RU124026U1 - POLARITON CRYSTAL DEVICE FOR RECORDING AND STORING QUANTUM INFORMATION - Google Patents

Abstract

A polariton crystal device for recording and storing quantum information, which is a semiconductor lattice with periodic defects that are optical microresonators, characterized in that a cluster of atoms is placed in each defect with the possibility of coupling between neighboring microresonators due to tunneling of atoms and photons.

Description

The utility model relates to devices intended for use in the fields of processing and storage of data by optical methods - quantum information, telecommunications.

An analogue of the utility model is a device based on a diamond structure with color centers - nitrogen-substituted vacancies or NV centers (scientific publication: Wrachtrup J., Kilin S.Ya., and Nizovtsev AP Quantum computation using the 13C nuclear spins near the single NV defect center in diamond // Optics and Spectroscopy. - 2001. - Vol. 91. - P. 429-437). Significant disadvantages of diamond NV centers are the sensitivity of their characteristics to a specific atomic environment, the very weak intensity of optical transitions without phonons, and the difficulty of obtaining periodic structures based on them.

Another analogue of the utility model is the atomic lattice in coupled resonators described in Greentree A.D., Tahan C, Cole J.H., and Hollenberg L.C.L. Quantum phase transitions of light // Nature Physics. - 2006. -Vol. 2. - P. 856-861. Its disadvantage compared to the utility model is, firstly, the presence of only a photon coupling between the resonators, and secondly, the linearity of the response of the system.

A device is also known based on semiconductor quantum wells (quantum dots) placed in Bragg microcavities. The device is a spatially periodic semiconductor (CdTe / CdMgTe or GaAs) structure with defects that are optical microresonators. A semiconductor quantum well (quantum dot) is placed in each defect. Bosonic particles called exciton polaritons are formed in the device (scientific publications: Kasprzak J., Richard M., Kundermann S. Bose-Einstein condensation of exciton polaritons // Nature. - 2006. - Vol.443. -№7110. - P .409-414; Balili R., Hartwell V., Snoke D., et al. Bose-Einstein Condensation of Microcavity Polaritons in a Trap // Science. - 2007. - Vol. 316. - No. 5827. - P. 1007. -1010). We accept this device as a prototype. The prototype has the following disadvantages: an extremely short coherence time of exciton polaritons, an extremely low temperature (up to five Kelvin) at which the device functions, and a weak nonlinear response of the medium.

The purpose of the proposed utility model is to increase the coherence time of particles used to store information, enhance the nonlinear response of the medium, and also increase the critical temperature of the device.

This goal is achieved using a polariton crystal device for recording and storing quantum information, including a semiconductor grating with periodic defects that are optical microresonators, while each defect contains a cluster of atoms with the possibility of coupling between neighboring microresonators due to tunneling of atoms and photons

A useful model of a polariton crystal makes it possible to effectively control the group velocity of a light pulse and form the so-called slow light. It is for the tasks of copying (writing) and storing quantum information that this problem is fundamental. Physically, the recording time of quantum optical information is determined by the delay time of the light pulse in the medium. The very change in the group velocity of the light pulse propagating in such systems is directly related to the formation of polaritons formed by a linear superposition of photons of the external (probe) light field and macroscopic (coherent) disturbances of the medium. To realize these capabilities, it is supposed to use nonlinear media, preferably with large phase incursions per photon.

The first essential sign necessary to achieve a technical result is the use of a semiconductor micro- or nanostructure with locally impaired spatial periodicity as the basis for a defective photonic crystal. Chains of coupled microcavities created on the basis of photonic crystals using nanotechnology and nanophotonics — called optical coupled resonator waveguides (CROW's) —are an effective tool for monitoring the propagation characteristics of light radiation, a condition necessary for processing optical information. The most promising is the use of a new generation of microresonators with a high level of quality factor, with a volume of the order of λ ³ , where λ is the wavelength of light, for which the strong coupling condition is satisfied up to a single atom. In this case, it is possible to obtain a cubic-nonlinear response of the medium for a relatively small, in the limit of a single number of photons.

