WO2016085367A2 - Compact device for generating single photons - Google Patents

Abstract

The utility model relates to generators of single photons. The essence of the solution consists in a device for generating single photons, the device comprising a waveguide and a diamond structure with at least one colour centre which is delivered by external radiation or electrical pumping, characterized in that a layer of metamaterial having hyperbolic dispersion is applied to a section of the external surface of the waveguide, and the diamond structure is arranged above the layer of metamaterial. The technical result is the creation of a portable device for generating a large number of single photons.

Description

 COMPACT DEVICE FOR SINGLE PHOTON GENERATION

 The utility model relates to single photon generators.

 State of the art

Single photons are fundamental elements of quantum information technologies such as quantum cryptography, quantum information storage, and optical or quantum computing. The key areas of development of the computer industry today are a significant increase in the operating frequency of the processor and the practical implementation of high-performance parallel computing mechanisms. Progress in this area can be achieved through the use of optical technologies and quantum computing algorithms. The practical implementation of these approaches requires stable and efficient sources of single photons and nanostructures to control the quantum dynamics of photons.

 In the following, the following terms and abbreviations are used in the description.

 NV centers in the diamond lattice are the most preferred sources of single photons due to the high stability of diamond itself and the ability to generate NV centers at normal temperatures, but they have their drawbacks. Namely, the radiation intensity of the NV centers is rather small, and this complicates their use as single-photon radiation sources, which are necessary for future computers. One solution to this problem is to use a hyperbolic metamaterial in the optical range. The manufacturing technology of a single photon source is based on the use of standard technological processes and materials used in the manufacture of microelectronic "chips".

 Hyperbolic metamaterial (GMM) is a nanostructured system consisting of alternating metal and dielectric layers several nanometers thick. The number of such pairs of layers can vary from units to several tens. A characteristic feature of the GMM is the high density of photon states described by the hyperbolic dispersion law. HMM makes it possible to accelerate the processes of both absorption of radiation by nanodiamonds and the emission of single photons by them.

A plasmon resonator is an electromagnetic or optical resonator that uses the properties of collective oscillations of electrons (plasmons) to create a local amplification of the electromagnetic field. The architecture of solid lenses is a design of the type “emitter - solid”, while the solid is the lens for the generated radiation.

 The architecture of nanowires is an architecture in which a nanowire from a material most often possessing plasmonic properties is brought into contact with a quantum emitter. In this interaction, the emissivity of the emitter is enhanced.

Plasmonic material is a material in which the collective behavior of electrons is observed. These collective vibrations under the influence of an external optical field can be substantially resonant, and can strongly affect the optical properties of the material. Examples of plasmonic materials are silver, gold, titanium nitride, platinum, aluminum.

 Meta-surface - in the present description we understand a special case of metamaterial in which a small number of layers (up to 1) are used.

 Prashant Shekhar, Jonathan Atkinson and Zubin Jacob, Hyperbolic metamaterials: fundamentals and applications, 2014 on pages 26-28 show that for single photon sources the number of emitted photons can increase in the presence of metamaterials, including GMM.

 Tsung-li Liu, Plasmonic Cavities for Enhanced Spontaneous Emission, PhD Thesis 2013 demonstrated that an increase in the number of emitted photons can be achieved by combining quantum emitters and plasmon resonators and creating a monolithic architecture such as solid lenses and nanowires. However, there is a need to increase the flux of photons in a wide spectral range, while ensuring the small dimensions of the device for generating photons.

 Sources of single photons using quantum emitters require certain mechanisms for pairing a particle with an optical particle pumping system and an optical system for collecting single photons. As such optical systems can act as lenses, lenses, optical waveguides. A quantum radiator, matched with an optical waveguide, represents the most practical implementation of a single-photon source for connecting to external devices used for data transmission or quantum computing.

As quantum emitters that stably operate at room temperature, color centers in diamond, such as nitrogen and silicon color centers, are widely used. The problem of increasing the output of single photons is solved by increasing the efficiency of photon collection on the one hand and reducing the lifetime of the excited state on the other. Ramachandrarao Yalta, Fam Le Kien, M. Morinaga, and K. Hakuta, Efficient channeling of fluorescence photons from single quantum dots into guided modes of optical nanofiber, 2012 show that the collection of single photons from a quantum emitter can improve when the emitter is placed at the outer surface of the waveguide.

 The device described in patent US 20110174995 A1, involves the use of a single photon source as a quantum emitter (including an NV center) located at the end of the optical fiber. The emitter is pumped in this invention using an external lens. The invention is primarily aimed at the localization of a quantum emitter and the collection of single photons.

