Optical waveguide, quantum operation device, and method for manufacturing optical waveguide

Abstract

The optical waveguide has a diamond layer having a first face and a second face, and including a complex defect; a first cladding layer in contact with the first face; a second cladding layer in contact with the second face, and having a polarity; and a metal layer in Schottky contact with the second cladding layer.

Description

Technical Field

[0001] This invention relates to optical waveguides, quantum computing devices, and methods for manufacturing optical waveguides. Background Technology

[0002] An optical waveguide for a quantum computing device that uses color centers as composite defects in diamond layers was studied.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: US Patent No. 8,837,544

[0006] Patent Document 2: Japanese Patent Publication No. 2007-526639

[0007] Patent Document 3: U.S. Patent Application Publication No. 2007 / 0277730 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] Quantum computing devices are used at extremely low temperatures of around K, but in conventional optical waveguides, the charged state of composite defects tends to become unstable at extremely low temperatures.

[0010] The purpose of this disclosure is to provide an optical waveguide, a quantum computing device, and a method for manufacturing the optical waveguide that can improve the stability of the charged state of composite defects.

[0011] Methods for solving problems

[0012] According to one aspect of this disclosure, an optical waveguide is provided, comprising: a diamond layer having a first surface and a second surface, and including composite defects; a first cladding layer in contact with the first surface; a second cladding layer in contact with the second surface and having polarity; and a metal layer having a Schottky contact with the second cladding layer.

[0013] Invention Effects

[0014] According to this disclosure, the stability of the charged state of composite defects can be improved. Attached Figure Description

[0015] Figure 1 This is a perspective view showing the optical waveguide of the first embodiment.

[0016] Figure 2 This is a cross-sectional view showing the optical waveguide of the first embodiment.

[0017] Figure 3This is a diagram showing the band structure in the case where the cladding of the optical waveguide in the first embodiment is an AlN layer.

[0018] Figure 4 This is a cross-sectional view (1) showing a method for manufacturing an optical waveguide according to the first embodiment.

[0019] Figure 5 This is a cross-sectional view (2) showing a method for manufacturing an optical waveguide according to the first embodiment.

[0020] Figure 6 This is a cross-sectional view (3) showing a method for manufacturing an optical waveguide according to the first embodiment.

[0021] Figure 7 This is a cross-sectional view (4) showing a method for manufacturing an optical waveguide according to the first embodiment.

[0022] Figure 8 This is a cross-sectional view (5) showing a method for manufacturing an optical waveguide according to the first embodiment.

[0023] Figure 9 This is a cross-sectional view (6) showing a method for manufacturing an optical waveguide according to the first embodiment.

[0024] Figure 10 This is a diagram showing the band structure in the case where the cladding of the optical waveguide in the first embodiment is a GaN layer.

[0025] Figure 11 This is a diagram showing the band structure in the case where the cladding of the optical waveguide in the first embodiment is a BN layer.

[0026] Figure 12 This is a graph showing the relationship between the wavelength of light and the transmittance in Au layers of various thicknesses.

[0027] Figure 13 This is a graph showing the relationship between the wavelength of light and the transmittance in various metal layers.

[0028] Figure 14 It is a diagram (1) showing the intensity distribution of propagating light in the 0th transverse mode in a cross section perpendicular to the length direction of the diamond layer.

[0029] Figure 15 Figure 2 shows the intensity distribution of propagating light in the 0th transverse mode in a cross section perpendicular to the length direction of the diamond layer.

[0030] Figure 16 Figure 3 shows the intensity distribution of propagating light in the 0th transverse mode in a cross section perpendicular to the length direction of the diamond layer.

[0031] Figure 17This is a diagram (Figure 1) showing the intensity distribution of the propagating light of the first mode in a cross section perpendicular to the length direction of the diamond layer.

[0032] Figure 18 Figure 2 shows the intensity distribution of the propagating light of the first mode in a cross section perpendicular to the length direction of the diamond layer.

[0033] Figure 19 Figure 3 shows the intensity distribution of the propagating light of the first mode in a cross section perpendicular to the length direction of the diamond layer.

