Set a Password on a Photonic Memory

In LPHYS'16 conference, I discussed with Prof. Alexey A. Kalachev and Prof. Lock Yue Chew about the idea of how to set a password on a photonic memory using a disordered laser field. One year later we got this idea published in Phys. Rev. A (Rapid Communication) 95, 061805(R) (2017). We also gave a talk in LPHYS'17 conference, which is a nice experience of collaboration. We had quite fun between two conferences. This work is also reported by Ars Technica.

The basic idea is quite straightforward and let's explain by what follows. When one shines an off-resonant laser to drive a quantum two-level atom. The two levels will be superposed, and the phase of the superposed state will also be shifted by the laser depending on how long the atom see the laser. Now imagine that we use a laser with spatially random speckles. In this case each atom at different position sees different strength of the laser field, which then introduces an inhomogeneous phase shift to the whole atomic ensemble. It is this random phase shift rendering password applicable to a memory. The above two levels can actually be level 2 and 4 in Fig. (b) while levels 1,2 and 3 form a typical three-level EIT memory system. Based on our calculation illustrated in Fig. (a), when shining a disordered laser only once (the encryption pulse) during EIT storage duration, namely, between time 50 and 195 in the figure, the stored probe signal will never be retrieved. The retrieval is successful only when applying the decryption pulse with the same speckle pattern of the decryption one and a minus detuning. That is it! One therefore can use a pair of disordered pulses to set password on any of memory schemes. As you may see that we may one day enter a continuous disordered password instead of a digit one, whose key length is relatively short, to login our cloud drives.