Ion addressing system for ion trap quantum computing

Abstract

The invention discloses an ion addressing system for ion trap quantum computing, and belongs to the technical field of quantum computing. The system comprises a laser unit, an acousto-optic deflector, a focusing and shaping unit, a translation stage and an addressing control module. The laser unit comprises a laser and an optical fiber collimator, the acousto-optic deflector is used for deflecting the laser propagation direction, the focusing and shaping unit is used for expanding and shaping laser and focusing the laser to the ion trap, and the addressing control module is used for controlling the acousto-optic deflector and the translation table according to a response signal of the ion trap to a laser focal spot. Therefore, the laser is accurately focused to a single target ion. According to the ion addressing system provided by the invention, the translation stage and the acousto-optic deflector are combined to deflect the laser, so that the structure of the system is compact, a tedious re-debugging process is avoided, the quality of a laser focal spot is improved, and the addressing range of the system is greatly expanded.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum computing, and particularly relates to an ion addressing system for ion trap quantum computing. Background Art

[0002] In ion trap-based quantum computing, the execution of quantum gates and algorithms often requires the manipulation of multiple qubits. Therefore, an accurate ion addressing system must be constructed. This system forms a focused light spot in the ion trap by regulating a laser beam. When the light spot is aligned with the target ion, the addressing of the ion is achieved.

[0003] However, there are many challenges in the use of the existing addressing systems. For example, they are vulnerable to interference from minute jitters of the platform. Due to the complex system structure, even a minute mechanical jitter may cause the deviation of the laser light spot from the target ion, thereby affecting the manipulation accuracy and even leading to failure. Secondly, the traditional addressing systems are bulky, which not only occupies the experimental space but also easily introduces additional unstable factors, restricting their application in multi-qubit manipulation. In addition, the structure of the existing addressing systems lacks fixity, resulting in unstable performance. For example, during handling, disassembly and assembly, performance fluctuations are likely to occur, affecting the system performance.

[0004] Chinese Patent Invention CN117852663B proposes an ion addressing device that integrally fixes optical elements including a mirror, a beam splitter, a lens group, and an acousto-optic modulator through a rigid housing, thereby ensuring the stability of the system structure and performance during short-distance movement and long-distance handling. However, after the optical elements in the above solution are fixed, the position of the light spot is also fixed and non-adjustable. If different ion chains need to be addressed, the system needs to be reassembled to adjust the light spot position to match different ion chains, which is very inconvenient and requires a large amount of work.

[0005] In summary, the existing technologies have obvious deficiencies in the adjustment convenience and adaptability of the addressing system. There is an urgent need to develop an addressing system that can automatically calibrate and is applicable to non-uniformly arranged ions to improve the practicality and reliability of the quantum computing system. Summary of the Invention

[0006] Based on this, the technical solution provided by the present invention aims to increase the ion addressing range of the ion addressing system and improve its compatibility with different ion addressing through a detection and control method combining an integrated translation stage and an acousto-optic deflector.

[0007] To achieve the above object, the present invention provides an ion addressing system for ion trap quantum computing, which is used to address a single target ion in a one-dimensional ion chain in an ion trap. The ion addressing system includes: a laser unit, including a laser and a fiber collimator, for outputting collimated laser light; an acousto-optic deflector, for deflecting the laser light according to a radio frequency signal; a focusing and shaping unit, for expanding, shaping and focusing the laser light output by the acousto-optic deflector, and outputting a focal spot to the ion trap; a translation stage, for mounting the fiber collimator, the acousto-optic deflector and the focusing and shaping unit, so that the fiber collimator, the acousto-optic deflector and the focusing and shaping unit are integrated as a whole; and an addressing control module, for detecting a response signal of the ion trap to the focal spot, and controlling the acousto-optic deflector and the translation stage according to the response signal, so that the laser light is focused on the single target ion.

[0008] Specifically, the translation stage is provided with movements in at least three dimensions.

[0009] Preferably, the acousto-optic deflector is provided with deflection degrees in at least two vertical directions.

[0010] Specifically, the central wavelength of the laser light output by the laser is 400 - 800 nm. The fiber collimator is used to output a Gaussian beam, and the waist spot size range of the Gaussian beam is 300 -3.5 mm.

[0011] Further, the addressing control module includes a detection unit and a control unit. The detection unit is used to detect the response signal. The control unit is used to control the radio frequency signal of the acousto-optic deflector according to the response signal, so as to control the propagation direction of the laser light output by the acousto-optic deflector.

[0012] Further, the focusing and shaping unit includes a lens group, for performing two-stage beam expansion and aberration correction on the laser light. And a focusing lens, for focusing the laser light on the ion trap to form the focal spot.

