An asymmetric josephson junction device, a preparation method and a superconducting quantum bit and a superconducting quantum chip
By employing an asymmetric Josephson junction design in superconducting qubits and utilizing the close-proximity coupling between high-gap superconducting materials and aluminum layers, the band gap difference is increased, solving the problem of qubit state flipping caused by high-energy radiation in existing technologies and achieving more efficient radiation protection.
Patent Information
- Application Number
- CN202611162053.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-31
- Publication Date
- 2026-11-03
AI Technical Summary
In superconducting quantum computing, existing technologies can lead to correlation errors such as quasiparticles caused by high-energy rays, which can cause qubit state flipping. Existing methods for adjusting the thickness of the aluminum film on both sides of the Josephson junction have performance limits and are difficult to effectively suppress multi-qubit correlation errors caused by high-energy ray events.
By employing an asymmetric Josephson junction design and utilizing the close-neighbor coupling between the high-gap superconducting material and the aluminum layer, a higher equivalent superconducting bandgap difference is formed, breaking through the upper limit of the superconducting bandgap difference in aluminum film thickness control schemes, and increasing the superconducting bandgap difference to suppress quasiparticle tunneling.
It effectively reduces multi-bit correlation errors induced by high-energy ray events, improves the radiation resistance of qubits, and reduces the probability of bit state flipping.
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Figure CN123035862A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of superconducting quantum computing technology, specifically to an asymmetric Josephson junction device and its fabrication method, as well as superconducting qubits and superconducting quantum chips. Background Technology
[0002] In superconducting quantum computing, the core component of a qubit is a Josephson junction composed of a superconducting aluminum / alumina / alumina thin film material. Experiments have shown that when cosmic ray muons or ambient gamma rays interact with the quantum chip substrate (typically silicon or sapphire), they deposit energy and generate a large number of high-energy phonons. These phonons propagate rapidly within the substrate, entering the superconducting film of the qubit and disrupting Cooper pairs, generating a large number of non-equilibrium quasiparticles. When these quasiparticles diffuse into the Josephson junction region and tunnel through the junction, they can cause correlation errors, such as state flips in multiple qubits. These correlation errors seriously threaten the effective operation of universal quantum computing, which relies on quantum error correction.
[0003] To address the aforementioned issues, existing technologies typically employ adjusting the thickness of the aluminum films on both sides of the Josephson junction. By regulating the thickness parameter, a band gap difference is generated to suppress the adverse effects of quasiparticles. This approach requires minimal modification to existing superconducting quantum bit structures, thus exhibiting good process compatibility.
[0004] However, due to limitations in the minimum achievable thickness of aluminum films and process stability, the thinnest aluminum films can only be a few nanometers thick. This thickness adjustment method has a significant performance upper limit; the band gap difference is generally only a few times larger than the bit frequency (typically 4-8 GHz), and is only applicable to low-energy quasiparticles (i.e., quasiparticles mainly distributed near the superconducting band gap). In contrast, quasiparticles generated by high-energy rays (such as high-energy ray events with deposition energies above MeV) have higher temperatures. They can absorb photons emitted by the bit as it relaxes from the 1 state to the 0 state, overcoming the junction barrier caused by the band gap difference, thus weakening the suppression effect of existing technologies.
[0005] In response, this application found that by further increasing the equivalent superconducting band gap difference between the two sides, the probability of the aforementioned quasiparticle-related errors can be reduced. Furthermore, this application also found that asymmetric junctions can allow quasiparticles on the high band gap side to tunnel to the low band gap side. If a photon with a bit frequency is emitted after tunneling, it can cause the bit state to change from state 0 to state 1, i.e., a bit state excitation error. Compared to the low band gap difference, the excitation error caused by this quasiparticle tunneling can be suppressed at a high band gap difference.
[0006] Therefore, in order to further reduce high-energy ray-induced multi-bit correlation errors, it is necessary to propose a technical solution that can increase the superconducting bandgap while maintaining the compatibility of existing aluminum-based Josephson junction processes. Summary of the Invention
[0007] To address the aforementioned deficiencies in this field, this application aims to provide an asymmetric Josephson junction device and its fabrication method, as well as superconducting qubits and superconducting quantum chips.
