Superconducting frequency mixing device, preparation method and superconducting quantum computer

Abstract

The invention discloses a superconducting frequency mixing device, a preparation method and a superconducting quantum computer, and relates to the technical field of electronics. In the application, the superconducting frequency mixing device comprises a first port, a second port, a third port, a first filter network, a second filter network and a parametric impedance converter, and the parametric impedance converter comprises at least one Josephson junction. Wherein the first port used for receiving microwave signals is connected with the input end of the first filter network, the second port used for receiving local oscillator signals is connected with one input end of the parametric impedance converter, and the other input end of the parametric impedance converter is connected with the output end of the first filter network. Therefore, the first port and the second port are isolated through the first filter network, that is, the microwave signal and the local oscillator signal are isolated through the filter network, the signal isolation degree is improved, and the frequency mixing effect is improved.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and in particular to a superconducting mixer, its fabrication method, and a superconducting quantum computer. Background Technology

[0002] Compared to conventional semiconductor mixers, superconducting mixers offer advantages such as low noise and high conversion gain, thus possessing broad application prospects. Currently, superconducting mixers can be implemented using a filter network incorporating a Josephson junction array. The Josephson junction array forms an equivalent nonlinear inductor, introducing a nonlinear effect to achieve the mixing function. This Josephson junction array can be connected to both a radio frequency (RF) port and a local oscillator (LO) port. The microwave signal enters the Josephson junction array through the RF port, and the LO signal enters through the LO port. The Josephson junction array mixes the microwave and LO signals, outputting a mixed signal. This mixed signal then undergoes frequency selection via a filter circuit within the filter network, resulting in an intermediate frequency (IF) signal. However, in this type of superconducting mixer, the microwave signal input from the RF port easily leaks to the LO port, and vice versa. The poor port isolation between the RF and LO ports negatively impacts the mixing performance. Summary of the Invention

[0003] This application provides a superconducting mixer, a fabrication method, and a superconducting quantum computer, which can improve the port isolation between the local oscillator port and the radio frequency port in the superconducting mixer, thereby improving the mixing effect.

[0004] To achieve the above objectives, this application adopts the following technical solution:

[0005] In a first aspect, a superconducting mixer is provided, comprising: a first port, a second port, a third port, a first filter network, a second filter network, and a parametric impedance converter, wherein the parametric impedance converter includes at least one Josephson junction; wherein, the input terminal of the first filter network is connected to the first port, and the output terminal of the first filter network is connected to the first input terminal of the parametric impedance converter, the first port is used to receive a microwave signal, and the first filter network is used to filter the microwave signal and output a first signal; the second input terminal of the parametric impedance converter is connected to the second port, and the output terminal of the parametric impedance converter is connected to the input terminal of the second filter network, the second port is used to receive a local oscillator signal, and the parametric impedance converter is used to mix the local oscillator signal and the first signal and output a mixed signal; the output terminal of the second filter network is connected to the third port, the second filter network is used to filter the mixed signal and output an intermediate frequency signal, and the third port is used to output the intermediate frequency signal.

[0006] In this application, a first port for receiving microwave signals is connected to the input of a first filter network, and a second port for receiving local oscillator signals is connected to one input of a parametric impedance converter, while the other input of the parametric impedance converter is connected to the output of the first filter network. Thus, the first and second ports are isolated by the first filter network. This reduces the portion of the microwave signal input from the first port that leaks to the second port after passing through the first filter network, and also reduces the portion of the local oscillator signal input from the second port that leaks to the first port. This improves the isolation between the first and second ports, and consequently, the isolation between the local oscillator signal and the microwave signal, thereby improving the mixing effect.

[0007] Optionally, the first filtering network is a high-pass filtering network, and the second filtering network is a band-pass filtering network.

[0008] In this application, the first filter network can suppress low-frequency signals in the microwave signal, thereby outputting a high-frequency signal with a significantly different center frequency from the local oscillator signal. Thus, after mixing this high-frequency signal with the local oscillator signal using a parametric impedance converter, the resulting mixed signal has a higher center frequency. Furthermore, by using a bandpass filter network to select the frequency of this mixed signal, the output intermediate frequency signal can better meet the requirements of superconducting quantum chips for broadband intermediate frequency signals.

[0009] Optionally, the center frequencies of the first filter network and the second filter network can satisfy: f2 = f1 - f LO f2 is the center frequency of the second filter network, f1 is the center frequency of the first filter network, and f LO The frequency of the local oscillator signal is given.

[0010] In this application, since the parametric impedance converter mixes the local oscillator signal and the first signal, the center frequency of the mixed signal is f1-f. LO Therefore, the center frequency of the second filter network can be equal to the center frequency of the mixing signal. Thus, the center frequency f1-f can be selected through the second filter network. LO Broadband intermediate frequency signal.

[0011] Optionally, the first filtering network includes a first filtering unit and a first inductor, the first filtering unit and the first inductor are connected in series, and the output terminal of the first inductor is connected to the first input terminal of the parametric impedance converter; the second filtering network includes a second filtering unit and a second inductor, the second filtering unit is connected in series with the second inductor, and the input terminal of the second inductor is connected to the output terminal of the parametric impedance converter.

[0012] In this application, the first filter network and the second filter network not only include filter units, but also a first inductor and a second inductor connected to a parametric impedance transformer, respectively. The first inductor, the second inductor and the parametric impedance transformer can be used to achieve impedance matching between the first filter network and the second filter network, thereby ensuring the mixing performance of the superconducting mixer.

[0013] Optionally, the actual inductance value of the first inductor, the actual inductance value of the second inductor, the static inductance value of the parametric impedance converter under the static bias signal, and the inductance change value of the local oscillator signal when passing through the parametric impedance converter satisfy the following: and Where L1 is the actual inductance value of the first inductor, L'1 is the designed inductance value of the first inductor, L2 is the actual inductance value of the second inductor, and L'2 is the designed inductance value of the second inductor. The designed inductance value refers to the theoretical inductance value of the corresponding inductor required by the filter network to achieve the filtering function, without considering the working environment of the filter network containing the corresponding inductor; L j δL is the static inductance value of the parametric impedance converter, and δL is the inductance variation value of the parametric impedance converter.

