A multi-ion quantum state resolution device and method based on EMCCD

Abstract

The present invention discloses a multi-ion quantum state resolution device based on EMCCD, comprising a vacuum chamber, wherein ions in the vacuum chamber are imaged onto an EMCCD camera through an imaging lens group, the EMCCD camera outputs ion image data and transmits it to a data acquisition card, and a computer processes the data in the data acquisition card to resolve the quantum state of the ions. The present invention also discloses a multi-ion quantum state resolution method based on EMCCD, which resolves the ion quantum state by performing two threshold discriminations on the collected ion images and combining the Rabi oscillation curve. The method of the present invention is suitable for the quantum state resolution of single ions and multiple ions, is convenient and fast, and has a simple implementation process.

Description

Technical Field

[0001] The present invention belongs to the field of quantum computing based on trapped ions, and specifically relates to a multi-ion quantum state resolution device based on EMCCD, and also relates to a multi-ion quantum state resolution method based on EMCCD, which is suitable for rapid resolution of multi-ion quantum states. Background Art

[0002] Since the realization of quantum computers requires a sufficient number of quantum bits, manipulating more and more quantum bits to independently address ions brings great difficulties. Before performing independent addressing operations, we need to distinguish the quantum state of each ion individually to determine what kind of pulse manipulation we want to perform next. Therefore, it is particularly important to achieve the resolution of multi-ion quantum states.

[0003] At present, there are two methods for distinguishing the quantum state of ions. One is to use a photomultiplier tube (PMT) to read the fluorescence count of ions, and the other is to use an electron multiplier CCD camera (EMCCD camera) to analyze the pixel brightness of the image to determine the quantum state. Since the photomultiplier tube PMT cannot perform spatial resolution on ions and is not suitable for the detection of multiple ions, the present invention has developed a quantum state resolution system based on an EMCCD camera. This method can determine the quantum state of ions based on the analysis of the pixel values ​​on the EMCCD camera ion image. However, the existing pixel value analysis method based on the EMCCD camera ion image is complex to implement, has a low program running rate, and is not conducive to continuous operation with subsequent experiments. Summary of the invention

[0004] The purpose of the present invention is to provide a multi-ion quantum state resolution device based on EMCCD and a multi-ion quantum state resolution method based on EMCCD in view of the above problems existing in the prior art.

[0005] The above-mentioned purpose of the present invention is achieved by the following technical means:

[0006] A multi-ion quantum state resolution device based on EMCCD includes a vacuum cavity, in which ions are trapped. The ions are imaged onto an EMCCD camera through an imaging lens group. The EMCCD camera outputs ion image data, which is transmitted to a data acquisition card. A computer processes the data in the data acquisition card to resolve the quantum state of the ions.

[0007] A multi-ion quantum state resolution method based on EMCCD, using the multi-ion quantum state resolution device based on EMCCD as described above, comprises the following steps:

[0008] Step 1: Build a multi-ion quantum state resolution device based on EMCCD;

[0009] Step 2, loading the ions into a three-dimensional trapped potential well in a vacuum chamber and cooling the ions;

[0010] Step 3, running the EMCCD camera and capturing ion dynamic images through the EMCCD camera;

[0011] Step 4, using the cooled ions as the pre-measured ions, preparing the pre-measured ions to a dark state, and using an EMCCD camera to collect dark state ion image data; preparing the pre-measured ions to a bright state and performing fluorescence excitation, and using an EMCCD camera to collect bright state ion image data; drawing a dark state pixel value distribution curve based on the dark state ion image data, and drawing a bright state pixel value distribution curve based on the bright state ion image data; the abscissa of the dark state pixel value distribution curve and the abscissa of the bright state pixel value distribution curve are both pixel values, and the ordinate of the dark state pixel value distribution curve and the ordinate of the bright state pixel value distribution curve are both pixel numbers;

[0012] Step 5, selecting a pixel value threshold A according to the bright pixel value distribution curve and the dark pixel value distribution curve, the pixel value threshold A is selected based on: the number of pixels whose pixel values ​​in the bright pixel value distribution curve are greater than the pixel value threshold A, recorded as the pixel number C; the number of pixels whose pixel values ​​in the dark pixel value distribution curve are greater than the pixel value threshold A, recorded as the pixel number D; setting a pixel number difference m, C-D≥m; then selecting an intermediate value between the pixel number C and the pixel number D as the number threshold B;

[0013] Step 6, by adjusting the quantum state preparation parameters, the quantum state of the predicted measured ion is cyclically converted between the bright state, the superposition state and the dark state to realize Rabi oscillation; after each round of quantum state conversion, the ion image is collected by the EMCCD camera; each time an ion image is collected, the computer determines whether the predicted measured ion corresponding to the image processing area in the ion image is a bright state or a dark state according to the pixel value threshold A and the quantity threshold B, and each time the number of ion images collected is equal to the specified number N, the computer performs a statistical resolution, and counts the number of ion images in which the predicted measured ion is a dark state or a bright state in the corresponding N ion images, thereby determining the quantum state population of the corresponding predicted measured ion;

[0014] At the same time, the computer predicts the quantum state population of the measured ions and determines the changes with the quantum state preparation parameters, and obtains the corresponding Rabi oscillation curve.

[0015] The pixel value threshold A and the quantity threshold B are adjusted until the peak value of the Rabi oscillation curve reaches a preset high threshold and the minimum value of the Rabi oscillation curve is below a preset low threshold, thereby obtaining an adjusted pixel value threshold A and an adjusted quantity threshold B;

[0016] Step 7, the EMCCD camera collects ion image data for the ions to be resolved, and the ions to be resolved and the predicted ions are the same ions; for each statistical resolution time point, the ion image data corresponding to the ions to be resolved includes N ion pictures; for each ion to be resolved, according to the corresponding adjusted pixel value threshold A and the adjusted quantity threshold B, it is determined whether the ion to be resolved corresponding to the image processing area in each ion picture is a bright state or a dark state, and according to the number of ion pictures in which the ion to be resolved is a dark state or a bright state in the N ion pictures, the quantum state population of the corresponding ion to be resolved is determined.

