Measurement method and device for quantum entanglement source, medium and equipment

Abstract

The invention relates to the technical field of quantum computing and quantum communication, in particular to a measurement method and device for a quantum entanglement source, a medium and equipment. The measurement method comprises the following steps: receiving first and second photon signals from a quantum entanglement source by adopting first and second single-photon detectors; acquiring a first electric pulse signal from the first single-photon detector, acquiring a second electric pulse signal from the second single-photon detector, and acquiring a reference clock signal from the quantum entanglement source; obtaining a first time deviation TE1 from the first electric pulse signal based on the reference clock signal, and obtaining a second time deviation TE2 from the second electric pulse signal; and determining a time error TEA between the first photon and the second photon which are emitted by the quantum entanglement source and are in an entangled state according to the first time deviation and the second time deviation. According to the invention, the measurement of the quantum entanglement source can be simply, rapidly and accurately realized.

Description

Technical Field

[0001] This invention relates to the fields of quantum computing and quantum communication technologies, and in particular to measurement methods, apparatus, media, and devices for quantum entanglement sources. Background Technology

[0002] Quantum information technology follows the laws of quantum mechanics to perform high-speed mathematical and logical operations, store, and process quantum information. Quantum entanglement plays a crucial role in quantum information processing and is an indispensable resource in many processes. For example, in quantum teleportation, a pair of entangled particles located at locations A and B can transmit an unknown quantum state from location A to location B. Quantum entanglement is closely related to the disorder of quantum systems and the degree of quantum information loss. The greater the quantum entanglement, the more disordered the subsystem and the more quantum information is lost; conversely, the smaller the quantum entanglement, the more ordered the subsystem and the less quantum information is lost. The degree of entanglement of quantum states is closely related to the successful implementation of quantum information processing.

[0003] There are several methods to generate entangled states in qubits, such as passing a laser beam through a parametric downconverter. When an electron in an atom transitions from a high energy level to a low energy level, the emitted photons are in a maximally entangled state due to the conservation of angular momentum. The device that generates entangled qubits is called a quantum entanglement source, and the performance of the quantum entanglement source determines the entanglement quality of the emitted photons. Summary of the Invention

[0004] The purpose of this invention is to provide a method, apparatus, medium, and device for measuring quantum entanglement sources, in order to solve the problem of accurate measurement of the entanglement quality of quantum entanglement sources.

[0005] According to one aspect of the present invention, a method for measuring quantum entanglement sources is provided, comprising: A first single-photon detector is used to receive the first photon signal from the quantum entanglement source, and a second single-photon detector is used to receive the second photon signal from the quantum entanglement source, wherein the first photon and the second photon are in an entangled state; The first electrical pulse signal is obtained from the first single-photon detector, the second electrical pulse signal is obtained from the second single-photon detector, and the reference clock signal is obtained from the quantum entanglement source; Obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal and the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal; The time error (TEA) between the first and second photons in an entangled state emitted by the quantum entanglement source is determined based on the first and second time deviations.

[0006] According to one embodiment of the present invention, the time error TEA is the difference between the first time deviation TE1 and the second time deviation TE2; or, The time error TEA is the absolute value of the difference between the first time deviation TE1 and the second time deviation TE2.

[0007] According to one embodiment of the present invention, obtaining a first time deviation TE1 of a first electrical pulse signal relative to a reference clock signal includes: The first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal is obtained by using the direct counting method, or by using the basic tap delay chain time digital conversion method, or by using the cyclic delay chain time digital conversion method.

[0008] According to one embodiment of the present invention, obtaining a second time deviation TE2 of the second electrical pulse signal relative to a reference clock signal includes: The second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal is obtained by using the direct counting method, or by using the basic tap delay chain time digital conversion method, or by using the cyclic delay chain time digital conversion method.

[0009] According to one embodiment of the present invention, the first and second single-photon detectors are photomultiplier tube single-photon detectors, avalanche diode single-photon detectors, superconducting nanowire single-photon detectors, superconducting conversion edge-type single-photon detectors, or quantum dot single-photon detectors.

[0010] According to another aspect of the present invention, a measuring device for a quantum entanglement source is provided, comprising: The first single-photon detector is configured to receive a first photon signal from a quantum entanglement source and output a first electrical pulse signal to a time-to-digital converter. The second single-photon detector is configured to receive a second photon signal from a quantum entanglement source and output a second electrical pulse signal to a time-to-digital converter. A time-to-digital converter is configured to receive a reference clock signal from a quantum entanglement source and acquire a first time deviation TE1 of a first electrical pulse signal relative to the reference clock signal and a second time deviation TE2 of a second electrical pulse signal relative to the reference clock signal. The data processing unit is configured to determine the time error TEA between the first photon and the second photon in an entangled state emitted by the quantum entanglement source based on the first time deviation TE1 and the second time deviation TE2.

