Microwave quantum frequency comb system

Abstract

The invention provides a microwave quantum frequency comb system which comprises at least three Josephson junction arrays, one end of the first Josephson junction array inputs a microwave signal or a high-speed pulse signal, and the other end of the first Josephson junction array inputs a microwave signal or a high-speed pulse signal. The first Josephson junction array is connected to the two ends of the branch leads with the Josephson junction number selectable on the first Josephson junction array through the filtering module from the two ends of the branch leads with the Josephson junction number selectable on the first Josephson junction array, and outputs voltage signals to the Josephson junctions with the specific number of the Josephson junctions of the other Josephson junction arrays; the microwave signals output by the two ends of the Josephson junction arrays are combined and output through a combiner, so that the microwave signals which contain a plurality of frequency components and have frequencies distributed in a comb shape can be realized; and the frequency of each component can be changed by controlling the switching in real time through opening and closing the corresponding Josephson junction array lead by an external circuit program.

Description

Technical Field

[0001] The present application relates to the technical field of integrated superconducting Josephson array circuit design, and in particular to a microwave quantum frequency comb system. Background Art

[0002] Frequency comb systems are specialized signal sources capable of emitting multiple spectral lines. They are widely used in precision testing applications such as optical clocks, lidar, and spectroscopy. On-chip frequency comb systems have achieved breakthroughs in optics, but reports on on-chip frequency combs in the microwave band are limited. In particular, microwave frequency combs are gaining attention in low-temperature applications, such as quantum computing, where thermal loads are severely limited.

[0003] Microwave sources based on superconducting Josephson junctions have inherent advantages for the aforementioned low-temperature applications, as they have very low power dissipation. Reported microwave frequency combs on-chip are based on the AC Josephson effect, which states that when a DC voltage is applied across a Josephson junction, an AC current signal is radiated across the junction. The frequency of the signal is directly determined by the voltage. According to the Josephson formula, f = V dc ·(2e / h). Where e is the electron charge, V dc is the DC voltage loaded on both ends of the Josephson junction, and h is Planck's constant. Signal resonance is achieved by embedding the Josephson junction in a microwave resonant cavity with extremely high quality parameters. The microwave signal generated is a series of equally spaced spectral lines in the spectrum and a series of highly coherent microwave signals in the time domain. This microwave frequency comb has a simple structure and is easy to operate. It is driven by only an extremely low-power DC signal. However, the frequency of the comb teeth is limited by the microwave resonant cavity, and the adjustable range of the microwave source frequency is limited. In addition, conventional constant voltage sources cannot achieve quantum flux (h / 2e, about 2.07×10 -15 Wb) precision control. Summary of the Invention

[0004] Based on this, in order to solve the problem of limited adjustable range of microwave source frequency, a microwave quantum frequency comb system is provided, which can realize a microwave signal containing multiple frequency components with comb-shaped frequency distribution, and the frequency of each component can be changed by real-time control switching of the corresponding Josephson junction array leads through an external circuit program.

[0005] The present application provides a microwave quantum frequency comb system, comprising at least three Josephson junction arrays, wherein a first end of a first Josephson junction array is a high-frequency input end for inputting microwave or high-speed pulse signals, and a second end is connected to a terminal resistor. A plurality of DC output leads are provided between the Josephson junctions of the first Josephson junction array. When two of the DC output leads are selected as DC output ends, the number of Josephson junctions included between the selected DC output ends is also different.

[0006] Both ends of the second to Nth Josephson junction arrays are high-frequency output ends. A plurality of DC input leads are provided between the Josephson junctions of the second to Nth Josephson junction arrays. When two of the DC input leads are selected as input ends, the number of Josephson junctions included between the selected input ends is also different.

[0007] Two DC output terminals of the first Josephson junction array are connected to two DC input terminals of the second to N-th Josephson junction arrays through two filter modules, respectively, and the first Josephson junction array outputs voltage signals to the second to N-th Josephson junction arrays;

[0008] Thus, both ends of the second to Nth Josephson junction arrays output frequency-converted microwave signals;

[0009] It also includes a combiner, which selectively connects any two or more of the second to Nth Josephson junction arrays to combine and output the microwave signals output from both ends of the connected Josephson junction arrays.

[0010] Optionally, the second to Nth Josephson junction arrays include different numbers of Josephson junctions.

