A non-suspended quantum transducer device for coherent photon conversion in the microwave communication band

Abstract

The present invention provides a non-suspended quantum transducer device for coherent conversion of photons in the microwave communication band. The transducer body is divided into two parts: a piezoelectric mechanical cavity and a photoacoustic crystal microcavity. Assisted by an optical waveguide and an electrode system, it uses a mechanical oscillator as an intermediary to complete the bidirectional conversion of microwave signals of solid-state quantum bits and photons in the communication band. The piezoelectric mechanical cavity uses lithium niobate material to convert microwave signals into mechanical vibrations through the piezoelectric effect. The mechanical vibrations are transmitted to the defect region of the photoacoustic crystal microcavity through the phonon waveguide and couple with the photons in the communication band. The present invention innovatively adopts a non-suspended structure. Through structural design, while ensuring low mechanical loss, it greatly improves the stability and heat dissipation capacity of the transducer. This device is suitable for microwave and photon signal conversion in the fields of quantum computing, quantum communication, etc., and is of great significance to the development of technologies such as long-distance transmission of quantum information and integrated quantum computers.

Description

Technical Field

[0001] The present invention belongs to the technical fields of quantum information, quantum computing, quantum optomechanics, etc., and is mainly used in large-scale, integrated quantum information processing and computing. Specifically, it is a non-suspended quantum transducer device for coherent conversion of photons in the microwave communication band. Background Art

[0002] Microwave signals are the most widely used signal carriers in quantum information processing and can effectively manipulate and read quantum bits. However, the quantum states encoded by microwave photons are easily overwhelmed by thermal noise at room temperature, and the losses are also high, which hinders the long-distance transmission of quantum signals. Therefore, the goal pursued by researchers is to convert microwave quantum signals into communication-band photons that can be transmitted efficiently and over long distances at room temperature. The huge frequency gap between microwaves and photons is the biggest obstacle to achieving conversion. Although top companies and universities such as IBM and Harvard University have developed some feasible quantum transducer systems (electro-optical quantum transducers, superconducting quantum transducers, etc.), these systems still face problems such as low energy conversion efficiency and high requirements for low-temperature experimental conditions.

[0003] In 2015, Noethrop Grumman proposed a transducer structure that uses mechanical resonance to couple light to superconducting quantum bits, opening up a new approach. In recent years, Professor Painter's research group at California Institute of Technology has developed a transducer that uses phonons as a resonator, leveraging the piezoelectric effect and photoacoustic coupling to achieve bidirectional microwave-acoustic-light conversion. Building on their work, our invention innovatively proposes a non-suspended transducer structure, addressing issues such as the instability of suspended nanobeams during experiments and the significant thermal noise generated by photoheating, contributing to the further development of the field of quantum transducers. Summary of the Invention

[0004] This invention provides a non-suspended quantum transducer structure based on a piezoelectric mechanical cavity and a photoacoustic crystal microcavity. Its purpose is to achieve bidirectional conversion between microwave signals and communication-band photons in solid-state quantum bits, using mechanical oscillators as an intermediary. Superconducting qubits have demonstrated fast, high-fidelity single- and two-qubit logic gates, showing great application prospects in quantum computing. The microwave interface of the quantum transducer can be directly coupled to such qubits via an on-chip coplanar waveguide, enabling the reading and control of microwave electrical signals.

[0005] In order to achieve the above-mentioned purpose of the invention, the technical solution of the present invention is as follows:

[0006] A non-suspended quantum transducer device for coherent photon conversion in the microwave communication band includes an SOI substrate: the SOI substrate is composed of three layers, the upper and lower layers are silicon, and the middle layer is a silicon dioxide insulating layer;

[0007] The top layer of silicon is etched to form a transducer device, including an auxiliary electrode system 1, a piezoelectric mechanical cavity 2, a photoacoustic crystal microcavity 3, and an optical waveguide 4. The entire transducer structure is directly in contact with the silicon dioxide substrate 5 and has no suspended parts.

