Method and circuit for measuring on-chip temperature and magnetic field environment of a quantum superconducting chip

Abstract

The application discloses a kind of quantum superconducting chip on-chip temperature and magnetic field environment measurement method and circuit, including quantum superconducting chip, the quantum superconducting chip is provided with temperature measurement magnetic field measurement module, the temperature measurement magnetic field measurement module uses two Josephson junctions and is connected in parallel to form DC-SQUID structure, and one of superconducting wire branch is placed near and tightly placed on external resistance, when temperature needs to be measured, current is passed into the resistance, the resistance temperature is raised, the local superconducting wire is heated, one way loses superconductivity, at this time only one Josephson junction is connected into circuit;When measuring magnetic field, the current in resistance is cut off, so that superconducting wire restores superconductivity, at this time two Josephson junctions are connected in parallel to form DC-SQUID structure.Compared with prior art superconducting chip temperature measurement method, the application has the advantages of simple structure, simple measurement, simple calibration and temperature calculation method, high sensitivity, wide measurement range, effectively solves the temperature and magnetic field measurement problem of quantum superconducting chip.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quantum superconducting measurement, and particularly relates to a method and circuit for measuring temperature and magnetic field environment on a quantum superconducting chip. BACKGROUND

[0002] Conductors all have certain resistance at normal temperature, however, certain special metal materials, such as lead, tin, niobium, etc., suddenly disappear to zero when cooled to a certain extremely low temperature, which is called superconductivity. At extremely low temperature, the metal materials showing superconductivity are called superconductors.

[0003] A piece of thin insulator or ordinary metal (about 10 angstroms in thickness) is sandwiched between two superconductors to form a structure of superconductor (S)-insulator (I)-superconductor or superconductor (S)-ordinary metal-superconductor, and the structure is in liquid helium temperature zone (4.2 K) and no voltage is applied to the structure. In this case, Cooper pairs in one superconductor can pass through the insulator to reach the other superconductor to form a current. This phenomenon is called superconducting Josephson effect, and the SIS (superconductor insulator-superconductor) or SNS (superconductor normal metal-superconductor) structure is called Josephson junction.

[0004] When the voltage V between the two ends of the Josephson junction is 0, superconducting current can exist in the junction, which is caused by the tunneling effect of Cooper pairs in the superconductor. As long as the superconducting current is less than a certain critical current Ic, the zero voltage phenomenon is always maintained, and Ic is called the Josephson critical current.

[0005] Josephson junction has many important applications in modern quantum circuits, such as Josephson voltage reference system (JVS), superconducting quantum interference device (SQUID), superconducting quantum computing and rapid single flux quantum (RSFQ) digital electronic device, etc. At present, Josephson junction and quantum superconducting chip based on Josephson junction are mostly manufactured by using superconducting material niobium and its alloy, and the superconducting transition temperature thereof is about 10K (-263.15℃). The normal working temperature of the above-mentioned devices is generally between several tens of mK and liquid helium temperature (4.2K), and the devices cannot be directly contacted with the outside during working and are generally small in space and sensitive to external heat source and magnetic field and difficult to measure temperature. Since the conventional liquid helium immersion quantum superconducting chip method can only maintain the temperature of the chip at 4.2K, for some quantum chips that need to work in a lower temperature environment, a dry refrigerator or other methods need to be used to further reduce the temperature. Since vacuum preservation is needed for such methods, there is no "immersion" environment similar to liquid helium on the cold head of the refrigerator. At the same time, due to the installation method of the chip, the thermal resistance of the intermediate layers and the heat generated by the chip during working, there is a temperature difference between the temperature on the chip and the temperature set at the cold head of the refrigerator, so the temperature of the quantum superconducting chip during working cannot be obtained in real time and accurately, which brings some adverse effects to the use of the quantum superconducting chip.

