Photon conversion element, metasurface, system, method

Abstract

A photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

Description

[0001] Our ref. : 240365EPWOP 1

[0002] Sony Semiconductor Solutions Corporation

[0003] PHOTON CONVERSION ELEMENT, METASURFACE, SYSTEM,

[0004] METHOD

[0005] TECHNICAL FIELD

[0006] The present disclosure generally pertains to a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, a metasurface, a system for generating an entangled photon pair, and a method for generating an entangled photon pair.

[0007] TECHNICAL BACKGROUND

[0008] Generally, quantum phenomena are increasingly exploited in various technical fields such as electronics, computing, communications or imaging.

[0009] Quantum imaging, for example, leverages quantum phenomena such as entanglement, superposition, and quantum correlations, which may provide the means to achieve resolutions beyond the limits of classical optics and benefit imaging applications such as microscopy, medical imaging, and remote sensing.

[0010] Some techniques in quantum imaging use entangled photon pairs and the generation of the entangled photon pairs may employ periodically poled birefringent non-linear crystals which, in some cases, however, may be bulky, may not be tunable after manufacturing or may require a high operating temperature (e.g., greater than 70 degrees centigrade) while being sensitive to temperature changes.

[0011] Although there exist techniques for generating entangled photon pairs, it is generally desirable to provide improved techniques for generating entangled photon pairs.

[0012] SUMMARY

[0013] According to a first aspect, the disclosure provides a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element comprises: a base body; a first protrusion on a first side surface of the base body, a second protrusion on a second side surface of the base body, and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair. Our ref. : 240365EPWOP 2

[0014] Sony Semiconductor Solutions Corporation

[0015] According to a second aspect, the disclosure provides a metasurface comprising a plurality of meta-atoms, wherein each meta-atom is a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element comprises: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0016] According to a third aspect, the disclosure provides a system for generating an entangled photon pair, comprising: a light source configured to emit a pump photon; and a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element comprises: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0017] According to a fourth aspect, the disclosure provides a method for generating an entangled photon pair, the method comprising: generating a light beam; and generating a spectrally separated entangled photon pair from a pump photon using a photon conversion element, wherein the photon conversion element comprises: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0018] Further aspects are set forth in the dependent claims, the drawings and the following description. Our ref. : 240365EPWOP 3

[0019] Sony Semiconductor Solutions Corporation

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Embodiments are explained by way of example with respect to the accompanying drawings, in which:

[0022] Fig. 1 A schematically illustrates in a block diagram an embodiment of a system for generating an entangled photon pair;

[0023] Fig. IB schematically illustrates in a block diagram an embodiment of a photon conversion element including a base body and a first protrusion provided on a first side surface of the base body;

[0024] Fig. 1C schematically illustrates in a block diagram an embodiment of a photon conversion element including a base body, a first protrusion provided on a first side surface of the base body, and a second protrusion provided on a second side surface of the base body;

[0025] Fig. ID schematically illustrates in a block diagram an embodiment of a metasurface;

[0026] Fig. 2A schematically illustrates in a graph a transmission spectrum of an embodiment of a metasurface including a plurality of meta-atoms;

[0027] Fig. 2B schematically illustrates in a two-dimensional grayscale heatmap an embodiment of an electrical dipole optical mode superimposed on the plan view of a meta-atom included in the metasurface of Fig. 2A;

[0028] Fig. 2C schematically illustrates in a two-dimensional grayscale heatmap an embodiment of a magnetic dipole optical mode superimposed on the plan view of a meta-atom;

[0029] Fig. 3 A schematically illustrates in a graph a transmission spectrum of an embodiment of a metasurface including a plurality of meta-atoms;

[0030] Fig. 3B schematically illustrates in a block diagram an embodiment of a meta-atom included in the metasurface of Fig. 3 A in plan view;

[0031] Fig. 3C schematically illustrates in a two-dimensional grayscale heatmap an embodiment of an electrical dipole optical mode superimposed on the plan view of a meta-atom;

[0032] Fig. 3D schematically illustrates in a two-dimensional grayscale heatmap an embodiment of a magnetic dipole optical mode superimposed on the plan view of a meta-atom;

[0033] Fig. 4A schematically illustrates in a graph a transmission spectrum of an embodiment of a metasurface including a plurality of meta-atoms; Our ref. : 240365EPWOP 4

[0034] Sony Semiconductor Solutions Corporation

[0035] Fig. 4B schematically illustrates in a block diagram an embodiment of a meta-atom included in the metasurface of Fig. 4A in plan view;

[0036] Fig. 4C schematically illustrates in a two-dimensional graph an embodiment of an electrical dipole optical mode superimposed on the plan view of a meta-atom;

[0037] Fig. 4D schematically illustrates in a two-dimensional graph an embodiment of a magnetic dipole optical mode superimposed on the plan view of a meta-atom; and

[0038] Fig. 5 schematically illustrates in a flow diagram an embodiment of a method for generating an entangled photon pair.

[0039] DETAILED DESCRIPTION OF EMBODIMENTS

[0040] Before a detailed description of the embodiments under reference of Fig. 1 A is given, general explanations are made.