[0017] As described above, in step 6, judging whether the predicted measured ions corresponding to the image processing area in the ion image are bright or dark according to the pixel value threshold A and the quantity threshold B, and in step 7, judging whether the ions to be distinguished corresponding to the image processing area in each ion image are bright or dark according to the corresponding adjusted pixel value threshold A and the adjusted quantity threshold B, both include the following steps:

[0018] Determine the image processing area corresponding to each target ion from the ion image, and in the image processing area corresponding to each target ion, if the total number of pixels whose pixel values ​​are greater than the first threshold is greater than the second threshold, it is considered that the quantum state of the corresponding target ion is a bright state; if the total number of pixels whose pixel values ​​are greater than the first threshold is less than or equal to the second threshold, the quantum state of the corresponding target ion is a dark state;

[0019] For step 6, the target ion is the predicted ion, the first threshold is the pixel value threshold A, and the second threshold is the quantity threshold B;

[0020] For step 7, the target ion is the ion to be resolved, the first threshold is the adjusted pixel value threshold A, and the second threshold is the adjusted quantity threshold B.

[0021] The above step 6 specifically includes the following steps:

[0022] Step 6.1, setting the initial value of the quantum state preparation parameter of the predicted measured ion; the computer records the initial value of the quantum state preparation parameter as the current quantum state preparation parameter;

[0023] Step 6.2, cooling the pre-measured ions and preparing them to a bright state;

[0024] Step 6.3, preparing the quantum state of the predicted measured ion according to the current quantum state preparation parameters;

[0025] Step 6.4, the predicted ions are excited for fluorescence, and the EMCCD camera collects an ion picture; the computer determines whether the predicted ions corresponding to the image processing area in the ion picture are bright or dark according to the pixel value threshold A and the quantity threshold B, and saves the judgment result;

[0026] If the number of ion images collected for the current quantum state preparation parameters is less than the specified number N, return to step 6.2;

[0027] If the number of ion images collected for the current quantum state preparation parameters is equal to the specified number N, then perform the following steps:

[0028] The computer counts the number of ion pictures of the predicted measured ion in the dark state among the N ion pictures corresponding to the current quantum state preparation parameters, recorded as the number of dark state ion pictures a, and obtains the corresponding quantum state population of the predicted measured ion, recorded as the dark state population n, n=a / N; or counts the number of ion pictures of the predicted measured ion in the bright state among the N ion pictures corresponding to the current quantum state preparation parameters, recorded as the number of bright state ion pictures b, and obtains the corresponding quantum state population of the predicted measured ion, recorded as the bright state population n', n'=b / N;

[0029] The computer draws a point in the Rabi oscillation curve based on the quantum state population and the current quantum state preparation parameter data;

[0030] Adjust the current quantum state preparation parameters, use the adjusted quantum state preparation parameters as the current quantum state preparation parameters and return to step 6.2; after drawing a period of Rabi oscillation curve, synchronously execute step 6.5;

[0031] Step 6.5, adjust the pixel value threshold A and the quantity threshold B until the peak value of the Rabi oscillation curve reaches the preset high threshold and the minimum value of the Rabi oscillation curve is below the preset low threshold, thereby obtaining the adjusted pixel value threshold A and the adjusted quantity threshold B, and stop the cycle of steps 6.2-6.4.

[0032] The above-mentioned step 7 specifically includes the following steps:

[0033] Step 7.1, record the preparation conditions of the ions to be resolved;

[0034] Step 7.2, the ions to be resolved are fluorescently excited, and the EMCCD camera collects an ion image for the ions to be resolved; the computer determines whether the ions to be resolved corresponding to the image processing area in the ion image are bright or dark based on the adjusted pixel value threshold A and the adjusted number threshold B, and saves the judgment result;

[0035] Step 7.3, when the number of collected ion images is less than the specified number N, the ions to be resolved are cooled and prepared to a bright state; then, according to the preparation conditions of the ions to be resolved recorded in 7.1, the quantum state of the ions to be resolved is prepared, and then the process returns to step 7.2;

[0036] When N ion images are collected, the computer records the current time point as the current statistical resolution time point, and counts the number of ion images in which the ions to be resolved are in the dark state among the corresponding N ion images, recorded as the number of dark state ion images a, and obtains the quantum state population number n of the ions to be resolved corresponding to the current statistical resolution time point, n=a / N; or counts the number of ion images in which the ions to be resolved are in the bright state among the N ion images corresponding to the current statistical resolution time point, recorded as the number of bright state ion images b, and obtains the corresponding quantum state population number of the ions to be resolved, recorded as the bright state population number n', n'=b / N.

[0037] As described above in step 6 and step 7, when there are multiple target ions, a single ion image displays multiple target ions, and the image processing area of ​​each target ion is a partial area divided in the ion image, and the image processing area corresponding to each target ion only includes the image of the corresponding target ion; and each target ion corresponds to a pair of first thresholds and second thresholds respectively;

[0038] For step 6, the target ion is the predicted ion, the first threshold is the pixel value threshold A, and the second threshold is the quantity threshold B;

[0039] For step 7, the target ion is the ion to be resolved, the first threshold is the adjusted pixel value threshold A, and the second threshold is the adjusted quantity threshold B.

[0040] In step 5, as described above, there are multiple pixel value thresholds A, and according to the statistics of the corresponding pixel number C and pixel number D of each pixel value threshold A, a pair of pixel value threshold A and number threshold B is selected to execute step 6;

[0041] When adjusting the pixel value threshold A in step 6, the value of the corresponding number threshold B is adjusted according to the corresponding pixel number C and pixel number D.

[0042] The above step 3 also includes the following steps:

[0043] The EMCCD camera captures the ion dynamic image and reduces the exposure time of the EMCCD camera.

[0044] As described above in step 6, the high threshold is 0.97~0.99, and the low threshold is 0~0.03.