[0014] In this application, the static inductance value L of the parametric impedance converter j The center frequency is f LO The inductance change δL of the local oscillator signal when passing through the parametric impedance transformer, the actual inductance L1 of the first inductor in the first filter network, and the actual inductance L2 of the second inductor in the second filter network can satisfy the above relationship, so that the first filter network and the second filter network can output signals with center frequencies of f1 and f2 respectively, and the first filter network and the second filter network can achieve impedance matching.

[0015] Optionally, both the first and second filter circuits include at least one superconducting capacitor and at least one superconducting inductor. For example, the superconducting capacitor can be a superconducting interdigital capacitor, and the superconducting inductor can be a superconducting solenoid inductor, which is simple to manufacture and has high flexibility in size and shape.

[0016] Optionally, the at least one Josephson junction is a low-temperature superconducting Josephson junction. That is, in this application, the nonlinear characteristics of the low-temperature superconducting Josephson junction are used to achieve frequency mixing. Therefore, compared with the use of high-temperature superconducting Josephson junctions in related technologies, there is no transition between superconducting and non-superconducting states during the mixing process, resulting in lower power consumption.

[0017] In addition, the components in the first and second filter networks in this application can all be made of low-temperature superconducting materials. In this way, the superconducting mixer can be compatible with the fabrication process of the superconducting quantum chip, thereby enabling on-chip integration with the superconducting quantum chip.

[0018] Optionally, the parametric impedance converter is a loop including at least two Josephson junctions. Compared with the Josephson junction array used in related technologies to achieve mixing, it has lower processing requirements, less processing difficulty, and lower cost.

[0019] In a second aspect, a method for fabricating a superconducting mixer is provided, the method comprising covering a superconducting thin film layer on a substrate; and fabricating the superconducting mixer described in the first aspect on the superconducting thin film layer based on the circuit layout of the superconducting mixer.

[0020] Thirdly, a superconducting quantum computer is provided, the superconducting quantum computer including a measurement and control system, a superconducting quantum chip and the superconducting mixing device described in the first aspect above.

[0021] The superconducting mixer and the superconducting quantum chip can operate in a cryogenic environment provided by a dilution refrigerator. In one possible scenario, the superconducting mixer and the superconducting quantum chip are integrated together. In another possible scenario, the superconducting mixer and the superconducting quantum chip can be configured independently.

[0022] Fourthly, a superconducting quantum chip is provided, the superconducting quantum chip comprising superconducting qubits and the superconducting mixer described in the first aspect above.

[0023] Fifthly, a computer-readable storage medium is provided, wherein instructions are stored therein, which, when executed on a computer device, cause the computer device to perform the method for preparing the superconducting mixer described in the second aspect above.

[0024] In a sixth aspect, a computer program product containing instructions is provided, which, when run on a computer device, causes the computer device to execute the method for preparing the superconducting mixer described in the second aspect above.

[0025] The technical effects achieved by the second to sixth aspects mentioned above are similar to those achieved by the corresponding technical means in the first aspect, and will not be repeated here. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a superconducting mixer provided in an embodiment of this application;

[0027] Figure 2This is a schematic diagram of another superconducting mixer provided in an embodiment of this application;

[0028] Figure 3 A circuit diagram of a superconducting mixer is provided for an embodiment of this application;

[0029] Figure 4 A schematic diagram of the equivalent mutual inductance circuit structure of a first inductor, a second inductor, and a parametric impedance converter provided in an embodiment of this application;

[0030] Figure 5 A schematic diagram of an equivalent two-port network for a mutual inductance circuit structure equivalent to a first inductor, a second inductor, and a parametric impedance transformer, provided in an embodiment of this application;

[0031] Figure 6 A flowchart illustrating a method for fabricating a superconducting mixer provided in this application embodiment;

[0032] Figure 7 A circuit layout for fabricating a superconducting mixer is provided as an embodiment of this application;

[0033] Figure 8 A schematic diagram of the intermediate frequency signal obtained by simulating a superconducting mixer using local oscillator signals of different frequencies through circuit simulation software, as provided in the embodiments of this application.

[0034] Figure 9 This is a schematic diagram of the structure of a superconducting quantum computer provided in an embodiment of this application. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0036] Before providing a detailed explanation of the embodiments of this application, let's first introduce the application scenarios involved in the embodiments of this application.

[0037] Superconducting quantum computers, as an important realization of quantum computing, are highly favored for their high efficiency and powerful computing capabilities. The core component of a superconducting quantum computer is the superconducting quantum chip operating within a dilution refrigerator. The dilution refrigerator is equipped with microwave transmission lines, through which microwave signals used to control the superconducting quantum chip are transmitted. However, as the scale of superconducting quantum chips continues to increase, the demand for microwave transmission lines within the dilution refrigerator is also increasing. Issues such as the thermal load and cost of these transmission lines have become bottlenecks for the further expansion of superconducting quantum chips. Therefore, currently, the microwave signals used to control the superconducting quantum chip can be transmitted to the dilution refrigerator using frequency division multiplexing (FDM), thereby reducing the demand for microwave transmission lines. Specifically, for microwave signals transmitted using FDM, a superconducting mixer within the dilution refrigerator can convert the microwave signal into an intermediate frequency (IF) signal that matches the operating frequency of the superconducting quantum chip, and then transmit this IF signal to the superconducting quantum chip to control its operation.

[0038] Superconducting Josephson junctions, with their high nonlinearity and tunability, have become core components in superconducting circuits. The nonlinear effects of superconducting Josephson junctions can be used to achieve frequency mixing. Therefore, commonly used superconducting mixing devices include those based on Josephson junctions.

[0039] For example, in one related technology, a superconducting mixer can be implemented using a filter network containing a superconducting Josephson junction array. The Josephson junction array can form an equivalent nonlinear inductor, and its nonlinear characteristics enable mixing. The Josephson junction array can be connected to both a radio frequency (RF) port and a local oscillator (LO) port. A microwave signal enters the Josephson junction array through the RF port, and the LO signal enters through the LO port. The Josephson junction array mixes the microwave and LO signals and outputs a mixed signal. This mixed signal can then be filtered by the filter circuit in the filter network to achieve frequency selection, thereby outputting an intermediate frequency (IF) signal. However, in this type of superconducting mixer, the microwave signal input from the RF port is prone to leakage to the LO port, and the LO signal input from the LO port is also prone to leakage to the RF port. The port isolation between the RF and LO ports is poor, thus affecting the mixing effect.

