KUGA LABORATORY AT THE UNIVERSITY OF TOKYO

The University of Tokyo

Graduate School of Arts and Sciences,

Department of Basic Science,


Kuga laboratory

Quantum non-demolition measurement of photon

We investigate a new method to detect weak light without absorption at single photon level. Moreover, we try to generate concave surface on a flat edge of optical fiber by laser machining with CO2 laser.

Quantum non-demolition measurement of photon

Light cannot be usually observed without losses. The laser beam propagating in free space can be seen by dust in air. In the case of weak light consisted from a few number of photons, the quantum state is destructed by the losses. A transparent detector which does not interrupt the propagation of light will be useful for quantum information processing based on post-selections.

It is not a ridiculous dream. Such technique is called as the quantum non-demolition measurement (QND), which many scientists try to realize it. In the microwave frequency domain, QND has been already realized by S. Haroche’s group, who won the Nobel physics prize in 2012. However, in the optical frequency domain, QND is difficult due to the short lifetime of the optical transition.

By combining cavity QED technique with single atoms in optical frequency domain, we are trying to demonstrate a new method of QND. A new experimental system is under construction (Figure 3-1).

Fig. 3-1: The part of the lasers.
Figure 3-1: The part of the lasers. The system is based on standard technique of laser cooling and trapping of neutral atoms such as external cavity diode laser, saturation absorption spectroscopy and polarization spectroscopy.
Moreover, we try to generate concave surface on a flat edge of optical fiber by laser machining with CO2 laser (Figure 3-2). It will be used as a mirror of the cavity QED system.

Fig.3-2: Light of CO2 laser.
Figure 3-2: Light of CO2 laser.
The beam cannot be seen by naked eyes because the wavenlength is far IR domain (10.6 um). After blocked by a brick, the shined area is heated and emits black body radiation, which can be seen by naked eyes.

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