Integrated microwave-light wave quantum converter based on composite substrate

Abstract

The invention provides an integrated microwave-light wave quantum converter based on a composite substrate, and relates to the technical field of quantum information. The integrated microwave-light wave quantum converter based on the composite substrate comprises the composite substrate, the composite substrate comprises a plurality of sub-substrates which are mutually stacked, and the sub-substrates are made of a high-thermal-conductivity material and / or a high-resistivity material; the coplanar waveguide layer is arranged above the composite substrate, is in direct contact with the composite substrate and is used for realizing conversion between a microwave signal and an optical signal; wherein the coplanar waveguide layer comprises a microwave signal input / output waveguide, a microwave cavity, a piezoelectric conversion waveguide, an acousto-optic crystal waveguide microcavity, a phase modulator, a pump light waveguide, an optical signal input / output waveguide and a phase modulator. According to the embodiment of the invention, the composite substrate in direct contact with the coplanar waveguide layer is adopted, heat generated in the working process can be directly transmitted to the substrate and then dissipated, and the heat dissipation capability and the thermal noise suppression capability of the whole system are greatly improved.

Description

Technical Field

[0001] This disclosure relates to the field of quantum information technology, and in particular to an integrated microwave-to-optical quantum converter based on a composite substrate. Background Technology

[0002] Microwaves, as the core carrier of large-scale superconducting quantum information processing systems, play an irreplaceable role in the reading, writing, and manipulation of superconducting qubits. However, their quantum states are constrained by thermal noise and transmission loss, requiring operation in ultra-low temperature environments at the mK level, which prevents long-distance, high-fidelity transmission and severely limits the development of quantum networks using superconducting qubits as nodes. In contrast, photons in the communication band (C-band) possess ultra-low transmission loss and strong resistance to environmental interference in optical fibers, making them an ideal carrier for long-distance quantum state transmission. Therefore, achieving high-fidelity coherent conversion between microwave and optical quantum states is a core technological path to breakthroughs in the interconnection of superconducting quantum processing systems.

[0003] Piezoelectric-based electro-optical microwave-to-optical conversion systems are an ideal choice for achieving high-fidelity conversion between microwave and optical quantum states due to their advantages in high conversion efficiency and compatibility with superconducting circuits. However, limitations in material platforms and device structure design mean that current mainstream devices employ nanoscale suspension structures, which suffer from poor mechanical stability leading to phase matching imbalance, heat accumulation due to heat dissipation difficulties, and process compatibility barriers between suspension designs and large-scale fabrication. These issues result in conversion efficiencies and added noise levels far below practical thresholds, limiting large-scale integrated applications. Summary of the Invention

[0004] In view of the above problems, embodiments of this disclosure provide an integrated microwave-to-optical quantum converter based on a composite substrate.

[0005] One aspect of this disclosure provides an integrated microwave-to-optical quantum converter based on a composite substrate, comprising: a composite substrate including multiple sub-substrates stacked on top of each other, the sub-substrates being composed of a high thermal conductivity material and / or a high resistivity material; a coplanar waveguide layer disposed above the composite substrate and in direct contact with the composite substrate, for realizing the conversion between microwave signals and optical signals; wherein the coplanar waveguide layer includes: a microwave signal input / output waveguide, a microwave cavity, a piezoelectric conversion waveguide, an acousto-optic crystal waveguide microcavity, a pump light waveguide, an optical signal input / output waveguide, and a phase modulator, wherein the pump light waveguide is used to transmit pump light to the acousto-optic crystal waveguide microcavity.

[0006] According to embodiments of this disclosure, the plurality of sub-substrates include: an uppermost substrate, the uppermost substrate representing a substrate in contact with the coplanar waveguide layer; wherein the optical refractive index of the uppermost substrate is less than that of the coplanar waveguide layer, and the acoustic wave propagation velocity of the uppermost substrate is greater than that of the coplanar waveguide layer.

