Broadband superconducting parametric amplifier based on Josephson inductor and matching network

Abstract

The invention discloses a broadband superconducting parametric amplifier based on a Josephson inductor and a matching network, which comprises an input / output port, a matching network transmission line, a nonlinear LC resonator and a direct current bias line, wherein the matching network transmission line is composed of a half-wavelength transmission line, a quarter-wavelength transmission line and a half-wavelength transmission line, a coplanar waveguide transmission line form is adopted, and the width of a coplanar waveguide center conductor and the width of a gap are adjusted according to a required impedance value; the nonlinear LC resonator is composed of a plate capacitor and a direct-current superconducting quantum interferometer (SQUID), and the nonlinear LC resonator is controlled by the size of a capacitor and the size of an inductor of the nonlinear LC resonator. According to the invention, the working bandwidth of parametric amplification is effectively improved, and meanwhile, the influence of external factors of the parametric amplifier on the working bandwidth is effectively reduced.

Description

Technical Field

[0001] The invention relates to the field of amplifier design, and in particular to a broadband superconducting parametric amplifier of a Josephson inductor and a matching network. Background Art

[0002] The Josephson parametric amplifier is a key component in the superconducting quantum computing architecture that relies on dispersion readout. As the first stage of the amplification chain, it can provide the first-stage gain with close to quantum-limited noise, and then connect the low-noise cryogenic amplifier and the room-temperature amplifier to form the entire amplification chain, which can quickly and accurately detect the low-power readout signal. For the effective reading of multi-bit superconducting quantum bits, the Josephson parametric amplifier needs to have a high instantaneous bandwidth (at least 500MHz) to accommodate sufficient spectral separation between the readout frequencies, and a high dynamic range (output 1-dB compression power exceeding -90dBm) to avoid loss of readout fidelity due to gain compression and intermodulation distortion.

[0003] At present, high dynamic range Josephson parametric amplifiers based on DC superconducting quantum interference devices (SQUIDs) and superconducting nonlinear asymmetric inductor elements (SNAIL) arrays have been verified, but it is very difficult to achieve a simple process and high gain-bandwidth product. The broadband performance and precise gain distribution of the Josephson parametric amplifier mainly come from the details that are difficult to control in the microwave environment. Therefore, we use an impedance matching network customized for a specific gain curve to achieve a controllable high-gain broadband response, making the simulation bandwidth of the Josephson parametric amplifier far higher than 1GHz, and the gain can reach up to 20dB. Summary of the invention

[0004] The purpose of the present invention is to provide a broadband superconducting parametric amplifier based on a Josephson inductor and a matching network with a simple structural design and a simple preparation process.

[0005] The technical solution to achieve the purpose of the present invention is: a broadband superconducting parametric amplifier based on Josephson inductance and matching network, including input and output ports, matching network transmission lines, nonlinear LC resonators and DC bias lines, wherein: one end of the matching network transmission line is connected to the input and output ports, and the other end is connected to the nonlinear LC resonator; the other end of the nonlinear LC resonator is close to the bias line;

[0006] The matching network transmission line is composed of a half-wavelength transmission line, a quarter-wavelength transmission line, and a half-wavelength transmission line, and adopts a coplanar waveguide transmission line form. The width of the coplanar waveguide center conductor and the gap width are adjusted according to the required impedance value. The specific design rules are as follows: Assume that the characteristic impedance of the three-section coplanar waveguide transformation line is Z 1 , Z 2 and Z 3, the impedance of the input and output ports and the nonlinear LC resonator is Z 0 , Z L , Z 1 , Z 2 and Z 3 Value by Z 1 / Z 0 =Z L / Z 3 and Z 2 / Z 1 =Z 3 / Z 2 Determine, assuming that the inductance and capacitance per unit length of the coplanar waveguide transmission line are L 0 and C 0 , the total length is d, then its phase velocity The impedance is The eigenfrequency of a half-wavelength transmission line Quarter-wavelength transmission line eigenfrequency n is a natural number and determines the resonant frequency of the nonlinear LC resonator in the nth mode.

[0007] Furthermore, the half wavelength transmission line, the quarter wavelength transmission line and the half wavelength transmission line are all made of aluminum, niobium or tantalum materials with a thickness of 70nm to 120nm.

[0008] Furthermore, the nonlinear LC resonator includes a capacitor part and an inductor part, which are in a parallel relationship, wherein the capacitor part adopts a flat plate capacitor, and the inductor part adopts a DC superconducting quantum interference device composed of two superconducting Josephson junctions in parallel to form an equivalent inductor, the flat plate capacitor is connected to the matching network transmission line, and the closed loop of the DC superconducting quantum interference device is close to the bias line. By adjusting the current of the bias line and changing the magnetic flux in the DC superconducting quantum interference device loop, the frequency adjustment of the nonlinear LC resonator is achieved.

