超级军网量子理论有了新进展
来源：百度文库 编辑：超级军网 时间：2024/04/27 20:30:59
Quantum probes that won't kill Schrödinger's cat
28 April 2011 by David Shiga
Magazine issue 2810. Subscribe and save
For similar stories, visit the Quantum World Topic Guide
IT MAY soon be possible to extract information from a quantum object - and even manipulate it - without simultaneously destroying its delicate quantum state. The result would be a boon for quantum computing, which requires control over such states. It would also defy a thought experiment dreamed up by physicist Erwin Schrödinger: in principle it is now possible to peek inside his box without endangering the life of the precarious pussycat inside.
States that are mutually exclusive in classical physics can exist simultaneously in the weird world of quantum mechanics - a situation called a superposition. To illustrate this effect, Schrödinger imagined putting a cat in a box along with a device that would release poison to kill it, depending on the random decay of a radioactive atom. Because the atom's quantum state only takes a definite value when someone looks at it, the cat is both dead and alive until the box is opened.
Superpositions are fragile, however. Outside disturbances, including observations, tend to destroy the "coherence" of these states, forcing the system to collapse into just one of the possibilities. The larger the system, the harder it is to isolate it from outside influences.
In 2010, physicists put the largest system yet into a superposition: a 40-micrometre-long strip of piezoelectric material, which expands and contracts in response to voltage changes. They put it into a superposition of both minimal and more vigorous oscillation, but the method they used to observe the system caused it to lose this dual state.
Another team now proposes going a step further, putting a wire of about the same size in a superposition and offering a scheme to observe, and even manipulate it, without destroying the weird quantum state. Kurt Jacobs at the University of Massachusetts, Boston, and his team describe their idea in a study to appear in Physical Review A.
The first step is to put the wire into a superposition in which vibrations simultaneously displace it by equal amounts in opposite directions, like a guitar string that gets plucked in two directions at once. Next, an electric charge can be added to the wire, creating an electromagnetic field that can be detected by a sensor (see diagram).
Even though the sensor cannot pinpoint the position of the charge - and therefore the wire - it can detect how far the charge is from a neutral, "unplucked" position. That reveals some information about the system - essentially providing a glimpse inside the box containing Schrödinger's cat. The key is that it avoids opening the box completely, which would destroy the superposition, says Jacobs: "I extract information, but in a way that I don't learn too much."
Previous schemes to glimpse inside the box involved partially destroying the superposition and then trying to restore it. "In our paper, the crucial thing is that the measurement does not destroy the coherence," says Jacobs.
The team also proposes adjusting the tension of the wire to change the size of the vibrations, an adjustment that would not destroy the fragile superposition.
Carrying out this experiment is still a few years away, the team says - the sensors needed to make the subtle measurements must be made less vulnerable to interfering noise. If the experiment eventually proves a success, it would be a step towards quantum computing.
Quantum computers, which have yet to be built, would be able to do many more calculations simultaneously than conventional computers can. Their capacity will stem from the ability of quantum systems to be in more than one state simultaneously. Making such a computer requires being able to read and alter the state of quantum systems, processes that the new experiment aims to achieve. "This proposal could prove very useful," says Aephraim Steinberg at the University of Toronto in Canada.
Teleporting schrödinger's cat
OBSERVING an object in more than one quantum state at once - in a superposition - is still an elusive goal (see main story), but teleporting such an object is now old hat. Noriyuki Lee at the University of Tokyo, Japan, and colleagues have managed to make light in a superposition of states vanish in one place and reappear in another.
They took advantage of entanglement, a quantum property that creates a spooky connection between separate objects which acts even at a distance. They entangled two light beams, so that measuring one affected the outcome of measuring the other. After mixing one of the entangled beams with pulses of light in a superposition of many quantum states, they were able to recreate the superposition in the second entangled beam (Science, DOI: 10.1126/science.1201034).
"It shows that the controlled manipulation of quantum objects has... achieved objectives that seemed impossible just a few years ago," says Philippe Grangier at the Institute of Optics in Palaiseau, France.