[0041] As mentioned in the outset, quantum imaging, for example, leverages quantum phenomena such as entanglement, superposition, and quantum correlations, which may provide the means to achieve resolutions beyond the limits of classical optics and benefit imaging applications such as microscopy, medical imaging, and remote sensing.

[0042] It has been recognized that quantum imaging with spectrally separated entangled photon pairs may enable new possibilities in the field of imaging applications where, for example, a tissue may be probed with an idler photon in the infrared spectral region and the result may be detected by the entangled signal photon in the visible spectral region.

[0043] As further mentioned in the outset, the generation of entangled photon pairs may be based on periodically poled birefringent non-linear crystals which, however, may have some limitations.

[0044] It has further been recognized that thin-sheet nonlinear materials, which include sub -wavelength sized nanostructures, so-called metasurfaces, may be employed to generate entangled photon pairs by spontaneous parametric down-conversion (“SPDC”).

[0045] SPDC is a nonlinear instant optical process that is generally known to convert one photon - the so-called pump photon - having a pump frequency into a pair of photons, namely the signal and the idler photon, that have signal and idler frequencies, respectively. The sum of the signal and idler frequencies equals the pump frequency in accordance with the law of conservation of energy.

[0046] It has been recognized that using patterned thin metasurface sheets over periodically poled designs allows for room temperature operability as well as control over the emission directions Our ref. : 240365EPWOP 5

[0047] Sony Semiconductor Solutions Corporation of the beams of the photons of the generated entangled photon pair, because the sub -wavelength thickness of the nonlinear sheet relaxes the longitudinal phase matching required for bulk birefringent crystals.

[0048] However, some known metasurface designs for the generation of entangled photon pairs are limited to the infrared (“IR”) spectral region, that is, the signal frequency is not in the visible spectral region.

[0049] Furthermore, some known metasurface designs for the generation of entangled photon pairs exploit degenerate SPDC, that is, the signal and idler frequencies are equal, while others have limited spectral separation in the case of non-degenerate SPDC.

[0050] Hence, some embodiments pertain to a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body, a second protrusion on a second side surface of the base body, and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0051] Generally, the photon conversion element allows a pump photon to be converted via SPDC into a non-degenerate entangled photon pair of a signal photon and an idler photon. In some embodiments, the signal photon has a wavelength in the visible spectral region.

[0052] The photon conversion element may be provided in various devices which exploit quantum phenomena such as in a quantum communication transmitter or in quantum computers or in quantum imaging devices for applications that may comprise, but are not limited to, superresolution imaging, low-light imaging, ghost imaging, and quantum-enhanced light detection and ranging. Areas of application may include medical diagnostics, remote sensing, and astronomical observations, without limiting the disclosure in this regard.

[0053] Typically, in some embodiments, the photon conversion element pertains to a solid-state structure which includes a material with a high second-order optical non-nonlinearity and a large bandgap, wherein the dimensions of the solid-state structure or of the base body and the first and second protrusion are in the range of or below the signal wavelength of the signal photon.

[0054] Moreover, typically, the photon conversion element has at least an optical resonance at the signal wavelength and an optical resonance at the idler wavelength such that a suitable pump Our ref. : 240365EPWOP 6

[0055] Sony Semiconductor Solutions Corporation wavelength allows the selection of the optical resonances at the signal wavelength and the idler wavelength.

[0056] These optical resonances may enhance the vacuum fluctuations at the signal wavelength and the idler wavelength such that the spontaneous emission of entangled photon pairs via SPDC may be enhanced.

[0057] In some embodiments, the photon conversion element supports bound state in continuum (“BIC”) resonances which are transformed by the shape of the base body and the first and second protrusion into quasi-BIC states that allow radiation to couple in an out of the photon conversion element due to an overall asymmetric shape of the base body and the first and second protrusion.

[0058] The optical resonance at the signal wavelength may correspond to an electric dipole (“ED”) resonance mode and the optical resonance at the idler wavelength may correspond to a magnetic dipole (“MD”) resonance mode.

[0059] Basically, the dimensions, the material, and the shape of the base body and the first and second protrusion control the characteristics of the optical resonances such that the spectral position and the spectral separation may be tuned by varying these parameters.

[0060] The optical resonances may be identified, for example, in a transmission spectrum of the photon conversion element, which, for example, may also be obtained in a simulation.

[0061] As mentioned above, the pump photon (incident on and) interacting with the photon conversion element is converted to an entangled photon pair in a process called spontaneous parametric down-conversion (“SPDC”). In some embodiments, the pump photon may have a wavelength in the visible spectral region or in the near or middle ultraviolet spectral region.

[0062] Generally, the visible spectral region, also known as the visible spectrum, refers to the portion of the electromagnetic spectrum that is detectable by the human eye. This range of wavelengths is typically considered to be from about 380 nanometers (“nm”) to about 780 nanometers. Within this range, different wavelengths correspond to different colors perceived by the human eye.

[0063] The near ultraviolet spectral region may range, for example, from 300 nanometers to 380 nanometers and the middle ultraviolet spectral region may range, e.g., from 200 nanometers to 300 nanometers.