[0040] In addition, in the aforementioned superconducting mixer, since the microwave signal and the local oscillator signal are in the same frequency band, the frequency of the mixed signal obtained after mixing them is relatively low. That is, the superconducting mixer can only achieve low-frequency modulation of the microwave signal and cannot output the broadband intermediate frequency signal required by the superconducting quantum chip. Furthermore, Josephson junction arrays have high requirements for fabrication technology, are difficult to manufacture, and are costly.

[0041] For example, in another related technology, a high-temperature superconducting Josephson junction can be used to fabricate a superconducting mixer. This type of superconducting mixer utilizes the nonlinear characteristics of the high-temperature superconducting Josephson junction near its critical current to achieve mixing. However, since the Josephson junction in this type of superconducting mixer uses a high-temperature superconducting material, while superconducting quantum chips typically use low-temperature superconducting materials, the fabrication processes of this superconducting mixer and superconducting quantum chips are incompatible, making it difficult to achieve on-chip integration of the superconducting mixer and the superconducting quantum chip. Furthermore, because this type of superconducting mixer utilizes the nonlinear characteristics of the high-temperature superconducting Josephson junction near its critical current to achieve mixing, the high-temperature superconducting Josephson junction undergoes a transition from a superconducting state to a nonconducting state during the mixing process, resulting in relatively high power consumption for this superconducting mixer.

[0042] To address the problems existing in the superconducting mixers in the aforementioned related technologies, this application provides a superconducting mixer applicable to the cryogenic environment provided by a dilution refrigerator. This superconducting mixer includes a first port, a second port, a third port, a first filter network, a second filter network, and a parametric impedance transformer (PEMT), wherein the PEMT includes at least one Josephson junction. In this superconducting mixer, the first port for receiving microwave signals is connected to the input terminal of the first filter network, the second port for receiving local oscillator signals is connected to one input terminal of the PEMT, and the other input terminal of the PEMT is connected to the output terminal of the first filter network. Thus, the first port and the second port are isolated by the first filter network. This reduces the portion of the microwave signal input from the first port that leaks to the second port after passing through the first filter network, and also reduces the portion of the local oscillator signal input from the second port that leaks to the first port, improving the isolation between the first and second ports, i.e., improving the isolation between the microwave signal and the local oscillator signal, thereby improving the mixing effect.

[0043] In addition, the first filter network in the superconducting mixer provided in this application embodiment can be a high-pass filter network, and the second filter network can be a band-pass filter network. Thus, the first filter network can suppress low-frequency signals in the microwave signal, thereby outputting a high-frequency signal with a significantly different center frequency from the local oscillator signal. Based on this, the center frequency of the mixed signal output after mixing the high-frequency signal and the local oscillator signal by the parametric impedance transformer will be relatively high. After filtering the mixed signal by the second filter network, the bandwidth of the output intermediate frequency signal is larger, which can better meet the requirements of superconducting quantum chips for broadband intermediate frequency signals. Moreover, the parametric impedance transformer in the superconducting mixer provided in this application embodiment can be a loop containing multiple superconducting Josephson junctions. Compared to Josephson junction arrays, it has lower processing requirements, lower processing difficulty, and lower cost.

[0044] Furthermore, the Josephson junction included in the parametric impedance transformer of the superconducting mixer provided in this embodiment can be a low-temperature superconducting Josephson junction, which is compatible with the fabrication process of superconducting quantum chips. Therefore, on-chip integration of the mixer and the superconducting quantum chip can be achieved. Moreover, since the superconducting mixer in this embodiment utilizes the nonlinear characteristics of a low-temperature superconducting Josephson junction for mixing, there is no transition between superconducting and non-superconducting states during the mixing process, resulting in low power consumption.

[0045] The superconducting mixer provided in the embodiments of this application will now be described in detail.

[0046] Figure 1 This is a schematic diagram of the structure of the superconducting mixer provided in the embodiments of this application. Figure 1 As shown, the superconducting mixer 10 includes a first port 11, a second port 12, a third port 13, a first filter network 14, a second filter network 15, and a parametric impedance converter 16. The input terminal of the first filter network 14 is connected to the first port 11, and the output terminal of the first filter network 14 is connected to the first input terminal 16a of the parametric impedance converter. The second input terminal 16b of the parametric impedance converter is connected to the second port 12, the output terminal 16c of the parametric impedance converter is connected to the input terminal of the second filter network 15, and the output terminal of the second filter network 15 is connected to the third port 13.

[0047] The first port 11 is used to receive microwave signals sent by other devices. For example, the superconducting mixer 10 is located inside the dilution refrigerator, and the first port 11 can be connected to an external measurement and control system of the dilution refrigerator via a microwave cable to receive microwave signals used to control the superconducting quantum chip. The frequency range of the microwave signal can be between 300 MHz and 300 GHz.

[0048] The input terminal of the first filtering network 14 is connected to the first port 11, and the microwave signal input from the first port 11 can enter the first filtering network 14. The first filtering network 14 filters the microwave signal, thereby filtering out some frequency signals in the microwave signal and outputting the remaining frequency signals.

[0049] For example, the first filter network 14 can be a high-pass filter network. This first filter network 14 can suppress low-frequency signals in the microwave signal, thereby outputting high-frequency signals in the microwave signal. For instance, the first filter network 14 can be a high-frequency filter network with a center frequency of 10 GHz.

[0050] Specifically, see Figure 2The first filter network 14 may include a first filter unit 141 and a first inductor 142. The input terminal of the first filter unit 141 is connected to the first port 11, and the first filter unit 141 and the first inductor 142 are connected in series.

[0051] The first filtering unit 141 is a high-pass filter circuit. This high-pass filter circuit can be an inductor-capacitor filter circuit including at least one superconducting capacitor and at least one superconducting inductor. The first inductor 142 is a superconducting inductor. The first filtering unit 141 and the first inductor 142 can filter low-frequency signals below a first frequency value in the microwave signal, thereby outputting a first signal in the microwave signal with a frequency not lower than the first frequency value. This first signal is a high-frequency signal. For example, if the center frequency of the first filtering network 14 is f1, then the first signal is a high-frequency signal with a center frequency of f1.

