Low-pass filter for qubit
By designing a low-pass filter for qubits and employing a low-pass filter structure combining capacitors and inductors, the space constraints and thermal load problems caused by different signal attenuation requirements in large-scale superconducting quantum chips were solved, enabling efficient transmission and thermal management of high-frequency and low-frequency signals.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- UNIV OF SCI & TECH OF CHINA
- Filing Date
- 2024-11-08
- Publication Date
- 2026-05-15
AI Technical Summary
In large-scale superconducting quantum chips, the attenuation requirements of high-frequency and low-frequency control signals in the cryogenic layer of the refrigerator are different, which leads to an increase in the number of infrared filters and space constraints. At the same time, the heat generated by the infrared filters increases the thermal load.
Design a low-pass filter for qubits, employing a combination of capacitors and inductors in a coplanar waveguide configuration. Utilize superconducting materials and Josephson junction inductors to achieve separate transmission of high-frequency and low-frequency signals, reducing the number of control lines and lowering thermal load.
It enables the simultaneous transmission of high-frequency and low-frequency control signals in large-scale quantum circuits, reduces the number of control lines, and lowers the space occupation and thermal load of low-pass filters in the refrigerator, making it suitable for waveform control in large-scale programmable quantum computing.
Smart Images
Figure CN2024130827_15052026_PF_FP_ABST
Abstract
Description
Low-pass filter for qubits Technical Field
[0001] This disclosure relates to the field of quantum computing technology, and more specifically, to a low-pass filter for qubits. Background Technology
[0002] Currently, quantum computing technology is in its early stages of development, and achieving precise control over quantum systems is a key focus of this development. Superconducting quantum chips, realized from superconducting qubits, are one of the most effective physical platforms for quantum computing. Achieving precise control over large-scale superconducting quantum chips is a core technology and challenge for improving the accuracy of quantum manipulation.
[0003] As the scale of superconducting quantum processors continues to increase, the number of superconducting qubits also increases, requiring more and more control lines. To reduce the number of control lines inside the cryocooler, the high-frequency and low-frequency control signals of the superconducting qubits have been combined at room temperature and transmitted to the cryocooler via the same cable. However, the attenuation required for these two signals in the cryocooler's cryogenic layer is different; the high-frequency signal requires attenuation of 20 dB more than the low-frequency signal.
[0004] The current solution involves installing infrared filters in the cryogenic layer, which exhibit significant attenuation at high frequencies and less at low frequencies. As the number of superconducting qubits increases, more infrared filters will be needed, and combined with other components, space within the cryo-system will become very limited. Furthermore, infrared filters generate heat, increasing the thermal load on the cryo-system.
[0005] Summary of the Invention
[0006] In view of this, the present disclosure provides a low-pass filter for qubits, comprising:
[0007] Ground wire;
[0008] The transmission line is configured to transmit input control signals within a preset frequency range;
[0009] Multiple capacitors, with the first end of each capacitor connected to the ground wire and the second end connected to the transmission line;
[0010] Multiple first inductors, with one of the first inductors disposed on the transmission line between two adjacent capacitors;
[0011] When the input control signal is input at 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, wherein the frequency of the first output control signal is higher than the frequency of the second output control signal.
[0012] According to embodiments of this disclosure, the first inductor includes an air-core inductor, a magnetic-core inductor, a copper-core inductor, or a Josephson junction inductor.
[0013] According to embodiments of this disclosure, the aforementioned Josephson junction inductor is composed of a predetermined number of Josephson junctions connected in series.
[0014] According to embodiments of this disclosure, the low-pass filter further includes:
[0015] The second inductor is disposed on the side of the transmission line closest to the output terminal, and a capacitor is disposed between the second inductor and the first inductor closest to the output terminal.
[0016] According to embodiments of this disclosure, for any inductor among the first inductor and the second inductor, the impedance is calculated based on the inductor and the capacitance corresponding to the inductor, wherein the parameter values are different for different impedances.
[0017] According to embodiments of this disclosure, the low-pass filter is implemented in the form of a coplanar waveguide, wherein the ground line and the transmission line are coplanar.
[0018] According to an embodiment of this disclosure, the capacitance of the capacitor is determined based on the cross-sectional width and spacing of the transmission line, wherein the spacing represents the planar distance between the transmission line and the ground line.
[0019] According to embodiments of this disclosure, the low-pass filter is made of a superconducting material, wherein the superconducting material includes superconducting aluminum, titanium nitride, superconducting niobium, or superconducting tantalum.
[0020] According to embodiments of this disclosure, the above response modes include the flattest response or the Chebyshev response.
[0021] According to embodiments of this disclosure, 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 below 1 GHz. Therefore, the 3 dB passband cutoff frequency range of the low-pass filter is 0.8 GHz to 1.2 GHz, and the attenuation reaches a preset decibel level within the stopband range of 4 GHz to 5 GHz.
