Single-photon detector and method of forming the same

Abstract

Various embodiments may relate to a single-photon detector. The single-photon detector may include a stacked arrangement. The stacked arrangement may include a plasmonic metal nanostructure, and a superconducting nanostructure over or under the plasmonic metal nanostructure, the superconducting nanostructure substantially aligned to the plasmonic metal nanostructure. Lateral dimensions of the plasmonic metal nanostructure may be substantially equal to lateral dimensions of the superconducting nanostructure.

Description

SINGLE-PHOTON DETECTOR AND METHOD OF FORMING THE SAMECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore application No. 10202402777U filed September 6, 2024, the contents of it being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] Various embodiments of this disclosure may relate to a single-photon detector. Various embodiments of this disclosure may relate to a method of forming a single-photon detector.BACKGROUND

[0003] Due to their record-high parameters, super conductor nanowire single-photon detectors (SNSPDs) have emerged as the leading single-photon detection technology. SNSPDs with photon detection efficiency of 99.5% at telecom wavelengths, timing jitter of sub-3 ps, recovery time of -510 ps, and dark count rate of 10-4Hz have been demonstrated Such high performance opens the way toward photonic-based quantum technologies, including quantum communication, quantum computing, quantum imaging and metrology. Moreover, applications with classical light, such as Light Detection and Ranging (LiDAR) and astronomy benefit from detection with SNSPDs.

[0004] However, further development of single-photon detection technology and its practical applications require multi-functional operation where the detector itself also performs other functions. Currently, these functions, such as lensing, polarization control, wavelength filtering etc., are implemented with bulky optical components inserted in front of the detectors. By alleviating the need for these components, the technology based on single-photon detection can be substantially miniaturized.

[0005] Unfortunately, the functionality of SNSPDs is limited. These limitations originate from the working principle and design restrictions of the devices. The operation of SNSPDs is based on breaking a super-current flowing through the nanowire by a photon absorption event. To achieve such sensitivity, the nanowire is fabricated out of thin (-5 - 10 nm) type-IIsuperconducting films and has a width of 70 - 120 nm. Such small dimensions and limited material selection (typically, niobium nitride (NbN), niobium titanium nitride (NbTiN), molybdenum silicide (MoSi) or tungsten silicide (WSi)) may not allow the tailoring optical properties of these devices and extending of their functionality

[0006] For instance, while the meandered design of SNSPDs as shown in FIG. 1A is naturally selective in linear polarization basis, one cannot achieve such sensitivity in circular polarization basis. FIG. 1 A shows a scanning electron microscopy (SEM) image of a meander superconductor nanowire single-photon detector (SNSPD). FIG. IB shows a plot of polarization extinction ratio (PER) (in decibels or dB) as a function of fill factor (in percent or %) illustrating polarization extinction ratio evolution with fill factor. For a typical 50% fill factor detector, PER values of 9 dB may be obtained. A SNSPD design can be optimized to get up to ~12 dB polarization extinction ratio (PER) for orthogonal linear polarizations by varying the filling factor and dimensions of the nanowire within the operational range (the range which are compatible with efficient single-photon detection). Indeed, four-pixel SNSPD devices have been demonstrated with horizontal (H), vertical (V), diagonal (D) and anti- diagonal (A) orientation of the nanowire. Accordingly, each pixel was tailored to predominantly detect one of the linear polarizations (H, V, D and A) thus enabling polarization imaging. Accordingly, each pixel was tailored to predominantly detect one of the linear polarizations (H, V, D and A) thus enabling polarization imaging. However, the dimension and material limitations do not allow design of SNSPD pixels with noticeable PER in circular polarization basis (an example is shown in FIG. 1C) and perform a full polarization tomography. FIG. 1C shows (left and middle) different views of a spiral single-photon detector (SNSPD) pixel; and (right) a plot of absorption as a function of thickness (in nanometers or nm) of the spiral SNSPD pixel.

[0007] Similarly, the design and material limitations restrict other functionalities of SNSPD devices, such as wavelength sensitivity and resonance behavior. The main reason for such limitations is a lack of plasmonic properties of SNSPD materials such that incoming electromagnetic wave cannot be effectively coupled to electron oscillation in the nanowire. Accordingly, the geometry and dimensions of the SNSPD nanowire cannot compensate for this.SUMMARY

[0008] Various embodiments may relate to a single-photon detector. The single-photon detector may include a stacked arrangement. The stacked arrangement may include a plasmonic metal nanostructure, and a superconducting nanostructure over or under the plasmonic metal nanostructure, the superconducting nanostructure substantially aligned to the plasmonic metal nanostructure. Lateral dimensions of the plasmonic metal nanostructure may be substantially equal to lateral dimensions of the superconducting nanostructure.

