Low pass filter for qubits

Abstract

The invention provides a low-pass filter for quantum bits. The low-pass filter comprises a ground wire; the transmission line is used for transmitting an input control signal in a preset frequency range; the first ends of the capacitors are connected with the ground wire, and the second ends of the capacitors are connected with the transmission line; a plurality of first inductors, wherein one first inductor is arranged on the transmission line between two adjacent capacitors; wherein under the condition that the input control signal is input into the input end of the transmission line, the output end of the transmission line outputs a first output control signal and a second output control signal through the response mode of the low-pass filter, and the frequency of the first output control signal is higher than that of the second output control signal.

Description

Technical Field

[0001] The present application relates to the field of quantum computing technology, and more specifically, to a low-pass filter for quantum bits. Background Art

[0002] Today is the early stage of the development of quantum computer technology. How to achieve precise control of quantum systems is the focus of quantum computing development. Superconducting quantum chips realized by superconducting quantum bits are one of the most effective physical platforms for quantum computing. How to achieve precise control of large-scale superconducting quantum chips is the core technology and challenge to improve the accuracy of quantum manipulation.

[0003] As the scale of superconducting quantum processors continues to increase, the number of superconducting quantum bits continues to increase, and more and more control lines will be needed. In order to reduce the number of control lines inside the refrigerator, the high-frequency and low-frequency control signals of the superconducting quantum bits have been combined at room temperature and transmitted to the refrigerator through the same cable. However, the attenuation required for these two signals in the low-temperature layer of the refrigerator is different. The high-frequency signal needs to be attenuated 20dB more than the low-frequency signal.

[0004] The current solution is to install infrared filters in the cryogenic layer, which have greater attenuation at high frequencies and less attenuation at low frequencies. As the number of superconducting quantum bits increases, more infrared filters will be needed, and with other devices, the space for the refrigerator will become very tight. In addition, infrared filters have the problem of heat generation, which will increase the heat load on the refrigerator. Summary of the invention

[0005] In view of this, the present application provides a low-pass filter for quantum bits, comprising:

[0006] Ground wire;

[0007] A transmission line, the transmission line is used to transmit an input control signal within a preset frequency range;

[0008] A plurality of capacitors, wherein a first end of the capacitor is connected to the ground line, and a second end of the capacitor is connected to the transmission line;

[0009] A plurality of first inductors, one of which is arranged on the transmission line between two adjacent capacitors;

[0010] In which, when the above-mentioned input control signal is input into the input end of the above-mentioned transmission line, the response mode of the above-mentioned low-pass filter causes the output end of the above-mentioned transmission line to output a first output control signal and a second output control signal, wherein the frequency of the above-mentioned first output control signal is higher than the frequency of the above-mentioned second output control signal.

[0011] According to an embodiment of the present application, the first inductor includes an air-core inductor, a magnetic-core inductor, a copper-core inductor or a Josephson junction inductor.

[0012] According to an embodiment of the present application, the above-mentioned Josephson junction inductor is composed of a preset number of Josephson junctions connected in series.

[0013] According to an embodiment of the present application, the low-pass filter further includes:

[0014] The second inductor is arranged on a side of the transmission line close to the output end, and the capacitor is arranged between the second inductor and the first inductor closest to the output end.

[0015] According to an embodiment of the present application, for any inductance of the first inductance and the second inductance, the impedance is calculated according to the inductance and the capacitance corresponding to the inductance, wherein parameter values ​​of different impedances are different.

[0016] According to an embodiment of the present application, the low-pass filter is implemented in the form of a coplanar waveguide, wherein the ground line is coplanar with the transmission line.

[0017] According to an embodiment of the present application, the capacitance of the capacitor is determined according to the cross-sectional width and spacing of the transmission line, and the spacing represents the plane spacing between the transmission line and the ground line.

[0018] According to an embodiment of the present application, the low-pass filter is made of superconducting material, wherein the superconducting material includes superconducting aluminum, titanium nitride, superconducting niobium or superconducting tantalum.

[0019] According to an embodiment of the present application, the above-mentioned response mode includes the flattest response or the Chebyshev response.

