Electro-optical component

Abstract

An electro-optical component includes an erbium and oxygen injected silicon waveguide and a superconducting microwave resonator. A barrier layer of opaque material is arranged between the waveguide and the microwave resonator. The microwave resonator is coherently coupled to the spin state of erbium.

Description

Technical Field

[0001] The present invention relates to a method for connecting quantum computers, and more particularly to providing a coherent interface between photons and superconducting quantum computers. Background Art

[0002] It has been previously shown in “Coupling of Erbium-Implanted Silicon to a Superconducting Resonator”, Physical Review Applied 16, 034006 (2021) that the spin state of erbium injected into silicon can be coupled to a superconducting resonator, and in “Optically modulated magnetic resonance of erbium implanted silicon”, Scientific Reports, 9, 19031 (2019) that 1550nm light can modulate the spin state of erbium injected into silicon; this suggests that erbium-implanted silicon can be used to couple 1550nm photons to superconducting resonators. This coupling would allow interfacing between photonic and superconducting quantum computers, since the superconducting circuits of superconducting quantum computers can be coherently coupled to superconducting resonators; however, superconducting resonators are sensitive to photons, which can cause localized losses of superconducting properties, which would adversely affect the superconducting resonators.

[0003] It is an object of one or more embodiments of the present invention to overcome or at least partially alleviate one or more problems of the prior art, and / or to provide improved optical to microwave coupling. Summary of the invention

[0004] According to a first aspect of the invention, there is provided an electro-optical component comprising an erbium and oxygen implanted silicon waveguide, and a superconducting microwave resonator, wherein a barrier layer of an opaque material is arranged between the waveguide and the microwave resonator, and wherein the microwave resonator coherently couples to the spin states of the erbium.

[0005] Advantageously, a barrier layer of opaque material is provided between the waveguide and the microwave resonator to ensure that photons guided through the waveguide are not absorbed by the superconducting component, thereby avoiding the formation of localized non-superconducting regions that would be detrimental to the operation of the device.

[0006] The barrier layer may be composed of an optically opaque material. The barrier layer may be electrically insulating at 10 mK to 200 mK. The optically opaque material may be opaque to light of 1550 nanometers (nm). The barrier layer may be a narrow bandgap semiconductor, preferably, the bandgap is less than 0.8 electron volts (eV). The narrow bandgap semiconductor may be indium antimonide (InSb). The narrow bandgap semiconductor may be gallium antimonide (GaSb). The barrier layer has a thickness between 5 nm and 500 nm, for example, a thickness between 5 nm and 100 nm, preferably a thickness between 20 nm and 40 nm, and more preferably a thickness of 30 nm.

[0007] Advantageously, the blocking layer ensures that optical photons from the optical part of the device do not reach the microwave resonator. Using InSb as a blocking layer is advantageous because it is opaque to 1550nm photons and has low conductivity at the operating temperature of the device. However, the blocking layer cannot be too thick because this will be detrimental to the coherent coupling of states in the waveguide and the microwave resonator.

[0008] Alternatively, the barrier layer may consist of two layers. The first layer may include a reflective metal or its alloy (e.g., gold). The second layer may include an electrical insulator (e.g., aluminum oxide (Al2O3)).

[0009] A barrier layer consisting of two layers is advantageous because a material can be selected that has excellent performance in one of the properties required for the barrier layer. For example, a layer of gold may be superior in blocking 1550nm photons from passing from an optical waveguide to a microwave resonator, but is not electrically insulating. On the other hand, Al2O3 may be an excellent electrical insulator, but is not suitable for blocking 1550nm photons. By using a layer of each material, an excellent barrier layer is obtained.

[0010] The silicon waveguide may be arranged on a silicon oxide layer. The silicon oxide layer may be arranged on a silicon layer. The height of the waveguide may be between 100 nm and 1000 nm, for example between 100 nm and 500 nm, preferably between 200 nm and 400 nm, i.e. 300 nm. The width of the waveguide may be between 200 nm and 2000 nm, for example between 300 nm and 1000 nm, preferably between 400 nm and 600 nm, i.e. 500 nm.