[0045] As mentioned above, step 6 also includes the following operations:

[0046] Step 6.6, if the quantum state population calculated in step 6.4 is the dark state population n, the quantum state preparation parameter corresponding to the peak value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to the preparation of the predicted measured ion to the dark state, and the quantum state preparation parameter corresponding to the minimum value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to the preparation of the predicted measured ion to the bright state, and then perform steps 4 to 6.5 again, and then perform step 7;

[0047] If the quantum state population calculated in step 6.4 is the bright state population n', the quantum state preparation parameter corresponding to the peak value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to preparing the predicted measured ion to the bright state, and the quantum state preparation parameter corresponding to the minimum value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to preparing the predicted measured ion to the dark state, then execute steps 4 to 6.5 again, and then execute step 7.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (i) Using an EMCCD camera and a data acquisition card to collect ion images and identify the quantum state of the ion images, compared with multi-channel PMT reading fluorescence counts, this method requires less cost, is more convenient and faster, and is easy to achieve more ion resolution in the future;

[0050] (ii) The two-threshold method used in the present invention is simpler and more efficient than the existing maximum likelihood method, reduces the difficulty in program writing, increases the speed of program operation, and improves the consistency of the overall experimental operation;

[0051] (III) The method of the present invention is applicable to the quantum state resolution of single ions and multiple ions;

[0052] (iv) The data acquisition card used can simultaneously process the ion image data generated by multiple EMCCD cameras;

[0053] (V) The results of quantum state resolution can be used in the main experimental program and synchronized with the timing of the main experimental program to facilitate the next step of experimental operation after completing quantum state resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a schematic diagram of the structure of a multi-ion quantum state resolution device based on EMCCD of the present invention;

[0055] Figure 2 The logical diagram of computer data processing, (a) is the processing of steps 4 to 5, (b) is the processing of steps 6 to 7;

[0056] Figure 3is a Rabi oscillation curve, and the figure contains four curves, representing the Rabi oscillation curves of four calcium ions; the abscissa is the time of Rabi oscillation, corresponding to the pulse duration of the 729nm pulsed laser used to prepare the quantum state during the Rabi oscillation process, and the ordinate represents the quantum state population number. In an embodiment of the present invention, the quantum state population number = the number of ion images in which the ion is in the dark state in 100 ion images / 100, and the population number is a value in the range of 0 to 1, wherein 1D-4D respectively represent the Rabi oscillation curves corresponding to the calcium ions numbered 1D-4D;

[0057] Figure 4 For calcium ions 40 Ca + The energy level diagram of For calcium ions 40 Ca + The existence time at different energy levels, the unit s represents seconds, ns represents nanoseconds, , , , and All are quantum states;

[0058] Figure 5 The image of ions displayed on the EMCCD camera;

[0059] Among them, 1-vacuum chamber; 2-imaging lens group; 3-EMCCD camera; 4-data acquisition card. DETAILED DESCRIPTION

[0060] In order to facilitate those skilled in the art to understand and use the present invention, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the implementation examples described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0061] Example 1

[0062] A multi-ion quantum state resolution device based on EMCCD, such as Figure 1 As shown, it includes: a vacuum chamber 1, in which ions are trapped, and the ions are imaged onto an EMCCD camera 3 through an imaging lens group 2. The EMCCD camera 3 captures the image of the ions and outputs ion image data. The ion image data is transmitted to a data acquisition card 4 via a data transmission line, and a computer processes the data in the data acquisition card 4 to distinguish the quantum state of the ions.

[0063] In this embodiment, it is not possible to directly control the EMCCD camera 3 through the host computer supporting software and then read the ion image data collected by the EMCCD camera 3 in real time; because the speed of directly controlling the EMCCD camera 3 to read the ion image data through the host computer supporting software is slow, a bitflow data acquisition card is used in this embodiment to collect the ion image data of the EMCCD camera 3.

[0064] In this embodiment, the EMCCD camera 3 and the bitflow data acquisition card are connected via a camera link data transmission line, so that data acquisition and processing can be performed more quickly, so that the ion image data captured by the EMCCD camera 3 can be quickly transmitted to the data acquisition card 4.

[0065] Example 2

[0066] A method for distinguishing multiple ion quantum states based on EMCCD, using a multiple ion quantum state distinguishing device based on EMCCD described in Example 1, using a data acquisition card 4 to collect ion image data output by an EMCCD camera 3, and then using a quantum state distinguishing program and an experimental main program in a computer to analyze and process the data in the data acquisition card 4, thereby achieving the distinction of the quantum state of the ions. Specifically comprising the following steps:

[0067] Step 1: Build a multi-ion quantum state resolution device based on EMCCD as described in Example 1.

[0068] Install the SDK software that comes with the data acquisition card 4. In this embodiment, the SDK software includes bitflow Preview software and SysReg software. Both bitflow Preview software and SysReg software are free software. Then, embed the data acquisition card 4 into the PCI interface of the computer.

[0069] The EMCCD camera 3 is connected to the data acquisition card 4 via a camera link data transmission line.

[0070] Run the SysReg software and the bitflow Preview software to enable the data acquisition card 4 to recognize the EMCCD camera 3. When the SDK software is successfully installed and the data acquisition card 4 can recognize the EMCCD camera 3, the image captured by the EMCCD camera 3 can be viewed on the computer display.

[0071] Step 2: Load the ions into the three-dimensional trapped potential well in the vacuum chamber 1 and cool the ions.

[0072] In this embodiment, the vacuum chamber 1 is first maintained at 10 -9In the ultra-high vacuum environment of Pa, independent stable DC voltage and RF high voltage are applied to the DC electrode and RF electrode of the ion trap in the vacuum chamber 1, respectively, so that the ion trap generates a three-dimensional trapped potential well, and the calcium atoms ejected from the atomic reactor are photoionized to generate calcium ions. 40 Ca + , and the calcium ion 40 Ca + Loaded into the three-dimensional trapped potential well, in this embodiment, 4 calcium ions are loaded 40 Ca + , 4 calcium ions displayed by the EMCCD camera 40 Ca + Images such as Figure 5 shown.

