CN114429215A - Method for realizing double-bit quantum gate based on superconducting quantum coupler - Google Patents
Method for realizing double-bit quantum gate based on superconducting quantum coupler Download PDFInfo
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- CN114429215A CN114429215A CN202210110484.XA CN202210110484A CN114429215A CN 114429215 A CN114429215 A CN 114429215A CN 202210110484 A CN202210110484 A CN 202210110484A CN 114429215 A CN114429215 A CN 114429215A
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Abstract
The present disclosure provides a method for implementing a bi-bit quantum gate based on a superconducting quantum coupler, the superconducting quantum coupler comprising two qubits and a quantum coupling unit located between the two qubits, the method comprising: increasing a forward coupling strength between the two qubits; raising the maximum eigenfrequency of the quantum coupling unit; and adjusting the circuit parameters of the quantum coupling unit to enable the frequency and the frequency of the quantum bit to be always kept above the set detuning amount; by applying current pulses to the quantum coupling unit, a dual bit quantum gate is realized.
Description
Technical Field
The present disclosure relates to the field of quantum computing technologies, and in particular, to a method for implementing a dual-bit quantum gate using a microwave pulse and a superconducting quantum coupler.
Background
At present, the technology development of quantum computers is the primary stage, and how to realize precise regulation and control of quantum systems is the key point of quantum computing development. The superconducting quantum chip realized by the superconducting quantum bit is one of the most effective physical platforms for quantum computing at present, and how to realize high-precision regulation and control on the superconducting quantum chip by utilizing the electrical pulse is a core technology and challenge for improving the quantum control precision.
In order to avoid the influence of the residual voltage generated by the unipolar control pulse on the quantum gate, it is necessary to develop a technology for implementing a dual-bit quantum gate using a microwave pulse. However, the speed of realizing the quantum gate by the microwave pulse is generally slow, and how to quickly realize the two-bit quantum gate while ensuring the performance of the single-bit quantum gate of the qubit through a proper superconducting quantum coupler design is one of the technical problems to be solved urgently.
Disclosure of Invention
Based on the above problems, the present disclosure provides a method for implementing a dual-bit quantum gate based on a superconducting quantum coupler, so as to alleviate the above technical problems in the prior art.
(II) technical scheme
The present disclosure provides a method for implementing a bi-bit quantum gate based on a superconducting quantum coupler, the superconducting quantum coupler comprising two qubits and a quantum coupling unit located between the two qubits, the method comprising: increasing a forward coupling strength between the two qubits; raising the maximum eigenfrequency of the quantum coupling unit; adjusting the circuit parameters of the quantum coupling unit to enable the frequency of the quantum coupling unit and the frequency of the quantum bit to be always above a set detuning amount; by applying current pulses to the quantum coupling unit, a dual bit quantum gate is realized.
According to an embodiment of the present disclosure, the increasing the forward coupling strength between the two qubits includes: and improving the capacitance value of the direct coupling capacitor between the two qubits.
According to the embodiment of the disclosure, the capacitance value of the direct coupling capacitor between the two qubits is increased to be more than 4 fF.
According to the embodiment of the present disclosure, the quantum coupling unit includes a capacitance branch and a superconducting quantum interferometer branch connected in parallel, and the increasing the maximum eigenfrequency of the quantum coupling unit includes: reducing the capacitance value of a capacitance branch of the quantum coupling unit; and reducing the inductance of the superconducting quantum interferometer branch of the quantum coupling unit.
According to an embodiment of the present disclosure, the superconducting quantum interferometer arm comprises an asymmetric double josephson junction.
According to the embodiment of the disclosure, the critical current ratio of the asymmetric double Josephson junction in the branch of the superconducting quantum interference device is adjusted, so that the frequency of the quantum coupling unit and the frequency of the quantum bit are always kept above the set detuning amount.
According to the embodiment of the disclosure, the critical current ratio of two Josephson junctions in the asymmetric double Josephson junctions is adjusted to be 1: 2-1: 2.5.
