Jan 15, 2024 06:33 PM
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Experiment could test quantum nature of large masses for the first time
https://www.ucl.ac.uk/news/2024/jan/expe...first-time
PRESS RELEASE: An experiment outlined by a UCL (University College London)-led team of scientists from the UK and India could test whether relatively large masses have a quantum nature, resolving the question of whether quantum mechanical description works at a much larger scale than that of particles and atoms.
Quantum theory is typically seen as describing nature at the tiniest scales and quantum effects have not been observed in a laboratory for objects more massive than about a quintillionth of a gram, or more precisely 10^(-20)g.
The new experiment, described in a paper published in Physical Review Letters (preprint) and involving researchers at UCL, the University of Southampton and the Bose Institute in Kolkata, India, could in principle test the quantumness of an object regardless of its mass or energy.
The proposed experiment exploits the principle in quantum mechanics that the act of measurement of an object can change its nature. (The term measurement encompasses any interaction of the object with a probe – for instance, if light shines on it, or if it emits light or heat).
The experiment focuses on a pendulum-like object oscillating like a ball on a string. A light is shone on one half of the area of oscillation, revealing information about the location of the object (i.e., if scattered light is not observed, then it can be concluded that the object is not in that half). A second light is shone, showing the location of the object further along on its swing.
If the object is quantum, the first measurement (the first flash of light) will disturb its path (by measurement induced collapse -- a property inherent to quantum mechanics), changing the likelihood of where it will be at the second flash of light, whereas if it is classical then the act of observation will make no difference. Researchers can then compare scenarios in which they shine a light twice to ones where only the second flash of light occurs to see if there is a difference in the final distributions of the object.
Lead author Dr Debarshi Das (UCL Physics & Astronomy and the Royal Society) said: “A crowd at a football match cannot affect the result of the game simply by staring strongly. But with quantum mechanics, the act of observation or measurement itself changes the system.
“Our proposed experiment can test if an object is classical or quantum by seeing if an act of observation can lead to a change in its motion.”
The proposal, the researchers say, could be implemented with current technologies using nanocrystals or, in principle, even using mirrors at LIGO (Laser Interferometer Gravitational-Wave Observatory) in the United States which have an effective mass of 10kg.
The four LIGO mirrors, which each weigh 40kg but together vibrate as if they were a single 10kg object, have already been cooled to the minimum-energy state (a fraction above absolute zero) that would be required in any experiment seeking to detect quantum behaviour.
Senior author Professor Sougato Bose (UCL Physics & Astronomy) said: “Our scheme has wide conceptual implications. It could test whether relatively large objects have definite properties, i.e., their properties are real, even when we are not measuring them. It could extend the domain of quantum mechanics and probe whether this fundamental theory of nature is valid only at certain scales or if it holds true for larger masses too.
“If we do not encounter a mass limit to quantum mechanics, this makes ever more acute the problem of trying to reconcile quantum theory with reality as we experience it.”
In quantum mechanics, objects do not have definite properties until they are observed or interact with their environment. Prior to observation they do not exist in a definite location but may be in two places at once (a state of superposition). This led to Einstein’s remark: “Is the moon there when no one is looking at it?”
Quantum mechanics may seem at odds with our experience of reality but its insights have helped the development of computers, smartphones, broadband, GPS, and magnetic resonance imaging.
Most physicists believe quantum mechanics holds true at larger scales, but is merely harder to observe due to the isolation required to preserve a quantum state. To detect quantum behaviour in an object, its temperature or vibrations must be reduced to its lowest possible level (its ground state) and it must be in a vacuum so that nearly no atoms are interacting with it. That is because a quantum state will collapse, a process called decoherence, if the object interacts with its environment.
The new proposed experiment is a development of an earlier quantum test devised by Professor Bose and colleagues in 2018. A project to conduct an experiment using this methodology, which will test the quantum nature of a nanocrystal numbering a billion atoms, is already underway, funded by the Engineering and Physical Sciences Research Council (EPSRC) and led by the University of Southampton.