[0073] Then, a low-power 397nm linear polarized laser, 866nm laser and 854nm laser were introduced from a quartz observation window of the vacuum chamber 1 to irradiate the calcium ions. 40 Ca + Doppler cooling is performed (here "low power" only means that the power of the 397nm linearly polarized laser in Doppler cooling is smaller than the power of the 397nm linearly polarized laser used for fluorescence excitation): 40 Ca + For capture, the power of the low-power 397nm linearly polarized laser was set to 5μW, the detuning was set to -30MHz, the power of the 866nm laser was set to 200μW, and the power of the 854nm laser was set to 30μW. The 854nm laser was used to prevent calcium ions from 40 Ca + Then, by adjusting the voltage of the compensation electrode of the ion trap, all the trapped calcium ions 40 Ca + The temperature of the nanostructured material is kept below 5 mK, thus achieving Doppler cooling.

[0074] Preferably, after Doppler cooling, calcium ions are irradiated with 729 nm laser and 854 nm laser. 40 Ca + Further sideband cooling allows calcium ions to 40 Ca + The phonon number drops to 0.1.

[0075] Step 3: Run the EMCCD camera 3 and capture the ion dynamic image through the EMCCD camera 3.

[0076] In this process, the ion image data output by the EMCCD camera 3 is an ion dynamic image. In this embodiment, the EMCCD camera 3 is operated, and the exposure time of the EMCCD camera 3 is set to 1 s. If an ion dynamic image appears on the bitflow Preview software, it indicates that the data acquisition card 4 is operating normally.

[0077] Determine calcium ions 40 Ca + After setting the position on the bitflow Preview software panel, set the exposure time of EMCCD camera 3 to about 5ms; when performing subsequent steps 4 and 6, it is necessary to compress the experimental steps as much as possible while ensuring the accuracy of the experiment to suppress the decoherence effect; the specific operation is to shorten the preparation time of each quantum state, which means that the time for quantum state detection also needs to be reduced accordingly, so as to ensure the coordination between the preparation of quantum states and the resolution of quantum states, so that after the ions have passed the preparation of quantum states, the EMCCD camera 3 can complete the acquisition of ion image data before the ions decoherence.

[0078] Step 4: Perform pre-measurement, use the ions cooled in step 2 as pre-measured ions, prepare the pre-measured ions to a dark state, and use the EMCCD camera 3 to collect dark state ion image data; prepare the pre-measured ions to a bright state and perform fluorescence excitation, and use the EMCCD camera 3 to collect bright state ion image data; draw a dark state pixel value distribution curve based on the dark state ion image data, and draw a bright state pixel value distribution curve based on the bright state ion image data.

[0079] In this embodiment, the selected pre-measured ions are the calcium ions treated in step 2. 40 Ca + , calcium ion 40 Ca + The energy level diagram is as follows Figure 4 As shown; the calcium ions obtained in step 2 are 40 Ca + Prepare to , state (i.e. calcium ion 40 Ca + The ground state, represents the magnetic quantum number), and then uses 729nm laser to , Calcium ion 40 Ca + Pump to state (calcium ions 40 Ca + Pump to The frequency of the 729nm laser used in the state is different from the frequency of the 729nm laser used in the sideband cooling process. The specific frequency is determined according to the energy levels selected in these two processes. 40 Ca + Pump to The 729nm laser used in the state is in pulse form), calcium ions 40 Ca + exist The existence time of the state is relatively long, within 1.168 s. If no other operations are performed, the calcium ion 40 Ca + It does not radiate photons, so for calcium ions 40 Ca + ,Will The quantum state of the state is called the dark state. In order to obtain the image data of the bright state ions, the 729nm laser is not used, and the high-power 397nm linear polarized laser is used for fluorescence excitation (here "high power" only means that the power of the 397nm linear polarized laser used for fluorescence excitation is greater than that of the 397nm linear polarized laser used in Doppler cooling). , Calcium ion 40 Ca + Pump to In terms of state, The state will radiate photons in a very short time and can be detected by the EMCCD camera 3, so for calcium ions 40 Ca + , , The quantum state of the state is called the bright state. The dark state pixel value distribution curve is drawn based on the dark state ion image data, and the bright state pixel value distribution curve is drawn based on the bright state ion image data. The horizontal coordinates of the dark state pixel value distribution curve and the bright state pixel value distribution curve are both pixel values ​​(i.e. pixel grayscale values), and the vertical coordinates are both pixel numbers. 40 Ca + In the case of stable trapping, each calcium ion 40 Ca + The pixel value distribution in the bright state and the dark state is basically the same, so only a single calcium ion needs to be obtained. 40 Ca + Distribution curve of bright and dark pixel values.

[0080] Step 5: Select the pixel value threshold A according to the bright pixel value distribution curve and the dark pixel value distribution curve. The pixel value threshold A is selected based on: the number of pixels in the bright pixel value distribution curve whose pixel values ​​are greater than the pixel value threshold A is recorded as the pixel number C, and the number of pixels in the dark pixel value distribution curve whose pixel values ​​are greater than the pixel value threshold A is recorded as the pixel number D; set the pixel number difference m, C-D≥m, in this embodiment, the preset number is 5 to 10. Then, the middle value between the pixel number C and the pixel number D is selected as the number threshold B.

[0081] Subsequently, the pixel value threshold A and the quantity threshold B can be used to determine whether each ion (including the predicted ions and the ions to be resolved) is bright or dark. The specific operation steps are shown in steps 6 and 7. The values ​​of the pixel value threshold A and the quantity threshold B need to be continuously debugged and finally confirmed in step 6.

[0082] If the pixel value threshold A is changed, the number of pixels C and the number of pixels D will also change accordingly. In step 4, multiple pixel value thresholds A can be obtained, and then multiple groups of pixel value thresholds A, pixel numbers C and pixel numbers D are counted, and then a pair of pixel value thresholds A and number thresholds B are selected to execute step 6. If the pixel value threshold A is adjusted in step 6, the value of the corresponding number of pixels C and pixel number D is adjusted according to the corresponding number of pixels C and pixel number D.