[0008] Assume that the direction from the photoacoustic crystal microcavity 3 to the piezoelectric mechanical cavity 2 on the top silicon plane is x, and the y direction is perpendicular to the x direction;

[0009] The auxiliary electrode system 1 is in the shape of an acoustic radiation wall and is arranged along the y-direction. The auxiliary electrode system 1 includes two layers: a lower layer of silicon material and an upper layer of electrode material. The piezoelectric material of the piezoelectric mechanical cavity 2 is arranged between the silicon material and the electrode material of the auxiliary electrode system 1. The two layers of material of the auxiliary electrode system 1 and the piezoelectric material of the piezoelectric mechanical cavity 2 together constitute the piezoelectric cavity. The auxiliary electrode system 1 and the photoacoustic crystal microcavity 3 form a T-shaped intersection at the piezoelectric mechanical cavity 2.

[0010] The optical waveguide 4 is located on one side of the photoacoustic crystal microcavity 3 and is parallel to the photoacoustic crystal microcavity 3 .

[0011] The photoacoustic crystal microcavity 3 is composed of a silicon nanobeam with holes. By setting the silicon nanobeam hole system of different shapes, sizes and spacings, the nanobeam is divided into three parts: a phonon waveguide 6, a defect region 7 and a periodic region 8. When phonons enter the periodic region 8, they are reflected back to the defect region 7, thereby achieving the localization of phonons in the defect region 7.

[0012] As a preferred embodiment, one end of the optical waveguide 4 is connected to an external optical fiber for laser input; and a hole system is provided at the other end to form acoustic and optical bandgap modes.

[0013] As a preferred embodiment, one end of the auxiliary electrode system 1 is connected to the piezoelectric mechanical cavity 2, and the other end is connected to an external microwave circuit.

[0014] As a preferred embodiment, the auxiliary electrode system 1 is wired in an interdigital transducer mode, and the microwave signal in the electrode is converted into mechanical vibration in the mechanical cavity through the piezoelectric effect.

[0015] As a preferred method, the mechanical oscillator in the piezoelectric mechanical cavity is used as an intermediary to complete the conversion of microwave photons into communication band photons: the mechanical vibration in the piezoelectric mechanical cavity generates mechanical oscillators, namely phonons, which are transmitted along the phonon waveguide 6 into the defect region 7 of the photoacoustic crystal microcavity and converted into communication band photons through photoacoustic coupling.

[0016] As a preferred method, the piezoelectric machine and the optomechanical system are connected by using mechanical oscillators and phonon waveguides 6, so as to complete the conversion from microwaves to communication band photons.

[0017] As a preferred embodiment, the piezoelectric mechanical cavity is covered with a 100nm thick z-cut lithium niobate layer on a silicon substrate as a piezoelectric material, and the lithium niobate layer is further covered with an 80nm thick aluminum electrode.

[0018] As a preferred embodiment, the auxiliary electrode system uses aluminum as the electrode material with a thickness of 80 nm, and the aluminum electrode is directly covered on the silicon substrate.

[0019] As a preferred embodiment, the number of pairs of fingers of the IDT of the auxiliary electrode system 1 is adjustable.

[0020] As a preferred embodiment, the unit structure of an acoustic radiation wall of the auxiliary electrode system 1 is one layer, and the total number of layers is 5-7 layers.

[0021] As a preferred embodiment, the optical waveguide 4 can introduce external laser photons and make them escape into the defect region 7 of the photoacoustic crystal microcavity 3 for photoacoustic coupling. The optical waveguide 4 is preferably made of silicon material.

[0022] The working principle of the present invention is as follows:

[0023] When converting microwaves to communication optical signals, the auxiliary electrode system conducts the electrical signals in the microwave circuit to the piezoelectric mechanical cavity. The piezoelectric mechanical cavity uses the piezoelectric effect to couple the electrical signals in the metal electrode to the mechanical vibrations in the silicon. The mechanical vibrations are then transmitted to the nanobeam defect area through the phonon waveguide on the photoacoustic crystal microcavity, and the mechanical vibrations are converted into photons in the communication band through radiation pressure. The communication photons are transmitted into the optical fiber network through the optical waveguide, thereby achieving long-distance transmission. When converting communication light to microwave signals, the operating principle is the same, and the operating process is reversed. The main structure of the transducer of the present invention is etched from the first layer of silicon and is in direct contact with the middle silicon dioxide insulating layer. No suspension structure is designed, and the stability and heat dissipation capacity of the device are greatly improved.

