A permanent magnet coil and a device for ultracold ion magnetic field compensation

Abstract

The utility model discloses a permanent magnet coil and a device for ultracold ion magnetic field compensation, the permanent magnet coil comprises a permanent magnet body, a rear plate and a front plate; the permanent magnet body is provided with a protruding ring column, the protruding ring column is provided with holes for placing the permanent magnet, and the permanent magnet is fixed by the front plate and the rear plate; the rear plate is used to be placed between the permanent magnet body and the main cavity of the ion trap; the front plate is provided with a groove for winding a common coil. The permanent magnet coil provided by the utility model adopts a magnet to provide a magnetic field, which can avoid the magnetic field change of the magnetic field coil caused by the current ripple of the power supply, and at the same time, the rear plate is placed between the permanent magnet body and the main cavity of the ion trap to avoid direct contact between the magnet and the main cavity of the ion trap, so as to ensure that a stable magnetic field can be generated; by providing a groove in the front plate for placing the common coil, the overall magnetic field compensation device is more concise and occupies less space.

Description

Technical Field

[0001] The utility model relates to the field of ion trap experiments, in particular to a permanent magnet coil and a device for ultracold ion magnetic field compensation. Background Art

[0002] Quantum computers have powerful parallel computing capabilities and can solve some problems that are difficult for classical computers to solve in a very short time. They have very broad application prospects. The ion trap system is the earliest device used to trap single charged particles. It is considered to be one of the most promising quantum hardware for quantum computing. One of its advantages is that it has a long coherence time. The coherence time directly limits the maximum number of consecutive quantum operations that a quantum computer can perform, and is also a prerequisite for achieving high-fidelity quantum operations.

[0003] An important factor affecting the length of coherence time is magnetic field noise. Magnetic field noise can cause the transition frequency of ions to shift, further leading to the decoherence of quantum bits. Environmental magnetic field noise is caused by electrical equipment and power supplies around the ion trap, especially the mains power supply that powers laboratory equipment, which will generate a 50Hz alternating magnetic field, and the nonlinear load in the circuit will cause 50Hz high-order harmonics to be generated. Therefore, suppressing mains noise is crucial to maintaining the low magnetic field noise environment required for quantum bit experiments. Utility Model Content

[0004] In view of the ultracold ion magnetic field noise problem existing in the prior art, a permanent magnet coil and device for ultracold ion magnetic field compensation with reasonable design, simple structure and convenient adjustment are provided to achieve the stability of the ultracold ion environment magnetic field.

[0005] To achieve the above purpose, the technical solution of the utility model is:

[0006] In the first aspect, the utility model provides a permanent magnet coil, comprising a permanent magnet body, a rear plate and a front plate; the permanent magnet body is provided with a protruding ring column, the protruding ring column is provided with holes for placing the permanent magnet, and the permanent magnet is fixed by the front plate and the rear plate; the rear plate is used to be placed between the permanent magnet body and the main cavity of the ion trap; the front plate is provided with a groove for winding a common coil.

[0007] Furthermore, mounting holes are arranged at four corners of the rear plate.

[0008] Furthermore, panels are protrudingly provided around the front plate, and fixing holes are provided in the panels.

[0009] Furthermore, a through hole and a threaded hole are also provided in the permanent magnet body.

[0010] In a second aspect, the utility model provides a device for ultracold ion magnetic field compensation, comprising a permanent magnet coil, a common coil and a signal generator;

[0011] The permanent magnet coil is any of the permanent magnet coils described above, and a pair is provided; the common coil is composed of enameled wire wound in the grooves of the front plates of a pair of permanent magnet coils, and the head and tail ends are respectively connected to the positive pole of the output end of the signal generator and the ground.

[0012] Furthermore, the signal generator is provided with two output ports, one output port is used to connect to a common coil to generate a compensation magnetic field; and the other output port is used to connect to an oscilloscope to observe the compensation signal.

[0013] Furthermore, the signal generator adopts an external trigger mode and is connected to a linear trigger via an external interface to achieve synchronization of the compensation signal with the mains.

[0014] Furthermore, the signal generator outputs a waveform to the common coil by receiving compensation signal parameters to generate a compensation magnetic field.

[0015] Furthermore, the compensation signal parameters include compensated signal frequency, amplitude, and phase.