[0064] Generally, a quantum entanglement of a physical system of multiple particles is given when the system as a whole has a defined quantum state, but the individual particles of the system do not have a defined quantum state, in particular, each particle typically exists in multiple of its possible quantum states. Our ref. : 240365EPWOP 7

[0065] Sony Semiconductor Solutions Corporation

[0066] Entangled photon pairs are generally known to consist of two photons whose states, such as the polarization or spin, are interconnected in such a way that a measurement of the state of one photon of the entangled photon pair affects the measurement of the state of the other photon of the entangled photon pair. In this way, measurements of the states of the two entangled photons are correlated in a non-classical way.

[0067] SPDC is generally known to be a nonlinear instant optical process, involving interactions of the pump photon with optical resonance modes of the photon conversion element, such as electric dipole resonance and magnetic dipole resonance modes, without limiting the disclosure in this regard. The interactions may be enabled by the nonlinear susceptibility of the material of the photon conversion element and generate lower-energy entangled photons from a higher-energy pump photon while conserving both energy and momentum. That is, the higher-frequency pump photon down-converts to the lower-frequency photons of the entangled photon pair. The terms “higher” and “lower” indicate the energy levels or frequencies of two photons relative to each other: A “higher-energy” photon has a higher energy than a “lower-energy” photon and likewise for the frequency.

[0068] The photon conversion element is provided so as to generate entangled photons of differing frequencies, which is generally referred to as non-degenerate SPDC. In other words, the photons of the entangled photon pair are spectrally separated.

[0069] In some embodiments, the energy of one of the photons of the entangled photon pair corresponds to a wavelength included in a wavelength range detectable with a silicon or indium gallium arsenide sensor or imager. In some embodiments, the silicon or indium gallium arsenide sensor or imager detects wavelengths in the visible (“VIS”), near infrared (“NIR”), and / or short wavelength infrared region (“SWIR”). In some embodiments, the energy of the other photon of the entangled photon pair corresponds to a wavelength in a spectral region beyond visible. In some embodiments, the energy of the other photon of the entangled photon pair corresponds to a wavelength in the infrared spectral region. The infrared spectral region may range from 780 nanometers to 1 millimeter.

[0070] As mentioned above, the photon conversion element includes a base body, a first protrusion on a first side surface of the base body and a second protrusion on a second side surface of the base body, wherein the base body and the first and second protrusion are shaped to generate the entangled photon pair via SPDC.

[0071] The base body may be a cube, a cuboid, a sphere, a cylinder, a cone, a pyramid, without limiting the disclosure in this regard, and may be at least one of axially and rotationally symmetric. Our ref. : 240365EPWOP 8

[0072] Sony Semiconductor Solutions Corporation

[0073] The first and / or second protrusion may be a cube, a cuboid, a sphere, a cylinder, a cone, a pyramid, without limiting the disclosure in this regard, and may be at least one of axially and rotationally symmetric.

[0074] The base body and the first and second protrusion may be made of one piece, that is, the base body and the first and second protrusion may be a single, unified element.

[0075] The overall shape of the object, consisting of the base body and the first and second protrusion, may be asymmetric. In some embodiments, the first and second protrusions are provided to break the symmetry of the base body.

[0076] In some embodiments, the first protrusion is flush with a first side surface of the base body adjacent to the side surface where the first protrusion is provided. In some other embodiments, the first protrusion is centered along the first side surface of the base body where the first protrusion is provided. The first protrusion may be provided anywhere on the first side surface of the base body.

[0077] In some embodiments, the second protrusion is flush with a second side surface of the base body adjacent to the side surface where the second protrusion is provided. In some other embodiments, the second protrusion is centered along the second side surface of the base body where the second protrusion is provided. The second protrusion may be provided anywhere on the second side surface of the base body.

[0078] The geometry or shape of the base body and the first and second protrusion, as well as the positions of the first and second protrusion relative to the base body in some embodiments, are provided such that the optical resonances of the photon conversion element at the signal wavelength and the idler wavelength enhance interactions between the pump photon and the photon conversion element to achieve efficient conversion of the pump photon via SPDC.

[0079] It has been recognized that a large or larger spectral separation of the signal frequency and the idler frequency may be achieved by providing a second protrusion to the base body on a different side surface.

[0080] It has been recognized that the base body may support optical resonances that have electric field peaks on the side surfaces of the base body (for example, MD resonance modes) and the electric field distribution basically forms a ring on the side surfaces.

[0081] Hence, by extending the side surfaces, the optical resonance may be red-shifted, since the size of the ring may be effectively increased such that the wavelength, at which the resonance occurs, is increased as well. Our ref. : 240365EPWOP 9

[0082] Sony Semiconductor Solutions Corporation

[0083] In this way, the spectral separation of the signal photon and the idler photon may be increased.

[0084] As mentioned above, the photon conversion element includes a second protrusion on a second side surface of the base body, which may increase spectral separation of the entangled photon pair.

[0085] Moreover, the second protrusion may increase a conversion efficiency due to an increase in a number of electric field peaks present in the optical resonances such that vacuum fluctuations at the signal wavelength and the idler wavelength may be enhanced and, thus, the spontaneous emission of entangled photon pairs via SPDC may be enhanced.

