Quantum bit material and method for producing quantum bit material

Abstract

This quantum bit material includes an oxide containing a first element and a second element, or a host material of an oxide containing a second element, a third element, and a fourth element. The host material has a doping element. The doping element is a lanthanoid element. The first element is any element from Groups 1 to 14. The second element is any element from Groups 14 to 17. The third element and the fourth element are any element from Group 1, Group 2, and Groups 4 to 14, a lanthanoid element other than the doping element, or an actinoid element.

Description

Quantum bit material and method for producing the same

[0001] This application claims priority to U.S. Provisional Application No. 63 / 534,584, filed August 25, 2023, which relates to quantum bit materials and methods for fabricating quantum bit materials.

[0002] As quantum applications develop, materials capable of storing quantum information are being researched.

[0003] For example, diamond with nitrogen-vacancy centers is one of the typical examples for storing quantum information (see, for example, Patent Document 1). The nitrogen-vacancy centers in diamond have an electron spin coherence time (T ２ ) is long. The nitrogen-vacancy center in diamond satisfies the properties required for a quantum bit, and research is being conducted on using the nitrogen-vacancy center as a quantum bit. In addition, host materials other than diamond, such as yttrium aluminum garnet (Y ３ Al ５ O １２ ) has been investigated (for example, Non-Patent Document 1).

[0004] JP 2024-023101 A

[0005] P. Siyushev et al., Nature Communications 5, 3895 (2014).

[0006] Diamond and yttrium aluminum garnet (Y ３ Al ５ O １２ ) are expensive. Also, it is difficult to increase the diameter of these wafers.

[0007] The present disclosure has been made in view of the above problems, and aims to provide a quantum bit material using a new host material and a method for manufacturing the quantum bit material.

[0008] To solve the above problems, the present disclosure provides the following means.

[0009] The quantum bit material according to the first aspect includes a host material that is an oxide containing a first element and a second element, or an oxide containing a second element, a third element, and a fourth element. The host material includes a doping element. The doping element is a lanthanoid element. The first element is any element from Group 1 to Group 14. The second element is any element from Group 14 to Group 17. The third element and the fourth element are any element from Group 1, Group 2, or Group 4 to Group 14, a lanthanoid element other than the doping element, or an actinoid element.

[0010] A method for producing a quantum bit material according to the second aspect includes an ion implantation step of ion-implanting a lanthanoid element as a doping element into an oxide host material, and a heat treatment step of heat-treating the host material into which the ions have been implanted.

[0011] The quantum bit material and the method for manufacturing the quantum bit material according to the above aspects use a new host material, and are expected to have expanded functionality.

[0012] 1 is a schematic diagram of a quantum bit material according to the first embodiment. FIG. 2 is a schematic diagram of a quantum bit material according to a first modification. FIG. 3 is a schematic diagram of a quantum bit material according to a second modification. FIG. 4 shows photoluminescence measurement results for the quantum bit materials of Examples 1 to 21. FIG. 5 shows the relationship between the heat treatment holding time and the luminescence intensity for the quantum bit materials of Examples 22 to 26. FIG. 6 is a schematic diagram of a measurement system for measuring the polarization dependence of a quantum bit material. FIG. 7 shows measurement results of the polarization properties of the quantum bit material of Example 1. FIG. 8 shows the measurement temperature dependence of polarized photoluminescence for the quantum bit material of Example 1. FIG. 9 shows measurement results of optically detected magnetic resonance for the quantum bit material of Example 1. FIG. 10 shows the results of determining the g-factor using the optically detected magnetic resonance measurement results for the quantum bit material of Example 1. FIG. 11 shows measurement results of the polarization properties of the quantum bit material of Example 8. FIG. 12 shows measurement results of the polarization properties of the quantum bit material of Example 15. FIG. 13 shows measurement results of the polarization properties of the quantum bit material of Example 27. FIG. 14 shows the magnetic field strength dependence of the polarization properties of the quantum bit material of Example 27. FIG. 15 shows measurement results of the polarization properties of the quantum bit material of Example 30.

[0013] The present embodiment will be described in detail below with reference to the accompanying drawings. The drawings used in the following description may show enlarged portions characteristic of the present invention for ease of understanding, and the dimensional proportions of each component may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications may be made within the scope of the present invention.

