Parameter determination method and apparatus for quantum chip, and filtering regulation and control method and apparatus for quantum chip

Abstract

The present application relates to the field of quantum chips, and discloses a parameter determination method and apparatus for a quantum chip, and a filtering regulation and control method and apparatus for a quantum chip, for use in solving the problem that a large amount of space of a quantum chip is occupied in order to meet a filtering function of the quantum chip having a large number of bits. Josephson junctions are provided on a coplanar waveguide of a filter. By adjusting the critical current of the Josephson junctions, the equivalent inductance corresponding to the filter is changed, thereby achieving the adjustment of the center frequency of the filter; and by screening for an initial length meeting a center frequency range and a bandwidth range and screening for an inductance set, the Josephson junctions can cover the frequencies required by all resonant cavities during adjustment, thereby achieving the coverage of all resonant cavity frequency bands through one filter. Since the center frequency of the filter is adjustable, the bandwidth of the filter can be designed to be narrower to improve a filtering effect, so that the frequency range for filtering is not compromised and the space required by a filtering circuit is also saved, and therefore, the filter can be integrated on a quantum chip having a large number of bits.

Description

Quantum chip parameter determination method and device, filtering control method and device Technical Field

[0001] The present application relates to the field of quantum chips, and in particular to a method and device for determining parameters of a quantum chip, and a method and device for filtering and controlling the same. Background Art

[0002] Quantum computers have advanced to the point where their computing power surpasses that of classical computers for certain specific problems. However, because the error rate of a single bit is less than ideal, hundreds of bits are required for fault-tolerant calculations to achieve the functionality of a single bit, significantly increasing the number of required qubits. Given the large number of bits and their generally short lifetimes, it is crucial to achieve fast, high-fidelity reading of the bit state without affecting its lifetime. In superconducting quantum circuits, the state of a qubit can be determined by measuring the state of the resonant cavity coupled to the qubit. This indirect measurement method enables non-destructive quantum measurement, significantly minimizing the impact of the measurement itself on the qubit. However, qubits still transfer energy to the outside world through this additional channel, which reduces the bit lifetime.

[0003] Introducing a filter circuit into the circuit can suppress this process while maintaining the coupling between the resonant cavity and the external environment, thereby enabling rapid readout of bit states and a long bit lifetime to coexist. Therefore, introducing a filter circuit into a superconducting circuit can effectively improve the performance of quantum chips. Due to the large number of qubits, equipping each bit with a filter would consume a significant amount of space on the quantum chip. To save space, several qubits typically share a single bandpass filter. When multiple bits share a single filter, resonant cavity frequency crosstalk between different bits becomes more pronounced. Reducing resonant cavity frequency crosstalk, however, requires a robust resonant cavity frequency coverage range. If the resulting filter's operating frequency band is offset and fails to cover the required frequency range, filtering for some bits will be poor, potentially even occurring outside the bandpass filter's operating band.

[0004] It can be seen from this that how to solve the filtering function on a quantum chip with a large number of bits without taking up a large amount of space on the quantum chip is a technical problem that needs to be urgently solved by people in this field.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a quantum chip parameter determination method and device, and a filtering control method and device to solve the problem of occupying a large amount of space on the quantum chip in order to meet the filtering function on the quantum chip with a large number of bits.

[0007] To solve the above technical problems, the present application provides a method for determining parameters of a quantum chip, wherein the quantum chip includes: a filter; the filter includes: a coplanar waveguide, at least one pair of parallel Josephson junctions, and an input coupling capacitor; wherein the coplanar waveguide is coupled to a readout line; the Josephson junction is provided on the coplanar waveguide; and the input coupling capacitor is provided at the input end of the coplanar waveguide;

[0008] Methods include:

[0009] Determine the center frequency range and bandwidth range of the corresponding filter according to the resonant cavity coupled to the read line;

[0010] Obtaining an initial length from an input end to an output end of the coplanar waveguide and an initial inductance set, wherein the initial inductance set is a set of preset Josephson junction equivalent inductances;

[0011] Judging whether there is an inductance value that satisfies both the center frequency range and the bandwidth range in the initial inductance set according to the initial length;

[0012] If so, the output is the screening inductor set;

[0013] If not, the initial length is adjusted until an inductance value that satisfies both the center frequency range and the bandwidth range exists in the initial inductance set;

[0014] The area of ​​the Josephson junction is determined according to the screening inductor set, and the length from the input end to the output end of the coplanar waveguide is determined according to the current initial length.

[0015] Optionally, in the above-mentioned method for determining parameters of the quantum chip, determining whether there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range based on the initial length includes:

[0016] Determine whether there is an inductance value that satisfies the center frequency range in the initial inductance set according to the initial length;

[0017] If it exists, obtain the corresponding filter bandwidth data set according to the inductance value set that meets the center frequency range;

[0018] Determine whether the filtering bandwidth data set meets the bandwidth range;

[0019] If so, it is determined that there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range;

[0020] If it does not exist or is not satisfied, it is determined that there is no inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range.