[0052] For example, see Figure 3 The first filter unit 141 includes two superconducting capacitors C1 and C2 and two superconducting inductors L1 and L2. The input terminal of L1 is connected to the input terminal of C1, and the output terminal of L1 is grounded. The output terminal of C1 is connected to the input terminals of both L2 and C2, and the output terminal of L2 is grounded. The output terminal of C2 is connected to the input terminal of the first inductor 142. After the microwave signal enters the first filter network 14, low-frequency signals below a first frequency value can be reflected, while first-frequency signals above the first frequency value can pass through the first filter unit 141 and the first inductor 142 before being output.

[0053] The output terminal of the first inductor 142 is connected to the first input terminal 16a of the parametric impedance converter 16. The parametric impedance converter 16 can receive the first signal through the first inductor 142 via the first input terminal 16a. In addition, the second input terminal 16b of the parametric impedance converter 16 can be connected to the output terminal of the local oscillator via the second port 12. Thus, the parametric impedance converter 16 can receive the local oscillator signal output by the local oscillator via the second input terminal 16b and the second port 12.

[0054] It should be noted that the parametric impedance transformer 16 may include one or more Josephson junctions. These one or more Josephson junctions may be low-temperature superconducting Josephson junctions. For example, the parametric impedance transformer 16 may be a loop composed of multiple Josephson junctions. Based on this, the parametric impedance transformer 16 can be equivalent to a nonlinear inductor. Utilizing the nonlinear characteristics of the parametric impedance transformer 16, the first signal output from the first filter network 14 and the local oscillator signal output from the local oscillator can be mixed to obtain a mixed signal.

[0055] In addition, in this embodiment, the second port 12 can also be connected to a DC bias circuit. Based on this, the parametric impedance converter 16 can receive a static bias signal output by the DC bias circuit through the second input terminal 16b and the second port 12. For example, the static bias signal can be a static bias voltage. By controlling the magnitude of the static bias signal output by the DC bias circuit, the magnitude of the magnetic flux inside and outside the loop of the parametric impedance converter 16 can be controlled, thereby controlling the magnitude of the static inductance value of the parametric impedance converter 16. The static inductance value is the inductance value of the parametric impedance converter 16 under the static bias signal, that is, the static inductance value of the parametric impedance converter 16 at the static operating point.

[0056] The output of the parametric impedance converter 16 is connected to the input of the second filter network 15. Therefore, after obtaining the mixing signal, the parametric impedance converter 16 can output the mixing signal to the second filter network 15, so that the second filter network 15 can select the frequency of the mixing signal.

[0057] The center frequency of the mixing signal can be equal to the frequency difference between the first signal and the local oscillator signal. For example, if the center frequency of the first signal is f1 and the center frequency of the local oscillator signal is f... LO Then the center frequency of the mixing signal is f1-f LO Based on this, the center frequency of the second filter network 15 can be equal to f1 - f LO Thus, the second filter network 15 can select a center frequency of f1-f from the mixed signal. LO The target intermediate frequency signal.

[0058] For example, the second filter network 15 can be a bandpass filter network. This second filter network 15 can suppress low-frequency and high-frequency signals in the mixing signal, thereby outputting a center frequency equal to f1-f. LO The target intermediate frequency signal. For example, the second filter network 15 can be a bandpass filter network with a passband frequency of 4 GHz to 5.5 GHz.

[0059] See Figure 2 The second filter network 15 may include a second filter unit 151 and a second inductor 152. The input terminal of the second inductor 152 is connected to the output terminal of the parametric impedance converter 16, and the second inductor 152 is connected in series with the second filter unit 151.

[0060] For example, the second inductor 152 is a superconducting inductor, and its output is connected to the input of the second filter unit 151. The second filter unit 151 can be a bandpass filter circuit, which can be an inductor-capacitor filter circuit including at least one superconducting capacitor and at least one superconducting inductor. Through the second inductor 152 and the second filter unit 151, signals in the mixing signal output by the parametric impedance converter 16 that are lower than the second frequency value and higher than the third frequency value can be suppressed, thereby outputting the target intermediate frequency signal to the third port 13.

[0061] For example, see Figure 3 The second filter unit 151 may include six superconducting capacitors C3 to C8 and two superconducting inductors L5 and L6. The output of the second inductor 152 is connected to the inputs of C3 and C4, with the output of C3 grounded. The output of C4 is connected to the inputs of L5, C5, and C6, with the outputs of L5 and C5 grounded. The output of C6 is connected to the inputs of L6, C7, and C8, with the outputs of L6 and C7 grounded. The output of C8 is connected to the third port 13. The mixing signal output from the parametric impedance converter 16 sequentially enters the second inductor 152 and the second filter unit 151. Through the multiple superconducting capacitors and inductors in the second inductor 152 and the second filter unit 151, high-frequency signals above the third frequency value and low-frequency signals below the second frequency value in the mixing signal can be suppressed, thereby enabling the second filter network 15 to output a target intermediate frequency signal with a frequency range between the second and third frequency values.

[0062] It is worth noting that each superconducting capacitor in the first filter network 14 and the second filter network 15 can be a superconducting interdigital capacitor, and each superconducting inductor can be a superconducting solenoid inductor. Furthermore, the first port 11 connected to the input of the first filter network 14, the second port 12 connected to the second input 16b of the parametric impedance transformer 16, and the third port 13 connected to the output of the second filter network 15 can all be implemented using coplanar waveguides.

[0063] As described above regarding the first filter network 14 and the second filter network 15, their center frequencies are different, and therefore their impedances are also different. Based on this, by connecting the first filter network 14 and the second filter network 15 through a parametric impedance transformer 16, the parametric impedance transformer 16 can also be used to achieve impedance matching between the first filter network 14 and the second filter network 15.

