Quantum device and superconducting quantum chip

Abstract

The utility model discloses a quantum device and a superconducting quantum chip, and belongs to the technical field of quantum computing. The quantum device includes: a Josephson junction; the metal film is electrically connected with the superconducting layer of the Josephson junction; wherein through holes for limiting penetration of quasi-particles are distributed in the metal film. According to the mode, the quasi-particles can be limited and limited in the through holes, so that the quasi-particles are prevented from being close to the Josephson junction, the quasi-particles are prevented from participating in the tunneling process of the junction region, bit representation as energy de-coherence is further avoided, and finally the performance of the superconducting quantum chip is improved.

Description

Technical Field

[0001] The present application belongs to the field of quantum computing technology, and in particular, relates to a quantum device and a superconducting quantum chip. Background Art

[0002] Quantum computers are devices that process information and perform calculations based on quantum mechanics. Compared with classical computers, they have shown great superiority in computing speed. The core of quantum computers, quantum chips, are key devices for realizing quantum computing. The superconducting qubit system based on the Josephson junction has been widely studied because of its advantages such as high gate operation fidelity, good system integration, and mature processing technology compatible with traditional semiconductors. This makes the superconducting qubit system based on the Josephson junction one of the important systems for realizing quantum computing.

[0003] At present, superconducting quantum chips are generally placed in the extremely low temperature space of a dilution refrigerator for operation. According to the BCS superconductivity theory, when a superconducting quantum chip enters the extremely low temperature space of a dilution refrigerator, the concentration of quasiparticles formed by the destruction of Cooper pairs increases. The behavior of these quasiparticles near the Josephson junction of the superconducting quantum chip is very complex. Quasiparticles may absorb or release photons or phonons, resulting in energy loss, and release them into the low temperature environment in the form of heat. This process will cause the tunneling process of the Josephson junction to introduce losses, causing the bits to show energy decoherence, thereby reducing the performance of the superconducting quantum chip. In short, how to prevent quasiparticles in superconducting quantum chips from approaching the Josephson junction has become an urgent problem to be solved in superconducting quantum chips. Utility Model Content

[0004] The purpose of the present application is to provide a quantum device and a superconducting quantum chip to solve the problem of energy decoherence caused by quasiparticles approaching a Josephson junction in the prior art. After the superconducting quantum chip enters the extremely low temperature space of a dilution refrigerator, the quasiparticles can be restricted to prevent the quasiparticles from approaching the junction area of ​​the Josephson junction, thereby improving the performance of the superconducting quantum chip.

[0005] In order to solve the above technical problems, the utility model provides a quantum device, comprising:

[0006] Josephson knots; and

[0007] A metal film electrically connected to the superconducting layer of the Josephson junction;

[0008] The metal film is provided with through holes for limiting the penetration of quasiparticles.

[0009] Preferably, the metal film is a capacitor.

[0010] Preferably, all of the through holes are in the shape of a triangular prism, a quadrangular prism or a cylinder.

[0011] Preferably, the quantum device further comprises a connector;

[0012] The connecting member is located between the Josephson junction and the metal film, and one end of the connecting member is electrically connected to one of the superconducting layers of the Josephson junction, and the other end of the connecting member is electrically connected to the metal film;

[0013] The connecting member is used to electrically connect the Josephson junction and the metal film.

[0014] Preferably, the quantum device further comprises a metal film layer for confining quasiparticles;

[0015] The metal film layer is electrically connected to an end of any superconducting layer of the Josephson junction away from the junction region.

[0016] Preferably, the metal film layer does not contact the metal film;

[0017] And / or, the material of the metal film layer is a superconducting metal or a common metal;

[0018] Wherein, the superconducting energy gap of the superconducting metal is smaller than the superconducting energy gap of the Josephson junction material.

[0019] The present application also provides a superconducting quantum chip, characterized in that it includes:

[0020] A quantum device as described in any of the preceding items;

[0021] substrate;

[0022] A superconducting metal layer is formed with a window, wherein the quantum device is located in the window; and

[0023] The quantum device and the superconducting metal layer are formed on the surface of the substrate in the same plane.

[0024] Preferably, the metal film is parallel to the surface of the substrate.

[0025] Preferably, the substrate is a sapphire substrate or a silicon substrate;

[0026] And / or, the material of the superconducting layer is aluminum.

[0027] Preferably, there are multiple quantum devices.