[0009] Various embodiments may relate to a method of forming a single-photon detector. The method may include forming a stacked arrangement. The stacked arrangement may include a plasmonic metal nanostructure, and a superconducting nanostructure over or under the plasmonic metal nanostructure, the superconducting nanostructure substantially aligned to the plasmonic metal nanostructure. Lateral dimensions of the plasmonic metal structure may be substantially equal to lateral dimensions of the superconducting nanostructure.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily drawn to scale, emphasis instead generally being placed upon illustrating the principles of various embodiments. In the following description, various embodiments of the invention are described with reference to the following drawings.FIG. 1A shows a scanning electron microscopy (SEM) image of a meander super conductor nanowire single-photon detector (SNSPD).FIG. 1B shows a plot of polarization extinction ratio (PER) (in decibels or dB) as a function of fill factor (in percent or %) illustrating polarization extinction ratio evolution with fill factor.FIG. 1C shows (left and middle) different views of a spiral single-photon detector (SNSPD) pixel; and (right) a plot of absorption as a function of thickness (in nanometers or nm) of the spiral SNSPD pixel.FIG. 2 shows a general illustration of a single-photon detector according to various embodiments.FIG. 3 shows a general illustration of a method of forming a single-photon detector according to various embodiments.FIG. 4A shows a schematic of a stacked arrangement over a spacer according to various embodiments.FIG. 4B shows a schematic illustrating the patterning of the stacked arrangement according to various embodiments.FIG. 5 shows a schematic of a stacked arrangement over a spacer according to various embodiments.FIG. 6 shows a schematic of a stacked arrangement over a spacer according to various embodiments.FIG. 7 shows a schematic of a stacked arrangement over a spacer according to various embodiments.FIG. 8A shows a schematic of a single-photon detector according to various embodiments.FIG. 8B shows a plot of absorption (in percent or %) / polarization extinction ratio PER (in decibels or dB) as a function of fill factor (in percent or %) illustrating the variation in absorption of parallel and orthogonal polarization light, along with PER, with increasing pixel fill factor of the single-photon detector according to various embodiments.FIG. 9 A shows a schematic of a single-photon detector according to various embodiments.FIG. 9B shows a plot of absorption (in percent or %) / polarization extinction ratio PER (in decibels or dB) as a function of wavelength (in nanometers or nm) illustrating variation in absorption of right (R) and left (L)-handed circularly polarized light, as well as associated PER evolution in the superconducting nanowire of the single-photon detector of FIG. 9A with wavelength according to various embodiments.FIG. 10A shows a schematic of another single-photon detector according to various embodimentsFIG. 10B shows a plot of absorption (in percent or %) / polarization extinction ratio PER (in decibels or dB) as a function of wavelength (in nanometers or nm) illustrating variation in absorption of right (H) and left (V)-handed circularly polarized light, as well as associated PER evolution in the superconducting nanowire of the single-photon detector of FIG. 10A with wavelength according to various embodiments.FIG. HA shows a scanning electron microscopy (SEM) image of a fabricated single-photon detector including multiple linked S-shaped segments according to various embodiments.FIG. 1 IB shows a plot of coincidence rate (in Hertz or Hz) as a function of current (in microAmperes or pA) illustrating the increase of the coincidence rate with bias current for both polarization states of the fabricated single-photon detector shown in FIG. HA according to various embodiments.FIG. 11C shows a plot of polarization extinction ratio PER (in decibels or dB) as a function in current (in micro-Amperes or p A) illustrating the variation of PER with bias current of the fabricated single-photon detector shown in FIG. 11 A according to various embodiments.DESCRIPTION

[0011] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments

[0012] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0013] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0014] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance, e.g., within 10% of the specified value.

[0015] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0016] By “comprising” it is meant including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0017] By “consisting of’ it is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0018] Embodiments described in the context of one of the single-photon detectors are analogously valid for the other single-photon detectors. Similarly, embodiments described in the context of a method are analogously valid for a single-photon detector, and vice versa.

[0019] To overcome these limitations and implement multifunctional SNSPD devices, a single photon detection method that combines optical properties of plasmonic nanostructures with electrical photon detection method that combines optical properties of plasmonic nanostructures with electrical properties of superconducting nanowires. The proposed metalinsulator-superconductor nanowire single-photon detector (Ml-SNSPD) may include a plasmonic metal nanostructure or layer (e.g., gold), an optional insulating layer (e.g., silicon oxide or SiCh) and a superconducting nanostructure or layer (e g., niobium nitride or NbN). All layers may be patterned in a common stacked arrangement, which may significantly simplify the fabrication workflow. Various embodiments may relate to a stacked arrangement including a plasmonic metal nanostructure or layer with the required optical response, and a superconducting nanostructure or layer with the desired electrical properties. The fabrication workflow may extend the functionality of the SNSPDs without degrading their detection performance.

[0020] FIG. 2 shows a general illustration of a single-photon detector according to various embodiments. The single-photon detector may include a stacked arrangement 200. The stacked arrangement 200 may include a plasmonic metal nanostructure (alternatively referred to as plasmonic metal layer) 202, and a superconducting nanostructure (alternatively referred to as superconducting layer) 204 over or under the plasmonic metal nanostructure 202, the superconducting nanostructure 204 substantially aligned to the plasmonic metal nanostructure 202. Lateral dimensions (i.e., lengths and widths) of the plasmonic metal nanostructure 202 may be substantially equal to lateral dimensions (i.e., lengths and widths) of the superconducting nanostructure 204.

[0021] In other words, various embodiments may relate to a stack arrangement 200 including a plasmonic metal nanostructure 202 and a superconducting nanostructure 204 aligned to the plasmonic metal nanostructure 202 and having the substantially same lateral geometry as the plasmonic metal nanostructure 202.

