compressing, twisting or stretching for example – breaking a specific chemical bond between two atoms or irreversibly pulling apart two complexes in the sensing molecule. This changes the wavelength – and thus the color – of the light emitted by the mechanophore. Once these molecules have radically changed their structure in response to this force, however, it is extremely difficult for them to return to the initial situation. So while these mechanophores are useful for understanding the mechanical properties of an item or a material, they are not well suited for investigating repeated exposure to mechanical stress. To overcome this issue, Georgy Filonenko and Julia Khusnutdinova from OIST’s Coordination Chemistry and Catalysis Unit designed a photoluminescent mechanophore that retains its properties over time and under repeated incidences of mechanical stress. The researchers incorporated this stress-sensing molecule into polyurethane, which is widely used in everyday items such as mattresses and cushions, inflatable boats, car interiors, woodworking glue and even spandex. The scientists then stretched the resulting material with increasing force, triggering a correspondingly brighter glow under an ultraviolet light. This reaction happens within hundreds of milliseconds, resulting in an up to two-fold increase in luminescence intensity. When the mechanical stress stops, the polymer material and the mechanophore revert to their initial position, leading to a drop in intensity. This is critical as it allows for repeated applications of mechanical force. This new mechanophore is a photoluminescent compound from recently published work by Filonenko and Khusnutdinova. Despite its very simple structure, the molecule is extremely responsive to the physical environment, producing the rapid change in luminescence intensity. The researchers incorporated these molecules directly within the repeated patterns of the polymer material. Filonenko and Khusnutdinova found that the high mobility of the mechanophore molecules in the polymer was key to the sensor performance. When the mechanophores could move rapidly in the relaxed polymer sample, the luminescence intensity was low due to these molecular motions preventing the mechanophore from emitting light. Subjecting the material to mechanical force slowed down the polymer chain motions, allowing the mechanophore to emit light more efficiently. “Our material shows how a macroscopic force as basic as stretching a flexible strand of material can efficiently trigger microscopic changes all the way down to isolated molecules,” said Filonenko. This story is adapted from material from OIST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


Traditional chemistry is immensely powerful when it comes to producing very diverse and very complex microscopic chemical molecules. But one thing out of reach is the synthesis of large structures up to the macroscopic scale, which would require tremendous amounts of chemicals as well as an elaborate and complicated technique. For this purpose, scientists rely instead on "self-assembling" molecules, compounds that can interact with other copies of themselves to spontaneously congregate into spheres, tubes or other desired shapes. Using this approach, researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) now reports in Chemical Communications new self-assembling molecules that can transform into novel, exotic and previously unobserved shapes by simply using UV light to force them to rearrange differently into "metastable" states. When designing self-assembly structures, scientists typically aim for the state of lowest energy – or "ground state," in which the structure would be at its highest stability. Less stable shapes are usually dismissed as incorrect and undesirable. However, this "ground state" being very stable makes it arduous to break down the structure if you wish to alter its shape. In this research, OIST scientists inserted a weakness into their ground-state self-assembled structures, resulting in structures requiring only a small nudge to collapse. In this case, the nudge is the use of ultraviolet light to snip a specific bond between two atoms within the molecule, splitting the structure into smaller fragments. The fragments are then able to co-assemble into less stable – called metastable - but novel and exotic shapes. "This report is about a new concept in material science," explained Prof. Zhang from the Bioinspired Soft Matter Unit and author of the study. "We converted a self-assembling phenomenon into co‑assembling in a spatially and temporally controllable manner using light. Eventually, we constructed exotic heterogeneous nanostructures inaccessible though conventional synthetic path." This new concept led to a fascinating discovery: because the remaining fragments are tightly packed following the collapse from the initial structure, they can form novel and exotic structures which are not attainable if you just mix the same molecules in free motion. Imagine these nanostructures made from Lego bricks: initially you have 2x5 bricks - 2 studs wide and 5 studs long – self-assembling into a nanofiber. Ultraviolet light will split these 2x5 bricks into two smaller pieces, for example a 2x3 brick and a 2x2 brick, destroying the entire fiber-like structure. But because these smaller bricks remain pre-organized spatially staying close to each other, they can easily recombine themselves into new shapes visible with the naked eye. In contrast, if in a separate experiment you just mix 2x3 and 2x2 Lego bricks in a random manner in a bucket with varying distances between bricks, their lack of spatial organization prevents the assembly of such