[0009] Furthermore, the upper plate of the flat plate capacitor is made of aluminum, the lower plate is made of aluminum, niobium, tantalum, etc., and the dielectric layer is made of silicon nitride.

[0010] Furthermore, the input and output ports are the same port, the signal enters through the input and output ports, is amplified and then output through the input and output ports, and a microwave circulator is connected to the input and output ports to separate the input and output signals.

[0011] Furthermore, the input and output ports, the matching network transmission lines, the lower plate of the flat plate capacitor of the nonlinear LC resonator and the DC bias line are patterned by one exposure and one etching using an ultraviolet lithography process, the flat plate capacitor dielectric layer is grown by plasma enhanced chemical vapor deposition and prepared by ultraviolet lithography and etching processes, and the flat plate capacitor upper plate is prepared by ultraviolet lithography, electron beam evaporation and stripping processes.

[0012] Furthermore, the DC superconducting quantum interference device of the nonlinear LC resonator is prepared by using the overlapping junction process.

[0013] Compared with the prior art, the present invention has the following significant advantages: 1) The preparation of the DC superconducting quantum interference device (SQUID) of the present invention adopts the overlapping junction process, which improves the yield and stability of the DC superconducting quantum interference device (SQUID), eliminates the sidewall deposition effect caused by angle evaporation, and has high uniformity. It can also reduce the loop area of ​​the junction array and resist the magnetic flux noise of the environment. 2) The matching network composed of three sections of coplanar waveguide transmission lines can achieve controllable engineering broadband response, reduce the influence of external factors of the parametric amplifier itself on the working bandwidth, and make the working bandwidth of the parametric amplifier far exceed 1GHz, and the gain can reach up to 20dB. 3) The operating frequency of the entire device can be controlled by the superconducting quantum interference device, and the central operating frequency can be changed within a certain range to achieve modulation of the relative working bandwidth. 4) With the design of the matching network, the device can achieve a large working bandwidth and have large bandwidth and high gain performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a planar structural design layout of a broadband superconducting parametric amplifier based on a Josephson inductor and a matching network of the present invention.

[0015] Figure 2 It is a planar structural design layout of the transmission line part of the matching network of the present invention.

[0016] Figure 3 It is a circuit design diagram of the nonlinear LC resonator of the present invention.

[0017] Figure 4 It is a process flow chart of the DC superconducting quantum interference device (SQUID) overlap junction of the present invention.

[0018] Figure 5 This is a simulation result diagram of the resonator frequency under the change of magnetic flux bias according to the present invention.

[0019] Figure 6 It is a simulation result diagram of the bandwidth gain performance of the device of the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0021] like Figure 1As shown, the broadband superconducting parametric amplifier based on Josephson inductance and matching network includes four parts: input and output ports 101, matching network transmission line 102, nonlinear LC resonator 103 and DC bias line 104. One end of the matching network transmission line 102 is connected to the input and output port 101, and the other end is connected to the nonlinear LC resonator 103; the other end of the nonlinear LC resonator 103 is connected to the DC bias line 104.

[0022] The input / output port 101 connects the external transmission line and the internal matching network transmission line 102 of the device. It is generally believed that the impedance of the input / output port is 50Ω to ensure matching with the characteristic impedance of the external transmission line. The external signal to be amplified enters the device through the input / output port 101, and is output through the input / output port 101 after amplification. A circulator is connected to the input / output port to separate the input signal from the output signal.

[0023] like Figure 2 As shown, the matching network transmission line 102 is composed of a half-wavelength transmission line 201, a quarter-wavelength transmission line 202, and a half-wavelength transmission line 203, and adopts the form of a coplanar waveguide transmission line. The width of the coplanar waveguide center conductor and the gap width are adjusted according to the required impedance value. One end 204 of the transmission line has an impedance of 50Ω, which is connected to the signal input and output port 101 and matches the characteristic impedance of the external transmission line. The other end 205 of the transmission line is connected in series with a nonlinear LC resonator 103, and the port characteristic impedance matches the characteristic impedance of the nonlinear LC resonator. The characteristic impedance value of the matching network transmission line is set according to the input and output port impedance and the nonlinear LC resonator impedance.