[0028] Compared with the prior art, the present application provides a quantum device, that is, the metal film connected to the two metal layers of the Josephson junction is improved, and a plurality of through holes penetrating the opposite surfaces of the metal film are distributed on the surface of the metal film; when the superconducting quantum chip enters the extremely low temperature space of the dilution refrigerator, the concentration of quasiparticles will increase greatly; the above-mentioned through holes can limit the quasiparticles and confine the quasiparticles in the through holes to prevent the quasiparticles from approaching the Josephson junction and avoiding them from participating in the tunneling process of the junction area, which can avoid causing bit energy decoherence, thereby greatly improving the performance of the superconducting quantum chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the structure of a quantum device provided in an embodiment of the present application;

[0030] Figure 2 A schematic diagram of the structure of a metal film layer and a Josephson junction provided in an embodiment of the present application;

[0031] Figure 3 A schematic diagram of the structure of a superconducting quantum chip provided in an embodiment of the present application.

[0032] Explanation of the reference numerals: 1 - Josephson junction, 2 - metal film, 21 - through hole, 3 - connector, 4 - metal film layer, 5 - substrate, 6 - superconducting metal layer. DETAILED DESCRIPTION

[0033] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as limiting the present application.

[0034] In the description of the present application, it should be understood that the terms "center", "up", "down", "left", "right", etc., indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present application.

[0035] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0036] During the operation of superconducting quantum chips, the operation of quantum bits is affected by different factors in the environment, such as radiation, light, sound, vibration, temperature and magnetic field. These environmental factors may cause quantum bit energy decoherence.

[0037] For superconducting quantum chips, the core component, the Josephson junction, is essentially an electronic circuit consisting of two superconducting layers and a non-superconducting layer tightly connected, and the thickness of the non-superconducting layer is as thin as nanometers. In superconducting quantum chips, one of the characteristics of the superconducting layer based on the substrate and the superconducting layer of the Josephson junction is that some electrons in the superconductor are combined in the form of Cooper pairs or BCS pairs, and each Cooper pair or BCS is a charged particle; in some cases, the two electrons that form the Cooper pair have a binding energy that makes them appear as a whole, which can be equivalent to the superconductor band gap energy. When the energy excitation received by the Cooper pair is greater than the band gap energy of the superconductor, the Cooper pair will separate and form separate quasiparticles.

[0038] At present, when a superconducting quantum chip is placed in the extremely low temperature space of a dilution refrigerator, the Cooper pairs in the superconducting material decompose due to environmental radiation to form a large number of quasiparticles; for high concentrations of quasiparticles, the behavior of quasiparticles near the junction area of ​​the Josephson junction is complex, for example: accompanied by the absorption or emission of photons or phonons, resulting in energy loss and release in the form of heat in a low temperature environment, specifically manifested as energy relaxation (the quantum bit changes its state) or dephasing (the quantum bit loses its phase coherence).

[0039] Generally speaking, one or more embodiments can restrict the position of quasiparticles by setting a quasiparticle capture structure, so that the quasiparticles cannot approach the junction region of the Josephson junction, reduce the quasiparticles' participation in the tunneling process of the junction region, and thus reduce the negative impact of the above-mentioned quasiparticles on the superconducting quantum chip.

[0040] Please refer to Figure 1 The present application provides a quantum device, comprising: a Josephson junction 1 and a metal film 2, wherein the metal film 2 is electrically connected to the superconducting layer of the Josephson junction 1; and the metal film 2 is provided with a through hole 21 penetrating two opposite surfaces, wherein the through hole 21 is used to restrict quasiparticles to prevent the quasiparticles from approaching the Josephson junction 1 and participating in the tunneling process of the junction region, resulting in decoherence of bit energy.

[0041] It is worth noting that the metal film 2 is a quantum device formed next to the Josephson junction 1 and is made of a superconducting metal. It can be made into, for example, a capacitor plate and together with the Josephson junction 1 construct a bit.

[0042] In addition, for the Josephson junction 1, the embodiment of the present application is that the Josephson junction 1 is composed of two intersecting superconducting layers, and a barrier layer is formed at the intersection of the two superconducting layers by oxidation or the like to form a weak connection between the two superconducting layers of the Josephson junction 1, forming an independent Josephson junction 1, and the intersection area is defined as a junction area, and the quasiparticles in the superconducting quantum chip will participate in the tunneling process of the junction area, causing energy decoherence, resulting in a decrease in the performance of the superconducting quantum chip; the parts of the two superconducting layers away from the junction area are respectively defined as the two electrodes of this Josephson junction 1; in connection with the above-mentioned metal film 2, that is, there can also be multiple metal films 2, and one metal film 2 corresponds to one electrode and is arranged close to each other.