[0011] The waveguide may define a path comprising a plurality of parallel lines. There may be 3 to 30 parallel lines. The length of the parallel lines may be between 50 μm and 1000 μm. The parallel lines may be connected by curved sections. The curved sections may include 180 degree turns. The bend radius of these turns may be between 1 μm and 30 μm, for example between 1 μm and 10 μm, preferably between 3 μm and 8 μm, i.e. a bend radius of 5 μm.

[0012] Superconducting resonators can be composed of niobium nitride.

[0013] According to a second aspect of the present invention, there is provided a method for producing an electro-optical component, the method comprising: providing a silicon substrate; implanting erbium and oxygen into the silicon substrate; annealing the silicon substrate; defining at least one optical waveguide on the silicon substrate; depositing a barrier layer of an opaque material on the waveguide; and manufacturing a superconducting resonator structure on the barrier layer.

[0014] The silicon substrate may be a silicon-on-insulator substrate. The silicon substrate may include a silicon base layer, a silicon oxide layer, and a silicon surface layer.

[0015] The waveguide may be defined by a silicon surface layer. The waveguide may have a thickness between 100 nm and 1000 nm, for example a thickness between 200 nm and 600 nm, preferably a thickness between 250 nm and 350 nm. The waveguide may have a thickness of 300 nm. The waveguide may have a width between 200 nm and 2000 nm, for example a width between 250 nm and 750 nm, preferably a width between 400 nm and 600 nm, more preferably a width of 500 nm.

[0016] Erbium may be implanted before oxygen. Ion implantation may be used to implant erbium. Erbium may be implanted at an energy between 20 keV and 4000 keV, for example 20 keV to 2000 keV, preferably between 40 keV and 1500 keV, more preferably between 50 keV and 1300 keV. Erbium may have a relative density of 1×10 14 cm -3 and 1×10 19 cm -3 The average concentration between 1×10 16 cm -3 and 1×10 18 cm -3 The average concentration is preferably 1×10 17 cm -3 The oxygen may be implanted at an energy between 5 keV and 300 keV, preferably between 5 keV and 200 keV, more preferably between 10 keV and 150 keV. The oxygen may have an average concentration of 1×10 15 cm -3 and 1×10 20 cm -3 The average concentration between 1×10 18 cm -3 and 1×10 20 cm -3The average concentration is preferably 1×10 19 cm -3 The average concentration of

[0017] The annealing step may include heating the silicon substrate to a first temperature for a first time period. The annealing step may include heating the silicon substrate to a second temperature for a second time period. The annealing step may include heating the silicon substrate to a third temperature for a third time period. The second temperature may be higher than the first temperature. The third temperature may be higher than the second temperature.

[0018] The first temperature may be between 400°C and 500°C, preferably between 425°C and 575°C, more preferably at 450°C. The first time period may be between 20 minutes and 60 minutes, for example between 20 minutes and 40 minutes, preferably between 25 minutes and 35 minutes, more preferably 30 minutes. The second temperature may be between 550°C and 650°C, preferably between 600°C and 640°C, more preferably 620°C. The second time period may be between 120 minutes and 300 minutes, for example between 120 minutes and 240 minutes, preferably between 160 minutes and 200 minutes, more preferably 180 minutes. The third temperature may be between 700°C and 1000°C, preferably between 800°C and 900°C, more preferably 850°C. The third time period may be between 10 seconds and 100 seconds, for example between 10 seconds and 50 seconds, preferably between 20 seconds and 40 seconds, more preferably 30 seconds.

[0019] The barrier layer may be composed of an optically opaque material. The optically opaque material may be opaque to light at 1550 nm. The barrier layer may be a narrow bandgap semiconductor. The narrow bandgap semiconductor may be InSb. The barrier layer may have a thickness between 5 nm and 500 nm, such as a thickness between 5 nm and 100 nm, preferably a thickness between 20 nm and 40 nm, more preferably a thickness of 30 nm.

[0020] The barrier layer may be deposited in two steps. The first deposition of the barrier layer may have a thickness approximately equal to the waveguide height. The second deposition of the barrier layer may have a thickness between 5 nm and 500 nm, such as a thickness of 10 nm to 100 nm, preferably a thickness of 20 nm to 40 nm, more preferably a thickness of 30 nm. The first deposition may be chemically mechanically planarized prior to depositing the second layer.