[0011] The measurement device for the quantum entanglement source further includes: a storage unit configured to store a first time deviation TE1 of the first electrical pulse signal relative to a reference clock signal, a second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal, and a time error TEA.

[0012] The time-to-digital converter is further configured to obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal using a direct counting method, or to obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal using a basic tap delay chain time-to-digital conversion method, or to obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal using a cyclic delay chain time-to-digital conversion method. The time-to-digital converter is further configured to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a direct counting method, or to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a basic tap delay chain time-to-digital conversion method, or to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a cyclic delay chain time-to-digital conversion method.

[0013] According to another aspect of the present invention, a computer-readable storage medium storing a computer program is provided. The computer-readable storage medium stores a computer program that, when executed by a processor, causes the processor to perform a measurement method for a quantum entangled source according to an exemplary embodiment of the present invention.

[0014] According to another aspect of the present invention, a computer device is provided, comprising: a processor; and a memory storing a computer program that, when executed by the processor, implements the measurement method for quantum entanglement sources as described above.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By configuring dual single-photon detectors and combining them with the application of time-to-digital converter (TDC), the time deviation of entangled photons can be obtained quickly and accurately, and the time error value can be obtained based on the time deviation.

[0016] (2) By applying the cyclic delay chain TDC, the degree of nonlinearity in the measurement process is reduced, thus saving resources in the FPGA.

[0017] (3) By connecting the first and last signals of the delay chain through a data selector and using a loop counter to count the number of signal cycles, the measurement range of the TDC can be expanded without changing the number of delay units. Attached Figure Description

[0018] The above-mentioned objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings.

[0019] Figure 1 The diagram shown is a schematic representation of a measurement apparatus for a quantum entanglement source according to an exemplary embodiment of the present invention.

[0020] Figure 2 The diagram shows a flowchart of a measurement method for a quantum entangled source according to an exemplary embodiment of the present invention.

[0021] Figure 3 The diagram shown is a schematic schematic of the direct counting method according to an exemplary embodiment of the present invention.

[0022] Figure 4 The diagram shown is a schematic diagram of a time-to-digital converter employing a basic tap delay chain according to an exemplary embodiment of the present invention.

[0023] Figure 5 The diagram illustrates the working principle of a basic tap delay chain time-to-digital converter according to an exemplary embodiment of the present invention.

[0024] Figure 6 The diagram shown is a schematic representation of the structural principle of a cyclic delay chain (TDC) according to an exemplary embodiment of the present invention.

[0025] Figure 7 The diagram shown illustrates the principle of time deviation acquisition according to an exemplary embodiment of the present invention.

[0026] Figure label: 100 - Quantum entanglement source, 101 - First single-photon detector, 102 - Second single-photon detector, 103 - Time-to-digital converter, 104 - Data processing unit, 105 - Storage unit. Detailed Implementation

[0027] The following detailed description of a measurement method, apparatus, medium, and device for quantum entanglement sources according to the present invention, with reference to specific embodiments, is provided in detail.

[0028] like Figure 1 As shown, a schematic diagram of the measurement device used for a quantum entanglement source is presented.

[0029] Figure 1 The measurement apparatus shown for a quantum entanglement source includes: The first photon detector 101 is configured to receive a first photon signal from the quantum entanglement source 100 and output a first electrical pulse signal to the time-to-digital converter 103; wherein, the first single-photon detector is a free-running single-light detector A, used to receive photon 1.

[0030] The second single-photon detector 102 is configured to receive a second photon signal from a quantum entanglement source and output a second electrical pulse signal to a time-to-digital converter; wherein the second single-photon detector is a free-running single-photon detector B, used to receive photon 2.

[0031] The time-to-digital converter 103 is configured to receive a reference clock signal from the quantum entanglement source 100, and obtain a first time deviation TE1 from a first electrical pulse signal and a second time deviation TE2 from a second electrical pulse signal based on the reference clock signal. The data processing unit 104 is configured to determine the time error TEA between the first photon and the second photon in an entangled state emitted by the quantum entanglement source based on the first and second time deviations.