[0022] For avoidance of doubt, FIG. 2 is intended to illustrate certain features of the singlephoton detector, and is not intended to limit, for instance, the dimensions, shapes, orientation, arrangement etc. of the various features. For instance, while FIG. 2 shows the superconducting nanostructure 204 over the plasmonic metal nanostructure 202, in various embodiments, the plasmonic nanostructure 202 may be over the superconducting nanostructure 204. While FIG. 2 shows that a thickness of the plasmonic nanostructure 202 and a thickness of the superconducting nanostructure 204 to be substantially equal, in various embodiments, a thickness of the plasmonic nanostructure 202 and a thickness of the superconducting nanostructure 204 may be different. Further, while FIG. 2 shows the plasmonic metal nanostructure 202 to be in contact with the superconducting nanostructure 204, various embodiments may include a stacked arrangement further including an insulator layer between the plasmonic metal nanostructure 202 and the superconducting nanostructure 204. The singlephotodetector may be a metal-insulator-superconducting nanowire single-photon detector (MI- SNSPD, alternatively referred to “MI-SNSPD platform”). For embodiments including the insulator layer, the insulator layer may be substantially aligned to both the plasmonic nanostructure 202 and the superconducting nanostructure 204. The lateral dimensions (i.e., lengths and widths) of the insulator layer may be substantially equal to lateral dimensions of both the plasmonic nanostructure 202 and the superconducting nanostructure 204. The insulator layer may include any suitable electrically insulating material, for instance silicon oxide, silicon nitride or aluminum oxide.

[0023] For avoidance of doubt, the term “substantially” may include a variance of ±3%. The phrase “substantially equal” may denote being exactly equal or having a variance of ±3%. For instance, lateral dimensions of a first layer / structure (e.g., the plasmonic metal nanostructure 202) being substantially equal to lateral dimensions of a second layer / structure (e.g., the superconducting nanostructure 204) may include situations in which a length of the first layer / structure (e.g., the plasmonic metal nanostructure 202) being of a value selected from a range from 97% to 103% of a length of the second layer / structure (e.g., the superconducting nanostructure 204), and a width of the first layer / structure (e.g., the plasmonic metal nanostructure 202) being of a value selected from a range from 97% to 103% of a width of the second layer / structure (e.g., the superconducting nanostructure 204). Similarly, the second layer / structure (e.g., the superconducting nanostructure 204) “substantially aligned” to the first layer / structure (e g., the plasmonic metal nanostructure 202) may include situations in whichan edge of the second layer / structure (e.g., the superconducting nanostructure 204) being exactly aligned to an edge of the first layer / structure (e.g., the plasmonic metal nanostructure 202) or having an alignment offset selected from 97% to 103% of a length or width of the first layer / structure (e.g., the plasmonic metal nanostructure 202).

[0024] In various embodiments, the single-photon detector may include a back-reflector or an anti-reflection coating. The back-reflector may include any suitable reflective material, such as aluminum, gold or titanium. The anti -refl ection coating may include any suitable antireflection material, such as magnesium fluoride, silicon oxide, silicon nitride, or yttrium fluoride.

[0025] In various embodiments, the single-photon detector may also include a spacer between the stacked arrangement 200 and either the back -reflector or the anti -reflection coating. The spacer may include any suitable dielectric material, such as silicon oxide, silicon nitride or titanium oxide.

[0026] In various embodiments, the plasmonic metal nanostructure 202 may be a metallic nanowire. The superconducting nanostructure 204 (alternatively referred to as superconducting nanowire single-photon detector) may be a superconducting nanowire.

[0027] In various embodiments, the plasmonic metal nanostructure 202 and the super conducting nanostructure 204 may be of any suitable lateral shape or geometry. For instance, the plasmonic metal nanostructure 202 may be a Z-shaped metallic resonating nanoantenna, and the superconducting nanostructure 204 may be a Z-shaped superconducting nanowire. In other embodiments, the plasmonic metal nanostructure 202 may be a S-shaped metallic resonating nanoantenna, and the superconducting nanostructure 204 may be a S-shaped superconducting nanowire.

[0028] The plasmonic metal nanostructure 202 may include any suitable plasmonic metal. For instance, the plasmonic metal nanostructure 202 may include a material selected from a group consisting of gold, silver, aluminum, palladium, bismuth, copper, tungsten and titanium nitride.

[0029] The superconducting nanostructure 204 may include any suitable superconducting material. For instance, the superconducting nanostructure 204 may include a material selected from a group consisting of niobium nitride (NbN), niobium titanium nitride (NbTiN), molybdenum silicide (MoSi), tungsten silicide (WSi), magnesium diboride (Mgfh), yttrium barium copper oxide (YBCO), molybdenum germanium (MoGe) and tungsten rhenium (WRe).

[0030] In various embodiments, the plasmonic metal nanostructure 202 may be configured to exhibit one or more plasmonic resonances in response to an electromagnetic wave incident onto the plasmonic metal nanostructure 202. The plasmonic metal nanostructure 202 may further be configured to couple the one or more plasmonic resonances to the superconducting nanostructure 204.

[0031] In various embodiments, the superconducting nanostructure 204 may be configured to induce chirality, wavelength selectivity, filtering, electric field localization, light focus enhancement, absorption enhancement, single-molecule biosensing or single-photon biosensing in response to the coupling of the one or more plasmonic resonances to the superconducting nanostructure 204.

[0032] FIG. 3 shows a general illustration of a method of forming a single-photon detector according to various embodiments. The method may include, in 302, forming a stacked arrangement. The stacked arrangement may include a plasmonic metal nanostructure, and a superconducting nanostructure over or under the plasmonic metal nanostructure, the superconducting nanostructure substantially aligned to the plasmonic metal nanostructure. Lateral dimensions of the plasmonic metal structure may be substantially equal to lateral dimensions of the superconducting nanostructure.

[0033] In other words, various embodiments may relate to a method of forming a stacked arrangement including a plasmonic metal nanostructure and a superconducting nanostructure aligned to the plasmonic metal nanostructure and having the substantially same lateral geometry as the plasmonic metal nanostructure.