[0007] According to an embodiment of this disclosure, the microwave cavity further includes: a transducer disposed above the piezoelectric conversion waveguide, used to convert a microwave signal into a first acoustic signal or to convert a second acoustic signal into a microwave signal; wherein the first acoustic signal is used to couple with pump light to generate an optical signal, and the second acoustic signal is obtained by coupling the pump light with the optical signal.

[0008] According to embodiments of this disclosure, the transducer employs an interdigitated electrode structure and uses an odd-even electrode asymmetric design to achieve unidirectional excitation of acoustic waves.

[0009] According to embodiments of this disclosure, the piezoelectric conversion waveguide has strong piezoelectric properties or the surface of the piezoelectric conversion waveguide is provided with a material with strong piezoelectric properties.

[0010] According to embodiments of this disclosure, the piezoelectric conversion waveguide, the acousto-optic crystal waveguide microcavity, and the pump waveguide are made of the same material and connected in sequence. The acousto-optic crystal waveguide microcavity is used to couple a first acoustic signal with the pump light to obtain an optical signal; or to couple an optical signal with the pump light to obtain a second acoustic signal.

[0011] According to embodiments of this disclosure, the acousto-optic crystal waveguide microcavity is composed of a one-dimensional periodic porous structure. The middle part of the acousto-optic crystal waveguide microcavity is a microcavity defect region, and the two sides of the acousto-optic crystal waveguide microcavity excluding the microcavity defect region are microcavity reflection regions. The diameter of the porous structure in the microcavity defect region is smaller than the diameter of the porous structure in the microcavity reflection region.

[0012] According to embodiments of this disclosure, the microcavity reflection region is a periodic porous structure region, and the microcavity defect region is a centrally symmetrical aperture gradient region, with the diameter of the porous structure decreasing sequentially from both sides to the center along the acousto-optic crystal waveguide microcavity.

[0013] According to embodiments of this disclosure, phase modulators are disposed on both sides of the acousto-optic crystal waveguide microcavity to generate a modulation electric field, which is used to modulate the phase of the acoustic mode and the optical mode of the acousto-optic crystal waveguide microcavity.

[0014] According to embodiments of this disclosure, the coplanar waveguide layer is stacked with the composite substrate by direct bonding or epitaxial growth.

[0015] The embodiments disclosed herein employ a composite substrate in direct contact with the coplanar waveguide layer, eliminating the floating structure design typically used in quantum converters. Heat generated during operation is directly transferred to the substrate and dissipated, significantly improving the overall system's heat dissipation and thermal noise suppression capabilities. Furthermore, this composite substrate possesses excellent thermal conductivity and high resistivity, avoiding substrate-induced losses of light waves, sound waves, and microwaves, as well as the accumulation of heat generated by these losses. Attached Figure Description

[0016] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 A schematic cross-sectional view of an integrated microwave-to-optical quantum converter based on a composite substrate according to an embodiment of the present disclosure is shown.

[0018] Figure 2 A schematic diagram of a coplanar waveguide layer according to an embodiment of the present disclosure is shown.

[0019] Figure 3 Various structural diagrams of a transducer according to embodiments of the present disclosure are schematically shown.

[0020] [Explanation of Labels in the Attached Image]

[0021] 1-Microwave signal input / output waveguide; 2-Microwave cavity; 3-Transducer; 4-Piezoelectric conversion waveguide; 5-Phase modulator; 6-Acousto-optic crystal waveguide microcavity; 7-Pump optical waveguide; 8-Optical signal input / output waveguide; 9-Uppermost substrate; 10-Other substrates. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0023] It should be noted that similar or identical parts are referred to by the same reference numerals in the accompanying drawings or description. The technical features of the various embodiments exemplified in the specification can be freely combined to form new solutions without conflict. Furthermore, each claim can stand alone as an embodiment, or the technical features in the various claims can be combined to form new embodiments. In the drawings, the shape or thickness of the embodiments may be enlarged and indicated in a simplified or convenient manner. Moreover, elements or implementations not shown or described in the drawings are those known to those skilled in the art. Additionally, although this document provides examples of parameters containing specific values, it should be understood that the parameters need not be exactly equal to the corresponding values, but can approximate the corresponding values ​​within acceptable error tolerances or design constraints.