The second essential feature is the use of atomic clusters as a multilevel energy structure. This allows one to fundamentally achieve the repulsive interaction of polaritons as information carriers, increase the nonlinear response of the system, and significantly increase the coherence time of the medium and field. In this case, the formation of polaritons becomes possible at high temperatures, up to room temperatures. In addition, the use of polaritons, which are in a state of condensation as coherent wave packets propagating in the medium, allows achieving unprecedented high reliability of information processing.

The third essential feature is the possibility of coupling neighboring cells of the periodic microresonator structure of the utility model by tunneling both atoms and field photons in the plane of the polariton crystal.

Figure 1 presents a schematic representation of a utility model of a polariton crystal. A photon crystal 1 with defects 2 is used as the basis. An atomic cluster 3 is placed in each of the defects. An optical lattice 4 is used to capture atoms. It is a standing wave, whose minima coincide with the position of the defects.

Figure 2 shows the dependence of the parameter D = Δ / | 2g |, characterizing the type of polaritons in a polariton crystal, on the normalized time T, which describes a three-step algorithm for recording and storing quantum optical information using the structure of a polariton crystal. The numbers indicate the stages of recording information (1), its storage (2), and reading (recovery) of optical information (3).

The utility model is based on a photonic crystal 1 in FIG. 1 with periodic defects 2 in FIG. 1, acting as optical microresonators with high quality factor. In order to form photonic crystal nodes on a semiconductor basis, as well as to create periodic defects, the widely known method of mask etching is used (Vučkovic J., M. Lončar, N. Mabuchi, et al. Design of photonic crystal microcavities for cavity QED // Physical Review E. - 2001.-Vol. 65. - No. 1. - P. 016608-1 - 016608-11; Lončar M., Yoshie T., and Scherer A. Low-threshold photonic crystal laser // Applied Physics Letters. - 2002. - Vol.81. -№15. -P. 2680-2682).

The characteristic spatial dimensions of microresonators are not more than a few micrometers. In each structural defect, a small but macroscopic (from 50) number of atoms 3 is placed in FIG. 1. The capture and movement of atoms is possible by atomic force microscopy - see distance O, Perez R. and Morita S. atomic force microscopy as a tool for atom manipulation // Nature Nanotechnology. - 2009. - Vol. 4. - P. 803-810.

To hold atoms in the defect region by interfering laser beams, an optical lattice 4 is created in Fig. 1, the minima of which coincide with the position of the defects.

The number of atoms in each resonator and the shape of the utility model are not regulated and can be dictated by the requirements of the potential user.

The device operates as follows.

Storage of quantum optical information using a PC structure involves a three-step physical implementation algorithm - see figure 2.

At the first stage, to record quantum information, we select a large and negative detuning Δ << - 2g, where g is the parameter, describes the atomic-optical coupling, Δ characterizes the difference in the frequencies of the optical field and atomic transitions. In this case, the polaritons of the lower dispersion branch are photon-like, and propagate due to the tunneling of photons in the lattice of a polariton crystal. The wave packet propagates at a speed close to the speed of light in vacuum.

At the second stage, in order to display optical information on coherent atomic perturbations of the medium, we switch the detuning, making it positive. In this limit, the polaritons of the lower branch become atom-like and their speed corresponds to the speed of movement of atoms in the lattice. The speed of polaritons can be reduced by several orders of magnitude relative to the speed of light, and it can reach values from several meters to several kilometers per second. The information contained in the light beam, while completely recorded on atomic disturbances. For example, in the case of the interaction of a light field with rubidium atoms in the absence of decoherence effects, the characteristic packet spreading time is 13.7 s with an input beam width of 0.04 cm.

At the third stage, to restore the optical information at the output from the medium after a certain time interval that determines the storage time of the information, we again make the polaritons photon-like, switching the detuning Δ in the reverse order.

Thus, the polariton crystal model corresponds to a new quantum structure in which greater non-linearity is achieved, the coherence time is increased, and the critical temperature of the formation of polaritons that are carriers of information increases.

Claims (1)

A polariton crystal device for recording and storing quantum information, which is a semiconductor lattice with periodic defects that are optical microresonators, characterized in that a cluster of atoms is placed in each defect with the possibility of coupling between adjacent microresonators due to tunneling of atoms and photons.

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