[0024] The piezoelectric mechanical cavity uses lithium niobate, a material with a high-voltage electrical coupling coefficient. When an alternating voltage is applied to the lithium niobate through electrodes, the electric dipole moment within the lithium niobate undergoes periodic changes, inducing stress or strain within the material, thereby generating mechanical vibration. Simultaneously, the strain caused by mechanical vibration in turn affects the charge distribution within the material, generating an electric field effect within the material that couples with the mechanical vibration mode.

[0025] The photoacoustic crystal microcavity is composed of silicon nanobeams with holes. By designing the shape, size, spacing, and number of the holes in the silicon nanobeams, the energy bands of phonons and photons are made to overlap, thereby simultaneously localizing both particles in a tiny area. The two particles interact through light radiation pressure, achieving coupling.

[0026] As a preferred embodiment, the acoustic radiation wall is designed as a cross-shaped structure with ten layers, symmetrical around the mechanical cavity, and five layers on each side.

[0027] As a preferred embodiment, the optical waveguide is provided on one side of the photoacoustic crystal microcavity and arranged in parallel therewith, so that the optical signal can directly enter the defect region of the photoacoustic crystal microcavity from the optical waveguide.

[0028] As a preferred embodiment, the thickness of the silicon dioxide layer used to place the device is 3000 nm.

[0029] As a preferred embodiment, all corners of the device are designed to be rounded structures.

[0030] The present invention has the following beneficial effects: It creatively utilizes a non-suspended structure, directly building complex structures within silicon materials onto a silicon dioxide substrate. Through rational nanostructure design, the high mechanical losses inherent in non-suspended structures are overcome, allowing mechanical resonance to be localized within a specific area. Furthermore, the non-suspended structure allows the photoacoustic crystal microcavity to maintain contact with the substrate over a large area, significantly improving the stability of the entire device while providing exceptional heat dissipation capabilities and mitigating the impact of noise caused by optical heating on the system.

[0031] In addition, the present invention uses lithium niobate materials with a large piezoelectric coupling rate, allowing the device to have more energy in the optomechanical cavity, which translates into greater intrinsic readout efficiency. The photoacoustic crystal microcavity used to achieve conversion between mechanical modes and optical signals has a high optomechanical coupling rate because it can simultaneously localize optical and mechanical modes at the nanoscale. Its excellent material compatibility, combined with the stability of the non-suspended device, further enhances the application potential of the system in large-scale integration and on-chip manufacturing. The phonon waveguide 6 on the photoacoustic crystal microcavity supports a variety of hybrid acoustic modes, ensuring that even if mode detuning is caused during the manufacturing process, the piezoelectric mechanical and optomechanical modes can still maintain a high piezoelectric and optomechanical coupling rate. By connecting the mechanical modes of the two conversion processes through the phonon waveguide 6, higher conversion efficiency and lower additional noise can be achieved, making the present invention promising to achieve light-mediated entanglement between remote superconducting qubits. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the complete structural diagram of the quantum transducer.

[0033] Figure 2 The three views of the quantum transducer structure. (a) is the top view, (b) is the side view, and (c) is the front view.

[0034] Figure 3 Capacitive routing from a piezomechanical cavity to a transmon qubit.

[0035] Figure 4 is the potential diagram of the piezoelectric mode.

[0036] Figure 5 is the vibration shape diagram of the mechanical mode.

[0037] Figure 6 is the electric field norm of the communication optical mode.