[0024] Unless there are technical obstacles or contradictions, the various embodiments described above in this disclosure can be freely combined to form other embodiments, all of which are within the protection scope of this disclosure.

[0025] Although this disclosure has been described in conjunction with the accompanying drawings, the embodiments disclosed in the drawings are intended to illustrate preferred embodiments of this disclosure and should not be construed as limiting the disclosure. The dimensions in the drawings are merely illustrative and should not be construed as limiting the disclosure.

[0026] While some embodiments of the general concept of this disclosure have been shown and described, those skilled in the art will understand that changes may be made to these embodiments without departing from the principles and spirit of the general concept of this disclosure, the scope of which is defined by the claims and their equivalents.

[0027] Figure 1 A schematic diagram illustrates the structure of an integrated microwave-to-optical quantum converter based on a composite substrate according to an embodiment of the present disclosure. Figure 1 As shown, embodiments of this disclosure provide an integrated microwave-to-optical quantum converter based on a composite substrate, comprising: a composite substrate, the composite substrate including multiple sub-substrates stacked on top of each other, the sub-substrates being composed of a high thermal conductivity material and / or a high resistivity material; and a coplanar waveguide layer disposed above the composite substrate and in direct contact with the composite substrate, used to realize the conversion between microwave signals and optical signals.

[0028] In some embodiments, the plurality of sub-substrates include: an uppermost substrate 9 and remaining substrates 10, wherein the uppermost substrate 9 represents the substrate in contact with the coplanar waveguide layer. The remaining substrates 10 may be made of materials such as diamond, silicon carbide, high-resistivity silicon, or aluminum nitride. The uppermost substrate 9 may be made of materials such as aluminum nitride. The composite substrate is composed of multiple layers of high thermal conductivity and high-resistivity materials to obtain excellent thermal conductivity and heat dissipation characteristics and low microwave, optical, and acoustic loss characteristics.

[0029] Figure 2 A schematic diagram of a coplanar waveguide layer according to an embodiment of the present disclosure is shown.

[0030] like Figure 2 As shown, the coplanar waveguide layer includes: a microwave signal input / output waveguide 1, a microwave cavity 2, a piezoelectric conversion waveguide 4, an acousto-optic crystal waveguide microcavity 6, a phase modulator 5, a pump waveguide 7, and an optical signal input / output waveguide 8. The microwave cavity 2 includes a transducer 3, and a layer of highly piezoelectric material can be inserted between the interdigitated electrodes of the transducer 3 and the underlying piezoelectric conversion waveguide 4.

[0031] The piezoelectric conversion waveguide 4, acousto-optic crystal waveguide microcavity 6, pump waveguide 7, and optical signal input / output waveguide 8 in the coplanar waveguide layer together constitute the coplanar waveguide structure group.

[0032] In some embodiments, the material of the uppermost substrate 9, which is in direct contact with the coplanar waveguide layer, not only possesses high thermal conductivity and high resistance, but also satisfies the following conditions: its optical refractive index is lower than that of the coplanar waveguide structure group, and its acoustic wave propagation velocity is higher than that of the coplanar waveguide structure group. This achieves strong confinement of acoustic and optical waves within the integrated structure, thereby realizing efficient acousto-optic coupling. Furthermore, these conditions are also met at ultra-low temperatures. Additionally, the thickness of this material layer is generally greater than three times the wavelength of the acoustic and optical waves.

[0033] Composite substrate layers and their coplanar waveguide structures can be bonded together via direct bonding or heteroepitaxial bonding. This allows heat generated during device operation within the coplanar waveguide layer to be directly conducted away, with the heat dissipation path being less than the subwavelength order of magnitude, significantly improving heat dissipation and device stability.

