- 3476 - QUANTUM WORLD - is confusing? Quantum mechanics is really confusing. All the rules of physics that we're used to simply don’t work in the quantum realm. Put a particle in a box. According to classical physics, and common sense, that particle should stay in that box forever. But under quantum mechanics, that particle can simply be outside the box the next time you look.
------------- 3476 - QUANTUM WORLD - is confusing?
- In classical thinking, you can measure the momentum and position of something to an arbitrary degree of precision. Not so in the quantum world. The more you know about one, the less you know about the other.
-
- Is something a “wave” or a “particle“? According to the classical viewpoint, you can pick one and only one. However, something can be both at the same time. The quantum world is hard to understand, but at some point the rules of the subatomic give way to the rules of the macroscopic.
-
- The first person to put some useful labels on the quantum world was physicist Niels Bohr. In the early 1900s, scientists around the world were beginning to awaken to the strange and unexpected behavior of atomic and subatomic systems.
-
- They had, after decades of grueling work, realized that certain properties, like energy, come in discrete packets of levels dubbed "quanta." And while physicists were beginning to sketch out a mathematical foundation to explain these experiments, nobody had yet developed a complete, consistent framework.
-
- In the 1920s, we had known through a variety of very cool experiments that the atom is made of a heavy, dense, positively charged nucleus surrounded by a swarm of tiny, light, negatively charged electrons. We also knew that these atoms could only absorb or emit radiation at very specific energies.
-
- Bohr put the electrons "in orbit" around the nucleus, orbiting around that dense core like planets in the smallest solar system. In a real solar system, the planets can have whatever orbit they like. But in Bohr's atom the electrons were stuck on little tracks. They could only have certain predefined orbital distances.
-
- By jumping from one orbit to another, the atom could receive or emit radiation at specific energies, or frequencies. Its “quantum nature” was thus encoded. Bohr found that when the electrons orbited very far away from the nucleus, their quantum nature disappeared and the atom could be perfectly described by classical electromagnetism. Just two charged particles in orbit.
-
- This was called the “Correspondence Principle“, and it was Bohr's argument that his model of the atom was the best. You can have any quantum theory you want, but the right ones are the ones that give way to classical physics under some limit. In the case of his atom, when the electrons got far away from the nucleus.
-
- Bohr's model would later be replaced by the “valence shell model” that remains to this day. But his Correspondence Principle lived on, and it formed a cornerstone of all quantum theories to come. It was a guiding light that allowed physicists to construct and select the right mathematics to describe the subatomic world.
-
- Werner Heisenberg came up with his “Uncertainty Principle“. Try to measure the position of a tiny particle, and you'll end up losing information about its momentum. Go for the opposite, trying to pin down its momentum, and you'll become ignorant about its position.
-
- Bohr saw Heisenberg's Uncertainty Principle as a part of a much larger facet of the quantum world: that everything comes in pairs. Consider the most famous pair in the quantum world, the wave and the particle.
-
- In classical systems, something is either purely a wave or purely a particle. You can pick one or the other to classify some behavior. But in quantum mechanics, these two properties are paired up: everything is simultaneously both a particle and a wave and always exhibits some properties of both.
-
- Quantum rules rely on “probabilities” while quantum mechanics only reproduces classical physics on average. Based on these two insights, Bohr argued that a quantum theory can never explain classical physics. In other words, atoms operate under one set of rules, and trains and people operate on another set of rules. They can and must be connected via the Correspondence Principle, but otherwise they live separate and parallel lives.
-
- Some physicists argue that we just haven't worked hard enough, and that we do fundamentally live in a quantum world, and that we can reproduce classical physics from purely quantum rules.
-
- Science is still pursuing this goal. In 2022 a new way of measuring atomic-scale magnetic fields with great precision, not only up and down but sideways as well, has been developed by researchers at MIT. The new tool could be useful in applications as diverse as mapping the electrical impulses inside a firing neuron, characterizing new magnetic materials, and probing exotic “quantum physical phenomena“.
-
- The new technique builds on a platform already developed to probe magnetic fields with high precision, using tiny defects in diamond called nitrogen-vacancy centers. These defects consist of two adjacent places in the diamond's orderly lattice of carbon atoms where carbon atoms are missing; one of them is replaced by a nitrogen atom, and the other is left empty. This leaves missing bonds in the structure, with electrons that are extremely sensitive to tiny variations in their environment, be they electrical, magnetic, or light-based.
-
- Previous uses of single nitrogen-vacancy centers to detect magnetic fields have been extremely precise but only capable of measuring those variations along a single dimension, aligned with the sensor axis.
-
- The new method solves that problem by using a secondary oscillator provided by the nitrogen atom's nuclear spin. The sideways component of the field to be measured nudges the orientation of the secondary oscillator.
-
- By knocking it slightly off-axis, the sideways component induces a kind of wobble that appears as a periodic fluctuation of the field aligned with the sensor, thus turning that perpendicular component into a wave pattern superimposed on the primary, static magnetic field measurement. This can then be mathematically converted back to determine the magnitude of the sideways component.
-
- The method provides as much precision in this second dimension as in the first dimension while still using a single sensor, thus retaining its nanoscale spatial resolution. In order to read out the results, the researchers use an optical confocal microscope that makes use of a special property of the nitrogen-vacancy centers.