[0083] Step 6: by adjusting the quantum state preparation parameters, the quantum state of the predicted measured ion is cyclically converted between the bright state, the superposition state and the dark state to realize Rabi oscillation; after each round of quantum state conversion, the ion image is collected by the EMCCD camera 3; each time an ion image is collected, the computer determines whether the predicted measured ion corresponding to the image processing area in the ion image is a bright state or a dark state according to the pixel value threshold A and the quantity threshold B, and each time the number of ion images collected is equal to the specified number N, the computer performs a statistical resolution, and counts the number of ion images in which the predicted measured ion is a dark state or a bright state in the corresponding N ion images, thereby determining the quantum state population number n of the corresponding predicted measured ion;

[0084] At the same time, the computer predicts that the quantum state population number n of the measured ion changes with different quantum state preparation parameters, and obtains the corresponding Rabi oscillation curve;

[0085] The pixel value threshold A and the quantity threshold B are adjusted until the peak value of the Rabi oscillation curve reaches the preset high threshold and the minimum value of the Rabi oscillation curve is below the preset low threshold, thereby obtaining the adjusted pixel value threshold A and the adjusted quantity threshold B; the adjusted pixel value threshold A and the adjusted quantity threshold B are used to finally determine whether the predicted measured ions are in a bright state or a dark state. Specifically, the following steps are included:

[0086] Step 6.1, setting the initial values ​​of the quantum state preparation parameters of the predicted measured ions;

[0087] In this embodiment, the calcium ion 40 Ca + When preparing the quantum state, the main quantum state preparation parameter is the pulse duration of the 729nm pulse laser, and the initial value of the pulse duration of the 729nm pulse laser is set to 0;

[0088] The computer records the initial value of the quantum state preparation parameter as the current quantum state preparation parameter;

[0089] Step 6.2, cooling the pre-measured ions and preparing them to a bright state;

[0090] In this embodiment, a low-power 397nm linearly polarized laser is used as cooling light and an 866nm laser is used as back pump light. 40 Ca + Doppler cooling is performed, and during this process, 854nm laser is simultaneously applied to calcium ions. 40 Ca + To prevent calcium ions 40 Ca + Falling to other energy levels;

[0091] Then, 729nm laser and 854nm laser were used to irradiate calcium ions. 40 Ca + Perform sideband cooling;

[0092] Then, 397nm circularly polarized laser (397nm sigma light) is used to inject calcium ions into the 40 Ca + Prepare to , state (i.e. calcium ion 40 Ca + ground state);

[0093] Step 6.3, preparing the quantum state of the predicted measured ion according to the current quantum state preparation parameters;

[0094] In this embodiment, calcium ions are injected into the 40 Ca + Prepare different quantum states, corresponding to 729nm pulse laser with different pulse durations, calcium ions 40 Ca + It may be prepared into a bright state, a dark state, or a superposition state;

[0095] Step 6.4, quantum state detection: the predicted ion is excited for fluorescence, and the EMCCD camera 3 collects an ion picture; the computer determines whether the predicted ion corresponding to the image processing area in the ion picture is a bright state or a dark state according to the pixel value threshold A and the quantity threshold B, and saves the judgment result;

[0096] If the number of ion images collected for the current quantum state preparation parameters is less than the specified number N, return to step 6.2;

[0097] If the number of ion images collected for the current quantum state preparation parameters is equal to the specified number N, then perform the following steps:

[0098] The computer counts the number of ion pictures of the predicted measured ion in the dark state among the N ion pictures corresponding to the current quantum state preparation parameters, recorded as the number of dark state ion pictures a, and obtains the corresponding quantum state population of the predicted measured ion, recorded as the dark state population n, n=a / N (the number of ion pictures of the predicted measured ion in the bright state among the N ion pictures corresponding to the current quantum state preparation parameters can also be counted, recorded as the number of bright state ion pictures b, and obtains the corresponding quantum state population of the predicted measured ion, recorded as the bright state population n', n'=b / N, the effect is the same as the number of ion pictures in the dark state, only the Rabi oscillation curve obtained is flipped upside down from the Rabi oscillation curve of the statistical dark state); the computer draws a point in the Rabi oscillation curve based on the quantum state population and the current quantum state preparation parameter data; adjusts the current quantum state preparation parameters so that the predicted measured ion can be prepared into different quantum states, uses the adjusted quantum state preparation parameters as the current quantum state preparation parameters and returns to step 6.2; after drawing a period of Rabi oscillation curve, synchronously execute step 6.5;

[0099] Step 6.5, adjust the pixel value threshold A and the quantity threshold B until the peak value of the Rabi oscillation curve reaches the preset high threshold and the minimum value of the Rabi oscillation curve is below the preset low threshold, thereby obtaining the adjusted pixel value threshold A and the adjusted quantity threshold B, and stop the cycle of steps 6.2-6.4.

[0100] In this embodiment, the specified number N is 100. Every time 100 ion images are collected, the computer calculates the quantum state population number n once, and then increases the pulse duration of the 729nm pulse laser by a preset pulse duration step based on the original pulse duration (in this embodiment, the preset pulse duration step is 5). ), and then the next round of statistical resolution is performed. In the cycle of Rabi oscillation, the horizontal coordinate of the Rabi oscillation curve is the pulse duration of the 729nm pulse laser, and the vertical coordinate is the corresponding quantum state population number n under the action of the pulse duration of the 729nm pulse laser. When the pulse duration of the 729nm pulse laser in step 6.3 is 0 or an integer multiple of the Rabi oscillation curve period, the calcium ion 40 Ca + When the pulse duration of the 729nm pulse laser is an odd multiple of the half period of the Rabi oscillation curve, the calcium ions 40 Ca + Prepared to the dark state; when the pulse duration of the 729nm pulse laser is other durations (that is, the pulse duration is not equal to 0, and is not equal to an integer multiple of the Rabi oscillation curve period, and is not equal to an odd multiple of the Rabi oscillation curve half period), calcium ions 40 Ca +Then, in step 6.4, a high-power 397nm linearly polarized laser is used to irradiate the calcium ions. 40 Ca + Fluorescence excitation is performed on the surface (no 854 nm laser is used in this process). If calcium ions 40 Ca + In the dark state, no fluorescence is emitted. If calcium ions 40 Ca + In the bright state (i.e. calcium ions 40 Ca + of state) then calcium ions 40 Ca + Be inspired state, it emits fluorescence due to spontaneous radiation. If calcium ions 40 Ca + In the superposition state, the calcium ion in step 6.4 40 Ca + It may or may not fluoresce. Regardless of the calcium ions in step 6.4 40 Ca + What quantum state is the calcium ion in after the operation in step 6.2? 40 Ca + All were prepared state (i.e. calcium ions 40 Ca + During the whole rabi oscillation process, the 866nm laser is continuously turned on.