[0008] According to one aspect of this application, an asymmetric Josephson junction device is provided, comprising: First superconducting electrode layer; Second superconducting electrode layer; and An insulating barrier layer is located between the first superconducting electrode layer and the second superconducting electrode layer; The first superconducting electrode layer and the second superconducting electrode layer have a superconducting band gap difference.
[0009] According to some embodiments of this application, the first superconducting electrode layer includes a high-gap superconducting material layer.
[0010] According to some embodiments of this application, the first superconducting electrode layer further includes a first aluminum layer; the second superconducting electrode layer is a second aluminum layer.
[0011] According to some embodiments of this application, the superconducting band gap difference between the first superconducting electrode layer and the second superconducting electrode layer is greater than 15 GHz.
[0012] According to some embodiments of this application, the superconducting band gap difference between the first superconducting electrode layer and the second superconducting electrode layer is greater than 24 GHz.
[0013] According to some embodiments of this application, the insulating barrier layer is an alumina insulating barrier layer.
[0014] According to some embodiments of this application, the material of the high bandgap superconducting material layer is selected from materials with a superconducting bandgap greater than that of aluminum, such as tantalum (Ta), niobium (Nb), lead (Pb), tin (Sn), indium (In), vanadium (V), rhenium (Re), or niobium-titanium-nitrogen (NbTiN).
[0015] According to some embodiments of this application, the material of the high bandgap superconducting material layer is selected from tantalum or niobium.
[0016] According to some embodiments of this application, the thickness of the high-bandgap superconducting material layer is 100-200 nm.
[0017] According to some embodiments of this application, the thickness of the first aluminum layer is 20-100 nm.
[0018] According to some embodiments of this application, the thickness of the second aluminum layer is 60-200 nm.
[0019] According to a second aspect of this application, a superconducting quantum bit is provided, comprising the aforementioned asymmetric Josephson junction device.
[0020] According to a third aspect of this application, a superconducting quantum chip is provided, comprising the superconducting quantum bits described above.
[0021] According to a fourth aspect of this application, a method for fabricating a superconducting quantum chip is provided, comprising: Provide substrate; A high-gap superconducting material layer is deposited on the first surface of the substrate, and the high-gap superconducting material layer is patterned to fabricate the external circuit, the quantum bit capacitor plate, and the contact area. An asymmetric Josephson junction is obtained by sequentially fabricating a first aluminum layer, an insulating barrier layer, and a second aluminum layer on the surface of the contact region away from the substrate.
[0022] According to some embodiments of this application, the thickness of the first aluminum layer is less than the thickness of the second aluminum layer.
[0023] According to some embodiments of this application, the thickness of the first aluminum layer is 20-100 nm; the thickness of the second aluminum layer is 60-200 nm.
[0024] According to some embodiments of this application, the thickness of the high-bandgap superconducting material layer is 100-200 nm.
[0025] Compared with the prior art, this application has at least the following beneficial effects: This application provides an asymmetric Josephson junction device, particularly an asymmetric superconducting bandgap Josephson junction design based on the superconducting nearest neighbor effect. This application utilizes the near-neighbor coupling between a superconducting material with a superconducting bandgap higher than that of aluminum and an aluminum layer to induce a higher equivalent superconducting bandgap in the aluminum layer on one side of the Josephson junction. This results in a larger superconducting bandgap difference with the aluminum layer on the other side, breaking through the upper limit of the superconducting bandgap difference in aluminum film thickness control schemes, thereby reducing multi-bit correlation errors induced by high-energy radiation events. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of the asymmetric Josephson junction of Example Embodiment 1 of this application.
[0027] Figure 2 This is a schematic diagram of the asymmetric Josephson junction, which is an example embodiment of this application.
[0028] Figure 3 This is a schematic diagram of the asymmetric Josephson junction, which is an example embodiment of this application.
[0029] Figure 4 This is a schematic diagram of the asymmetric Josephson junction, which is an example embodiment of this application.
[0030] Figure 5 This is a schematic diagram of the asymmetric Josephson junction, which is an example embodiment of this application.
