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

Abstract

The invention discloses a method and a circuit for measuring temperature and magnetic field environment on a quantum superconducting chip, the circuit comprises the quantum superconducting chip, the quantum superconducting chip is provided with a temperature measurement magnetic field measurement module, and the temperature measurement magnetic field measurement module uses two Josephson junctions in parallel connection to form a DC-SQUID structure. One superconducting wire branch is closely placed on an external resistor, when temperature measurement is needed, current is introduced into the resistor, the temperature of the resistor is increased, the local superconducting wire is heated, one superconducting wire is quenched, and at the moment, only one Josephson junction is connected into the circuit; when a magnetic field is measured, the current in the resistor is cut off, the superconducting wire recovers superconduction, and at the moment, the two Josephson junctions are connected in parallel to form a DC-SQUID structure. Compared with an existing superconducting chip temperature measurement method, the quantum superconducting chip temperature measurement method has the advantages of being simple in structure, simple in measurement, simple in calibration and temperature calculation method, high in sensitivity and wide in measurement range, and effectively solves the problem of temperature and magnetic field measurement of the quantum superconducting chip.

Description

Technical Field

[0001] The present invention relates to the field of quantum superconducting measurement technology, and in particular to a method and circuit for measuring the temperature and magnetic field environment on a quantum superconducting chip. Background Art

[0002] Conductors have a certain resistance at room temperature. However, when certain special metals, such as lead, tin, and niobium, are cooled to below a certain, extremely low temperature, the resistance between their terminals suddenly disappears to zero, resulting in superconductivity. Metals that exhibit superconductivity at extremely low temperatures are called superconductors.

[0003] When a thin layer of insulator or normal metal (about 10 angstroms thick) is sandwiched between two superconductors, forming a superconductor (S)-insulator (I)-superconductor or superconductor (S)-normal metal-superconductor structure, Cooper electron pairs within one superconductor can pass through the insulator to the other superconductor at liquid helium temperatures (4.2 K) without applying any voltage, generating an electric current. This phenomenon is known as the superconducting Josephson effect, and this SIS (superconductor insulator-superconductor) or SNS (superconductor normal metal-superconductor) structure is called a Josephson junction.

[0004] When the voltage V across a Josephson junction is zero, a superconducting current can flow through the junction. This current is caused by the tunneling effect of Cooper pairs in the superconductor. This zero-voltage phenomenon persists as long as the superconducting current is less than a certain critical current, Ic, known as the Josephson critical current.

[0005] Josephson junctions have many important applications in modern quantum circuits, such as Josephson voltage standards (JVS), superconducting quantum interference devices (SQUIDs), superconducting quantum computing, and rapid single-flux quantum (RSFQ) digital electronics. Currently, Josephson junctions and quantum superconducting chips based on them are mostly made of the superconducting material niobium and its alloys, with a superconducting transition temperature of approximately 10K (-263.15°C). These devices typically operate at temperatures ranging from tens of milliK to the temperature of liquid helium (4.2K). During operation, they lack direct contact with the outside world and are typically confined to small enclosures, making them highly sensitive to external heat sources and magnetic fields, making temperature measurement difficult. Conventional methods of immersing quantum superconducting chips in liquid helium can only maintain the chip temperature at 4.2K. For quantum chips requiring even lower temperatures, dry refrigerators or other methods are required to further reduce the temperature. These methods require vacuum for insulation, so the cryocooler head does not have a similar "immersion" environment as liquid helium. At the same time, due to the limitations of the chip installation method, the thermal resistance of the intermediate layers, and the heat generated by the chip during operation, there is a temperature difference between the temperature on the chip and the temperature set at the cold head of the refrigerator. Therefore, it is impossible to accurately obtain the temperature of the quantum superconducting chip during operation in real time, which has some adverse effects on the use of the quantum superconducting chip.