[0032] The measurement device for the quantum entanglement source also includes a storage unit 105 configured to store a first time deviation, a second time deviation, and a time error TEA, and can also store first and second electrical pulse signals.

[0033] The time-to-digital converter 103 obtains the first time deviation based on the reference clock signal by using a direct counting method, a basic tap delay chain time-to-digital conversion method, or a cyclic delay chain time-to-digital conversion method for the first electrical pulse signal. The time-to-digital converter 103 obtains the second time deviation based on the reference clock signal and the second electrical pulse signal using a direct counting method, a basic tap delay chain time-to-digital conversion method, or a cyclic delay chain time-to-digital conversion method.

[0034] like Figure 2 The flowchart shown illustrates a measurement method for quantum entanglement sources. The measurement method for quantum entanglement sources includes the following steps: Step S1: The first single-photon detector 101 is used to receive the first photon signal from the quantum entanglement source 100; the second single-photon detector 102 is used to receive the second photon signal from the quantum entanglement source 100; the first photon and the second photon are in an entangled state; Step S2: Obtain a first electrical pulse signal from the first single-photon detector 101, a second electrical pulse signal from the second single-photon detector 102, and a reference clock signal from the quantum entanglement source 100; Step S3: Based on the reference clock signal, obtain the first time deviation TE1 from the first electrical pulse signal and the second time deviation TE2 from the second electrical pulse signal; Step S4: Determine the time error TEA between the first photon and the second photon in the entangled state emitted by the quantum entanglement source based on the first and second time deviations.

[0035] In the above Figure 1 The measuring device shown and Figure 2 In the measurement method shown, the first and second single-photon detectors are photomultiplier tube single-photon detectors, avalanche diode single-photon detectors, superconducting nanowire single-photon detectors, superconducting conversion edge-type single-photon detectors, or quantum dot single-photon detectors. The time-to-digital converter is further configured to obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal using a direct counting method, or by using a basic tapped delay chain time-to-digital conversion method, or by using a cyclic delay chain time-to-digital conversion method. The time-to-digital converter is further configured to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a direct counting method, or to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a basic tap delay chain time-to-digital conversion method, or to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a cyclic delay chain time-to-digital conversion method.

[0036] The time error TEA is the difference between the first time deviation TE1 and the second time deviation TE2; or, the time error TEA is the absolute value of the difference between the first time deviation TE1 and the second time deviation TE2.

[0037] like Figure 3 As shown, a schematic diagram of the direct counting method is presented.

[0038] The direct counting method uses the system's clock cycle to count the number of complete clock cycles within a time interval, thereby measuring the time interval. For example... Figure 3 As shown, T0 is the measured time interval, T1 is the start time of the measured time interval, and T2 is the end time of the measured time interval. Theoretically, the time interval T0 = T1 - T2. However, since the clock signal is counted for an integer number of cycles t0, the start or end signal does not completely coincide with the rising edge of the clock signal during actual measurement. Therefore, the final measurement result will have an error of up to two clock cycles, i.e., t1 + t2.

[0039] like Figure 4 The diagram shows the structural principle of a time-to-digital converter using a basic tap delay chain. The basic tap delay chain TDC (Time-to-Digital Converter) consists of a "D flip-flop" and a delay unit. Utilizing the delay characteristics of the delay unit, the state of the delay unit is brought out through taps to measure the time interval, and the output is generated through a decoding circuit (Q0-Qn).

[0040] like Figure 5 The diagram shown illustrates the working principle of the basic tap delay chain time-to-digital conversion.

[0041] The start signal Start is delayed by a certain amount after passing through the delay unit. The output of the delay unit is connected to the signal input D of the D flip-flop. The stop signal Stop is used as the clock signal input to the input C of the D flip-flop.

[0042] During measurement, when the rising edge of the stop signal arrives, the D flip-flop latches the state of all taps. The time measurement is achieved by calculating the number of delay units the start signal passes through, and the result is output to the decoding circuit via the output terminal Q. When the stop signal arrives, the flip-flops that have already passed through the delay units for the start signal are latched as 1, while those that haven't are latched as 0. Therefore, the time interval between the start signal and the stop signal is the product of the number of 1s output by the D flip-flops and the delay time of a single delay unit.

[0043] The number of delay units N_TDC that the start signal (Start) passes through before the stop signal (Stop) arrives is used to obtain the final time interval value:

[0044] Where T BUF The delay time of a single delay unit. The resolution of a basic tap delay chain (TDC) is the delay time of a single delay unit in the delay chain, and the delay time of a delay unit should be the sum of the delay time of the delay element and its trace delay.

