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Antoine de Saint-exupéry

Created a new type of device for quantum-optical memory, whose size is a thousand times smaller than previous variants

12 Sep 2017

The area of quantum communications is currently undergoing a period of rapid development.

In this direction was already made many discoveries and developed a number of technologies, which in some places on the globe unfold quantum network that uses quantum state of photons of light as a carrier of information. However, the main “stumbling block” of quantum communication technologies are devices quantum-optical memory, the key components, which are used for short-term storage of information and encoding this information in the photons. Unfortunately, all used to date the device quantum-optical memory are big enough to be placed directly on the crystals of the specialized chips write novostiit

Recently, a group of researchers from the California Institute of Technology, National Institute of standards and technology and University of Verona, Italy, have finished creating and testing a new device for quantum-optical memory whose size is at least 1000 times smaller than all other similar devices. In addition, this device perfectly fits to the crystal communications chip, it has a very high energy efficiency.

The basis of the new device is a nanoscale optical cavity, combined with a crystal resonator. This combination allows to significantly increase the level of interaction between single photons of light and atoms of neodymium. The device of quantum-optical memory operates while maintaining individual photons of light in the tiny groups of atoms of neodymium, and these atoms “in the trap” of the crystal lattice of orthovanadate yttria (yttrium orthovanadate, YVO).

In order for the neodymium atoms become able to store the photons, they are pre-prepared using a sequence of pulses of laser light so that their absorption spectrum was generated in the frequency comb. This training guarantees that after absorption of photons by atoms, these photons are re-emitted back exactly 75 nanoseconds.

In the period after the absorption of photons by atoms and re-emission of photons the atoms are exposed to a pair of complementary pulses of laser light, which can cause additional delay reradiation to 10 nanoseconds depending on their intensity. This additional delay gives time for the device for carrying out the process of non-destructive search of prisoners in the photon data.

In this memory device there is an interesting and unusual effect. The photons stored in the atom of neodymium, are in a state of quantum superposition, and they are entangled on a quantum level with the first and last pulse of laser light. Experiments with the device memory showed that the wave function of a photon re-emitted light practically corresponds to the wave function of the initial photon, in other words, the device of quantum-optical memory capable of storing photons without distorting the contained quantum information.

The stability of a new device for quantum-optical memory corresponds to the level of stability of other similar devices, despite the fact that their sizes differ by more than a thousand times. Secondly, devices of the previous generation there was no possibility of retrieval of the stored data in it.

In order to give people the opportunity to use the new device quantum memory for practical purposes, scientists will need to develop more simple and convenient technology for mass production of such devices. Now the experimental device of quantum-optical memory has been manufactured by the technology of etching and cutting with an ion beam, which is a slow process that requires a high energy expenditure. And, in parallel, the researchers intend to conduct a number of additional activities aimed at increasing the efficiency of the device and increase the storage time of the information.