[0022] According to embodiments of this disclosure, the low-pass filter can simultaneously transmit high-frequency and low-frequency control signals for superconducting qubits. This solves the scaling problem in large-scale complex quantum circuits. In future large-scale programmable quantum circuits, it can reduce the number of control lines, decrease the space occupied by the low-pass filter in the refrigerator, and reduce the thermal load of the low-pass filter, showing broad application prospects in waveform control for large-scale programmable quantum computing. Attached Figure Description
[0023] The above and other objects, features, and advantages of this disclosure will become clearer from the following description of embodiments of the present disclosure with reference to the accompanying drawings, in which:
[0024] Figure 1 shows a schematic diagram of a low-pass filter according to an embodiment of the present disclosure;
[0025] Figure 2 shows a schematic diagram of a low-pass filter according to another embodiment of the present disclosure;
[0026] Figure 3 shows a prototype circuit diagram of a 5th-order low-pass filter according to an embodiment of the present disclosure.
[0027] The meanings of the reference numerals in the above figures are as follows:
[0028] 100-Ground wire;
[0029] 200-Transmission Line
[0030] 300-capacitor;
[0031] 400 - First Inductor;
[0032] 500 - Second inductor. Detailed Implementation
[0033] The embodiments of the present disclosure will now 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 disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.
[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.
[0035] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.
[0036] When using expressions such as "at least one of A, B, and C", they should generally be interpreted in accordance with the meaning that is commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B, and C, etc.).
[0037] Figure 1 shows a schematic diagram of a low-pass filter according to an embodiment of the present disclosure.
[0038] As shown in Figure 1, the low-pass filter used for qubits includes:
[0039] Ground wire 100;
[0040] Transmission line 200, the transmission line 200 being configured to transmit input control signals within a preset frequency range;
[0041] Multiple capacitors 300, with a first end of each capacitor 300 connected to the ground wire 100 and a second end connected to the transmission line 200;
[0042] Multiple first inductors 400, with one first inductor 400 disposed on the transmission line 200 between two adjacent capacitors 300;
[0043] When the input control signal is input at the input terminal of the transmission line 200, the response mode of the low-pass filter causes the output terminal 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.
[0044] According to embodiments of this disclosure, 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, or five capacitors 300 and four first inductors 400 can be set.
[0045] According to embodiments of this disclosure, the preset frequency range can be specifically set according to requirements, for example, a signal of 0 to 6 GHz.
[0046] According to embodiments of this disclosure, after an input control signal with a preset frequency range is input to the low-pass filter of this disclosure, 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.
[0047] According to embodiments of this disclosure, the low-pass filter can simultaneously transmit high-frequency and low-frequency control signals for superconducting qubits. This solves the scaling problem in large-scale complex quantum circuits. In future large-scale programmable quantum circuits, it can reduce the number of control lines, decrease the space occupied by the low-pass filter in the refrigerator, and reduce the thermal load of the low-pass filter, showing broad application prospects in waveform control for large-scale programmable quantum computing.
[0048] According to embodiments of this disclosure, the first inductor 400 includes an air-core inductor, a magnetic-core inductor, a copper-core inductor, or a Josephson junction inductor.
[0049] According to embodiments of this disclosure, the first inductor 400 can be any type of inductor. To further reduce the size of the inductor segment (typically on the order of millimeters), existing superconducting quantum bit fabrication techniques can be fully utilized. Connecting multiple superconducting Josephson junctions in series forms a very large linear inductance, while the superconducting Josephson junction itself is extremely small (on the order of hundreds of nanometers), thus simultaneously increasing the inductance and reducing the size. When the first inductor 400 is a Josephson junction inductor, it is composed of a predetermined number of Josephson junctions connected in series. The predetermined number can be specifically set according to actual needs, for example, it can be 5.
[0050] Figure 2 shows a schematic diagram of a low-pass filter according to another embodiment of the present disclosure.
[0051] As shown in Figure 2, the low-pass filter also includes:
[0052] The second inductor 500 is disposed on the transmission line 200 on the side near the output terminal, and a capacitor 300 is disposed between the second inductor 500 and the first inductor 400 closest to the output terminal.
[0053] According to embodiments of this disclosure, the second inductor 500 is of the same type as the first inductor 400, and may also be a Josephson junction inductor.
[0054] According to embodiments of this disclosure, for any inductor among the first inductor 400 and the second inductor 500, the impedance is calculated based on the inductor and the capacitor 300 corresponding to the inductor, wherein the parameter values are different for different impedances.
[0055] According to embodiments of this disclosure, in this disclosure, it is assumed that the first inductor 400 uses L jjs i This indicates that the corresponding capacitor 300 (e.g., the capacitor 300 to the left of the first inductor 400) is represented by C. i This indicates that the impedance
[0056] Figure 3 shows a prototype circuit diagram of a 5th-order low-pass filter according to an embodiment of the present disclosure.
[0057] According to an embodiment of this disclosure, the low-pass filter is implemented in the form of a coplanar waveguide, wherein the ground line 100 and the transmission line 200 are coplanar.
[0058] According to embodiments of this disclosure, the low-pass filter fabrication process can be a coplanar waveguide process, a stripline process, or a microstrip line process. Among these, the filter fabricated 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, 200 segments of high-impedance and low-impedance transmission lines can be easily achieved, while being compatible with current superconducting quantum bit chip fabrication processes.