[0045] like Figure 6 The diagram shown illustrates the structural principle of the cyclic delay chain (TDC).

[0046] Because the basic tapped delay chain (TDC) suffers from inconsistent delay times among its delay cells, it increases the nonlinearity of the TDC system. This nonlinearity increases with the length of the delay chain, sometimes covering one or even several least significant bits and generating substantial errors. When the time interval to be measured is large, the delay chain length needs to be increased. However, limited FPGA resources sometimes cannot meet these requirements, necessitating a circular delay chain design. By reusing identical delay cells, the impact of inconsistent delay times on system linearity can be reduced, and FPGA resources can be saved.

[0047] The Cyclic Delay Chain (TDC) is constructed by connecting the start and end signals of the delay chain through a data selector and using a loop counter to count the number of signal cycles. This design allows for an expanded measurement range of the TDC while maintaining the same number of delay units. In this TDC, when the rising edge of the stop signal arrives, the stop signal acts as a clock signal, latching the states of all flip-flops and stopping the loop counter. The time interval measurement function can be achieved through the loop counter and the latched values ​​of the flip-flops.

[0048] The parameters of TDC can be adjusted or configured with reference to the following indicators.

[0049] Resolution refers to the smallest time interval that a TDC can distinguish, also known as the least significant bit (LSB). The smaller this parameter is, the better. It is the quantization step size of the TDC's input-output transfer characteristic curve.

[0050] The measurement range refers to the maximum time interval that TDC can measure. To obtain a larger measurement range, it generally requires more chip area and logic resources.

[0051] The nonlinearity error of TDC refers to the deviation between the actual and ideal quantization characteristics of TDC caused by factors such as inconsistent delay times of delay units, different chip manufacturing processes, voltage and temperature variations of the chip, and signal crosstalk. The analysis of TDC nonlinearity is mainly measured by two metrics: differential nonlinearity (DNL) and integral nonlinearity (INL). DNL refers to the deviation between the actual delay time of a TDC delay unit and the ideal delay time (average value), which is the difference between the actual step size and the theoretical step size in the input-output transfer characteristic curve. INL, on the other hand, refers to the integral value of DNL along the entire delay chain from the starting position to the current position. DNL and INL are generally expressed in units of the delay time of an ideal delay unit, i.e., the time of one LSB.

[0052] Measurement accuracy, also known as single-shot accuracy or standard deviation, refers to the distribution of the actual measured value around the true time value when the TDC measures the time interval of a pulse signal due to the influence of internal and external factors.

[0053] Dead time is the time required for a TDC to complete a conversion and be ready to perform a new measurement. This metric reflects the measurement rate that the TDC can operate at. Modern applications require TDCs to have a high sampling rate, so the smaller the dead time, the better.

[0054] In digital ICs, power consumption is mainly composed of a combination of static power consumption and dynamic power consumption. The former is determined by the manufacturing process, while the latter is determined by the clock frequency and toggle frequency. Furthermore, the logic resources occupied by the time-to-displacement (TDC) also need to be considered, ensuring the rational allocation of system logic resources to maximize energy efficiency. like Figure 7 As shown, a schematic diagram illustrating the principle of time deviation acquisition is presented.

[0055] For a single electrical pulse signal obtained from a single photon, the ideal pulse duration is the time T between the rising edge of the start signal (Start) and the rising edge of the stop signal (Stop). Based on the reference clock signal ref_clk, the first duration T1 = (t2 - t1) is the measured time. In actual measurement, the start and end points are determined by the rising edges, and the actual measured value is the second duration T2.

[0056] If the delay of the first rising edge in the test period is equal to the delay of the last rising edge, then the test is ideal, and it is exactly equal to an integer multiple of the reference clock signal period Tref.

[0057] Time deviation error is represented as: However, if not, an integer number of reference clock signal periods cannot be obtained. Therefore, this error is the reference clock signal period under both positive and negative conditions.

[0058] because so This allows us to determine the range of values ​​for the time deviation error: Furthermore, according to exemplary embodiments of the present invention, a computer-readable storage medium storing a computer program may also be provided. This computer-readable storage medium stores a computer program that, when executed by a processor, causes the processor to perform a measurement method for a quantum entangled source according to exemplary embodiments of the present invention. This computer-readable recording medium is any data storage device capable of storing data read from a computer system. Examples of computer-readable recording media include: read-only memory, random access memory, read-only optical disk, magnetic tape, floppy disk, optical data storage device, and carrier waves (such as data transmission via the Internet through wired or wireless transmission paths).

