A cryogenic coupler and method of use thereof

Abstract

The application provides a low-temperature coupler and a use method thereof, the low-temperature coupler comprising a cavity, a cover being covered on an opening of the cavity, a PCB board being installed in the cavity, the PCB board comprising an AC part and a DC part; the AC part being provided with an AC function module, an input port of the AC part inputting a radio frequency signal and a pulse signal; the DC part being provided with an intermediate frequency function module and a low frequency pulse function module which are connected with each other, and the intermediate frequency function module and the low frequency pulse function module are both provided with a device for suppressing signal interference; signals of the AC part and the DC part are output through a same output port. The application can not only be compatible with 4-8GHz continuous microwave signals, but also can be compatible with any wave pulse signals with a minimum of 10MHz, and can suppress serious signal deformation.

Description

[0001] This application is a divisional application filed on July 2, 2018, with application number 201810707677.7, and the patent name is "A low-temperature coupler and method of use thereof." Technical Field

[0002] The present invention relates to the technical field of couplers, and in particular to a low-temperature coupler and a method for using the same. Background Art

[0003] The control of quantum bits depends on high-precision analog input signals. For superconducting quantum bits, the signals they rely on are mainly divided into three categories: high-frequency pulses (4-8GHz frequency band), medium-frequency pulses (0.01-500MHz frequency band), and DC bias signals (<1kHz). When manipulating superconducting quantum bits, we not only need to apply these three types of pulse signals at the same time, but also need to synthesize the above signals in one channel. Usually, we use multi-port coupling devices or modules to complete the signal synthesis. Taking into account the characteristics of the pulse signal, the coupling device or module must have an extremely high port impedance matching design while synthesizing the signal. The port impedance matching performance of passive multi-port coupling devices is generally poor, and sometimes complex active modules are required to achieve high-quality signal synthesis.

[0004] Superconducting qubits operate at extremely low temperatures, around 30mK. Before entering the quantum chip containing the superconducting qubits, the three types of signals mentioned above require completely different low-temperature circuit optimizations, and therefore can only be synthesized at extremely low temperatures. However, existing technologies are unable to meet the following application requirements: synthesizing the intermediate frequency pulses and DC bias signals of superconducting qubits at extremely low temperatures.

[0005] First, active multi-port coupling modules require additional power and signal input, consuming significant power and preventing their use in cryogenic environments. Second, passive multi-port coupling devices capable of stable operation in cryogenic environments lack good port impedance matching, severely distorting and degrading the intermediate frequency (IF) pulse signal. More generally, existing technologies lack a solution for achieving perfect synthesis of IF pulse signals and DC bias signals. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that the existing technology cannot meet the problem of realizing the synthesis of the intermediate frequency pulse and DC bias signal of the superconducting quantum bit at extremely low temperature.

[0007] The present invention adopts the following technical means to solve the above technical problems:

[0008] A cryogenic coupler and a method for using the same include a cavity, an opening of the cavity being covered with a lid, a PCB being installed in the cavity, and the PCB including an AC part and a DC part;

[0009] The AC part is provided with an AC function module, and the AC part input port inputs radio frequency signals and pulse signals;

[0010] The DC part is provided with an intermediate frequency function module and a low frequency pulse function module which are interconnected, and both the intermediate frequency function module and the low frequency pulse function module are provided with a device for suppressing signal interference;

[0011] The signal of the AC part and the signal of the DC part are output through the same output port.

[0012] Furthermore, the cavity is surrounded by a bottom and side walls, and an isolation block is connected to the middle of the cavity. The isolation block divides the interior of the cavity into two interconnected parts, namely a first signal cavity and a second signal cavity. A DC input port is provided on the side wall of the first signal cavity; an AC input port is provided on the side wall of the second signal cavity, and a mixed output port is also provided on the side wall. Connectors are installed at the DC input port, the AC input port, and the mixed output port.

[0013] The AC part input port of the PCB board corresponds to the AC input port on the cavity; the DC part signal input port of the PCB board corresponds to the DC input port on the cavity; the output port of the PCB board corresponds to the hybrid output port on the cavity.