[0021] Superconducting resonators can be composed of niobium nitride.

[0022] According to a third aspect of the present invention, there is provided a quantum interface device comprising the electro-optical component of the first aspect of the present invention (including any optional features thereof), and further comprising a superconducting quantum computer and a photonic quantum computer; wherein the superconducting quantum computer is operably coupled to a superconducting resonator, and the qubits of the photonic quantum are composed of photons in a waveguide.

[0023] The device thus allows photonic quantum computers to be coherently connected to superconducting quantum computers, allowing hybrid systems to take advantage of the strengths of both types. For example, superconducting quantum computers currently have greater flexibility in how the gates can be programmed to operate, but photonic quantum computers may have lower levels of random noise. DETAILED DESCRIPTION

[0024] In order to more clearly understand the present invention, one or more embodiments thereof will now be described by way of example only with reference to the accompanying drawings, in which:

[0025] Figure 1 is a schematic cross section of an embodiment of an electro-optical component according to the present invention;

[0026] Figure 2 for Figure 1 A plan view of a waveguide in an electro-optical component;

[0027] Figure 3 for Figure 1 A plan view of a resonator of an electro-optical component;

[0028] Figure 4 (a)-(f) are schematic cross-sections of an embodiment of a method for producing an electro-optical component according to the present invention.

[0029] Figure 5 is a schematic cross section of an embodiment of an electro-optical component according to the present invention;

[0030] Figure 6 (a)-(d) are schematic cross-sections of an embodiment of a method for producing an electro-optical component according to the present invention.

[0031] One or more embodiments have been described above by way of example only. Many variations are possible without departing from the scope of protection provided by the appended claims.

[0032] Figure 1A schematic cross section of an electro-optical component 10 according to the present invention is shown. The electro-optical component comprises a silicon layer 11, on top of which a silicon oxide layer 12 is arranged to provide a refractive index contrast layer. A first InSb layer 13 is arranged on top of the silicon oxide layer 12. An erbium and oxygen implanted silicon waveguide 14 is embedded in the first InSb layer 13 and is also arranged on top of the silicon dioxide layer 12. In some embodiments, the waveguide 14 and the InSb 13 may be arranged directly on the silicon layer 11. Both the waveguide 14 and the first InSb layer 13 are covered by a second InSb layer 15, which provides a barrier layer. A niobium nitride superconducting resonator 16 is arranged on top of the second InSb layer 15.

[0033] By providing an InSb layer 15 between the waveguide 14 and the superconducting resonator 16, photons escaping from the waveguide 14 are blocked from striking the superconducting resonator 16. As will be appreciated by those skilled in the art, other materials, such as other narrow bandgap semiconductors, may be used to provide a barrier between the waveguide 14 and the superconducting resonator 16, provided that they are optically opaque to light of wavelengths in the 1550 nm range used in the waveguide 14.

[0034] refer to Figure 1 and Figure 2 , the structure of the waveguide 14 is developed. The waveguide 14 is formed of a silicon layer which is implanted with erbium and oxygen to form erbium oxygen centres. The waveguide 14 has a rectangular cross section with a height of 300 nm and a width of 500 nm. Figure 2 The trace of the waveguide 14 on the silicon oxide layer 12 is shown when viewed from above. The path includes nine parallel linear sections 20, each section is 300 μm long and the spacing between each section is 10 μm. Adjacent sections 20 are connected by 180 degree turns 21 with a bending radius of 5 μm, which are located at alternating ends of the linear sections so that the sections form a single tortuous path.

[0035] refer to Figure 1 and Figure 3 , the structure of the superconducting resonator 16 is developed. The superconducting resonator 16 is composed of niobium nitride and has a rectangular cross section with a height of 100 nm and a width of 1000 nm. Figure 3 The footprint of the resonator 16 on the second InSb layer 15 is shown when viewed from above. The resonator comprises a lumped capacitor portion 31 and a coupling portion 32.