[0086] The second protrusion may be a cube, a cuboid, a sphere, a cylinder, a cone, a pyramid, without limiting the disclosure in this regard, and may be axially or rotationally symmetric.

[0087] In some embodiments, the first protrusion and the second protrusion are shaped identically. For example, the shape of the first protrusion and the second protrusion may be a cuboid, without limiting the disclosure in this regard.

[0088] The second protrusion may be provided such that the overall shape of the object, consisting of the base body, the first protrusion, and the second protrusion, is asymmetric.

[0089] In some embodiments, the second side surface is adjacent to the first side surface of the base body.

[0090] It has further been recognized that a third protrusion may enhance the conversion efficiency of the conversion of pump photons into entangled signal and idler photons, since a number of electric field peaks present in the optical resonances may be increased such that vacuum fluctuations at the signal wavelength and the idler wavelength may be enhanced and, thus, the spontaneous emission of entangled photon pairs via SPDC may be enhanced.

[0091] In addition, it has further been recognized that a third protrusion may enhance the flexibility in generating resonances at certain target wavelengths.

[0092] In some embodiments, the photon conversion element includes a third protrusion on a third side surface of the base body, which may increase spectral separation of the entangled photon pair and may increase a conversion efficiency.

[0093] The third protrusion may be a cube, a cuboid, a sphere, a cylinder, a cone, a pyramid, without limiting the disclosure in this regard, and may be axially or rotationally symmetric. Our ref. : 240365EPWOP 10

[0094] Sony Semiconductor Solutions Corporation

[0095] In some embodiments, the third protrusion is flush with a side surface of the base body adjacent to the third side surface of the base body. In some other embodiments, the third protrusion is centered along the third side surface of the base body.

[0096] In some embodiments, the photon conversion element includes more than a first, a second, and a third protrusion. The photon conversion element may include any number of protrusions. In some embodiments, a first and a second protrusion may be provided on a first side surface of the base body. In some embodiments, more than two protrusions are provided on a first side surface. In some embodiments, more than two protrusions are provided on each of a first and second side surface. The one or more protrusions, that may be provided on one or more side surfaces of the base body, may have different shapes and may be provided at any position of the one or more side surfaces of the base body. The present disclosure is not limited to any number of protrusions provided on one or more side surfaces of the base body. The present disclosure is not limited to a number of side surfaces of the base body where one or more protrusions are provided. The present disclosure is not limited to particular shapes of the one or more protrusions provided on the one or more side surfaces of the base body. The present disclosure is not limited to any particular position or positions where the protrusion or protrusions are provided on one or more side surfaces of the base body.

[0097] In some embodiments, the base body and the first and second protrusion include a material having a bandgap higher than the energy of the photon of the entangled photon pair in the visible spectral region. In other words, the energy difference between the valence band and the conduction band of the material of the base body and the first and second protrusion is higher than the energy of the photon of the entangled photon pair in the visible region, which may ensure that the material transmits the photons of the entangled photon pair with high probability.

[0098] In some embodiments, the photon conversion element generates entangled photons that both have energy levels corresponding to the visible spectral region. In such embodiments, the base body and the first and second protrusion may include a material having a bandgap higher than the energy of the higher-energy photon of the entangled photon pair.

[0099] In some embodiments, the energy of the pump photon is lower than the bandgap of the material of the base body and the first and second protrusion, which may allow the material to transmit the pump photon with high probability.

[0100] The material is not particularly limited and may include, for example, a semiconductor material or a glass or other types of materials that may have a large bandgap and a high second-order susceptibility. Our ref. : 240365EPWOP 11

[0101] Sony Semiconductor Solutions Corporation

[0102] In some embodiments, the material includes gallium phosphide. In some embodiments, the material includes gallium arsenide. In some embodiments, the material includes lithium niobate. In some embodiments, the material includes potassium titanyl phosphate.

[0103] In some embodiments, the base body, the first protrusion, and the second protrusion include the same material. In some embodiments, the base body, the first protrusion, the second protrusion, and the third protrusion include the same material.

[0104] In some embodiments, the spatial dimensions of the photon conversion element are smaller than the wavelength in the visible spectral region. In some embodiments, the spatial dimensions of the base body are smaller than the wavelength in the visible spectral region. In some embodiments, the spatial dimensions of the first protrusion are smaller than the wavelength in the visible spectral region. In some embodiments, the spatial dimensions of the second protrusion are smaller than the wavelength in the visible spectral region.

[0105] In some embodiments, the photon conversion element further includes a layer that includes silicon dioxide and that embeds the base body. The layer may insulate the base body. In some embodiments, the layer embeds the base body and the first protrusion. In some embodiments, the layer embeds the base body, the first protrusion, and the second protrusion. In some embodiments, the layer embeds the base body, the first protrusion, the second protrusion, and the third protrusion. In some embodiments, the layer embeds the photon conversion element.

[0106] Some embodiments pertain to a metasurface including a plurality of meta-atoms, wherein each meta-atom is a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0107] Generally, the general explanations made above for the photon conversion element also apply to the meta-atoms of the metasurface.