[0064] It should be noted that, theoretically, for the first filter network 14, when the designed inductance value of the first inductor 142 is L'1, the center frequency of the first filter network 14 is equal to f1. That is, without considering the working environment of the first filter network 14 or the circuit in which the first filter network 14 is located, theoretically, when the inductance value of the first inductor 142 is L'1, the first filter network 14 can output a first signal with a center frequency of f1. For the second filter network 15, when the designed inductance value of the second inductor 152 is L'2, the center frequency of the second filter network 15 is equal to f2. That is, without considering the working environment of the second filter network 15 or the circuit in which the second filter network 15 is located, theoretically, when the inductance value of the second inductor 152 is L'2, the second filter network 15 can output a target intermediate frequency signal with a center frequency of f2. However, in the superconducting mixer provided in this embodiment, after connecting the first filter network 14 and the second filter network 15 through the parametric impedance transformer 16, the center frequency and impedance of the first filter network 14 are affected by the subsequently connected circuit elements, and the center frequency and impedance of the second filter network 15 are also affected by the front-end circuit elements. Based on this, the designed inductance values ​​of the first inductor 142 and the second inductor 152 can be corrected so that when the first filter network 14 and the second filter network 15 are working in the current circuit, the center frequency of the first filter network 14 remains at f1, the center frequency of the second filter network 15 remains at f2, and their impedances are matched. The corrected inductance value of the first inductor 142 is the actual inductance value of the first inductor 142, and the corrected inductance value of the second inductor 152 is the actual inductance value of the second inductor 152. These actual inductance values ​​are the true inductance values ​​of the corresponding inductors in the superconducting mixer.

[0065] For example, combined Figure 2 and Figure 3 As shown in the circuit diagram of the superconducting mixer, the first inductor 142 in the first filter network 14, the parametric impedance transformer 16, and the second inductor 152 in the second filter network 15 can form a T-shaped circuit structure. Since the parametric impedance transformer 16 can be equivalent to a nonlinear inductor, this T-shaped circuit structure can be equivalent to a mutual inductance circuit structure. Assume the static inductance of the parametric impedance transformer 16 under a static bias signal is L. j The inductance change of the local oscillator signal after passing through the parametric impedance transformer 16 is δL. Then, as... Figure 4 As shown, this T-type circuit structure can be equivalent to a mutual inductance circuit structure including two inductors ESL1 and ESL2 and their mutual inductance M, where the inductance value of ESL1 is (L1 + L... j The inductance value of ESL2 is (L2 + L).j The inductance value of mutual inductance M is δL.

[0066] based on Figure 4 The mutual inductance circuit structure shown has the following relationship between the voltage and current of ESL1 and ESL2, which satisfies the following relationship (1).

[0067]

[0068] Where V1(t) is the voltage value of ESL1 at time t, I1(t) is the current value of ESL1 at time t, and ω1 = 2πf1, that is, ω1 is the angular frequency corresponding to the center frequency of the first filter network 14. V2(t) is the voltage value of ESL2 at time t, I2(t) is the current value of ESL2 at time t, and ω2 = 2πf2, that is, ω2 is the angular frequency corresponding to the center frequency of the second filter network 15. LO =2πf LO That is, ω LO This is the angular frequency corresponding to the center frequency of the local oscillator signal.

[0069] Since ESL1 is part of the first filter network 14, the angular frequency of the current allowed to flow through ESL1 is ω1. Since ESL2 is part of the second filter network 15, the angular frequency of the current allowed to flow through ESL2 is ω2. The difference in angular frequencies between the currents on ESL1 and ESL2 is equal to the angular frequency of the local oscillator signal, that is, ω1 - ω2 = ω LO Based on this, the relationship between voltage and current shown in equations (1) and (2) above can be simplified to equations (3) and (4) below.

[0070]

[0071] Based on the voltage and current relationship shown in equations (3) and (4) above, the impedance matrix of the mutual inductance circuit structure can be determined, and the impedance matrix Z is shown in equation (5) below.

[0072]

[0073] The impedance matrix Z is transformed to obtain the admittance matrix of the mutual inductance circuit structure. The admittance matrix Y is shown in equation (6).

[0074]

[0075] in,

[0076] Further simplification of the above admittance matrix yields the admittance matrix Y shown in equation (7).

[0077]

[0078] The admittance matrix Y is transformed to obtain the transmission matrix T of the mutual inductance circuit structure, as shown in equation (8).

[0079]

[0080] Based on the transmission matrix described above, it can be seen that this mutual inductance circuit structure can be equivalent to... Figure 5 The diagram shows three cascaded two-port networks. The transmission matrix T1 of the first two-port network P1 is shown in equation (9). According to T1, P1 has a parallel admittance value of y. 11 The transmission matrix T of the second two-port network P2 j As shown in equation (10) below, according to T j It can be seen that P2 is an admittance converter. The transmission matrix T2 of the third two-port network P3 is shown in equation (11) below. According to T2, P3 is also a parallel admittance, and the admittance value is y. 22 .

[0081]

[0082] Furthermore, combining the y in the aforementioned equation (7) 11 and y 22 As can be seen from the expression, the first two-port network and the third two-port network are both parallel inductors. As mentioned above, the second two-port network is an admittance converter. Therefore, the second two-port network can correspond to the parametric impedance converter 16 in the superconducting transmission device. The first two-port network and the third two-port network can correspond to the first inductor 142 and the second inductor 152, respectively. At this time, the inductance value L'1 of the first two-port network is the design inductance value of the first inductor 142, and the inductance value L'2 of the third two-port network is the design inductance value of the second inductor 152. Specifically, L'1 and L'2 can be shown as shown in equation (12) and equation (13) below.

[0083]

[0084] By combining the aforementioned expression for α and rearranging equations (12) and (13), it can be determined that when the design inductance value of the first inductor is L'1 and the design inductance value of the second inductor is L'2, the actual inductance value L1 of the first inductor and the actual inductance value L2 of the second inductor satisfy the relationship in equations (14) to (16) below.