That project already aims for a jump in terms of mass, with previous attempts to test the quantum nature of a macroscopic object limited to hundreds of thousands of atoms. The newly published scheme, meanwhile, could be achieved with current technologies using a nanocrystal with trillions of atoms.
The new paper was co-authored by Dr Das and Professor Bose at UCL along with Professor Dipankar Home of India’s Bose Institute (who also co-authored the 2018 paper) and Professor Hendrik Ulbricht of the University of Southampton.
RELATED (PhysicsWorld): Protocol could make it easier to test the quantum nature of large objects
Physicists identify overlooked uncertainty in real-world experiments
https://www.santafe.edu/news-center/news...aecd686038
PRESS RELEASE: The equations that describe physical systems often assume that measurable features of the system — temperature or chemical potential, for example — can be known exactly. But the real world is messier than that, and uncertainty is unavoidable. Temperatures fluctuate, instruments malfunction, the environment interferes, and systems evolve over time.
The rules of statistical physics address the uncertainty about the state of a system that arises when that system interacts with its environment. But they’ve long missed another kind, say SFI Professor David Wolpert and Jan Korbel, a postdoctoral researcher at the Complexity Science Hub in Vienna, Austria. In a new paper published in Physical Review Research, the pair of physicists argue that uncertainty in the thermodynamic parameters themselves — built into equations that govern the energetic behavior of the system — may also influence the outcome of an experiment.
“At present, almost nothing is known about the thermodynamic consequences of this type of uncertainty despite its unavoidability,” says Wolpert. In the new paper, he and Korbel consider ways to modify the equations of stochastic thermodynamics to accommodate it.
When Korbel and Wolpert met at a 2019 workshop on information and thermodynamics, they began talking about this second kind of uncertainty in the context of non-equilibrium systems.
“We wondered, what happens if you don’t know the thermodynamic parameters governing your system exactly?” recalls Korbel. “And then we started playing around.” The equations that describe thermodynamic systems often include precisely defined terms for things like temperature and chemical potentials. “But as an experimenter or an observer you don’t necessarily know these values” to very large precision, says Korbel.
Even more vexing, they realized that it’s impossible to measure parameters like temperature, pressure, or volume precisely, both because of the limitations of measurement and the fact that these quantities change quickly. They recognized that uncertainty about those parameters not only influences information about the original state of the system, but also how it evolves.
It’s almost paradoxical, Korbel says. “In thermodynamics, you’re assuming uncertainty about your state so you describe it in a probabilistic way. And if you have quantum thermodynamics, you do this with quantum uncertainty,” he says. “But on the other hand, you’re assuming that all the parameters are known with exact precision.”
Korbel says the new work has implications for a range of natural and engineered systems. If a cell needs to sense the temperature to carry out some chemical reaction, for example, then it will be limited in its precision. The uncertainty in the temperature measurement could mean that the cell does more work — and uses more energy. “The cell has to pay this extra cost for not knowing the system,” he says.
Optical tweezers offer another example. These are high-energy laser beams configured to create a kind of trap for charged particles. Physicists use the term “stiffness” to describe the particle’s tendency to resist being moved by the trap. To determine the optimal configuration for the lasers they measure the stiffness as precisely as possible. They typically do this by taking repeated measurements, assuming that the uncertainty arises from the measurement itself.
But Korbel and Wolpert offer another possibility — that the uncertainty arises from the fact that the stiffness itself may be changing as the system evolves. If that’s the case, then repeated identical measurements won’t capture it, and finding the optimal configuration will remain elusive. “If you keep doing the same protocol, then the particle doesn’t end up in the same point, you may have to do a little push,” which means extra work that’s not described by the conventional equations.