[0006] In the prior art, the measurement of temperature in an extremely low temperature environment by using a thermistor needs to measure extremely weak current signals, and the measurement precision is difficult to guarantee due to the influence of the thermoelectric potential of the wire. Moreover, the temperature measuring resistor is independent of the quantum superconducting chip, and even if it is installed into the superconducting quantum system, it must be arranged outside the quantum superconducting chip, and the measurement result is also difficult to reflect the temperature of the quantum superconducting chip itself. Or the temperature measuring bit is composed of a Josephson junction and a capacitor in parallel, and the resonant cavity required for signal reading also uses a capacitor. Although the temperature measuring circuit is directly integrated on the quantum chip, due to the limitation of the semiconductor manufacturing process, the relative area occupied by the capacitor on the chip is large, which is not conducive to the circuit design of the quantum superconducting chip which is sensitive to space utilization. Moreover, the calibration, signal reading and temperature calculation methods are relatively complex, and the measurement range is narrow, and the liquid helium temperature measurement cannot be well performed. Therefore, a quantum superconducting chip on-chip temperature and magnetic field environment measurement method and circuit are needed. SUMMARY

[0007] The purpose of the present application is to provide a quantum superconducting chip on-chip temperature and magnetic field environment measurement method and circuit.

[0008] In order to achieve the above-mentioned purpose, the present application is implemented according to the following technical solutions:

[0009] The application includes a quantum superconducting chip, which is provided with a temperature measurement module and a magnetic field measurement module, the temperature measurement module and the magnetic field measurement module are arranged on a silicon wafer and are packaged on the quantum superconducting chip through 3D packaging, the temperature measurement module includes one or more series-connected Josephson junctions for temperature measurement integrated; the magnetic field measurement module includes a direct current superconducting quantum interference device (DC-SQUID) structure integrated by two parallel-connected Josephson junctions connected by a superconducting wire.

[0010] In another aspect, a quantum superconducting chip on-chip temperature and magnetic field environment measurement circuit includes a quantum superconducting chip, which is provided with a temperature measurement and magnetic field measurement module, the temperature measurement and magnetic field measurement module uses two Josephson junctions in parallel to form a DC-SQUID structure, and an external resistance is placed close to one of the superconducting wire branches, when temperature measurement is needed, current is passed through the resistance to raise the resistance temperature, heat the local superconducting wire, and make one of the superconducting wire branches lose superconductivity, at this time, only one Josephson junction is connected to the circuit; when magnetic field measurement is needed, the current in the resistance is cut off, and the superconducting wire restores superconductivity, at this time, the two Josephson junctions are connected in parallel to form a DC-SQUID structure.

[0011] In another aspect, a quantum superconducting chip on-chip temperature and magnetic field environment measurement method is applied to a measurement circuit, and includes the following steps:

[0012] When the chip temperature drops below 10K, the Josephson junction begins to enter a superconducting state, the critical current size and the temperature of the Josephson junction are measured, and the actual temperature on the chip is obtained according to the temperature-critical current relationship;

[0013] The magnetic flux size and the magnetic field strength passing through the superconducting ring are obtained by measuring the voltage across the DC-SQUID, and the average magnetic field size in the vertical direction on the quantum superconducting chip is obtained.

[0014] Further, the temperature measurement step using the temperature measurement and magnetic field measurement module includes passing current through the resistance to raise the resistance temperature, heat the local superconducting wire, and make one of the superconducting wire branches lose superconductivity, at this time, only one Josephson junction is connected to the circuit, the critical current of the Josephson junction connected to the circuit is measured, and the actual temperature on the chip is obtained according to the temperature-critical current relationship.

[0015] Further, the magnetic field measurement step using the temperature measurement and magnetic field measurement module includes cutting off the current in the resistance, restoring the superconductivity of the superconducting wire, at this time, the two Josephson junctions are connected in parallel to form a DC-SQUID structure, the magnetic flux size passing through the superconducting ring is obtained by measuring the voltage across the DC-SQUID, and the average magnetic field size in the vertical direction on the quantum superconducting chip is obtained.