[0034] Figure 20 This is a block diagram illustrating a quantum computing device according to a second embodiment. Detailed Implementation

[0035] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, in this specification and the accompanying drawings, elements having substantially the same functional structure are sometimes omitted from repeated descriptions by using the same reference numerals.

[0036] (First Implementation)

[0037] First, the first embodiment will be described. The first embodiment relates to an optical waveguide. The optical waveguide of the first embodiment is used, for example, in quantum computing devices such as quantum computers. Figure 1 This is a perspective view showing the optical waveguide of the first embodiment. Figure 2 This is a cross-sectional view showing the optical waveguide of the first embodiment.

[0038] like Figure 1 and Figure 2 As shown, the optical waveguide 1 of the first embodiment has a support substrate 21, a diamond layer 10, a cladding layer 22 and a metal layer 30.

[0039] The support substrate 21 is, for example, a sapphire substrate. The refractive index of the support substrate 21 is lower than that of the diamond layer 10. The refractive index of sapphire is 1.76, and that of diamond is 2.419. The support substrate 21 can also be, for example, an AlN substrate, a BN substrate, or a GaN substrate. The refractive index of AlN is 2.1, that of BN is 2.17, and that of GaN is 2.38. The support substrate 21 is an example of a first cladding layer.

[0040] The diamond layer 10 has a first surface 11 and a second surface 12. A support substrate 21 is in contact with the first surface 11. The second surface 12 is the side opposite to the first surface 11. The thickness of the diamond layer 10 is, for example, about 250 nm. The diamond layer 10 includes color centers 13. Color centers 13 are, for example, nitrogen-vacancy centers (NV centers) composed of nitrogen and vacancies. Color centers 13 can also be silicon-vacancy centers (SiV centers) composed of silicon and vacancies, germanium-vacancy centers (GeV centers) composed of germanium and vacancies, tin-vacancy centers (SnV centers) composed of tin and vacancies, lead-vacancy centers (PbV centers) composed of lead and vacancies, or boron-vacancy centers (BV centers) composed of boron and vacancies. Color center 13 is an example of a composite defect.

[0041] Cladding layer 22 is in contact with the second surface 12 of diamond layer 10. Cladding layer 22 may cover the side surface of diamond layer 10, that is, the surface connecting the first surface 11 and the second surface 12. The thickness of cladding layer 22 is, for example, about 100 nm. Cladding layer 22 is polar in the thickness direction. That is, cladding layer 22 does not have a reverse center of symmetry in the thickness direction. Cladding layer 22, for example, has spontaneous polarization oriented from the metal layer 30 side to the diamond layer 10 side. Cladding layer 22, for example, contains a nitride semiconductor. The band gap of the nitride semiconductor is preferably 3.4 eV or more and 6.4 eV or less at room temperature (300 K). Cladding layer 22 is, for example, an AlN layer. The refractive index of cladding layer 22 is lower than that of diamond layer 10. Cladding layer 22 may be, for example, a BN layer or a GaN layer. The material of cladding layer 22 may be a mixed crystal containing two or three of Al, B and Ga. Cladding layer 22 is an example of a second cladding layer.

[0042] Metal layer 30 is in Schottky contact with cladding layer 22. Metal layer 30 is, for example, made of a metal with a work function greater than the electron affinity of the nitride semiconductor constituting cladding layer 22. The thickness of metal layer 30 is, for example, about 5 nm. Metal layer 30 is, for example, an Au layer. Metal layer 30 can also be an Ag layer or a Cu layer. Metal layer 30 can also be an Al layer.

[0043] Here, the characteristics of the optical waveguide 1 of the first embodiment will be explained. Figure 3 This is a diagram showing the band structure when the cladding 22 of the optical waveguide 1 in the first embodiment is an AlN layer. Figure 3 The results of a one-dimensional Poisson simulation are shown. In this simulation, the ambient temperature was 5K, the support substrate 21 was a sapphire substrate, the diamond layer 10 was 250nm thick, the cladding layer 22 was 100nm thick AlN, and the metal layer 30 was 5nm thick Au. The composite defect is the NV center. Figure 3 The horizontal axis represents the position in the depth direction with reference to the interface between the metal layer 30 and the cladding 22, and the vertical axis represents the potential energy of electrons formed by the charge distribution.