[0038] 1-Auxiliary electrode system, 2-Piezoelectric mechanical cavity, 3-Photoacoustic crystal microcavity, 4-Optical waveguide, 5-Silicon dioxide substrate, 6-Phononic waveguide, 7-Defect region, 8-Periodic region. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] like Figure 1 As shown, this embodiment provides a non-suspended quantum transducer device for coherent conversion of photons in the microwave communication band, including an SOI substrate: the SOI substrate is composed of three layers, the upper and lower layers are silicon, and the middle layer is a silicon dioxide insulating layer;

[0041] The top layer of silicon is etched to form a transducer device, including an auxiliary electrode system 1, a piezoelectric mechanical cavity 2, a photoacoustic crystal microcavity 3, and an optical waveguide 4. The entire transducer structure is directly in contact with the silicon dioxide substrate 5 and has no suspended parts.

[0042] Assume that the direction from the photoacoustic crystal microcavity 3 to the piezoelectric mechanical cavity 2 on the top silicon plane is x, and the y direction is perpendicular to the x direction;

[0043] The auxiliary electrode system 1 is in the shape of an acoustic radiation wall and is arranged along the y-direction. The auxiliary electrode system 1 includes two layers: a lower layer of silicon material and an upper layer of electrode material. The piezoelectric material of the piezoelectric mechanical cavity 2 is arranged between the silicon material and the electrode material of the auxiliary electrode system 1. The two layers of material of the auxiliary electrode system 1 and the piezoelectric material of the piezoelectric mechanical cavity 2 together constitute the piezoelectric cavity. The auxiliary electrode system 1 and the photoacoustic crystal microcavity 3 form a T-shaped intersection at the piezoelectric mechanical cavity 2.

[0044] The optical waveguide 4 is located on one side of the photoacoustic crystal microcavity 3 and is parallel to the photoacoustic crystal microcavity 3 .

[0045] The photoacoustic crystal microcavity 3 is composed of a silicon nanobeam with holes. By setting the silicon nanobeam hole system of different shapes, sizes and spacings, the nanobeam is divided into three parts: a phonon waveguide 6, a defect region 7 and a periodic region 8. When phonons enter the periodic region 8, they are reflected back to the defect region 7, thereby achieving the localization of phonons in the defect region 7.

[0046] Preferably, one end of the optical waveguide 4 is connected to an external optical fiber for laser input; and the other end is provided with a hole system to form acoustic and optical bandgap modes.

[0047] Preferably, one end of the auxiliary electrode system 1 is connected to the piezoelectric mechanical cavity 2 , and the other end is connected to an external microwave circuit.

[0048] Preferably, the auxiliary electrode system 1 is wired in an interdigital transducer mode, and converts microwave signals in the electrode into mechanical vibrations in the mechanical cavity through the piezoelectric effect.

[0049] Preferably, the mechanical oscillator in the piezoelectric mechanical cavity is used as an intermediary to complete the conversion of microwave photons into communication band photons: the mechanical vibration in the piezoelectric mechanical cavity generates mechanical oscillators, namely phonons, which are transmitted along the phonon waveguide 6 into the defect region 7 of the photoacoustic crystal microcavity and are converted into communication band photons through photoacoustic coupling.

[0050] Preferably, the piezoelectric machine and the optomechanical system are connected by using the mechanical vibrator and the phonon waveguide 6, so as to complete the conversion from microwaves to communication band photons.

[0051] Preferably, the piezoelectric mechanical cavity is covered with a 100 nm thick layer of z-cut lithium niobate on a silicon substrate as the piezoelectric material, and the lithium niobate layer is further covered with an 80 nm thick aluminum electrode.

[0052] Preferably, the auxiliary electrode system uses aluminum as the electrode material with a thickness of 80 nm, and the aluminum electrode directly covers the silicon substrate.

[0053] Preferably, the number of pairs of fingers of the IDT of the auxiliary electrode system 1 is adjustable.

[0054] Preferably, the unit structure of one acoustic radiation wall of the auxiliary electrode system 1 is one layer, and the total number of layers is 5-7 layers.

[0055] Preferably, the optical waveguide 4 can introduce external laser photons and make them escape into the defect region 7 of the photoacoustic crystal microcavity 3 for photoacoustic coupling. The optical waveguide 4 is preferably made of silicon material.