[0021] Optionally, in the above-mentioned method for determining parameters of the quantum chip, obtaining a corresponding filter bandwidth data set according to a set of inductance values ​​that satisfy a center frequency range includes:

[0022] Obtaining a corresponding filter quality factor data set according to an inductance value set that satisfies a center frequency range;

[0023] A corresponding filter bandwidth data set is obtained according to the filter quality factor data set.

[0024] Optionally, in the above-mentioned method for determining parameters of a quantum chip, the coplanar waveguide includes a first coplanar waveguide segment and a second coplanar waveguide segment;

[0025] The first coplanar waveguide section is a section from the input end to the output end of the coplanar waveguide; the second coplanar waveguide section is a section from the output end to the ground end of the coplanar waveguide;

[0026] The Josephson junction is arranged at the intersection of the first coplanar waveguide section and the second coplanar waveguide section.

[0027] Optionally, in the above-mentioned method for determining parameters of a quantum chip, the filter further comprises: an output coupling capacitor;

[0028] The output coupling capacitor is arranged at the output end of the read line.

[0029] To solve the above problems, the present application also provides a filtering control method for a quantum chip, which is applied to a quantum chip prepared by the above quantum chip parameter determination method;

[0030] Methods include:

[0031] Scanning the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line;

[0032] Determine the bias current corresponding to each resonant cavity according to the ratio curve as the working current corresponding to the resonant cavity;

[0033] Under the working current, the state of the corresponding resonant cavity is read.

[0034] Optionally, in the above-mentioned filtering control method of the quantum chip, scanning the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line includes:

[0035] Scanning the current control end of the Josephson junction with a bias current of a first preset current interval to obtain a first curve of an output end signal and an input end signal of the read line;

[0036] Determining the target center frequency and bandwidth of each resonant cavity according to the first curve, that is, the corresponding current bias range;

[0037] Scanning the current control end of the Josephson junction with a bias current of a second preset current interval within the current bias range to obtain a second curve of the output end signal and the input end signal of the read line;

[0038] The second curve is taken as the ratio curve.

[0039] Optionally, in the filtering control method of the quantum chip, scanning the current control end of the Josephson junction with a bias current of a first preset current interval includes:

[0040] During an oscillation period of the Josephson junction, a current control terminal of the Josephson junction is scanned with a bias current of a first preset current interval.

[0041] To solve the above problems, the present application further provides a parameter determination device for a quantum chip, wherein the quantum chip includes: a filter; the filter includes: a coplanar waveguide, at least one pair of parallel Josephson junctions, and an input coupling capacitor; wherein the coplanar waveguide is coupled to a readout line; the Josephson junction is provided on the coplanar waveguide; and the input coupling capacitor is provided at the input end of the coplanar waveguide;

[0042] The device includes:

[0043] An adjustment range determination module is used to determine the center frequency range and bandwidth range of the corresponding filter according to the resonant cavity coupled to the read line;

[0044] An initial data acquisition module is used to obtain an initial length from the input end to the output end of the coplanar waveguide and an initial inductance set, wherein the initial inductance set is a set of preset Josephson junction equivalent inductances;

[0045] A judgment module is used to judge whether there is an inductance value that satisfies both the center frequency range and the bandwidth range in the initial inductance set according to the initial length; if so, trigger the result output module; if not, trigger the adjustment module;

[0046] A result output module, used for outputting the screened inductance set;

[0047] An adjustment module, configured to adjust the initial length until an inductance value that satisfies both the center frequency range and the bandwidth range exists in the initial inductance set;

[0048] The parameter determination module is used to determine the area of ​​the Josephson junction according to the screening inductor set and to determine the length from the input end to the output end of the coplanar waveguide according to the current initial length.

[0049] To solve the above problems, the present application also provides a filtering control device for a quantum chip, which is applied to a quantum chip prepared according to the above parameter determination method;

[0050] The device includes:

[0051] A scanning module is used to scan the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line;

[0052] An analysis module is used to determine the bias current corresponding to each resonant cavity according to the ratio curve as the working current corresponding to the resonant cavity;

[0053] The reading module is used to read the state of the corresponding resonant cavity under the working current.

[0054] The present application provides a method for determining parameters of a quantum chip, wherein the quantum chip includes: a filter; the filter includes: a coplanar waveguide, at least one pair of parallel Josephson junctions, and an input coupling capacitor; wherein the coplanar waveguide is coupled to a readout line; the Josephson junction is disposed on the coplanar waveguide; the input coupling capacitor is disposed at the input end of the coplanar waveguide; the center frequency range and bandwidth range of the corresponding filter are determined based on the resonant cavity coupled to the readout line; an initial length and an initial inductance set from the input end to the output end of the coplanar waveguide are obtained, wherein the initial inductance set is a set of preset Josephson junction equivalent inductors; based on the initial length, it is determined whether there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range; if so, a screening inductance set is output; if not, the initial length is adjusted until an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range is present; the area of ​​the Josephson junction is determined based on the screening inductance set, and the length from the input end to the output end of the coplanar waveguide is determined based on the current initial length. The filter provided in the present application has a Josephson junction disposed on its coplanar waveguide. By adjusting the critical current of the Josephson junction, the corresponding equivalent inductance of the filter is changed to adjust the center frequency of the filter. By screening the initial length that meets the center frequency range and bandwidth range and screening the inductance set, the Josephson junction can cover the required frequencies of all resonant cavities during adjustment. All resonant cavity frequency bands can be covered by a single filter, and during use, the bandwidth and the center frequency of the filter can be adjusted by adjusting the critical current of the Josephson junction, thereby achieving a better filtering effect.