[0031] Figure 6The superconducting bandgap change caused by the proximity effect after contact of tantalum (Ta) / aluminum (Al) materials in an example embodiment of this application.
[0032] Figure 7 The diagram shows a side view of a superconducting quantum bit thin aluminum / alumina / thick aluminum Josephson junction structure as an example of the present application, the relationship between the aluminum film thickness and the size of the aluminum film superconducting bandgap, and a schematic diagram showing that the relaxation behavior of the qubit is suppressed due to tunneling of conventional low-temperature quasiparticles.
[0033] Figure 8 This is a schematic diagram comparing the bit relaxation behavior caused by high-temperature quasi-particle tunneling in an asymmetric superconducting bandgap junction, which is an example embodiment and a comparative example of this application.
[0034] Figure 9 This is a schematic diagram comparing the qubit excitation behavior caused by high-temperature quasi-particle tunneling in an example embodiment and a comparative example of an asymmetric superconducting bandgap junction in this application.
[0035] Figure 10 The diagram illustrates the effect of suppressing bit errors caused by high-energy rays in example embodiments and comparative examples of this application. Detailed Implementation
[0036] The technical solution of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0037] It should be particularly noted that similar substitutions and modifications made to this application are obvious to those skilled in the art, and they are all considered to be included in this application. Those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.
[0038] Unless otherwise specified, this application is conducted under standard conditions or conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, whose manufacturers are not specified, are all conventional products that can be obtained commercially.
[0039] The following is a detailed description of this application.
[0040] This application observes a saturation phenomenon in the logic bit error rate of quantum error correction chips based on existing technologies. This phenomenon may be related to the limited ability of existing asymmetric bandgap structures to suppress high-energy non-equilibrium quasiparticles.
[0041] This application employs an asymmetric superconducting bandgap Josephson junction with a higher superconducting bandgap to suppress qubit relaxation and excitation processes caused by quasiparticle tunneling. The basic principle for relaxation is that when the superconducting bandgap difference across the Josephson junction is greater than the energy corresponding to the qubit's operating frequency, the energy released by the qubit relaxing from state 1 to state 0 is insufficient to assist quasiparticles in tunneling from the lower bandgap side to the higher bandgap side, thus suppressing the related quasiparticle tunneling process and achieving a certain degree of qubit state protection. The higher the superconducting bandgap difference, the better the protection effect. The basic principle for excitation is that when a quasiparticle tunnels from the higher bandgap side to the lower bandgap side, it can emit a photon and excite the qubit. Again, the higher the bandgap difference, the lower the probability of this excitation occurring.
[0042] In some examples, the asymmetric Josephson junction device of this application includes: First superconducting electrode layer; Second superconducting electrode layer; and An insulating barrier layer is located between the first superconducting electrode layer and the second superconducting electrode layer; The first superconducting electrode layer and the second superconducting electrode layer have a band gap difference.
[0043] According to an optional embodiment of this application, the first superconducting electrode layer includes a high bandgap superconducting material layer and a first aluminum layer; the second superconducting electrode layer is a second aluminum layer.
[0044] According to an optional embodiment of this application, the superconducting band gap difference between the first superconducting electrode layer and the second superconducting electrode layer is greater than 15 GHz.
[0045] According to an optional embodiment of this application, the superconducting band gap difference between the first superconducting electrode layer and the second superconducting electrode layer is greater than 24 GHz.
[0046] In some examples, the superconducting band gap difference between the first superconducting electrode layer and the second superconducting electrode layer of this application is greater than the band gap difference limit in the prior art.
[0047] According to an optional embodiment of this application, the insulating barrier layer is an alumina insulating barrier layer.
[0048] According to optional embodiments of this application, the materials of the high bandgap superconducting material layer include, but are not limited to: tantalum (Ta), niobium (Nb), lead (Pb), tin (Sn), indium (In), vanadium (V), rhenium (Re), or niobium-titanium-nitrogen (NbTiN) and other materials with a superconducting bandgap greater than that of aluminum.
[0049] According to an optional embodiment of this application, the material of the high bandgap superconducting material layer is selected from tantalum or niobium.
[0050] According to an optional embodiment of this application, the thickness of the high bandgap superconducting material layer is 100-200 nm.