[0036] In this embodiment, niobium nitride (NbN) is used as a superconductor, but other materials (such as Al and Nb) can also be used. The cross-section of each channel of the superconducting resonator has a height of 100nm and a width of 1000nm. In this embodiment, the coupling portion 32 of the superconducting resonator includes 10 parallel tracks 33, which are about 250μm long and are separated by a distance of about 30μm. Adjacent tracks are connected at alternating ends by straight connection parts 34 arranged at 90 degrees to the parallel tracks 33. The outermost tracks 33a, 33b have a larger linear range, extending about 50μm beyond the coupling portion 32. Five additional tracks 36 protrude from each of these extensions 35. The additional tracks 36 are arranged at 90 degrees to the extension 35 and point to the opposite extension. The additional tracks 36 are adjacent to the tracks extending from the opposite extension so that they alternate and form a lumped capacitor 31.

[0037] Those skilled in the art will appreciate that the exact geometry of the superconducting resonator can be altered to meet the needs of coupling with a superconducting quantum computer. For example, the lumped capacitor portion 31 can be modified to achieve the resonant frequency. The superconducting resonator and the meandering waveguide structure should be of approximately the same size, and the superconducting resonator should be directly on top of the meandering waveguide structure so that the erbium spins in the waveguide are "inductively coupled" to the superconducting resonator.

[0038] refer to Figure 4 (a) to (f) of the present invention describe a method for producing an electro-optical component according to the present invention. Figure 4 As shown in (a) of FIG. 1 , a silicon-on-insulator (SOI) substrate 40 is provided, and the substrate 40 includes a lower silicon layer 11 and an upper silicon layer 41, with a silicon oxide layer 12 arranged therebetween. The substrate 40 is cooled to 77 K, and then ion implantation is used to implant erbium into the upper silicon layer 41 at an energy between 50 keV and 1300 keV until the average concentration of erbium reaches 1×10 17 cm -3 Then oxygen is implanted into the upper silicon layer 41 at an energy between 10keV and 150keV, with an average concentration of 1×10 19 cm -3 .

[0039] The implanted SOI was then annealed at 450°C for 30 minutes, then at 620°C for 180 minutes, and then at 850°C for 30 seconds.

[0040] Next reference Figure 2 and Figure 4In (b), the upper silicon layer 41 is processed using known photolithography and etching processes to form the waveguide 14. The portion of the upper silicon layer 41 that does not form part of the waveguide is completely etched to the oxide layer 12. The waveguide 14 is arranged along the Figure 2 The curved path shown has the above dimensions.

[0041] like Figure 4 As shown in (c) and (d) in FIG. 1 , the first InSb layer 13 is then deposited to a thickness of 500 nm. Figure 4 As shown, in areas without waveguides 14, the layer 13 extends beyond the height of the waveguides 14. Directly above the waveguides 14, the surface of the first InSb layer 13 is distorted and there are topographical features 42. Such features 42 will affect any subsequent layers (e.g., superconducting resonators 16), so a chemical mechanical planarization process is performed on the device and the top of the first InSb layer 13 is removed until the surface 43 is roughly flush with the upper surface 14a of the waveguide 14.

[0042] After planarization, a second InSb layer 15 is then deposited to a thickness of 30 nm, as Figure 4 On top of the second InSb layer 15, a superconducting resonator 16 is deposited using known photographic techniques, such as Figure 3 and Figure 4 As shown in (f) in FIG. , as described above, the geometry of this layer can be adjusted according to the specific needs of the device.

[0043] The device may undergo further processing steps to allow its integration into quantum systems and / or to provide protection for the components.

[0044] In use, the device is arranged in a cryostat and cooled to a temperature that results in a low probability of thermal excitation to the first excited state of the superconducting resonator, typically 10mK to 200mK; a magnetic field between 0.01T and 0.5T is also required. The waveguide 14 is operably coupled to a 1550nm light source that transmits a coherent optical signal from an external photonic quantum computer (not shown). The light is absorbed by the erbium centers in the waveguide 14 and changes their spin state; the spin state of the erbium centers is coupled to the superconducting resonator 16 through the InSb layer 15, allowing a coherent transfer of quantum states from optical wavelengths to microwave wavelengths, thereby allowing the interface of photonic quantum computers and superconducting quantum computers.