[0055] In addition, the present application also provides a device for determining parameters of a quantum chip, which corresponds to the above-mentioned method for determining parameters of a quantum chip and has the same effect as above.

[0056] The filtering control method for a quantum chip provided in this application is applied to a quantum chip prepared according to the above-mentioned quantum chip parameter determination method. The method involves scanning the current control terminal of the Josephson junction with different bias currents to obtain a ratio curve between the output signal and the input signal of the read line. Based on the ratio curve, the bias current corresponding to each resonant cavity is determined as the corresponding operating current of the resonant cavity. Under the operating current, the state of the corresponding resonant cavity is read. The operating current of each resonant cavity is obtained by scanning. When a reading is required, the operating current of the Josephson junction is adjusted so that the filter operates within the corresponding center frequency and bandwidth range. Because the center frequency of the filter is adjustable, the filter bandwidth can be designed to be narrow to improve the filtering effect without sacrificing the filtering frequency range. Multiple resonant cavities share a single filter, significantly saving space required for the filter circuit, allowing integration on quantum chips with a large number of bits.

[0057] In addition, the present application also provides a filtering and control device for a quantum chip, which corresponds to the filtering and control method for the above-mentioned quantum chip and has the same effect as above. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0059] FIG1 is a flow chart of a method for determining parameters of a quantum chip provided in an embodiment of the present application;

[0060] Figure 2 is a schematic diagram of a common quantum chip;

[0061] FIG3 is a schematic diagram of a quantum chip provided in an embodiment of the present application;

[0062] FIG4 is a schematic diagram of another quantum chip provided in an embodiment of the present application;

[0063] FIG5 is an equivalent circuit diagram of a quantum chip provided in an embodiment of the present application;

[0064] FIG6 is a flow chart of a filtering control method for a quantum chip provided in an embodiment of the present application;

[0065] FIG7 is a structural diagram of a device for determining parameters of a quantum chip provided in an embodiment of the present application;

[0066] FIG8 is a structural diagram of a filtering and control device for a quantum chip provided in an embodiment of the present application. DETAILED DESCRIPTION

[0067] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0068] The core of this application is to provide a quantum chip parameter determination method and device, and a filtering control method and device.

[0069] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0070] In superconducting quantum circuits, directly measuring the state of a qubit causes the bit's energy to dissipate rapidly, thus destroying the state. A common solution is to indirectly determine the state of the qubit by measuring the state of the resonant cavity coupled to the qubit. Specifically, because the qubit and the resonant cavity are typically strongly coupled, the state of the qubit can be determined by measuring the frequency shift of the resonant cavity, avoiding direct manipulation of the bit and thus achieving non-destructive measurement of the qubit.

[0071] Since the number of quantum bits is very large, if a filter is provided for each bit, the space overhead on the quantum chip will be very large. To save space, it is common practice for several quantum bits to share a bandpass filter. Using multiple resonant cavities with the same frequency as a filter will improve the filtering effect, but since a single resonant cavity occupies a large space, this will greatly increase the space occupied by the filter on the chip, further compressing the space left for bits. In addition, when multiple bits share a filter, the crosstalk between the resonant cavity frequencies of different bits will be more obvious. A common approach is to separate the resonant cavity frequencies corresponding to different bits as much as possible to reduce crosstalk, but this requires a bandpass filter with a larger bandwidth so that the frequency range it can pass can cover the eigenfrequencies of the resonant cavities corresponding to all bits. This greatly reduces the filtering effect on a single bit, which is particularly noticeable for resonant cavities whose frequencies are far away from the center frequency of the bandpass filter.

[0072] The filter needs to be integrated on the quantum chip, with the resonant cavities corresponding to several bits sharing a single filter. However, minimizing crosstalk in the resonant cavity frequencies requires a wide frequency range. If the resulting filter's operating frequency band is offset and fails to cover the required frequency range, the filtering effect on some bits will be poor, potentially even outside the bandpass filter's operating frequency band.

[0073] Therefore, it is necessary to provide a filter that can cover all resonant cavity frequency bands, has a narrow bandwidth, and does not shift the center frequency of the filter. This embodiment provides a parameter determination method for a quantum chip, wherein the quantum chip includes: a filter; the filter includes: a coplanar waveguide, at least one pair of parallel Josephson junctions, and an input coupling capacitor; wherein the coplanar waveguide is coupled to a read line; the Josephson junction is provided on the coplanar waveguide; and the input coupling capacitor is provided at the input end of the coplanar waveguide;

[0074] As shown in FIG1 , the method includes:

[0075] S11: determining the center frequency range and bandwidth range of the corresponding filter according to the resonant cavity coupled to the read line;

[0076] S12: Obtaining an initial length from an input end to an output end of the coplanar waveguide and an initial inductance set, wherein the initial inductance set is a set of preset Josephson junction equivalent inductances;

[0077] S13: determining, based on the initial length, whether there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range;

[0078] S14: If yes, output the screening inductor set;

[0079] S15: If not, adjust the initial length until an inductance value that satisfies both the center frequency range and the bandwidth range exists in the initial inductance set;

[0080] S16: Determine the area of ​​the Josephson junction based on the screening inductor set, and determine the length from the input end to the output end of the coplanar waveguide based on the current initial length.