[0014] The quantum bit material according to this embodiment is an oxide into which a doping element is ion-implanted. The doping element is a lanthanoid element. FIG. 1 is a schematic diagram of a quantum bit material 10 according to this embodiment.

[0015] The quantum bit material 10 includes an oxide host material 5. The oxide host material is, for example, an oxide containing a first element 1 and a second element 2.

[0016] The first element 1 is, for example, any element of Groups 1 to 14. The first element 1 may be ionized or may not be ionized. The first element 1 is, for example, Si or Mg.

[0017] The second element 2 is, for example, any one of elements in Groups 14 to 17. The second element 2 may be ionized or may not be ionized. The second element 2 is, for example, O or C.

[0018] Here, an example is shown in which the host material 5 is a binary oxide composed of two elements, but the host material 5 may be a ternary oxide composed of three elements. For example, the oxide host material may be an oxide containing a second element, a third element, and a fourth element. The third element and the fourth element are, for example, any element of Group 1, Group 2, or Group 4 to Group 14, a lanthanoid element other than the lanthanoid element used as a doping element, or an actinide element. For example, the third element is Mg, and the fourth element is Al. It is preferable that the host material 5 contains Mg or Al.

[0019] The host material 5 is, for example, SiO ２ , MgO, MgAl ２ O４ The host material 5 is SiO ２ In this case, the host material 5 may be single-crystal silicon oxide, amorphous silicon oxide, or thermal silicon oxide, regardless of the crystallinity.

[0020] Fig. 2 is a schematic diagram of a quantum bit material 11 according to a first modified example. Fig. 2 is a schematic diagram of a quantum bit material 11 according to a first modified example. Fig. 2 is a schematic diagram of a case where the host material 5 is amorphous silicon oxide, in which elements are irregularly arranged and amorphous. Fig. 3 is a schematic diagram of a case where the host material 5 is thermal silicon oxide, in which the silicon near the surface is oxidized and amorphous.

[0021] The host material 5 contains a doping element 3. The doping element 3 is ion-implanted into the host material 5.

[0022] The doping element 3 is a lanthanoid element. The lanthanoid element is an element having an atomic number from 57 to 71, and is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The doping element 3 is, for example, cerium (Ce). The doping element 3 may include two or more elements.

[0023] In the quantum bit material 10, the doping amount of the doping element 3 is, for example, 1×10 １４ cm －２ When the doping element 3 is doped, defect centers are formed in the host material, so there is no lower limit to the doping amount of the doping element 3. The lower limit of the doping amount of the doping element 3 is, for example, 1×10 ７ cm －２ or more, 1 × 10 １３ cm －２ The doping amount of the doping element 3 may be, for example, 1×10 ７ cm －２ 1x10 or more １４ cm －２ In the quantum bit material 10, the doping amount of the doping element 3 is preferably 1×10 １６ cm －3 The doping amount of the doping element 3 may be, for example, 1×10 ９cm －３ 1x10 or more １６ cm －３ The following is preferred:

[0024] The quantum bit material 10 includes defect centers in the host material 5 by ion-implanting the doping element 3. The defect centers can function as one quantum bit. The concentration of defect centers in the quantum bit material 10 is, for example, 1×10 １４ cm －２ The lower limit of the defect center concentration is not important because a quantum bit can function with just one defect center. The defect center concentration in the quantum bit material 10 is, for example, 1×10 ７ cm －２ or more, 1 × 10 １３ cm －２ The concentration of defect centers in the quantum bit material 10 may be, for example, 1×10 ７ cm －２ 1x10 or more １４ cm －２ The concentration of defect centers in the quantum bit material 10 is preferably, for example, 1×10 １6 cm －3 The concentration of defect centers in the quantum bit material 10 may be, for example, 1×10 ９ cm －３ 1x10 or more １６ cm －３ The following is preferred:

[0025] Next, a description will be given of a method for manufacturing the quantum bit material 10 according to this embodiment. The method for manufacturing the quantum bit material 10 according to this embodiment includes an ion implantation step and a heat treatment step.