novel nanostructures. According to Prof. Zhang, the ability to create new structures is vital: "In material science, the function is always related to the structure. If you create a different structure, you manipulate the function and even create new applications." For example, the toxicity of a molecule in a nanofiber shape might be much lower or higher than the same molecule assembled in a spherical shape." The present research performed at OIST strongly suggests the initial conditions are the most critical parameter influencing the final shape taken by self-assembling molecules. "If you know how the molecules pack with each other from the parameters of the initial state, then it will give you more clues to aim towards a specific macroscopic shape," commented Prof. Zhang. This shapeshifting ability holds great potential for biological applications. Prof. Zhang suggested, "For example you introduce the molecule into a living organism and it adopts a certain structure. Then using light, you break a chemical bond and then the molecule will switch to another structure with the function you want." In pharmaceutical design, such a concept would allow a drug to reach its target in a living organism – an organ or a tumor – in an inactive state, thus limiting potential side effects. Once broken down in this targeted location, the drug would reshape itself into a different structure with therapeutic activity. Prof. Zhang concluded, "For now, using ultraviolet light as we do is not ideal as it is toxic for living cells. The next step for us is to move towards more biocompatible self-assembling structures with better adaptability to living systems." Explore further: Nanoscale engineering transforms particles into 'LEGO- like' building blocks More information: Wei Ji et al. Co-organizing synthesis of heterogeneous nanostructures through the photo-cleavage of pre-stabilized self-assemblies, Chem. Commun. (2017). DOI: 10.1039/c7cc01912b


News Article | May 19, 2017
Site: www.eurekalert.org

Traditional chemistry is immensely powerful when it comes to producing very diverse and very complex microscopic chemical molecules. But one thing out of reach is the synthesis of large structures up to the macroscopic scale, which would require tremendous amounts of chemicals as well as an elaborate and complicated technique. For this purpose, scientists rely instead on "self-assembling" molecules, compounds that can interact with other copies of themselves to spontaneously congregate into spheres, tubes or other desired shapes. Using this approach, researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) now reports in Chemical Communications new self-assembling molecules that can transform into novel, exotic and previously unobserved shapes by simply using UV light to force them to rearrange differently into "metastable" states. When designing self-assembly structures, scientists typically aim for the state of lowest energy -- or "ground state," in which the structure would be at its highest stability. Less stable shapes are usually dismissed as incorrect and undesirable. However, this "ground state" being very stable makes it arduous to break down the structure if you wish to alter its shape. In this research, OIST scientists inserted a weakness into their ground-state self-assembled structures, resulting in structures requiring only a small nudge to collapse. In this case, the nudge is the use of ultraviolet light to snip a specific bond between two atoms within the molecule, splitting the structure into smaller fragments. The fragments are then able to co-assemble into less stable -- called metastable -- but novel and exotic shapes. "This report is about a new concept in material science," explained Prof. Zhang from the Bioinspired Soft Matter Unit and author of the study. "We converted a self-assembling phenomenon into co?assembling in a spatially and temporally controllable manner using light. Eventually, we constructed exotic heterogeneous nanostructures inaccessible though conventional synthetic path." This new concept led to a fascinating discovery: because the remaining fragments are tightly packed following the collapse from the initial structure, they can form novel and exotic structures which are not attainable if you just mix the same molecules in free motion. Imagine these nanostructures made from Lego bricks: initially you have 2x5 bricks - 2 studs wide and 5 studs long - self-assembling into a nanofiber. Ultraviolet light will split these 2x5 bricks into two smaller pieces, for example a 2x3 brick and a 2x2 brick, destroying the entire fiber-like structure. But because these smaller bricks remain pre-organized spatially staying close to each other, they can easily recombine themselves into new shapes visible with the naked eye. In contrast, if in a separate experiment you just mix 2x3 and 2x2 Lego bricks in a random manner in a bucket with varying distances between bricks, their lack of spatial organization prevents the assembly of such novel nanostructures. According to Prof. Zhang, the ability to create new structures is vital: "In material science, the function is always related to the structure. If you create a different structure, you manipulate the function and even create new applications." For example, the toxicity of a molecule in a nanofiber shape might be much lower or higher than the same molecule assembled in a spherical shape." The present research performed at OIST strongly suggests the initial conditions are the most critical parameter influencing the final shape taken by self-assembling molecules. "If you know how the molecules pack with each other from the parameters of the initial state, then it will give