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From the article: "squeezed light removes the generally accepted cooling limit". Generally removing a limit in physics is a huge deal. What was this limit bas

by daveguy 10y ago

From the article: "squeezed light removes the generally accepted cooling limit". Generally removing a limit in physics is a huge deal. What was this limit based on? Has some fundamental quantum physical property been disproven? Is this a breakthrough more significant than setting a coldness record? Was the generally accepted limit based on what would be "really tough" or something else? Anyone know?

jessriedel 10y ago
> What was this limit based on? It's base on an assumption that the cooling apparatus isn't using squeezed light. If you can squeeze light, then the limit no longer applies. > Was the generally accepted limit based on what would be "really tough" or something else? Squeezed light is experimentally difficult to produce. But the definition of "squeezed" is defined as a particular, precise mathematical property of the state of light generated. So it was not some arbitrarily level of "toughness". An analogy: Historically, there weren't many practical ways to cool things besides putting it along side things that were already cold and allowing them to transfer heat. (This is why ice harvesting existed: https://en.wikipedia.org/wiki/Ice_trade https://en.wikipedia.org/wiki/Ice_trade ). Therefore, there was a "limit" to how cold you could easily make something, namely, the temperature of the coldest natural stuff you had access to. But once you can build cheap refrigerators, the limit disappeared, and you could easily cool things much colder than ice. > Has some fundamental quantum physical property been disproven? No. Squeezing light doesn't violate any laws of physics. > Is this a breakthrough more significant than setting a coldness record? Coldness records themselves are almost never intrinsically important. They just make good popular press releases. So the technique is more important than the coldness record, but it's not necessarily that important.
- lisivka 10y ago
  > Coldness records themselves are almost never intrinsically important. Temperatures below 0K (i.e. you need to heat a system to have 0K back) are very important to physics. They will allow to understand vacuum much better than today.
  - jessriedel 10y ago
    I don't think you know what a negative temperatures is. The wikipedia page is pretty good. https://en.wikipedia.org/wiki/Negative_temperature https://en.wikipedia.org/wiki/Negative_temperature
    - lisivka 10y ago
      I clearly understand what negative temperature is: if somebody squeezed an amount of energy out of a system, it's temperature drops. If somebody squeezed energy from a system at arbitrary zero point at temperature scale, then system temperature is below zero: system needs energy to return back to zero. Zero point at Kelvin scale is chosen when a system has no kinetic motion. But system at 0°K still has lot of energy, which can be released. I'm talking about energy of "hot" vacuum, which causes Casimir effect. This energy can do some mechanical work even at 0°K, so system still have some energy.
      - jessriedel 10y ago
        Your comment makes many confusing/wrong statements, but in particular this > Zero point at Kelvin scale is chosen when a system has no kinetic motion. is unambiguously wrong. The idea that temperature is monotonic function of kinetic energy is only an approximation to the fundamental definition of temperature, and that approximation isn't valid for systems that have negative temperature.
        lisivka 10y ago
        Definition of Absolute Zero from Wikipedia: > Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. > Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0. > In the quantum-mechanical description, matter (solid) at absolute zero is in its ground state, the point of lowest internal energy. It's still possible to squeeze some energy from a system past Absolute Zero as defined using Casimir effect, so it's possible to reach temperature below 0K. I know, that current interpretation of negative temperatures at Kelvin scale is different, but definition of temperature is different in that interpretation too, so let ignore it.

by daveguy 10y ago

jessriedel 10y ago

> What was this limit based on? It's base on an assumption that the cooling apparatus isn't using squeezed light. If you can squeeze light, then the limit no longer applies. > Was the generally accepted limit based on what would be "really tough" or something else? Squeezed light is experimentally difficult to produce. But the definition of "squeezed" is defined as a particular, precise mathematical property of the state of light generated. So it was not some arbitrarily level of "toughness". An analogy: Historically, there weren't many practical ways to cool things besides putting it along side things that were already cold and allowing them to transfer heat. (This is why ice harvesting existed: https://en.wikipedia.org/wiki/Ice_trade https://en.wikipedia.org/wiki/Ice_trade ). Therefore, there was a "limit" to how cold you could easily make something, namely, the temperature of the coldest natural stuff you had access to. But once you can build cheap refrigerators, the limit disappeared, and you could easily cool things much colder than ice. > Has some fundamental quantum physical property been disproven? No. Squeezing light doesn't violate any laws of physics. > Is this a breakthrough more significant than setting a coldness record? Coldness records themselves are almost never intrinsically important. They just make good popular press releases. So the technique is more important than the coldness record, but it's not necessarily that important.

lisivka 10y ago
> Coldness records themselves are almost never intrinsically important. Temperatures below 0K (i.e. you need to heat a system to have 0K back) are very important to physics. They will allow to understand vacuum much better than today.
- jessriedel 10y ago
  I don't think you know what a negative temperatures is. The wikipedia page is pretty good. https://en.wikipedia.org/wiki/Negative_temperature https://en.wikipedia.org/wiki/Negative_temperature
  - lisivka 10y ago
    I clearly understand what negative temperature is: if somebody squeezed an amount of energy out of a system, it's temperature drops. If somebody squeezed energy from a system at arbitrary zero point at temperature scale, then system temperature is below zero: system needs energy to return back to zero. Zero point at Kelvin scale is chosen when a system has no kinetic motion. But system at 0°K still has lot of energy, which can be released. I'm talking about energy of "hot" vacuum, which causes Casimir effect. This energy can do some mechanical work even at 0°K, so system still have some energy.
    - jessriedel 10y ago
      Your comment makes many confusing/wrong statements, but in particular this > Zero point at Kelvin scale is chosen when a system has no kinetic motion. is unambiguously wrong. The idea that temperature is monotonic function of kinetic energy is only an approximation to the fundamental definition of temperature, and that approximation isn't valid for systems that have negative temperature.
      - lisivka 10y ago
        Definition of Absolute Zero from Wikipedia: > Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics. > Absolute zero is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0. > In the quantum-mechanical description, matter (solid) at absolute zero is in its ground state, the point of lowest internal energy. It's still possible to squeeze some energy from a system past Absolute Zero as defined using Casimir effect, so it's possible to reach temperature below 0K. I know, that current interpretation of negative temperatures at Kelvin scale is different, but definition of temperature is different in that interpretation too, so let ignore it.