[0081] The common implementation method of the filter is based on a coplanar waveguide with a wavelength of λ / 2 or λ / 4. This embodiment takes a filter based on a coplanar waveguide with a wavelength of λ / 4 as an example. FIG2 is a schematic diagram of a common quantum chip. As shown in FIG2, a filter based on a coplanar waveguide with a wavelength of λ / 4 is obtained by adjusting the input capacitance C. in The value of can also adjust the bandwidth of the filter; considering the lumped element model, the quality factor of the filter can be simplified to:

[0082] Among them, Q F is the quality factor, l b is the distance from the output end to the ground end of the filter coplanar waveguide, l = l a +l b is the total length of the filter coplanar waveguide, l a is the distance from the input to the output of the filter’s coplanar waveguide. The filter’s external quality factor and dissipation rate satisfy: γ=ω F / QF ,ω F Indicates the passband frequency of the filter, which can be used to characterize the bandwidth of the filter. Therefore, the bandwidth of the filter is also related to l b With the size of l b As the value of increases, the voltage at the filter output gradually increases, and the corresponding bandwidth also gradually increases. If a filter based on a λ / 2 wavelength resonant cavity is used instead, it is only necessary to add an output coupling capacitor to the right side of the coplanar waveguide of the filter.

[0083] FIG3 is a schematic diagram of a quantum chip provided in an embodiment of the present application. As shown in FIG3 , C in is the input coupling capacitor; the dotted box portion is the parallel Josephson junction 11, and the control end of the Josephson junction 11 is represented by the DC end; F c is the coplanar waveguide part of the filter, l a The distance from the input to the output of the coplanar waveguide. The distance from the filter output coupling capacitor or the distance from the coplanar waveguide output to the ground. b It is replaced by a parallel-connected Josephson junction, and the DC is a coplanar waveguide with the end grounded. It provides a DC current bias and can provide a local magnetic field inside the parallel Josephson junction, thereby changing the critical current of the Josephson junction, and then changing the equivalent inductance corresponding to the filter, thereby adjusting the center frequency of the filter.

[0084] FIG4 is a schematic diagram of another quantum chip provided in an embodiment of the present application. As shown in FIG4 , l a Two parallel Josephson junctions a Divide into l a1 and l a2 Two parts, the coplanar waveguide output end to the ground end b Part of it is retained and is also connected by two parallel Josephson junctions J b Divide into l b1 and l b2 Two parts; two sets of Josephson junctions a and J b The local magnetic field is adjusted by direct current bias DC1 and DC2 respectively.

[0085] The difference between Figure 3 and Figure 4 is whether there is a separate coplanar waveguide output end to the ground end portion l b If it exists, another Josephson junction is set from the output end to the ground end. If it does not exist, a Josephson junction is set at the output end.

[0086] FIG5 is an equivalent circuit diagram of a quantum chip provided in an embodiment of the present application. As shown in FIG5 , the coplanar waveguide portion of the filter can be represented by the equivalent capacitor C in the dotted box. f and equivalent inductance L fCapacitor C 1r Until C nr is the coupling capacitance between the resonant cavity and the filter corresponding to n different bits, C 12 Until C n2 C is the coupling capacitance between n different bits and the corresponding resonant cavities, and the resonant cavities corresponding to these different bits share the same filter. n1 , L n1 The parallel structure represents the resonant cavity; C n3 、J n1 The parallel structure represents the quantum bit.

[0087] According to the above description, it can be seen that the length from the input to the output of the filter affects the center frequency range and bandwidth range of the filter; in addition, the area of ​​the Josephson junction also affects the center frequency range and bandwidth range of the filter, and its specific parameters need to be determined during the quantum chip design stage.

[0088] In this embodiment, step S11 determines the center frequency range and bandwidth range of the corresponding filter based on the resonant cavity coupled to the read line. A large center frequency range and bandwidth range are determined based on the parameters of the resonant cavity to be used to ensure that the filter can cover these resonant cavities.

[0089] A Josephson junction, also known as a superconducting tunnel junction, is typically composed of two superconductors sandwiched by a very thin barrier layer (thickness ≤ the coherence length of a Cooper pair), such as an S (superconductor)-I (semiconductor or insulator)-S (superconductor) structure, abbreviated as SIS. The critical current of a Josephson junction is determined by its area; a larger area indicates a higher critical current. A Josephson junction can be used as an inductor in a circuit. The Josephson junction equation can be used to derive the equivalent inductance of a Josephson junction.

[0090] Step S12 presets an initial length from the input end to the output end and an initial inductance set. The initial inductance set is a set of preset Josephson junction equivalent inductances. The area of ​​the Josephson junction can be reversely calculated through the inductance value.