[0045] refer to Figure 5 and Figure 6 , another electro-optical component 110 according to the present invention is described. The structure of the electro-optical component 110 generally follows that of the electro-optical component 10, corresponding features having the same numbering, increased by 100.

[0046] Figure 5A schematic cross section of an electro-optical component 110 according to the present invention is shown. The electro-optical component 110 includes a silicon layer 111, on top of which a silicon oxide layer 112 is arranged to provide an insulating layer. An erbium and oxygen implanted silicon waveguide 114 is arranged on top of the silicon oxide layer 112. The difference between this embodiment and the previous embodiment lies in the composition of the barrier layer. A gold layer 130 is arranged on top of the waveguide 114 and the silicon oxide layer 112. In some embodiments, the waveguide 114 and the gold can be arranged directly on the silicon layer 111. The waveguide 114 and the gold layer 130 are covered by an Al2O3 layer 131. The combined gold layer 130 and the Al2O3 layer 131 provide a barrier layer. A niobium nitride superconducting resonator 116 is arranged on top of the Al2O3 layer 131.

[0047] By providing a gold layer 130 and an Al2O3 131 barrier layer between the waveguide 114 and the superconducting resonator 116, photons escaping from the waveguide 114 are blocked from striking the superconducting resonator 116. The use of a combination of two materials is advantageous because it allows their properties to fit the two functions of the barrier layer, namely being optically opaque to light having a wavelength of 1550 nm and being electrically insulating. The gold layer 130 blocks light more effectively than narrow bandgap semiconductors, and the Al2O3 layer 131 provides excellent electrical insulation. As will be appreciated by those skilled in the art, other materials (e.g., other metals that reflect at 1550 nm) may be used in place of the gold layer 130, and other insulators may be used in place of the Al2O3 layer 131.

[0048] The geometry of the waveguide 114 and superconducting resonator 116 is the same as in the previous embodiment. Again, those skilled in the art will appreciate that the precise geometry of the superconducting resonator can be varied to meet the needs of coupling to a superconducting quantum computer. For example, the lumped capacitor portion 31 can be modified to achieve the desired resonant frequency. The superconducting resonator and the meandering waveguide structure should have approximately the same size, and the superconducting resonator should be directly located on top of the meandering waveguide structure so that the erbium spins in the waveguide are "inductively coupled" to the superconducting resonator.

[0049] refer to Figure 6 (a)-(d) in FIG. 1 describe a method for producing an electro-optical component 110 according to the present invention.

[0050] The steps up to and including etching the waveguide 114 are the same as those described above. Figure 6 In (a) the deposition of a gold layer 130 is shown in place of the first InSb layer 13. Sufficient gold is deposited to ensure that photons escaping from the waveguide 114 cannot reach the superconducting resonator 116.

[0051] On top of the gold layer 130, an Al2O3 layer 131 is deposited. Figure 6As shown in (b) and (c) in FIG. 1 , above the waveguide 114, the surface of the Al2O3 layer 131 is distorted and there are topographical features 142. Such features 142 will affect any subsequent layers (e.g., the superconducting resonator 116), so a chemical mechanical planarization process is performed on the device and the top of the Al2O3 layer 131a is removed until the surface 143 is roughly flush with the upper surface 130a of the gold layer 130.

[0052] After planarization, a second Al2O3 layer 131 is then deposited, such as Figure 6 As shown in (d) in FIG. 1 , a superconducting resonator 116 is deposited on top of the Al 2 O 3 layer 131 as described above.

[0053] The device may undergo further processing steps to allow its integration into quantum systems and / or to provide protection for the components.

[0054] One or more embodiments have been described above by way of example only. Many variations are possible without departing from the scope of protection provided by the appended claims.

Claims

1. An electro-optical component, comprising: An erbium and oxygen implanted silicon waveguide and a superconducting microwave resonator, wherein a barrier layer of an opaque material is arranged between the waveguide and the microwave resonator, and wherein the microwave resonator coherently couples to the spin state of the erbium.

2. The electro-optical component according to claim 1, wherein The opaque material is optically opaque to light at 1550 nm.

3. The electro-optical component according to claim 1 or 2, wherein: Optically opaque materials are narrow bandgap semiconductors.

4. An electro-optical component according to any one of the preceding claims, wherein The optically opaque material is InSb.