[0016] The beneficial effects of the present invention are:

[0017] The present invention proposes an on-chip integrated Josephson junction-based quantum superconducting chip temperature and magnetic field environment measurement method and circuit. Compared with existing superconducting chip temperature measurement methods, the present invention has the advantages of simple structure, simple measurement method, simple calibration and temperature calculation method, high sensitivity and wide measurement range, which can effectively solve the temperature and magnetic field measurement problems of quantum superconducting chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the temperature measurement module and magnetic field measurement module of the measurement circuit for the temperature and magnetic field environment on the quantum superconducting chip;

[0019] Figure 2 Schematic diagram of the temperature and magnetic field measurement module for measuring the temperature and magnetic field environment on a quantum superconducting chip; DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The exemplary embodiments of the present invention are used to illustrate the present invention but are not intended to limit the present invention.

[0021] like Figure 1 As shown, a method and circuit for measuring temperature and magnetic field environment on a quantum superconducting chip based on a Josephson junction are provided. The circuit includes a temperature measurement portion consisting of one or a group of serially connected Josephson junctions for temperature measurement integrated on the quantum superconducting chip, and a magnetic field measurement portion consisting of a direct current superconducting quantum interference device (DC-SQUID) structure consisting of two Josephson junctions connected in parallel via a superconducting loop.

[0022] As an improvement to the circuit, two Josephson junctions can be connected in parallel to form a superconducting quantum interference device structure, and a resistor can be placed close to one of the superconducting wire branches, such as Figure 2 shown.

[0023] To measure temperature, a current is passed through the resistor, raising its temperature and heating the local superconducting wire, causing one path to lose superconductivity. This leaves only one Josephson junction connected to the circuit. Because the Josephson junction connected to the circuit is superconducting, the critical current measured based on the current distribution characteristics of the other path, due to the series connection of a resistor, remains the critical current of the Josephson junction connected to the circuit. This allows the on-chip temperature to be measured.

[0024] When the magnetic field needs to be measured, the current in the resistor is cut off to restore the superconducting wire to superconductivity. At this time, the two Josephson junctions are connected in parallel to form a superconducting quantum interference device structure, through which the magnetic field perpendicular to the chip is measured.

[0025] 1) Temperature measurement part

[0026] The temperature measuring part contains Josephson junctions integrated in one or a series of the quantum superconducting chip for temperature measurement. When the chip temperature drops below 10K, the Josephson junctions begin to enter the superconducting state, and the critical current increases with the decrease of temperature. By measuring the critical current of the Josephson junction, the actual temperature on the chip can be obtained according to the temperature-critical current relationship.

[0027] 2) Magnetic field measurement part

[0028] The magnetic field measurement part contains a direct current superconducting quantum interference device (DC-SQUID) structure composed of two parallel Josephson junctions integrated on the quantum superconducting chip and connected by superconducting wires.

[0029] The SQUID is essentially a magnetic flux voltage converter, and the critical current at both ends changes with the magnetic flux. Due to the modulation of magnetic flux on the critical current of SQUID, when the SQUID current is biased slightly above the critical current, the voltage across the SQUID will also be modulated by the magnetic field and change between the maximum and minimum values with a flux quantum as the period. At this time, by measuring this voltage, the magnetic flux passing through the superconducting loop can be obtained, and the average magnetic field in the vertical direction on the quantum superconducting chip can be obtained.

[0030] 3) Improvement of temperature and magnetic field measurement circuit

[0031] As shown in Figure 2 As an improvement of the temperature and magnetic field measurement circuit, a DC-SQUID structure composed of two parallel Josephson junctions can be used, and a resistor is placed close to one of the superconducting wire branches.

[0032] When temperature measurement is needed, current is passed through the resistor to raise the resistance temperature and heat the local superconducting wire, causing one of the wires to lose superconductivity. At this time, only one Josephson junction is connected to the circuit. Since the Josephson junction connected to the circuit is in the superconducting state, the critical current measured according to the current distribution characteristics is still the critical current of the Josephson junction connected to the circuit, and the on-chip temperature can be measured accordingly.