[0034] The embodiments disclosed herein employ a composite substrate in direct contact with the coplanar waveguide layer, eliminating the floating structure design typically used in quantum converters. Heat generated during operation is directly transferred to the substrate and dissipated, significantly improving the overall system's heat dissipation and thermal noise suppression capabilities. Furthermore, this composite substrate possesses excellent thermal conductivity and high resistivity, avoiding heat loss due to light, sound, and microwave waves caused by the substrate.

[0035] Please continue reading. Figure 2 The basic working principle of the integrated microwave-to-optical quantum converter in the embodiments of this application is as follows:

[0036] The conversion from microwave quantum state to optical quantum state: Microwave signals transmitted from other microwave quantum systems are coupled into microwave cavity 2 through microwave signal input / output waveguide 1. Then, through transducer 3 in microwave cavity 2, the piezoelectric effect generated in piezoelectric conversion waveguide 4 converts the microwave signal into a first acoustic wave signal of the same frequency. The first acoustic wave signal enters the acousto-optic crystal waveguide microcavity 6 and is confined within the cavity. Simultaneously, pump light entering from the other end of the microcavity through pump light waveguide 7 is also confined within microcavity 6, undergoing acousto-optic coupling with the first acoustic wave signal to generate an optical signal. In this way, the microwave quantum state is converted into the optical quantum state.

[0037] The conversion from optical quantum state to microwave quantum state: The optical signal transmitted from other optical quantum systems is coupled into the acousto-optic crystal waveguide microcavity through the optical signal input / output waveguide 8. It is coupled with the pump light entering from one end of the acousto-optic crystal waveguide microcavity in the cavity, generating a second acoustic signal. The second acoustic signal enters the transducer 3 through the piezoelectric conversion waveguide 4 and is then converted into a microwave signal. It then leaves the microwave cavity 2 through the coupling between the microwave cavity 2 and the microwave signal input / output waveguide 1 and enters other microwave quantum systems. In this way, the optical quantum state is converted into the microwave quantum state.

[0038] In some embodiments, the microwave cavity 2 is made of a superconducting material and can be fabricated by metal lift-off or photolithography. The microwave cavity 2 consists of a ring waveguide structure and a transducer 3. Through coupling with adjacent waveguides, it enables the input and output of microwave signals within the cavity. The adjacent waveguides are directly connected to other microwave quantum systems. The microwave cavity significantly enhances the coupling between microwaves and piezoelectric media, improving the conversion efficiency between microwaves and acoustic waves, thereby promoting the improvement of device conversion efficiency. The material of the coplanar waveguide layer waveguide structure 6-8 can be gallium nitride, gallium arsenide, lithium niobate, etc. The material of the microwave cavity 2 can be niobium nitride, titanium niobium nitride, aluminum, etc. The shape of the microwave cavity 2 is not limited to a circle, but the corners should be rounded to avoid sharp structures. The waveguide width is on the order of microwave wavelength, and the thickness is less than the wavelength.

[0039] In some embodiments, the coplanar waveguide structure is fabricated by photolithography and includes an acousto-optic crystal waveguide microcavity 6, with its two sides connected to a pump light input terminal and an acoustic wave input waveguide; a signal light waveguide is located on one side of the acousto-optic crystal waveguide microcavity. A phase modulator 5, consisting of a pair of electrodes, is located on both sides of the acousto-optic microcavity and can modulate the phase of the optical and acoustic fields in the microcavity by applying a DC electric field. In this way, the acoustic and optical fields can achieve strong spatial confinement in a non-suspended structure, thereby significantly improving the acousto-optic coupling strength. In addition, the phase modulation maximizes the efficiency of this process, ultimately resulting in a significant improvement in the conversion efficiency of the device.

[0040] Please continue reading. Figure 2 Transducer 3 is located on the acoustic wave input waveguide on one side of the acousto-optic crystal waveguide microcavity, achieving bidirectional conversion between microwaves and acoustic waves through the piezoelectric effect. A layer of material with an ultra-high piezoelectric coefficient can be inserted between transducer 3 and the waveguide to improve the conversion efficiency between microwaves and acoustic waves. Transducer 3 adopts an interdigitated electrode odd-even asymmetric design to achieve unidirectional excitation of acoustic waves, thereby improving transducer efficiency.