[0034] As mentioned above, in various embodiments, the stacked arrangement may include an insulator layer between the plasmonic metal nanostructure and the superconducting nanostructure, while in various other embodiments, the plasmonic metal nanostructure may be in contact with the superconducting nanostructure.

[0035] In various embodiments, the stacked arrangement may be patterned using a single step lithography and subsequently etched using a single step etching.

[0036] In various embodiments, the method may include forming a back -reflector or an anti-reflection coating.

[0037] In various embodiments, the method may also include forming a spacer between the stacked arrangement and either the back-reflector or the anti -reflection coating.

[0038] In various embodiments, the plasmonic metal nanostructure may be a metallic nanowire The superconducting nanostructure may be a superconducting nanowire

[0039] In various embodiments, the plasmonic metal nanostructure and the super conducting nanostructure may be of any suitable lateral shape or geometry. For instance, the plasmonic metal nanostructure may be a Z-shaped metallic resonating nanoantenna, and the superconducting nanostructure may be a Z-shaped superconducting nanowire. In other embodiments, the plasmonic metal nanostructure may be a S-shaped metallic resonating nanoantenna, and the superconducting nanostructure may be a S-shaped superconducting nanowire.

[0040] The plasmonic metal nanostructure may include any suitable plasmonic metal. For instance, the plasmonic metal nanostructure may include a material selected from a group consisting of gold, silver, aluminum, palladium, bismuth, copper, tungsten and titanium nitride.

[0041] The superconducting nanostructure may include any suitable superconducting material. For instance, the superconducting nanostructure may include a material selected from a group consisting of niobium nitride (NbN), niobium titanium nitride (NbTiN), molybdenum silicide (MoSi), tungsten silicide (WSi), magnesium diboride (MgBs), yttrium barium copper oxide (YBCO), molybdenum germanium (MoGe) and tungsten rhenium (WRe).

[0042] In various embodiments, the plasmonic metal nanostructure may be configured to exhibit one or more plasmonic resonances in response to an electromagnetic wave incident onto the plasmonic metal nanostructure. The plasmonic metal nanostructure may further be configured to couple the one or more plasmonic resonances to the superconducting nanostructure.

[0043] In various embodiments, the superconducting nanostructure may be configured to induce chirality, wavelength selectivity, filtering, electric field localization, light focus enhancement, absorption enhancement, single-molecule biosensing or single-photon biosensing in response to the coupling of the one or more plasmonic resonances to the superconducting nanostructure.

[0044] In one previous study, the use of three-dimensional integrated superconducting and plasmonic nanostructures to achieve polarization-independent high absorption efficiency in single-photon detectors has been demonstrated using simulation. In another previous study, silver antennas are used to improve the absorptance of NbN wires, exploiting polarizationdependent resonances. In a third previous study, 95% absorptance and a polarization extinctionratio (PER) of 1.5 x 104have been shown to be achieved through a composite mirror design using simulation. A fourth previous study has shown that integrating one-dimensional periodic plasmonic structures can significantly and selectively improve the absorptance of p- polarized light, which is advantageous for specific quantum information processing (QIP) applications. A fifth previous study introduced a design that integrates SN SPDs with gap- plasmon-enhanced structures. This configuration involved a 5 nm thick aluminum oxide (AI2O3) layer deposited by atomic layer deposition (ALD) and silver nanocubes to form gap-plasmon nanoresonators. The multilayer fabrication process included defining theNbN microwire, depositing the AI2O3 layer, and fabricating the Ag nanocube array using electron-beam lithography and evaporation techniques. This design demonstrated enhanced photon response, although it required meticulous control over surface roughness and multiple fabrication steps. Tn a previous sixth study, the use of tungsten silicide (WSi) and metallic nano-antennas to amplify absorption induced by localized surface plasmons has been demonstrated. Their structure involved a metal slot between hydrogen silsesquioxane (HSQ) layers and an NbN nanowire, all over a sapphire substrate. A seventh previous study introduced an asymmetric split ring (ASR) metamaterial to create a metal-insulator-metal nanocavity. This design aimed to enhance absorption efficiency and shorten response time, representing a significant step towards practical applications of SNSPDs

[0045] The limitations with the above approaches arise from the distinct design requirements of SNSPDs and plasmonic nanostructures. Each of these demonstrations simply stack two separate devices - plasmonic nanostructure on top of the SNSPD or vice versa. As a result, there is a characteristic complexity of the fabrication workflow with multiple fabrication steps as two devices must be fabricated consequently. The complex fabrication process can jeopardize nanowire performance by degrading the nanowire surface roughness and introducing defects or impurities. Accordingly, this may reduce the efficiency of the device, increase the dark count rate, and / or worsen the temporal performance of the SNSPD.

[0046] In contrast, various embodiments may relate to a single integrated platform, the Ml- SNSPD, which may allow for a common design for all two or three layers, effectively combining the optical and electrical properties.

[0047] As an example of application, a device which can perform polarization state tomography of quantum light has been demonstrated. Various embodiments may relate to a device sensitive to circular polarization with a substantial dichroism and / or linear polarization.Various embodiments may relate to a more efficient and compact implementation of quantum state tomography without conventional bulky optical components.

[0048] Various embodiments may offer potential advancements in operating in other degrees of freedom of light, including spatial, temporal, and frequency domains. Various embodiments may provide a robust pathway for miniaturized single-photon detection technology with multi-functional operation for practical quantum technologies.