[0051] According to an optional embodiment of this application, the thickness of the first aluminum layer is 20-100 nm.
[0052] According to an optional embodiment of this application, the thickness of the second aluminum layer is 60-200 nm.
[0053] In some examples, the superconducting qubits of this application include the aforementioned asymmetric Josephson junction devices.
[0054] In some examples, the superconducting quantum chip of this application includes the superconducting qubits described above.
[0055] In some examples, superconducting qubits fabricated using this asymmetric Josephson junction can be directly applied to existing superconducting quantum chips. Multiple qubit arrays can utilize this asymmetric Josephson junction, either wholly or partially, to reduce multi-qubit correlation errors induced by high-energy radiation events.
[0056] In some examples, the fabrication method of the superconducting quantum chip of this application includes: Provide substrate; A high-gap superconducting material layer is deposited on the first surface of the substrate, and the high-gap superconducting material layer is patterned to fabricate the external circuit, the quantum bit capacitor plate, and the contact area. An asymmetric Josephson junction is obtained by sequentially fabricating a first aluminum layer, an insulating barrier layer, and a second aluminum layer on the surface of the contact region away from the substrate.
[0057] In optional embodiments of this application, the external circuit, the quantum bit capacitor plate, and the contact area are located in different regions of the first surface of the substrate, and the specific locations depend on the quantum bit design requirements.
[0058] According to an optional embodiment of this application, the thickness of the first aluminum layer is less than the thickness of the second aluminum layer.
[0059] According to an optional embodiment of this application, the thickness of the first aluminum layer is 20-100 nm; the thickness of the second aluminum layer is 60-200 nm.
[0060] According to an optional embodiment of this application, the thickness of the high bandgap superconducting material layer is 100-200 nm.
[0061] The asymmetric Josephson junction device of this application includes a first superconducting electrode, an insulating barrier layer, and a second superconducting electrode. The first superconducting electrode includes a high-bandgap superconducting material layer and a first aluminum layer in contact with or in close proximity to the high-bandgap superconducting material layer; the second superconducting electrode includes a second aluminum layer; and an alumina insulating barrier layer is disposed between the first aluminum layer and the second aluminum layer. The first aluminum layer forms a high equivalent superconducting bandgap under the proximity effect of the high-bandgap superconducting material layer, while the second aluminum layer maintains a relatively low aluminum layer superconducting bandgap, thereby forming an asymmetric superconducting bandgap Josephson junction with a "high equivalent bandgap aluminum side / alumina barrier / low bandgap aluminum side".
[0062] Furthermore, to minimize process modifications and reduce process complexity, this invention preferably uses high-bandgap superconducting materials for the external circuitry of the quantum bit chip and the quantum bit capacitor plate, allowing the proximity effect structure to be formed simultaneously during the processing of the relevant film layers. Taking tantalum film as an example, a tantalum film can be deposited and patterned on a sapphire or high-resistivity silicon substrate to form the external circuitry, the quantum bit capacitor plate, and the tantalum / aluminum proximity effect contact region; subsequently, a first aluminum film, an alumina barrier layer, and a second aluminum film are prepared using the standard Josephson junction process, thereby completing the fabrication of an asymmetric Josephson junction with a large bandgap difference.
[0063] Optionally, the first aluminum layer of this application can be in contact with the high-gap superconducting material layer through stacking, lateral contact, partial coverage, embedded contact, or multi-region contact; the length, width, coverage area, or relative position of the adjacent coupling region can be used to adjust the size of the induced superconducting gap.
[0064] Optionally, the thickness of the high-bandgap superconducting material layer can be adjusted according to the film preparation process, step coverage capability, proximity effect modulation requirements, and device structure. The thickness of the first aluminum film (thin aluminum layer) can be from a few nanometers to tens of nanometers; the thickness of the second aluminum film (thick aluminum layer) can be adjusted according to requirements, for example, it can be greater than 60 nm. In a preferred embodiment, the equivalent superconducting bandgap difference formed between the first aluminum layer and the second aluminum layer is greater than the energy corresponding to the operating frequency of the quantum bit; for example, this bandgap difference can be designed to be greater than 0.1 meV.