According to the embodiment of the disclosure, the flux of the coupler of the quantum coupling unit is adjusted, the rapid change of the equivalent coupling strength exceeding the range of-10 MHz to 10MHz is realized, and when the changed frequency is equal to the frequency difference of the dual-quantum bit |11> state and |20> state, the dual-bit quantum gate is realized.
According to the embodiment of the disclosure, the equivalent coupling strength is the sum of the positive coupling strength and the negative coupling strength of the quantum coupling unit.
According to the embodiment of the disclosure, the set detuning amount is 1 GHz.
(III) advantageous effects
From the above technical solutions, the method for implementing a dual-bit quantum gate based on a superconducting quantum coupler of the present disclosure has at least one or some of the following beneficial effects:
(1) the AC CZ (Controlled-Z) gate can be realized in a shorter time;
(2) the relatively short quantum gate time can reduce the decoherence error of the quantum bit, and the fidelity and the experimental application value of the alternating current CZ gate are improved;
(3) the CZ gate is realized rapidly through microwave pulse, the CZ gate is reduced, and control errors caused by residual voltage are reduced.
Drawings
Fig. 1 is a flow chart of a method of implementing a dual bit quantum gate based on a superconducting quantum coupler according to an embodiment of the present disclosure;
FIG. 2 is a schematic diagram of a circuit for implementing a dual bit quantum gate based on a superconducting quantum coupler according to an embodiment of the present disclosure;
FIG. 3 illustrates an equivalent coupling strength between qubits and a magnetic flux Φ of a quantum coupling unit according to an embodiment of the disclosurecSchematic diagram of the variation curve of (2).
[ description of main reference numerals in the drawings ] of the embodiments of the present disclosure
100 first qubit
200 second qubit
300 quantum coupling unit
310 capacitor branch
320 superconducting quantum interferometer branch
Detailed Description
The disclosure provides a method for realizing a double-bit quantum gate, which can increase the absolute value of equivalent coupling strength to be more than 10MHz in positive and negative directions. Based on the quantum coupler design, the quick change of equivalent coupling strength exceeding the range of-10 MHz to 10MHz can be realized by changing the magnetic flux of the coupler, and when the changed frequency is equal to the frequency difference of |11> state and |20> state of two bits, the two-bit CZ gate can be realized. Due to the fact that the adjustable range of equivalent coupling strength of the quantum coupler design is large, the alternating current CZ gate realized based on the coupler can be realized in a shorter time. The short quantum gate time can reduce the decoherence error of the quantum bit and improve the fidelity and the experimental application value of the alternating current CZ gate.
In the superconducting quantum chip, microwave pulses applied to a quantum coupler are utilized to realize high-fidelity control phase gates with small microwave residual pulses and frequency division multiplexing possibility, and the superconducting quantum chip can be well applied to the expansion of future large-scale quantum bits. Certain changes are made on the basis of the prior technical scheme, so that a quantum computer with higher performance is formed.
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
In an embodiment of the present disclosure, a method for implementing a dual-bit quantum gate based on a superconducting quantum coupler is provided, which is shown in conjunction with fig. 1 and 2, the superconducting quantum coupler includes two qubits (a first qubit 100 and a second qubit 200) and a quantum coupling unit 300 located between the two qubits; as shown in FIG. 2, the first qubit 100 includes a first capacitive branch and a first quantum interferometer branch, wherein the first capacitive branch has a capacitance value Cqubit1The inductance value of the first quantum interferometer branch is Lq1Corresponding magnetic flux of phiQ1(ii) a The second qubit 100 comprises a second capacitive branch and a second quantum interferometer branch, wherein the second capacitive branch has a capacitance value of Cqubit2The inductance value of the second quantum interferometer branch is Lq2Corresponding magnetic flux of phiQ2(ii) a The quantum bit and the quantum coupling unit are different in that the capacitance value parameter C of the capacitance branch circuitqubit1、Cqubit2Value of (A) and CcouplerValue of (d), and inductance parameter Lq1、Lq2And LcThe difference in (c). CqqIs a direct coupling capacitance between two qubits, Cqc1Is the coupling capacitance between the first qubit and the quantum coupling unit, Cqc2Is the coupling capacitance between the second qubit and the quantum coupling unit.