[0049] Various embodiments may relate to the integration of plasmonic metal nanostructures and superconducting nanowire single-photon detectors (SNSPDs) (i.e., superconducting nanostructures) into a unified metal-insulator-superconductor (MIS) platform. This integrated metal-insulator-superconducting nanowire single-photon detector (MI- SNSPD) platform may not only combine the advanced optical properties of plasmonic metal nanostructures with the electrical properties of superconducting nanostructures, but may also simplify the fabrication process by constructing multiple functional layers into a single-step fabrication workflow.

[0050] The stacked arrangement may include different combinations of plasmonic metal layer(s), superconducting layer(s) and insulating layer(s). FIG. 4A shows a schematic of a stacked arrangement 400 over a spacer 408 according to various embodiments. There may be a reflector or an anti -reflection coating 410 in contact with a surface of the spacer 408 opposite the surface in contact with the stacked arrangement 400. The stacked arrangement 400 may include a layer 402 of plasmonic metal, a layer 404 of superconductor material, and a layer 406 of insulating material between layers 402, 404.

[0051] In various embodiments, the reflector or coating 410 may be formed on a substrate, the spacer 408 may be formed on the reflector or coating 410, the layer 404 may be formed on the spacer 408, the layer 406 may be formed on the layer 404, and the layer 402 may be formed on the layer 406. In various other embodiments, the layer 404 may be formed on a substrate, the layer 406 may be formed on the layer 404, and the layer 402 may be formed on the layer 406. The substrate may then be removed, and the spacer 408 may be provided or formed in contact with the layer 404. The reflector or coating 410 may be formed or provided in contact with the spacer 408.

[0052] FIG. 4B shows a schematic illustrating the patterning of the stacked arrangement 400 according to various embodiments. In (i), the arrangement shown in FIG. 4A is provided. In (ii) a layer 412 of photoresist may be deposited over the stacked arrangement 400 via spin-coating, i.e., on layer 402 of plasmonic metal in this case. In (iii), the layer 412 of photoresist may be patterned via a suitable lithographic technique such as electron beam lithography or photolithography. Portions of the layer 412 of photoresist may be exposed to an electron beam or optical radiation to define a nano-pattern In (iv), the layer 412 of the photoresist may be developed, and portions of the layer 412 may be removed based on the nano-pattern, thereby forming a photoresist structure 412’. In (v), the stacked arrangement 400 including layers 402, 404, 406 may be etched in a single step to form a plasmonic metal nanostructure 402’, a superconducting nanostructure 404’ and a (patterned) dielectric layer 406’, which may be aligned to one another, and which may have the same lateral geometry.

[0053] FIG. 5 shows a schematic of a stacked arrangement 500 over a spacer 508 according to various embodiments There may be a reflector or an anti -refl ection coating 510 in contact with a surface of the spacer 508 opposite the surface in contact with the stacked arrangement 500. The stacked arrangement 500 may include a layer 502 of plasmonic metal, a layer 504 of superconductor material, and a layer 506 of insulating material between layers 502, 504.

[0054] In various embodiments, the reflector or coating 510 may be formed on a substrate, the spacer 508 may be formed on the reflector or coating 510, the layer 502 may be formed on the spacer 508, the layer 506 may be formed on the layer 502, and the layer 504 may be formed on the layer 506. In various other embodiments, the layer 502 may be formed on a substrate, the layer 506 may be formed on the layer 502, and the layer 504 may be formed on the layer 506. The substrate may then be removed, and the spacer 508 may be provided or formed in contact with the layer 502. The reflector or coating 510 may be formed or provided in contact with the spacer 508.

[0055] The stacked arrangement 500 may then be patterned using a method similar to the one shown in FIG. 4B, but with the layer of photoresist formed on the uppermost layer 504 of the superconducting material.

[0056] FIG. 6 shows a schematic of a stacked arrangement 600 over a spacer 608 according to various embodiments. There may be a reflector or an anti -reflection coating 610 in contact with a surface of the spacer 608 opposite the surface in contact with the stacked arrangement 600. The stacked arrangement 600 may include a layer 602 of plasmonic metal and a layer 604 of superconductor material.

[0057] In various embodiments, the reflector or coating 610 may be formed on a substrate, the spacer 608 may be formed on the reflector or coating 610, the layer 602 may be formed onthe spacer 608, and the layer 604 may be formed on the layer 602. In various other embodiments, the layer 602 may be formed on a substrate, and the layer 604 may be formed on the layer 606. The substrate may then be removed, and the spacer 608 may be provided or formed in contact with the layer 602. The reflector or coating 610 may be formed or provided in contact with the spacer 608.

[0058] The stacked arrangement 600 may then be patterned using a method similar to the one shown in FIG. 4B, but with the layer of photoresist formed on the uppermost layer 604 of the superconducting material, and with the stacked arrangement 600 devoid of an insulator layer.

[0059] FIG. 7 shows a schematic of a stacked arrangement 700 over a spacer 708 according to various embodiments There may be a reflector or an anti -refl ection coating 710 in contact with a surface of the spacer 708 opposite the surface in contact with the stacked arrangement 700. The stacked arrangement 700 may include a layer 702 of plasmonic metal and a layer 704 of superconductor material.

[0060] In various embodiments, the reflector or coating 710 may be formed on a substrate, the spacer 708 may be formed on the reflector or coating 710, the layer 704 may be formed on the spacer 708, and the layer 702 may be formed on the layer 704. In various other embodiments, the layer 704 may be formed on a substrate, and the layer 702 may be formed on the layer 704. The substrate may then be removed, and the spacer 708 may be provided or formed in contact with the layer 704. The reflector or coating 710 may be formed or provided in contact with the spacer 708.