来源：http://www.newscientist.com/arti ... hrodingers-cat.htmlQuantum probes that won't kill Schrödinger's cat
28 April 2011 by David Shiga
Magazine issue 2810. Subscribe and save
For similar stories, visit the Quantum World Topic Guide
IT MAY soon be possible to extract information from a quantum object - and even manipulate it - without simultaneously destroying its delicate quantum state. The result would be a boon for quantum computing, which requires control over such states. It would also defy a thought experiment dreamed up by physicist Erwin Schrödinger: in principle it is now possible to peek inside his box without endangering the life of the precarious pussycat inside.
States that are mutually exclusive in classical physics can exist simultaneously in the weird world of quantum mechanics - a situation called a superposition. To illustrate this effect, Schrödinger imagined putting a cat in a box along with a device that would release poison to kill it, depending on the random decay of a radioactive atom. Because the atom's quantum state only takes a definite value when someone looks at it, the cat is both dead and alive until the box is opened.
Superpositions are fragile, however. Outside disturbances, including observations, tend to destroy the "coherence" of these states, forcing the system to collapse into just one of the possibilities. The larger the system, the harder it is to isolate it from outside influences.
In 2010, physicists put the largest system yet into a superposition: a 40-micrometre-long strip of piezoelectric material, which expands and contracts in response to voltage changes. They put it into a superposition of both minimal and more vigorous oscillation, but the method they used to observe the system caused it to lose this dual state.
Another team now proposes going a step further, putting a wire of about the same size in a superposition and offering a scheme to observe, and even manipulate it, without destroying the weird quantum state. Kurt Jacobs at the University of Massachusetts, Boston, and his team describe their idea in a study to appear in Physical Review A.
The first step is to put the wire into a superposition in which vibrations simultaneously displace it by equal amounts in opposite directions, like a guitar string that gets plucked in two directions at once. Next, an electric charge can be added to the wire, creating an electromagnetic field that can be detected by a sensor (see diagram).
Even though the sensor cannot pinpoint the position of the charge - and therefore the wire - it can detect how far the charge is from a neutral, "unplucked" position. That reveals some information about the system - essentially providing a glimpse inside the box containing Schrödinger's cat. The key is that it avoids opening the box completely, which would destroy the superposition, says Jacobs: "I extract information, but in a way that I don't learn too much."
Previous schemes to glimpse inside the box involved partially destroying the superposition and then trying to restore it. "In our paper, the crucial thing is that the measurement does not destroy the coherence," says Jacobs.
The team also proposes adjusting the tension of the wire to change the size of the vibrations, an adjustment that would not destroy the fragile superposition.
Carrying out this experiment is still a few years away, the team says - the sensors needed to make the subtle measurements must be made less vulnerable to interfering noise. If the experiment eventually proves a success, it would be a step towards quantum computing.
Quantum computers, which have yet to be built, would be able to do many more calculations simultaneously than conventional computers can. Their capacity will stem from the ability of quantum systems to be in more than one state simultaneously. Making such a computer requires being able to read and alter the state of quantum systems, processes that the new experiment aims to achieve. "This proposal could prove very useful," says Aephraim Steinberg at the University of Toronto in Canada.
Teleporting schrödinger's cat
OBSERVING an object in more than one quantum state at once - in a superposition - is still an elusive goal (see main story), but teleporting such an object is now old hat. Noriyuki Lee at the University of Tokyo, Japan, and colleagues have managed to make light in a superposition of states vanish in one place and reappear in another.
They took advantage of entanglement, a quantum property that creates a spooky connection between separate objects which acts even at a distance. They entangled two light beams, so that measuring one affected the outcome of measuring the other. After mixing one of the entangled beams with pulses of light in a superposition of many quantum states, they were able to recreate the superposition in the second entangled beam (Science, DOI: 10.1126/science.1201034).
"It shows that the controlled manipulation of quantum objects has... achieved objectives that seemed impossible just a few years ago," says Philippe Grangier at the Institute of Optics in Palaiseau, France.
