Carrying out continuous measurements of certain quantum systems may cause them to change their state to a more ordered or less ordered state (when a system is more ordered, it can be said to be colder).
Measurement / Gershon Kuritsky
"Let me take your temperature," the nurse told me
and pulled out some kind of sophisticated device.
"Lie still, it will take at least two minutes",
So I answered her: "It's not food.
I will not share my heat with another person,
Lest I mix my brown with your brown.
I will not be an object of observation, beautiful,
Not before you say your name."
"Arrogant like you, different from the people",
That's what she said and her face lit up.
"Calm down, act like a human being,
Lie down and don't play hero to me."
"No, I understand, I've been craving freedom ever since,
I just have to be the observer here:
In you, in the light, in the brave new world,
Please call the doctor."
"Sir", she said to me in such a quiet voice,
"Please limit the observation space.
The interweaving will keep you from the truth,
So stop confusing my mind."
"In the day-to-day world, we must inject energy directly into bodies that we want to heat or cool. But when you want to change the temperature of tiny bodies with quantum dimensions, such as atoms or subatomic particles, it is enough to 'measure their heat,'" says Prof. Gershon Kuritsky from the Department of Chemical Physics in the Faculty of Chemistry at the Weizmann Institute of Science. Recently, Prof. Kuritsky, together with Prof. Lucio Friedman from the same department, managed to demonstrate this principle. The results of their experiment may, in the future, open the door to new applications in the field of nuclear magnetic resonance, and new methods for storing information.
About two years ago Prof. Kuritsky, Dr. Noam Erez and (then) research student Dr. Goren Gordon published an article in the scientific journal Nature, in which they predicted that performing continuous measurements of certain quantum systems may cause them to change their state to a more ordered or orderly state less (when a system is more organized, it can be said to be colder). This prediction is based on one of the principles of quantum physics: a large number of consecutive measurements changes the properties of the system. The key to the result, according to the findings of Prof. Kuritsky and his research partners, is in the timing, that is, in the frequency of the periodic measurements. A measurement at a very fast rate, for example, may heat up the system, while the very same measurements, made at a slightly slower frequency, may cool it down (see issue 51 of the "Institute" newspaper - the quanta heat up and cool down).
At this point Prof. Friedman came into the picture, who saw here an opportunity to expand the limits of the capabilities of nuclear magnetic resonance (NMR). Together with Prof. Kuritsky and the postdoctoral researchers Dr. Gonzalo Alvarez and Dr. Dorja Bhaktavatsela Ra Dasari, he found a way to examine in NMR the possibilities for heating or cooling by changing the measurement rate.
"The NMR is actually the ideal technology for performing such experiments," says Prof. Friedman. "Thanks to the lower frequency and slower electromagnetic waves on which it is based, the NMR is, in most cases, more accurate."
The work that led to Prof. Kuritsky's prediction was based on a model of an open quantum system: a system in which a small composition of quantum particles interacts with a large number of particles contained within a "bath". Similar to how a (relatively) large object immersed in a water bath will exchange heat with them until their temperature is equal, so also quantum objects found in a particle bath tend to reach a point of balance with their surroundings. On the quantum plane, this balance may be expressed in additional quantum properties to the heat property. For example, it can affect the attack of the vortex ("spin") of particles that make up the nuclei of atoms. The spin is characterized by one of two possible directions: "up" or "down". When the spins of the particles are arranged - that is, when they are arranged in the same direction - the system is "cooled".
The more random the spin arrangements, the "hotter" the system. According to Prof. Kuritsky's prediction, the measurements may disrupt the process of reaching a balance between the quantum object and the bath - which contradicts the predictions based on the classical rules of thermodynamics. In other words, the measurement is able to partially free the particles from the effect of the bath, thus allowing the researchers to "reset" their temperature.
In the experiment carried out by the team of scientists, the bath was made of a large number of protons (nuclei of hydrogen atoms). The quantum particles were nuclei of the isotope carbon 13. To simulate a measurement process, the scientists used short magnetic pulses, while checking the spin order of the carbon 13 nuclei. At the start of the experiment, these nuclei were in a state of disorder, and their spins pointed in all directions. But when the researchers changed the frequency of the magnetic pulses - in the range between one pulse and ten pulses per thousandth of a second - it was possible to make the spins organize parallel to the magnetic field or in the opposite direction. "It is similar to a man wandering back and forth on the path," says Prof. Friedman. "By deciding when and where to stop him, we can 'reset' his gait, thus controlling the direction in which he walks. In our experimental system, we were able, using this approach, to arrange the spins of the groups of quantum particles 'upwards' or 'downwards', according to our will. In some cases, we got a better array than what we could get with other methods."
The scientists were surprised to find an almost complete agreement between the results of the experiment and the theory, and they are starting to think about possible applications. Prof. Friedman, for example, believes that a method that makes it possible to control the spins of quantum particles may improve the efficiency of certain NMR and MRI experiments. Prof. Kuritsky intends to investigate how this principle can help overcome one of the barriers to building quantum computers. "In order to create a record of quantum memory", he says, "one must start from a situation where all the spins are arranged in the same direction. Our method can reach this state without using unnecessary 'violence'. It is possible that in order to create the correct arrangement we will only have to find the appropriate frequency of the measurement cycle."
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I didn't really understand - if frequent measurement increases the heat and measurements with the help of MRI can create more order - that means arranging the spin direction of the particles in the same direction - that means cooling the system - it's actually contradictory - because the more you measure, the more the system is cooled...
lion,
The concept of heat is much more inclusive than the degree of mobility of molecules. First of all, the article does not talk about the heat of a single molecule (which can also be defined) but about the heat of a large number of molecules. Heat in a microscopic sense or more correctly temperature is determined by how the energy of the system is distributed between the different degrees of freedom. For example the degrees of freedom can be the kinetic energy of the molecules or their spin arrangement. In a single molecule you can look at the arrangement of the electrons in the electronic levels to define the temperature of the molecule.
I believed that the temperature of a body is the degree of mobility of its molecules. So what does the temperature of a molecule, or one atom or smaller particle mean. Please an exact definition and not the insinuations in the article.
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