[0016] Compared with the prior art, the utility model has the following beneficial effects:

[0017] The permanent magnet coil provided by the utility model adopts a magnet to provide a magnetic field, which can avoid the magnetic field change caused by the power supply current ripple of the magnetic field coil. At the same time, the rear plate is placed between the permanent magnet body and the main cavity of the ion trap to avoid direct contact between the magnet and the main cavity of the ion trap, so as to ensure that a stable magnetic field can be generated; by providing a groove for placing an ordinary coil in the front plate, the overall magnetic field compensation device is more concise and occupies less space. Since the device for ultracold ion magnetic field compensation provided by the utility model is mainly composed of permanent magnet coils, the entire device is more concise and stable, and a more stable magnetic field strength is provided in a smaller space, so that while compensating for the mains noise, the overall magnetic field compensation device is further made more concise and occupies less space. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the structure of a permanent magnet coil provided in Example 1 of the utility model;

[0019] Figure 2 This is a schematic diagram of the overall structure of the compensation device provided in Example 2 of the utility model;

[0020] Figure 3 This is a schematic diagram of the assembly of the compensation device of the utility model and the ion trap main cavity;

[0021] Figure 4 This is the structural connection diagram of the signal generator RedPitaya 125-14;

[0022] Figure 5 This is a schematic diagram of the control program user page;

[0023] Figure 6 This is the Zeeman spectrum of ions in one cycle when no compensation device is added;

[0024] Figure 7 This is the Zeeman comparison spectrum of ions in one cycle without and after adding the compensation device;

[0025] In the figure: 1-permanent magnet body; 2-ring column; 3-hole; 4-through hole; 5-threaded hole; 6-front plate; 7-groove; 8-fixing hole; 9-rear plate; 10-ion trap main cavity; 11-flange window; 12-output waveform type; 13-output signal frequency, amplitude, phase; 14-output voltage bias; 15-trigger source; 16-signal generation / stop; 17-RedPitaya IP address; 18-save / read parameters. DETAILED DESCRIPTION

[0026] The technical solution of the utility model is further described below in conjunction with the accompanying drawings and embodiments.

[0027] Embodiment 1:

[0028] See also Figure 1-2 As shown, the permanent magnet coil provided in this embodiment mainly includes a permanent magnet body 1, a rear plate 9 and a front plate 6. Among them, a protruding ring column 2 is provided on the permanent magnet body 1, and the protruding ring column 2 is evenly covered with cylindrical holes 3, which is used to place the columnar permanent magnet. After the permanent magnet is placed, it is fixed by the front plate 6 and the rear plate 9. In this way, the entire permanent magnet coil structure can be made more compact. At the same time, by using a magnet to provide a magnetic field, the magnetic field change caused by the power supply current ripple of the magnetic field coil can be avoided. The rear plate 9 is used to be placed between the permanent magnet body 1 and the ion trap main cavity to avoid direct contact between the magnet and the ion trap main cavity 10, so as to ensure that a stable magnetic field can be generated; the front plate 6 is provided with an annular groove 7, which is used to be placed outside the permanent magnet body to fix the magnet and wind the ordinary coil. In this way, by providing a groove 7 for placing the ordinary coil in the front plate 6, the overall magnetic field compensation device is more concise and occupies less space.

[0029] In a specific embodiment, the rear plate 9 is a thin plate with mounting holes at four corners. The front plate 6 is provided with an arc panel protruding around it, and a fixing hole 8 is provided in the arc panel; the permanent magnet body 1 is also provided with a through hole 4 and a threaded hole 5. In this way, since the fixing hole 8 is provided in the arc panel and the threaded hole 5 is provided in the permanent magnet body, it is convenient to fix the front plate to the permanent magnet body by screws; at the same time, since the mounting holes are provided on the rear plate 9 and the through hole 4 is provided in the permanent magnet body, the permanent magnet coil and the ordinary coil can be fixed to the outer circle of the flange window 11 of the ion trap main cavity 10 by screws.

[0030] Embodiment 2:

[0031] See also Figure 2 As shown, it is a schematic diagram of the composition of the device for ultracold ion magnetic field compensation provided in this embodiment, which mainly includes a permanent magnet coil, a common coil and a signal generator.

[0032] The permanent magnet coil is the permanent magnet coil described in Example 1, and a pair of them are provided. The common coil is formed by winding an enameled wire in the grooves of the front plate of a pair of permanent magnet coils. An enameled wire is continuously wound in the pair of grooves, and the two ends are respectively connected to the positive pole of the output end of the signal generator and the ground. The common coil is used to generate a corresponding magnetic field to compensate for the environmental magnetic field noise. After the permanent magnet coil is assembled, it is installed on the main cavity of the ion trap, such as Figure 3 It should be noted that when winding the ordinary coil, a suitable length should be reserved between the two permanent magnets so as to be respectively mounted on a pair of flange windows 11 of the ion trap main cavity 10.