[0061] The stacked arrangement 700 may then be patterned using a method similar to the one shown in FIG. 4B, but with the stacked arrangement 700 devoid of an insulator layer.

[0062] The plasmonic metal nanostructure may be used to create and enhance polarization selectivity of superconducting nanostructure. A device including such a stacked arrangement including the plasmonic metal nanostructure and the superconducting nanostructure may be used for full-Stokes polarimetry and quantum state tomography of light.

[0063] The MLSNSPD platform may not be limited to polarization control and sensing. It can be extended to design multifunctional detectors tailored for various applications, including but not limited to wavelength selection and filtering for spectrometers, electric field localization and enhancement for light focusing, and absorption enhancement in shortnanowires. Additionally, by properly functionalizing the plasmonic components, it may be possible to achieve single-molecule or single-photon biosensing using the MI-SNSPD.

[0064] Various embodiments may provide access to the full range of plasmonic applications combined with single-photon detection capabilities. Certain metals, such as gold, silver, aluminum and palladium, have a strong free electron response and exhibit plasmonic resonances. By patterning thin plasmonic films into different nanostructures, one can achieve a wide range of functionalities, including strongly localized field enhancement, high quality factor (Q) resonances, light focusing, dichroism, absorption and transmission control. Such plasmonic metasurfaces may offer an efficient alternative to conventional bulky optical components, allowing for the miniaturization of optical technologies and the creation of multifunctional devices.

[0065] Example of MI-SNSPD integration platform for quantum state tomoeraphy

[0066] The MI-SNSPD platform may exhibit strong dichroism, and may be used in a quantum state tomography camera. Due to their geometry, SNSPDs naturally exhibit selectivity in the linear polarization basis, but lack selectivity in the circular polarization basis, which may be required for full Stokes polarimetry and quantum state tomography. To address this, SNSPDs (i.e., superconducting nanostructures) may be coupled with self-aligned resonant plasmonic metal nanostructures. In the MI-SNSPD, superconducting nanowires and plasmonic metal nanostructures may the same design (i.e., lateral geometry) and may be optimized for both the optical response of the plasmonic metal nanostructure and the electrical response of the superconducting nanostructures.

[0067] FIG. 8A shows a schematic of a single-photon detector according to various embodiments. The single-photon detector may be formed from the resultant arrangement shown in FIG. 4B by removing the photoresist structure 412’. The single-photon detector may include a stacked arrangement 800 including a plasmonic metal nanostructure 802 (e g., metallic nanowire), a superconducting nanostructure 804 (e.g., superconducting nanowire) and insulator layer 806 between the plasmonic metal nanostructure 802 and the superconducting nanostructure 804. The stacked arrangement 800 may be in contact with a first surface of a dielectric spacer 808. A back-reflector 810 (e.g., thick metal backplane) may be in contact with a second surface of the dielectric spacer 808 opposite the first surface. The single-photon detector may leverage the plasmonic resonance induced by the plasmonic metal nanostructure 802 (e g., metallic nanowire), coupling the plasmonic resonance to the superconductingnanostructure 804 (e.g., superconducting nanowire), and thereby enhancing its polarization sensitivity. For straight nanowires, this configuration may achieve a polarization extinction ratio (PER) of more than 20 dB for a 50% fill factor device, as shown in FIG. 8B. FIG. 8B shows a plot of absorption (in percent or %) / polarization extinction ratio PER (in decibels or dB) as a function of fill factor (in percent or %) illustrating the variation in absorption of parallel and orthogonal polarization light, along with PER, with increasing pixel fill factor of the single-photon detector according to various embodiments.

[0068] FIG. 9A shows a schematic of a single-photon detector according to various embodiments. The single-photon detector may be a chiral metamaterial absorber, which may selectively absorb light of a particular handedness while reflecting the other. The single-photon detector may include a stacked arrangement 900 including a plasmonic metal nanostructure 902 (e.g., a Z-shaped metallic resonating nanoantenna such as a silver nanoantenna for generating plasmonic resonance), a superconducting nanostructure 904 (e g., a Z-shaped superconducting nanowire) and insulator layer 906 between the plasmonic metal nanostructure 902 and the superconducting nanostructure 904. The stacked arrangement 900 may be in contact with a first surface of a dielectric spacer 908. A back-reflector 910 (e g., thick metal backplane acting as a mirror to enhance plasmonic resonance) may be in contact with a second surface of the dielectric spacer 908 opposite the first surface The plasmonic metal nanostructure 902, the superconducting nanostructure 904 and the insulator layer 906 may have planar surfaces that are of a chiral shape. The plasmonic metal nanostructure 902 may be patterned to selectively absorb circularly polarized photons of a particular handedness and generate plasmonic resonance in response to the absorbed photons. The plasmonic resonance may then be coupled to the superconducting nanostructure 904. The superconducting nanostructure 904 may also be patterned to selectively absorb circularly polarized photons of a particular handedness FIG. 9B shows a plot of absorption (in percent or %) / polarization extinction ratio PER (in decibels or dB) as a function of wavelength (in nanometers or nm) illustrating variation in absorption of right (R) and left (L)-handed circularly polarized light, as well as associated PER evolution in the superconducting nanowire of the single-photon detector of FIG. 9A with wavelength according to various embodiments. FIG. 9B shows that substantial circular polarization sensitivity can be obtained with Z-shaped nanowires 902, 904.