[0059] According to an embodiment of this disclosure, Figure 1 shows a prototype circuit of a 5th-order low-pass filter, consisting of three parallel capacitors 300C and two series-connected first inductors 400L. JJs Composition. Each L JJs It consists of multiple Josephson junction inductors connected in series, where × represents a Josephson junction. Figure 3 shows the coplanar waveguide implementation of a 5th-order low-pass filter circuit. The alternating thick and thin gray lines in the middle represent the core metal, and the gray lines on both sides represent the ground metal. The thickness of the core wire determines its impedance. Here, the capacitor 300 is the thick segment (i.e., low impedance), and the inductor is the thin segment (i.e., high impedance) plus the series Josephson junctions. The more series Josephson junctions, the larger the inductance. The core wire does not have to be straight; to accommodate the wiring space on the chip, it can be designed into other shapes, such as a curled S-shape.
[0060] According to an embodiment of this disclosure, the capacitance of the capacitor 300 is determined based on the cross-sectional width and spacing of the transmission line 200, wherein the spacing represents the planar distance between the transmission line 200 and the ground line 100.
[0061] According to embodiments of this disclosure, the low-pass filter is made of a superconducting material, wherein the superconducting material includes superconducting aluminum, titanium nitride, superconducting niobium, or superconducting tantalum.
[0062] According to embodiments of this disclosure, the advantage of using superconducting materials is that there is no heat generation problem, which reduces the thermal load on the refrigerator caused by the low-pass filter.
[0063] According to embodiments of this disclosure, the response mode includes the flattest response or the Chebyshev response.
[0064] According to embodiments of this disclosure, the response curve of the low-pass filter can be designed as either the flattest response or a 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 stopband does not need to attenuate too quickly; therefore, the flattest response is more suitable.
[0065] According to an embodiment of this disclosure, 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 below 1 GHz. Therefore, the 3 dB passband cutoff frequency range of the low-pass filter is 0.8 GHz to 1.2 GHz, and the attenuation reaches a preset decibel level within the stopband range of 4 GHz to 5 GHz.
[0066] According to embodiments of this disclosure, the preset decibel level can be specifically set according to actual needs, for example, it can be 20dB.
[0067] According to embodiments of this disclosure, a superconducting low-pass filter can be implemented using a 200-segment step impedance transmission line, or using a stub or a coupled resonator. The step impedance filter has a simple structure, is easy to design, and has a compact size, making it very suitable for fabrication as an on-chip micro-device.
[0068] According to embodiments of this disclosure, a step-impedance low-pass filter can be implemented using alternating high-impedance transmission line segments 200 and low-impedance transmission line segments 200. The prototype device for the low-pass filter is a capacitor 300 and an inductor connected in parallel or series. When the high-impedance transmission line segment 200 is short, it can be approximated as a series inductor; when the low-impedance transmission line segment 200 is short, it can be approximated as a parallel capacitor 300. Alternating these components constitutes the low-pass filter. Typically, the impedance ratio can be 10:1. By adjusting the values of the inductor and capacitor 300, the cutoff frequency, passband, and stopband attenuation of the filter can be changed.
[0069] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. This disclosure does not depart from its scope, and those skilled in the art can make various substitutions and modifications, all of which should fall within the scope of this disclosure.
Claims
1. A low-pass filter for qubits, comprising: Ground wire; A transmission line configured to transmit input control signals within a preset frequency range; Multiple capacitors, wherein the first end of each capacitor is connected to the ground wire and the second end is connected to the transmission line; Multiple first inductors are provided, with one first inductor disposed on the transmission line between two adjacent capacitors; When the input control signal is input at 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, wherein the first inductor comprises 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, wherein the Josephson junction inductor is composed of a predetermined number of Josephson junctions connected in series.
4. The low-pass filter according to claim 1, further comprising: A second inductor is disposed on the side of the transmission line closer to the output terminal, and a capacitor is disposed between the second inductor and the first inductor closest to the output terminal.
5. The low-pass filter according to claim 4, wherein, for any inductor among the first inductor and the second inductor, the impedance is calculated based on the inductor and the capacitance corresponding to the inductor, wherein, Different impedances have different parameter values.
6. The low-pass filter according to claim 1, wherein the low-pass filter is implemented in the form of a coplanar waveguide, wherein, The ground wire and the transmission line are coplanar.
7. The low-pass filter according to claim 6, wherein the capacitance is determined based on the cross-sectional width and spacing of the transmission lines, the spacing representing the planar distance between the transmission lines and the ground line.
8. The low-pass filter according to claim 3, wherein the low-pass filter is made of a superconducting material, wherein, The superconducting material includes superconducting aluminum, titanium nitride, superconducting niobium, or superconducting tantalum.
9. The low-pass filter of claim 1, wherein the response mode includes the flattest response or the Chebyshev response.
10. The low-pass filter according to claim 1 or 9, wherein 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 less than 1 GHz, so the 3 dB passband cutoff frequency range of the low-pass filter is 0.8 GHz to 1.2 GHz, and the attenuation reaches a preset decibel level within the stopband range of 4 GHz to 5 GHz.