[0085]

[0086]

[0087] In summary, without considering the operating environment of the first filter network 14 and the second filter network 15, in order for the first filter network 14 and the second filter network 15 to output signals with center frequencies of f1 and f2 respectively, the designed inductance values ​​of the first inductor and the second inductor can be L'1 and L'2 respectively. Based on this, when the first filter network 14 and the second filter network 15 are connected through the parametric impedance transformer 16, when the static inductance value L of the parametric impedance transformer 16... j The center frequency is f LO When the inductance change δL of the local oscillator signal passing through the parametric impedance transformer 16, the actual inductance L1 of the first inductor 142 in the first filter network 14, and the actual inductance L2 of the second inductor 152 in the second filter network 15 satisfy the relationships in equations (14) to (16) above, the first filter network 14 and the second filter network 15 can still maintain signals with output center frequencies of f1 and f2, and the first filter network 14 and the second filter network 15 can achieve impedance matching. As can be seen from the above introduction, the static inductance value of the parametric impedance transformer 16 is the inductance value under the static bias signal. By adjusting the magnitude of the static bias signal, the magnitude of the static inductance value can be controlled. In addition, when the local oscillator signal passes through the parametric impedance transformer 16, the inductance change value of the parametric impedance transformer 16 is affected by the center frequency f of the local oscillator signal. LO The influence of this. Based on this, in the embodiments of this application, when using the superconducting mixer, the static inductance value and the inductance change value can be adjusted by adjusting the magnitude of the static bias signal and the center frequency of the local oscillator signal, so that the actual inductance value of the first inductor 142, the actual inductance value of the second inductor 152, the static inductance value of the parametric impedance converter 16 and the inductance change value under the local oscillator signal in the superconducting mixer can satisfy the relationship shown in the above equations (14) to (16).

[0088] In this embodiment, the superconducting mixer includes a first port 11, a second port 12, a third port 13, a first filter network 14, a second filter network 15, and a parametric impedance transformer 16, wherein the parametric impedance transformer 16 includes at least one Josephson junction. In this superconducting mixer, the first port 11, used to receive microwave signals, is connected to the input terminal of the first filter network 14; the second port 12, used to receive local oscillator signals, is connected to one input terminal of the parametric impedance transformer 16; and the other input terminal of the parametric impedance transformer 16 is connected to the output terminal of the first filter network 14. Thus, the first port 11 and the second port 12 are isolated by the first filter network 14. This reduces the portion of the microwave signal input from the first port 11 that leaks to the second port 12 after passing through the first filter network 14, and also reduces the portion of the local oscillator signal input from the second port 12 that leaks to the first port 11, improving the isolation between the first port 11 and the second port 12, i.e., improving the isolation between the microwave signal and the local oscillator signal, thereby improving the mixing effect.

[0089] In addition, the first filter network 14 in the superconducting mixer provided in this application embodiment can be a high-pass filter network. This first filter network 14 can suppress low-frequency signals in the microwave signal, thereby outputting a high-frequency signal with a significantly different center frequency from the local oscillator signal. When this high-frequency signal is mixed with the local oscillator signal by the parametric impedance transformer 16, the resulting mixed signal has a higher center frequency. Furthermore, by using a band-pass filter network to select the frequency of this mixed signal, the output intermediate frequency signal can better meet the requirements of the superconducting quantum chip for a wideband intermediate frequency signal. Moreover, when the center frequency of the first filter network 14 differs significantly from the center frequency of the local oscillator signal, the center frequencies of the first filter network 14 and the second filter network 15 are also relatively large. Correspondingly, the impedance difference between the first filter network 14 and the second filter network 15 is also relatively large. In this case, the parametric impedance transformer 16 can achieve impedance matching between the first filter network 14 and the second filter network 15, thereby ensuring the mixing performance of the superconducting mixer.

[0090] The parametric impedance converter 16 in the superconducting mixer provided in this application embodiment can be a loop containing multiple superconducting Josephson junctions. Compared with the Josephson junction array used in related technologies to achieve mixing, it has lower processing requirements, less processing difficulty, and lower cost.

[0091] Furthermore, the Josephson junction included in the parametric impedance transformer 16 of the superconducting mixer provided in this embodiment can be a low-temperature superconducting Josephson junction, which is compatible with the fabrication process of superconducting quantum chips. Therefore, on-chip integration of the superconducting mixer and the superconducting quantum chip can be achieved. Moreover, since the superconducting mixer in this embodiment utilizes the nonlinear characteristics of a low-temperature superconducting Josephson junction for mixing, compared to the use of high-temperature superconducting Josephson junctions in related technologies, there is no transition between superconducting and non-superconducting states during the mixing process, resulting in lower power consumption.

[0092] Regarding the superconducting mixer described in the above embodiments, this application also provides a method for preparing the aforementioned superconducting mixer. See [link to relevant documentation]. Figure 6 The preparation method may include the following steps:

[0093] S601: A superconducting thin film layer is coated on the substrate.

[0094] In this embodiment, the substrate can be a substrate for a superconducting quantum chip, for example, a silicon substrate. The superconducting thin film layer can be made of a low-temperature superconducting metal material, for example, an aluminum thin film.

[0095] S602: Fabrication of a superconducting mixer on a superconducting thin film layer based on circuit layout.

[0096] In this embodiment, the circuit layout refers to a design drawing describing how the components in the superconducting mixer are arranged, positioned, and connected; it is a description of the planar geometry of the actual circuit of the superconducting mixer. This circuit layout is generated based on manufacturing processes, timing parameters, and pre-calculated parameters of each component in the superconducting mixer. The circuit layout may include the shape, area, and position information of each component on the substrate. Using this circuit layout, the superconducting mixer of the above embodiment is fabricated sequentially on the superconducting thin film layer through photolithography and etching.

[0097] Figure 7 Based on the foregoing embodiments Figure 3 The circuit layout of the superconducting mixer shown is based on the circuit diagram. Figure 7As shown, the first port 11, the second port 12, and the third port 13 can all be coplanar waveguides with a characteristic impedance of 50 ohms. The coplanar waveguide used to implement the second port 12 can be a pump line. Through this pump line, a static bias signal can be input to the parametric impedance converter 16 to control the static inductance value of the parametric impedance converter. Furthermore, through this pump line, a local oscillator signal can also be input to the parametric impedance converter 16 to feed energy into it. The superconducting capacitors in the first filter network 14 and the second filter network 15 can be superconducting interdigitated capacitors, and the superconducting inductors can be superconducting solenoid inductors. The superconducting Josephson junction included in the parametric impedance converter 16 can be a three-layer structure of aluminum-alumina-alumina.