[0069] FIG. 10A shows a schematic of another single-photon detector according to various embodiments The single-photon detector may also be a chiral metamaterial absorber, whichmay selectively absorb light of a particular handedness while reflecting the other. The singlephoton detector may include a stacked arrangement 1000 including a plasmonic metal nanostructure 1002 (e.g., a S-shaped metallic resonating nanoantenna such as a silver nanoantenna for generating plasmonic resonance), a superconducting nanostructure 1004 (e.g., a S-shaped superconducting nanowire) and insulator layer 1006 between the plasmonic metal nanostructure 1002 and the superconducting nanostructure 1004. The stacked arrangement 1000 may be in contact with a first surface of a dielectric spacer 1008. A back-reflector 1010 (e.g., thick metal backplane acting as a mirror to enhance plasmonic resonance) may be in contact with a second surface of the dielectric spacer 1008 opposite the first surface. FIG. 10B shows a plot of absorption (in percent or %) / polarization extinction ratio PER (in decibels or dB) as a function of wavelength (in nanometers or nm) illustrating variation in absorption of right (H) and left (V)-handed circularly polarized light, as well as associated PER evolution in the superconducting nanowire of the single-photon detector of FIG. 10A with wavelength according to various embodiments. FIG. 10B shows that substantial circular polarization sensitivity can be obtained with S-shaped nanowires 1002, 1004.

[0070] FIG. 11 A shows a scanning electron microscopy (SEM) image of a fabricated singlephoton detector including multiple linked S-shaped segments according to various embodiments The single-photon detector may be placed inside a pulse-tube cryocooler and operated at a temperature of 3K. Light emitted from a fiber-pulsed laser at a wavelength of 1550 nm may be delivered to the single-photon detector through an optical window. The input beam may pass through a linear polarizer, while a combination of a quarter-wave plate and a half-wave plate may be used to modulate the polarization state of the light reaching the detector. A commercial polarimeter may be used to monitor and verify the polarization state at the detector input.

[0071] FIG. 1 IB shows a plot of coincidence rate (in Hertz or Hz) as a function of current (in micro- Amperes or pA) illustrating the increase of the coincidence rate with bias current for both polarization states of the fabricated single-photon detector shown in FIG. 11A according to various embodiments. However, FIG. 1 IB also shows that when the detector is illuminated with right-handed circular polarization I / ?), the coincidence rate is significantly higher compared to left-handed circular polarization |L), confirming the strong polarization selectivity of the detector. FIG. 1 1 C shows a plot of polarization extinction ratio PER (in decibels or dB) as a function in current (in micro- Amperes or p A) illustrating the variation of PER with biascurrent of the fabricated single-photon detector shown in FIG. HA according to various embodiments. The PER reaches values above 15 dB when the detector is biased at 5 / / A, and gradually decreases with increasing bias, reaching about 8 zA at 6.5 / A.

[0072] Various embodiments may relate to a MI-SNSPD platform integrating a superconducting nanostructure with a plasmonic metal nanostructure, which may extend the functionalities of SNSPDs.

[0073] For instance, the MI-SNSPD platform may integrate multiple sensing and detection capabilities within a single device Each pixel may perform advanced sensing functions alongside serving as a superconducting single-photon detector. This integration may simplify experimental setups, reducing complexity and the need for multiple separate optical components.

[0074] By incorporating metamaterial concepts, MI-SNSPD pixels may be able to respond to a wide range of electromagnetic phenomena. The plasmonic nanostructures may be engineered to exhibit specific resonances, allowing precise control over interactions with photons possessing specific spatial, temporal, and frequency characteristics. This coupling of plasmonic resonances to SNSPDs may significantly enhance polarization sensitivity.

[0075] The MI-SNSPD platform may not be limited to enabling polarization sensitivity. In various embodiments, the enhanced SNSPDs can be used for various applications in nanophotonics and quantum information science. The device may enable direct and efficient measurement of various photon properties, enabling real-time characterization of quantum states without extensive auxiliary equipment.

[0076] Various embodiments may integrate multiple functions into a single device, thereby eliminating the need for bulky and expensive optical components traditionally required in various setups. This simplification may reduce costs and enhance the portability and scalability of the device, making it practical for both laboratory and field applications.

[0077] Various embodiments may be applicable in the growing field of quantum technologies. Various embodiments may be suitable for various applications. For instance, various embodiments may be a major tool in research toolkit for researchers in quantum mechanics, quantum optics, and / or quantum information science. Research institutions and laboratories developing quantum technologies may use this platform in their studies. Marketing efforts can target academic institutions, government research agencies, and private laboratories to showcase the platform's potential in advancing quantum research.

[0078] Various embodiments may be used in quantum key distribution (QKD) and quantum cryptography, which may depend on the precise characterization of quantum states. The MI- SNSPD platform, exemplified by its ability to create polarization-resolving single-photon cameras, may enhance the development and testing of QKD systems, improving their security and reliability. Companies specializing in quantum communication systems may integrate the MI-SNSPD platform into their product offerings to boost performance and innovation.

[0079] Various embodiments may be ideal for quantum metrology applications such as precision measurement and sensing. Industries involved in precision manufacturing, biomedical imaging, and environmental monitoring can use this platform to enhance their measurement capabilities. The high temporal and spatial resolution provided by MI-SNSPD technology may make it a valuable asset for these sectors

[0080] The accurate characterization of quantum states may be crucial for the development and operation of quantum computers. Companies and research institutions working on quantum computing hardware and algorithms can integrate the MI-SNSPD platform into their systems for state tomography and error correction purposes. The platform's advanced detection and sensing capabilities may support the precise measurements needed for quantum computing

Claims

Claims1. A single-photon detector comprising: a stacked arrangement comprising: a plasmonic metal nanostructure; and a superconducting nanostructure over or under the plasmonic metal nanostructure, the superconducting nanostructure substantially aligned to the plasmonic metal nanostructure; wherein lateral dimensions of the plasmonic metal nanostructure are substantially equal to lateral dimensions of the superconducting nanostructure.