[0044] like Figure 3 As shown, through the Schottky contact between the metal layer 30 and the cladding 22, the cladding 22 is essentially depleted throughout its thickness in a state without bias, i.e., at 0 bias. This means that the AlN constituting the cladding 22 has a band gap as large as 6.4 eV, and at a set temperature of 5 K, there are no defect energy levels capable of releasing sufficient hot electrons. Therefore, the cladding 22 is essentially depleted throughout its thickness through the Schottky contact.

[0045] Furthermore, the cladding 22 is polarized in the thickness direction, and for example, it has spontaneous polarization oriented from the metal layer 30 side to the diamond layer 10 side. Therefore, the cladding 22 contains polarization charge (σ) caused by its own spontaneous polarization. + Therefore, in order to satisfy the charge neutrality condition, a considerable amount of negative charge needs to be induced at the interface between cladding 22 and diamond layer 10. However, the band gap of diamond is also large, reaching 5.4 eV. At 5 K, the polarization charge (σ) of cladding 22 needs to be compensated separately. + The thermionic electrons are insufficient. Therefore, a negative fixed charge (σ) is induced near the second surface 12 of the diamond layer 10. - The density of negative fixed charge is, for example, 10. 12 / cm 2 .

[0046] Furthermore, the band shift at the interface between the cladding 22 and the diamond layer 10 is small, so the Fermi energy of the diamond layer 10 is generally higher than the activation energy (-2.58 eV) of the color center 13 in the thickness direction. Therefore, it is easy to form a negatively charged state for the color center 13.

[0047] According to this first embodiment, even at extremely low temperatures of around 5K, the negatively charged state of the color center 13 can be easily maintained. That is, according to the first embodiment, the stability of the charged state of the color center 13 can be improved.

[0048] Next, the manufacturing method of the optical waveguide 1 according to the first embodiment will be described. Figures 4-9 This is a cross-sectional view showing a method for manufacturing the optical waveguide 1 according to the first embodiment.

[0049] First, such as Figure 4 As shown, a diamond substrate 41 is prepared, and a diamond layer 10 is formed on the diamond substrate 41. For example, a type IIa diamond substrate with a nitrogen concentration of less than 5 ppb is used as the diamond substrate 41. The diamond layer 10 can be formed by, for example, chemical vapor deposition (CVD).

[0050] Color centers 13 are formed at the desired depth by temporarily adding a gas containing impurity atoms to the feed gas during the formation of the diamond layer 10. For example, NH3 gas is temporarily added when forming NV centers as color centers 13. This allows for the in-situ formation of color centers 13.

[0051] Next, as Figure 5 As shown, for example, a focused ion beam (FIB) is used to process the diamond layer 10 into the shape of the core layer of an optical waveguide.

[0052] Then, as Figure 6 As shown, a cladding layer 22 is formed on the diamond layer 10. The cladding layer 22 can be formed, for example, by metal-organic chemical vapor deposition (MOCVD). The cladding layer 22 is formed to cover the second surface 12 of the diamond layer 10. The cladding layer 22 can cover the side surface of the diamond layer 10. The cladding layer 22 can also be formed on the diamond substrate 41.

[0053] Next, as Figure 7 As shown, a transfer substrate 42 is attached to the upper surface of the cladding layer 22. Next, the diamond substrate 41 is removed by grinding.

[0054] Then, as Figure 8 As shown, the diamond layer 10 is bonded to the support substrate 21. The first surface 11 of the diamond layer 10 contacts the support substrate 21. Next, the transfer substrate 42 is removed.