you more clues to aim towards a specific macroscopic shape," commented Prof. Zhang. This shapeshifting ability holds great potential for biological applications. Prof. Zhang suggested, "For example you introduce the molecule into a living organism and it adopts a certain structure. Then using light, you break a chemical bond and then the molecule will switch to another structure with the function you want." In pharmaceutical design, such a concept would allow a drug to reach its target in a living organism - an organ or a tumor - in an inactive state, thus limiting potential side effects. Once broken down in this targeted location, the drug would reshape itself into a different structure with therapeutic activity. Prof. Zhang concluded, "For now, using ultraviolet light as we do is not ideal as it is toxic for living cells. The next step for us is to move towards more biocompatible self-assembling structures with better adaptability to living systems."


News Article | May 19, 2017
Site: www.rdmag.com

Traditional chemistry is immensely powerful when it comes to producing very diverse and very complex microscopic chemical molecules. But one thing out of reach is the synthesis of large structures up to the macroscopic scale, which would require tremendous amounts of chemicals as well as an elaborate and complicated technique. For this purpose, scientists rely instead on "self-assembling" molecules, compounds that can interact with other copies of themselves to spontaneously congregate into spheres, tubes or other desired shapes. Using this approach, researchers at the Okinawa Institute of Science and Technology Graduate University (OIST) now reports in Chemical Communications new self-assembling molecules that can transform into novel, exotic and previously unobserved shapes by simply using UV light to force them to rearrange differently into "metastable" states. When designing self-assembly structures, scientists typically aim for the state of lowest energy -- or "ground state," in which the structure would be at its highest stability. Less stable shapes are usually dismissed as incorrect and undesirable. However, this "ground state" being very stable makes it arduous to break down the structure if you wish to alter its shape. In this research, OIST scientists inserted a weakness into their ground-state self-assembled structures, resulting in structures requiring only a small nudge to collapse. In this case, the nudge is the use of ultraviolet light to snip a specific bond between two atoms within the molecule, splitting the structure into smaller fragments. The fragments are then able to co-assemble into less stable -- called metastable -- but novel and exotic shapes. "This report is about a new concept in material science," explained Prof. Zhang from the Bioinspired Soft Matter Unit and author of the study. "We converted a self-assembling phenomenon into co?assembling in a spatially and temporally controllable manner using light. Eventually, we constructed exotic heterogeneous nanostructures inaccessible though conventional synthetic path." This new concept led to a fascinating discovery: because the remaining fragments are tightly packed following the collapse from the initial structure, they can form novel and exotic structures which are not attainable if you just mix the same molecules in free motion. Imagine these nanostructures made from Lego bricks: initially you have 2x5 bricks - 2 studs wide and 5 studs long - self-assembling into a nanofiber. Ultraviolet light will split these 2x5 bricks into two smaller pieces, for example a 2x3 brick and a 2x2 brick, destroying the entire fiber-like structure. But because these smaller bricks remain pre-organized spatially staying close to each other, they can easily recombine themselves into new shapes visible with the naked eye. In contrast, if in a separate experiment you just mix 2x3 and 2x2 Lego bricks in a random manner in a bucket with varying distances between bricks, their lack of spatial organization prevents the assembly of such novel nanostructures. According to Prof. Zhang, the ability to create new structures is vital: "In material science, the function is always related to the structure. If you create a different structure, you manipulate the function and even create new applications." For example, the toxicity of a molecule in a nanofiber shape might be much lower or higher than the same molecule assembled in a spherical shape." The present research performed at OIST strongly suggests the initial conditions are the most critical parameter influencing the final shape taken by self-assembling molecules. "If you know how the molecules pack with each other from the parameters of the initial state, then it will give you more clues to aim towards a specific macroscopic shape," commented Prof. Zhang. This shapeshifting ability holds great potential for biological applications. Prof. Zhang suggested, "For example you introduce the molecule into a living organism and it adopts a certain structure. Then using light, you break a chemical bond and then the molecule will switch to another structure with the function you want." In pharmaceutical design, such a concept would allow a drug to reach its target in a living organism - an organ or a tumor - in an inactive state, thus limiting potential side effects. Once broken down in this targeted location, the drug would reshape itself into a different structure with therapeutic activity. Prof. Zhang concluded, "For now, using ultraviolet light as we do is not ideal as it is toxic for living cells. The next step for us is to move towards more biocompatible self-assembling structures with better adaptability to living systems."