[0026] First, a host material 5 is prepared as a substrate for producing the quantum bit material 10. The host material 5 is, for example, the oxide described above. The host material 5 is formed by depositing Al on the surface of a body containing MgO. ２ O ３ The cap layer may be formed on the body containing MgAl. The cap layer suppresses deliquescence of MgO. In the heat treatment process described later, the body and a part of the cap layer react to form MgAl ２ O ４ Form.

[0027] Next, in the ion implantation step, a lanthanoid element is ion-implanted as the doping element 3 into the host material 5. The energy during the ion implantation is, for example, 100 keV. The depth of the ion implantation is, for example, 50 nm.

[0028] The doping element 3 to be ion-implanted is, for example, cerium. The doping amount of the doping element 3 is, for example, 1×10 １４ cm －２ The doping amount of the doping element 3 is, for example, 1×10 ７ cm －２ 1x10 or more １４ cm －２ The doping amount of the doping element 3 may be, for example, 1×10 １６ cm －３ The doping amount of the doping element 3 may be, for example, 1×10 ９ cm －３ 1x10 or more １６ cm －３ The following is also acceptable.

[0029] Next, in the heat treatment step, the host material 5 into which the lanthanoid element has been implanted as the doping element 3 is heat treated.

[0030] The heat treatment temperature is, for example, 700°C or higher and 1100°C or lower, and preferably 700°C or higher and 900°C or lower. If the heat treatment temperature is too high, the doping elements 3 will cluster. If the doping elements 3 cluster, the portion that functions as a quantum bit will decrease. Furthermore, if the heat treatment temperature is even higher, the doping elements 3 will react with the host material. For example, if the host material is SiO ２ When the doping element 3 is Ce, CeSiO ｘ is formed.

[0031] The heat treatment time is, for example, 0.5 hours or more and 2 hours or less, where the heat treatment time is the time from when the predetermined heat treatment temperature is reached.

[0032] By going through the above procedure, the quantum bit material 10 according to this embodiment can be fabricated.

[0033] The quantum bit material 10 according to this embodiment can be produced inexpensively because it uses a material other than diamond as the host material. The functionality and applicability of the quantum bit material 10 also depend heavily on the host material. For example, SiO ２ , MgO, MgAl ２ O ４ is widely used in semiconductor devices, spintronics devices, etc., and has a wide range of applications. In other words, the quantum bit material 10 according to this embodiment has a high degree of applicability.

[0034] The present disclosure has been described in detail above using several embodiments as examples, but the present disclosure is not limited to the above-mentioned embodiments and modifications, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims.

[0035] Example 1 A single crystal substrate of α-quartz was prepared. Ce was ion-implanted into this substrate with an implantation energy of 100 keV. The implantation dose of Ce was 1.0×10 １４ atoms / cm ２ (0.7 at %), the implantation depth position was 50 nm, and the implantation depth distribution was 50 nm. The implantation depth position was the design position when implanting Ce ions, and was the position where the Ce ion concentration was highest. The implantation depth distribution indicates the degree of variation in the position where Ce ions are implanted, based on the implantation depth position.

[0036] Next, the sample after ion implantation was heat-treated in an Ar atmosphere for 1 hour. The heat treatment involved raising the temperature to 800°C over 0.5 hours and holding it at 800°C for 1 hour. Through the above procedure, the quantum bit material of Example 1 was produced.

[0037] Examples 2 to 7 Examples 2 to 7 differ from Example 1 in that the holding temperature during heat treatment was changed. The holding temperatures during heat treatment in each of Examples 2 to 7 are as follows: Example 2: 600°C Example 3: 700°C Example 4: 900°C Example 6: 1000°C Example 7: 1100°C In each of Examples 2 to 7, the quantum bit material was produced under the same conditions as in Example 1 except for the holding temperature.

[0038] Examples 8 to 14 Examples 8 to 14 differ from Example 1 in that the substrate was changed to amorphous quartz glass. Other conditions were the same as those for Examples 1 to 7, and quantum bit materials were fabricated. Example 8 was fabricated under the same conditions as Example 1. Example 9 was fabricated under the same conditions as Example 2. Example 10 was fabricated under the same conditions as Example 3. Example 11 was fabricated under the same conditions as Example 4. Example 12 was fabricated under the same conditions as Example 5. Example 13 was fabricated under the same conditions as Example 6. Example 14 was fabricated under the same conditions as Example 7.