来源：http://www.newscientist.com/arti ... hrodingers-cat.html
28 April 2011 by David Shiga
Magazine issue 2810. Subscribe and save
For similar stories, visit the Quantum World Topic Guide
IT MAY soon be possible to extract information from a quantum object - and even manipulate it - without simultaneously destroying its delicate quantum state. The result would be a boon for quantum computing, which requires control over such states. It would also defy a thought experiment dreamed up by physicist Erwin Schrödinger: in principle it is now possible to peek inside his box without endangering the life of the precarious pussycat inside.
States that are mutually exclusive in classical physics can exist simultaneously in the weird world of quantum mechanics - a situation called a superposition. To illustrate this effect, Schrödinger imagined putting a cat in a box along with a device that would release poison to kill it, depending on the random decay of a radioactive atom. Because the atom's quantum state only takes a definite value when someone looks at it, the cat is both dead and alive until the box is opened.
Superpositions are fragile, however. Outside disturbances, including observations, tend to destroy the "coherence" of these states, forcing the system to collapse into just one of the possibilities. The larger the system, the harder it is to isolate it from outside influences.
In 2010, physicists put the largest system yet into a superposition: a 40-micrometre-long strip of piezoelectric material, which expands and contracts in response to voltage changes. They put it into a superposition of both minimal and more vigorous oscillation, but the method they used to observe the system caused it to lose this dual state.
Another team now proposes going a step further, putting a wire of about the same size in a superposition and offering a scheme to observe, and even manipulate it, without destroying the weird quantum state. Kurt Jacobs at the University of Massachusetts, Boston, and his team describe their idea in a study to appear in Physical Review A.
The first step is to put the wire into a superposition in which vibrations simultaneously displace it by equal amounts in opposite directions, like a guitar string that gets plucked in two directions at once. Next, an electric charge can be added to the wire, creating an electromagnetic field that can be detected by a sensor (see diagram).
Even though the sensor cannot pinpoint the position of the charge - and therefore the wire - it can detect how far the charge is from a neutral, "unplucked" position. That reveals some information about the system - essentially providing a glimpse inside the box containing Schrödinger's cat. The key is that it avoids opening the box completely, which would destroy the superposition, says Jacobs: "I extract information, but in a way that I don't learn too much."
Previous schemes to glimpse inside the box involved partially destroying the superposition and then trying to restore it. "In our paper, the crucial thing is that the measurement does not destroy the coherence," says Jacobs.
The team also proposes adjusting the tension of the wire to change the size of the vibrations, an adjustment that would not destroy the fragile superposition.
Carrying out this experiment is still a few years away, the team says - the sensors needed to make the subtle measurements must be made less vulnerable to interfering noise. If the experiment eventually proves a success, it would be a step towards quantum computing.
Quantum computers, which have yet to be built, would be able to do many more calculations simultaneously than conventional computers can. Their capacity will stem from the ability of quantum systems to be in more than one state simultaneously. Making such a computer requires being able to read and alter the state of quantum systems, processes that the new experiment aims to achieve. "This proposal could prove very useful," says Aephraim Steinberg at the University of Toronto in Canada.
Teleporting schrödinger's cat
OBSERVING an object in more than one quantum state at once - in a superposition - is still an elusive goal (see main story), but teleporting such an object is now old hat. Noriyuki Lee at the University of Tokyo, Japan, and colleagues have managed to make light in a superposition of states vanish in one place and reappear in another.
They took advantage of entanglement, a quantum property that creates a spooky connection between separate objects which acts even at a distance. They entangled two light beams, so that measuring one affected the outcome of measuring the other. After mixing one of the entangled beams with pulses of light in a superposition of many quantum states, they were able to recreate the superposition in the second entangled beam (Science, DOI: 10.1126/science.1201034).
"It shows that the controlled manipulation of quantum objects has... achieved objectives that seemed impossible just a few years ago," says Philippe Grangier at the Institute of Optics in Palaiseau, France.
来源：http://www.newscientist.com/arti ... hrodingers-cat.htmlQuantum probes that won't kill Schrödinger's cat
28 April 2011 by David Shiga
Magazine issue 2810. Subscribe and save
For similar stories, visit the Quantum World Topic Guide
IT MAY soon be possible to extract information from a quantum object - and even manipulate it - without simultaneously destroying its delicate quantum state. The result would be a boon for quantum computing, which requires control over such states. It would also defy a thought experiment dreamed up by physicist Erwin Schrödinger: in principle it is now possible to peek inside his box without endangering the life of the precarious pussycat inside.