News Article | May 25, 2017
Site: www.eurekalert.org

The quantum world is both elegant and mysterious. It is a sphere of existence where the laws of physics experienced in everyday life are broken--particles can exist in two places at once, they can react to each other over vast distances, and they themselves seem confused over whether they are particles or waves. For those not involved in the field, this world may seem trifling, but recently, researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have theoretically described two quantum states that are extraordinary in both the physics that define them and their visual appeal: a complex quantum system that simulates classical physics and a spellbinding necklace-like state. Their study is published in the journal Physical Review A. The quest for these states begins with a doughnut, or rather, a doughnut-shaped container housing a rotating superfluid. This superfluid, which is a fluid that moves with no friction, is made of Bose-Einstein condensates (BECs) comprising particles with no charge that are cooled to near-zero degrees kelvin, a temperature so cold, that it does not exist in the universe outside of laboratories. At this temperature, particles begin to exhibit strange properties--they clump together, and eventually become indistinguishable from one another. In effect, they become a single entity and thus move as one. Since this whirling BEC superfluid is operating at a quantum scale, where tiny distances and low temperatures reign, the physical characteristics of its rotation are not those seen in the classical world. Consider a father who is swinging his daughter around in a circle by the arms. Classical physics mandates that the child's legs will move faster than her hands around the circle, since her legs must travel further to make a complete turn. In the world of quantum physics the relationship is the opposite. "In a superfluid...things which are very far away [from the center] move really slowly, whereas things [that] are close to the center move very fast," explains OIST Professor Thomas Busch, one of the researchers involved in the study. This is what is happening in the superfluid doughnut. In addition, the superfluid inside of the doughnut shows a uniform density profile, meaning that it is distributed around the doughnut evenly. This would be the same for most liquids that are rotating via classical or quantum rules. But what happens if another type of BEC is added, one that is made from a different atomic species and that cannot mix with the original BEC? Like oil and water, the two components will separate in a way that minimizes the area in which they are touching and form two semicircles on opposite sides of the doughnut container. "The shortest boundary [between the components] is in the radial direction," Dr. Angela White, first author on the study, explains. The two components separate into different halves of the doughnut along this boundary, which is created by passing through the doughnut's radius. In this configuration, they will use less energy to remain separated than they would via any other. In the immiscible, or unmixable, configuration shown in Figure 1, the quantum world surprises. Since the boundary between the two superfluids must remain aligned along the radial direction, the superfluid present at this boundary must rotate like a classical object. This happens in order to maintain that low-energy state. If at the boundary the superfluids continued to rotate faster on the inside, then the two semicircles would start to twist, elongating the line that separates them, and thus requiring more energy to stay separated. The result is a sort of classical physics mimicry, where the system appears to jump into the classical realm, facilitated by complex quantum mechanical behavior. At this stage, the superfluid doughnut has reached its first extraordinary state which is one that mimics classical rotation. But there is one more step needed to transform this already mind-boggling system into the necklace end-goal: spin-orbit coupling. "In a very abstract way, [spin is] just a thing that has two possible states," Busch explains. "It can be this way or it can be that way." For this experiment, which involves particles that have no charge, or no spin, the researchers "faked" a spin by assigning a "this or that" property to their particles. When coupling the particles based on this property, the two semicircles inside of the doughnut break into multiple alternating parts, thus forming the necklace configuration (Figure 2). By digging further into its composition, the researchers found that the number of "pearls" in the necklace depends on the strength of the spin-orbit coupling and, more surprisingly, that there must always be an odd number of these pearls. Researchers have predicted quantum necklaces before, but they were known to be unstable--expanding or dissipating themselves to oblivion only a short time after being created. In this theoretical model, the OIST researchers believe they have found a way to create a stable necklace, one that would allow for more time to study it and appreciate its refined majesty.