The method for realizing the double-bit quantum gate based on the superconducting quantum coupler comprises the following steps:
operation S1: increasing a forward coupling strength between the two qubits;
operation S2: raising the maximum eigenfrequency of the quantum coupling unit; and
operation S3: adjusting the circuit parameters of the quantum coupling unit to enable the frequency and the frequency of the quantum bit to be always kept above a set detuning amount;
operation S4: the dual bit quantum gate is realized by applying current pulses to the quantum coupling unit.
According to the embodiment of the disclosure, the direct coupling capacitance C between two quantum bits is improvedqqTo improve the forward coupling strength between the first qubit 100 and the second qubit 200, in the disclosed embodiment, the capacitor C will be directly coupledqqThe capacity of (A) is increased to 4fF or more.
According to the embodiment of the present disclosure, the quantum coupling unit includes a capacitance branch 310 and a superconducting quantum interferometer branch 320 connected in parallel, and the increasing the maximum eigenfrequency of the quantum coupling unit includes: reducing the capacitance value C of the capacitive branch of the quantum coupling unitcoupler(ii) a And reducing the inductance L of the superconducting quantum interference device branch of the quantum coupling unitc. So that the maximum eigenfrequency of the quantum coupling unit is raised to 10GHz or more.
According to the embodiment of the present disclosure, the superconducting quantum interferometer branch 320 includes an asymmetric dual josephson junction, and the critical current ratio of the asymmetric dual josephson junction in the superconducting quantum interferometer branch is adjusted to keep the quantum coupling unit frequency and the qubit frequency above a set detuning amount all the time; for example, the critical current ratio of two asymmetrical double Josephson junctions is adjusted to 1: 2-1: 2.5.
By the above operation, the capacitor C is directly coupledqqThe direct coupling strength (or referred to as forward coupling strength) between the qubits is increased; meanwhile, due to the improvement of the maximum eigenfrequency of the quantum coupling unit, when the frequency of the quantum coupling unit is the maximum eigenfrequency, the quantum bit and the quantum coupling unit have larger frequency detuning, and the indirect coupling strength (or referred to as negative coupling strength) realized by the quantum coupling unit is smaller. Under the action of two aspects, the magnetic flux phi of the quantum coupling unit can becWhen the coupling strength is 0, the forward equivalent coupling strength (i.e., direct coupling strength + indirect coupling strength) of 10MHz or more is realized.
When the positive equivalent coupling strength is larger (more than 10MHz), the negative coupling can be realized for realizing (1)A coupling strength; (2) the equivalent coupling strength is near 0 and phicHas better linear relation; (3) the frequency of the quantum coupling unit and the frequency of the quantum bit always keep the detuning quantity above 1GHz in the magnetic flux adjusting process; the critical current parameters of two asymmetric Josephson junctions in a superconducting quantum interference device (SQUID) of a quantum coupling unit need to be adjusted to be 1: 2-1: 2.5.
According to the embodiment of the disclosure, a dual-bit quantum gate is realized by applying a current pulse to a superconducting quantum interferometer branch of a quantum coupling unit.
According to the disclosed embodiment, rapid changes in equivalent coupling strength over the range of-10 MHz to 10MHz can be achieved by varying the magnetic flux of the coupler, which can be used to implement a two-bit CZ gate when the frequency of the change is equal to the difference in frequency between the two bits |11> and |20> states.
