Diamond layers in photonic circuits

Abstract

A photonic integrated circuit (PIC) and a single crystal diamond layer disposed on the PIC, the single crystal diamond substrate containing at least one spin defect and having a surface area of ​​at least 250,000 μm 2 The PIC comprises the single crystal diamond layer including at least one alignment structure and at least one corresponding diamond alignment structure, and further comprises at least one photonic structure optically coupled to at least one spin defect.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to photonic circuits having diamond layers and methods of fabricating photonic circuits having diamond layers. [Background technology]

[0002] Spin defects, particularly quantum spin defects and / or optically active defects, in synthetic diamond materials have been proposed for use in a variety of sensing, detection and quantum processing applications, including magnetometers; spin resonance devices, such as nuclear magnetic resonance (NMR) and electron spin resonance (ESR) devices; spin resonance imaging devices for magnetic resonance imaging (MRI); and quantum information processing (QIP) devices, such as for quantum computing.

[0003] The problem with quantum materials is that single-photon emission from quantum spin defects in such materials can be very weak. For example, the NVs in diamond - Even at low temperatures, defects exhibit broad spectral emission, related to the Debye-Waller factor of about 0.05. Furthermore, single-photon emission at the zero-phonon line (ZPL) is extremely weak, typically on the order of a few thousand photons per second. Such count rates may be insufficient for the realization of advanced QIP protocols based on coupling of spin states and optical transitions within reasonable data acquisition times.

[0004] In addition to the problem of weak emission mentioned above, the high refractive index of diamond material means that only very few photons can be collected within a small solid angle due to total internal reflection. Therefore, there is a need to increase light collection from quantum spin defects in diamond material for applications involving quantum information processing.

[0005] To create effective photonic circuits, the spin defects in the diamond must therefore be precisely optically coupled to the waveguides of the photonic integrated circuit (PIC) in which the diamond is mounted.

[0006] A limitation to the wider application of diamond in quantum technologies is the difficulty in processing photonic circuits, as large areas of single-crystal diamond are not readily available as thin films of a few hundred nanometers covering PICs.

[0007] Photonic circuits typically include a handle layer, a cladding layer, and a waveguide or active layer. The waveguide layer is typically formed from silicon nitride, gallium phosphide, or aluminum nitride, because these contain diamond defects, such as NV. - This is because it has the necessary transparency at the typical emission wavelengths of the SiV and SiC centers. The diamond can be structured to have spin defects at specific locations, which must be aligned with the corresponding optical waveguides in the PIC. This is difficult to achieve with large-area single-crystal diamond layers.

[0008] It is desirable to realize low-loss interconnections (<0.1 dB / cm possible) between different spin defects. Additional functions in advanced photonic circuits, such as splitters, interferometers, delay lines, and resonators, may be utilized. The difficulty in fabricating low-loss waveguides and other photonic structures on single-crystal diamond is due to the difficulties in microfabrication caused by the strong chemical inertness of single-crystal diamond.

[0009] Furthermore, materials such as SiN have high nonlinear coefficients, allowing for photon pair generation and photon frequency conversion, which may be used to realize quantum computing and quantum communication protocols in addition to the operations supported by diamond defect spin qubits.

[0010] The integration of diamond layers on large area substrates can facilitate the integration of further elements due to their improved compatibility with standard cleanroom microfabrication techniques, such as the fabrication of microwave waveguides for the manipulation of diamond defect spins, or the co-integration of other components such as single photon detectors.

[0011] (Summary of the Invention) The present invention aims to provide a photonic circuit having a large area single crystal diamond layer containing spin defects, which precisely optically couple to waveguides and other structures in the waveguide layer of a photonic integrated circuit.

[0012] According to a first aspect, there is provided a PIC (e.g., including a waveguide layer and a cladding layer) and a single crystal diamond layer disposed on the PIC. The single crystal diamond substrate comprises at least one spin defect and has a surface area of ​​at least 250,000 μm. 2 The PIC comprises at least one alignment structure, and the single crystal diamond layer comprises at least one corresponding diamond alignment structure. The PIC further comprises at least one photonic structure optically coupled to the at least one spin defect.

[0013] Optionally, the spin defect is selected from the group consisting of a negatively charged nitrogen vacancy center, a silicon vacancy center, a germanium vacancy center, a tin vacancy center, a nickel vacancy NE4, and a nickel vacancy nitrogen defect NE8.