States that are mutually exclusive in classical physics can exist simultaneously in the weird world of quantum mechanics - a situation called a superposition. To illustrate this effect, Schrödinger imagined putting a cat in a box along with a device that would release poison to kill it, depending on the random decay of a radioactive atom. Because the atom's quantum state only takes a definite value when someone looks at it, the cat is both dead and alive until the box is opened.
Superpositions are fragile, however. Outside disturbances, including observations, tend to destroy the "coherence" of these states, forcing the system to collapse into just one of the possibilities. The larger the system, the harder it is to isolate it from outside influences.
In 2010, physicists put the largest system yet into a superposition: a 40-micrometre-long strip of piezoelectric material, which expands and contracts in response to voltage changes. They put it into a superposition of both minimal and more vigorous oscillation, but the method they used to observe the system caused it to lose this dual state.
Another team now proposes going a step further, putting a wire of about the same size in a superposition and offering a scheme to observe, and even manipulate it, without destroying the weird quantum state. Kurt Jacobs at the University of Massachusetts, Boston, and his team describe their idea in a study to appear in Physical Review A.
The first step is to put the wire into a superposition in which vibrations simultaneously displace it by equal amounts in opposite directions, like a guitar string that gets plucked in two directions at once. Next, an electric charge can be added to the wire, creating an electromagnetic field that can be detected by a sensor (see diagram).
Even though the sensor cannot pinpoint the position of the charge - and therefore the wire - it can detect how far the charge is from a neutral, "unplucked" position. That reveals some information about the system - essentially providing a glimpse inside the box containing Schrödinger's cat. The key is that it avoids opening the box completely, which would destroy the superposition, says Jacobs: "I extract information, but in a way that I don't learn too much."
Previous schemes to glimpse inside the box involved partially destroying the superposition and then trying to restore it. "In our paper, the crucial thing is that the measurement does not destroy the coherence," says Jacobs.
The team also proposes adjusting the tension of the wire to change the size of the vibrations, an adjustment that would not destroy the fragile superposition.
Carrying out this experiment is still a few years away, the team says - the sensors needed to make the subtle measurements must be made less vulnerable to interfering noise. If the experiment eventually proves a success, it would be a step towards quantum computing.
Quantum computers, which have yet to be built, would be able to do many more calculations simultaneously than conventional computers can. Their capacity will stem from the ability of quantum systems to be in more than one state simultaneously. Making such a computer requires being able to read and alter the state of quantum systems, processes that the new experiment aims to achieve. "This proposal could prove very useful," says Aephraim Steinberg at the University of Toronto in Canada.
Teleporting schrödinger's cat
OBSERVING an object in more than one quantum state at once - in a superposition - is still an elusive goal (see main story), but teleporting such an object is now old hat. Noriyuki Lee at the University of Tokyo, Japan, and colleagues have managed to make light in a superposition of states vanish in one place and reappear in another.
They took advantage of entanglement, a quantum property that creates a spooky connection between separate objects which acts even at a distance. They entangled two light beams, so that measuring one affected the outcome of measuring the other. After mixing one of the entangled beams with pulses of light in a superposition of many quantum states, they were able to recreate the superposition in the second entangled beam (Science, DOI: 10.1126/science.1201034).
"It shows that the controlled manipulation of quantum objects has... achieved objectives that seemed impossible just a few years ago," says Philippe Grangier at the Institute of Optics in Palaiseau, France.