[0056] Figure 1 Figure 2 For the complete structure of the quantum transducer, Figure 2 In the top view, the left side is a piezoelectric mechanical cavity, which realizes the conversion between microwave electrical signals and mechanical modes, and the right side is a photoacoustic crystal microcavity, which realizes the conversion between mechanical modes and communication optical signals. It can be seen from the main view that the device is placed on the silicon dioxide layer.

[0057] The piezoelectric mechanical cavity utilizes a 100nm-thick z-cut lithium niobate layer placed atop a silicon substrate, while an 80nm-thick aluminum electrode covers the surface of the lithium niobate. To reduce mechanical losses, the piezoelectric mechanical cavity is designed to be small (~500nm × 800nm), making the piezoelectric mechanical mode more sensitive to changes in cavity size. The IDT is replicated from the acoustic radiation wall of the unit structure and adopts a double-layer design: the upper layer is an aluminum electrode, and the lower layer is silicon material. To suppress energy leakage from mechanical vibrations, the present invention designs this acoustic radiation wall within the band gap of the mechanical mode, effectively suppressing longitudinal phonon dispersion and allowing mechanical vibration energy to propagate only laterally to the phonon waveguide 6, thereby further improving the piezoelectric mechanical coupling efficiency and enhancing the efficiency and stability of energy transmission. The number of IDTs and the number of layers in the acoustic radiation wall unit structure can be increased or decreased according to actual needs. Due to the strong piezoelectric properties of lithium niobate, the piezoelectric mechanical coupling efficiency remains sufficiently high even when only two IDTs are used. Therefore, the present invention preferably uses two IDTs.

[0058] Figure 3 For the capacitive routing of the piezoelectric mechanical cavity to the transmon qubit, in the experimental process of the present invention, voltages (5V and ground) are applied to the two IDTs respectively to couple the mechanical vibration of the piezoelectric mechanical cavity with capacitance. The typical qubit capacitance value C is used. q =70fF, the capacitance value of IDT is C IDT =0.25fF. The piezoelectric mode and mechanical mode are as follows Figure 4 and Figure 5 As shown in Figure 3, the piezoelectric mechanical coupling coefficient in the piezoelectric mechanical conversion process reaches 9 MHz.

[0059] The photoacoustic crystal microcavity is divided into three regions: periodic region, defect region and phonon waveguide, such as Figure 2 As shown. The periodic region is located on both sides of the defect region and has a symmetrical structure, which can provide mechanical and optical band gaps at the same time, thereby preventing the propagation of phonons and photons, causing them to be reflected back to the defect region in this area. In the defect region, the unit structure of the periodic region is replaced by a defect unit, which can simultaneously localize the required mechanical mode phonons and communication band photons through radiation pressure. By designing the shape, size and spacing of the elliptical holes on the silicon nanobeam, the other side of the defect region is adjusted to a phonon waveguide, which only conducts mechanical modes and is within the band gap range of the optical mode. This enables the mechanical vibration mode converted by the piezoelectric mechanical cavity to be effectively transmitted to the defect region, and coupled with the optical mode to complete the signal conversion and regulation. Finally, the mechanical mode vibration shape and communication band light field obtained by the simulation of this experiment are shown as follows: Figure 5 and Figure 6 As shown, the acoustic and optical frequencies are 4.83 GHz and 193.6 THz, respectively, and the photoacoustic coupling coefficient reaches 0.7 MHz.