[0014] The photonic circuit optionally includes a plurality of spin defects and a plurality of corresponding photonic structures, the plurality of photonic structures being designed to connect different spin defects according to a quantum computing protocol.

[0015] Examples of photonic structures include optical waveguides and photonic cavities. Optionally, the thickness of the single crystal diamond layer is selected from the group consisting of 50 nm to 50 μm, 100 nm to 10 μm, and 150 nm to 5 μm.

[0016] The PIC alignment structure and the diamond alignment structure optionally include corresponding structures that allow light to pass through when the alignment structures are aligned, it being understood that the alignment structures will be as close as possible when the amount of light passing through is maximized.

[0017] In an optional embodiment, the PIC alignment structure and the diamond alignment structure include corresponding diffraction gratings arranged to diffract light during alignment.

[0018] In an optional embodiment, the PIC alignment structure and the diamond alignment structure include corresponding waveguide couplers for connecting optical waveguides of the PIC.

[0019] It should be noted that a combination of the above two embodiments may be used, using a diffraction grating to achieve approximate alignment and further using a waveguide coupler to achieve more precise alignment.

[0020] As a further option, the PIC alignment structure and the diamond alignment structure include alignment markers.

[0021] The PIC alignment structure and the diamond alignment structure are optionally fabricated using any of implantation, electron beam lithography, and inductively coupled plasma reactive ion etching.

[0022] Optionally, the single crystal diamond layer is at least 500,000 μm thick. 2 , 1mm 2 , 4mm 2 , 25mm 2 and 100mm 2 As the area of ​​the diamond layer increases, alignment becomes more difficult and more important. Optionally, multiple single crystal diamond layers are disposed on the PIC.

[0023] In a second aspect, there is provided a method for manufacturing a photonic circuit, the method comprising the steps of providing a PIC, and disposing a single crystal diamond layer on the PIC by aligning diamond alignment features in the diamond layer with corresponding PIC alignment features in the PIC, the single crystal diamond layer having a thickness of at least 250,000 μm 2 and containing at least one spin defect, and further comprising the step of optically coupling the spin defect to an optical waveguide of the PIC after alignment.

[0024] The spin defect is optionally selected from a negatively charged nitrogen-vacancy center, a silicon-vacancy center, a germanium-vacancy center, a tin-vacancy center, a nickel-vacancy NE4, and a nickel-vacancy nitrogen defect, NE8.

[0025] Optionally, the diamond layer comprises a plurality of spin defects and the PIC comprises a plurality of corresponding photonic structures, the photonic structures being designed to connect different spin defects according to a quantum computing protocol. As optional examples, the photonic structures include any optical waveguide and photonic cavity.

[0026] Optionally, the PIC alignment structure and the diamond alignment structure include corresponding structures that allow light to pass when the alignment structures are aligned, and the aligning step includes passing light through the alignment structures, where closest alignment is achieved when the intensity of the passing light is maximized.

[0027] Optionally, the PIC alignment structure and the diamond alignment structure include corresponding diffraction gratings, and the aligning step includes passing light through the diffraction gratings.

[0028] Optionally, the PIC alignment structure and the diamond alignment structure include corresponding waveguide couplers in the diamond layer, and the step of connecting and aligning the waveguides of the PIC includes the step of passing light through the waveguide couplers.

[0029] Optionally, the PIC alignment structure and the diamond alignment structure include alignment markers, and aligning includes aligning corresponding alignment markers.

[0030] Optionally, prior to aligning the diamond alignment features of the diamond layer with corresponding PIC alignment features of the PIC, the PIC alignment features and diamond alignment features are fabricated using any of implantation, electron beam lithography, and inductively coupled plasma reactive ion etching.

[0031] In an optional embodiment, multiple single crystal diamond layers are disposed on the PIC.

[0032] Optionally, before disposing the diamond layer on the PIC, the method comprises forming the spin defects in the diamond layer, mapping the locations of the spin defects in the diamond layer, and forming the photonic structure in the PIC to correspond to the locations of the spin defects, and optically coupling the spin defects and the photonic structure after disposing the diamond layer on the PIC.