[0013] Furthermore, the lens group includes a first-stage beam expansion lens group, a second-stage beam expansion lens group and an aberration correction lens group. The first-stage beam expansion lens group includes a first achromatic lens and a second achromatic lens. The second-stage beam expansion lens group includes a first plano-concave lens and a third achromatic lens. The aberration correction lens group includes a plano-convex lens and a second plano-concave lens. The beam expansion ratio of the lens group to the laser light is set to 2 - 7.

[0014] Specifically, the focusing lens is a flat-field apochromatic objective lens, the working distance of the focusing lens is set to 30 - 40 mm, and the focal length of the focusing lens is set to 15 - 25 mm.

[0015] In particular, the ion addressing system further includes a cage coaxial device for coaxially connecting the fiber collimator, the acousto-optic deflector, and the focusing and shaping unit by hard connection, and the coaxial body is fixedly installed on the translation stage.

[0016] Preferably, the one-dimensional ion chain includes any one of calcium ions, barium ions, and ytterbium ions.

[0017] The beneficial technical effects achieved by the present invention through the above technical solutions are as follows:

[0018] (1) By using an acousto-optic deflector (AOD) to replace the DOE + multi-channel AOM structure, only a single ion is irradiated at the same time, avoiding multi-channel beam splitting, greatly reducing the optical power requirement. The optical power required by the system is about 1 / N (N is the number of ions) of the original scheme, effectively reducing the load of the laser source and energy consumption.

[0019] (2) The AOD has continuous deflection ability and is not limited by the fixed channel spacing. It can individually address ions at any position on the ion chain within the set addressing range (0–140 μm), compatible with the unevenness of the ion chain arrangement. Even if the ion spacing changes due to adjusting the axial trapping frequency, there is no need to redesign the optical system, and the flexibility is significantly enhanced.

[0020] (3) The solution of the present invention is applicable to various different structures such as an integrated blade-type ion trap, a segmented blade ion trap, and a chip-type ion trap, improving the versatility and expandability of the system.

[0021] (4) By using a large-size initial light spot and reducing the beam expansion ratio, under the condition of a certain scanning angle of the acousto-optic deflector, the addressing range is effectively expanded, covering about 140 (corresponding to about 30 ion lengths), exceeding the addressing limit of the traditional multi-channel AOM scheme.

[0022] (5) By using a focusing lens with a long working distance, a short focal length, and a moderate numerical aperture, and selecting a flat-field apochromatic objective lens, spherical aberration and coma are effectively reduced, improving the quality of the focused light spot and the ion addressing accuracy. It is ensured that under a large-range addressing, the light spot still maintains a small size and high contrast.

[0023] (6) Through the design of a long-focal-length fiber collimator and a low beam expansion ratio, the optical path length is greatly shortened, the number of optical elements is reduced, and the overall volume of the system is significantly reduced. After miniaturization, the entire optical system can be installed on a precision displacement stage, further improving the optical path stability, and helping to reduce the influence of environmental interference and vibration on the addressing accuracy.

[0024] (7) A precision translation stage is used to drive the overall optical path to move. Without changing the system structure, precise positioning of the focused spot on the ion chain can be achieved, avoiding the problems of coma and spot distortion caused by the independent movement of some components, and ensuring the stability and high reliability of multi-ion addressing. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of the ion addressing system according to an embodiment of the present invention.

[0026] Figure 2 It is a schematic optical path structure diagram of the beam expander lens group according to an embodiment of the present invention.

[0027] Figure 3 It is a schematic diagram of the working principle of the acousto-optic deflector according to an embodiment of the present invention.

[0028] Figure 4 It is a measured diagram of the focused spot at different deflection angles of the ion addressing system according to an embodiment of the present invention.

[0029] Figure 5 It is a schematic structural diagram of other ion addressing systems according to an embodiment of the present invention.

[0030] Each label in the figure represents: 1. Fiber collimator; 2. Coaxial mirror mount; 3. Acousto-optic deflector; 4. First achromatic lens; 5. Second achromatic lens; 6. First plano-concave lens; 7. Third achromatic lens; 8. Plano-convex lens; 9. Second plano-concave lens; 10. Focusing lens; 11. Target ion; 12. Coaxial connecting rod; 13. First reflector; 14. 45-degree mounting and adjustment bracket; 15. Second reflector; 16. Coaxial gripper; 17. Rigid sleeve; 18. Coaxial mounting plate; 19. Lens group; 20. Translation stage; 21. First actuator; 22. Second actuator; 23. Third actuator; 24. Rigid housing; 25. Polarizing beam splitter prism; 26. Acousto-optic modulator; 27. Positive lens; 28. Beam collector; 29. Third reflector; 30. Fourth reflector; 31. Fiber coupler; 32. Optical fiber; 33. RF signal access terminal; 34. Bragg angle; 35. +1 / -1 order diffracted light; 36. Scanning angle; 37. Normal line. Specific Embodiments

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the specific embodiments of the present invention will be further described in detail below in conjunction with the embodiments. It should be understood that the embodiments described herein are only used to explain the present invention, but not to limit the scope of the present invention.