[0091] The Josephson junction is placed on a coplanar waveguide, with two parallel Josephson junctions connected to ground. The filter's frequency and bandwidth can be adjusted by adjusting the position of the Josephson junction within the coplanar waveguide and the DC bias near the junction. If one or more Josephson junctions are made floating, that is, connected directly in series within the center conductor of the coplanar waveguide, the filter size can be reduced while achieving the same effect.

[0092] In step S13, it is determined whether there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range based on the initial length. This can be done by simulating in sequence whether any set of combined conditions are satisfied, or by first screening parameters that meet one condition and then screening parameters that meet another condition.

[0093] If no parameter satisfies the condition, the initial length is adjusted until an inductance value that satisfies both the center frequency range and the bandwidth range exists in the initial inductance set.

[0094] The area of ​​the Josephson junction is determined based on the screened inductor set, and the length from the input end to the output end of the coplanar waveguide is determined based on the current initial length to determine the design parameters of the quantum chip.

[0095] In actual chip processing, there may be an overall offset between the center frequency of the filter and the resonant cavity frequency. Since the center frequency of a typical bandpass filter is not adjustable, this offset cannot usually be corrected after processing. For filters that add a Josephson junction as an adjustable inductor, the center frequency of the filter can be adjusted by DC current bias, thereby correcting the frequency offset and achieving better filtering effects. This can reduce the pressure of overall frequency offset in filter parameter design and provide greater fault tolerance for chip preparation. In addition, the Josephson junction on the filter can be prepared together with the Josephson junction on the bit, so the complexity of the process is not increased, and only simple adjustments on the layout are required to complete it.

[0096] The quantum chip parameter determination method provided in this embodiment includes: a filter; the filter includes: a coplanar waveguide, at least one pair of parallel Josephson junctions, and an input coupling capacitor; wherein the coplanar waveguide is coupled to a readout line; the Josephson junction is disposed on the coplanar waveguide; the input coupling capacitor is disposed at the input end of the coplanar waveguide; a center frequency range and a bandwidth range of the corresponding filter are determined based on a resonant cavity coupled to the readout line; an initial length from the input end to the output end of the coplanar waveguide and an initial inductance set are obtained, wherein the initial inductance set is a set of preset Josephson junction equivalent inductors; based on the initial length, it is determined whether the initial inductance set has an inductance value that satisfies both the center frequency range and the bandwidth range; if so, a screening inductance set is output; if not, the initial length is adjusted until an inductance value that satisfies both the center frequency range and the bandwidth range is present in the initial inductance set; the area of ​​the Josephson junction is determined based on the screening inductance set, and the length from the input end to the output end of the coplanar waveguide is determined based on the current initial length. The filter provided in the present application has a Josephson junction disposed on its coplanar waveguide. By adjusting the critical current of the Josephson junction, the corresponding equivalent inductance of the filter is changed to adjust the center frequency of the filter. By screening the initial length that meets the center frequency range and bandwidth range and screening the inductance set, the Josephson junction can cover the required frequencies of all resonant cavities during adjustment. All resonant cavity frequency bands can be covered by a single filter, and during use, the bandwidth and the center frequency of the filter can be adjusted by adjusting the critical current of the Josephson junction, thereby achieving a better filtering effect.

[0097] According to the above embodiment, this embodiment provides a specific screening solution, which determines whether there is an inductance value that satisfies both the center frequency range and the bandwidth range in the initial inductance set based on the initial length, including:

[0098] Determine whether there is an inductance value that satisfies the center frequency range in the initial inductance set according to the initial length;

[0099] If it exists, obtain the corresponding filter bandwidth data set according to the inductance value set that meets the center frequency range;

[0100] Determine whether the filtering bandwidth data set meets the bandwidth range;

[0101] If so, it is determined that there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range;

[0102] If it does not exist or is not satisfied, it is determined that there is no inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range.

[0103] This embodiment first determines whether an initial inductance set contains an inductance value that satisfies the center frequency range based on the initial length. After selecting the inductance values ​​that meet the requirements, the filter bandwidth range corresponding to each inductance value is determined. It is then determined whether each filter bandwidth data set satisfies the bandwidth range, that is, whether the bandwidth range is included in the bandwidth range in the filter bandwidth data set. The inductance value corresponding to the bandwidth range is then selected. If no inductance value satisfies the center frequency range or does not meet the bandwidth range, the initial length needs to be adjusted and the determination repeated.

[0104] Determining the area of ​​a Josephson junction by selecting a set of inductors is related to the process details of the Josephson junction. It is important to ensure that the internal magnetic field corresponding to the designed Josephson junction area S is adjustable and that the adjustment range of the equivalent inductance of the double junction connected in parallel to ground can cover this set of inductance values. Since the resonant cavity frequency is typically set at 6-7 GHz, the equivalent inductance of the filter at the junction only occupies a limited width, so this condition is usually met.

[0105] As for the correction of bandwidth offset, refer to the quality factor formula of the filter. a The increase of l b As it gets smaller, the quality factor of the filter becomes larger and the bandwidth of the filter becomes narrower. Therefore, the bandwidth of the filter is related to l a is negatively correlated and changes monotonically. Therefore, by selecting a set of l a Simulation can roughly determine l a Quantitative relationship with filter bandwidth.