[0033] When magnetic field measurement is needed, the current in the resistor is cut off, and the superconducting wire returns to the superconducting state. At this time, the two Josephson junctions form a superconducting quantum interference device structure in parallel, and the vertical magnetic field of the chip can be measured.

[0034] 4) Installation method of the temperature and magnetic field measurement circuit

[0035] The temperature and magnetic field measuring circuit can be integrated on the same silicon chip as the main part of the quantum superconducting chip at the design time to realize on-chip temperature and magnetic field measurement. Advanced packaging technology can also be used to process the temperature and magnetic field measuring circuit on a new silicon chip without changing the original quantum superconducting chip silicon chip design. Through 3D packaging technology, the silicon chip with the processed temperature and magnetic field measuring circuit is covered above the quantum superconducting chip to realize the temperature and magnetic field measurement of the superconducting chip, reducing the chip design and production cost.

[0036] The critical current width of the Josephson junction after superconducting has a good negative correlation with the temperature of the Josephson junction in a wide range, so the temperature of the quantum superconducting chip can be deduced by the critical current width of the Josephson junction.

[0037] In the linear temperature measurement range, the relationship between the critical current and the temperature is as follows:

[0038]

[0039] Where T represents the temperature to be measured; k is a sensitivity coefficient, which is a negative number, with a unit of K / mA, indicating that the temperature needs to be reduced by 1 mA of the critical current; The critical current width of the temperature measuring Josephson junction, The range needs to be limited to avoid exceeding the linear region of the critical current-temperature relationship, resulting in a large error in the measurement result; The temperature when the equivalent critical current is 0, it should be noted that It is not the superconducting transition temperature, which cannot be measured by actual measurement, and needs to be calculated by the calibration result.

[0040] In the linear temperature measurement range (3.8~4.5K), the relationship between the calculated critical current and the temperature is:

[0041]

[0042] If the current critical current measured by the Josephson junction is 10 mA, the calculated temperature of the Josephson junction is 4.02K.

[0043] Two Josephson junctions in parallel through the superconducting loop form a direct current superconducting quantum interference device structure, which can be used to measure the magnetic field. SQUID is essentially a magnetic flux voltage converter, and the critical current at both ends changes with the magnetic flux period:

[0044]

[0045] When the SQUID current is biased slightly above the critical current, the voltage across the SQUID will also be modulated by the magnetic field and will vary periodically between a maximum value and a minimum value of ( = 2.067833758×10^-15Wb), when the magnetic flux through the SQUID loop increases from n times the flux quantum to n+1 / 2 times the flux quantum, the I-V curve moves to the right and down to the maximum distance, and continues to increase to n+1 times the flux quantum, the I-V curve moves to the left and up to restore the level when n times. When the SQUID current is biased at I a , as the magnetic flux in the SQUID superconducting loop changes, the voltage across the SQUID will vary periodically between V 1 , V 2 , the specific value of V 1 , V 2 needs to be calibrated after the integrated quantum chip is manufactured, and the output voltage of a single DC-SQUID is in the order of μV.

[0046] The voltage-flux curve of the DC-SQUID is periodic, but due to the nonlinearity of the SQUID voltage-flux curve, a feedback circuit is usually needed to obtain a linearized output, so as to realize the magnetic flux measurement.

[0047] When the readout circuit is working, the DC-SQUID is calibrated in advance, and a working point is selected, and its voltage is recorded as V s . First, the voltage output by the DC-SQUID is compared with V s , and the difference voltage is input into the integrator. Second, the integrator outputs a feedback voltage V f , which drives R f to generate a feedback current acting on the feedback inductor. Third, the feedback inductor generates a feedback magnetic flux, which acts on the DC-SQUID through the mutual inductance M f between the feedback inductor and the DC-SQUID superconducting loop to change the magnetic flux received by the DC-SQUID. Fourth, the DC-SQUID receives the feedback magnetic flux, which causes the output voltage to change towards the working point V s . This process is repeated until the output voltage of the DC-SQUID becomes V s, the circuit no longer adjusts. In the fifth step, the feedback loop is disconnected, and the feedback voltage output by the integrator V f The input magnetic flux received by the DC-SQUID is in a linear relationship with the input magnetic flux, and the formula is:

