Non-suspended quantum transducer device for photon coherent conversion of microwave communication band

Abstract

The invention provides a non-suspended quantum transducer device for photon coherent conversion of a microwave communication band. A transducer main body is divided into a piezoelectric mechanical cavity and a photoacoustic crystal microcavity, an optical waveguide and an electrode system are assisted, a mechanical oscillator is used as a medium, and bidirectional conversion between a microwave signal of a solid quantum bit and communication band photons is completed. Wherein the piezoelectric mechanical cavity utilizes a lithium niobate material, and converts a microwave signal into mechanical vibration through a piezoelectric effect. The mechanical vibration is transmitted to a defect area of the photoacoustic crystal microcavity through the phonon waveguide and is coupled with photons in a communication band. A non-suspension structure is innovatively adopted, and through the structural design, the stability and the heat dissipation capacity of the transducer are greatly improved while low mechanical loss is guaranteed. The device is suitable for microwave and photon signal conversion in the fields of quantum calculation, quantum communication and the like, and has important significance on development of technologies such as long-range 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, converting microwave quantum signals into communication band photons that can be efficiently and long-distance transmitted at room temperature is the goal pursued by researchers. 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 with superconducting quantum bits, opening up a new idea. In recent years, Professor Painter's research group at the California Institute of Technology has built a transducer that uses phonons as a resonator to achieve microwave-acoustic-optical bidirectional conversion using piezoelectric effect and photoacoustic coupling effect. Based on their invention, our invention innovatively proposed a non-suspended transducer structure, which solved the problems of instability of suspended nanobeams during experiments and a large amount of thermal noise caused by light heating, and contributed to the further development of the field of quantum transducers. Summary of the invention

[0004] The present invention provides a non-suspended quantum transducer structure based on a piezoelectric mechanical cavity and a photoacoustic crystal microcavity, the purpose of which is to achieve bidirectional conversion of microwave signals of solid-state quantum bits and communication band photons with mechanical oscillators as intermediaries. Superconducting quantum bits have demonstrated fast, high-fidelity single-qubit and double-qubit logic gates, showing great application prospects in quantum computing. The microwave end interface of the quantum transducer can be directly coupled to this quantum bit through an on-chip coplanar waveguide to read and control microwave electrical signals.

[0005] 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 conversion of photons in a microwave communication band, comprising an SOI substrate: the SOI substrate is composed of three layers, the upper and lower layers are silicon, and the middle is a silicon dioxide insulating layer;

[0007] The topmost 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 a 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. The auxiliary electrode system 1 is arranged along the y direction. The auxiliary electrode system 1 includes two layers: 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 cross 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 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 the phonon enters the periodic area 8, it is reflected back to the defect area 7, thereby realizing the localization of the phonon in the defect area 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 externally connected to a 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 directly covers 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 to 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, but 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 directly in 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 material with a high-voltage electric coupling coefficient. When an alternating voltage is applied to the lithium niobate through electrodes, the electric dipole moment inside the lithium niobate changes periodically, inducing stress or strain inside the material, thereby generating mechanical vibration. At the same time, the strain caused by the mechanical vibration will in turn affect the charge distribution inside the material, thereby generating an electric field effect inside the material that is coupled with the mechanical vibration mode.

[0025] The photoacoustic crystal microcavity is composed of silicon nanobeams with holes. By designing the different shapes, sizes, spacings, numbers and other parameters of the holes in the silicon nanobeams, the energy bands of phonons and photons are made to overlap, thereby localizing the two particles simultaneously in a tiny area. The two particles interact through light radiation pressure to achieve 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 disposed 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 beneficial effects of the present invention are as follows: the present invention creatively adopts a non-suspended structure to directly build the complex structure in the silicon material on the silicon dioxide substrate. Through reasonable nanostructure design, the problem of large mechanical loss of the non-suspended structure is overcome, so that the mechanical resonance can be localized to a certain area. At the same time, the non-suspended structure enables the photoacoustic crystal microcavity to contact the substrate over a large area, greatly improving the stability of the entire device while having a strong heat dissipation capacity, which can reduce the impact of noise caused by light 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 a greater inherent readout efficiency. The optoacoustic crystal microcavity used to achieve the conversion of mechanical modes to 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 optoacoustic crystal microcavity supports a variety of hybrid acoustic modes, ensuring that the piezoelectric mechanical and optomechanical modes can maintain a high piezoelectric and optomechanical coupling rate even when mode detuning is caused during the manufacturing process. By connecting the mechanical modes of the two conversion processes through the phonon waveguide 6, a 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 a top view, (b) is a side view, and (c) is a front view.