News Article | May 25, 2017
Site: www.rdmag.com

The quantum world is both elegant and mysterious. It is a sphere of existence where the laws of physics experienced in everyday life are broken--particles can exist in two places at once, they can react to each other over vast distances, and they themselves seem confused over whether they are particles or waves. For those not involved in the field, this world may seem trifling, but recently, researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have theoretically described two quantum states that are extraordinary in both the physics that define them and their visual appeal: a complex quantum system that simulates classical physics and a spellbinding necklace-like state. Their study is published in the journal Physical Review A. The quest for these states begins with a doughnut, or rather, a doughnut-shaped container housing a rotating superfluid. This superfluid, which is a fluid that moves with no friction, is made of Bose-Einstein condensates (BECs) comprising particles with no charge that are cooled to near-zero degrees kelvin, a temperature so cold, that it does not exist in the universe outside of laboratories. At this temperature, particles begin to exhibit strange properties--they clump together, and eventually become indistinguishable from one another. In effect, they become a single entity and thus move as one. Since this whirling BEC superfluid is operating at a quantum scale, where tiny distances and low temperatures reign, the physical characteristics of its rotation are not those seen in the classical world. Consider a father who is swinging his daughter around in a circle by the arms. Classical physics mandates that the child's legs will move faster than her hands around the circle, since her legs must travel further to make a complete turn. In the world of quantum physics the relationship is the opposite. "In a superfluid...things which are very far away [from the center] move really slowly, whereas things [that] are close to the center move very fast," explains OIST Professor Thomas Busch, one of the researchers involved in the study. This is what is happening in the superfluid doughnut. In addition, the superfluid inside of the doughnut shows a uniform density profile, meaning that it is distributed around the doughnut evenly. This would be the same for most liquids that are rotating via classical or quantum rules. But what happens if another type of BEC is added, one that is made from a different atomic species and that cannot mix with the original BEC? Like oil and water, the two components will separate in a way that minimizes the area in which they are touching and form two semicircles on opposite sides of the doughnut container. "The shortest boundary [between the components] is in the radial direction," Dr. Angela White, first author on the study, explains. The two components separate into different halves of the doughnut along this boundary, which is created by passing through the doughnut's radius. In this configuration, they will use less energy to remain separated than they would via any other. In the immiscible, or unmixable, configuration shown in Figure 1, the quantum world surprises. Since the boundary between the two superfluids must remain aligned along the radial direction, the superfluid present at this boundary must rotate like a classical object. This happens in order to maintain that low-energy state. If at the boundary the superfluids continued to rotate faster on the inside, then the two semicircles would start to twist, elongating the line that separates them, and thus requiring more energy to stay separated. The result is a sort of classical physics mimicry, where the system appears to jump into the classical realm, facilitated by complex quantum mechanical behavior. At this stage, the superfluid doughnut has reached its first extraordinary state which is one that mimics classical rotation. But there is one more step needed to transform this already mind-boggling system into the necklace end-goal: spin-orbit coupling. "In a very abstract way, [spin is] just a thing that has two possible states," Busch explains. "It can be this way or it can be that way." For this experiment, which involves particles that have no charge, or no spin, the researchers "faked" a spin by assigning a "this or that" property to their particles. When coupling the particles based on this property, the two semicircles inside of the doughnut break into multiple alternating parts, thus forming the necklace configuration (Figure 2). By digging further into its composition, the researchers found that the number of "pearls" in the necklace depends on the strength of the spin-orbit coupling and, more surprisingly, that there must always be an odd number of these pearls. Researchers have predicted quantum necklaces before, but they were known to be unstable--expanding or dissipating themselves to oblivion only a short time after being created. In this theoretical model, the OIST researchers believe they have found a way to create a stable necklace, one that would allow for more time to study it and appreciate its refined majesty.