[0033] Alternatively, the method comprises forming the photonic structure on the PIC, disposing the diamond layer on the PIC, and forming spin defects in the diamond layer to optically couple the spin defects to the photonic structure. Note that the steps of disposing the diamond layer on the PIC and forming spin defects in the diamond layer may be in any order.

[0034] Some embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0035] [Figure 1] 1 shows a schematic cross-sectional side view of a typical PIC. [Figure 2] 1 shows a schematic cross-sectional side view of a representative PIC and corresponding diamond layer. [Figure 3] 1 shows a schematic cross-sectional side view of a representative PIC and corresponding diamond layer, showing the diamond layer aligned with the PIC. [Figure 4] 1 shows a schematic plan view of a representative photonic circuit including a PIC and corresponding aligned diamond layers. [Figure 5] 10A-10C are schematic side cross-sectional views of a further exemplary PIC and corresponding diamond layer, showing the diamond layer aligned with the PIC; [Figure 6] 10A-10C are schematic side cross-sectional views of a further exemplary PIC and corresponding diamond layer, showing the diamond layer aligned with the PIC; [Figure 7] 1 is a flow diagram illustrating an exemplary process for fabricating a photonic circuit. [Figure 8] 1 is a flow diagram illustrating a further exemplary process for fabricating a photonic circuit. [Figure 9] 1 is a flow diagram illustrating an alternative exemplary process for fabricating a photonic circuit. DETAILED DESCRIPTION OF THE INVENTION

[0036] (Detailed explanation) To precisely align large areas of single crystal diamond layers with corresponding PICs to produce heterogeneously integrated photonic circuits, the PICs are provided with at least one PIC alignment structure and the diamond layers are provided with at least one corresponding diamond alignment structure.

[0037] To illustrate the above process and structure, in a first example, and with reference to Figures 1 to 3, it is assumed that the alignment structure is a diffraction grating.

[0038] FIG. 1 shows a schematic side cross-sectional view of a PIC 1, which includes a first alignment light waveguide 2. The first alignment light waveguide 2 is located near the surface of the PIC 1 and terminates in a first PIC diffraction grating 3. A second alignment light waveguide 4 is also provided near the surface of the PIC 1. The second alignment light waveguide 4 terminates in a second PIC diffraction grating 5. Because the first and second diffraction gratings 3, 5 are not optically coupled to each other, light (shown by the black arrows in FIG. 1) passes through the first alignment light waveguide 2 but does not subsequently pass through the second alignment light waveguide 4.

[0039] As shown in Figure 2, a diamond layer 6 with a diamond diffraction grating 7 is prepared. If the diamond layer is placed on the surface of the PIC1 while the diffraction gratings 3, 5, and 7 are not aligned, the light passing through the first alignment optical waveguide 2 will not subsequently pass through the second alignment optical waveguide 4 because the light will scatter out of plane. If the diamond layer 6 is precisely (but not perfectly) aligned to the PIC1, the alignment signal will be partially reflected back into the same waveguide or an adjacent waveguide (depending on the design). Using a multi-axis micromanipulator, the position of the diamond layer 6 relative to the PIC1 is optimized by monitoring the optical signal, and the optimal position is achieved when the reflected signal is maximized. The use of multiple gratings can increase the accuracy of the alignment.

[0040] As shown in Figure 3, when the gratings 3, 5, and 7 are aligned, light passing through the first alignment light waveguide 2 is diffracted by the first PIC grating 3 and directed towards the diamond grating 7. The light is then diffracted by the diamond grating 7 and directed towards the second PIC grating 5. The light is then diffracted by the second PIC grating 5 and enters the second alignment light waveguide 4. If light is detected from the second alignment light waveguide 4, then the diamond layer 6 is properly aligned with the PIC grating 1.

[0041] It will be appreciated that multiple corresponding gratings of different angles may be used, ensuring that the diamond layer 6 is aligned two-dimensionally on the PIC1.

[0042] Diffraction gratings can be realized, for example, using rigorous coupled wave analysis simulations and fabrication techniques including lithography and inductively coupled plasma reactive ion etching (ICP-RIE).