[0055] Next, as Figure 9 As shown, a metal layer 30 is formed on the cladding 22. In the formation of the metal layer 30, for example, a resist film with openings in a predetermined region of the metal layer 30 is formed using photolithography. This resist film is then used as a growth mask to form an Au layer via vapor deposition. The resist film and the Au layer thereon are then removed together. In other words, the metal layer 30 can be formed by vapor deposition and stripping.

[0056] In this way, the optical waveguide 1 of the first embodiment can be manufactured.

[0057] Alternatively, color centers 13 can be formed on the diamond substrate 41 by means of ion implantation, and the diamond substrate 41 can be processed into the shape of the core layer of the optical waveguide as the diamond layer 10.

[0058] As described above, the cladding layer 22 can be a GaN layer or a BN layer. Figure 10 This is a diagram showing the band structure when the cladding 22 of the optical waveguide 1 in the first embodiment is a GaN layer. Figure 11This is a diagram showing the band structure when the cladding 22 in the optical waveguide 1 of the first embodiment is a BN layer.

[0059] like Figure 10 As shown, when the cladding 22 is a GaN layer, it is almost entirely depleted without bias, inducing a negative fixed charge near the second surface 12 of the diamond layer 10, resulting in the color center 13 easily becoming negatively charged. Similarly, as... Figure 11 As shown, when the cladding 22 is a BN layer, the cladding 22 is almost entirely depleted in the absence of bias voltage, and negative fixed charges are induced near the second surface 12 of the diamond layer 10, forming a state where the color center 13 is prone to being negatively charged.

[0060] For the optical waveguide 1, light can be irradiated through the supporting substrate 21, through the metal layer 30 and the cladding layer 22, or directly onto the diamond layer 10. Here, the relationship between the wavelength of light and the transmittance in the Au layer will be explained. Figure 12 This is a graph showing the relationship between the wavelength of light and the transmittance in Au layers of various thicknesses. Figure 12 The horizontal axis represents the wavelength of the incident light, and the vertical axis represents the transmittance.

[0061] When the wavelength of light propagating using optical waveguide 1 is 520nm to 740nm, such as Figure 12 As shown, if the thickness of the Au layer is 10 nm or less, a transmittance of 60% or more can be obtained. Therefore, the thickness of the Au layer used for the metal layer 30 is preferably 10 nm or less, and more preferably 5 nm or less. For example, when the thickness of the Au layer is 5 nm, a transmittance of about 80% can be obtained for light with a wavelength of 650 nm.

[0062] As described above, the metal layer 30 can be an Ag layer, a Cu layer, or an Al layer. Here, the relationship between the material of the metal layer 30 and its transmittance will be explained. Figure 13 This is a graph showing the relationship between the wavelength of light and the transmittance in various metal layers. Figure 13 The horizontal axis represents the wavelength of the incident light, and the vertical axis represents the transmittance. Additionally, the thickness of each metal layer is 5 nm.

[0063] When the wavelength of light propagating using optical waveguide 1 is 520nm to 740nm, such as Figure 13 As shown, a transmittance of 70% or more is obtained in the Au layer, Ag layer, or Cu layer. On the other hand, the transmittance of the Al layer is 40% or less. Therefore, when light is irradiated onto the diamond layer 10 through the metal layer 30 and the cladding layer 22, the metal layer 30 is preferably an Au layer, an Ag layer, or a Cu layer.

[0064] Next, the core diameter dependence of the propagation characteristics of the 0th transverse mode in the optical waveguide 1 of the first embodiment will be explained. Figures 14-16 This is a diagram showing the intensity distribution of propagated light in the 0th transverse mode in a cross section perpendicular to the length direction of the diamond layer 10. Figure 14 The distribution of light intensity is shown when the cross-sectional shape of the diamond layer 10 is such that one side has a length of 500 nm. Figure 15 The distribution of light intensity is shown when the cross-sectional shape of the diamond layer 10 is such that one side has a length of 250 nm. Figure 16 The distribution of light intensity is shown when the cross-sectional shape of the diamond layer 10 is such that one side has a length of 150 nm. Figures 14-16 The horizontal axis represents the position in the direction parallel to the first surface 11 (width direction) with the center of the diamond layer 10 as the reference, and the vertical axis represents the position in the direction perpendicular to the first surface 11 (thickness direction) with the center of the diamond layer 10 as the reference. In this calculation, light is considered as a continuous wave with a Gaussian intensity distribution, that is, a traveling wave with a wavenumber vector in the direction perpendicular to the cross-section of the optical waveguide 1.