-
- When exposed to green light, they emit a red glow, or fluorescence, whose intensity depends on their exact spin state. These nitrogen-vacancy centers can function as qubits, the quantum-computing equivalent of the bits used in ordinary computing. We can tell the spin state from the fluorescence. "If it's dark," producing less fluorescence, that's a 'one' state, and if it's bright, that's a 'zero' state. If the fluorescence is some number in between then the spin state is somewhere in between 'zero' and 'one.'
-
- The needle of a simple magnetic compass tells the direction of a magnetic field, but not its strength. Some existing devices for measuring magnetic fields can do the opposite, measuring the field's strength precisely along one direction, but they tell nothing about the overall orientation of that field. That directional information is what the new detector system can provide.
-
- In this new kind of "compass“, we can tell where it's pointing from the brightness of the fluorescence, and the variations in that brightness. The primary field is indicated by the overall, steady brightness level, whereas the wobble introduced by knocking the magnetic field off-axis shows up as a regular, wave-like variation of that brightness, which can then be measured precisely.
-
- An interesting application for this technique would be to put the diamond nitrogen-vacancy centers in contact with a neuron. When the cell fires its action potential to trigger another cell, the system should be able to detect not only the intensity of its signal, but also its direction, thus helping to map out the connections and see which cells are triggering which others.
-
- Similarly, in testing new magnetic materials that might be suitable for data storage or other applications, the new system should enable a detailed measurement of the magnitude and orientation of magnetic fields in the material.
-
- Unlike some other systems that require extremely low temperatures to operate, this new magnetic sensor system can work well at ordinary room temperature making it feasible to test biological samples without damaging them.
-
- The system only provides a measurement of the total perpendicular component of the magnetic field, not its exact orientation. Now, we only extract the total transverse component; we can't pinpoint the direction.
-
- But adding that third dimensional component could be done by introducing an added, static magnetic field as a reference point. As long as we can calibrate that reference field, it would be possible to get the full three-dimensional information about the field's orientation.
-
- This is indeed the first step toward “vector nanoscale magnetometry“. It remains to be seen whether their technique can indeed be applied to actual samples, such as molecules or condensed matter systems.
-
- This is a new way of measuring atomic-scale magnetic fields with great precision, not only up and down but sideways as well. The new tool could be useful in applications as diverse as mapping the electrical impulses inside a firing neuron, characterizing new magnetic materials, and probing exotic “quantum physical phenomena“.
-
- The technique builds on a platform already developed to probe magnetic fields with high precision, using tiny defects in diamond called nitrogen-vacancy (NV) centers. These defects consist of two adjacent places in the diamond's orderly lattice of carbon atoms where carbon atoms are missing; one of them is replaced by a nitrogen atom, and the other is left empty. This leaves missing bonds in the structure, with electrons that are extremely sensitive to tiny variations in their environment, be they electrical, magnetic, or light-based.
-
- This new method is using a secondary oscillator provided by the nitrogen atom's nuclear spin. The sideways component of the field to be measured nudges the orientation of the secondary oscillator.
-
- By knocking it slightly off-axis, the sideways component induces a kind of wobble that appears as a periodic fluctuation of the field aligned with the sensor, thus turning that perpendicular component into a wave pattern superimposed on the primary, static magnetic field measurement. This can then be mathematically converted back to determine the magnitude of the sideways component.
-
- The researchers use an optical confocal microscope that makes use of a special property of the nitrogen-vacancy centers. When exposed to green light, they emit a red glow, or fluorescence, whose intensity depends on their exact spin state. These nitrogen-vacancy centers can function as qubits, the quantum-computing equivalent of the bits used in ordinary computing.
-
- They can tell the spin state from the fluorescence. If it's dark," producing less fluorescence, that's a 'one' state, and if it's bright, that's a 'zero' state. If the fluorescence is some number in between then the spin state is somewhere in between 'zero' and 'one.'
-
- The needle of a simple magnetic compass tells the direction of a magnetic field, but not its strength. Some existing devices for measuring magnetic fields can do the opposite, measuring the field's strength precisely along one direction, but they tell nothing about the overall orientation of that field. That directional information is what the new detector system can provide.
-
- In this new kind of "compass," we can tell where it's pointing from the brightness of the fluorescence, and the variations in that brightness. The primary field is indicated by the overall, steady brightness level, whereas the wobble introduced by knocking the magnetic field off-axis shows up as a regular, wave-like variation of that brightness, which can then be measured precisely.
-
- Unlike some other systems that require extremely low temperatures to operate, this new magnetic sensor system can work well at ordinary room temperature making it feasible to test biological samples without damaging them.
-
- The system only provides a measurement of the total perpendicular component of the magnetic field, not its exact orientation. By adding that third dimensional component done by introducing an added, static magnetic field as a reference point. It would be possible to get the full three-dimensional information about the field's orientation.
-
- New tools to learn the quantum world!
-
February 22, 2022 QUANTUM WORLD - is confusing? 3476
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ---
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
----------------------------- Tuesday, March 1, 2022 ---------------------------
No comments:
Post a Comment