[0065] The technical solution of this application will be further described below with reference to specific embodiments.
[0066] Example 1 like Figure 1 As shown, an asymmetric Josephson knot with a "cross" structure is prepared.
[0067] Provide sapphire substrates; A tantalum layer is deposited and patterned on the first surface of the substrate to fabricate the external circuit, the quantum bit capacitor plate, and the contact area; An asymmetric Josephson junction is obtained by sequentially fabricating a first aluminum layer, an insulating barrier layer, and a second aluminum layer on the surface of the contact region away from the substrate.
[0068] In an optional embodiment, the junction size of the first aluminum film, the alumina barrier layer, and the second aluminum film can be determined according to experimental requirements. Tantalum strips can be fabricated simultaneously when preparing the quantum bit capacitor plate. In principle, increasing the effective contact area between the tantalum strip and the first aluminum film, and increasing the thickness of the tantalum film, while ensuring that the tantalum strip is completely covered by the first aluminum film and does not form an electrical connection with the second aluminum film, is beneficial for enhancing the proximity effect and increasing the induced bandgap size. Since excessively thick or large tantalum strips may expose their edges due to incomplete coverage by the first aluminum film, leading to unintended electrical connections with the second aluminum film and consequently Josephson junction failure, a tolerance margin should be reserved based on the specific process.
[0069] In an optional embodiment, the thickness of the tantalum strip can be approximately 200 nm; a gap of at least 100 nm should be reserved between the edge of the tantalum strip in the width direction and the edge of the corresponding first aluminum film to reduce the risk of electrical connection between the tantalum strip and the second aluminum film. Figure 1 This is for illustrative purposes only; the specific shape, size, and orientation of the aluminum and tantalum layers can be adjusted according to the actual process.
[0070] Example 2 The method described in this application is used to prepare an asymmetric Josephson junction with a Dolan Bridge structure.
[0071] like Figure 2 As shown, before fabricating the Josephson junction, a tantalum strip perpendicular to the direction of the aluminum junction can be fabricated first. The length and thickness of the tantalum strip can be determined according to the proximity effect modulation requirements and process conditions; in one embodiment, the thickness of the tantalum strip can be selected as approximately 200 nm. The position of the tantalum strip should be such that it forms an effective proximity coupling with the first aluminum film, while avoiding unintended electrical connections with the second aluminum film; a gap of at least 100 nm should preferably be reserved between the edge of the tantalum strip and the corresponding edge of the first aluminum film.
[0072] In an alternative embodiment, such as Figure 3 As shown, the tantalum strip can also be configured to be aligned with the direction of the first aluminum film. As long as the tantalum strip can be effectively contacted or closely coupled with the first aluminum film and short-circuited with the second aluminum film, the purpose of this invention can be achieved.
[0073] In an optional embodiment, since the size of the equivalent superconducting bandgap induced by the tantalum film in the aluminum film is related to the distance of the target location from the tantalum / aluminum interface, when it is necessary to adjust the bandgap difference of the asymmetric junction, it can be done as follows: Figure 4 As shown, by adjusting the distance between the edge of the tantalum strip and the edge of the first aluminum film, the intensity of the nearest neighbor effect can be changed and the bandgap difference can be controlled. Figure 4 The diagram only illustrates the Dolan knot structure; the cross knot or other Josephson knot structures can also be implemented in a similar manner.
[0074] Example 3 The sandwich knot structure was prepared using the method described in this application. Figure 5 As shown, a tantalum film, a first aluminum film, an aluminum oxide layer, and a second aluminum film can be deposited sequentially on a substrate. Then, the predetermined lateral thin film structure is retained through patterning and etching processes, and the second aluminum film, the aluminum oxide layer, and the first aluminum film are etched while retaining the junction region, so that the tantalum strip is part of the electrode structure. Finally, the second aluminum film is prepared in the direction perpendicular to the tantalum strip and covers the junction region to complete the fabrication of the asymmetric Josephson junction.
[0075] In an alternative embodiment, Figure 5 The structure shown is for illustrative purposes only. As long as the tantalum film and the aluminum layer on one side of the Josephson junction can form an effective close-proximity coupling, the specific shape, size and orientation of the film can be adjusted according to the process conditions.
