Virtual Photons Become Real in a Vacuum

By changing the position of a mirror inside a vacuum, virtual particles can be transformed into real photons that can be experimentally observed.

In a vacuum, there is energy and noise, the existence of which follows the uncertainty principle in quantum mechanics. These virtual particles in the vacuum can momentarily appear and disappear, and can be converted into detectable light particles.

Now, researchers at Aalto University and the VTT Technical Research Center of Finland have showed experimentally that vacuums have properties not previously observed. They demonstrated that by changing the position of the mirror in a vacuum, virtual photons can be transformed into real ones that can be observed experimentally.

Artist's impression of the creation of an entangled photon pair, a process that is seeded by the vacuum fluctuations. The source of the pair is an actual microscope image of the chain of superconducting quantum interference devices (SQUID) of the metamaterial sample in which the dynamical Casimir effect was studied. The speed of light in this material could be varied by changing the magnetic field through the SQUID loops. Images courtesy of Aalto University.

“If we act fast enough, we can prevent the particles from recombining — they will then be transformed into real particles that can be detected,” said Dr. Sorin Paraoanu of Aalto University.

An array of superconducting quantum-interference devices (SQUID) — parts resembling devices used in imaging small magnetic fields in the brain — were used in the experiment. By changing the magnetic field, the speed of light in the device can be altered. Radiation reflecting from such a device experiences it as a moving mirror from the standpoint of the vacuum’s electromagnetic field.

Optical microscope image of the chain of SQUID of the metamaterial sample in which the dynamical Casimir effect was studied. The speed of light in this material could be varied by changing the magnetic field through the SQUID loops.

“By quickly varying the speed of light in the array, we can extract microwave photons out of the vacuum's quantum noise,” said Aalto University doctoral student Pasi Lähteenmäki.

These devices could be used to create an artificial event horizon and observation or Hawking radiation emanating from it. It could also help cosmologists to better understand how the universe was formed and to advance the development of quantum computers.

The study was published in the Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1212705110).

For more information, visit: www.aalto.fi/en