[0101] In this embodiment, the pixel value threshold A and the quantity threshold B obtained in step 4 are written into the quantum state discrimination program; the quantum state discrimination program determines whether the predicted measured ion corresponding to the image processing area in the ion image is a bright state or a dark state according to the pixel value threshold A and the quantity threshold B, and counts the number of ion images in which the predicted measured ion is a dark state (or the number of ion images in which the ion is a bright state), thereby determining the corresponding quantum state population number n; the main experimental program draws the Rabi oscillation curve (such as Figure 3 The peak and minimum values ​​of the Rabi oscillation curve can be read directly.

[0102] Among them, judging whether the predicted measured ion corresponding to the image processing area in the ion image is a bright state or a dark state specifically includes the following steps: determining the image processing area corresponding to each predicted measured ion from the ion image, in the image processing area corresponding to each predicted measured ion, if the total number of pixels with pixel values ​​greater than the pixel value threshold A is greater than the number threshold B, then it is considered that the quantum state of the corresponding predicted measured ion is a bright state; if the total number of pixels with pixel values ​​greater than the pixel value threshold A is less than or equal to the number threshold B, then the quantum state of the corresponding predicted measured ion is a dark state.

[0103] In order to facilitate the subsequent simultaneous resolution of multiple ions, multiple pre-measured ions may be included in step 6, and a single ion image may display multiple pre-measured ions. The image processing area of ​​each pre-measured ion is a partial area divided in the ion image, and the image processing area corresponding to each pre-measured ion only includes the image of the corresponding pre-measured ion; and each pre-measured ion corresponds to a pair of pixel value threshold A and quantity threshold B. In this embodiment, the EMCCD camera 3 collects four calcium ions. 40 Ca + By dividing the area in the ion image, we can determine the 40 Ca + image processing area, and based on the individual calcium ions 40 Ca + The corresponding image processing areas are used to determine whether the ion is in a bright state or a dark state, calculate the quantum state population number n, draw the Rabi oscillation curve, and adjust the corresponding pixel value threshold A and quantity threshold B. In this embodiment, four calcium ions 40 Ca + There are four pairs of pixel value threshold A and quantity threshold B values, each calcium ion 40 Ca + Each corresponds to a Rabi oscillation curve.

[0104] Furthermore, in order to improve the accuracy of the pixel value threshold A and the quantity threshold B finally obtained, after executing step 6.5 once, step 6.6 is also included to obtain the precise quantum state preparation parameters required for preparing the predicted measured ions to the bright state and the dark state through the Rabi oscillation curve. The specific operation is as follows:

[0105] If the quantum state population calculated in step 6.4 is the dark state population n, the quantum state preparation parameter corresponding to the peak value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to the preparation of the predicted measured ion to the dark state, and the quantum state preparation parameter corresponding to the minimum value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to the preparation of the predicted measured ion to the bright state, and then steps 4 to 6.5 are performed again, and then step 7 is performed;

[0106] If the quantum state population calculated in step 6.4 is the bright state population n', the quantum state preparation parameter corresponding to the peak value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to preparing the predicted measured ion to the bright state, and the quantum state preparation parameter corresponding to the minimum value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to preparing the predicted measured ion to the dark state, then execute steps 4 to 6.5 again, and then execute step 7.

[0107] In this embodiment, the high threshold is 0.99, the low threshold is 0.03, and the pixel value threshold A and the quantity threshold B are appropriately adjusted until the peak value of the first three cycles of the Rabi oscillation curve reaches about 0.99 and the minimum value is below 0.03 (e.g. Figure 3 As shown in the figure), the corresponding adjusted pixel value threshold A and the adjusted quantity threshold B are used to finally determine whether the ion to be distinguished is in a bright state or a dark state, so that other subsequent experiments can use it normally.

[0108] Step 7. In other subsequent experiments, the quantum state of the ion to be resolved is resolved. The ion to be resolved is the same as the ion to be measured, but the quantum state of the ion to be resolved is unknown. The EMCCD camera 3 collects ion image data for the ion to be resolved. For each statistical resolution time point, the ion image data corresponding to the ion to be resolved includes N ion pictures; for each ion to be resolved, according to the corresponding adjusted pixel value threshold A and the adjusted number threshold B, it is determined whether the ion to be resolved in each ion picture is bright or dark, and according to the number of ion pictures in which the ion to be resolved is dark or bright in the N ion pictures, the corresponding quantum state population of the ion to be resolved is determined. Specifically, it includes the following steps:

[0109] Step 7.1, recording the preparation conditions of the ions to be resolved, such as the pulse duration of the 729 nm pulsed laser in this embodiment;

[0110] Step 7.2, the ions to be resolved are fluorescently excited, and then the EMCCD camera 3 collects an ion image for the ions to be resolved; the computer determines whether the ions to be resolved corresponding to the image processing area in the ion image are bright or dark according to the adjusted pixel value threshold A and the adjusted number threshold B, and saves the judgment result;

[0111] Judging whether the ion to be distinguished corresponding to the image processing area in the ion image is a bright state or a dark state specifically includes the following steps: determining the image processing area corresponding to each ion to be distinguished from the ion image, in the image processing area corresponding to each ion to be distinguished, if the total number of pixels with pixel values ​​greater than pixel value threshold A is greater than number threshold B, it is considered that the quantum state of the corresponding ion to be distinguished is a bright state; if the total number of pixels with pixel values ​​greater than pixel value threshold A is less than or equal to number threshold B, the quantum state of the corresponding ion to be distinguished is a dark state.

[0112] Step 7.3, when the number of collected ion images is less than the specified number N: cool the ions to be resolved and prepare them to a bright state; then prepare the quantum state of the ions to be resolved according to the preparation conditions of the ions to be resolved recorded in 7.1, and then return to step 7.2;

[0113] When N ion images are collected, the computer records the current time point as the current statistical resolution time point, and counts the number of ion images in which the ions to be resolved are in the dark state in the corresponding N ion images, recorded as the number of dark state ion images a, and obtains the quantum state population number of the ions to be resolved corresponding to the current statistical resolution time point, recorded as the dark state population number n, n=a / N (the number of ion images in which the ions to be resolved are in the bright state in the N ion images corresponding to the current statistical resolution time point can also be counted, recorded as the number of bright state ion images b, and the corresponding quantum state population number of the ions to be resolved can be obtained, recorded as the bright state population number n', n'=b / N).