[0065] like Figures 14 to 16 As shown, single-mode propagation is achieved in the diamond layer 10 used as the core under any circumstances. However, when the length of one side is less than 150 nm, the leakage electromagnetic field (evanescent field) to the support substrate 21 side becomes significant, which may cause propagation loss. Therefore, when the cross-sectional shape of the diamond layer 10 is square, the length of one side is preferably 150 nm or more, and generally, the minor axis is preferably 150 nm or more.

[0066] Next, the core diameter dependence of the propagation characteristics of the higher-order modes (1st-order modes) in the optical waveguide 1 of the first embodiment will be explained. Figures 17-19 This is a diagram showing the intensity distribution of propagated light in the first mode in a cross section perpendicular to the length direction of the diamond layer 10. Figure 17 The distribution of light intensity is shown when the cross-sectional shape of the diamond layer 10 is such that one side has a length of 250 nm. Figure 18 The distribution of light intensity is shown when the cross-sectional shape of the diamond layer 10 is such that one side has a length of 200 nm. Figure 19 The distribution of light intensity is shown when the cross-sectional shape of the diamond layer 10 is such that one side has a length of 150 nm. Figures 17-19The horizontal axis represents the position in the direction parallel to the first surface 11 (width direction) with the center of the diamond layer 10 as the reference, and the vertical axis represents the position in the direction perpendicular to the first surface 11 (thickness direction) with the center of the diamond layer 10 as the reference. In this calculation, light is considered as a continuous wave with a Gaussian intensity distribution, that is, a traveling wave with a wavenumber vector in the direction perpendicular to the cross-section of the optical waveguide 1.

[0067] like Figures 17-19 As shown, if the length of one side exceeds 250 nm, waveguide propagation based on higher-order modes may not be negligible. Therefore, when the cross-sectional shape of the diamond layer 10 is square, the length of one side is preferably less than 250 nm, and generally, the minor axis is preferably less than 250 nm.

[0068] Based on the above, the minor axis of the cross section perpendicular to the length direction of the diamond layer 10 is preferably 150 nm or more and 250 nm or less, more preferably 170 nm or more and 230 nm or less.

[0069] Furthermore, the metal layer 30 does not need to cover the entire upper surface of the cladding 22. Preferably, the metal layer 30 overlaps at least with the color center 13 when viewed from a direction perpendicular to the second surface 12.

[0070] (Second Implementation)

[0071] Next, a second embodiment will be described. The second embodiment relates to a quantum computing device including the optical waveguide 1 according to the first embodiment. Figure 20 This is a block diagram illustrating a quantum computing device according to a second embodiment.

[0072] like Figure 20 As shown, the quantum computing device 2 of the second embodiment has multiple optical waveguides 1. The quantum computing device 2 includes a computing unit 51, a He cryostat 52, a beam splitter 53, a first single-photon detector 54A, a second single-photon detector 54B, a comparator 55, and an A / D (analog-to-digital) converter 56. The quantum computing device 2 also includes multiple control systems 61 and multiple optical waveguides 62.

[0073] The cryostat 52 houses multiple optical waveguides 1 and cools them to extremely low temperatures. The control system 61 is configured for each color center 13 constituting a qubit, applying magnetic fields, electric fields, microwaves, lasers, etc., to the color center 13. For example, magnetic and electric fields are used to adjust the intrinsic energy of the color center 13 (adjusting the frequency of photons for state readout), microwaves are used to control the quantum state of the color center 13, and lasers are used for state readout (generation of single photons). Optical waveguides 62 are positioned relative to each optical waveguide 1, incident through beamsplitter 53 in any two paths. Each optical waveguide 62 is configured such that the optical path length from the color center 13 to the beamsplitter 53 is approximately equal.

