Analyzing quantum vacuum by studying a cloud of ultra cold atoms

Analyzing quantum vacuum by studying a cloud of ultra cold atoms

A laser beam hitting a cloud of ultra cold atoms. Credit: Vienna University of Technology

The Unruh-effect connects scientific theory and relativity. Until now, it couldn’t be measured. a replacement idea could change this as well as quantum vacuum concept.

Is the vacuum of space really empty? Not necessarily. This is often one among the strange results obtained by connecting scientific theory and therefore the theory of relativity: The Unruh effect suggests that if you fly through a quantum vacuum with extreme acceleration, the vacuum not seems like a vacuum: rather, it’s sort of a warm bath filled with particles. This phenomenon is closely associated with the Hawking radiation from black holes.

A research team from TU Wien, the Erwin Schrödinger Center for Quantum Science and Technology (ESQ) and therefore the University of Nottingham’s region Laboratory together with University of British Columbia has shown that rather than studying the empty space during which particles suddenly appear when accelerating, you’ll create a two-dimensional cloud of ultra-cold atoms (Bose-Einstein condensate) during which sound particles, phonons, become audible to an accelerated observer within the silent phonon vacuum. The sound isn’t created by the detector, rather it’s hearing what’s there simply because of the acceleration (a non-accelerated detector would still hear nothing).

The vacuum is filled with particles

One of the essential ideas of Albert Einstein’s theory of relativity is: Measurement results can depend upon the state of motion of the observer. how briskly does a clock tick? How long is an object? what’s the wavelength of a ray of light? there’s no universal answer to the present , the result’s relative—it depends on how briskly the observer is moving. But what about the question of whether a particular area of space is empty or not? Shouldn’t two observers a minimum of agree on that?

No—because what seems like an ideal vacuum to at least one observer are often a turbulent swarm of particles and radiation to the opposite . The Unruh effect, discovered in 1976 by William Unruh, says that for a strongly accelerated observer the vacuum features a temperature. this is often thanks to so-called virtual particles, which also are liable for other important effects, like Hawking radiation, which causes black holes to evaporate.

“To observe the Unruh effect directly, as William Unruh described it, is totally impossible for us today,” explains Dr. Sebastian Erne who came from the University of Nottingham to the Atomic Institute of the Vienna University of Technology as an ESQ Fellow a couple of months ago. “You would wish a measuring instrument accelerated to almost the speed of sunshine within a microsecond to ascertain even a small Unruh-effect -we can’t do this .” However, there’s differently to find out about this strange effect: using so-called quantum simulators.

Quantum simulators

“Many laws of physics are universal. they will be shown to occur in very different systems. One can use an equivalent formulas to elucidate completely different quantum systems,” says Jörg Schmiedmayer from the Vienna University of Technology. “This means you’ll often learn something important a few particular quantum system by studying a special quantum system.”

“Simulating one system with another has been especially useful for understanding black holes, since real black holes are effectively inaccessible,” Dr. Cisco Gooding from the region laboratory emphasizes. “In contrast, analog black holes are often readily produced right here within the lab.”

This is also true for the Unruh effect: If the first version can’t be demonstrated for practical reasons, then another quantum system are often created and examined so as to ascertain the effect there.

Atomic clouds and laser beams

Just as a particle may be a “disturbance” in empty space, there are disturbances within the cold Bose-Einstein condensate—small irregularities (sound waves) that opened up in waves. As has now been shown, such irregularities should be detectable with special laser beams. Using special tricks, the Bose-Einstein condensate is minimally disturbed by the measurement, despite the interaction with the laser light.

Jörg Schmiedmayer explains: “If you progress the beam , in order that the purpose of illumination moves over the Bose-Einstein condensate, that corresponds to the observer moving through the empty space. If you guide the beam in accelerated motion over the atomic cloud, then you ought to be ready to detect disturbances that aren’t seen within the stationary case—just like an accelerated observer during a vacuum would perceive a heat bath that’s not there for the stationary observer.”

“Until now, the Unruh effect was an abstract idea,” says Professor Silke Weinfurtner who leads the region laboratory at the University of Nottingham, “Many had given up hope of experimental verification. the likelihood of incorporating a particle detector during a quantum simulation will give us new insights into theoretical models that are otherwise not experimentally accessible.”

Preliminary planning is already underway to hold out a version of the experiment using superfluid helium at the University of Nottingham. “It is feasible , but very time-consuming and there are technical hurdles for us to beat ,” explains Jörg Schmiedmayer. “But it might be an exquisite thanks to study a crucial effect that was previously thought to be practically unobservable.”