[0048]

[0049] wherein, is the magnetic flux to be measured, k is a positive number, and the unit is Wb / V, which indicates that the magnetic flux needs to be increased by 1 V for each increase of 1 V of the feedback voltage; is the feedback voltage; is the magnetic flux at the set operating point. The parameters in the above formula need to be obtained by calibration. After obtaining the magnetic flux to be measured , the formula of the magnetic induction intensity on the chip is as follows: B

[0050]

[0051] wherein, B is the magnetic induction intensity of the magnetic field on the chip, which indicates the magnetic field intensity of the environment in which the superconducting chip is located, and the unit is T (Tesla); is the magnetic flux on the chip measured by the DC-SQUID; S is the equivalent area of the superconducting loop.

[0052] The above describes the embodiments of the present application in detail, and the principle and implementation mode of the present application are described by applying specific examples. The above embodiment is only used to help understand the core idea of the present application; meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the above description should not be understood as the limitation of the present application.​

Claims

1. A quantum superconducting chip on-chip temperature and magnetic field environment measurement circuit, comprising a quantum superconducting chip, characterized in that: The quantum superconducting chip is provided with a temperature measurement and magnetic field measurement module. The temperature measurement and magnetic field measurement module uses two Josephson junctions connected in parallel to form a DC-SQUID structure, and an external resistor is placed closely near one of the superconducting wire branches. When temperature measurement is required, current is passed through the resistor to increase the resistor temperature, heat the local superconducting wire, and cause one of the branches to quench the superconducting wire. At this time, only one Josephson junction is connected to the circuit; when the magnetic field needs to be measured, the current in the resistor is cut off to restore the superconducting wire to superconductivity. At this time, the two Josephson junctions are connected in parallel to form a DC-SQUID structure.

2. The measuring circuit according to claim 1, characterized in that The steps of using the temperature measurement magnetic field measurement module to measure temperature include: passing current into the resistor, increasing the resistor temperature, heating the local superconducting wire, causing it to quench superconducting. At this time, only one Josephson junction is connected to the circuit, measuring the critical current of the Josephson junction connected to the circuit, and obtaining the actual temperature on the current chip based on the relationship between temperature and critical current.

3. The measurement circuit according to claim 1, characterized in that The steps for measuring the magnetic field using the temperature-measuring magnetic field measurement module include: cutting off the current in the resistor to restore the superconducting wire to superconductivity. At this time, the two Josephson junctions are connected in parallel to form a DC-SQUID structure. By measuring the voltage across the DC-SQUID, the magnetic flux passing through the superconducting ring is obtained, and then the average magnetic field size in the vertical direction on the quantum superconducting chip is obtained.

4. A method for measuring the temperature and magnetic field environment on a quantum superconducting chip, characterized in that: The quantum superconducting chip is provided with a temperature measurement module and a magnetic field measurement module. The temperature measurement module and the magnetic field measurement module are arranged on a silicon wafer and 3D packaged on the quantum superconducting chip. The temperature measurement module includes one or more integrated series-connected Josephson junctions for temperature measurement; the magnetic field measurement module includes a DC superconducting quantum interference device (DC-SQUID) structure composed of two integrated parallel Josephson junctions connected by superconducting wires. The process includes the following steps: When the chip temperature drops below 10K, the Josephson junction begins to enter the superconducting state. The critical current and temperature of the Josephson junction are measured, and the actual temperature on the chip is obtained based on the relationship between temperature and critical current. By measuring the voltage across the DC-SQUID, the magnetic flux and magnetic field strength passing through the superconducting ring are obtained, and then the average magnetic field size in the vertical direction on the quantum superconducting chip is obtained.

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