[0014] Furthermore, the signal input port of the DC part is connected to a low-frequency pulse function module.

[0015] Furthermore, the device for suppressing signal interference of the intermediate frequency functional module includes multiple high-frequency inductors, and the device for suppressing signal interference of the low-frequency pulse functional module includes multiple low-frequency inductors.

[0016] Furthermore, the device for suppressing signal interference includes a plurality of resistance elements.

[0017] Furthermore, the isolation block includes a first isolation block and a second isolation block that are opposite to each other and spaced apart, and the first isolation block and the second isolation block are both integrally formed with the side walls of the corresponding sides.

[0018] Furthermore, the DC input port, AC input port and mixed output port are all provided with grooves, a through hole is provided in the middle of the groove, the connector is tightly connected to the groove, and the needle core passes through the through hole.

[0019] Furthermore, the PCB board is fixed to the bottom of the cavity by screws.

[0020] Furthermore, a fixing block is connected to the back side of the cavity, and a connecting hole is provided on the fixing block.

[0021] Furthermore, the fixing block is integrally formed with the back side of the cavity.

[0022] Furthermore, a cover groove is formed on the end surface of the side wall, and the cover groove matches the outer edge of the cover, and the cover groove and the cover are fastened together by screws.

[0023] Furthermore, the material used for the low-temperature coupler is copper, which has excellent thermal conductivity. During operation, the heat generated is conducted to the external environment through the contact of the copper.

[0024] The present invention also provides a method for using a cryogenic coupler, wherein the DC input port of the coupler is connected to a DC source, and the AC input port of the coupler is connected to an arbitrary waveform generator. The output port of the coupler is connected to a quantum chip, and both the coupler and the quantum chip are in an extremely low temperature environment of less than 30mK inside a dilution refrigerator; when in use, the DC signal output by the DC source and the pulse signal output by the AWG are simultaneously input into the coupler through a cryogenic circuit, and are combined and output to the quantum chip from the output port. As can be seen from the signal synthesis example, the synthesized signal can perfectly retain both the pulse component and the DC component, so this application method can meet the requirements of the aforementioned quantum chip to realize the synthesis of the intermediate frequency pulse and DC bias signal of the superconducting quantum bit at an extremely low temperature.

[0025] The present invention has the following beneficial effects:

[0026] The present invention arranges low-frequency pulse and intermediate-frequency functional modules on a PCB board. By using a device that suppresses signal interference, signal fluctuations are suppressed within a certain range. This makes the microwave device compatible not only with 4-8 GHz continuous microwave signals but also with arbitrary wave pulse signals down to 10 MHz. The physical structure of the cavity is utilized to increase the isolation between each port. This microwave device can effectively reduce the standing wave ratio between the three ports, achieving good impedance matching, significantly increasing isolation between ports, and suppressing severe signal distortion. The microwave device has a simple circuit design and uses a limited number of electronic components, reducing design costs, facilitating installation, and ensuring reliable performance.

[0027] The present invention can operate stably in an extremely low temperature environment below 30mK; has extremely low power consumption and does not cause heat; the operating frequency band fully meets the requirements for perfect synthesis of the intermediate frequency pulses and DC bias signals required by superconducting quantum bits; the port impedance is close to 50 ohms, the pulse waveform of the intermediate frequency pulse signal will not be deteriorated, and the amplitude of the DC bias signal will not be uncontrollably reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a perspective view of a coupler according to an embodiment of the present invention, wherein the cover is not shown;

[0029] Figure 2 is a three-dimensional diagram of the coupler from another angle in an embodiment of the present invention;

[0030] Figure 3 is a structural diagram of a cover in an embodiment of the present invention;

[0031] Figure 4 is a functional schematic diagram of a PCB board in an embodiment of the present invention;

[0032] Figure 5 It is a schematic diagram of a method for using an embodiment of the present invention in the field of superconducting quantum chip measurement and control. DETAILED DESCRIPTION

[0033] In order to have a further understanding and recognition of the structural features and the effects achieved by the present invention, a detailed description is given using preferred embodiments and accompanying drawings, as follows:

[0034] A cryogenic coupler and method of using the same, such as Figure 1-3 As shown, it includes a cavity 1, a cover 2, a connector 3 and a PCB board 4.

