Researchers Detect Photon Without Destroying It
17 December 2013
At the Max Planck Institute of Quantum Optics, researchers have devised a way to spot a single photon without harming it during the detection process, something which has been impossible before due to the extreme fragility of photons.
The experiment, described in the journal Science Express, provides important insights for single-photon sources and their potential application in quantum networking, cryptography and information processing.
In order to see the photons, physicists Andreas Reiserer, Stephan Ritter and Gerhard Rempe put a rubidium atom inside a cavity with mirrors reflecting each other on the sides. The researchers observed how the atom bounced back and forth thousands of times before getting transmitted or lost, which resulted in strong interaction between the light particle and the rubidium atom inside the cavity. The reflection of the photon away from the device gave the team the opportunity to see the photon by altering its phase rather than its energy.
The trick was to manipulate the atom so that it was in a superposition of the two states, Reiserer explained. Once the photon is reflected from the cavity, the resonant state undergoes a phase shift relative to the non-resonant one. This change in phases can be then read out from the atom, ensuring that the photon and its properties can stay untouched during the detection process, he said.
The researchers also noted that if the photon stays intact during detection it can be seen more than once, a phenomenon that can provide for an increase in the efficiency of future detectors.