  Security enhancement is important in terms of both classical and quantum
information. The recent development of a quantum storage device is noteworthy,
and a coherence time of one second or longer has been demonstrated. On the
other hand, although the encryption of a quantum bit or quantum memory has been
proposed theoretically, no experiment has yet been carried out. Here we report
the demonstration of a quantum memory with an encryption function that is
realized by scrambling and retrieving the recorded quantum phase. We developed
two independent Ramsey interferometers on an atomic ensemble trapped below a
persistent supercurrent atom chip. By operating the two interferometers with
random phases, the quantum phase recorded by a pulse of the first
interferometer was modulated by the second interferometer pulse. The scrambled
quantum phase was restored by employing another pulse of the second
interferometer with a specific time delay. This technique paves way for
improving the security of quantum information technology.