In US patent US8842949 B2, published September 23, 2014, a single photon source is considered, consisting of a quantum emitter in a resonator designed at the outputs of two optical waveguides, one of which is used for pumping, the second for outputting radiation of single photons.

 US patent application US20090034737 A1 describes a single photon source at a center of color in a diamond using a wavelength converter to create a narrow-band single photon generator.

 The disadvantage of the described solutions is the limitation on the number of generated photons.

 US Patent Application US20130056704 A1, which is selected as a prototype published March 7, 2013, discusses a device for creating a photon flux using metamaterial to increase the yield of single photons from a quantum emitter. A quantum emitter is located on the surface of a metamaterial substrate. The disadvantage of this device is the relatively large size of the generator of single photons.

 Technical challenge

 The technical task is to create a portable device for generating the number of single photons. The technical result consists in reducing the dimensions, as well as in the generation of a large number of single photons.

 Decision

To solve this problem, a device is proposed for generating single photons, including a waveguide, a diamond structure with at least one color center, which is pumped by external radiation or electric pumping, characterized in that a portion is applied on the outer surface of the waveguide a layer of metamaterial having hyperbolic dispersion, and a diamond structure is located above the layer of metamaterial.

 The device can be made in such a way that the diamond structure is a diamond film or diamond nanoparticles with sizes up to 200 nm, and the waveguide is an optical fiber filament. Moreover, the optical fiber thread may have a constriction at the place of application of the metamaterial less than 2 microns.

 The metamaterial may be at least 1 metal layer and 1 dielectric layer or at least 1 metal layer.

The color center in the nanodiamond crystal can be created due to an admixture of nitrogen or silicon, and the distance between the color center and the surface of the metamaterial should be less than 1000 nm.

 The metamaterial can be made of titanium nitride and scandium aluminum nitride. In this case, the output radiation of photons is in a wide spectral range of 600-800 nm.

 The device can be used in quantum computers and should operate at temperatures no higher than 450 ° C.

 For finer control over the optical field, the metamaterial may have optical anisotropy and contain layers of plasmon and dielectric materials, and at least one of the layers is thinner than 100 nm. The layer of plasmonic material contains at least one layer of silver, or a layer of conductive transparent oxide, for example, aluminum oxide - sapphire, or transition metal nitride. The plasmonic material may be made of scandium aluminum nitride and titanium nitride, and the dielectric material layer may be an alumina film.

 List of figures

 In FIG. 1 shows a schematic diagram of a device. The following notation is used:

 1- pump radiation,

 2 quantum emitter,

 3 strand of optical fiber,

 4 metamaterial

5 signal of single photons. In this case, the pump radiation can be carried out as a lens, by focusing with a lens, another fiber, or through the same fiber, it is also possible to use nanoantennas (metamaterials) to focus the pump radiation near a quantum emitter.

 In FIG. 2 shows a variant of the circuit with an emitter on the side surface, with 1 being a pump radiation, 2 a quantum emitter, 5 a signal of single photons, 4 metamaterial, 3 an optical fiber filament.

 In FIG. Figure 3 shows a variant of the basic scheme with an elongated fiber without breaking, with a constriction. The following notation is introduced: 1 — pump radiation, 3 — optical fiber filament, 4 — metamaterial, 6 — excitation region, 5 — single photon signal, 2 — quantum emitter, 7 — fiber rotation angle, alpha., This angle affects the optimal operation devices, in particular at small angles, the pumping radiation will pass more through the constriction and create spurious illumination. In the case of a large angle, it will not pass.

 Decision Disclosure

 To solve this problem, a device for generating single photons, shown in FIG. 1-2. The device includes a waveguide (item 3 - for example, an elongated fiber), a diamond structure with at least one color center (item 2 - a quantum emitter), metamaterial (item 4), which has a hyperbolic dispersion and is deposited on plot of the outer surface of the waveguide (Fig. 1, -3). In this case, a diamond structure with a color center is located above the metamaterial and can be pumped by external radiation (pos. 1) or by electric pumping (i.e., an external voltage is applied to the p-i-n semiconductor contact made of diamond). As a result of the operation of the device, a stream of single photons appears (item 5 - signal of single photons).