[0106] Specifically, the corresponding filter bandwidth is obtained by calculating the filter quality factor corresponding to each inductance value, and the corresponding filter bandwidth data set is obtained according to the inductance value set that meets the center frequency range, including:

[0107] Obtaining a corresponding filter quality factor data set according to an inductance value set that satisfies a center frequency range;

[0108] A corresponding filter bandwidth data set is obtained according to the filter quality factor data set.

[0109] According to the above embodiment, in a specific embodiment, the coplanar waveguide includes a first coplanar waveguide segment and a second coplanar waveguide segment;

[0110] The first coplanar waveguide section is a section from the input end to the output end of the coplanar waveguide; the second coplanar waveguide section is a section from the output end to the ground end of the coplanar waveguide;

[0111] The Josephson junction is arranged at the intersection of the first coplanar waveguide section and the second coplanar waveguide section.

[0112] The Josephson junction is arranged at the intersection of the first coplanar waveguide section and the second coplanar waveguide section, and the two coplanar waveguide sections are adjusted by a pair of Josephson junctions.

[0113] If the filter is based on a λ / 2 wavelength resonant cavity, an output coupling capacitor needs to be added to the right side of the coplanar waveguide of the filter. Specifically, the filter also includes: an output coupling capacitor;

[0114] The output coupling capacitor is arranged at the output end of the read line.

[0115] According to the above embodiment, the center frequency and bandwidth of the filter can be adjusted by adjusting the three variables of the position of the Josephson junction, the area of ​​the Josephson junction, and the DC bias current in the filter. The first two parameters are determined in the filter design stage and can determine the center frequency range and bandwidth range of the filter, while the DC bias current is determined in the use stage of the filter and can be used to adjust the center frequency of the filter. This embodiment provides a filtering control method for a quantum chip, which is applied to a quantum chip prepared according to the above-mentioned quantum chip parameter determination method;

[0116] As shown in FIG6 , the method includes:

[0117] S21: scanning the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line;

[0118] S22: determining the bias current corresponding to each resonant cavity according to the ratio curve as the working current corresponding to the resonant cavity;

[0119] S23: Under the working current, read the state of the corresponding resonant cavity.

[0120] After the quantum chip is fabricated, this embodiment provides a method for adjusting the filter frequency during use. By scanning the current control terminal of the Josephson junction with different bias currents, a curve is obtained showing the ratio of the output signal to the input signal of the readout line. In quantum computing, the interaction between qubits is controlled by microwave signals. To achieve efficient quantum computing, it is necessary to ensure that the frequency of the microwave signal matches the center frequency of the qubit. By measuring the ratio between the output microwave signal and the input microwave signal, the frequency of the microwave signal can be determined, and the eigenfrequency of the resonant cavity corresponding to each qubit can be obtained.

[0121] Therefore, the ratio curve can be used to determine the bias current corresponding to each resonant cavity, which serves as the operating current for subsequent resonant cavities. To read the state of a specific resonant cavity, the corresponding resonant cavity's state is read at the operating current. A detailed measurement provides the corresponding operating current relationship for each resonant cavity, allowing subsequent use by simply querying the available operating current value. Setting the center frequency of the filter for each resonant cavity corresponding to each bit improves filtering efficiency while maintaining the filterable frequency range.

[0122] The quantum chip filtering control method provided in this embodiment is applied to a quantum chip prepared according to the above-mentioned quantum chip parameter determination method. The current control terminal of the Josephson junction is scanned with different bias currents to obtain a ratio curve of the output signal to the input signal of the read line. The bias current corresponding to each resonant cavity is determined based on the ratio curve and used as the corresponding operating current of the resonant cavity. The state of the corresponding resonant cavity is read under the operating current. The operating current of each resonant cavity is obtained by scanning. When reading is required, the operating current of the Josephson junction is adjusted so that the filter operates within the corresponding center frequency and bandwidth range. Because the center frequency of the filter is adjustable, the filter bandwidth can be designed to be narrow to improve the filtering effect without compromising the filtering frequency range. Multiple resonant cavities share a single filter, which greatly saves the space required for the filter circuit, making it possible to integrate it on quantum chips with a large number of bits.

[0123] According to the above embodiment, specifically, scanning the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line includes:

[0124] Scanning the current control end of the Josephson junction with a bias current of a first preset current interval to obtain a first curve of an output end signal and an input end signal of the read line;

[0125] Determining the target center frequency and bandwidth of each resonant cavity according to the first curve, that is, the corresponding current bias range;

[0126] Scanning the current control end of the Josephson junction with a bias current of a second preset current interval within the current bias range to obtain a second curve of the output end signal and the input end signal of the read line;

[0127] The second curve is taken as the ratio curve.

