It’s been ‘common knowledge’ in the physics community that experiments with quantum entanglement, that weird state where two objects share the same existence, can only take place at extremely low temperatures – roughly a maximum of 4 degrees Kelvin above absolute zero. (That’s about -457F or –272C.) It therefore gives physicists something like what Americans call ‘the willies’ (shivers up and down the spine) to see studies from plant biologists indicating that photosynthesis uses some kind of quantum entanglement at room temperatures. (See the post SciTechStory: Quantum mechanics in photosynthesis, oh my.) Now a research team under Fernando Galve at The University of the Balearic Islands (Spain) adds to the mix by demonstrating quantum entanglement (in a physics lab) at much higher temperatures.

By ‘higher temperatures’ this does not mean room temperature, but it does mean up to 50 degrees Kelvin, which is substantially warmer than 4 degrees Kelvin. They accomplished this by doing what physicists call “squeezing.” In quantum physics, the more accurately positions (of atomic particles) are measured, the less can be determined about their momentum. Similarly, measuring time decreases the measurement of energy, or phase amplitude. (This is remindful of the old bromide: You want quick, easy, and cheap? Pick any two.) The effect is called the Heisenberg uncertainty principle, which places limits on how well pairs of complementary properties can be observed.

Physicists have learned how to juggle the measurements to optimize one measurement or another. This is “squeezing.” What the Spanish team wanted to know was could squeezing be applied to a quantum situation where everything was changing (that is, in disequilibrium – whereas most such research is done in an equilibrium state). To test this, they used a pair of driven (by magnetic fields) quantum oscillators that are entangled in a ‘hot’ environment. Because they could control temperature and the driving force of the oscillators, they could constantly squeeze the system, and the entanglement was retained at higher temperatures. How high could this go?

Galve and co say this depends on the coupling between the oscillators. But they calculate that entanglement between a pair of calcium ions in an rf trap–a standard set up in many labs–and show how it could be sustained at 50K. That’s significantly better than the sub-4K systems that experimenters have to manage with today. “We believe this to be a huge experimental step,” they say.

What about room temperature experiments? That would require a very strong coupling and may cause other problems. The squeezing causes the quantum states to become more delocalised, in other words they become smeared out in space. That could be a problem if the ions end up largely outside the trap in which they are supposed to be confined.

[Source: Technology Review]

This new approach – exploring quantum entanglement in non-equilibrium systems – is not only an important step for quantum physics, but apparently it’s also a step in the direction already taken by Nature.