[0011] Optionally, the high-frequency input end of the first Josephson junction array is a microwave with a frequency of f1 or a pulse with a repetition frequency of f1; a first filtering module, the first end of the first filtering module is connected to the DC output end of the first Josephson junction array, and the second end is respectively connected to the DC input end of the second to N-th Josephson junction arrays; a second filtering module, the first end of the second filtering module is connected to the DC output end of the first Josephson junction array, and the second end is connected to the DC input end of the second to N-th Josephson junction arrays; the second end of the first filtering module is a positive DC output end; the second end of the second filtering module is a negative DC output end; the voltage between the positive output end and the negative output end is V dc =M(h / 2e)f1, where V dc is the voltage generated across M Josephson junctions, e is the electron charge, and h is Planck's constant.

[0012] Optionally, both ends of the second to Nth Josephson junction arrays are connected to high-frequency output terminals; the output microwave signal frequency f m =(M / N m )f1.

[0013] Optionally, the combiner combines the microwave signals output by the selected Josephson junction array and outputs a microwave signal containing the selected combined m frequency components: f = M·f1·[(1 / N1)+(1 / N2)+…+(1 / N m)], M is the number of junctions between the DC output terminals of the first Josephson junction array, m is the number of junction arrays selected and merged in the second to Nth Josephson junction arrays, N1 to N m is the number of junctions in the second to Nth Josephson junction arrays selected for merging.

[0014] Optionally, two ends of the second to Nth Josephson junction arrays are further connected to a third filter module and a fourth filter module respectively, and a direct current is input to the other ends of the third filter module and the fourth filter module.

[0015] Optionally, the input end of the first Josephson junction array is a microwave with a frequency of f1, and the two ends of the first Josephson junction array are respectively connected to a fifth filter module and a sixth filter module, and a DC current is input at the other ends of the fifth filter module and the sixth filter module.

[0016] Optionally, the Josephson junction includes a superconductor layer, an insulator layer and a superconductor layer arranged in sequence.

[0017] Optionally, the Josephson junction includes a superconductor layer, a non-superconducting metal layer and a superconductor layer arranged in sequence.

[0018] Optionally, the frequency conversion ratio is adjusted by switching on and off the corresponding combiners and the second to Nth Josephson junction arrays through an external circuit program, and controlling the number of switched Josephson junction arrays in real time.

[0019] The technical solution adopted in this application can achieve precise frequency conversion of microwave signals with quantum precision. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings involved in the embodiments, which are part of the present invention. It should be pointed out that the exemplary embodiments and their related descriptions are only used to explain the technical content of the present invention and do not constitute any undue limitation of the present invention. In the drawings:

[0021] Figure 1 Schematic diagram of the microwave quantum frequency comb system of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0023] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application include direct and indirect connections (couplings) unless otherwise specified. In the description of this application, it should be understood that the orientations or positional relationships indicated by the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to this application.

[0024] In this application, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0025] A microwave quantum frequency comb system of the present application includes at least three Josephson junction arrays. The first end of the first Josephson junction array is a high-frequency input end for inputting microwave or high-speed pulse signals, and the second end is connected to a terminal resistor. A plurality of DC output leads are provided between the Josephson junctions of the first Josephson junction array. When two of the DC output leads are selected as DC output ends, the number of Josephson junctions included between the selected DC output ends is also different.

[0026] Both ends of the second to Nth Josephson junction arrays are high-frequency output ends. A plurality of DC input leads are provided between the Josephson junctions of the second to Nth Josephson junction arrays. When two of the DC input leads are selected as input ends, the number of Josephson junctions included between the selected input ends is also different.

[0027] Two DC output terminals of the first Josephson junction array are connected to two DC input terminals of the second to N-th Josephson junction arrays through two filter modules, respectively, and the first Josephson junction array outputs voltage signals to the second to N-th Josephson junction arrays;

[0028] Thus, both ends of the second to Nth Josephson junction arrays output frequency-converted microwave signals;

[0029] It also includes a combiner, which selectively connects any two or more of the second to Nth Josephson junction arrays to combine and output the microwave signals output from both ends of the connected Josephson junction arrays.

[0030] In one embodiment, the second to Nth Josephson junction arrays include different numbers of Josephson junctions.