[0128] In this embodiment, a ratio curve is determined by scanning the current control terminal of the Josephson junction with a bias current of a first preset current interval, obtaining a first curve of the output and input signals of the readout line. This is intended to roughly determine the frequency of all resonant cavities. Further, a more refined analysis is performed, and within the current bias range corresponding to each resonant cavity, the current control terminal of the Josephson junction is scanned with a bias current of a second preset current interval, obtaining a second curve of the output and input signals of the readout line. Naturally, the second preset current interval is smaller than the first preset current interval. By measuring the second curve at a smaller current interval, the specific operating current value corresponding to the target center frequency and bandwidth of each resonant cavity can be determined.

[0129] In addition, scanning the current control terminal of the Josephson junction with a bias current of a first preset current interval includes:

[0130] During an oscillation period of the Josephson junction, a current control terminal of the Josephson junction is scanned with a bias current of a first preset current interval.

[0131] The equivalent inductance of the Josephson junction changes periodically with the DC current bias, so the scanning current only needs to change within one oscillation period.

[0132] In the above embodiments, the method for determining the parameters of a quantum chip is described in detail. This application also provides corresponding embodiments of a device for determining the parameters of a quantum chip. It should be noted that this application describes the embodiments of the device part from the perspective of functional modules.

[0133] From the perspective of functional modules, an embodiment of the present application provides a structural diagram of a parameter determination device for a quantum chip, wherein the quantum chip includes: a filter; the filter includes: a coplanar waveguide, at least one pair of parallel Josephson junctions, and an input coupling capacitor; wherein the coplanar waveguide is coupled to a readout line; the Josephson junction is provided on the coplanar waveguide; and the input coupling capacitor is provided at the input end of the coplanar waveguide;

[0134] FIG7 is a structural diagram of a device for determining parameters of a quantum chip provided in an embodiment of the present application. As shown in FIG7 , the device includes:

[0135] An adjustment range determination module 21 is used to determine the center frequency range and bandwidth range of the corresponding filter according to the resonant cavity coupled to the read line;

[0136] An initial data acquisition module 22 is used to obtain an initial length from an input end to an output end of the coplanar waveguide and an initial inductance set, wherein the initial inductance set is a set of preset Josephson junction equivalent inductances;

[0137] The judgment module 23 is used to judge whether there is an inductance value that satisfies both the center frequency range and the bandwidth range in the initial inductance set according to the initial length; if so, the result output module is triggered; if not, the adjustment module is triggered;

[0138] A result output module 24 is used to output the screened inductance set;

[0139] An adjustment module 25 is configured to adjust the initial length until an inductance value that satisfies both the center frequency range and the bandwidth range exists in the initial inductance set;

[0140] The parameter determination module 26 is configured to determine the area of ​​the Josephson junction according to the screening inductor set, and determine the length from the input end to the output end of the coplanar waveguide according to the current initial length.

[0141] In the filter of the parameter determination device of the quantum chip provided in the embodiment of the present application, a Josephson junction is provided on its coplanar waveguide. By adjusting the critical current of the Josephson junction, the corresponding equivalent inductance of the filter is changed to adjust the center frequency of the filter. By screening the initial length that meets the center frequency range and bandwidth range and screening the inductance set, the Josephson junction can cover the required frequencies of all resonant cavities during adjustment. All resonant cavity frequency bands can be covered by a single filter, and the bandwidth and center frequency of the filter can be adjusted by adjusting the critical current of the Josephson junction during use, thereby achieving better filtering effect.

[0142] In the above embodiments, the filtering control method of the quantum chip is described in detail. This application also provides corresponding embodiments of the filtering control device of the quantum chip. It should be noted that this application describes the embodiments of the device part from the perspective of functional modules.

[0143] From the perspective of functional modules, an embodiment of the present application provides a structural diagram of a filtering and control device for a quantum chip, which is applied to a quantum chip prepared according to the above-mentioned method for determining parameters of a quantum chip;

[0144] FIG8 is a structural diagram of a filtering and control device for a quantum chip provided in an embodiment of the present application. As shown in FIG8 , the device includes:

[0145] The scanning module 31 is used to scan the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line;

[0146] An analysis module 32 is configured to determine a bias current corresponding to each resonant cavity according to the ratio curve as a working current corresponding to the resonant cavity;

[0147] The reading module 33 is used to read the state of the corresponding resonant cavity under the working current.

[0148] In this embodiment, the operating current of each resonant cavity is obtained by scanning. When reading is required, the operating current of the Josephson junction is adjusted so that the filter operates within the corresponding center frequency and bandwidth range. Since the center frequency of the filter is adjustable, the bandwidth of the filter can be designed to be narrower to improve the filtering effect without sacrificing the filtering frequency range. Multiple resonant cavities share one filter, which greatly saves the space required for the filtering circuit. Therefore, it can be integrated on a quantum chip with a large number of bits.

[0149] The parameter determination method and device, and the filtering control method and device of the quantum chip provided by the present application are introduced in detail above. The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of this application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of this application.