[0020] According to an embodiment of the present application, the frequency of the above-mentioned first output control signal is between 4.5GHz and 5.5GHz, and the frequency of the above-mentioned second output control signal is lower than 1GHz, so the 3dB passband cutoff frequency range of the low-pass filter is 0.8GHz~1.2GHz, and the attenuation of the preset decibel amount is achieved within the stopband range of 4GHz~5GHz.

[0021] According to the embodiments of the present application, the low-pass filter of the present application can realize the simultaneous transmission of high-frequency and low-frequency control signals of superconducting quantum bits. This can solve the scale expansion problem in large-scale complex quantum circuits. In future-oriented large-scale programmable quantum circuits, the number of control lines can be reduced, the space occupied by the low-pass filter in the refrigerator can be reduced, and the heat load of the low-pass filter can be reduced, which has broad application prospects in the waveform control of large-scale programmable quantum computing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and advantages of the present application will become more apparent through the following description of the embodiments of the present application with reference to the accompanying drawings, in which:

[0023] Figure 1 shows a schematic diagram of a low-pass filter according to an embodiment of the present application;

[0024] Figure 2 shows a schematic diagram of a low-pass filter according to another embodiment of the present application;

[0025] Figure 3 A prototype circuit diagram of a 5th-order low-pass filter according to an embodiment of the present application is shown.

[0026] In the above drawings, the meanings of the reference numerals are as follows:

[0027] 100- ground wire;

[0028] 200-Transmission Line

[0029] 300-capacitor;

[0030] 400-first inductor;

[0031] 500-second inductor. DETAILED DESCRIPTION

[0032] Below, embodiments of the present application will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present application. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present application. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present application.

[0033] The terms used herein are only for describing specific embodiments and are not intended to limit the present application. The terms "include", "comprising", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0034] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0035] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0036] Figure 1 A schematic diagram of a low-pass filter according to an embodiment of the present application is shown.

[0037] like Figure 1 As shown, the low-pass filter for the quantum bit includes:

[0038] Ground wire 100;

[0039] A transmission line 200, wherein the transmission line 200 is used to transmit an input control signal within a preset frequency range;

[0040] A plurality of capacitors 300, wherein a first end of the capacitor 300 is connected to the ground line 100, and a second end of the capacitor 300 is connected to the transmission line 200;

[0041] A plurality of first inductors 400, wherein one first inductor 400 is disposed on the transmission line 200 between two adjacent capacitors 300;

[0042] When the input control signal is input to the input end of the transmission line 200, the response mode of the low-pass filter causes the output end of the transmission line 200 to output a first output control signal and a second output control signal, wherein the frequency of the first output control signal is higher than the frequency of the second output control signal.

[0043] According to an embodiment of the present application, the number of capacitors 300 and first inductors 400 can be specifically set according to actual needs. For example, three capacitors 300 and two first inductors 400 can be set, or five capacitors 300 and four first inductors 400 can be set.

[0044] According to an embodiment of the present application, the preset frequency range can be specifically set according to requirements, such as a signal of 0~6GHz.

[0045] According to an embodiment of the present application, after an input control signal in a preset frequency range is input into the low-pass filter of the present application, the low-pass filter can output a high-frequency control signal and a low-frequency control signal, namely a first output control signal and a second output control signal, through a response mode.

[0046] According to the embodiments of the present application, the low-pass filter of the present application can realize the simultaneous transmission of high-frequency and low-frequency control signals of superconducting quantum bits. This can solve the scale expansion problem in large-scale complex quantum circuits. In future-oriented large-scale programmable quantum circuits, the number of control lines can be reduced, the space occupied by the low-pass filter in the refrigerator can be reduced, and the heat load of the low-pass filter can be reduced, which has broad application prospects in the waveform control of large-scale programmable quantum computing.

[0047] According to an embodiment of the present application, the first inductor 400 includes an air-core inductor, a magnetic-core inductor, a copper-core inductor or a Josephson junction inductor.