[0108] A metasurface, which may also be referred to as an optical metasurface, as generally known, typically corresponds to an array, typically two-dimensional, of nanostructures that may manipulate light in particular ways such that structures with a specific electromagnetic response may be designed. These nanostructures, typically referred to as meta-atoms, interact with the Our ref. : 240365EPWOP 12

[0109] Sony Semiconductor Solutions Corporation incoming light at sub -wavelength scale to provide the desired electromagnetic response of the metasurface and, thus, the functionality of the metasurface.

[0110] The metasurface may be provided in various devices which exploit quantum phenomena such as a quantum communication transmitter or in quantum computers or in quantum imaging devices for applications that may comprise, but are not limited to, super-resolution imaging, low-light imaging, ghost imaging, and quantum-enhanced light detection and ranging. Areas of application may include medical diagnostics, remote sensing, and astronomical observations, without limiting the disclosure in this regard.

[0111] The metasurface may be a an unpoled, thin-sheet nonlinear material. Interactions enabled by the material’s nonlinear susceptibility allow the generation of a spectrally separated entangled photon pair. In some embodiments, one photon of the entangled photon pair has a wavelength in the visible spectral region. In some embodiments, the other photon of the entangled photon pair has a wavelength beyond visible, that is, a wavelength longer than a wavelength in the visible spectral range. In some embodiments, the other photon of the entangled photon pair has a wavelength in the infrared spectral region.

[0112] The material is not particularly limited and may include a semiconductor material or a glass or other types of materials that may have a large bandgap and a high second-order optical susceptibility.

[0113] The material of the metasurface may include gallium phosphide. In some embodiments, the material of the metasurface includes gallium arsenide. In some embodiments, the material includes lithium niobate. In some embodiments, the material includes potassium titanyl phosphate.

[0114] The material of the meta-atoms may include gallium phosphide. In some embodiments, the material of the meta-atoms includes gallium arsenide. In some embodiments, the material includes lithium niobate. In some embodiments, the material includes potassium titanyl phosphate.

[0115] In some embodiments, the metasurface or the meta-atom includes a material having a bandgap higher than the energy of the photon of the entangled photon pair in the visible region. In some embodiments, the metasurface generates entangled photons that both have energy levels corresponding to the visible region. In such embodiments, the metasurface includes a material having a bandgap higher than the energy of the higher-energy photon of the entangled photon pair. Our ref. : 240365EPWOP 13

[0116] Sony Semiconductor Solutions Corporation

[0117] A meta-atom includes a base body, a first protrusion on a first side surface of the base body, and a second protrusion on a second side surface of the base body, wherein the base body and the first and second protrusion are shaped to generate an entangled photon pair via SPDC. In some embodiments, a meta-atom includes a first protrusion on a first side surface of the base body, a second protrusion on a second side surface of the base body, and a third protrusion on a third side surface of the base body. The present disclosure is not limited to the number of protrusions provided on one side surface of the base body. The present disclosure is not limited to the number of side surfaces that have one or more protrusions. The present disclosure is not limited to the shape of the one or more protrusions provided on the one or more side surfaces of the base body.

[0118] The geometry or shape of the base body and the first and second protrusion, as well as the position of the first and second protrusion relative to the base body in some embodiments, are provided such that the optical resonances of a meta-atom at the signal wavelength and the idler wavelength enhance interactions between the pump photon and the meta-atom to achieve efficient conversion of the pump photon via SPDC.

[0119] In some embodiments, the metasurface includes a layer that includes silicon dioxide and that embeds the base bodies of the meta-atoms. The layer may insulate the base bodies. In some embodiments, the layer embeds the base bodies and the first protrusions of the meta-atoms, and the second protrusions of the meta-atoms. In some embodiments, the layer embeds the base bodies, the first protrusions, the second protrusions, and the third protrusions of the meta-atoms.

[0120] In some embodiments, the meta-atoms of the plurality of meta-atoms included in the metasurface are shaped identically. In other words, the meta-atoms may have identical base bodies and the same number of protrusions, wherein the protrusions may also be shaped identically.

[0121] Some embodiments pertain to a system for generating an entangled photon pair, wherein the system includes: a light source configured to emit a pump photon; and a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair. Our ref. : 240365EPWOP 14

[0122] Sony Semiconductor Solutions Corporation

[0123] Generally, the general explanations made above for the photon conversion element, the metaatoms and the metasurface also apply to systems which include photon conversion elements, meta-atoms and a metasurface, respectively.

[0124] The light source may be a light-emitting diode, a laser, such as a diode laser, or the like without limiting the disclosure in this regard.

[0125] In some embodiments, the wavelength of the pump photon is selected such that the pump photon energy equals the sum of the photon energies at which the optical resonance of the signal photon and the idler photon occurs.

[0126] As mentioned above, the signal and idler resonances may be identified, for example, in a transmission spectrum of the photon conversion element or metasurface, which may also be obtained in a simulation.

[0127] Typically, the transmission spectrum may indicate the presence of several different optical resonances and the different optical resonance modes may be selected by selecting a suitable pump photon energy, since energy conservation has to be satisfied.