[0043] In one embodiment provided in the present application, a metal film 2 made of a superconducting metal is provided with through holes 21, and there may be multiple through holes 21 that are evenly arranged on the surface of the metal film 2; in addition, when supported by the process, the multiple through holes 21 can be etched to have a density as high as possible and a number as large as possible to achieve the maximum limiting effect on the quasi-particles.

[0044] In one embodiment of the present application, the metal film 2 is made into a capacitor. A superconducting quantum bit is constructed by combining the Josephson junction 1 with the capacitor. In addition, according to product requirements, the metal film 2 can also be made into other devices, not limited to the above examples.

[0045] In one embodiment of the present application, the shape of all the through holes 21 can be a triangular prism, a quadrangular prism, or a cylinder, and there is no special limitation on the shape of the through holes 21; according to the inventor's experiments, almost all through holes 21 with "long strips" of internal space can effectively limit the position of the aligned particles; therefore, when etching to form the through holes 21, the shape of the through holes 21 can be arbitrarily selected according to needs and is not limited to the above examples.

[0046] In addition, when the through hole 21 is configured as a rectangular parallelepiped column with a square cross section, the side length of the cross section can be configured to be 2 μm-5 μm.

[0047] It is worth noting that the through hole 21 is formed by etching on the metal film 2, and what needs to be ensured is that the through hole 21 must pass through the two opposite surfaces of the metal film 2; according to the manufacturing process, the metal film 2 is generally attached to a certain planar carrier, and when the through hole 21 is manufactured, the metal film 2 can be punched by etching; in this regard, in order to ensure that the through hole 21 completely passes through the metal film 2, the metal film 2 can be etched first during the etching process, and the etching stop time can be delayed until the etching part of the above-mentioned planar carrier is etched, so as to achieve the purpose of the above-mentioned through hole 21 completely passing through the metal film 2.

[0048] In one embodiment of the present application, the above-mentioned quantum device also includes a connector 3; the connector 3 is located between the Josephson junction 1 and the metal film 2, and one end of the connector 3 is electrically connected to one of the superconducting layers of the Josephson junction 1, and the other end of the connector 3 is electrically connected to the metal film 2; the connector 3 is used to electrically connect the Josephson junction 1 and the metal film 2.

[0049] For quantum devices, the Josephson junction 1 and the metal film 2 need to be electrically connected. However, due to the influence of the manufacturing process and the materials of the Josephson junction 1 and the metal film 2, a connector 3 is added to electrically connect the two, and the material of the connector 3 can be ordinary metal.

[0050] For the Josephson junction 1 described above, two electrodes of the Josephson junction 1 can be electrically connected to a metal film 2 respectively, and a connector 3 is used as an electrical connection medium between the electrode of the Josephson junction 1 and the metal film 2; in this regard, the connector 3 can be a device with electrical connection function such as a metal flying wire or a connection port.

[0051] Please refer to Figure 2 In order to more deeply and comprehensively restrict the quasi-particles generated by the superconducting material, a metal film layer 4 may be added; the metal film layer 4 is formed at one end of the superconducting metal of the Josephson junction 1 away from the junction region.

[0052] It is worth noting that the metal film layer 4 in the above embodiment does not contact the metal film 2. According to the inventor's experiments, when the length of the metal film layer 4 is too long until it contacts the metal film 2, the metal film layer 4 and the metal film 2 will be electrically connected, resulting in a weakened restriction effect of the through holes 21 on the metal film layer 4 on the aligned particles.

[0053] In addition, the material of the metal film layer 4 is a superconducting metal or an ordinary metal; when the material of the metal film layer 4 is a superconducting metal, the superconducting metal satisfies that the superconducting energy gap is smaller than the superconducting energy gap of the Josephson junction 1 material, thereby limiting the position of the quasi-particles and reducing energy decoherence, so as to improve the performance of the superconducting quantum chip.

[0054] Specifically, when the metal is in a superconducting state, the formula of the superconducting gap Δ is: Δ = 1.75kTc, where k is the Boltzmann constant and Tc is the superconducting critical temperature. When aluminum is used as the material of the superconducting metal layer 6, the Tc of aluminum is 1.2K. At this time, titanium (Ti) and zirconium (Zr) can be used as the material of the metal film layer 4; wherein the Tc of Ti is 0.39K and the Tc of Zr is 0.55K, indicating that the superconducting energy gaps of titanium and zirconium are smaller than the superconducting energy gap of aluminum. In addition, when the material of the superconducting film layer 4 is selected as an ordinary metal, copper metal can be selected as an example.