Figure 1: Density profile of two superfluid components that either mix (left) or do not mix (right). In a rotating superfluid with two components that are miscible, or mixable, the matter will be distributed evenly within the doughnut-shaped container. This is the same density profile seen in a rotating, single-component superfluid. When the two components are immiscible, or not mixable, they will separate from each other and form two semicircle clumps on opposite sides. Credit: Okinawa Institute of Science and Technology The quantum world is both elegant and mysterious. It is a sphere of existence where the laws of physics experienced in everyday life are broken—particles can exist in two places at once, they can react to each other over vast distances, and they themselves seem confused over whether they are particles or waves. For those not involved in the field, this world may seem trifling, but recently, researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have theoretically described two quantum states that are extraordinary in both the physics that define them and their visual appeal: a complex quantum system that simulates classical physics and a spellbinding necklace-like state. Their study is published in the journal Physical Review A. The quest for these states begins with a doughnut, or rather, a doughnut-shaped container housing a rotating superfluid. This superfluid, which is a fluid that moves with no friction, is made of Bose-Einstein condensates (BECs) comprising particles with no charge that are cooled to near-zero degrees kelvin, a temperature so cold, that it does not exist in the universe outside of laboratories. At this temperature, particles begin to exhibit strange properties—they clump together, and eventually become indistinguishable from one another. In effect, they become a single entity and thus move as one. Since this whirling BEC superfluid is operating at a quantum scale, where tiny distances and low temperatures reign, the physical characteristics of its rotation are not those seen in the classical world. Consider a father who is swinging his daughter around in a circle by the arms. Classical physics mandates that the child's legs will move faster than her hands around the circle, since her legs must travel further to make a complete turn. In the world of quantum physics the relationship is the opposite. "In a superfluid…things which are very far away [from the center] move really slowly, whereas things [that] are close to the center move very fast," explains OIST Professor Thomas Busch, one of the researchers involved in the study. This is what is happening in the superfluid doughnut. In addition, the superfluid inside of the doughnut shows a uniform density profile, meaning that it is distributed around the doughnut evenly. This would be the same for most liquids that are rotating via classical or quantum rules. But what happens if another type of BEC is added, one that is made from a different atomic species and that cannot mix with the original BEC? Like oil and water, the two components will separate in a way that minimizes the area in which they are touching and form two semicircles on opposite sides of the doughnut container. "The shortest boundary [between the components] is in the radial direction," Dr. Angela White, first author on the study, explains. The two components separate into different halves of the doughnut along this boundary, which is created by passing through the doughnut's radius. In this configuration, they will use less energy to remain separated than they would via any other. In the immiscible, or unmixable, configuration shown in Figure 1, the quantum world surprises. Since the boundary between the two superfluids must remain aligned along the radial direction, the superfluid present at this boundary must rotate like a classical object. This happens in order to maintain that low-energy state. If at the boundary the superfluids continued to rotate faster on the inside, then the two semicircles would start to twist, elongating the line that separates them, and thus requiring more energy to stay separated. The result is a sort of classical physics mimicry, where the system appears to jump into the classical realm, facilitated by complex quantum mechanical behavior. At this stage, the superfluid doughnut has reached its first extraordinary state which is one that mimics classical rotation. But there is one more step needed to transform this already mind-boggling system into the necklace end-goal: spin-orbit coupling. "In a very abstract way, [spin is] just a thing that has two possible states," Busch explains. "It can be this way or it can be that way." For this experiment, which involves particles that have no charge, or no spin, the researchers "faked" a spin by assigning a "this or that" property to their particles. When coupling the particles based on this property, the two semicircles inside of the doughnut break into multiple alternating parts, thus forming the necklace configuration (Figure 2). By digging further into its composition, the researchers found that the number of "pearls" in the necklace depends on the strength of the spin-orbit coupling and, more surprisingly, that there must always be an odd number of these pearls. Researchers have predicted quantum necklaces before, but they were known to be unstable—expanding or dissipating themselves to oblivion only a short time after being created. In this theoretical model, the OIST researchers believe they have found a way to create a stable necklace, one that would allow for more time to study it and appreciate its refined majesty. Explore further: Bridging the gap between the quantum and classical worlds More information: Angela C. White et al. Odd-petal-number states and persistent flows in spin-orbit-coupled Bose-Einstein condensates, Physical Review A (2017). DOI: 10.1103/PhysRevA.95.041604