[0060] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A non-suspended quantum transducer device for coherent photon conversion in the microwave communication band, characterized by: Including SOI substrate: SOI substrate consists of three layers, the upper and lower layers are silicon, and the middle layer is a silicon dioxide insulating layer; The topmost silicon layer is etched to form a transducer device, including an auxiliary electrode system (1), a piezoelectric mechanical cavity (2), a photoacoustic crystal microcavity (3), and an optical waveguide (4). The entire transducer structure is directly in contact with the silicon dioxide substrate (5) and has no suspended parts. Assume that the direction from the photoacoustic crystal microcavity (3) to the piezoelectric mechanical cavity (2) on the uppermost silicon plane is x, and the y direction is perpendicular to the x direction; The auxiliary electrode system (1) is in the shape of an acoustic radiation wall. The auxiliary electrode system (1) is arranged along the y direction. The auxiliary electrode system (1) includes two layers of material: a lower layer is a silicon material and an upper layer is an electrode material. The piezoelectric material of the piezoelectric mechanical cavity (2) is arranged between the silicon material and the electrode material of the auxiliary electrode system (1). The two layers of material of the auxiliary electrode system (1) and the piezoelectric material of the piezoelectric mechanical cavity (2) together constitute the piezoelectric cavity. The auxiliary electrode system (1) and the photoacoustic crystal microcavity (3) are T-shaped and intersected at the piezoelectric mechanical cavity (2). The optical waveguide (4) is located on one side of the photoacoustic crystal microcavity (3) and is parallel to the photoacoustic crystal microcavity (3); The photoacoustic crystal microcavity (3) is composed of a silicon nanobeam with holes. By setting different shapes, sizes and spacings of the silicon nanobeam hole system, the nanobeam is divided into three parts: a phonon waveguide (6), a defect area (7) and a periodic area (8). When phonons enter the periodic area (8), they are reflected back to the defect area (7), thereby achieving localization of phonons in the defect area (7); The conversion of microwave photons into communication-band photons is accomplished through the intermediary of mechanical oscillators in the piezoelectric mechanical cavity: the mechanical vibrations in the piezoelectric mechanical cavity generate mechanical oscillators, i.e., phonons, which are transmitted along the phonon waveguide (6) into the defect region (7) of the photoacoustic crystal microcavity and converted into communication-band photons through photoacoustic coupling.

2. The non-suspended quantum transducer device for coherent photon conversion in the microwave communication band according to claim 1, characterized in that: One end of the optical waveguide (4) is connected to an external optical fiber for laser input; the other end is provided with a hole system to form acoustic and optical bandgap modes.

3. The non-suspended quantum transducer device for coherent photon conversion in the microwave communication band according to claim 1, characterized in that: One end of the auxiliary electrode system (1) is connected to the piezoelectric mechanical cavity (2), and the other end is connected to an external microwave circuit; And / or the unit structure of an acoustic radiation wall of the auxiliary electrode system (1) is one layer, and the total number of layers is 5-7 layers.

4. The non-suspended quantum transducer device for coherent photon conversion in the microwave communication band according to claim 1, characterized in that: The auxiliary electrode system (1) is wired in an interdigital transducer pattern, which converts the microwave signal in the electrode into mechanical vibration in the mechanical cavity through the piezoelectric effect.

5. The non-suspended quantum transducer device for coherent photon conversion in the microwave communication band according to claim 1, characterized in that: By using mechanical oscillators and phonon waveguides (6), the piezoelectric machine and the optomechanical system are connected, so that the conversion from microwaves to communication band photons can be completed.

6. The non-suspended quantum transducer device for coherent photon conversion in the microwave communication band according to claim 1, characterized in that: The piezoelectric mechanical cavity is covered with a 100 nm layer of z-cut lithium niobate as piezoelectric material on a silicon substrate, and the lithium niobate layer is covered with an 80 nm thick aluminum electrode.

7. The non-suspended quantum transducer device for coherent photon conversion in the microwave communication band according to claim 1, characterized in that: The auxiliary electrode system (1) uses aluminum as the electrode material with a thickness of 80nm, and the aluminum electrode is directly covered on the silicon substrate.

8. The non-suspended quantum transducer device for coherent photon conversion in the microwave communication band according to claim 4, characterized in that: The number of finger pairs of the interdigital transducer of the auxiliary electrode system (1) is adjustable.

9. The non-suspended quantum transducer device for coherent photon conversion in the microwave communication band according to claim 1, characterized in that: The optical waveguide (4) can introduce external laser photons and cause them to escape into the defect region (7) of the photoacoustic crystal microcavity (3) for photoacoustic coupling. The optical waveguide (4) is made of silicon material.

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