[0024] Here are the design rules: Assume the input and output port impedance is Z 0 , the impedance that the nonlinear LC resonator needs to match is Z L The characteristic impedance setting values ​​of the three sections of coplanar waveguide transformation lines are Z 1 , Z 2 and Z 3 , first satisfy rule Z 1 / Z 0 =Z L / Z 3 and Z 2 / Z 1 =Z 3 / Z 2 , at the same time, Z 1 , Z 2 , Z 3 The specific value of is limited by the silicon-based coplanar waveguide transmission line structure. Assume that the inductance and capacitance per unit length of the coplanar waveguide transmission line are L 0 and C 0 , the total length is d, then its phase velocity The impedance is The eigenfrequency of a half-wavelength transmission line Quarter-wavelength transmission line eigenfrequency n is a natural number, which determines the resonant frequency of the nonlinear LC resonator as the nth mode. It is generally believed that the characteristic impedance value of the input and output ports is 50Ω. As an optional implementation, the three sections of coplanar waveguide transmission lines 201, 202 and 203 can be made of materials such as aluminum, niobium, and tantalum, and the thickness can be selected between 70nm and 120nm, which is adjusted according to the experimental conditions.

[0025] like Figure 3 The nonlinear LC resonator 103 includes two parts, a capacitor part and an inductor part, which are in parallel relationship. The capacitor part adopts a flat plate capacitor 301, and the inductor part adopts a DC superconducting quantum interference device 302 composed of two superconducting Josephson junctions in parallel, which can be regarded as an equivalent inductor, and the equivalent inductance value of the equivalent inductor is equal to the sum of the modulated inductance and parasitic inductance of the DC superconducting quantum interference device composed of two parallel superconducting Josephson junctions. The nonlinear LC resonator 103 is provided with two ports, the port 303 on the capacitor side is connected to the impedance matching transmission line, and the port 304 on the inductor side is grounded. The driving signal enters the nonlinear LC resonator through the port 204 of the impedance matching transmission line part and is output along the same port 204. As an optional embodiment, the upper plate of the flat plate capacitor 301 is aluminum, the lower plate is niobium or aluminum, and the dielectric layer is silicon nitride.

[0026] The bias line 104 is designed near the loop of the superconducting quantum interference device. The frequency of the nonlinear LC resonator 103 is controlled by the magnetic flux entering the superconducting ring of the superconducting quantum interference device. That is, the on-chip bias line designed near the superconducting quantum interference device is used as a bias circuit, and the DC voltage value of the bias line is adjusted to control the magnetic flux in the superconducting ring, thereby finally realizing the frequency adjustment of the nonlinear LC resonator.

[0027] like Figure 4 The superconducting quantum interference device adopts the overlapping junction process. Figure a shows the appearance of the lower electrode after photoresist coating, photolithography, and electron beam evaporation. Figure b shows the appearance of the sample after removing the photoresist. Figure c shows the appearance of the upper electrode after photoresist coating, photolithography, and Ar ion cleaning. Figure d shows the appearance after static oxidation. Figure e shows the appearance after electron beam evaporation of the upper electrode. Figure f shows the appearance of the sample after the second de-coating.

[0028] For the broadband superconducting parametric amplifier structure of the above-mentioned Josephson inductor and matching network, the input and output ports 101, the matching network transmission line 102, the lower plate of the planar capacitor of the nonlinear LC resonator and the bias line 104 can all be patterned by one exposure and one etching using an ultraviolet lithography process; the capacitor dielectric layer is prepared by plasma enhanced chemical vapor deposition, one exposure and one etching using ultraviolet lithography; a DC superconducting quantum interference device composed of two superconducting Josephson junctions of the inductor connected in parallel can be prepared by an overlapping junction process.

[0029] Example

[0030] In order to verify the effectiveness of the solution of the present invention, the following simulation design is carried out.

[0031] In this implementation sample, the single junction area of ​​the DC superconducting quantum interference device is 1.5μm*1.3μm, the single junction critical current is 1.7μA, the capacitance of the plate capacitor is 2.8pF, and the resonant frequency of the LC resonant cavity without flux bias is 6GHz. The matching network part consists of three sections of coplanar waveguide transmission lines with characteristic impedances of 80Ω, 38Ω and 70Ω, and lengths of 9857μm, 4932μm and 9857μm, respectively.

[0032] Figure 5 The figure is a simulation diagram of the working frequency of the embodiment under the magnetic flux bias of -0.5 to 0.5. By adjusting the bias magnetic flux on the bias circuit (104), the working frequency of the nonlinear LC resonator can be changed. For example, when the bias magnetic flux value gradually changes from -0.5 to 0.5, the resonant frequency of the device changes from the lowest 4 GHz to the highest 9.5 GHz, thereby achieving frequency adjustment.