[0041] The acousto-optic crystal waveguide microcavity 6 possesses phonon and photon bandgaps. The acoustic and optical modes during the acousto-optic coupling process reside within these bandgaps, confining them within the microcavity and enhancing coupling strength. The acousto-optic crystal waveguide microcavity 6 is composed of a one-dimensional periodic aperture structure, the shape of which can be circular, elliptical, rectangular, etc. Its structure can consist of two side reflection regions and a central defect region, or two side gradient regions and a central periodic region.

[0042] Pump light and signal light waveguides can be connected to other optical systems via optical fibers.

[0043] Figure 3 Various structural diagrams of a transducer according to embodiments of the present disclosure are schematically shown.

[0044] like Figure 3As shown, in the embodiments of this disclosure, the transducer 3 adopts an asymmetric unidirectional electrode design, and its shape is not limited. Figure 2 As shown, it can also be used Figure 3 The structures shown in (a), (b), (c), and (d) are as follows. The number of interdigitated electrodes, period, and duty cycle of transducer 3 can be determined according to actual conditions. Transducer 3 preferably operates at frequencies covering hundreds of MHz to tens of GHz to meet application requirements in the microwave quantum field.

[0045] In some embodiments, the piezoelectric conversion waveguide below the transducer 3 is used to achieve the conversion between sound waves and microwaves. The piezoelectric conversion waveguide 4 should have strong piezoelectric properties or have a layer of a material with strong piezoelectric properties disposed on its surface. Preferred materials with strong piezoelectric properties are aluminum nitride, scandium aluminum nitride, lithium niobate, etc., which can maintain strong piezoelectric properties at low temperatures. The use of a material with strong piezoelectric properties can be selected according to the situation; for example, it may not be used when the material of the piezoelectric conversion waveguide 4 is lithium niobate.

[0046] In some embodiments, the acousto-optic crystal waveguide microcavity 6 is composed of a periodic aperture structure, preferably with circular or elliptical apertures. The preferred microcavity structure is divided into three regions: a microcavity reflection region and a microcavity defect region. These regions form the bandgap for the acoustic and optical modes required for acousto-optic coupling. By changing the periodic structural parameters of the microcavity reflection region, the desired modes can appear in the phonon and photon bandgap, thus confining the acoustic and optical modes to the defect region. The number of periods in the microcavity reflection region is 4-20, sufficient to satisfy the injection of acoustic and optical fields and the constraint of the target modes. The preferred number of apertures in the microcavity reflection region is 5-20, and the size and spacing of the apertures can be adjusted according to the actual acoustic and optical modes and frequencies. Alternatively, the acousto-optic crystal waveguide microcavity can also adopt an antisymmetric structure with the center of the microcavity defect region as the axis of symmetry.

[0047] In some embodiments, the crystal orientation of the material of the coplanar waveguide structure group is preferably set to have the maximum electro-optic coefficient and electro-acoustic coefficient along the plane direction, which is consistent with the direction of the electric field in the phase modulator 5, so as to maximize the modulation efficiency of the modulator.

[0048] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process may be rearranged without departing from the scope of this disclosure. The appended method claims provide elements of various steps in an exemplary order and are not intended to limit the scope to a specific order or hierarchy.

[0049] It should also be noted that the directional terms mentioned in the embodiments, such as "up," "down," "front," "back," "left," and "right," are only for reference to the directions in the accompanying drawings and are not intended to limit the scope of protection of this disclosure. Throughout the drawings, the same elements are represented by the same or similar reference numerals. Conventional structures or constructions will be omitted when they may cause confusion in understanding this disclosure. Furthermore, the shapes, sizes, and positional relationships of the components in the drawings do not reflect their actual size, scale, or actual positional relationships.