[0114] When there are multiple ions to be resolved, a single ion image displays multiple ions to be resolved, and the image processing area for each ion to be resolved is a partial area divided in the ion image. The image processing area corresponding to each ion to be resolved only includes the image of the corresponding ion to be resolved; and each ion to be resolved corresponds to a pair of adjusted pixel value threshold A and adjusted quantity threshold B.

[0115] Figure 2 It is a logical diagram of computer data processing. In this embodiment, the collected ion image is divided into four rectangular image processing areas, each of which covers one ion (can be determined according to the number of ions. The number of ions manipulated in this embodiment is 4. It should be noted that due to the instability of the experimental system, the position of the ions changes. Every two to three days, the position of the rectangular image processing area needs to be appropriately adjusted). The number of pixels in the image processing area that is greater than the pixel value threshold A is counted, and then the statistical results are further judged. A value greater than the number threshold B is a bright state, and a value less than the number threshold B is a dark state.

[0116] Figure 4 Also shown is calcium ion 40 Ca + The existence time of each energy level is the basis for the experimental timing control and experimental operation of this embodiment.

[0117] It should be noted that the embodiments described in the present invention are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the described embodiments or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims.

Claims

1. A multi-ion quantum state resolution method based on EMCCD, characterized in that: The steps include: Step 1: constructing a multi-ion quantum state resolution device based on EMCCD, the multi-ion quantum state resolution device based on EMCCD comprising a vacuum chamber (1), wherein ions are trapped in the vacuum chamber (1), the ions are imaged onto an EMCCD camera (3) through an imaging lens group (2), the EMCCD camera (3) outputs ion image data, the ion image data is transmitted to a data acquisition card (4), and a computer processes the data in the data acquisition card (4) to resolve the quantum state of the ions; Step 2, loading the ions into a three-dimensional trapped potential well in the vacuum chamber (1), and cooling the ions; Step 3, running the EMCCD camera (3), and capturing ion dynamic images through the EMCCD camera (3); Step 4: using the cooled ions as the pre-measured ions, preparing the pre-measured ions to a dark state, and using an EMCCD camera (3) to collect dark state ion image data; preparing the pre-measured ions to a bright state and performing fluorescence excitation, and using an EMCCD camera (3) to collect bright state ion image data; drawing a dark state pixel value distribution curve based on the dark state ion image data, and drawing a bright state pixel value distribution curve based on the bright state ion image data; the abscissa of the dark state pixel value distribution curve and the abscissa of the bright state pixel value distribution curve are both pixel values, and the ordinate of the dark state pixel value distribution curve and the ordinate of the bright state pixel value distribution curve are both pixel numbers; Step 5, selecting a pixel value threshold A according to the bright pixel value distribution curve and the dark pixel value distribution curve, wherein the pixel value threshold A is selected based on: the number of pixels whose pixel values ​​in the bright pixel value distribution curve are greater than the pixel value threshold A, recorded as the number of pixels C; the number of pixels whose pixel values ​​in the dark pixel value distribution curve are greater than the pixel value threshold A, recorded as the number of pixels D; Set the pixel number difference m, C-D≥m; then select the middle value between the pixel number C and the pixel number D as the number threshold B; Step 6, by adjusting the quantum state preparation parameters, the quantum state of the predicted measured ion is cyclically converted between the bright state, the superposition state and the dark state to realize Rabi oscillation; after each round of quantum state conversion, the ion image is collected by the EMCCD camera (3); each time an ion image is collected, the computer determines whether the predicted measured ion corresponding to the image processing area in the ion image is a bright state or a dark state according to the pixel value threshold A and the number threshold B, and each time the number of collected ion images is equal to the specified number N, the computer performs a statistical resolution, and counts the number of ion images of the predicted measured ion in the corresponding N ion images that are in the dark state or the bright state, thereby determining the quantum state population of the corresponding predicted measured ion; At the same time, the computer predicts the quantum state population of the measured ions and determines the changes with the quantum state preparation parameters, and obtains the corresponding Rabi oscillation curve. The pixel value threshold A and the quantity threshold B are adjusted until the peak value of the Rabi oscillation curve reaches a preset high threshold and the minimum value of the Rabi oscillation curve is below a preset low threshold, thereby obtaining an adjusted pixel value threshold A and an adjusted quantity threshold B; Step 7, the EMCCD camera (3) collects ion image data for the ions to be resolved, the ions to be resolved and the predicted ions are the same ions; for each statistical resolution time point, the ion image data corresponding to the ions to be resolved includes N ion images; for each ion to be resolved, according to the corresponding adjusted pixel value threshold A and the adjusted number threshold B, it is determined whether the ion to be resolved corresponding to the image processing area in each ion image is a bright state or a dark state, and according to the number of ion images in which the ion to be resolved is a dark state or a bright state in the N ion images, the quantum state population of the corresponding ion to be resolved is determined.

2. According to claim 1, a multi-ion quantum state resolution method based on EMCCD is characterized in that: In step 6, judging whether the predicted measured ions corresponding to the image processing area in the ion image are bright or dark according to the pixel value threshold A and the quantity threshold B, and in step 7, judging whether the ions to be distinguished corresponding to the image processing area in each ion image are bright or dark according to the corresponding adjusted pixel value threshold A and the adjusted quantity threshold B, both include the following steps: Determine the image processing area corresponding to each target ion from the ion image, and in the image processing area corresponding to each target ion, if the total number of pixels whose pixel values ​​are greater than the first threshold is greater than the second threshold, it is considered that the quantum state of the corresponding target ion is a bright state; if the total number of pixels whose pixel values ​​are greater than the first threshold is less than or equal to the second threshold, the quantum state of the corresponding target ion is a dark state; For step 6, the target ion is the predicted ion, the first threshold is the pixel value threshold A, and the second threshold is the quantity threshold B; For step 7, the target ion is the ion to be resolved, the first threshold is the adjusted pixel value threshold A, and the second threshold is the adjusted quantity threshold B.