2. The single-photon detector according to claim 1, wherein the stacked arrangement comprises an insulator layer between the plasmonic metal nanostructure and the superconducting nanostructure3. The single-photon detector according to claim 1, wherein the plasmonic metal nanostructure is in contact with the superconducting nanostructure.

4. The single-photon detector according to any one of claims 1 to 3, further comprising: a back-reflector or an anti-reflection coating.

5. The single-photon detector according to claim 4, further comprising: a spacer between the stacked arrangement and either the back-reflector or the anti-reflection coating.

6. The single-photon detector according to any one of claims 1 to 5, wherein the plasmonic metal nanostructure is a metallic nanowire; and wherein the superconducting nanostructure is a superconducting nanowire.

7. The single-photon detector according to any one of claims 1 to 6, wherein the plasmonic metal nanostructure is a Z-shaped metallic resonating nanoantenna; and wherein the superconducting nanostructure is a Z-shaped superconducting nanowire.

8. The single-photon detector according to any one of claims 1 to 6, wherein the plasmonic metal nanostructure is a S-shaped metallic resonating nanoantenna; and wherein the superconducting nanostructure is a S-shaped superconducting nanowire.

9. The single-photon detector according to any one of claims 1 to 8, wherein the plasmonic metal nanostructure comprises a material selected from a group consisting of gold, silver, aluminum, palladium, bismuth, copper, tungsten and titanium nitride.

10. The single-photon detector according to any one of claims 1 to 9, wherein the superconducting nanostructure comprises a material selected from a group consisting of niobium nitride (NbN), niobium titanium nitride (NbTiN), molybdenum silicide (MoSi), tungsten silicide (WSi), magnesium diboride (MgE ), yttrium barium copper oxide (YBCO), molybdenum germanium (MoGe) and tungsten rhenium (WRe).1 1 . The single-photon detector according to any one of claims 1 to 10, wherein the plasmonic metal nanostructure is configured to exhibit one or more plasmonic resonances in response to an electromagnetic wave incident onto the plasmonic metal nanostructure; and wherein the plasmonic metal nanostructure is further configured to couple the one or more plasmonic resonances to the superconducting nanostructure.

12. The single-photon detector according to claim 11, wherein the superconducting nanostructure is configured to induce chirality, wavelength selectivity, filtering, electric field localization, light focus enhancement, absorption enhancement, single-molecule biosensing or singlephoton biosensing in response to the coupling of the one or more plasmonic resonances to the superconducting nanostructure.

13. A method of forming a single-photon detector, the method comprising: forming a stacked arrangement comprising: a plasmonic metal nanostructure; and a superconducting nanostructure over or under the plasmonic metal nanostructure, the superconducting nanostructure substantially aligned to the plasmonic metal nanostructure; wherein lateral dimensions of the plasmonic metal nanostructure are substantially equal to lateral dimensions of the superconducting nanostructure.

14. The method according to claim 13, wherein the stacked arrangement comprises an insulator layer between the plasmonic metal nanostructure and the superconducting nanostructure.

15. The method according to claim 13, wherein the plasmonic metal nanostructure is in contact with the superconducting nanostructure.

16. The method according to any one of claims 13 to 15, wherein the stacked arrangement is patterned using a single step lithography and subsequently etched using a single step etching.

17. The method according to claims 13 to 16, further comprising: forming a back-reflector or an anti-reflection coating.

18. The method according to claim 17, further comprising: forming a spacer between the stacked arrangement and either the back- reflector or the anti-reflection coating.

19. The method according to any one of claims 13 to 18, wherein the plasmonic metal nanostructure is a metallic nanowire; and wherein the superconducting nanostructure is a superconducting nanowire.

20. The method according to any one of claims 13 to 19, wherein the plasmonic metal nanostructure is a Z-shaped metallic resonating nanoantenna; and wherein the superconducting nanostructure is a Z-shaped superconducting nanowire.

21. The method according to any one of claims 13 to 19, wherein the plasmonic metal nanostructure is a S-shaped metallic resonating nanoantenna; and wherein the superconducting nanostructure is a S-shaped superconducting nanowire.

22. The method according to any one of claims 13 to 21, wherein the plasmonic metal nanostructure comprises a material selected from a group consisting of gold, silver, aluminum, palladium, bismuth, copper, tungsten and titanium nitride.

23. The method according to any one of claims 13 to 22, wherein the superconducting nanostructure comprises a material selected from a group consisting of niobium nitride (NbN), niobium titanium nitride (NbTiN), molybdenum silicide (MoSi), tungsten silicide (WSi), magnesium diboride (MgBs), yttrium barium copper oxide (YBCO), molybdenum germanium (MoGe) and tungsten rhenium (WRe).

24. The method according to any one of claims 13 to 23, wherein the plasmonic metal nanostructure is configured to exhibit one or more plasmonic resonances in response to an electromagnetic wave incident onto the plasmonic metal nanostructure; and wherein the plasmonic metal nanostructure is further configured to couple the one or more plasmonic resonances to the superconducting nanostructure.

25. The method according to claim 24, wherein the superconducting nanostructure is configured to induce chirality, wavelength selectivity, filtering, electric field localization, light focus enhancement, absorption enhancement, single-molecule biosensing or singlephoton biosensing in response to the coupling of the one or more plasmonic resonances to the superconducting nanostructure.

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