[0035] The cavity 1 is surrounded by a bottom 11 and a side wall 12. An isolation block 121 is connected to the middle of the cavity 1. The isolation block 121 includes a first isolation block 1211 and a second isolation block 1212 that are opposite and spaced apart. The first isolation block 1211 and the second isolation block 1212 are both integrally formed with the side wall 12 on the corresponding side. The first isolation block 1211 and the second isolation block 1212 are separated by a distance, so that the isolation block 121 divides the interior of the cavity 1 into two interconnected parts, namely the first signal cavity 13 and the second signal cavity 14. The side wall of the first signal cavity 13 is provided with a DC input port 15, and the side wall of the second signal cavity 14 is provided with an AC input port 16 and a mixed output port 17. In this embodiment, Figure 1 As shown, the first signal cavity 13 is located on the left side of the isolation block 121, and the second signal cavity 14 is located on the right side of the isolation block 121. The DC input port 15 is located on the left side wall of the cavity, the AC input port 16 is located on the upper side wall of the cavity, and the mixed output port 17 is located on the second signal cavity 14 and on the lower side wall of the cavity. The provision of the isolation block 121 can greatly enhance the isolation between the ports. Preferably, a fixing block 19 is integrally formed on the back of the cavity 1, and the fixing block 19 is provided with multiple connection holes 191 for connecting the coupler to other components.

[0036] A cover groove 122 is formed on the end surface of the side wall 12 , and the outer edge of the cover 2 matches the cover groove 122 . The cover 2 and the cover groove 122 are fastened together by M2 screws.

[0037] The connector 3 is mounted on the DC input port 15, AC input port 16, and hybrid output port 17. Each of these ports has a groove 18 at its outer end, with a through hole (not shown) located in the middle. The two sides of the connector 3 are fastened to the groove 18 via screws, and the contact 31 of the connector 3 passes through the through hole. In this embodiment, the connector 3 is an SMA connector.

[0038] The PCB 4 is installed inside the cavity 1 and securely fastened to the bottom 11 using M2 screws. The connector contacts 31 pass through through-holes and rest on the surface of the PCB 4. The PCB 4 includes both AC and DC components. The surface of the PCB 4 is constructed of bare copper, ensuring a closer fit with the cavity bottom 11.

[0039] like Figure 4 As shown, the AC part is provided with an AC functional module 41 , and the position of the AC part input port 411 corresponds to the AC input port 16 on the cavity 1 , which inputs RF signals and pulse signals; the AC part signal output port is the hybrid output port 17 .

[0040] The DC part is provided with an intermediate frequency function module 421 and a low frequency pulse function module 422, and both the intermediate frequency function module 421 and the low frequency pulse function module 422 are provided with a device for suppressing signal interference (not shown in the figure). The signal input port 423 of the DC part can be connected to the low frequency pulse function module 422 or the intermediate frequency function module 421. In this embodiment, the signal input port 423 of the DC part is connected to the low frequency pulse function module 422. Preferably, the device for suppressing signal interference of the intermediate frequency function module 421 includes a plurality of high frequency inductors, and the device for suppressing signal interference of the low frequency pulse function module 422 includes a plurality of low frequency inductors. In addition, the device for suppressing signal interference may also include a plurality of resistors (not shown in the figure). In this embodiment, 3 high frequency inductors and 3 low frequency inductors are respectively provided, and the high frequency inductors and low frequency inductors can be arranged arbitrarily. The DC part signal input port 423 is the DC input port 15 on the cavity 1, connected to the DC signal input end; the DC part signal output port is the hybrid output port 17 on the cavity 1.

