While scientists do have the technology to detect individual photons, the photon itself is absorbed and altered. A new technique has allowed physicists to detect the photon without changing any of its properties. This technique was developed by researchers in the Quantum Dynamics Division at the Max Planck Institute of Quantum Optics and was published in Science Express.
The biggest downside to destroying photons by measuring them is that it is impossible to conduct multiple experiments with them. Additionally, absorbing photons alters the shape and polarization, preventing scientists from observing the light as it naturally occurs. This new manner of detection reflects the photon off of the sensor, leaving the photon in quantum superposition. The device is successful at detecting single photons 74% of the time and has a 66% success rate of leaving the photons intact. This has been a major goal for optics research and the ability to detect photons without annihilating them will lead to devices that can detect single photons more sensitively.
The ability to keep photons intact is accomplished by reflecting the particle off of a rubidium atom in a mirrored cavity with a faint laser light. This forces the atom into two ground states. The first ground state does not resonate with either the photon or the cavity, while the second state does. Because of these two distinct states, the photon has special properties that are not seen when either state occurs alone. The photon is then reflected out of the cavity, completely unharmed. The researchers were able to detect that the rubidium atom had been affected by the photon and used the changes caused by a phase shift to determine that a photon had, in fact, been present.
This technique has the ability to revolutionize how optic measurements are taken. Without damaging photons, researchers will be able to design experiments that allow a single photon to engage in multiple measurement exercises. Additionally, this could affect quantum communications by allowing a photon to travel and be detected without altering any information. Additionally, this technique could be used to develop quantum gates; the component for a quantum computing.