[0039] Examples 15 to 21 Examples 15 to 21 differ from Example 1 in that the substrate was changed to thermally oxidized silicon. The thickness of the oxide film of the thermally oxidized silicon was 500 nm. The other conditions were the same as those of Examples 1 to 7, and quantum bit materials were fabricated. Example 15 was under the same conditions as Example 1. Example 16 was under the same conditions as Example 2. Example 17 was under the same conditions as Example 3. Example 18 was under the same conditions as Example 4. Example 19 was under the same conditions as Example 5. Example 20 was under the same conditions as Example 6. Example 21 was under the same conditions as Example 7.

[0040] The photoluminescence properties of each of the quantum bit materials in Examples 1 to 21 were measured. A He—Cd laser with a wavelength of 325 nm was used as the incident laser. The quantum bit material was irradiated with the laser, and the light emitted from the quantum bit material was measured with a spectrometer.

[0041] Figure 4 shows the photoluminescence measurement results for each quantum bit material. The vertical axis represents the emission intensity at 450 nm, which is the emission peak of Ce, and the horizontal axis represents the holding temperature during fabrication of the quantum bit material. The α-quartz results are from Examples 1 to 7, the amorphous results are from Examples 8 to 14, and the th-ox results are from Examples 15 to 21.

[0042] The luminescence intensity from the quantum bit material increased from 600 to 700 °C. This is because the heat treatment temperature was high enough to induce the formation of luminescence centers (Ce ３＋The emission intensity decreased between 900 and 1000°C. This is thought to be because Ce clusters, in which Ce is localized, were formed, suppressing the formation of emission centers. The emission intensity then increased again between 1000 and 1100°C. This is thought to be because Ce reacted with silicon oxide to form CeSiO ｘ This is thought to be due to the formation of

[0043] Examples 22 to 26 Examples 22 to 26 differ from Example 1 in that the holding time during heat treatment was changed. The holding times during heat treatment in Examples 22 to 26 are shown below. Example 22: 0 hours Example 23: 2 hours Example 24: 3 hours Example 25: 5 hours Example 26: 9 hours In each of Examples 22 to 26, the conditions other than the holding time were the same as in Example 1, and quantum bit materials were produced.

[0044] Figure 5 shows the relationship between the heat treatment holding time and the luminescence intensity. The horizontal axis of Figure 5 represents the heat treatment holding time, and the vertical axis represents the luminescence intensity of the quantum bit material. As shown in Figure 5, the strongest luminescence was observed when the heat treatment temperature was held for one hour.

[0045] Next, the polarization characteristics of the quantum bit material of Example 1 were measured. Fig. 6 is a schematic diagram of a measurement system for measuring the polarization dependence of the quantum bit material.

[0046] The measurement system includes a laser 21, a polarizer 22, a quarter-wave plate 23, a dichroic mirror 24, a lens 25, a lens 26, a quarter-wave plate 27, a polarizer 28, and a spectrometer 29. The laser light output from the laser 21 is converted into a circularly polarized laser by the polarizer 22 and the quarter-wave plate 23, and is irradiated onto the quantum bit material 10. The quantum bit material 10 emits light upon excitation by the laser light. The emitted light from the quantum bit material 10 passes through the lens 25, the dichroic mirror 24, the lens 26, the quarter-wave plate 27, and the polarizer 28 in this order, and is detected by the spectrometer 29. The measurement temperature of the measurement system was set to 5K.

[0047] 7 shows the measurement results of the polarization characteristics of the quantum bit material of Example 1. The vertical axis of FIG. 7 represents the degree of circular polarization (DOCP), and the horizontal axis represents the wavelength of light emitted from the quantum bit material 10. DOCP is expressed as DOCP=(Iσ ＋ -Iσ － ) / (Iσ ＋ +Iσ － ) is expressed as Iσ ＋ corresponds to the emission due to the transition between the up-spin of the 5d orbital and the down-spin of the 4f orbital, and Iσ － corresponds to the emission due to the transition between the up-spin of the 5d orbital and the up-spin of the 4f orbital.