This uncertainty could play out at all scales, Korbel says. What’s often interpreted as uncertainty in measurement may be uncertainty in the parameters in disguise. Maybe an experiment was done near a window where the sun was shining, and then repeated when it was cloudy. Or perhaps the air conditioner kicked on between multiple trials. In many situations, he says, “it’s relevant to look at this other type of uncertainty.”
https://www.ucl.ac.uk/news/2024/jan/expe...first-time
PRESS RELEASE: An experiment outlined by a UCL (University College London)-led team of scientists from the UK and India could test whether relatively large masses have a quantum nature, resolving the question of whether quantum mechanical description works at a much larger scale than that of particles and atoms.
Quantum theory is typically seen as describing nature at the tiniest scales and quantum effects have not been observed in a laboratory for objects more massive than about a quintillionth of a gram, or more precisely 10^(-20)g.
The new experiment, described in a paper published in Physical Review Letters (preprint) and involving researchers at UCL, the University of Southampton and the Bose Institute in Kolkata, India, could in principle test the quantumness of an object regardless of its mass or energy.
The proposed experiment exploits the principle in quantum mechanics that the act of measurement of an object can change its nature. (The term measurement encompasses any interaction of the object with a probe – for instance, if light shines on it, or if it emits light or heat).
The experiment focuses on a pendulum-like object oscillating like a ball on a string. A light is shone on one half of the area of oscillation, revealing information about the location of the object (i.e., if scattered light is not observed, then it can be concluded that the object is not in that half). A second light is shone, showing the location of the object further along on its swing.
If the object is quantum, the first measurement (the first flash of light) will disturb its path (by measurement induced collapse -- a property inherent to quantum mechanics), changing the likelihood of where it will be at the second flash of light, whereas if it is classical then the act of observation will make no difference. Researchers can then compare scenarios in which they shine a light twice to ones where only the second flash of light occurs to see if there is a difference in the final distributions of the object.
Lead author Dr Debarshi Das (UCL Physics & Astronomy and the Royal Society) said: “A crowd at a football match cannot affect the result of the game simply by staring strongly. But with quantum mechanics, the act of observation or measurement itself changes the system.
“Our proposed experiment can test if an object is classical or quantum by seeing if an act of observation can lead to a change in its motion.”
The proposal, the researchers say, could be implemented with current technologies using nanocrystals or, in principle, even using mirrors at LIGO (Laser Interferometer Gravitational-Wave Observatory) in the United States which have an effective mass of 10kg.
The four LIGO mirrors, which each weigh 40kg but together vibrate as if they were a single 10kg object, have already been cooled to the minimum-energy state (a fraction above absolute zero) that would be required in any experiment seeking to detect quantum behaviour.
Senior author Professor Sougato Bose (UCL Physics & Astronomy) said: “Our scheme has wide conceptual implications. It could test whether relatively large objects have definite properties, i.e., their properties are real, even when we are not measuring them. It could extend the domain of quantum mechanics and probe whether this fundamental theory of nature is valid only at certain scales or if it holds true for larger masses too.
“If we do not encounter a mass limit to quantum mechanics, this makes ever more acute the problem of trying to reconcile quantum theory with reality as we experience it.”
In quantum mechanics, objects do not have definite properties until they are observed or interact with their environment. Prior to observation they do not exist in a definite location but may be in two places at once (a state of superposition). This led to Einstein’s remark: “Is the moon there when no one is looking at it?”
Quantum mechanics may seem at odds with our experience of reality but its insights have helped the development of computers, smartphones, broadband, GPS, and magnetic resonance imaging.
Most physicists believe quantum mechanics holds true at larger scales, but is merely harder to observe due to the isolation required to preserve a quantum state. To detect quantum behaviour in an object, its temperature or vibrations must be reduced to its lowest possible level (its ground state) and it must be in a vacuum so that nearly no atoms are interacting with it. That is because a quantum state will collapse, a process called decoherence, if the object interacts with its environment.
The new proposed experiment is a development of an earlier quantum test devised by Professor Bose and colleagues in 2018. A project to conduct an experiment using this methodology, which will test the quantum nature of a nanocrystal numbering a billion atoms, is already underway, funded by the Engineering and Physical Sciences Research Council (EPSRC) and led by the University of Southampton.