[0059] Furthermore, according to exemplary embodiments of the present invention, a computing device may also be provided. The computing device includes a processor and a memory. The memory stores a computer program. The computer program is executed by the processor, causing the processor to perform a computer program for measuring quantum entanglement sources according to exemplary embodiments of the present invention.

[0060] It should be noted that the terms "first," "second," "third," "fourth," etc., in the above description are used to distinguish features with the same name in the same or different embodiments, and are not intended to limit the number of features. Furthermore, the present invention is not limited to the specific configurations and processes described above or shown in the figures. The above descriptions are merely specific embodiments of the present invention. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the described systems, devices, modules, or modules can be referred to the corresponding processes in the method embodiments, and need not be repeated. It should be understood that the scope of protection of the present invention is not limited thereto. Any equivalent modifications or substitutions conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A measurement method for quantum entanglement sources, characterized in that, include: A first single-photon detector is used to receive the first photon signal from the quantum entanglement source, and a second single-photon detector is used to receive the second photon signal from the quantum entanglement source, wherein the first photon and the second photon are in an entangled state; The first electrical pulse signal is obtained from the first single-photon detector, the second electrical pulse signal is obtained from the second single-photon detector, and the reference clock signal is obtained from the quantum entanglement source; Obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal and the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal; The time error (TEA) between the first and second photons in an entangled state emitted by the quantum entanglement source is determined based on the first and second time deviations.

2. The method according to claim 1, characterized in that, The time error TEA is the difference between the first time deviation TE1 and the second time deviation TE2; or, The time error TEA is the absolute value of the difference between the first time deviation TE1 and the second time deviation TE2.

3. The method according to claim 1, characterized in that, Obtaining the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal includes: The first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal is obtained by using the direct counting method, or by using the basic tap delay chain time digital conversion method, or by using the cyclic delay chain time digital conversion method.

4. The method according to claim 1, characterized in that, Obtaining the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal includes: The second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal is obtained by using the direct counting method, or by using the basic tap delay chain time digital conversion method, or by using the cyclic delay chain time digital conversion method.

5. The method according to claim 1, characterized in that, The first and second single-photon detectors are photomultiplier tube single-photon detectors, avalanche diode single-photon detectors, superconducting nanowire single-photon detectors, superconducting conversion edge-type single-photon detectors, or quantum dot single-photon detectors.

6. A measuring device for a quantum entanglement source, characterized in that, include: The first single-photon detector is configured to receive a first photon signal from a quantum entanglement source and output a first electrical pulse signal to a time-to-digital converter. The second single-photon detector is configured to receive a second photon signal from a quantum entanglement source and output a second electrical pulse signal to a time-to-digital converter. A time-to-digital converter is configured to receive a reference clock signal from a quantum entanglement source and acquire a first time deviation TE1 of a first electrical pulse signal relative to the reference clock signal and a second time deviation TE2 of a second electrical pulse signal relative to the reference clock signal. The data processing unit is configured to determine the time error TEA between the first photon and the second photon in an entangled state emitted by the quantum entanglement source based on the first time deviation TE1 and the second time deviation TE2.

7. The apparatus according to claim 6, characterized in that, The measuring device for the quantum entanglement source further includes: The storage unit is configured to store a first time deviation TE1 of the first electrical pulse signal relative to a reference clock signal, a second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal, and a time error TEA.

8. The apparatus according to claim 6, characterized in that, The time-to-digital converter is further configured to obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal using a direct counting method, or to obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal using a basic tap delay chain time-to-digital conversion method, or to obtain the first time deviation TE1 of the first electrical pulse signal relative to the reference clock signal using a cyclic delay chain time-to-digital conversion method. The time-to-digital converter is further configured to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a direct counting method, or to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a basic tap delay chain time-to-digital conversion method, or to obtain the second time deviation TE2 of the second electrical pulse signal relative to the reference clock signal using a cyclic delay chain time-to-digital conversion method.

9. A computer-readable storage medium storing a computer program, wherein, When the computer program is executed by a processor, it implements the measurement method for quantum entanglement sources as described in any one of claims 1 to 5.

10. A computing device, comprising: processor; A memory storing a computer program that, when executed by a processor, implements the measurement method for a quantum entanglement source as described in any one of claims 1 to 5.

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