[0043] Figure 4 shows a plan view of a representative photonic circuit 8. The heterogeneously integrated photonic circuit 8 includes the PIC 1 and the diamond layer 6 disposed on the PIC 1. Alignment is performed as described above using a diffraction grating 7 and alignment optical waveguides 2, 4. In this example, the diamond layer 6 includes three spin defects 9, which are optically coupled to corresponding waveguides 10 disposed on the PIC. By way of example, three further spin defects 11 in the diamond layer 6 are optically coupled to corresponding photonic cavities 12.

[0044] It will be appreciated that by providing two sets of diffraction gratings and alignment optical waveguides, and positioning one diffraction grating at 90° to the other, alignment of the diamond 6 on the PIC1 is reliably achieved in two dimensions.

[0045] Although the above example describes a diffraction grating, other types of optical coupling may be used, for example, an optical waveguide with an adiabatic coupler. As with the diffraction grating example, waveguides are structured in the diamond layer 6 before transfer. The waveguides terminate in tapered adiabatic couplers. An array of waveguides is fabricated on the PIC1. When the diamond layer 6 is aligned with the PIC1, optical signals from one set of aligned waveguides on the PIC1 couple to the next set of aligned waveguides on the PIC1.

[0046] To illustrate a second exemplary method of aligning the substrate 1 with the diamond layer, FIG. 5 shows a schematic side cross-sectional view of a further exemplary PIC and corresponding diamond layer, the diamond layer aligned with the PIC.

[0047] In the example of Figure 5, a first alignment optical waveguide 2 is located near the surface of PIC 1 and terminates in a first substrate optical coupler 13. When diamond layer 6 and the substrate are aligned, the first substrate optical coupler 13 optically couples to a first diamond optical coupler 14. The first diamond optical coupler 14 is connected to a second diamond optical coupler 16 by a diamond waveguide 15. A second substrate optical coupler 17 is provided on the surface of the substrate and optically couples to the second diamond optical coupler 16 when the diamond layer 6 is aligned with the substrate 1. When the two corresponding sets of optical couplers are aligned, light passing through the first alignment optical waveguide 2 can be detected by a second alignment optical waveguide 5. The diamond waveguide 15 can be a ridge waveguide, a rib waveguide, a slot waveguide, or a photonic crystal waveguide fabricated in the diamond layer prior to the transfer.

[0048] An advantage of the structure shown in Figure 5 is that the corresponding sets of optical couplers can be offset from each other, allowing the diamond to be aligned in two dimensions by passing light only through the first alignment optical waveguide 2.

[0049] Figure 6 shows a simpler version of the structure shown in Figure 5. In this case, the first alignment optical waveguide 2 terminates in a single substrate optical coupler 18, and light cannot pass from the first alignment optical waveguide 2 to the second alignment optical waveguide 5 unless the single substrate optical coupler 18 is aligned with a corresponding diamond optical coupler 19 in the diamond layer 6. In this example, at least one pair of corresponding optical couplers is required to align the diamond layer 6 and the PIC1 in two dimensions.

[0050] The above example alignment structures have different advantages and disadvantages, and the optimal configuration may involve using a diffraction grating for coarse alignment and a waveguide coupler for finer alignment. It will be appreciated that any other photonic structure that can be used to redirect optical signals from one waveguide to another in the PIC may also be used.

[0051] In addition to, or instead of, the alignment features shown in Figures 1 to 6, the alignment features may be simple markings that can be aligned by visual or automatic means to ensure that the diamond layer 6 is properly aligned with the PIC1.

[0052] It should also be noted that if large area diamond layers are used, it may be desirable to place multiple diamond layers on a single PIC to fabricate larger and more complex photonic circuits.

[0053] There are various ways to form alignment structures in both the diamond layer 6 and the PIC 1. These include implantation, electron beam lithography, and inductively coupled plasma reactive ion etching.

[0054] Figure 7 shows a flow diagram of the exemplary steps described above. The following numbers correspond to those in Figure 7:

[0055] S1. Prepare a PIC that includes at least one PIC alignment structure, such as a diffraction grating, waveguide coupler, or alignment marker. In most practical applications, at least two PIC alignment structures are prepared.

[0056] S2. Placing a single crystal diamond layer on the PIC by aligning diamond alignment features of the diamond layer with corresponding PIC alignment features of the PIC. The single crystal diamond layer has a thickness of at least 250,000 μm. 2 and includes at least one spin defect. After alignment, the spin defect is optically coupled to an optical waveguide of the PIC. Typical spin defects are any of the negatively charged nitrogen vacancy centers, silicon vacancy centers, germanium vacancy centers, and tin vacancy centers. In most cases, multiple spin defects are prepared, and each is optically coupled to a corresponding optical waveguide.