来源：http://www.newscientist.com/arti ... hrodingers-cat.html
科学家终于“看”到了又死又活的薛定谔之猫
2012-10-09 14:07:13 1286 人阅读 编辑：上方文Q [复制链接] [我要爆料]
薛定谔的猫，这个量子力学的永恒象征，终于在不打开箱子的情况下被观测到了。据果壳网报道，通过巧妙的实验设计，物理学家成功探测了一个精细量子态而没有破坏它，相当于偷窥了一眼薛定谔的猫而没有让它死掉。
量子力学中一个重要的概念是“态叠加”，而基于此最为著名的思想实验莫过于“薛定谔的猫”：小猫被关进一个装有毒气触发装置的箱子里面，里面还有50%可能会衰变的原子，如果原子衰变了，放射出来的粒子就会触发毒气让小猫死亡。
要进行观测，就需要打开箱子，而我们所观测到的猫，要么是活着的，要么已经献身于科学了；而我们若是不打开箱子，小猫按照量子力学的理论，是既死又活的，用精确的语言描述，是处于“死”│0>和“活”│1>两个状态的叠加。我们观测到的，要么是│0>要么是│1>，而不可能是│0>和│1>的叠加——a*│0>+b*│1>：只要观测，叠加态便不复存在。
注：│>是狄拉克符号的右矢量，代表状态，│1>可以想象成1，但不是自然数的1。
有趣的是，这个思想实验本来旨在驳斥哥本哈根基于概率的量子力学解释的荒谬性，可历史车轮滚滚，哪想到后来却被作为解释叠加态的必要小菜，还补充说明了量子力学在宏观尺度下由于不确定性原理：一切都归于确定，不会真有既死又活的宏观小猫存在。
那么，有没有可能进行不用打开箱子的间接观测呢？数学上已经证明这种被称为“弱观测”的观测是完全可能的。这种观测不是直接观测到│0>或者│1>，而是通过观测某个量子系统的其他信息，间接推测出来这个量子系统处于什么样的叠加态。
然而，直到最近，都没有实验真正做到了数学理论预测的结果。去年，麻省大学波城分校的K.Jacobs所领导的小组设计了一个可能实现这个理论的实验。今年，加州大学伯克利分校的R.Vijay所领导的小组完成名为《量子位的量子反馈控制》的弱观测实验(论文PDF)，其结果被发表在了今年10月的《自然》上，论文的第二作者C.Macklin也在reddit上开了一个IAmA帖子介绍这个研究成果。
这个实验干了一件什么事情呢？首先，我们观测的对象是一个超导回路，由于超导体的特殊性质，这个回路能储存一个量子位(qubit)的信息。——经典的比特位只能是0或者1，而量子位可以是0和1的叠加态。
接着，这个回路进入了│0>态和在│1>态之间的高频振动状态，使得系统会经历所有的叠加态。然后，我们开始测量这个振动的频率，而不是去观测这个振动在某一时刻处于│0>或者处于│1>，或者是两者之间的某个状态。
但天理难撼，这个基于频率测量的弱观测依然会破坏叠加态，对回路的振动频率有不可预知的随机扰动，不过，R.Vijay小组的博士生们巧妙的设计了一个“循环回馈机制”(feedback control loop)，某次观测会对振动进行扰动，但是在振动被这次观测随机扰动的同时，回路中的回馈系统会产生一个回馈信号，抵消掉观测对回路的状态的随机影响，于是乎，实验成功实现了“观测→扰动→回馈→回到正常→再观测”的循环，并且基本正确测量出了超导回路应该有的高频振动。
实验的结果并不是最完美的，但却在测量量子位的叠加态上迈出了一大步，人类正往实现量子计算机的道路上前进着。
来源：http://news.mydrivers.com/1/243/243228.htm
2012-10-09 14:07:13 1286 人阅读 编辑：上方文Q [复制链接] [我要爆料]
薛定谔的猫，这个量子力学的永恒象征，终于在不打开箱子的情况下被观测到了。据果壳网报道，通过巧妙的实验设计，物理学家成功探测了一个精细量子态而没有破坏它，相当于偷窥了一眼薛定谔的猫而没有让它死掉。
量子力学中一个重要的概念是“态叠加”，而基于此最为著名的思想实验莫过于“薛定谔的猫”：小猫被关进一个装有毒气触发装置的箱子里面，里面还有50%可能会衰变的原子，如果原子衰变了，放射出来的粒子就会触发毒气让小猫死亡。