That project already aims for a jump in terms of mass, with previous attempts to test the quantum nature of a macroscopic object limited to hundreds of thousands of atoms. The newly published scheme, meanwhile, could be achieved with current technologies using a nanocrystal with trillions of atoms.
The new paper was co-authored by Dr Das and Professor Bose at UCL along with Professor Dipankar Home of India’s Bose Institute (who also co-authored the 2018 paper) and Professor Hendrik Ulbricht of the University of Southampton.
RELATED (PhysicsWorld): Protocol could make it easier to test the quantum nature of large objects
Physicists identify overlooked uncertainty in real-world experiments
https://www.santafe.edu/news-center/news...aecd686038
PRESS RELEASE: The equations that describe physical systems often assume that measurable features of the system — temperature or chemical potential, for example — can be known exactly. But the real world is messier than that, and uncertainty is unavoidable. Temperatures fluctuate, instruments malfunction, the environment interferes, and systems evolve over time.
The rules of statistical physics address the uncertainty about the state of a system that arises when that system interacts with its environment. But they’ve long missed another kind, say SFI Professor David Wolpert and Jan Korbel, a postdoctoral researcher at the Complexity Science Hub in Vienna, Austria. In a new paper published in Physical Review Research, the pair of physicists argue that uncertainty in the thermodynamic parameters themselves — built into equations that govern the energetic behavior of the system — may also influence the outcome of an experiment.
“At present, almost nothing is known about the thermodynamic consequences of this type of uncertainty despite its unavoidability,” says Wolpert. In the new paper, he and Korbel consider ways to modify the equations of stochastic thermodynamics to accommodate it.
When Korbel and Wolpert met at a 2019 workshop on information and thermodynamics, they began talking about this second kind of uncertainty in the context of non-equilibrium systems.
“We wondered, what happens if you don’t know the thermodynamic parameters governing your system exactly?” recalls Korbel. “And then we started playing around.” The equations that describe thermodynamic systems often include precisely defined terms for things like temperature and chemical potentials. “But as an experimenter or an observer you don’t necessarily know these values” to very large precision, says Korbel.
Even more vexing, they realized that it’s impossible to measure parameters like temperature, pressure, or volume precisely, both because of the limitations of measurement and the fact that these quantities change quickly. They recognized that uncertainty about those parameters not only influences information about the original state of the system, but also how it evolves.
It’s almost paradoxical, Korbel says. “In thermodynamics, you’re assuming uncertainty about your state so you describe it in a probabilistic way. And if you have quantum thermodynamics, you do this with quantum uncertainty,” he says. “But on the other hand, you’re assuming that all the parameters are known with exact precision.”
Korbel says the new work has implications for a range of natural and engineered systems. If a cell needs to sense the temperature to carry out some chemical reaction, for example, then it will be limited in its precision. The uncertainty in the temperature measurement could mean that the cell does more work — and uses more energy. “The cell has to pay this extra cost for not knowing the system,” he says.
Optical tweezers offer another example. These are high-energy laser beams configured to create a kind of trap for charged particles. Physicists use the term “stiffness” to describe the particle’s tendency to resist being moved by the trap. To determine the optimal configuration for the lasers they measure the stiffness as precisely as possible. They typically do this by taking repeated measurements, assuming that the uncertainty arises from the measurement itself.
But Korbel and Wolpert offer another possibility — that the uncertainty arises from the fact that the stiffness itself may be changing as the system evolves. If that’s the case, then repeated identical measurements won’t capture it, and finding the optimal configuration will remain elusive. “If you keep doing the same protocol, then the particle doesn’t end up in the same point, you may have to do a little push,” which means extra work that’s not described by the conventional equations.
This uncertainty could play out at all scales, Korbel says. What’s often interpreted as uncertainty in measurement may be uncertainty in the parameters in disguise. Maybe an experiment was done near a window where the sun was shining, and then repeated when it was cloudy. Or perhaps the air conditioner kicked on between multiple trials. In many situations, he says, “it’s relevant to look at this other type of uncertainty.”