[0055] Please refer to Figure 3 In another embodiment of the present application, a superconducting quantum chip is provided, comprising the aforementioned quantum device, a substrate 5 and a superconducting metal layer 6. According to the common manufacturing process of the superconducting quantum chip, a substrate 5 is provided, and a uniform superconducting metal layer 6 for manufacturing a quantum circuit can be formed on the surface of the substrate 5 by a magnetron sputtering process, and a window exposing the substrate 5 is etched on the superconducting metal layer 6, so that the aforementioned quantum device can be fabricated in the window by subsequent processes and attached to the substrate 5. According to the above-mentioned part, the quantum device and the superconducting metal layer 6 are finally formed together on one surface of the substrate 5.

[0056] In addition, the metal film 2 is manufactured to be parallel to the surface of the substrate 5 to form a through hole 21 on the metal film 2 for confining quasiparticles, preventing the quasiparticles from approaching the junction area of ​​the Josephson junction 1 and participating in the tunneling process, thereby causing energy decoherence of the quantum bit.

[0057] Furthermore, the substrate 5 is a sapphire substrate or a silicon substrate, which can be selected according to needs, and the material of the substrate 5 is not limited to the above examples.

[0058] In addition, the material of the superconducting layer is aluminum; according to the formula of the superconducting gap Δ: Δ=1.75kTc, when aluminum is used as the material of the superconducting layer, the Tc of aluminum is 1.2K, which meets the requirements of the superconducting energy gap of the above-mentioned superconducting layer and the metal film layer 4, that is, the superconducting energy gap of the metal film layer 4 is smaller than the superconducting energy gap of the superconducting layer.

[0059] In one embodiment of the present application, there are multiple quantum devices, that is, a superconducting quantum chip often includes more than one bit, and the corresponding number of Josephson junctions 1 and metal films 2 is also more than one; each quantum device is connected and signals are exchanged through a quantum circuit formed on the superconducting metal layer 6.

[0060] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example" or "specific example" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0061] The above describes in detail the structure, features and effects of the present application based on the embodiments shown in the drawings. The above is only a preferred embodiment of the present application, but the present application does not limit the scope of implementation to what is shown in the drawings. Any changes made in accordance with the concept of the present application, or modifications to equivalent embodiments with equivalent changes, which still do not exceed the spirit covered by the description and drawings, should be within the protection scope of the present application.

Claims

1. A quantum device, characterized in that: include: Josephson knot (1); as well as A metal film (2) electrically connected to the superconducting layer of the Josephson junction (1); The metal film (2) is provided with through holes (21) for limiting the penetration of quasiparticles.

2. The quantum device according to claim 1, characterized in that The metal film (2) is a capacitor.

3. The quantum device according to claim 1, characterized in that The shapes of all the through holes (21) are triangular prisms, quadrangular prisms or cylinders.

4. The quantum device according to claim 1, characterized in that The quantum device also includes a connecting element (3); The connecting member (3) is located between the Josephson junction (1) and the metal film (2), and one end of the connecting member (3) is electrically connected to one of the superconducting layers of the Josephson junction (1), and the other end of the connecting member (3) is electrically connected to the metal film (2); The connecting member (3) is used to electrically connect the Josephson junction (1) and the metal film (2).

5. The quantum device according to claim 1, characterized in that The quantum device also includes a metal film layer (4) for confining quasiparticles; The metal film layer (4) is electrically connected to an end of any superconducting layer of the Josephson junction (1) away from the junction region.

6. The quantum device according to claim 5, characterized in that The metal film layer (4) is not in contact with the metal film (2); And / or, the material of the metal film layer (4) is a superconducting metal or a common metal; The superconducting energy gap of the superconducting metal is smaller than the superconducting energy gap of the Josephson junction (1) material.

7. A superconducting quantum chip, characterized in that: include: The quantum device according to any one of claims 1 to 6; Base (5); A superconducting metal layer (6) is formed with a window, wherein the quantum device is located in the window; and The quantum device and the superconducting metal layer (6) are formed on the surface of the substrate (5) in the same plane.

8. The superconducting quantum chip according to claim 7, characterized in that: The metal film (2) is parallel to the surface of the substrate (5).

9. The superconducting quantum chip according to claim 7, characterized in that: The substrate (5) is a sapphire substrate or a silicon substrate; And / or, the material of the superconducting layer is aluminum.

10. The superconducting quantum chip according to claim 7, characterized in that: There are multiple quantum devices.

Images