[0031] In one embodiment, the high-frequency input end of the first Josephson junction array is a microwave with a frequency of f1 or a pulse with a repetition frequency of f1; a first filtering module, the first end of the first filtering module is connected to the DC output end of the first Josephson junction array, and the second end is respectively connected to the DC input end of the second to N-th Josephson junction arrays; a second filtering module, the first end of the second filtering module is connected to the DC output end of the first Josephson junction array, and the second end is connected to the DC input end of the second to N-th Josephson junction arrays; the second end of the first filtering module is a positive DC output end; the second end of the second filtering module is a negative DC output end; the voltage between the positive output end and the negative output end is V dc =M(h / 2e)f1, where V dc is the voltage generated across M Josephson junctions, e is the electron charge, and h is Planck's constant.

[0032] In one embodiment, both ends of the second to Nth Josephson junction arrays are connected to high-frequency output terminals; the output microwave signal frequency f m =(M / N m )f1, in Figure 1 The middle one is f2 or f3.

[0033] In one embodiment, the combiner combines the microwave signals outputted by the selected Josephson junction array to output a microwave signal comprising the selected combined m frequency components: f=M·f1·[(1 / N1)+(1 / N2)+…+(1 / N m )], M is the number of junctions between the DC output terminals of the first Josephson junction array, m is the number of junction arrays selected and merged in the second to Nth Josephson junction arrays, N1 to N m is the number of junctions in the second to Nth Josephson junction arrays selected for merging.

[0034] In one embodiment, the DC input ends of the second to Nth Josephson junction arrays are further connected to a third filter module and a fourth filter module, respectively, and DC current is input to the other ends of the third filter module and the fourth filter module.

[0035] In one embodiment, the input end of the first Josephson junction array is a microwave with a frequency of f1. The two ends of the first Josephson junction array are respectively connected to a fifth filter module and a sixth filter module. A DC current is input to the other ends of the fifth filter module and the sixth filter module. Since a first Josephson junction array having a series of M Josephson junctions is used to input a microwave with a frequency of f1 or a pulse with a repetition frequency of f1, V dc =M(h / 2e)f1 voltage. When using microwaves, it is necessary to input appropriate bias current to the first Josephson junction array from port 1 and port 2, but it is not necessary when inputting pulses.

[0036] In one embodiment, the Josephson junction includes a superconductor layer, an insulator layer, and a superconductor layer arranged in sequence.

[0037] In one embodiment, the Josephson junction includes a superconductor layer, a non-superconducting metal layer, and a superconductor layer arranged in sequence.

[0038] In one embodiment, the frequency conversion ratio is adjusted by switching the corresponding combiners and the second to Nth Josephson junction arrays through an external circuit program, and controlling the number of switched Josephson junction arrays in real time.

[0039] In this embodiment, each of the Josephson junctions may be composed of two weakly connected superconductors, and the weakly connected structure may be a thin insulating layer, forming a superconductor-insulator-superconductor structure (ie, SIS structure).

[0040] The Josephson junction can also consist of two superconductors that are weakly connected to each other, where the weak connection can be a small section of non-superconducting metal, forming an SNS structure. The Josephson junction can also consist of two superconductors that are weakly connected to each other, where the superconductivity is weakened in a narrow section at the contact point, forming an SsS structure.

[0041] like Figure 1 As shown, a microwave quantum frequency comb system of the present application includes at least three Josephson junction arrays. Figure 1 In the embodiment shown, three are taken as an example. The first end of the first Josephson junction array 10 is a high-frequency input end, which inputs a microwave or high-speed pulse signal. The second end is connected to a terminal resistor. Several DC output leads are arranged between the Josephson junctions of the first Josephson junction array. When two of the DC output leads are selected as DC output ends, the number of Josephson junctions included between the DC output ends selected each time is also different.

[0042] The two ends of the second Josephson junction array 20 to the third Josephson junction array 30 are high-frequency output ends. A number of DC input leads are set between the Josephson junctions of the second to third Josephson junction arrays. When two of the DC input leads are selected as input ends, the number of Josephson junctions included between the input ends selected each time is also different.

[0043] Two DC output terminals of the first Josephson junction array are connected to two DC input terminals of the second to third Josephson junction arrays through two filter modules, respectively. The first Josephson junction array outputs voltage signals to the second to third Josephson junction arrays.

[0044] Thus, both ends of the second and third Josephson junction arrays output frequency-converted microwave signals;

[0045] The system further includes a combiner 40 connected to the output ends of the second to third Josephson junction arrays to combine and output the microwave signals output from both ends of the connected Josephson junction arrays. In this embodiment, there is a combiner 40 at each of the two output ends.