According to an embodiment of the present disclosure, as shown in FIG. 3, the axis of ordinate represents the equivalent coupling strength (g/2 π) and the axis of abscissa represents the magnetic flux φcThe unit is magnetic flux quantum (phi)0) By combining the operations and settings of the above points, the equivalent coupling strength variation curve in fig. 3 can be realized. The change curve meets the requirement that (1) the absolute value of the bidirectional equivalent coupling strength can reach more than 10 MHz; (2) the equivalent coupling strength is near 0 and phicHas better linear relation; (3) the frequency of the quantum coupler and the frequency of the quantum bit are always kept at the detuning amount above 1GHz in the flux adjusting process, so that the flux phi of the quantum coupler can be well adjustedcWhen the frequency of the change is equal to two bits |11>State sum |20>When the frequency difference of the states is within 100ns, the alternating current CZ gate is realized rapidly. And in the interval of the quantum bit frequency difference of 0-500MHz, more than half of frequency intervals can realize the high-fidelity CZ gate with the simulation fidelity of more than 99.99 percent.
So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. Further, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by those of ordinary skill in the art.
From the above description, those skilled in the art should clearly recognize that the method for implementing a dibit quantum gate based on a superconducting quantum coupler of the present disclosure.
In summary, the present disclosure provides a method for implementing a dual-bit quantum gate based on a superconducting quantum coupler, which can be well implemented in experiments by adjusting the flux Φ of the quantum couplercThe ac CZ gate is implemented quickly in 100 ns. And in the interval of the quantum bit frequency difference of 0-500MHz, more than half of frequency intervals can realize the high-fidelity CZ gate with the simulation fidelity of more than 99.99 percent. The requirements of rapidly realizing the CZ gate through microwave pulse and reducing the non-receding coherent error of the alternating current CZ gate are well met.
It should also be noted that directional terms, such as "upper", "lower", "front", "rear", "left", "right", and the like, used in the embodiments are only directions referring to the drawings, and are not intended to limit the scope of the present disclosure. Throughout the drawings, like elements are represented by like or similar reference numerals. Conventional structures or constructions will be omitted when they may obscure the understanding of the present disclosure. And the shapes and sizes of the respective components in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of the embodiments of the present disclosure.
The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify a corresponding element does not by itself connote any ordinal number of the element or any ordering of one element from another or the order of manufacture, and the use of the ordinal numbers is only used to distinguish one element having a certain name from another element having a same name.
In addition, unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be changed or rearranged as desired by the desired design. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.
Claims (10)
1. A method of implementing a bi-bit quantum gate based on a superconducting quantum coupler, the superconducting quantum coupler comprising two qubits and a quantum coupling unit located between the two qubits, the method comprising:
increasing a forward coupling strength between the two qubits;
raising the maximum eigenfrequency of the quantum coupling unit;
adjusting the circuit parameters of the quantum coupling unit to enable the frequency and the frequency of the quantum bit to be always kept above a set detuning amount; and
by applying current pulses to the quantum coupling unit, a dual bit quantum gate is realized.
2. The method of claim 1, wherein the increasing the strength of the forward coupling between the two qubits comprises:
and improving the capacitance value of the direct coupling capacitor between the two qubits.
3. The method of claim 2, wherein the capacitance of the direct coupling capacitance between the two qubits is raised to above 4 fF.
4. The method of claim 1, wherein the quantum coupling unit comprises a capacitive branch and a superconducting quantum interferometer branch connected in parallel, and the raising the maximum eigenfrequency of the quantum coupling unit comprises:
reducing the capacitance value of a capacitance branch of the quantum coupling unit; and
and reducing the inductance of the superconducting quantum interference device branch of the quantum coupling unit.
5. The method of claim 4, wherein the superconducting quantum interference arm comprises an asymmetric double Josephson junction.
6. The method of claim 5, wherein the critical current ratio of asymmetric double Josephson junctions in the branch of the superconducting quantum interference device is adjusted to keep the frequency of the quantum coupling unit and the frequency of the qubit above a predetermined detuning amount.