[0057] As mentioned above, a key requirement for accurate alignment of the diamond layer 6 to the PIC 1 is to ensure that the spin defect is optically coupled to a corresponding optical waveguide or other optical structure such as a photonic cavity. To achieve this, the position of the spin defect and the corresponding optical structure must be controlled to ensure optical coupling after alignment.

[0058] In a first example, the locations of the spin defects in the diamond layer 6 are mapped and the optical structure is formed in the PIC 1 based on the known locations of the spin defects. Figure 8 is a flow diagram showing exemplary steps of this method, and the following numbers correspond to those in Figure 8:

[0059] S3. Provide a single crystal diamond layer 6 containing spin defects. There are several ways in which spin defects can be incorporated into the diamond layer 6. For example, spin defects can be added to the diamond crystal lattice as the diamond is grown in a CVD reactor. For example, adding nitrogen to the process gas during growth, as described in WO2010149775, incorporates nitrogen into the diamond crystal lattice. Subsequent irradiation and annealing convert some of the nitrogen into NV - Another method of incorporating spin centers into diamond is by ion implantation, as described for example in WO2015071487. Using this technique, NV centers are formed by nitrogen ion implantation and annealing (optionally including a vacancy-generating irradiation step before or after ion implantation). - Ion implantation has many advantages over incorporating nitrogen into the crystal lattice during growth. The first advantage is that the NV - The point is that the depth of the center can be controlled to some extent. - The center is required near the diamond surface. The second advantage is that it is possible to control where the nitrogen is implanted on the diamond surface, allowing the nitrogen to be implanted at a desired location close to the expected location of the photonic structure. The third advantage is that low concentrations (10 15 cm -2 An advantage of ion implantation is that it allows for greater control of the nitrogen concentration within the diamond, where a nitrogen concentration of less than 1000 nm is desired. Of course, similar considerations apply to the formation of other types of defects.

[0060] S4. Map the location of the spin defects in the diamond layer 6. This may be achieved by characterizing the diamond layer 6 with microphotoluminescence spectroscopy and further using autocorrelation measurements to confirm the presence of defects within the volume of interest.

[0061] S5. Prepare a PIC1 with a photonic structure, such as an optical waveguide or a photonic cavity, and after depositing a diamond layer 6 on the PIC1, deposit the PIC1 in a position such that the spin defects are optically coupled to the corresponding optical structure in the insulating layer 1. Note that part of the optical structure may be formed within the diamond layer 6.

[0062] S6. Using the alignment structure, the diamond layer 6 is placed on the PIC1.

[0063] In a second example, an optical structure is formed in the PIC 1, and then spin defects are introduced at desired positions in the diamond, and the diamond layer 6 is aligned and placed on the PIC 1 before optically coupling with the optical structure in the insulating layer 1. Figure 9 is a flow diagram showing representative steps of this method, and the following numbers correspond to those in Figure 9:

[0064] S7. Prepare a PIC1 with photonic structures, such as optical waveguides and photonic cavities, positioned to form a photonic circuit.

[0065] S8. Introduce spin defects into the diamond layer 6 at locations such that the spin defects will optically couple with the corresponding photonic structure after the diamond layer 6 is placed in the PIC 1. These spin defects may be formed, for example, using the ion implantation techniques described in step S3 above.

[0066] S9. The alignment structure is used to place the diamond layer 6 on the PIC1.

[0067] It should be noted that steps S8 and S9 can be reversed, with the spin defects being formed in the diamond layer 6 before the diamond layer 6 is deposited on the PIC1, or alternatively, the spin defects can be formed in the diamond layer 6 after the diamond layer 6 is deposited on the PIC1. However, it should be noted that because the ion implantation can be performed once the diamond layer 6 is already deposited on the PIC1, precise alignment between the diamond layer 6 and the PIC1 is not required, only alignment between the ion beam and the target, although other defect creation procedures may not be compatible with the photonic platform used. After implantation, a high temperature (typically above 1000°C) annealing step is required to repair much of the damage caused by the implantation and to diffuse the vacancies to form ion-vacancy centers that act as spin defects. The annealing temperature may exceed the thermal budget of the photonic platform, in which case the annealing step must be performed before the diamond layer 6 is placed on the PIC1 target.