[0098] It should be noted that, as described above, when the first and second filter networks are connected via a parametric impedance converter, the static inductance value L of the parametric impedance converter... j The center frequency is f LO The inductance change δL of the local oscillator signal when passing through the parametric impedance transformer, the actual inductance L1 of the first inductor in the first filter network, and the actual inductance L2 of the second inductor in the second filter network can satisfy the relationship of the above equations (14) to (16), so that the first filter network and the second filter network can output signals with center frequencies of f1 and f2 respectively, and the first filter network and the second filter network can achieve impedance matching. Based on this, when generating the circuit layout, the first filter network with a center frequency of f1 and the second filter network with a center frequency of f2 can be designed first without considering the working environment. Then, based on the designed inductance L'1 of the first inductor in the first filter network and the designed inductance L'2 of the second inductor in the second filter network, L1, L2, and L'2 that satisfy the relationship of the above equations (12) to (14) are determined. j And δL. Then, based on L1 and L2, the first and second inductors in the circuit layout are modified so that the inductance value of the first inductor is L1 and the inductance value of the second inductor is L2. Subsequently, using this circuit layout, the patterns of each component in the superconducting mixer and the connecting lines are fabricated on the superconducting thin film layer. Subsequently, when using this superconducting mixer, the values ​​of L1, L2, and L2 in the superconducting mixer can be adjusted by changing the magnitude of the static bias signal of the parametric impedance transformer and the center frequency of the local oscillator signal input from the second port. j δL and δL can satisfy the relationship shown in equations (14) to (16) above.

[0099] Regarding the superconducting mixer described above, this application embodiment uses circuit simulation software to simulate the frequency conversion gain performance of the superconducting mixer. Specifically, a local oscillator signal with a fixed frequency and power is input to the parametric impedance converter from the second port of the superconducting mixer, and a microwave signal with a fixed power and varying frequency is input to the first filter network from the first port of the superconducting mixer. The power of the difference frequency signal between the microwave signal and the local oscillator signal is monitored at the third port; the power of this difference frequency signal is the power of the intermediate frequency signal. In this application embodiment, four sets of simulations were performed using four local oscillator signals with different center frequencies. In the first set of simulations, the center frequency of the local oscillator signal input from the second port was 6.5 GHz, and the center frequency of the microwave signal input from the first port was 11 GHz; in the second set of simulations, the center frequency of the local oscillator signal was 8 GHz, and the center frequency of the microwave signal was 13 GHz; in the third set of simulations, the center frequency of the local oscillator signal was 11 GHz, and the center frequency of the microwave signal was 15 GHz; and in the fourth set of simulations, the center frequency of the local oscillator signal was 12.5 GHz, and the center frequency of the microwave signal was 17 GHz. The intermediate frequency signals output from the four sets of simulation experiments are as follows: Figure 8 As shown in (a) to (d) in the diagram. Figure 8 As can be seen, when inputting local oscillator signals of different frequencies, the superconducting mixer provided in this application embodiment can output intermediate frequency signals with a frequency range of 4GHz to 5.5GHz, with a frequency conversion loss of about 5 dB. Therefore, the superconducting mixer provided in this application embodiment has good mixing performance.

[0100] This application also provides a superconducting quantum computer, see [link to relevant documentation]. Figure 9 The superconducting quantum computer may include a measurement and control system 20, a superconducting quantum chip 30, and the superconducting mixer 10 described in the foregoing embodiments.

[0101] The measurement and control system 20 is used to manipulate the superconducting quantum chip 30 to control and measure it. For example, the measurement and control system 20 may include a control subsystem 201 and a measurement subsystem 202. The control subsystem 201 can generate microwave control signals according to the needs of computational operations and input these signals into the superconducting mixer 10.

[0102] The superconducting mixer 10 and the superconducting quantum chip 30 can operate in the low-temperature environment provided by the dilution refrigerator. The dilution refrigerator is equipped with a microwave transmission line. The control subsystem 201 can input microwave control signals to the superconducting mixer 10 via this microwave transmission line using frequency division multiplexing.

[0103] After receiving the microwave control signal, the superconducting mixer 10 can mix the microwave control signal and the local oscillator signal to obtain the intermediate frequency control signal, and then input the intermediate frequency control signal into the superconducting quantum chip 30.

[0104] The superconducting quantum chip 30 is used to carry quantum computing information. The superconducting quantum chip 30 includes superconducting qubits 301, and the quantum states of the superconducting qubits 301 can be manipulated using the intermediate frequency control signal provided by the superconducting mixer 10.

[0105] After all operations on the superconducting quantum bit 301 are completed, the measurement subsystem 202 can output a microwave measurement signal to the superconducting mixer 10. The superconducting mixer 10 can then convert the microwave measurement signal to an intermediate frequency (IF) measurement signal, which is then input into the superconducting quantum chip 30. The superconducting quantum chip 30 can return a signal to the measurement subsystem 202 based on the IF measurement signal. The measurement subsystem 202, based on the changes in the returned signal, obtains the state information of the superconducting quantum bit 301 in the superconducting quantum chip 30, and thus obtains the calculation result.

[0106] It should be noted that, in the embodiments of this application, the superconducting mixer 10 can be integrated with the superconducting quantum chip 30, or the superconducting mixer 10 and the superconducting quantum chip 30 can be set independently.

[0107] In addition, as an example, the measurement and control system 20 may include devices such as a microwave source, an arbitrary wave generator, and an integrated measurement and control board. The superconducting quantum chip 30 may also include a readout cavity structure for reading out the quantum state in the chip. This application embodiment does not limit this.

[0108] It is worth noting that, Figure 9 The illustrated device structure of the superconducting quantum computer does not constitute a limitation on the superconducting quantum computer. The superconducting quantum computer may include more or fewer components than illustrated, or combine certain components, or have different component arrangements. This application embodiment does not limit this.