7. The method of claim 6, wherein the critical current ratio of two josephson junctions in the asymmetric double josephson junction is adjusted to be 1: 2-1: 2.5.
8. The method of claim 1, wherein the flux of the coupler of the quantum coupling unit is adjusted to achieve a fast variation of the equivalent coupling strength over a range of-10 MHz to 10MHz, and the dibit quantum gate is implemented when the variation frequency is equal to the difference between the frequency of the dibit |11> state and the frequency of the |20> state.
9. The method of claim 8, wherein the equivalent coupling strength is a sum of a positive coupling strength and a negative coupling strength of the quantum coupling unit.
10. The method of claim 1, wherein the amount of detuning is set to 1 GHz.
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| CN202210110484.XA CN114429215A (en) | 2022-01-28 | 2022-01-28 | Method for realizing double-bit quantum gate based on superconducting quantum coupler |
| PCT/CN2022/096264 WO2023142324A1 (en) | 2022-01-28 | 2022-05-31 | Method for achieving double-bit quantum gate on basis of superconducting quantum coupler |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114692884A (en) * | 2022-05-31 | 2022-07-01 | 浙江大学杭州国际科创中心 | Method, system and device for realizing anti-noise superconducting quantum bit control |
| CN115470923A (en) * | 2022-08-22 | 2022-12-13 | 合肥本源量子计算科技有限责任公司 | Method and device for acquiring DC spectrum of adjustable coupler and quantum computer |
| CN115660093A (en) * | 2022-10-17 | 2023-01-31 | 北京百度网讯科技有限公司 | Performance test information output method and device of coupler-containing superconducting quantum bit structure |
| WO2023142324A1 (en) * | 2022-01-28 | 2023-08-03 | 中国科学技术大学 | Method for achieving double-bit quantum gate on basis of superconducting quantum coupler |
| WO2024022280A1 (en) * | 2022-07-25 | 2024-02-01 | 阿里巴巴达摩院(杭州)科技有限公司 | Method and circuit for implementing two-qubit gate |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7898282B2 (en) * | 2005-04-26 | 2011-03-01 | D-Wave Systems Inc. | Systems, devices, and methods for controllably coupling qubits |
| CN111598248B (en) * | 2020-05-18 | 2024-03-12 | 南京优算量子科技有限公司 | Superconducting quantum chip and method for realizing control of phase gate |
| CN111931941B (en) * | 2020-07-15 | 2021-09-17 | 北京百度网讯科技有限公司 | High-fidelity superconducting circuit structure, superconducting quantum chip and superconducting quantum computer |
| CN114429215A (en) * | 2022-01-28 | 2022-05-03 | 中国科学技术大学 | Method for realizing double-bit quantum gate based on superconducting quantum coupler |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2023142324A1 (en) * | 2022-01-28 | 2023-08-03 | 中国科学技术大学 | Method for achieving double-bit quantum gate on basis of superconducting quantum coupler |
| CN114692884A (en) * | 2022-05-31 | 2022-07-01 | 浙江大学杭州国际科创中心 | Method, system and device for realizing anti-noise superconducting quantum bit control |
| WO2024022280A1 (en) * | 2022-07-25 | 2024-02-01 | 阿里巴巴达摩院(杭州)科技有限公司 | Method and circuit for implementing two-qubit gate |
| CN115470923A (en) * | 2022-08-22 | 2022-12-13 | 合肥本源量子计算科技有限责任公司 | Method and device for acquiring DC spectrum of adjustable coupler and quantum computer |
| CN115470923B (en) * | 2022-08-22 | 2024-04-05 | 本源量子计算科技（合肥）股份有限公司 | Method and device for acquiring DC spectrum of adjustable coupler and quantum computer |
| CN115660093A (en) * | 2022-10-17 | 2023-01-31 | 北京百度网讯科技有限公司 | Performance test information output method and device of coupler-containing superconducting quantum bit structure |
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