Tuesday, April 24, 2018

Nondestructive Photon Detection

APS Physics publishes Washington University article "Viewpoint: Single Microwave Photons Spotted on the Rebound" by Kater W. Murch.

"Single optical photon detectors typically absorb an incoming photon and use that energy to generate an electrical signal, or “click,” that indicates the arrival of a single quantum of light. Such a high-precision measurement—at the quantum limit of detection—is a remarkable achievement, but the price of that click is in some cases too high, as the measurement completely destroys the photon. If the photon could be saved, then it could be measured by other detectors or entangled with other photons. Fortunately, there is a way to detect single photons without destroying them.

This quantum nondemolition photon detection was recently demonstrated in the optical domain, and now the feat has been repeated for microwaves. Two research groups—one based at the Swiss Federal Institute of Technology (ETH) in Zurich and the other at the University of Tokyo in Japan—have utilized a cavity-qubit combination to detect a single microwave photon through its reflection off the cavity.

The non-destructive optical photon detection paper has been published in 2013 and described in Photonics magazine:

"Andreas Reiserer and colleagues at the Max Planck Institute of Quantum Optics have developed a device that leaves the photon untouched upon detection.

In their experiment, Reiserer, Dr. Stephan Ritter and professor Gerhard Rempe developed a cavity consisting of two highly reflecting mirrors closely facing each other. When a photon is put inside the cavity, it travels back and forth thousands of times before it is transmitted or lost, leading to strong interaction between the light particle and a rubidium atom trapped in the cavity. By reflecting the photon away from the device, the team was able to detect the photon by changing its phase rather than its energy.

The phase shift of the atomic state is detected using a well-known technique.

I'm not sure what is the practical use of this for image sensing. In theory, this opens a way to an invisible image sensor that detects and releases all the incoming photons without absorbing them.


  1. Is this decay for invisibility? I hope someone will be so kind to elaborate on this.

    Thanking in advance.


  2. Does this technique also apply to EUV--IR? Then you could have a single sensor sensitive to all wavelengths, since absorption of photons (& thus material, material thickness) is not a concern.


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