[0128] Some embodiments pertain to a method for generating an entangled photon pair, the method including: generating a light beam; and generating a spectrally separate entangled photon pair from a pump photon using a photon conversion element, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0129] The method may benefit, for example, quantum communications, quantum computing or quantum imaging applications that may include, but are not limited to, super-resolution imaging, low-light imaging, ghost imaging, and quantum-enhanced light detection and ranging. Areas of application may include medical diagnostics, remote sensing, and astronomical observations, without limiting the disclosure in this regard.

[0130] Returning to Fig. 1 A, the schematic illustration represents an embodiment of a system 10 for generating an entangled photon pair 14, wherein the system 10 includes a light source 11 that emits a pump photon 12. Upon interaction of the pump photon 12 with the photon conversion Our ref. : 240365EPWOP 15

[0131] Sony Semiconductor Solutions Corporation element 13, an entangled photon pair 14 is generated. The entangled photon pair 14 includes a first photon 14a and a second photon 14b. The entanglement of the photon pair is illustrated by the vertically oriented infinity symbol.

[0132] Two embodiments of the photon conversion element 13 are illustrated in Figs. IB and 1C.

[0133] Fig. IB illustrates an embodiment of a photon conversion element 13a that includes a base body 13b and a protrusion 13c. The left sides of the base body 13b and the protrusion 13c are flush with each other. The x- and y-coordinates representing spatial dimensions relative to the photon conversion element 13a are provided for later reference.

[0134] Fig. 1C illustrates an embodiment of a photon conversion element 13d that includes a base body 13e, a first protrusion 13f, and a second protrusion 13g. Both protrusions 13f and 13g are centered along a first side surface and an adjacent second side surface of the base body 13e, respectively, and are shaped identically. The x- and y-coordinates representing spatial dimensions relative to the photon conversion element 13d are provided for later reference.

[0135] In another embodiment of the system 10 of Fig. 1A, the photon conversion element 13 may be replaced by a metasurface as illustrated in Fig. ID.

[0136] Fig. ID depicts an embodiment of a metasurface 13h including a plurality of meta-atoms 13i. Each of the meta-atoms 13i includes a base body and one or more protrusions, as described herein, and corresponds to a photon conversion element as described herein.

[0137] For example, each meta-atom 13i may be a photon conversion element 13a of Fig. IB or a photon conversion element 13d of Fig. 1C.

[0138] Fig. 2A illustrates an embodiment of a simulated transmission spectrum as a function of wavelength, obtained by broadband light illumination of a metasurface. Resonances occur at 790 and 810 nanometers, respectively, as reflected by the peaks in the transmission spectrum.

[0139] A pump wavelength of about 400 nanometers may be used to select the two resonances of the metasurface for generating a spectrally separated entangled photon pair via SPDC, wherein the signal photon has an energy that corresponds to a wavelength close to the visible spectral region.

[0140] Fig. 2B depicts an embodiment of an electric dipole mode profile superimposed on the plan view of an embodiment of a meta-atom. The electric dipole optical mode is resonant at 790 nanometers.

[0141] The meta-atom depicted in Fig. 2B includes a base body and a protrusion whose left sides are flush with each other. The base body is a cube with an edge length of a = 179.2 nanometers, Our ref. : 240365EPWOP 16

[0142] Sony Semiconductor Solutions Corporation while the protrusion is a cuboid with edge lengths of b = 96.88 nanometers and w = 64.4 nanometers, respectively.

[0143] A three-dimensional schematic illustration of the meta-atom is depicted in Fig. IB which also introduces the x- and y-coordinates labeling the horizontal and vertical axes in Fig. 2B.

[0144] Fig. 2C shows an embodiment of a magnetic dipole mode profile superimposed on the plan view of the same embodiment of the meta-atom of Fig. 2B. The magnetic dipole optical mode is resonant at 810 nanometers.

[0145] Again, a three-dimensional schematic illustration of the meta-atom is depicted in Fig. IB which also introduces the x- and y-coordinates labeling the horizontal and vertical axes in Fig. 2C.

[0146] The electric dipole mode profile illustrated in Fig. 2B is maximized at the cube’s center, whereas the magnetic dipole profile shown in Fig. 2C forms a ring with nodes at each face of the cube. By extending these faces it is possible to redshift the magnetic dipole mode.

[0147] Fig. 3 A illustrates an embodiment of a simulated transmission spectrum as a function of wavelength, obtained by broadband light illumination of a metasurface. Resonances occur at 695 and 851 nanometers, respectively, as reflected by the peaks in the transmission spectrum.

[0148] Fig. 3B depicts the plan view of a meta-atom included in the metasurface. The meta-atom includes a base body and a first and a second protrusion which are provided on adjacent side surfaces of the base body. In this embodiment, both protrusions have identical geometries and are centered along the side surfaces of the base body. A three-dimensional view of the meta- atom is schematically illustrated in Fig. 1C. In other embodiments, both protrusions have differing geometries (sizes) and are not necessarily centered on the side surfaces.

[0149] The base body is a cube with an edge length of a = 179 nanometers, while the first protrusion is a cuboid with edge lengths of b = 102 nanometers and w = 68 nanometers. In the vertical, that is the spatial dimension perpendicular to the x- and y-dimensions, the base body and the first protrusion each have a thickness of t = 280 nanometers. The same applies to the second protrusion.