[0046] According to the inverse effect of the AC Josephson effect, using a current bias and irradiating the Josephson junction with microwaves of frequency f will generate a constant voltage across the Josephson junction, called the "Shapino voltage step", with the formula V dc =(h / 2e)f. This effect is used to realize a voltage reference that can achieve quantum precision. Using a string of M series-connected Josephson junctions with an input frequency of f1, V dc =M(h / 2e)f1, a quantum-precise voltage applied to another string of N series-connected Josephson junctions yields a quantum-precise microwave signal with a frequency of f2 = (M / N)f1. From a macroscopic perspective, these two strings of junctions enable quantum-precise frequency conversion of microwave signals.

[0047] According to the inverse effect of the AC Josephson effect, using a current bias and irradiating the Josephson junction with microwaves of frequency f will generate a constant voltage across the Josephson junction, called the "Shapino voltage step", with the formula V dc =(h / 2e)f. This effect is used to realize a voltage reference that can achieve quantum precision. Using a string of M series-connected Josephson junctions with an input frequency of f1, V dc =M(h / 2e)f1, a quantum-precise voltage applied to another string of N series-connected Josephson junctions yields a quantum-precise microwave signal with a frequency of f2 = (M / N)f1. From a macroscopic perspective, these two strings of junctions enable quantum-precise frequency conversion of microwave signals.

[0048] In this embodiment, the number of Josephson junctions included between the DC input ends of the second and third Josephson junction arrays is different. The number of Josephson junctions included in the second Josephson junction array is N1, and the number of Josephson junctions included in the third Josephson junction array is N2.

[0049] In this embodiment, the high-frequency input end of the first Josephson junction array is a microwave with a frequency of f1 or a pulse with a repetition frequency of f1; Figure 1 As shown, in this embodiment, the DC output end of the first Josephson junction array and the DC input end of the second to N-th Josephson junction arrays are respectively connected to a first filtering module for filtering. The other DC output end of the first Josephson junction array and the other DC input end of the second to N-th Josephson junction arrays are respectively connected to a second filtering module. The second end of the first filtering module is a positive DC output end; the second end of the second filtering module is a negative DC output end; the voltage between the positive output end and the negative output end is V dc =M(h / 2e)f1, where V dc is the voltage generated across M Josephson junctions, e is the electron charge, and h is Planck's constant.

[0050] In this embodiment, both ends of the second to third Josephson junction arrays are connected to the high-frequency output end; the output microwave signal frequency f m =(M / N m )f1.

[0051] In this embodiment, the combiner combines the microwave signals output by the selected Josephson junction array to output a microwave signal containing the selected combined m frequency components: f = M·f1·[(1 / N1)+(1 / N2)+…+(1 / N m )], M is the number of junctions between the DC output terminals of the first Josephson junction array, m is the number of junction arrays selected and merged from the second to the third Josephson junction arrays, in this embodiment m=2, N1 and N2 are the number of junctions of the junction arrays selected and merged from the second to the third Josephson junction arrays.

[0052] In this embodiment, the DC input ends of the second to third Josephson junction arrays are further connected to the third filter module 13 and the fourth filter module 14 respectively, and DC current is input to the other ends of the third filter module 13 and the fourth filter module 14, namely, port 3 and port 4.

[0053] In this embodiment, the input terminal of the first Josephson junction array is a microwave with a frequency of f1. A fifth filter module 15 and a sixth filter module 16 are connected to the two ends of the first Josephson junction array, respectively. A DC current is input to the other ends of the fifth filter module 15 and the sixth filter module 16. When using microwaves, a suitable bias current must be input to the first Josephson junction array from ports 1 and 2; this is not required when using pulses.

[0054] In this embodiment, a low-pass filter may be provided at each DC output lead of the first Josephson junction array, and a low-pass filter may be provided at each DC input lead of the second Josephson junction array.

[0055] In this embodiment, the Josephson junction includes a superconductor layer, an insulator layer, and a superconductor layer arranged in sequence.

[0056] In this embodiment, the Josephson junction includes a superconductor layer, a non-superconducting metal layer, and a superconductor layer arranged in sequence.

[0057] In this embodiment, the frequency conversion ratio is adjusted by switching the corresponding combiner and the second to third Josephson junction arrays through an external circuit program, and controlling the number of Josephson junction arrays to be switched in real time.