Abstract: The quantum world is both elegant and mysterious. It is a sphere of existence where the laws of physics experienced in everyday life are broken--particles can exist in two places at once, they can react to each other over vast distances, and they themselves seem confused over whether they are particles or waves. For those not involved in the field, this world may seem trifling, but recently, researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have theoretically described two quantum states that are extraordinary in both the physics that define them and their visual appeal: a complex quantum system that simulates classical physics and a spellbinding necklace-like state. Their study is published in the journal Physical Review A. The quest for these states begins with a doughnut, or rather, a doughnut-shaped container housing a rotating superfluid. This superfluid, which is a fluid that moves with no friction, is made of Bose-Einstein condensates (BECs) comprising particles with no charge that are cooled to near-zero degrees kelvin, a temperature so cold, that it does not exist in the universe outside of laboratories. At this temperature, particles begin to exhibit strange properties--they clump together, and eventually become indistinguishable from one another. In effect, they become a single entity and thus move as one. Since this whirling BEC superfluid is operating at a quantum scale, where tiny distances and low temperatures reign, the physical characteristics of its rotation are not those seen in the classical world. Consider a father who is swinging his daughter around in a circle by the arms. Classical physics mandates that the child's legs will move faster than her hands around the circle, since her legs must travel further to make a complete turn. In the world of quantum physics the relationship is the opposite. "In a superfluid...things which are very far away [from the center] move really slowly, whereas things [that] are close to the center move very fast," explains OIST Professor Thomas Busch, one of the researchers involved in the study. This is what is happening in the superfluid doughnut. In addition, the superfluid inside of the doughnut shows a uniform density profile, meaning that it is distributed around the doughnut evenly. This would be the same for most liquids that are rotating via classical or quantum rules. But what happens if another type of BEC is added, one that is made from a different atomic species and that cannot mix with the original BEC? Like oil and water, the two components will separate in a way that minimizes the area in which they are touching and form two semicircles on opposite sides of the doughnut container. "The shortest boundary [between the components] is in the radial direction," Dr. Angela White, first author on the study, explains. The two components separate into different halves of the doughnut along this boundary, which is created by passing through the doughnut's radius. In this configuration, they will use less energy to remain separated than they would via any other. In the immiscible, or unmixable, configuration shown in Figure 1, the quantum world surprises. Since the boundary between the two superfluids must remain aligned along the radial direction, the superfluid present at this boundary must rotate like a classical object. This happens in order to maintain that low-energy state. If at the boundary the superfluids continued to rotate faster on the inside, then the two semicircles would start to twist, elongating the line that separates them, and thus requiring more energy to stay separated. The result is a sort of classical physics mimicry, where the system appears to jump into the classical realm, facilitated by complex quantum mechanical behavior. At this stage, the superfluid doughnut has reached its first extraordinary state which is one that mimics classical rotation. But there is one more step needed to transform this already mind-boggling system into the necklace end-goal: spin-orbit coupling. "In a very abstract way, [spin is] just a thing that has two possible states," Busch explains. "It can be this way or it can be that way." For this experiment, which involves particles that have no charge, or no spin, the researchers "faked" a spin by assigning a "this or that" property to their particles. When coupling the particles based on this property, the two semicircles inside of the doughnut break into multiple alternating parts, thus forming the necklace configuration (Figure 2). By digging further into its composition, the researchers found that the number of "pearls" in the necklace depends on the strength of the spin-orbit coupling and, more surprisingly, that there must always be an odd number of these pearls. Researchers have predicted quantum necklaces before, but they were known to be unstable--expanding or dissipating themselves to oblivion only a short time after being created. In this theoretical model, the OIST researchers believe they have found a way to create a stable necklace, one that would allow for more time to study it and appreciate its refined majesty. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | May 25, 2017