[0041] The RF signal and the pulse signal flow into the AC function module 41 from the AC part input port 411, and then flow to the hybrid output port 17; the DC signal flows into the low-frequency pulse function module 422 and the intermediate frequency function module 421 in sequence from the DC part signal input port 423, and then flows to the hybrid output port 17. The DC part signal and the AC part signal merge and flow out at the hybrid output port 17.

[0042] The following is an example of signal synthesis: the intermediate frequency pulse signal T=10us, t=1us with a duty cycle of 10% is input from the AC part input port 411 through the AC function module 41, and the DC bias signal with a current I=10mA is input to the DC signal port 423. The two signals overlap at the node, and the signal at the hybrid output port 17 is T=10us, t=1us with a duty cycle of 10% and an overshoot of 2%.

[0043] The above coupler is manufactured by the following steps:

[0044] (1) The dimensions of the cavity 1, the first signal cavity 13, the second signal cavity 14, and the isolation block 121 are determined according to the designed outer contour of the PCB board 4. To ensure that the connector pin 31 can be located above the PCB board 4, the depth of the cavity 1 is determined according to the specifications of the connector 3 and the thickness of the PCB board 4. Since an insulating layer is attached to the upper surface of the connector pin 31, the depth of the groove 18 and the diameter of the through hole are reserved.

[0045] (2) Clean the workpiece, place the PCB board 4 flat on the bottom of the cavity 1 so that the functional module of the PCB board 4 is placed in the corresponding signal cavity, adjust the screw hole position of the PCB board 4 so that the position of the screw hole corresponds to the position of the screw hole in the cavity, and use screws to fix it.

[0046] (3) Use the connector 3 in the groove 18 on the side wall of the workpiece, so that the connector flange (not shown in the figure) is located in the groove 18, and at the same time, the insulating sleeve of the connector 3 is located at the through hole of the groove, and the pin core 31 of the connector 3 is located on the side wall of the cavity and on the surface of the PCB board 4. Fix the connector 3 with screws at the connector flange, and use solder to weld the signal port of the PCB board and the pin core of the connector together.

[0047] (4) Place the cover into the cover slot and secure it with screws.

[0048] This embodiment arranges low-frequency pulse and intermediate-frequency functional modules on a PCB board. By using devices that suppress signal interference, signal fluctuations are suppressed within a certain range. This makes the microwave device compatible not only with 4-8 GHz continuous microwave signals, but also with arbitrary wave pulse signals down to 10 MHz. The physical structure of the cavity is utilized to increase isolation between ports. This microwave device effectively reduces the standing wave ratio (SWR) between the three ports, achieving good impedance matching, significantly increasing isolation between ports, and suppressing severe signal distortion. This microwave device features a simple circuit design and uses a limited number of electronic components, reducing design costs, facilitating installation, and ensuring reliable performance.

[0049] The coupler provided in this embodiment can operate stably in an extremely low temperature environment below 30mK. The materials used can withstand differences in thermal expansion and contraction, electrical conductivity, thermal conductivity, mechanical properties, etc. caused by temperature changes, and can operate stably in an extremely low temperature environment below 30mK.

[0050] It has extremely low power consumption and will not cause heat. The insertion loss from the DC bias signal coupling input to the intermediate frequency pulse coupling input is 0.7dB. The output frequency band of the coupling output is 4-8G, the insertion loss is 1.8dB, and the voltage standing wave ratio is 1.3.

[0051] The operating frequency band fully meets the requirements for perfect synthesis of the intermediate frequency pulses and DC bias signals required by superconducting quantum bits. The input frequency band of the intermediate frequency pulse coupling input is 4-8GHz, and the voltage standing wave ratio is 1.5, which can perfectly support the input of intermediate frequency pulse signals.