5. The electro-optical component according to claim 1 or 2, wherein: The barrier layer comprises two layers of different materials.

6. The electro-optical component according to claim 5, wherein The first layer includes reflective metal.

7. The electro-optical component according to claim 5 or 6, wherein: The first layer comprises gold.

8. The electro-optical component according to any one of claims 5 to 7, wherein: The second layer includes an electrical insulator.

9. The electro-optical component according to any one of claims 5 to 8, wherein: The second layer includes Al2O3.

10. An electro-optical component according to any one of the preceding claims, wherein The thickness of the barrier layer is between 5 nm and 500 nm.

11. An electro-optical component according to any one of the preceding claims, wherein The thickness of the barrier layer is 30 nm.

12. An electro-optical component according to any one of the preceding claims, wherein The silicon waveguide is arranged on a silicon dioxide layer.

13. A quantum communication device, comprising the electro-optical component according to any one of claims 1 to 7, and further comprising a superconducting quantum computer and a photonic quantum computer; wherein: The superconducting quantum computer is operably coupled to the microwave resonator, and the qubits of the photonic quantum computer are composed of photons in the waveguide.

14. A method for producing an electro-optical component, the method comprising: -Provide silicon substrate; - implanting erbium and oxygen into the silicon substrate; - annealing the silicon substrate; - defining at least one optical waveguide on said silicon substrate; - depositing a barrier layer of opaque material on said waveguide; - Fabricating a superconducting resonator structure on said semiconductor.

15. The method for producing an electro-optical component according to claim 14, wherein: The silicon substrate is a silicon-on-insulator substrate.

16. The method for producing an electro-optical component according to claim 14 or 15, wherein: The silicon substrate comprises: a silicon base layer, a silicon dioxide layer and a silicon surface layer.

17. The method for producing an electro-optical component according to claim 16, wherein: The waveguide is defined by the silicon surface layer.

18. The method for producing an electro-optical component according to any one of claims 14 to 17, wherein: The thickness of the waveguide is between 100 nm and 1000 nm.

19. The method for producing an electro-optical component according to claim 16, wherein: The thickness of the waveguide is 300 nm.

20. The method for producing an electro-optical component according to any one of claims 14 to 19, wherein: The erbium is implanted before the oxygen.

21. A method for producing an electro-optical component according to any one of claims 14 to 20, wherein: The erbium is implanted at an energy between 20 keV and 4000 keV.

22. A method for producing an electro-optical component according to any one of claims 14 to 21, wherein: The average concentration of erbium is 1×10 14 cm -3 and 1×10 19 cm -3 between.

23. A method for producing an electro-optical component according to any one of claims 14 to 22, wherein: The oxygen is implanted at an energy between 5 keV and 300 keV.

24. A method for producing an electro-optical component according to any one of claims 14 to 23, wherein: The annealing step includes heating the silicon substrate to a first temperature for a first time period, then to a second temperature for a second time period, and then to a third temperature for a third time period; wherein the second temperature is higher than the first temperature and the third temperature is higher than the second temperature.

25. A method for producing an electro-optical component according to any one of claims 14 to 24, wherein: The annealing step includes heating the silicon substrate to between 400°C and 500°C for 20 minutes to 60 minutes, then heating to between 550°C and 650°C for 120 minutes to 300 minutes, and then heating to between 700°C and 1000°C for 10 seconds to 100 seconds.

26. A method for producing an electro-optical component according to any one of claims 14 to 25, wherein: The barrier layer includes a narrow bandgap material.

27. A method for producing an electro-optical component according to any one of claims 14 to 26, wherein: The barrier layer includes InSb.

28. A method for producing an electro-optical component according to any one of claims 14 to 27, wherein: The barrier layer has a thickness of 5 nm to 500 nm.

29. A method for producing an electro-optical component according to any one of claims 14 to 28, wherein: An optically opaque layer is deposited in two steps; first, at a thickness approximately equal to the height of the waveguide; and second, at a thickness between 5 nm and 500 nm; wherein the first deposition is chemically mechanically planarized prior to depositing the second layer.

30. A method for producing an electro-optical component according to any one of claims 14 to 29, wherein: The resonator consists of niobium nitride.

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