[0033] The signal generator uses RedPitaya 125-14 as the hardware device. The structure of RedPitaya 125-14 is as follows: Figure 4 As shown. Connect RedPitaya output 1 to a common coil, output 2 to an oscilloscope, and expansion interface E3 to a linear trigger as an external trigger signal source. Connect RedPitaya to a laboratory computer via wireless or wired connection, and run the control program on the computer. The control program is written in Python and controls the hardware circuit through SCPI commands. The instructions include: GEN:RST, initialize the output signal; SOURCE <n>:FUNC <type>, set the output waveform of channel n; SOUR <n>:FREQ:FIX <frequency>, set the output frequency of channel n; SOUR <n>:VOLT <amplitude>, set the output amplitude of channel n; SOUR <n>:PHAS <phase>, set the output phase of channel n; SOUR <n>:VOLT:OFFS <offset>, set the output bias voltage of channel n; SOUR <n>:TRAC:DATA:DATA <array>, import the data within one cycle of an arbitrary waveform to channel n; SOUR <n>:BURS:STAT BURST, set channel n output to burst mode; SOUR <n>:BURS:NCYC <num>, set the number of cycles for channel n to trigger repeated output once; SOUR <n>:TRig:SOUR <trigger>, set the trigger source of channel n; OUTPUT:STATE <state>, turn on / off channel output. The user obtains the compensation signal parameters through measurement and calculation, and sets the parameters through the user interface. The control program written in Python is responsible for translating the input parameters of the user interface into RedPitaya executable instructions, and then RedPitaya generates the target signal. The relevant control codes are shown in the table:

[0034]

[0035]

[0036] The control program user interface is as follows Figure 5 The user page can control information including output signal waveform 12 and voltage bias 14, as well as the frequency, amplitude, and phase of multiple signals 13, and also includes selecting the signal trigger source 15 and controlling the generation and stop of the output signal 16. In addition, the RedPitaya IP address 17 can be seen from the user page, and the frequency, amplitude, and phase parameters of the signal can be saved / read 18. Enter the compensation signal parameters into the user interface of the control program, click the start button 16, and the signal generator will output the appropriate waveform to the compensation coil to complete the magnetic field noise compensation.

[0037] In a specific embodiment, the compensation signal parameter is obtained by:

[0038] Step 1: Without applying any compensation signal, measure the Zeeman spectrum of ultracold ions within a mains cycle (20ms), such as Figure 6 As shown;

[0039] Step 2: From the figure, we can see that the maximum transition frequency ν within the period max =245.1331MHz, minimum transition frequency ν within the cycle min =245.1320MHz, ultracold ion transition frequency ν at 20ms 20 =245.1325MHz, ultracold ion transition frequency at time 0 ν0 = 245.1322MHz, slow drift noise frequency at the beginning and end of the period

[0040] ν 20 -ν0=300Hz;

[0041] Calculate the noise frequency difference Δν within the cycle,

[0042] Δν=2*ν max -ν min -ν 20 -ν0=1.6KHz

[0043] ν max At time t in the cycle max =16ms, ν min At time t in the cycle min =3.5ms;

[0044] Step 3: Calculate the magnetic field noise based on the type of ultracold ions used in the experiment

[0045]

[0046] Among them, Planck constant h = 6.626*10 -34 J·s, Bohr magneton μ=9.274*10 -24 J.T. -1 , ground state energy level m S =1 / 2, excited state energy level m D =5 / 2, the noise frequency difference Δν calculated in the previous step = 1.6KHz, then

[0047]

[0048] The calculated magnetic field size that needs to be compensated is B = 5.716*10 -1 mG.

[0049] Step 4: Calculate the current that should be applied to the ordinary coil based on the magnetic field noise calculated in the above steps:

[0050]

[0051] Among them, vacuum magnetic permeability μ0=4π*10 -7 N.A -2 , the radius of the ordinary coil r = 0.08m, the distance from the center of a single ordinary coil to the center of the ion trap X = 0.195m, the number of turns of a single ordinary coil N0 = 19, calculate the current size of the compensation coil

[0052]

[0053] The calculated current of the compensation coil is i=3.5026mA;

[0054] Step 5. According to the current value i calculated in the above steps, calculate the voltage amplitude U that the signal generator should apply to the common coil:

[0055] U=iR

[0056] Among them, the total resistance of the entire compensation loop is R = 70Ω, and the voltage of the compensation coil is calculated to be U = 245.2mV;

[0057] Step 6: Calculate the compensation signal phase (Unit: degrees):

[0058] If max >t min ,

[0059] If max <t min ,

[0060] From step 2, we can know that t max =16ms, t min =3.5ms, then the compensation signal phase

[0061]

[0062] It should be noted that since the mains synchronization in the experiment starts with the cooling of ions, the compensation signal should also delay the phase of ion cooling and state preparation. According to the different experimental platforms, the compensation signal phase is calculated. Finally, the phase delay in the experimental operation should be added to obtain the signal phase that the actual signal generator should produce.