[0076] Figure 6 This figure shows the superconducting bandgap change caused by the proximity effect after the tantalum (Ta) / aluminum (Al) materials come into contact. The leftmost part of the figure represents the superconducting bandgap of tantalum (680 μeV), and the rightmost part represents the superconducting bandgap of aluminum (180 μeV). The horizontal axis at 0 nm represents the tantalum-aluminum contact interface.
[0077] As can be seen, the asymmetric Josephson junction of this application, while ensuring good contact between the tantalum and aluminum films, can induce an equivalent superconducting gap higher than the intrinsic gap of aluminum at a distance of tens of nanometers from the interface. The specific size of the induced gap is related to factors such as the contact quality of the tantalum / aluminum interface, the contact resistance, and the distance of the target position in the aluminum film from the tantalum / aluminum interface, and can be adjusted according to specific experimental requirements. Taking tantalum as an example, the superconducting gap difference of this asymmetric junction can reach tens of GHz, which is greater than the upper limit of 15 GHz in the prior art.
[0078] Comparative Example 1 Provide sapphire substrates; A first aluminum film, an aluminum oxide layer, and a second aluminum film are sequentially deposited on the first surface of the substrate, wherein the thickness of the first aluminum film is less than the thickness of the second aluminum film.
[0079] like Figure 7 The left figure shows a side view of the superconducting quantum bit thin aluminum / alumina / thick aluminum Josephson junction structure of Comparative Example 1, and the relationship between the aluminum film thickness and the size of the aluminum film superconducting bandgap.
[0080] like Figure 7The right figure shows an asymmetric superconducting bandgap structure formed by the different thicknesses of the aluminum films on both sides of the Josephson junction. The quasiparticles (solid dots) in the superconducting material have low temperatures and are located almost at the edge of the superconducting bandgap. When the bandgap difference exceeds the energy corresponding to the operating frequency of the qubit, the qubit in state 1 cannot easily change its state by exchanging energy equivalent to the qubit's transition frequency (dashed arrow) through quasiparticle tunneling (solid arrow). Therefore, the qubit's state can be somewhat protected.
[0081] like Figure 8 It can be seen that when the temperature of the quasiparticle (solid dot) is high, it can occupy a position far away from the edge of the band gap.
[0082] like Figure 8 As shown in the left figure, the existing asymmetric superconducting bandgap junction can no longer prevent high-temperature quasiparticle tunneling (solid arrow). Quasiparticles can tunnel by absorbing the energy released by the quantum bit when it transitions from state 1 to state 0 (dashed arrow).
[0083] like Figure 8 As shown in the right figure, further increasing the band gap helps to suppress the tunneling behavior of this type of high-energy quasiparticle.
[0084] like Figure 9 As shown, in the asymmetric Josephson junction of this application, when a quasiparticle tunnels from the high-gap side to the low-gap side, it releases energy equivalent to the operating frequency of the qubit (dashed arrow), causing the qubit state to be excited from state 0 to state 1. The probability of this event is related to the density of states of the final state (the direction of the arrow indicates the final state). Compared to a low-gap asymmetric junction ( Figure 9 Left figure), larger bandgap structure ( Figure 9 The lower density of states in the final state (as shown in the right figure) helps to suppress qubit excitation errors caused by quasiparticle tunneling.
[0085] Test case A test superconducting quantum chip was fabricated, consisting of two types of Dolan junction qubits designed on the same substrate. One type used an Al film as the qubit capacitor plate and fabricated an Al (40 nm thick) / AlOx / Al (80 nm thick) Josephson junction. The other type used a Ta (200 nm thick) qubit capacitor plate, and the Josephson junction was as follows. Figure 3 The asymmetric junction design shown has Ta directly below the first Al electrode (40 nm thick) and a second aluminum electrode with a thickness of 80 nm. After the chip was fabricated, it was tested on a superconducting quantum computer in the laboratory.
[0086] The testing method involves preparing the qubit in state 1 and observing the relaxation behavior from state 1 to state 0 induced by high-energy radiation. The behavior of two different qubit designs was continuously observed (event resolution 5.6 μs), multiple sets of data on the effects of high-energy radiation were collected, and the results were averaged and converted into bit errors, yielding the following result: Figure 10 The result.