[0048] According to an embodiment of the present application, the first inductor 400 can be any type of inductor. In order to further reduce the size of the inductor segment (usually in the order of millimeters), the existing superconducting quantum bit preparation technology can be fully utilized. Connecting multiple superconducting Josephson junctions in series will form a very large linear inductor, and the superconducting Josephson junction itself is extremely small (in the order of hundreds of nanometers), which simultaneously increases the inductance and reduces the size. In the case where the first inductor 400 is a Josephson junction inductor, the first inductor 400 is composed of a preset number of Josephson junctions connected in series. Among them, the preset number can be specifically set according to actual needs, for example, it can be 5.

[0049] Figure 2 A schematic diagram of a low-pass filter according to another embodiment of the present application is shown.

[0050] like Figure 2 As shown, the low-pass filter also includes:

[0051] The second inductor 500 is disposed on one side of the transmission line 200 close to the output end, and a capacitor 300 is disposed between the second inductor 500 and the first inductor 400 closest to the output end.

[0052] According to an embodiment of the present application, the second inductor 500 is of the same type as the first inductor 400 and may also be a Josephson junction inductor.

[0053] According to an embodiment of the present application, for any inductor of the first inductor 400 and the second inductor 500 , the impedance is calculated according to the inductor and the capacitor 300 corresponding to the inductor, wherein parameter values ​​of different impedances are different.

[0054] According to the embodiment of the present application, in the present application, it is assumed that the first inductor 400 is L jjs i The corresponding capacitor 300 (for example, the capacitor 300 on the left side of the first inductor 400) is represented by C i Said that the impedance .

[0055] Figure 3 A prototype circuit diagram of a 5th-order low-pass filter according to an embodiment of the present application is shown.

[0056] According to an embodiment of the present application, the low-pass filter is implemented in the form of a coplanar waveguide, wherein the ground line 100 is coplanar with the transmission line 200 .

[0057] According to an embodiment of the present application, the low-pass filter preparation process can be a coplanar waveguide process, a stripline process or a microstrip line process, wherein the filter prepared by the coplanar waveguide process has the smallest size, and by changing the width of the core line and the spacing between the core line and the ground planes on both sides, it is easy to achieve 200 segments of high-impedance and low-impedance transmission lines, while being compatible with current superconducting quantum bit chip preparation processes.

[0058] According to an embodiment of the present application, Figure 1 The prototype circuit of the 5th order low pass filter consists of 3 parallel capacitors 300C and 2 series first inductors 400L. JJs Composition. Each L JJs It consists of multiple Josephson junction inductors connected in series, where × represents the Josephson junction. Figure 3 This is a coplanar waveguide implementation of a 5th-order low-pass filter circuit. The gray lines in the middle represent the core metal, and the gray lines on both sides represent the grounding metal. The thickness of the core determines the size of its impedance. Here, the capacitor 300 is a thick line segment (that is, low impedance), and the inductor is a thin line segment (that is, high impedance) plus a series-connected Josephson junction. The more series-connected Josephson junctions, the greater the inductance. The core wire may not be a straight line. In order to adapt to the wiring space on the chip, it can be designed into other shapes, such as a curled S-shape.

[0059] According to an embodiment of the present application, the capacitance of the capacitor 300 is determined according to the cross-sectional width and spacing of the transmission line 200 , where the spacing represents the plane spacing between the transmission line 200 and the ground line 100 .

[0060] According to an embodiment of the present application, the low-pass filter is made of superconducting material, wherein the superconducting material includes superconducting aluminum, titanium nitride, superconducting niobium or superconducting tantalum.

[0061] According to the embodiments of the present application, the advantage of using superconducting materials is that there is no heating problem, and the heat load brought by the low-pass filter to the refrigerator is reduced.

[0062] According to an embodiment of the present application, the response mode includes a flattest response or a Chebyshev response.

[0063] According to the embodiment of the present application, the response curve of the low-pass filter can be designed as the flattest response or the Chebyshev response. Since the frequency of the high-frequency control signal is between 4.5 GHz and 5.5 GHz, the signal strength in this frequency range should not differ too much, so the stop band does not need to decay too quickly, so the flattest response is more suitable.