[0109] Based on the superconducting mixer described above, this application also provides a superconducting quantum chip, which may include superconducting qubits and the superconducting mixer described in the foregoing embodiments. The superconducting mixer can receive a local oscillator signal and a microwave signal for manipulating the superconducting qubits, and mix the local oscillator signal and the microwave signal to output an intermediate frequency signal. Through this intermediate frequency signal, the state of the superconducting qubits can be controlled, thereby realizing quantum computing.

[0110] Furthermore, based on the fabrication method of the superconducting mixer described in the above embodiments, this application also provides a fabrication apparatus for a superconducting mixer. This fabrication apparatus may include one or more modules, which are used to execute S601 and S602 in the above embodiments to fabricate the superconducting mixer. The one or more modules in this fabrication apparatus may be implemented entirely or partially through software, hardware, firmware, or any combination thereof. When the above fabrication apparatus is implemented as a software functional module, it may be implemented entirely or partially as a computer program product. The computer program product includes one or more computer instructions. When the computer instructions are loaded and executed on a computer, the process or function of the fabrication method described in this application may be generated wholly or partially. The computer program product may be stored in a computer-readable storage medium, including several instructions to cause a computer device or processor to execute all or part of the steps of the fabrication method. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0111] In the various embodiments of this application, unless otherwise specified or logically conflicting, the terminology and / or descriptions between different embodiments are consistent and can be referenced mutually. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships. In the embodiments of this application, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone, where A and B can be singular or plural. In the textual description of the embodiments of this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship. In this application, "first," "second," and various numerical designations are only for ease of description and are not used to limit the scope of the embodiments of this application. For example, they are used to distinguish different messages, rather than to describe a specific order or sequence.

[0112] It is understood that the various numerical designations used in the embodiments of this application are merely for descriptive convenience and are not intended to limit the scope of the embodiments of this application. The order of the process numbers does not imply the order of execution; the execution order of each process should be determined by its function and internal logic.

[0113] Finally, it should be noted that the above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A superconducting mixer, characterized in that, The superconducting mixer (10) includes: a first port (11), a second port (12), a third port (13), a first filter network (14), a second filter network (15), and a parametric impedance transformer (16), wherein the parametric impedance transformer (16) includes at least one Josephson junction; The input end of the first filter network (14) is connected to the first port (11), and the output end of the first filter network (14) is connected to the first input end (16a) of the parametric impedance transformer. The first port (11) is used to receive microwave signals, and the first filter network (14) is used to filter the microwave signals and output a first signal. The second input terminal (16b) of the parametric impedance converter is connected to the second port (12), the output terminal (16c) of the parametric impedance converter is connected to the input terminal of the second filter network (15), the second port (12) is used to receive the local oscillator signal, and the parametric impedance converter (16) is used to mix the local oscillator signal and the first signal and output a mixed signal. The output of the second filter network (15) is connected to the third port (13). The second filter network (15) is used to filter the mixing signal and output an intermediate frequency signal. The third port (13) is used to output the intermediate frequency signal.

2. The superconducting mixer according to claim 1, characterized in that, The first filtering network (14) is a high-pass filtering network, and the second filtering network (15) is a band-pass filtering network.

3. The superconducting mixer according to claim 2, characterized in that, The center frequency of the first filter network (14) and the center frequency of the second filter network (15) satisfy: f2 = f1 - f LO Where f2 is the center frequency of the second filter network (15), f1 is the center frequency of the first filter network (14), and f LO The frequency of the local oscillator signal is given.

4. The superconducting mixer according to any one of claims 1 to 3, characterized in that, The first filter network (14) includes a first filter unit (141) and a first inductor (142), the first filter unit (141) and the first inductor (142) are connected in series, and the output terminal of the first inductor (142) is connected to the first input terminal (16a) of the parametric impedance transformer. The second filter network (15) includes a second filter unit (151) and a second inductor (152). The second filter unit (151) and the second inductor (152) are connected in series. The input terminal of the second inductor (152) is connected to the output terminal (16c) of the parametric impedance transformer.

5. The superconducting mixer according to claim 4, characterized in that, The actual inductance value of the first inductor (142), the actual inductance value of the second inductor (152), the static inductance value of the parametric impedance converter (16) under the static bias signal, and the inductance change value of the local oscillator signal when passing through the parametric impedance converter satisfy the following: and Wherein, L1 is the actual inductance value of the first inductor (142), L'1 is the designed inductance value of the first inductor (142), L2 is the actual inductance value of the second inductor (152), and L'2 is the designed inductance value of the second inductor (152). The designed inductance value refers to the theoretical inductance value of the corresponding inductor required by the filter network to achieve the filtering function without considering the working environment of the filter network containing the corresponding inductor; L j δL is the static inductance value of the parametric impedance converter (16), and δL is the inductance variation value of the parametric impedance converter (16).

6. The superconducting mixer according to claim 4 or 5, characterized in that, Both the first filter unit (141) and the second filter unit (151) include at least one superconducting capacitor and at least one superconducting inductor.

7. The superconducting mixer according to any one of claims 1 to 6, characterized in that, The at least one Josephson junction is a low-temperature superconducting Josephson junction.

8. The superconducting mixer according to any one of claims 1 to 7, characterized in that, The parametric impedance transformer (16) is a loop that includes at least two Josephson junctions.

9. A method for fabricating a superconducting mixer, characterized in that, The method includes: A superconducting thin film layer is coated on the substrate; Based on the circuit layout of the superconducting mixer, the superconducting mixer is fabricated on the superconducting thin film layer; The superconducting mixer includes a first port, a second port, a third port, a first filter network, a second filter network, and a parametric impedance transformer, wherein the parametric impedance transformer includes at least one Josephson junction; The input terminal of the first filter network is connected to the first port, and the output terminal of the first filter network is connected to the first input terminal of the parametric impedance transformer. The first port is used to receive microwave signals. The second input terminal of the parametric impedance transformer is connected to the second port, and the output terminal of the parametric impedance transformer is connected to the input terminal of the second filter network. The second port is used to receive local oscillator signals and static bias signals. The output terminal of the second filter network is connected to the third port, and the third port is used to output intermediate frequency signals.

10. A superconducting quantum computer, characterized in that, The superconducting quantum computer includes a measurement and control system (20), a superconducting quantum chip (30), and a superconducting mixer (10) as described in any one of claims 1 to 8.

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