[0087] like Figure 10 As shown, the vertical axis represents the probability of a qubit error, and the horizontal axis represents the time before and after the impact of high-energy radiation. It can be seen that with conventionally designed qubits, there is approximately a 70% probability of error when high-energy radiation strikes, with the error lasting for several milliseconds. In contrast, the asymmetric junction design of this application reduces the probability of a qubit error to only a few percent, and the duration is significantly shorter.
[0088] Therefore, the Ta / Al qubits prepared based on this application ( Figure 2 Compared to qubits fabricated using conventional aluminum / alumina / aluminum junctions, the ability to resist errors caused by high-energy radiation is significantly improved.
[0089] In summary, this application breaks through the upper limit of the bandgap difference in existing aluminum film thickness control schemes. Comparative technical solutions rely on aluminum film thickness to change the bandgap, which is limited by the minimum aluminum film thickness and process stability. This application improves the equivalent superconducting bandgap of one side of the aluminum layer through the proximity effect of high-bandgap superconducting materials—aluminum—and can obtain a larger bandgap difference.
[0090] The technical solution of this application suppresses high-energy ray-induced non-equilibrium quasiparticle tunneling. A larger bandgap difference can more effectively block quasiparticles from the low bandgap side from entering the high bandgap side, resulting in a reduced probability of the bit state relaxing from state 1 to state 0; it can also suppress quasiparticles from the high bandgap side from entering the low bandgap side, resulting in a reduced probability of the bit state being excited from state 0 to state 1.
[0091] The technical solution of this application is compatible with Ta / Nb superconducting quantum bit chip technology and can retain the relevant performance advantages brought by tantalum film or niobium film capacitor electrodes.
[0092] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.
Claims
1. An asymmetric Josephson junction device, characterized in that, include: First superconducting electrode layer; Second superconducting electrode layer; and An insulating barrier layer is located between the first superconducting electrode layer and the second superconducting electrode layer; Wherein, the first superconducting electrode layer and the second superconducting electrode layer have a superconducting band gap difference; The first superconducting electrode layer includes a high-bandgap superconducting material layer.
2. The asymmetric Josephson junction device according to claim 1, characterized in that, The first superconducting electrode layer also includes a first aluminum layer; The second superconducting electrode layer is a second aluminum layer.
3. The asymmetric Josephson junction device according to claim 1 or 2, characterized in that, The superconducting band gap difference between the first superconducting electrode layer and the second superconducting electrode layer is greater than 15 GHz.
4. The asymmetric Josephson junction device according to claim 1 or 2, characterized in that, The superconducting band gap difference between the first superconducting electrode layer and the second superconducting electrode layer is greater than 24 GHz.
5. The asymmetric Josephson junction device according to claim 1, characterized in that, The insulating barrier layer is an alumina insulating barrier layer.
6. The asymmetric Josephson junction device according to claim 2, characterized in that, The materials of the high-bandgap superconducting material layer include: tantalum, niobium, lead, tin, indium, vanadium, rhenium, or niobium-titanium-nitrogen.
7. A method for fabricating an asymmetric Josephson junction device, characterized in that, include: Provide substrate; A high-gap superconducting material layer is deposited on the first surface of the substrate, and the high-gap superconducting material layer is patterned to obtain an external circuit, a quantum bit capacitor plate, and a contact area. A first aluminum layer, an insulating barrier layer, and a second aluminum layer are sequentially prepared on the surface of the contact area away from the substrate to obtain an asymmetric Josephson junction.
8. The preparation method according to claim 7, characterized in that, The thickness of the first aluminum layer is 20-100 nm; the thickness of the second aluminum layer is 60-200 nm. The thickness of the high-bandgap superconducting material layer is 100-200 nm.
9. A superconducting quantum bit, characterized in that, Includes the asymmetric Josephson junction device according to any one of claims 1-6 or the asymmetric Josephson junction device prepared by the preparation method according to claim 7 or 8.
10. A superconducting quantum chip, characterized in that, Includes the superconducting quantum bit as described in claim 9.