[0064] According to an embodiment of the present application, the frequency of the first output control signal is between 4.5 GHz and 5.5 GHz, and the frequency of the second output control signal is lower than 1 GHz, so the 3dB passband cutoff frequency range of the low-pass filter is 0.8 GHz~1.2 GHz, and the attenuation of a preset decibel amount is achieved within the stopband range of 4 GHz~5 GHz.

[0065] According to an embodiment of the present application, the preset decibel amount can be specifically set according to actual needs, for example, it can be 20dB.

[0066] According to an embodiment of the present application, a superconducting low-pass filter can be implemented using a step impedance transmission line 200 segment, or using a short line or a coupled resonator, wherein the step impedance filter has a simple structure, is easy to design, and has a compact size, making it very suitable for making an on-chip micro device.

[0067] According to an embodiment of the present application, a step impedance low-pass filter can be realized by using alternating high impedance transmission line 200 segments and low impedance transmission line 200 segments. The prototype device of the low-pass filter is a capacitor 300 and an inductor connected in parallel or in series. The high impedance transmission line 200 segment can be approximated as a series inductor when the length is short, and the low impedance transmission line 200 segment can be approximated as a parallel capacitor 300 when the length is short. Connecting them alternately constitutes a low-pass filter. Generally, the impedance ratio can be ten to one. The cut-off frequency of the filter, the attenuation of the passband and the stopband can be changed by adjusting the size of the inductor and the capacitor 300.

[0068] The embodiments of the present application are described above. However, these embodiments are only for the purpose of illustration, and are not intended to limit the scope of the present application. Although each embodiment is described above, this does not mean that the measures in each embodiment cannot be used in combination advantageously. The present application does not depart from the scope of the present application, and those skilled in the art may make various substitutions and modifications, which should all fall within the scope of the present application.

Claims

1. A low-pass filter for a quantum bit, characterized in that: include: Ground wire; A transmission line, the transmission line being used to transmit an input control signal within a preset frequency range; A plurality of capacitors, wherein a first end of the capacitor is connected to the ground line, and a second end of the capacitor is connected to the transmission line; A plurality of first inductors, one of the first inductors being arranged on the transmission line between two adjacent capacitors; When the input control signal is input to the input end of the transmission line, the response mode of the low-pass filter causes the output end of the transmission line to output a first output control signal and a second output control signal, wherein the frequency of the first output control signal is higher than the frequency of the second output control signal.

2. The low-pass filter according to claim 1, characterized in that The first inductor includes an air-core inductor, a magnetic-core inductor, a copper-core inductor or a Josephson junction inductor.

3. The low-pass filter according to claim 2, characterized in that The Josephson junction inductor is composed of a preset number of Josephson junctions connected in series.

4. The low-pass filter according to claim 1, characterized in that Also includes: The second inductor is arranged on a side of the transmission line close to the output end, and a capacitor is arranged between the second inductor and the first inductor closest to the output end.

5. The low-pass filter according to claim 4, characterized in that For any inductance of the first inductance and the second inductance, the impedance is calculated according to the inductance and the capacitance corresponding to the inductance, wherein parameter values ​​of different impedances are different.

6. The low-pass filter according to claim 1, characterized in that The low-pass filter is implemented in the form of a coplanar waveguide, wherein the ground line is coplanar with the transmission line.

7. The low-pass filter according to claim 6, characterized in that The capacitance of the capacitor is determined according to the cross-sectional width and spacing of the transmission line, and the spacing represents the plane spacing between the transmission line and the ground line.

8. The low-pass filter according to claim 3, characterized in that The low-pass filter is made of superconducting material, wherein the superconducting material includes superconducting aluminum, titanium nitride, superconducting niobium or superconducting tantalum.

9. The low-pass filter according to claim 1, characterized in that: The response modes include a flattest response or a Chebyshev response.

10. The low-pass filter according to claim 1 or 9, characterized in that: The frequency of the first output control signal is between 4.5 GHz and 5.5 GHz, and the frequency of the second output control signal is lower than 1 GHz, so the 3dB passband cutoff frequency range of the low-pass filter is 0.8 GHz to 1.2 GHz, and the attenuation of the preset decibel amount is achieved within the stopband range of 4 GHz to 5 GHz.

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