[0058] While the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to these specific embodiments. The above embodiments are merely illustrative and non-restrictive. Those skilled in the art will appreciate that various modifications may be made based on the teachings of the present invention without departing from the scope of protection of the present invention and the claims, and such modifications shall be deemed to be within the scope of protection of the present invention.

Claims

1. A microwave quantum frequency comb system, characterized by: The device comprises at least three Josephson junction arrays, wherein a first end of the first Josephson junction array is a high-frequency input end for inputting microwave or high-speed pulse signals, and a second end is connected to a terminal resistor. A plurality of DC output leads are provided between the Josephson junctions of the first Josephson junction array. When two of the DC output leads are selected as DC output ends, the number of Josephson junctions included between the selected DC output ends is also different. Both ends of the second to N-th Josephson junction arrays are high-frequency output ends. A plurality of DC input leads are provided between the Josephson junctions of the second to N-th Josephson junction arrays. When two of the DC input leads are selected as input ends, the number of Josephson junctions included between the selected input ends is also different. The two DC output terminals of the first Josephson junction array are connected to the second to Nth Two DC input terminals of the Josephson junction array, the first Josephson junction array outputs a voltage signal to the second to Nth Josephson junction arrays; Thus, both ends of the second to Nth Josephson junction arrays output frequency-converted microwave signals; It also includes a combiner, which selectively connects any two or more of the second to Nth Josephson junction arrays to combine and output the microwave signals output from both ends of the connected Josephson junction arrays.

2. The microwave quantum frequency comb system according to claim 1, characterized in that: The second to Nth Josephson junction arrays include different numbers of Josephson junctions.

3. The microwave quantum frequency comb system according to claim 2, characterized in that: The high-frequency input end of the first Josephson junction array is a microwave with a frequency of f1 or a pulse with a repetition frequency of f1; a first filtering module, wherein the first end of the first filtering module is connected to the DC output end of the first Josephson junction array, and the second end of the first filtering module is connected to the DC input end of the second to Nth Josephson junction arrays respectively; The second filtering module has a first end connected to the DC output end of the first Josephson junction array, and a second end connected to the DC input end of the second to Nth Josephson junction arrays; the second end of the first filtering module is a positive DC output end; the second end of the second filtering module is a negative DC output end; the voltage between the positive output end and the negative output end is V dc =M(h / 2e)f1, where V dc is the voltage generated across M Josephson junctions, e is the electron charge, and h is Planck's constant.

4. The microwave quantum frequency comb system according to claim 3, characterized in that: The two ends of the second to Nth Josephson junction arrays are connected to the high-frequency output terminal; the output microwave signal frequency f m =(M / N m )f1.

5. The microwave quantum frequency comb system according to claim 3, characterized in that: The combiner combines the microwave signals output by the selected Josephson junction array and outputs a microwave signal containing the selected combined m frequency components: f = M·f1·[(1 / N1)+(1 / N2)+…+(1 / N m )], M is the number of junctions between the DC output terminals of the first Josephson junction array, m is the number of junction arrays selected and merged in the second to Nth Josephson junction arrays, N1 to N m is the number of junctions in the second to Nth Josephson junction arrays selected for merging.

6. The microwave quantum frequency comb system according to claim 3, characterized in that: The DC input ends of the second to Nth Josephson junction arrays are further connected to a third filter module and a fourth filter module respectively, and DC current is input to the other ends of the third filter module and the fourth filter module.

7. The microwave quantum frequency comb system according to claim 3, characterized in that: The input end of the first Josephson junction array is a microwave with a frequency of f1. The DC output end of the first Josephson junction array is also connected to a fifth filter module and a sixth filter module respectively. DC current is input to the other ends of the fifth filter module and the sixth filter module.

8. The microwave quantum frequency comb system according to claim 1, characterized in that: The Josephson junction includes a superconductor layer, an insulator layer and a superconductor layer arranged in sequence.

9. The microwave quantum frequency comb system according to claim 1, characterized in that: The Josephson junction includes a superconductor layer, a non-superconducting metal layer and a superconductor layer which are arranged in sequence.

10. The microwave quantum frequency conversion circuit according to claim 1, characterized in that: The frequency conversion ratio is adjusted by switching on and off the corresponding combiner and the second to Nth Josephson junction arrays through an external circuit program, and controlling the number of switched Josephson junction arrays in real time.

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