[0074] Beam splitter 53 branches the incident light, outputting it to a first single-photon detector 54A and a second single-photon detector 54B, respectively. The first single-photon detector 54A and the second single-photon detector 54B detect single photons from the light output from beam splitter 53. Comparator 55 compares the detection signals of the single photons in the first single-photon detector 54A and the second single-photon detector 54B. For example, comparator 55 determines which single-photon detector, the first single-photon detector 54A or the second single-photon detector 54B, detected the photon in what order. Arithmetic unit 51 analyzes the output from comparator 55. A / D converter 56 converts the analog control signals output from arithmetic unit 51 into digital signals and outputs them to each control system 61.

[0075] The quantum computing device 2 includes an optical waveguide 1, and color center 13 is used as a qubit. Therefore, even at extremely low temperatures, the charged state of color center 13 remains stable, and the analytical results can be obtained with excellent reliability.

[0076] The preferred embodiments have been described in detail above, but are not limited to the embodiments described above. Various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

[0077] Explanation of reference numerals in the attached figures

[0078] 1: Optical waveguide

[0079] 2: Quantum computing device

[0080] 10: Diamond layer

[0081] 13: Lust

[0082] 21:Support base plate

[0083] 22: Cladding

[0084] 30: Metal layer

Claims

1. An optical waveguide, characterized in that, This optical waveguide has the following characteristics: The diamond layer has a first facet and a second facet that are opposite to each other and contains composite defects that are used as qubits; The first cladding layer is in contact with the first surface; A second cladding layer, which is in contact with the second surface, and is made of semiconductor; and A metal layer, which makes a Schottky contact with the second cladding layer, is configured to face the diamond layer across the second cladding layer. The second cladding layer has spontaneous polarization oriented from the metal layer side to the diamond layer side.

2. The optical waveguide according to claim 1, characterized in that, The refractive indices of the first cladding layer and the second cladding layer are less than the refractive index of the diamond layer.

3. The optical waveguide according to claim 1 or 2, characterized in that, The metal layer overlaps at least with the composite defect when viewed from above.

4. The optical waveguide according to claim 1 or 2, characterized in that, The composite defect consists of nitrogen, silicon, germanium, tin, lead or boron, and vacancies.

5. The optical waveguide according to claim 1 or 2, characterized in that, The second cladding layer comprises a nitride semiconductor.

6. The optical waveguide according to claim 5, characterized in that, The band gap of the nitride semiconductor is above 3.4 eV and below 6.4 eV at room temperature.

7. The optical waveguide according to claim 1 or 2, characterized in that, The minor axis of the cross section perpendicular to the length direction of the diamond layer is greater than 150 nm and less than 250 nm.

8. The optical waveguide according to claim 1 or 2, characterized in that, The metal layer contains Au, Cu, or Ag. The thickness of the metal layer is less than 10 nm.

9. The optical waveguide according to claim 1 or 2, characterized in that, The first cladding layer has a supporting substrate.

10. A quantum computing device, characterized in that, The quantum computing device includes the optical waveguide as described in any one of claims 1 to 9.

11. A method for manufacturing an optical waveguide, characterized in that, The manufacturing method of this optical waveguide includes the following steps: A diamond layer is formed having a first and a second facet that are opposite to each other and containing composite defects that serve as qubits; A first cladding layer is formed that is in contact with the first surface, and a second cladding layer that is in contact with the second surface and is made of semiconductor. as well as A metal layer is formed that makes a Schottky contact with the second cladding and is positioned opposite the diamond layer through the second cladding. The second cladding layer has spontaneous polarization oriented from the metal layer side to the diamond layer side.

12. The method for manufacturing an optical waveguide according to claim 11, characterized in that, The refractive indices of the first cladding layer and the second cladding layer are less than the refractive index of the diamond layer.

13. The method for manufacturing an optical waveguide according to claim 11 or 12, characterized in that, The metal layer overlaps at least with the composite defect when viewed from above.

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