[0033] Figure 6 The bandwidth gain of this embodiment when the center frequency is 6 GHz. In the actual circuit, the bias circuit is adjusted to a suitable bias flux operating point, a microwave signal generator is used to generate a driving signal and fed into the bias line, and a signal generated by a vector network analyzer is fed into the input and output ports through an attenuator. The output signal is separated from the input signal through a circulator, and then input into the vector network analyzer after passing through a low-temperature amplifier and a normal temperature amplifier, and the S21 curve is measured. By comparing the changes in the S21 curve before and after applying the driving signal, the bandwidth gain characteristics of the device can be obtained, for example, there is a 20dB gain in the range of 5.5 GHz to 6.5 GHz.

[0034] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0035] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A broadband superconducting parametric amplifier based on Josephson inductance and matching network, characterized in that: It comprises an input / output port (101), a matching network transmission line (102), a nonlinear LC resonator (103) and a DC bias line (104), wherein: one end of the matching network transmission line (102) is connected to the input / output port (101), and the other end is connected to the nonlinear LC resonator (103); the other end of the nonlinear LC resonator (103) is connected to the DC bias line (104); The matching network transmission line (102) is composed of a half-wavelength transmission line (201) plus a quarter-wavelength transmission line (202) plus a half-wavelength transmission line (203), and adopts a coplanar waveguide transmission line form. The width of the coplanar waveguide center conductor and the gap width are adjusted according to the required impedance value. The specific design rules are as follows: the characteristic impedances of the three coplanar waveguide transformation lines are assumed to be Z1, Z2 and Z3, and the impedances of the input and output ports (101) and the nonlinear LC resonator (103) are Z0, Z1, Z2 and Z3. L , Z1, Z2 and Z3 values ​​are given by Z1 / Z0=Z L / Z3 and Z2 / Z1=Z3 / Z2, assuming the inductance and capacitance per unit length of the coplanar waveguide transmission line are L0 and C0, and the total length is d, then its phase velocity The impedance is The eigenfrequency of a half-wavelength transmission line Quarter-wavelength transmission line eigenfrequency Where n is a natural number that determines the resonant frequency of the resonator in the nth mode.

2. The broadband superconducting parametric amplifier based on Josephson inductance and matching network according to claim 1, characterized in that: The half wavelength transmission line (201), the quarter wavelength transmission line (202) and the half wavelength transmission line (203) are all made of aluminum, niobium or tantalum materials, and have a thickness of 70nm to 120nm.

3. The broadband superconducting parametric amplifier based on Josephson inductance and matching network according to claim 1, characterized in that: The nonlinear LC resonator (103) comprises a capacitor part and an inductor part, which are in a parallel relationship. The capacitor part adopts a flat plate capacitor (301), and the inductor part adopts a DC superconducting quantum interference device (302) composed of two superconducting Josephson junctions connected in parallel to form an equivalent inductor. The flat plate capacitor (301) is connected to an impedance matching transmission line (102), and the closed loop of the DC superconducting quantum interference device (302) is connected to a DC bias line (104). By adjusting the current of the DC bias line (104), the magnetic flux in the loop of the DC superconducting quantum interference device (302) is changed to achieve the adjustment of the working frequency of the nonlinear LC resonator (103).

4. The broadband superconducting parametric amplifier based on Josephson inductance and matching network according to claim 3, characterized in that: The upper plate of the flat plate capacitor (301) is made of aluminum, the lower plate is made of aluminum, niobium or tantalum, and the dielectric layer is made of silicon nitride.

5. The broadband superconducting parametric amplifier based on Josephson inductance and matching network according to claim 1, characterized in that: The input and output ports (101) are the same port. Signals enter through the input and output ports (101), are amplified, and are output through the input and output ports (101). A microwave circulator is connected to the input and output ports (101) to separate the input and output signals.

6. The broadband superconducting parametric amplifier based on Josephson inductance and matching network according to claim 3, characterized in that: The input / output port (101), the matching network transmission line (102), the lower plate of the flat plate capacitor (301) of the nonlinear LC resonator and the DC bias line (104) are patterned by one exposure and one etching using an ultraviolet photolithography process; the dielectric layer of the flat plate capacitor is grown by plasma enhanced chemical vapor deposition and is prepared by one exposure and one etching using an ultraviolet photolithography process; the upper plate of the flat plate capacitor is prepared by an ultraviolet photolithography process, an electron beam evaporation process and a stripping process.

7. The broadband superconducting parametric amplifier based on Josephson inductance and matching network according to claim 3, characterized in that: The DC superconducting quantum interference device (302) of the nonlinear LC resonator is prepared by using an overlapping junction process.

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