Site: www.sciencedaily.com

The quantum world is both elegant and mysterious. It is a sphere of existence where the laws of physics experienced in everyday life are broken -- particles can exist in two places at once, they can react to each other over vast distances, and they themselves seem confused over whether they are particles or waves. For those not involved in the field, this world may seem trifling, but recently, researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have theoretically described two quantum states that are extraordinary in both the physics that define them and their visual appeal: a complex quantum system that simulates classical physics and a spellbinding necklace-like state. Their study is published in the journal Physical Review A. The quest for these states begins with a doughnut, or rather, a doughnut-shaped container housing a rotating superfluid. This superfluid, which is a fluid that moves with no friction, is made of Bose-Einstein condensates (BECs) comprising particles with no charge that are cooled to near-zero degrees kelvin, a temperature so cold, that it does not exist in the universe outside of laboratories. At this temperature, particles begin to exhibit strange properties -- they clump together, and eventually become indistinguishable from one another. In effect, they become a single entity and thus move as one. Since this whirling BEC superfluid is operating at a quantum scale, where tiny distances and low temperatures reign, the physical characteristics of its rotation are not those seen in the classical world. Consider a father who is swinging his daughter around in a circle by the arms. Classical physics mandates that the child's legs will move faster than her hands around the circle, since her legs must travel further to make a complete turn. In the world of quantum physics the relationship is the opposite. "In a superfluid...things which are very far away [from the center] move really slowly, whereas things [that] are close to the center move very fast," explains OIST Professor Thomas Busch, one of the researchers involved in the study. This is what is happening in the superfluid doughnut. In addition, the superfluid inside of the doughnut shows a uniform density profile, meaning that it is distributed around the doughnut evenly. This would be the same for most liquids that are rotating via classical or quantum rules. But what happens if another type of BEC is added, one that is made from a different atomic species and that cannot mix with the original BEC? Like oil and water, the two components will separate in a way that minimizes the area in which they are touching and form two semicircles on opposite sides of the doughnut container. "The shortest boundary [between the components] is in the radial direction," Dr. Angela White, first author on the study, explains. The two components separate into different halves of the doughnut along this boundary, which is created by passing through the doughnut's radius. In this configuration, they will use less energy to remain separated than they would via any other. In the immiscible, or unmixable, configuration, the quantum world surprises. Since the boundary between the two superfluids must remain aligned along the radial direction, the superfluid present at this boundary must rotate like a classical object. This happens in order to maintain that low-energy state. If at the boundary the superfluids continued to rotate faster on the inside, then the two semicircles would start to twist, elongating the line that separates them, and thus requiring more energy to stay separated. The result is a sort of classical physics mimicry, where the system appears to jump into the classical realm, facilitated by complex quantum mechanical behavior. At this stage, the superfluid doughnut has reached its first extraordinary state which is one that mimics classical rotation. But there is one more step needed to transform this already mind-boggling system into the necklace end-goal: spin-orbit coupling. "In a very abstract way, [spin is] just a thing that has two possible states," Busch explains. "It can be this way or it can be that way." For this experiment, which involves particles that have no charge, or no spin, the researchers "faked" a spin by assigning a "this or that" property to their particles. When coupling the particles based on this property, the two semicircles inside of the doughnut break into multiple alternating parts, thus forming the necklace configuration. By digging further into its composition, the researchers found that the number of "pearls" in the necklace depends on the strength of the spin-orbit coupling and, more surprisingly, that there must always be an odd number of these pearls. Researchers have predicted quantum necklaces before, but they were known to be unstable -- expanding or dissipating themselves to oblivion only a short time after being created. In this theoretical model, the OIST researchers believe they have found a way to create a stable necklace, one that would allow for more time to study it and appreciate its refined majesty.


News Article | May 14, 2017
Site: www.PR.com

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