[0150] The meta-atoms included in the metasurface are spaced with a periodicity of p = 417 nanometers, corresponding to the spatial extent in x- and y-directions of the black box surrounding the meta-atom shown in Fig. 3B.

[0151] The meta-atoms include gallium phosphide with a refractive index of n = 3.178 at a wavelength of 850 nanometers and are mounted on and insulated by silicon dioxide (n = 1.46). Our ref. : 240365EPWOP 17

[0152] Sony Semiconductor Solutions Corporation

[0153] As depicted in the transmission spectrum in Fig. 3 A, the metasurface, including the meta-atom design illustrated in Fig. 3B, has two strong resonances at 695nm and 851nm and allows a spectral separation of the photons of the entangled photon pairs generated via SPDC of approximately 156 nanometers.

[0154] Fig. 3C depicts an embodiment of an electric dipole mode profile superimposed on the plan view of an embodiment of a meta-atom. The electric dipole optical mode is resonant at 695 nanometers. Fig. 1C introduces the x- and y-coordinates labeling the horizontal and vertical axes in Fig. 3C.

[0155] Fig. 3D shows an embodiment of a magnetic dipole mode profile superimposed on the plan view of the same meta-atom embodiment as in Fig. 3C. The magnetic dipole optical mode is resonant at 851 nanometers. Fig. 1C introduces the x- and y-coordinates labeling the horizontal and vertical axes in Fig. 3D.

[0156] Compared to Fig. 2C depicting the magnetic dipole mode along with a meta-atom including one protrusion, Fig. 3D shows that adding a second protrusion effectively increases the size of the MD mode ring and hence increases its wavelength.

[0157] Fig. 4A illustrates an embodiment of a simulated transmission spectrum as a function of wavelength, obtained by broadband light illumination of a metasurface. Resonances occur at 692 and 985 nanometers, respectively, as reflected by the peaks in the transmission spectrum.

[0158] The metasurface is pumped with a laser having a pump photon wavelength of 406 nanometers.

[0159] Fig. 4B illustrates the spatial dimensions of the meta-atom according to the present embodiment. To obtain a larger frequency separation of the signal photon and idler photon, parameters of the base body and the first and second protrusion are varied and a notable effect with the cube width has been recognized. The spatial dimensions are identical to those shown in Fig. 3B and described in the corresponding paragraph herein, except for a 40 percent increase in edge length of the base body. In the present embodiment, the edge length of the base body equals a = 250 nanometers.

[0160] Fig. 4C depicts an embodiment of an electric dipole mode profile superimposed on the plan view of an embodiment of a meta-atom. The electric dipole optical mode is resonant at 692 nanometers. Fig. 1C introduces the x- and y-coordinates labeling the horizontal and vertical axes in Fig. 4C.

[0161] Fig. 4D shows an embodiment of a magnetic dipole mode profile superimposed on the plan view of the same meta-atom embodiment as depicted in Fig. 4C. The magnetic dipole optical mode is Our ref. : 240365EPWOP 18

[0162] Sony Semiconductor Solutions Corporation resonant at 985 nanometers. Fig. 1C introduces the x- and y-coordinates labeling the horizontal and vertical axes in Fig. 4D.

[0163] With the metasurface design illustrated in Fig. 4B, resonances occur at 692nm and 985nm, yielding a spectral separation of 293 nanometers of the photons of the entangled photon pair generated by the metasurface via SPDC. While also other modes are possible in this design, maybe yielding even stronger resonances, the law of energy conservation allows selection of the desired modes by selecting a suitable pump frequency. Here it requires a pump wavelength of 406 nanometers to induce the mode resonances at 692 nanometers and 985 nanometers.

[0164] Fig. 5 depicts an embodiment of a method 50 for generating an entangled photon pair.

[0165] At 51, a light beam is generated, as described herein.

[0166] At 52, a spectrally separated entangled photon pair is generated from a pump photon using a photon conversion element, wherein the photon conversion element includes a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair, as described herein.

[0167] Note that the present technology can also be configured as described below.

[0168] (1) A photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0169] (2) The photon conversion element according to (1), wherein one photon of the entangled photon pair has a wavelength included in a wavelength range detectable with a silicon or indium gallium arsenide sensor or imager.

[0170] (3) The photon conversion element according to (1) or (2), wherein one photon of the entangled photon pair has a wavelength in the visible spectral region.

[0171] (4) The photon conversion element according to (3), wherein the other photon of the generated photon pair has a wavelength in a spectral region beyond visible. Our ref. : 240365EPWOP 19

[0172] Sony Semiconductor Solutions Corporation

[0173] (5) The photon conversion element according to any one of (1) to (4), wherein the first protrusion is centered at the first side surface of the base body and / or the second protrusion is centered at the second side surface of the base body.

[0174] (6) The photon conversion element according to any one of (1) to (5), wherein the first protrusion and the second protrusion are shaped identically.

[0175] (7) The photon conversion element according to any one of (1) to (6), wherein the second side surface is adjacent to the first side surface of the base body.

[0176] (8) The photon conversion element according to any one of (1) to (7), further including a third protrusion on a third side surface of the base body.