[0006] In existing technologies, using thermistors to measure temperature in extremely low-temperature environments requires measuring extremely weak current signals. This, combined with the influence of the conductor's thermoelectric potential, makes measurement accuracy difficult to guarantee. Furthermore, the temperature-measuring resistor is independent of the quantum superconducting chip. Even if installed in a superconducting quantum system, it must be located outside the quantum superconducting chip, and its measurement results are similarly difficult to reflect the temperature of the quantum superconducting chip itself. Alternatively, the temperature measurement bit used consists of a Josephson junction and a capacitor in parallel, and the resonant cavity required for signal readout also uses a capacitor. Although the temperature measurement circuit is directly integrated on the quantum chip, due to limitations in semiconductor manufacturing processes, the capacitor occupies a relatively large chip area, which is disadvantageous for the circuit design of space-sensitive, large-scale integrated quantum superconducting chips. Furthermore, the calibration, signal readout, and temperature calculation methods are relatively complex, and the measurement range is narrow, making it inadequate for temperature measurement in the liquid helium temperature range. Therefore, a method and circuit for measuring the temperature and magnetic field environment on a quantum superconducting chip are needed. Summary of the Invention

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

[0008] To achieve the above object, the present invention is implemented according to the following technical solutions: The present invention 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 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.

[0009] On the other hand, a circuit for measuring the temperature and magnetic field environment on a quantum superconducting chip includes a quantum superconducting chip, wherein the quantum superconducting chip is provided with a temperature and magnetic field measurement module. The temperature and magnetic field measurement module uses two Josephson junctions in parallel to form a DC-SQUID structure, and an external resistor is placed close to 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 measurement is required, 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.

[0010] On the other hand, a method for measuring the temperature and magnetic field environment on a quantum superconducting chip is applied to a measurement circuit and 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 of 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.

[0011] Furthermore, 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 wire, 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.

[0012] Furthermore, the steps of using the temperature-measuring magnetic field measurement module to measure the magnetic field 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.

[0013] The beneficial effects of the present invention are: 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

[0014] 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; 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 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 1) Temperature measurement part The temperature measurement section includes one or a group of serially connected Josephson junctions integrated into the quantum superconducting chip. When the chip temperature drops below 10K, the Josephson junction enters a superconducting state, and the critical current increases as the temperature decreases. By measuring the critical current of the Josephson junction, the actual chip temperature can be determined based on the temperature-critical current relationship.

[0020] 2) Magnetic field measurement part The magnetic field measurement part includes a direct current superconducting quantum interference device (DC-SQUID) structure composed of two parallel Josephson junctions connected by superconducting wires integrated on the quantum superconducting chip.

[0021] A SQUID is essentially a flux-voltage converter, with the critical current across it varying with the periodicity of the magnetic flux. Because the magnetic flux modulates the SQUID's critical current, when the SQUID current is biased slightly above the critical current, the voltage across the SQUID is also modulated by the magnetic field, fluctuating between maximum and minimum values with a periodicity of one magnetic flux quantum. Measuring this voltage reveals the magnitude of the magnetic flux passing through the superconducting ring, and thus the average magnetic field perpendicular to the quantum superconducting chip.

[0022] 3) Improvement of temperature and magnetic measurement circuits like Figure 2 As shown, as an improvement to the temperature and magnetism measurement circuit, two Josephson junctions can be connected in parallel to form a DC superconducting quantum interference device (DC-SQUID) structure, and a resistor can be placed close to one of the superconducting wire branches.

[0023] To measure temperature, a current is passed through the resistor, raising its temperature and heating the local superconducting wire, causing one path to quench. At this point, only one Josephson junction is connected to the circuit. Because the Josephson junction connected to the circuit is in a superconducting state, the critical current measured based on the current distribution characteristics of the other path, due to the series connection of a resistor, is still 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 can be measured.

[0025] 4) Installation method of the temperature and magnetic measurement circuit The temperature and magnetic measurement circuits can be integrated with the main body of the quantum superconducting chip during design onto the same silicon wafer, enabling on-chip temperature and magnetic measurement. Advanced packaging technology can also be used to fabricate the temperature and magnetic measurement circuits onto a new silicon wafer without changing the original quantum superconducting chip silicon wafer design. This silicon wafer, with the temperature and magnetic measurement circuits fabricated, can then be overlaid on the quantum superconducting chip using 3D packaging technology to achieve temperature and magnetic measurement on the superconducting chip, reducing chip design and production costs.

[0026] The critical current width of the Josephson junction after superconducting has a good linear negative correlation with the temperature of the Josephson junction over a large range. Therefore, the temperature of the current quantum superconducting chip can be inferred from the critical current width of the Josephson junction.