[0034] Figure 3 Capacitive routing for 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- phonon waveguide, 7- defect region, 8- periodic region. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways 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 is a silicon dioxide insulating layer;

[0041] The topmost 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 a 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. The auxiliary electrode system 1 is arranged along the y direction. The auxiliary electrode system 1 includes two layers: 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 cross 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 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 the phonon enters the periodic area 8, it is reflected back to the defect area 7, thereby realizing the localization of the phonon in the defect area 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 externally connected to a 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 mechanical system is connected with the optomechanical system by using the mechanical vibrator and the phonon waveguide 6, so as to complete the conversion from microwave to communication band photons.

[0051] Preferably, the piezoelectric mechanical cavity is covered with a 100 nm thick z-cut lithium niobate layer on a silicon substrate as a 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 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 to 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 The complete structure of the quantum transducer. Figure 2 In the top view, the left side is a piezoelectric mechanical cavity to realize the conversion between microwave electrical signals and mechanical modes, and the right side is a photoacoustic crystal microcavity to realize the conversion between mechanical modes and communication optical signals. From the main view, it can be seen that the device is placed on the silicon dioxide layer.

[0057] The piezoelectric mechanical cavity uses a 100nm thick z-cut lithium niobate layer and places it on the silicon substrate, while covering the surface of the lithium niobate with an 80nm thick aluminum electrode. In order to reduce mechanical loss, the size of the piezoelectric mechanical cavity is designed to be small (~500nm×800nm), so that the piezoelectric mechanical mode is more sensitive to changes in the cavity size. The IDT is replicated by the acoustic radiation wall of the unit structure, and adopts an upper and lower double-layer design: the upper layer is an aluminum electrode and the lower layer is a silicon material. In order to suppress the energy leakage of mechanical vibration, the present invention designs this acoustic radiation wall to be within the band gap of the mechanical mode, so that the longitudinal phonon escape is effectively suppressed, and the mechanical vibration energy can only be transmitted laterally to the phonon waveguide 6, thereby further improving the piezoelectric mechanical coupling rate and improving the efficiency and stability of energy transmission. The number of IDTs and the number of layers of the acoustic radiation wall unit structure can be increased or decreased according to actual needs. Since lithium niobate has strong piezoelectric properties, the piezoelectric mechanical coupling rate is still high enough even when only two IDTs are used, so two IDTs are preferably used in the present invention.

[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, the piezoelectric mechanical coupling coefficient in the piezoelectric mechanical conversion process reaches 9MHz.

[0059] The photoacoustic crystal microcavity is divided into three regions: a periodic region, a defect region and a phonon waveguide. 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 and 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 familiar with 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 a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still 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 in that: Including SOI substrate: SOI substrate consists of three layers, the upper and lower layers are silicon, and the middle is a silicon dioxide insulating layer; The uppermost 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), wherein the entire transducer structure is directly in contact with a 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) comprises two layers: 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 crossed in a T-shape 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 the hole system of the silicon nanobeam in 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 a phonon enters the periodic region (8), it is reflected back to the defect region (7), thereby achieving localization of the phonon in the defect region (7).

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 externally connected to a 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 mode, 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: The conversion of microwave photons into communication band photons is completed through the intermediary of mechanical oscillators in the piezoelectric mechanical cavity: 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.

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 machine and the optical machine system are connected by using a mechanical vibrator and a phonon waveguide (6), so that the conversion from microwave to communication band photons can be completed.

7. 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 100nm layer of z-cut lithium niobate as piezoelectric material on a silicon substrate, and the lithium niobate layer is covered with an 80nm thick aluminum electrode.

8. 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 80 nm, and the aluminum electrode directly covers the silicon substrate.

9. A non-suspended quantum transducer device for coherent photon conversion in the microwave communication band as claimed in claim 4, characterized in that: The number of fingers of the interdigital transducer of the auxiliary electrode system (1) is adjustable.

10. 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 to the defect area (7) of the photoacoustic crystal microcavity (3) for photoacoustic coupling. The optical waveguide (4) is preferably made of silicon material.

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