[0048] As shown in Figure 7, the light emitted from Example 1 has a region where the DOCP is shifted from 0%, and significant polarized photoluminescence was confirmed. At the shoulder wavelength (approximately 560 nm), σ ― The emission due to excitation was confirmed. This polarization dependence is due to the ３＋ This is consistent with the 4f-5d optical transition selection rule of Ce. ３＋ Furthermore, by utilizing the polarization dependence of photoluminescence, it is possible to perform initialization and detection processes on quantum dots.

[0049] The measurement temperature dependence of polarized photoluminescence was also measured for the quantum bit material 10 of Example 1. Figure 8 shows the measurement temperature dependence of polarized photoluminescence for the quantum bit material 10 of Example 1. The left graph in Figure 8 shows the measurement results at a measurement temperature of 5 K, the center graph in Figure 8 shows the measurement results at a measurement temperature of 77 K, and the right graph in Figure 8 shows the measurement results at a measurement temperature of 300 K.

[0050] 8, as the measurement temperature increased, the amount of polarized photoluminescence decreased (DOCP approached 0). Up to about 150K, a significant difference in the amount of polarized photoluminescence was confirmed.

[0051] Furthermore, optically detected magnetic resonance (ODMR) was measured for the quantum bit material 10 of Example 1 using an optically detected magnetic resonance (ODMR) microscope. Figure 9 shows the results of measuring optically detected magnetic resonance for the quantum bit material 10 of Example 1. Figure 10 shows the results of determining the g-factor using the optically detected magnetic resonance measurement results. The g-factor is a dimensionless proportionality constant measured in elemental units as the ratio between the total magnetic moment and total angular momentum of the outer electrons.

[0052] The ODMR measurement results demonstrated that the writing operation in the quantum dots can be realized. ２ In Example 1 using a substrate, yttrium aluminum garnet (Y ３ Al ５ O １２ The g-factor was comparable to that of cesium-doped SiO. ２ and Y ３ Al ５ O １２ The confirmation of equivalent g-factors in the two oxides suggests that oxides doped with lanthanide elements can function as quantum bit materials, regardless of the oxide that constitutes the host material. The spin properties of the doped cerium ions exist in isolation from the host material 5, so equivalent g-factors were obtained even when the host material 5 was different.

[0053] The polarization properties of the quantum bit material were also measured for Examples 8 and 15. Figure 11 shows the measurement results of the polarization properties of the quantum bit material of Example 8. Figure 12 shows the measurement results of the polarization properties of the quantum bit material of Example 15. As shown in Figures 11 and 12, significant polarized photoluminescence was observed in both cases where the substrate was amorphous silicon oxide and thermal silicon oxide.

[0054] Example 27 In Example 27, the substrate was MgAl ２ O ４ The other conditions were the same as in Example 6, and the quantum bit material was fabricated.

[0055] The polarization characteristics of the quantum bit material of Example 27 were also measured. The measurement temperature was 4 K. FIG. 13 shows the measurement results of the polarization characteristics of the quantum bit material of Example 27. When measuring the polarization characteristics of the quantum bit material of Example 27, the dependence on the magnetic field was also measured. The magnetic field was applied in a direction parallel to the incident direction of the light. FIG. 14 shows the magnetic field strength dependence of DOCP.

[0056] As shown in FIG. 13, the substrate is MgAl ２ O ４ Significant polarized photoluminescence was observed even in the case of . Furthermore, the DOCP could be further increased by applying an external magnetic field. This is probably because the hybridization of states due to nuclear spins is suppressed by the application of an external magnetic field.

[0057] Examples 28 and 29 Example 28 differs from Example 6 in that the substrate is changed to MgO. Example 29 has a substrate of MgO with Al ２ O ３ The difference from Example 6 is that a cap layer made of the above was formed. The other conditions were the same as in Example 6, and a quantum bit material was fabricated.

[0058] A broad emission peak was also observed around 450 nm in Examples 28 and 29. The emission intensity of the photoluminescence light in Example 29 was stronger than that of the photoluminescence light in Example 28. ２ O ３ On the other hand, the emission intensity of the photoluminescence light of Example 27 was 14 times that of the photoluminescence light of Example 28 and 8 times that of the photoluminescence light of Example 29.