The location of the diamond structure above the metamaterial layer is used to increase the number of single photons. The deposition of a layer of metamaterial on the outer surface of the waveguide is used to focus the radiation in the fashion of a photon waveguide. A waveguide in the form of an optical fiber or nanofibre fiber coated with a metamaterial or metasurface provides a more efficient input of radiation into the waveguide mode due to the effective capture of radiation by the metamaterial and further transition of the plasmon mode into the waveguide mode. This solves such a problem as low collecting ability for such methods of collecting radiation as collecting cure using a lens, collecting radiation with an optical fiber when a quantum emitter is located at the end of the waveguide. Finally, when applying metamaterial to the external surface of the waveguide is solved the main technical problem of reducing the dimensions of the device by placing a photon generation source (diamond structure with metamaterial) directly on the surface of the waveguide. Note that for the selected prototype, the photon generation source was located on a separate substrate, which had to be connected to the waveguide (see US20130056704, Fig. 1), and in the proposed solution they are combined (see Fig. 1-3 of this solution).

 The color center (aka quantum emitter) in a nanodiamond crystal can be created due to an admixture of nitrogen or silicon and the distance between the color center and the surface of the metamaterial should be less than 1000 nm.

 The device can be made in such a way that the diamond structure is a diamond film or diamond nanoparticles with sizes up to 200 nm, and the waveguide is an optical fiber filament. Moreover, the fiber of the optical fiber can have a constriction of less than 2 μm at the place of application of the metamaterial (Fig. 1-3), which determines the amount of radiation energy of a quantum emitter that will fall into the waveguide, i.e. the fraction of photons entering the waveguide to the total number of photons emitted by the quantum radiator.

 The metamaterial may be at least 1 metal layer and 1 dielectric layer or at least 1 metal layer. In this case, the output radiation of photons is in a wide spectral range of 600-800 nm. A wide range of radiation is due to the dielectric properties of the materials that make up the metamaterial. In the above example, a metamaterial consisting of titanium nitride and scandium aluminum nitride is used. Creating a gain band more is difficult. Need to look for new materials.

 The device can operate in a wide temperature range. The upper limit is determined by the temperature of the destruction of diamond and is 450 ° C. The lower limit can be taken equal to the temperature of absolute zero, i.e. - 273 ° C.

The metamaterial can have optical anisotropy and contain layers of plasmon and dielectric materials, and at least one of the layers is thinner than 100 nm. The layer of plasmonic material contains at least one layer of silver, or a layer of conductive transparent oxide, for example, aluminum oxide - sapphire, or transition metal nitride. Due to this, a layered structure is obtained hyperbolic dispersion of the metamaterial. Examples were experimentally implemented with scandium aluminum nitride and titanium nitride (link to article http: //onlinelibrarv.wilev.eom/doi/10.1002/lpor.201400185/full). Plasmon material can be made of aluminum nitride scandium and titanium nitride, and the layer of dielectric material may be a film of aluminum oxide.

Claims

USEFUL MODEL FORMULA  1. A device for generating single photons, including a waveguide, a diamond structure with color centers that are pumped by external radiation, characterized in that a layer of metamaterial having hyperbolic dispersion is deposited on the outer surface of the waveguide, and the diamond structure is located above the metamaterial layer. 2. The device according to p. 1, characterized in that the diamond structure is a diamond film or diamond nanoparticles with sizes up to 200 nm. 3. The device according to p. 2, characterized in that the waveguide is a filament of an optical fiber.  4. The device according to p. 3, characterized in that the optical fiber thread has a constriction at the place of application of the metamaterial less than 2 microns.  5. The device according to p. 3, characterized in that the metamaterial is at least 1 metal layer and 1 dielectric layer.  6. The device according to p. 3, characterized in that the metamaterial is at least 1 metal layer.  7. The device according to claim 3, characterized in that an admixture of nitrogen or silicon is used to create a color center in the nanodiamond crystal.  8. The device according to p. 1-7, characterized in that the distance between the center of the color and the surface of the metamaterial is less than 1000 nm.  9. The device according to p. 1-7, characterized in that the metamaterial consists of titanium nitride and scandium aluminum nitride.  10. The device according to p. 1-7, characterized in that the output radiation of photons is in a wide spectral range of 600-800 nm. 11. The device according to p. 1-7, characterized in that it operates at temperatures not higher than 450 ° C.  12. The device according to p. 1-7, characterized in that the metamaterial has optical anisotropy.  13. The device according to p. 1-7, characterized in that the metamaterial contains layers of plasmonic and dielectric materials, with at least one of the layers thinner than 100 nm.  14. The device according to p. 13, characterized in that the layer of plasmonic material contains at least one layer of silver, or a layer of conductive transparent oxide, for example, aluminum oxide - sapphire, or transition metal nitride. 15. The device according to p. 13, characterized in that the plasmon material is made of scandium aluminum nitride and titanium nitride. 16. The device according to p. 13, characterized in that the layer of dielectric material is an alumina film.