[0150] It should also be noted that, in this specification, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

Claims

1. A method for determining parameters of a quantum chip, characterized in that: The quantum chip comprises: a filter; the filter comprises: a coplanar waveguide, at least one pair of parallel Josephson junctions, and an input coupling capacitor; wherein the coplanar waveguide is coupled with a read line; the Josephson junction is arranged on the coplanar waveguide; the input coupling capacitor is arranged at the input end of the coplanar waveguide; The method comprises: Determine the center frequency range and bandwidth range of the corresponding filter according to the resonant cavity coupled to the read line; Obtaining an initial length from an input end to an output end of the coplanar waveguide and an initial inductance set, wherein the initial inductance set is a set of preset Josephson junction equivalent inductances; Determining whether there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range according to the initial length; If so, the output is a set of filtered inductors; If not, adjusting the initial length until an inductance value that satisfies both the center frequency range and the bandwidth range exists in the initial inductance set; The area of ​​the Josephson junction is determined according to the screening inductor set, and the length from the input end to the output end of the coplanar waveguide is determined according to the current initial length.

2. The method for determining parameters of a quantum chip according to claim 1, characterized in that: The determining, according to the initial length, whether there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range includes: Determining whether there is an inductance value satisfying the center frequency range in the initial inductance set according to the initial length; If it exists, obtaining a corresponding filter bandwidth data set according to the inductance value set satisfying the center frequency range; Determining whether the filtering bandwidth data set satisfies the bandwidth range; If so, it is determined that there is an inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range; If it does not exist or is not satisfied, it is determined that there is no inductance value in the initial inductance set that satisfies both the center frequency range and the bandwidth range.

3. The method for determining parameters of a quantum chip according to claim 2, characterized in that: The step of obtaining a corresponding filter bandwidth data set according to an inductance value set satisfying the center frequency range includes: Obtaining a corresponding filter quality factor data set according to an inductance value set satisfying the central frequency range; A corresponding filter bandwidth data set is obtained according to the filter quality factor data set.

4. The method for determining parameters of a quantum chip according to claim 1, characterized in that: The coplanar waveguide comprises a first coplanar waveguide segment and a second coplanar waveguide segment; Wherein, the first coplanar waveguide section is a section from the input end to the output end of the coplanar waveguide; the second coplanar waveguide section is a section from the output end to the ground end of the coplanar waveguide; The Josephson junction is arranged at the intersection of the first coplanar waveguide segment and the second coplanar waveguide segment.

5. The method for determining parameters of a quantum chip according to claim 4, characterized in that: The filter further comprises: an output coupling capacitor; The output coupling capacitor is arranged at the output end of the read line.

6. A filtering control method for a quantum chip, characterized in that: A quantum chip prepared by the method for determining parameters of a quantum chip according to any one of claims 1 to 5; The method comprises: Scanning the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line; Determining the bias current corresponding to each resonant cavity according to the ratio curve as the working current corresponding to the resonant cavity; Under the working current, the state of the corresponding resonant cavity is read.

7. The filtering and control method of a quantum chip according to claim 6, characterized in that: The method of scanning the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line includes: Scanning the current control end of the Josephson junction with a bias current of a first preset current interval to obtain a first curve of an output end signal and an input end signal of the read line; Determining the target center frequency and bandwidth of each of the resonant cavities according to the first curve, that is, the corresponding current bias range; Scanning the current control end of the Josephson junction with a bias current of a second preset current interval within the current bias range to obtain a second curve of the output end signal and the input end signal of the read line; The second curve is used as the ratio curve.

8. The filtering and control method of a quantum chip according to claim 7, characterized in that: Scanning the current control end of the Josephson junction with a bias current of a first preset current interval includes: During an oscillation period of the Josephson junction, a current control end of the Josephson junction is scanned with a bias current of a first preset current interval.

9. A device for determining parameters of a quantum chip, characterized in that: The quantum chip comprises: a filter; the filter comprises: a coplanar waveguide, at least one pair of parallel Josephson junctions, and an input coupling capacitor; wherein the coplanar waveguide is coupled with a read line; the Josephson junction is arranged on the coplanar waveguide; the input coupling capacitor is arranged at the input end of the coplanar waveguide; The device comprises: An adjustment range determination module, used to determine a center frequency range and a bandwidth range of a corresponding filter according to the resonant cavity coupled to the read line; An initial data acquisition module, used to acquire an initial length from an input end to an output end of the coplanar waveguide and an initial inductance set, wherein the initial inductance set is a set of preset Josephson junction equivalent inductances; A judgment module, used for judging whether there is an inductance value that satisfies both the center frequency range and the bandwidth range in the initial inductance set according to the initial length; if so, triggering a result output module, and if not, triggering an adjustment module; The result output module is used to output the screened inductor set; The adjustment module is used to adjust the initial length until an inductance value that satisfies both the center frequency range and the bandwidth range exists in the initial inductance set; The parameter determination module is used to determine the area of ​​the Josephson junction according to the screening inductor set, and determine the length from the input end to the output end of the coplanar waveguide according to the current initial length.

10. A filtering and control device for a quantum chip, characterized in that: A quantum chip prepared by the method for determining parameters of a quantum chip according to any one of claims 1 to 5; The device comprises: A scanning module is used to scan the current control end of the Josephson junction with different bias currents to obtain a ratio curve of the output end signal and the input end signal of the read line; An analysis module, used for determining the bias current corresponding to each resonant cavity according to the ratio curve as the working current corresponding to the resonant cavity; The reading module is used to read the state of the corresponding resonant cavity under the working current.

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