[0059] Example 30: In Example 30, the amount of Ce ions implanted into the substrate was 1.0×10 １３ atoms / cm ２The difference from Example 1 is that the polarization characteristics of the quantum bit material were measured under the same conditions as in Example 1. Figure 15 shows the measurement results of the polarization characteristics of the quantum bit material of Example 30. As shown in Figure 15, the light emitted from Example 30 has a region where the DOCP is shifted from 0%, and significant polarized photoluminescence was confirmed. This polarization dependence is due to the Ce ３＋ The qubit material of Example 30 is consistent with the optical transition selection rule between 4f and 5d of Ce. ３＋ Furthermore, by utilizing the polarization dependence of photoluminescence, it is possible to perform initialization and detection processes on quantum dots.

[0060] As mentioned above, diamond and yttrium aluminum garnet (Y ３ Al ５ O １２ It has been confirmed that the quantum bit material according to the present invention can function as a quantum dot without using an expensive substrate such as a silicon substrate.

[0061] REFERENCE SIGNS LIST 1 First element 2 Second element 3 Doped element 5 Host material 10, 11, 12 Qubit material 21 Laser 22, 28 Polarizer 23, 27 Quarter wave plate 24 Dichroic mirror 25, 26 Lens 29 Spectrometer

Claims

1. A quantum bit material comprising a host material of an oxide containing a first element and a second element, or an oxide containing a second element, a third element, and a fourth element, the host material comprising a doping element, the doping element being a lanthanide element, the first element being any element of Groups 1 to 14, the second element being any element of Groups 14 to 17, and the third element and the fourth element being any element of Groups 1, 2, or 4 to 14, a lanthanide element other than the doping element, or an actinide element.

2. The host material has a defect center concentration of 1×10 １４ cm －２ Less than or equal to 1 x 10 １６ cm －３ 2. The quantum bit material of claim 1 , wherein:

3. The quantum bit material of claim 1, wherein the host material comprises Mg or Al.

4. The host material is SiO ２ , MgO or MgAl ２ O ４ 10. The quantum bit material of claim 1 , comprising:

5. The quantum bit material of claim 1, wherein the host material is one selected from the group consisting of monocrystalline silicon oxide, amorphous silicon oxide, and thermal silicon oxide.

6. The quantum bit material of claim 1, wherein the doping element is cerium.

7. The doping amount of the doping element is 1×10 ７ cm －２ Above 1 x 10 １４ cm －２ Less than or equal to 1 x 10 ９ cm －３ Above 1 x 10 １６ cm －３ 2. The quantum bit material of claim 1 , wherein:

8. A method for producing a quantum bit material, comprising: an ion implantation step of ion-implanting a lanthanoid element as a doping element into an oxide host material; and a heat treatment step of heat-treating the host material into which the ions have been implanted.

9. The method for producing a quantum bit material according to claim 8, wherein the host material is an oxide containing a first element and a second element, or an oxide containing a second element, a third element, and a fourth element, the first element being any element of Groups 1 to 14, the second element being any element of Groups 14 to 17, and the third element and the fourth element being any element of Groups 1, 2, or 4 to 14, a lanthanide element other than the doping element, or an actinide element.

10. The method of claim 8, wherein the host material comprises Mg or Al.

11. The host material is SiO ２ , MgO or MgAl ２ O ４ The method of claim 8 , comprising:

12. The method for producing a quantum bit material according to claim 8, wherein the host material is one selected from the group consisting of single crystal silicon oxide, amorphous silicon oxide, and thermal silicon oxide.

13. The host material has a body and a cap layer formed on one surface of the body, the body being MgO, and the cap layer being Al ２ O ３ The method of claim 8 , wherein 14. The method of claim 8, wherein the doping element is cerium.

15. In the ion implantation process, the doping amount of the doping element is 1×10 ７ cm －２ Above 1 x 10 １４ cm －２ Less than or equal to 1 x 10 ９ cm －３ Above 1 x 10 １６ cm －３ 9. The method of claim 8, wherein:

16. The method for producing a quantum bit material according to claim 8, wherein the temperature of the heat treatment step is 700° C. or higher and 900° C. or lower.

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