[0068] A typical process flow can be summarized as follows: The diamond substrate is appropriately processed to have the required surface roughness, flatness, parallelism, distortion, and subsurface damage.

[0069] The diamond substrate is implanted with light ions to create a damaged layer for subsequent electrochemical lift-off. The diamond substrate is enlarged in a microwave plasma CVD reactor to form a high-purity diamond layer 6 .

[0070] Isolated defects can be injected (eg, N, Si, Ge, Sn, etc.) and then processed to form spin defects. The diamond layer 6 is annealed to create the spin defects and convert the damaged layer to graphite for subsequent electrochemical lift-off.

[0071] Alignment structures are fabricated in the diamond layer 6 using photo or electron beam lithography and ICP-RIE etching. The positions of the spin defects in the diamond layer 6 are mapped using the alignment structure as a reference.

[0072] Additional photonic structures are optionally fabricated in the diamond layer to create any waveguides and photonic cavities required for the operation of the photonic chip. A layout of the target PIC1 is created, and the PIC is manufactured.

[0073] Electrochemical lift-off of the diamond layer 6 is performed to remove the damaged layer from the diamond substrate. Using transfer printing and a micromanipulator, the diamond layer 6 is aligned to the PIC1 while the optical signal of the alignment waveguide of the PIC1 is monitored.

[0074] Further fabrication steps may be performed, such as deposition of cladding layers, creation of strip microwave waveguides for spin defect control, or heterogeneous integration of other components, such as single photon detectors or lasers or control electronics.

[0075] The process allows the integration of large (>500 μm lateral size) diamond layers 6 with high thickness uniformity (an inherent property of implantation and lift-off techniques) onto PICs to form photonic circuits. The lateral size is primarily limited by the size of the starting single-crystal substrate. Furthermore, fabrication using implantation and lift-off results in improved thickness uniformity over large areas compared to mechanical polishing or ICP-RIE etching. Thickness uniformity is a key factor in this application because it ensures uniformity in optical performance, such as mode volume, effective refractive index, and resonant frequency, across the entire area of ​​the film and between different films, making the photonic platform robust for mass production.

[0076] As diamond layers are used over large surface areas, alignment becomes more difficult and important. The use of alignment structures such as those described above allows for alignment of large diamond layers with maximum linear dimensions exceeding 500 μm.

[0077] Although the present disclosure has been particularly shown and described with reference to embodiments, it will be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the scope of the present disclosure as defined by the appended claims.

Claims

1. 1. A heterogeneously integrated photonic circuit, comprising: Photonic integrated circuits; a single crystal diamond layer disposed on the photonic integrated circuit, the single crystal diamond substrate comprising at least one spin defect, the single crystal diamond being at least 250,000 μm 2 a layer having a maximum surface area of Including, the photonic integrated circuit includes at least one photonic integrated circuit alignment structure and the single crystal diamond layer includes at least one corresponding diamond alignment structure; and the photonic integrated circuit further comprising at least one photonic structure optically coupled to the at least one spin defect; Heterogeneously integrated photonic circuits.

2. 2. The photonic circuit of claim 1, wherein the spin defect is selected from the group consisting of a negatively charged nitrogen-vacancy center, a silicon-vacancy center, a germanium-vacancy center, a tin-vacancy center, a nickel-vacancy NE4, and a nickel-vacancy nitrogen defect, NE8.

3. 3. The photonic circuit of claim 1, comprising a plurality of spin defects and a plurality of corresponding photonic structures, the plurality of photonic structures designed to connect to different spin defects according to a quantum computing protocol.

4. The photonic circuit according to any one of claims 1 to 3, wherein the photonic structure is selected from the group consisting of an optical waveguide and a photonic cavity.

5. 5. The photonic circuit of claim 1, wherein the single crystal diamond layer has a thickness selected from the group consisting of 50 nm to 50 μm, 100 nm to 10 μm, and 150 nm to 5 μm.

6. The photonic circuit of any of claims 1 to 5, wherein the photonic integrated circuit alignment structure and the diamond alignment structure include corresponding structures that allow the passage of light when the alignment structures are aligned.