[0052] The port impedance is close to 50 ohms, the pulse waveform of the intermediate frequency pulse signal will not be degraded, and the amplitude of the DC bias signal will not be uncontrollably reduced;

[0053] The materials and processing techniques used do not introduce any magnetic contaminants, which is extremely important for the control of superconducting quantum bits and can avoid the degradation of superconducting quantum bit quality caused by the magnetism of the coupler;

[0054] It is small in size, with an overall size of only 51.70x29.6x16.5mm, and is extremely easy to integrate. It can be used in the control engineering of large-scale superconducting quantum bit chips.

[0055] like Figure 5 The figure shows a schematic diagram of the method of using the coupler in the field of superconducting quantum chip measurement and control. The DC input port of the coupler is connected to a DC source, and the AC input port of the coupler is connected to an arbitrary waveform generator (AWG). The output port of the coupler is connected to the quantum chip, and both the coupler and the quantum chip are in an extremely low temperature environment of less than 30mK inside the dilution refrigerator. When in use, the DC signal output by the DC source and the pulse signal output by the AWG are simultaneously input into the coupler through the low-temperature circuit, and are combined and output to the quantum chip from the output port. It can be seen from the signal synthesis example that the synthesized signal can perfectly retain the pulse component and the DC component at the same time, so this application method can meet the requirements of the aforementioned quantum chip to realize the synthesis of the intermediate frequency pulse and DC bias signal of the superconducting quantum bit at extremely low temperature.

[0056] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A cryogenic coupler for a superconducting quantum bit, comprising: The DC part is used to connect a DC source to provide the DC bias signal required by the quantum bit; The AC part is used to connect to an arbitrary waveform generator to provide the intermediate frequency signal required by the quantum bit; a coupling part, connecting the DC part and the AC part, and used for synthesizing the DC bias signal and the intermediate frequency signal; It is characterized by further comprising a cavity; The cavity includes a first signal cavity and a second signal cavity that are isolated from each other but communicated with each other, and are used to accommodate and isolate the AC part and the DC part. The DC input port corresponding to the DC part and the AC input port corresponding to the AC part are respectively arranged on the side walls of the first signal cavity and the second signal cavity; The output port of the coupling portion is arranged on a side wall of the second signal cavity.

2. The cryogenic coupler for superconducting quantum bits according to claim 1, characterized in that: The cavity is isolated into a first signal cavity and a second signal cavity that are communicated with each other by an isolation block provided in the cavity.

3. The cryogenic coupler for superconducting quantum bits according to claim 2, characterized in that: The isolation block extends from the side wall of the cavity into the cavity and is integrally formed with the side wall of the cavity.

4. The cryogenic coupler for superconducting quantum bits according to claim 3, characterized in that: The isolation block includes two oppositely arranged sub-isolation blocks.

5. The cryogenic coupler for superconducting quantum bits according to claim 1, characterized in that: Connectors are installed at the DC input port corresponding to the DC part, the AC input port corresponding to the AC part, and the output port.

6. The cryogenic coupler for superconducting quantum bits according to claim 5, characterized in that: The cavity is provided with a groove having a size matching that of the connector at the connection position with the connector.

7. The cryogenic coupler for superconducting quantum bits according to claim 1, characterized in that: The opening of the cavity is covered with a lid, and the connection between the cavity and the lid is provided with a cover groove with a size matching that of the lid.

8. The cryogenic coupler for superconducting quantum bits according to claim 1, characterized in that: A fixing block is provided on the back of the cavity, and a connection hole for mechanical connection with an external device is provided on the outer side of the fixing block.

9. The cryogenic coupler for superconducting quantum bits according to claim 1, characterized in that: The DC part includes a medium frequency function module and a low frequency pulse function module connected in series, and both the medium frequency function module and the low frequency pulse function module are provided with a device for suppressing signal interference.

10. The cryogenic coupler for superconducting quantum bits according to claim 9, characterized in that: The device for suppressing signal interference in the intermediate frequency function module includes a plurality of high-frequency inductors, and the device for suppressing signal interference in the low-frequency pulse function module includes a plurality of low-frequency inductors.

11. The cryogenic coupler for superconducting quantum bits according to claim 1, 9 or 10, characterized in that: The device for suppressing signal interference includes a plurality of resistance elements.

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