[0063] In this way, the compensation signal parameters can be calculated through the above steps, and then the hardware circuit can be connected. Figure 4 , specifically including: 1. Connect a resistor in series to the output port Out1 of RedPitaya125-14 and connect it to a common coil for magnetic field compensation; 2. Connect the output port Out2 of RedPitaya125-14 to an oscilloscope; 3. Connect the external trigger expansion interface of RedPitaya125-14 to a 3.3V trigger signal; 4. Connect RedPitaya125-14 to a laboratory computer via a wired cable or wireless network. After connecting the hardware circuit, use the mains signal as the compensation signal trigger signal (rising edge trigger), and input the compensation signal frequency, amplitude and phase obtained in the above steps through the control program to complete the preliminary signal compensation;

[0064] After applying the compensation signal, the above steps are repeated several times to fine-tune the compensation signal until the Zeeman spectrum of the ultracold ion is stable within one cycle.

[0065] like Figure 7 As shown, it is a comparison of the Zeeman spectra of ions in one cycle before and after adding the compensation device; the Zeeman spectrum of the ion can reflect the magnitude of the magnetic field noise experienced by the ion. The flatter the Zeeman spectrum, the smaller the magnetic field change experienced by the ion, that is, the smaller the magnetic field noise. Figure 7 In the figure, the lower broken line represents the Zeeman spectrum of the ion before compensation; the middle broken line represents the Zeeman spectrum of the ion after preliminary compensation; the upper broken line represents the Zeeman spectrum of the ion after fine-tuning. It can be seen from the comparison that the magnetic field noise is significantly suppressed after compensation.

[0066] The above embodiments are only for illustrating the technical concept and features of the utility model, and their purpose is to enable ordinary technicians in the field to understand the content of the utility model and implement it accordingly, and they cannot be used to limit the protection scope of the utility model. Any equivalent changes or modifications made according to the essence of the content of the utility model should be included in the protection scope of the utility model.< / state> < / trigger> < / n> < / num> < / n> < / n> < / array> < / n> < / offset> < / n> < / phase> < / n> < / amplitude> < / n> < / frequency> < / n> < / type> < / n>

Claims

1. A permanent magnet coil, characterized in that: It includes a permanent magnet body, a rear plate and a front plate; the permanent magnet body is provided with a protruding ring column, the protruding ring column is provided with holes for placing the permanent magnet, and the permanent magnet is fixed by the front plate and the rear plate; the rear plate is used to be placed between the permanent magnet body and the main cavity of the ion trap; the front plate is provided with a groove.

2. The permanent magnet coil according to claim 1, characterized in that The four corners of the rear plate are all provided with mounting holes.

3. The permanent magnet coil according to claim 1, characterized in that: Panels are protrudingly arranged around the front plate, and fixing holes are arranged in the panels.

4. The permanent magnet coil according to claim 1, characterized in that: A through hole and a threaded hole are also provided in the permanent magnet body.

5. A device for ultracold ion magnetic field compensation, characterized in that: It includes a permanent magnet coil, a common coil and a signal generator; The permanent magnet coil is a permanent magnet coil as described in any one of claims 1-4, and is provided in pair; the ordinary coil is composed of enameled wire wound in the groove of the front plate of a pair of permanent magnet coils, and the head and tail ends are respectively connected to the positive pole of the signal generator output end and the ground.

6. The device for ultracold ion magnetic field compensation according to claim 5, characterized in that: The signal generator is provided with two output ports, one output port is used to connect to a common coil, and the other output port is used to connect to an oscilloscope.

7. The device for ultracold ion magnetic field compensation according to claim 6, characterized in that: The signal generator adopts an external trigger mode and is connected to a linear trigger via an external interface.

8. The device for ultracold ion magnetic field compensation according to claim 6, characterized in that: The signal generator outputs a waveform to the common coil by receiving compensation signal parameters to generate a compensation magnetic field.

9. The device for ultracold ion magnetic field compensation according to claim 8, characterized in that: The compensation signal parameters include the compensated signal frequency, amplitude, and phase.

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