7. The photonic circuit of claim 6 , wherein the photonic integrated circuit alignment structure and the diamond alignment structure include corresponding diffraction gratings arranged to diffract light during alignment.

8. 8. The photonic circuit of claim 6 or claim 7, wherein the photonic integrated circuit alignment structure and diamond alignment structure include corresponding waveguide couplers in the diamond layer for connecting optical waveguides of the photonic integrated circuit.

9. The photonic circuit of any one of claims 1 to 8, wherein the photonic integrated circuit alignment structure and diamond alignment structure include alignment markers.

10. The photonic circuit of any one of claims 6 to 9, wherein the photonic integrated circuit alignment structure and the diamond alignment structure are fabricated using any one of implantation, electron beam lithography, and inductively coupled plasma reactive ion etching.

11. The single crystal diamond layer is at least 500,000 μm 2 , 1 mm 2 , 4mm 2 , 25mm 2 , and 100 mm 2 11. The photonic circuit of claim 1, having a maximum surface area selected from:

12. A photonic circuit according to any preceding claim, wherein a plurality of single crystal diamond layers are disposed on the photonic integrated circuit.

13. 1. A method for manufacturing a photonic circuit, comprising: Providing a photonic integrated circuit; placing a single crystal diamond layer onto the photonic integrated circuit by aligning diamond alignment structures of the diamond layer with corresponding photonic integrated circuit alignment structures of the PIC; Including, The single crystal diamond layer is at least 250,000 μm 2 having a maximum surface area of containing at least one spin defect, optically coupling the spin defect to an optical waveguide of the photonic integrated circuit; The method for fabricating a photonic circuit further comprises:

14. 14. The method of claim 13, wherein the spin defect is selected from any of a negatively charged nitrogen vacancy center, a silicon vacancy center, a germanium vacancy center, a tin vacancy center, a nickel vacancy NE4, and a nickel vacancy nitrogen defect, NE8.

15. 15. The method of claim 13 or 14, wherein the diamond layer comprises a plurality of spin defects and the photonic integrated circuit comprises a plurality of corresponding photonic structures, the photonic structures being designed to connect different spin defects according to a quantum computing protocol.

16. The method according to any one of claims 13 to 15, wherein the photonic structure is selected from the group consisting of an optical waveguide and a photonic cavity.

17. 17. The method of any of claims 13 to 16, wherein the photonic integrated circuit alignment structure and the diamond alignment structure include corresponding structures that allow light to pass through when the alignment structures are aligned, and the aligning step includes passing light through the alignment structures.

18. 20. The method of claim 17, wherein the photonic integrated circuit alignment structure and the diamond alignment structure include corresponding diffraction gratings, and the aligning step includes passing light through the diffraction gratings.

19. 19. The method of claim 17 or claim 18, wherein the photonic integrated circuit alignment structure and the diamond alignment structure include corresponding waveguide couplers in the diamond layer, and the step of connecting and aligning waveguides of the photonic integrated circuit includes the step of passing light through the waveguide couplers.

20. The method of any of claims 13 to 19, wherein the photonic integrated circuit alignment structure and the diamond alignment structure include alignment markers, and the aligning comprises aligning corresponding alignment markers.

21. 21. A method according to any of claims 17 to 20, further comprising the step of fabricating any photonic integrated circuit alignment structures and the diamond alignment structures using any of implantation, electron beam lithography and inductively coupled plasma reactive ion etching prior to aligning the diamond alignment structures of the diamond layer with corresponding photonic integrated circuit alignment structures of the photonic integrated circuit.

22. A method according to any one of claims 13 to 21, further comprising the step of depositing a plurality of single crystal diamond layers on the photonic integrated circuit.

23. Prior to disposing the diamond layer on the photonic integrated circuit: forming the spin defects in the diamond layer; mapping the locations of the spin defects in the diamond layer; and forming the photonic structure of the photonic integrated circuit to correspond to the location of the spin defect; optically coupling the spin defects and the photonic structure after disposing the diamond layer on the photonic integrated circuit; 23. The method of any of claims 13 to 22, comprising:

24. forming the photonic structure in the photonic integrated circuit; disposing the diamond layer on the photonic integrated circuit; and 23. A method according to any one of claims 13 to 22, comprising forming the spin defects in the diamond layer and optically coupling the spin defects and the photonic structure.

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