‘Quantum holograms’ for information storage and computation

November 4, 2014

Setup of an experiment showing orthogonal side illumination for quantum information storage (credit: Vetlugin et al.)

Russian scientists have developed a theoretical model for quantum information storage using holograms.

These findings from Anton Vetlugin and Ivan Sokolov from St. Petersburg State University in Russia are published in a study in The European Physical Journal D.

The authors demonstrate that it is theoretically possible to retrieve, on demand, a given portion of the stored quantized light signal of a holographic image by shaping the control field both in space and time.

Holograms are well-known classical memory devices that allow optical images to be written and retrieved. Extending this to a quantum domain, the hologram would be written on a medium able to store quantum superposition, not just the intensity of a light beam, as with traditional holograms.

The readout of both classical and quantum holograms would be performed by illuminating the medium with an external light pulse (the control field is scattered on the internal structure of the hologram).

The authors apply standard theoretical methods of quantum optics, including quantum description of cold atoms that compose the storage medium, as well as quantum theory of light propagation and interaction with the medium.

The ultimate goal is to also perform transformations of the quantum states, which could be useful for quantum communication and computation.

Abstract of Addressable parallel cavity-based quantum memory

We elaborate theoretically a model of addressable parallel cavity-based quantum memory for light able to store multiple transverse spatial modes of the input light signal of finite duration and, at the same time, a time sequence of the signals by side illumination. Having in mind possible applications for, e.g., quantum repeaters, we reveal the addressability of our memory, that is, its handiness for the read-out on demand of a given transverse quantized signal mode and of a given signal from the time sequence. The addressability is achieved by making use of different spatial configurations of pump wave during the write-in and the readout. We also demonstrate that for the signal durations of the order of few cavity decay times, better efficiency is achieved when one excites the cavity with zero light-matter coupling and finally performs fast excitation transfer from the intracavity field to the collective spin. On the other hand, the light-matter coupling control in time, based on dynamical impedance matching, allows to store and retrieve time restricted signals of the on-demand smooth time shape.