[0027] In the linear temperature measurement range, the relationship between critical current and temperature is shown as follows:

[0028] Wherein, T represents the temperature to be measured; k is the sensitivity coefficient, which is a negative number with the unit of K / mA, indicating the amount by which the temperature needs to be lowered for every 1 mA increase in the critical current; is the critical current width measured by the thermometric Josephson junction, The range needs to be limited to avoid exceeding the linear region of the critical current-temperature relationship, which may cause large errors in the measurement results. is the temperature when the equivalent critical current is 0. It should be noted that, It is not the superconducting transition temperature and cannot be measured through actual measurement. It needs to be calculated through calibration results.

[0029] In the linear temperature measurement range (3.8~4.5K), the calculated relationship between critical current and temperature is:

[0030] If the current critical current measured by the Josephson junction is 10 mA, substituting it into the formula, it can be calculated that the current temperature of the Josephson junction is 4.02K.

[0031] Two Josephson junctions connected in parallel via superconducting loops form a DC superconducting quantum interference device structure that can be used to measure magnetic fields. The SQUID is essentially a flux-voltage converter, and the critical current at both ends varies with the flux cycle:

[0032] Due to the modulation effect of magnetic flux on the critical current of SQUID, when the SQUID current is biased slightly larger than the critical current, the voltage across the SQUID will also be modulated by the magnetic field and will fluctuate between the maximum and minimum values by a flux quantum. ( =2.067833758×10^-15Wb) is a periodic change. When the magnetic flux passing through the SQUID superconducting ring increases from n times to n+1 / 2 times, the IV characteristic curve moves to the lower right to the maximum distance. When it continues to increase to n+1 times, the IV characteristic curve moves to the upper left and returns to the level of n times. When the SQUID current bias is I a As the magnetic flux in the SQUID superconducting loop changes, the voltage across the SQUID will V 1 、 V 2 Inter-periodic changes, about V 1 、 V 2 The specific value needs to be calibrated after the integrated quantum chip is manufactured. The output voltage of a single DC-SQUID is in the μV range.

[0033] The voltage-flux curve of the DC-SQUID varies periodically, but since the SQUID voltage-flux curve is nonlinear, a feedback circuit is usually required to obtain a linearized output to achieve flux measurement.

[0034] When the readout circuit is working, the DC-SQUID is calibrated in advance, and an operating point is selected, and its voltage is recorded as V s In the first step, the voltage output by the DC-SQUID is V s The difference voltage is input into the integrator for comparison. In the second step, the integrator outputs the feedback voltage V f ,drive R f The feedback current is generated and acts on the feedback inductor. In the third step, the feedback inductor generates feedback flux, which is generated by the mutual inductance between the feedback inductor and the DC-SQUID superconducting ring. M f The action on the DC-SQUID changes the magnetic flux received by the DC-SQUID. In the fourth step, the DC-SQUID receives the feedback magnetic flux, causing the output voltage to tend to return to the operating point. V s This process repeats until the output voltage of the DC-SQUID becomes V s , the circuit is no longer regulated. Step 5, disconnect the feedback loop, the feedback voltage output by the integrator V f There is a quasi-linear relationship between the input magnetic flux received by the DC-SQUID and the formula is:

[0035] in, is the magnetic flux to be measured, k is the sensitivity coefficient, which is a positive number with the unit of Wb / V, indicating the amount by which the magnetic flux needs to increase for every 1 V increase in the feedback voltage; is the feedback voltage; is the magnetic flux at the working point of the setting. The parameters in the above formula need to be obtained through calibration. After that, the on-chip magnetic induction intensity B The formula is as follows:

[0036] in, B is the magnetic induction intensity of the on-chip magnetic field, indicating the magnetic field intensity of the environment in which the superconducting chip is located, with the unit being T (Tesla); is the on-chip magnetic flux measured by DC-SQUID; S is the equivalent area of the superconducting loop.

[0037] The embodiments of the present invention are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention. At the same time, for those skilled in the art, according to the idea of the present invention, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

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 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 3D packaged on the quantum superconducting chip. The temperature measurement module includes one or more integrated serially connected Josephson junctions for temperature measurement; the magnetic field measurement module includes a DC superconducting quantum interference device (DC-SQUID) structure consisting of two integrated parallel Josephson junctions connected by superconducting wires.

2. 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.

3. A method for measuring the temperature and magnetic field environment on a quantum superconducting chip, applied to the measurement circuit according to claim 1 or 2, characterized in that: The following steps are involved: 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.

4. The measuring method according to claim 3, 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.

5. The measuring method according to claim 3, 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.

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