3. The method for distinguishing multiple ion quantum states based on EMCCD according to claim 2, characterized in that: The step 6 specifically includes the following steps: Step 6.1, setting the initial value of the quantum state preparation parameter of the predicted measured ion; the computer records the initial value of the quantum state preparation parameter as the current quantum state preparation parameter; Step 6.2, cooling the pre-measured ions and preparing them to a bright state; Step 6.3, preparing the quantum state of the predicted measured ion according to the current quantum state preparation parameters; Step 6.4, the pre-measured ions are fluorescently excited, and the EMCCD camera (3) collects an ion image; The computer determines whether the predicted measured ions corresponding to the image processing area in the ion picture are bright or dark according to the pixel value threshold A and the quantity threshold B, and saves the determination result; If the number of ion images collected for the current quantum state preparation parameters is less than the specified number N, return to step 6.2; If the number of ion images collected for the current quantum state preparation parameters is equal to the specified number N, then perform the following steps: The computer counts the number of ion pictures of the predicted measured ion in the dark state among the N ion pictures corresponding to the current quantum state preparation parameters, recorded as the number of dark state ion pictures a, and obtains the corresponding quantum state population of the predicted measured ion, recorded as the dark state population n, n=a / N; or counts the number of ion pictures of the predicted measured ion in the bright state among the N ion pictures corresponding to the current quantum state preparation parameters, recorded as the number of bright state ion pictures b, and obtains the corresponding quantum state population of the predicted measured ion, recorded as the bright state population n', n'=b / N; The computer draws a point in the Rabi oscillation curve based on the quantum state population and the current quantum state preparation parameter data; Adjust the current quantum state preparation parameters, use the adjusted quantum state preparation parameters as the current quantum state preparation parameters and return to step 6.2; after drawing a period of Rabi oscillation curve, synchronously execute step 6.5; Step 6.5, adjust the pixel value threshold A and the quantity threshold B until the peak value of the Rabi oscillation curve reaches the preset high threshold and the minimum value of the Rabi oscillation curve is below the preset low threshold, thereby obtaining the adjusted pixel value threshold A and the adjusted quantity threshold B, and stop the cycle of steps 6.2-6.

4.

4. The method for distinguishing multiple ion quantum states based on EMCCD according to claim 2, characterized in that: The step 7 specifically includes the following steps: Step 7.1, record the preparation conditions of the ions to be resolved; Step 7.2, the ions to be resolved are subjected to fluorescence excitation, and the EMCCD camera (3) collects an ion image for the ions to be resolved; the computer determines whether the ions to be resolved corresponding to the image processing area in the ion image are bright or dark based on the adjusted pixel value threshold A and the adjusted number threshold B, and saves the determination result; Step 7.3, when the number of collected ion images is less than the specified number N, the ions to be resolved are cooled and prepared to a bright state; then, according to the preparation conditions of the ions to be resolved recorded in 7.1, the quantum state of the ions to be resolved is prepared, and then the process returns to step 7.2; When N ion images are collected, the computer records the current time point as the current statistical resolution time point, and counts the number of ion images in which the ions to be resolved are in the dark state among the corresponding N ion images, recorded as the number of dark state ion images a, and obtains the quantum state population number n of the ions to be resolved corresponding to the current statistical resolution time point, n=a / N; or counts the number of ion images in which the ions to be resolved are in the bright state among the N ion images corresponding to the current statistical resolution time point, recorded as the number of bright state ion images b, and obtains the corresponding quantum state population number of the ions to be resolved, recorded as the bright state population number n', n'=b / N.

5. The multi-ion quantum state resolution method based on EMCCD according to claim 1, characterized in that: In step 6 and step 7, when there are multiple target ions, a single ion image displays multiple target ions, and the image processing area of ​​each target ion is a partial area divided in the ion image, and the image processing area corresponding to each target ion only includes the image of the corresponding target ion; and each target ion corresponds to a pair of first thresholds and second thresholds respectively; For step 6, the target ion is the predicted ion, the first threshold is the pixel value threshold A, and the second threshold is the quantity threshold B; For step 7, the target ion is the ion to be resolved, the first threshold is the adjusted pixel value threshold A, and the second threshold is the adjusted quantity threshold B.

6. The multi-ion quantum state resolution method based on EMCCD according to claim 2, characterized in that: In step 5, there are multiple pixel value thresholds A, and the corresponding pixel quantity C and pixel quantity D are counted according to each pixel value threshold A, and a pair of pixel value threshold A and quantity threshold B is selected to execute step 6; When adjusting the pixel value threshold A in step 6, the value of the corresponding number threshold B is adjusted according to the corresponding pixel number C and pixel number D.

7. The multi-ion quantum state resolution method based on EMCCD according to claim 2, characterized in that: The step 3 also includes the following steps: After the EMCCD camera (3) captures the ion dynamic image, the exposure time of the EMCCD camera (3) is reduced.

8. The multi-ion quantum state resolution method based on EMCCD according to claim 2, characterized in that: In step 6, the high threshold is 0.97-0.99, and the low threshold is 0-0.

03.

9. The method for distinguishing multiple ion quantum states based on EMCCD according to claim 3, characterized in that: The step 6 also includes the following operations: Step 6.6, if the quantum state population calculated in step 6.4 is the dark state population n, the quantum state preparation parameter corresponding to the peak value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to the preparation of the predicted measured ion to the dark state, and the quantum state preparation parameter corresponding to the minimum value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to the preparation of the predicted measured ion to the bright state, and then perform steps 4 to 6.5 again, and then perform step 7; If the quantum state population calculated in step 6.4 is the bright state population n', the quantum state preparation parameter corresponding to the peak value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to preparing the predicted measured ion to the bright state, and the quantum state preparation parameter corresponding to the minimum value of the Rabi oscillation curve is used as the quantum state preparation parameter corresponding to preparing the predicted measured ion to the dark state, then execute steps 4 to 6.5 again, and then execute step 7.

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