[0177] (9) The photon conversion element according to any one of (3) to (8), wherein the base body and the first and second protrusion include a material having a bandgap higher than the energy of the photon of the entangled photon pair in the visible spectral region.

[0178] (10) The photon conversion element according to (9), wherein the material includes gallium phosphide.

[0179] (11) The photon conversion element according to any one of (3) to (10), wherein the spatial dimensions of the photon conversion element are smaller than the wavelength in the visible spectral region.

[0180] (12) The photon conversion element according to any one of (1) to (11), wherein the base body has a cuboid shape, in particular, wherein the base body is a cube.

[0181] (13) The photon conversion element according to any one of (1) to (12), wherein the photon conversion element further includes a layer that includes silicon dioxide and that embeds the base body.

[0182] (14) A metasurface comprising a plurality of meta-atoms, wherein each meta-atom is a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0183] (15) A system for generating an entangled photon pair, including: Our ref. : 240365EPWOP 20

[0184] Sony Semiconductor Solutions Corporation a light source configured to emit a pump photon, and a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

[0185] (16) The system according to (15), wherein one photon of the entangled photon pair has a wavelength in the visible spectral region and, in particular, wherein the other photon of the generated photon pair has a wavelength in a spectral region beyond visible.

[0186] (17) The system according to (15) or (16), wherein the second side surface is adjacent to the first side surface of the base body.

[0187] (18) The system according to any one of (15) to (17), wherein the first protrusion and the second protrusion are shaped identically.

[0188] (19) The system according to any one of (15) to (18), wherein the photon conversion element further includes a third protrusion on a third side surface of the base body.

[0189] (20) The system according to any one of (16) to (19), wherein the base body and the first and second protrusion of the photon conversion element include a material having a bandgap higher than the energy of the photon of the entangled photon pair in the visible spectral region.

[0190] (21) A method for generating an entangled photon pair, the method including: generating a light beam; and generating a spectrally separated entangled photon pair from a pump photon using a photon conversion element, wherein the photon conversion element includes: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

Claims

Our ref. : 240365EPWOP 1Sony Semiconductor Solutions CorporationCLAIMS1. A photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element comprises: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

2. The photon conversion element according to claim 1, wherein one photon of the entangled photon pair has a wavelength included in a wavelength range detectable with a silicon or indium gallium arsenide sensor or imager.

3. The photon conversion element according to claim 1, wherein one photon of the entangled photon pair has a wavelength in the visible spectral region.

4. The photon conversion element according to claim 3, wherein the other photon of the generated photon pair has a wavelength in a spectral region beyond visible.

5. The photon conversion element according to claim 1, wherein the first protrusion is centered at the first side surface of the base body or the second protrusion is centered at the second side surface of the base body.

6. The photon conversion element according to claim 1, wherein the first protrusion and the second protrusion are shaped identically.

7. The photon conversion element according to claim 1, wherein the second side surface is adjacent to the first side surface of the base body.

8. The photon conversion element according to claim 1, further comprising a third protrusion on a third side surface of the base body.

9. The photon conversion element according to claim 3, wherein the base body and the first and second protrusion include a material having a bandgap higher than the energy of the photon of the entangled photon pair in the visible spectral region.

10. The photon conversion element according to claim 9, wherein the material includes gallium phosphide.

11. The photon conversion element according to claim 3, wherein the spatial dimensions of the photon conversion element are smaller than the wavelength in the visible spectral region.Our ref. : 240365EPWOP 2Sony Semiconductor Solutions Corporation12. The photon conversion element according to claim 1, wherein the base body has a cuboid shape, in particular, wherein the base body is a cube.

13. The photon conversion element according to claim 1, wherein the photon conversion element further comprises a layer that includes silicon dioxide and that embeds the base body.

14. A metasurface comprising a plurality of meta-atoms, wherein each meta-atom is a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element comprises: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

15. A system for generating an entangled photon pair, comprising: a light source configured to emit a pump photon, and a photon conversion element for generating a spectrally separated entangled photon pair from a pump photon, wherein the photon conversion element comprises: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

16. The system according to claim 15, wherein one photon of the entangled photon pair has a wavelength in the visible spectral region and, in particular, wherein the other photon of the generated photon pair has a wavelength in a spectral region beyond visible.

17. The system according to claim 15, wherein the second side surface is adjacent to the first side surface of the base body.

18. The system according to claim 15, wherein the first protrusion and the second protrusion are shaped identically.

19. The system according to claim 15, wherein the photon conversion element further comprises a third protrusion on a third side surface of the base body.Our ref. : 240365EPWOP 3Sony Semiconductor Solutions Corporation20. The system according to claim 16, wherein the base body and the first and second protrusion of the photon conversion element include a material having a bandgap higher than the energy of the photon of the entangled photon pair in the visible spectral region.

21. A method for generating an entangled photon pair, the method comprising: generating a light beam; and generating a spectrally separated entangled photon pair from a pump photon using a photon conversion element, wherein the photon conversion element comprises: a base body; a first protrusion on a first side surface of the base body; a second protrusion on a second side surface of the base body; and wherein the base body and the first and second protrusion are shaped such that the pump photon is converted via spontaneous parametric down-conversion to the entangled photon pair.

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