[0050] In the detailed description above, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, this disclosure is in a state of having fewer features than all of the features of the single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, with each claim representing a separate preferred embodiment of this disclosure.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly specified. The term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," as "including" is used as a conjunction in the claims. The use of any term "or" in the specification or claims is intended to mean "non-exclusive or."

[0052] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. An integrated microwave-to-optical quantum converter based on a composite substrate, characterized in that, include: A composite substrate comprising a plurality of sub-substrates stacked on top of each other, the sub-substrates being composed of a material with high thermal conductivity and / or a material with high resistivity; A coplanar waveguide layer is disposed above the composite substrate and in direct contact with the composite substrate, used to realize the conversion between microwave signals and optical signals; The coplanar waveguide layer includes: The system includes a microwave signal input / output waveguide, a microwave cavity, a piezoelectric conversion waveguide, an acousto-optic crystal waveguide microcavity, a pump optical waveguide, an optical signal input / output waveguide, and a phase modulator, wherein the pump optical waveguide is used to transmit pump light into the acousto-optic crystal waveguide microcavity.

2. The integrated microwave-to-optical quantum converter according to claim 1, characterized in that, The plurality of sub-substrates include: an uppermost substrate, wherein the uppermost substrate represents a substrate in contact with the coplanar waveguide layer; The uppermost substrate has a lower optical refractive index than the coplanar waveguide layer, and the uppermost substrate has a higher acoustic wave propagation velocity than the coplanar waveguide layer.

3. The integrated microwave-to-optical quantum converter according to claim 1, characterized in that, The microwave cavity further includes: A transducer, disposed above the piezoelectric conversion waveguide, is used to convert the microwave signal into a first acoustic signal or a second acoustic signal into the microwave signal; Wherein, the first acoustic signal is used to couple with the pump light to generate the optical signal, and the second acoustic signal is obtained by coupling the pump light with the optical signal.

4. The integrated microwave-to-optical quantum converter according to claim 3, characterized in that... The transducer adopts an interdigitated electrode structure and uses an odd-even electrode asymmetry design to achieve unidirectional excitation of sound waves.

5. The integrated microwave-to-optical quantum converter according to claim 1, characterized in that... The piezoelectric conversion waveguide has strong piezoelectric properties or the surface of the piezoelectric conversion waveguide is provided with a material with strong piezoelectric properties.

6. The integrated microwave-to-optical quantum converter according to claim 3, characterized in that, The piezoelectric conversion waveguide, the acousto-optic crystal waveguide microcavity, and the pump waveguide are made of the same material and connected in sequence. The acousto-optic crystal waveguide microcavity is used to couple the first acoustic signal with the pump light to obtain the optical signal; or The optical signal is coupled with the pump light to obtain the second acoustic signal.

7. The integrated microwave-to-optical quantum converter according to claim 1, characterized in that, The acousto-optic crystal waveguide microcavity is composed of a one-dimensional periodic aperture structure. The middle part of the acousto-optic crystal waveguide microcavity is a microcavity defect region. The two sides of the acousto-optic crystal waveguide microcavity excluding the microcavity defect region are microcavity reflection regions. The diameter of the aperture structure in the microcavity defect region is smaller than the diameter of the aperture structure in the microcavity reflection region.

8. The integrated microwave-to-optical quantum converter according to claim 7, characterized in that, The microcavity reflection region is a periodic porous structure region, and the microcavity defect region is a centrally symmetrical aperture gradient region. The diameter of the porous structure decreases sequentially from both sides to the middle of the acousto-optic crystal waveguide microcavity.

9. The integrated microwave-to-optical quantum converter according to claim 1, characterized in that, The phase modulator is disposed on both sides of the acousto-optic crystal waveguide microcavity to generate a modulation electric field, which is used to modulate the phase of the acoustic mode and the optical mode of the acousto-optic crystal waveguide microcavity.

10. The integrated microwave-to-optical quantum converter according to claim 1, characterized in that, The coplanar waveguide layer is stacked with the composite substrate by direct bonding or epitaxial growth.

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