要进行观测，就需要打开箱子，而我们所观测到的猫，要么是活着的，要么已经献身于科学了；而我们若是不打开箱子，小猫按照量子力学的理论，是既死又活的，用精确的语言描述，是处于“死”│0>和“活”│1>两个状态的叠加。我们观测到的，要么是│0>要么是│1>，而不可能是│0>和│1>的叠加——a*│0>+b*│1>：只要观测，叠加态便不复存在。
注：│>是狄拉克符号的右矢量，代表状态，│1>可以想象成1，但不是自然数的1。
有趣的是，这个思想实验本来旨在驳斥哥本哈根基于概率的量子力学解释的荒谬性，可历史车轮滚滚，哪想到后来却被作为解释叠加态的必要小菜，还补充说明了量子力学在宏观尺度下由于不确定性原理：一切都归于确定，不会真有既死又活的宏观小猫存在。
那么，有没有可能进行不用打开箱子的间接观测呢？数学上已经证明这种被称为“弱观测”的观测是完全可能的。这种观测不是直接观测到│0>或者│1>，而是通过观测某个量子系统的其他信息，间接推测出来这个量子系统处于什么样的叠加态。
然而，直到最近，都没有实验真正做到了数学理论预测的结果。去年，麻省大学波城分校的K.Jacobs所领导的小组设计了一个可能实现这个理论的实验。今年，加州大学伯克利分校的R.Vijay所领导的小组完成名为《量子位的量子反馈控制》的弱观测实验(论文PDF)，其结果被发表在了今年10月的《自然》上，论文的第二作者C.Macklin也在reddit上开了一个IAmA帖子介绍这个研究成果。
这个实验干了一件什么事情呢？首先，我们观测的对象是一个超导回路，由于超导体的特殊性质，这个回路能储存一个量子位(qubit)的信息。——经典的比特位只能是0或者1，而量子位可以是0和1的叠加态。
接着，这个回路进入了│0>态和在│1>态之间的高频振动状态，使得系统会经历所有的叠加态。然后，我们开始测量这个振动的频率，而不是去观测这个振动在某一时刻处于│0>或者处于│1>，或者是两者之间的某个状态。
但天理难撼，这个基于频率测量的弱观测依然会破坏叠加态，对回路的振动频率有不可预知的随机扰动，不过，R.Vijay小组的博士生们巧妙的设计了一个“循环回馈机制”(feedback control loop)，某次观测会对振动进行扰动，但是在振动被这次观测随机扰动的同时，回路中的回馈系统会产生一个回馈信号，抵消掉观测对回路的状态的随机影响，于是乎，实验成功实现了“观测→扰动→回馈→回到正常→再观测”的循环，并且基本正确测量出了超导回路应该有的高频振动。
实验的结果并不是最完美的，但却在测量量子位的叠加态上迈出了一大步，人类正往实现量子计算机的道路上前进着。
来源：http://news.mydrivers.com/1/243/243228.htm
伟大，致以崇敬！是不是诺贝尔奖了？
伟大，致以崇敬！是不是诺贝尔奖了？
太高深了。
太高深了，不想装bi，哪位大虾解释下。
三个字：看不懂
coolfile 发表于 2012-10-9 15:08 ![]()
科学家终于“看”到了又死又活的薛定谔之猫
2012-10-09 14:07:13 1286 人阅读 编辑：上方文Q [复制链接] [ ...
能看懂的都是牛逼。
科学家终于“看”到了又死又活的薛定谔之猫
2012-10-09 14:07:13 1286 人阅读 编辑：上方文Q [复制链接] [ ...
能看懂的都是牛逼。
能看懂的都是牛逼。
看懂这则"报道"只需要普通高等教育第二学年合格的水平
看懂这则"报道"只需要普通高等教育第二学年合格的水平
AAFox 发表于 2012-10-22 00:55 ![]()
看懂这则"报道"只需要普通高等教育第二学年合格的水平
考试可不考这个．．．并不是课本上有就表示大家都懂的．
体育卫生课本上还有几套拳术呢，那本书估计都没几人真正看过．
看懂这则"报道"只需要普通高等教育第二学年合格的水平
考试可不考这个．．．并不是课本上有就表示大家都懂的．
体育卫生课本上还有几套拳术呢，那本书估计都没几人真正看过．
看着头大啊
就是"观察"的本身就改变了状况。