[0032] Embodiment 1

[0033] In an embodiment of the present invention, the ion addressing system includes a laser unit, an acousto-optic deflector 3, a focusing and shaping unit, a translation stage 20, and an addressing control module. The laser unit includes a laser and an optical fiber collimator 1, and is used to output collimated laser light. The acousto-optic deflector 3 is used to deflect the laser light according to a radio frequency signal. The focusing and shaping unit is used to expand, shape, and focus the laser light output by the acousto-optic deflector 3, and output a focal spot to the ion trap. The translation stage 20 is used to mount the optical fiber collimator 1, the acousto-optic deflector 3, and the focusing and shaping unit. The addressing control module is used to detect a response signal of the ion trap to the focal spot, and control the acousto-optic deflector 3 and the translation stage 20 according to the response signal, so that the laser light is focused on the single target ion 11.

[0034] Please refer to the attached Figure 1 , Figure 1 FIG. is a schematic structural diagram of the ion addressing system according to an embodiment of the present invention. As can be seen from the figure, the ion addressing system includes an optical fiber collimator 1, an acousto-optic deflector 3, a lens group 19, a focusing lens 10, and a translation stage 20. In an embodiment of the present invention, the central wavelength of the laser light output by the laser is 729 nm. In one or other embodiments of the present invention, the central wavelength can be selected between 400 - 800 nm, which is mainly determined according to the response wavelength of the focusing lens 10.

[0035] The optical fiber collimator 1 is used to output a Gaussian beam, and the waist spot size range of the Gaussian beam is 300 -3.5 mm. The larger the diameter of the output spot of the optical fiber collimator, the longer the Rayleigh range. When the diameter of the output laser light is greater than 1.2 mm, the Rayleigh range exceeds the total length of the system, and within this range, the laser beam can be approximately regarded as a parallel beam. In an embodiment of the present invention, the optical fiber collimator 1 of the SKFiber Collimator series 60FC series products with a long focal length is selected to ensure that the waist spot size of the laser light after being processed by the focusing and shaping unit is close to the designed diffraction limit. In one or other embodiments of the present invention, other models of optical fiber collimators 1 that can meet the required waist spot size within 60 cm can be selected. In addition, a telescope system can also be selected to obtain a larger initial waist spot size. Since the selected optical fiber collimator 1 can output a Gaussian beam with a larger waist spot size, the required beam expansion ratio in the focusing and shaping unit is reduced, thereby optimizing the system design.

[0036] Please refer to the attached Figure 2 , Figure 2 FIG. is a schematic optical path structure diagram of the beam expander lens group according to an embodiment of the present invention. In the figure, is the first deflection angle, indicating the maximum deflection of the laser light output by the acousto-optic deflector 3 relative to the optical axis of the system, is the second deflection angle, representing the deflection of the laser corresponding to the first deflection angle relative to the system optical axis when it exits from the beam expander lens group. As can be seen from the figure, in the case of a relatively small first deflection angle, the addressing range of this addressing system can be approximately calculated from geometric optics: ;

[0037] where M is the beam expansion ratio of lens group 19, f is the focal length of focusing lens 10, and R is the addressing range. Thus, it can be seen that under the preconditions of unchanged focusing lens and first deflection angle, the addressing system of the embodiment of the present invention can obtain a larger addressing range by reducing the beam expansion ratio.

[0038] Please refer to the appendix Figure 3 , Figure 3 is a schematic diagram of the working principle of the acousto-optic deflector in the embodiment of the present invention. The acousto-optic deflector 3 is used to deflect the laser output from the fiber collimator 1 according to the radio frequency signal. When the angle between the incident laser and the normal 37 of the incident surface is equal to the Bragg angle 34, if the acousto-optic deflector 3 does not deflect the incident laser, the laser output at this time is called the 0th-order light, and its propagation direction is the same as the incident direction and still forms the Bragg angle 34 with the normal 37. When the laser diffracts in the crystal, by adjusting the incident angle to be equal to the Bragg angle 34, the maximum diffraction efficiency of the +1st-order or -1st-order diffracted light can be achieved. Further, within a certain range, by changing the frequency of the radio frequency signal, the propagation direction and frequency of the diffracted light can be adjusted, thereby realizing the continuous deflection of the laser. The deflection angle range of the +1st-order or -1st-order diffracted light is the scanning angle 36. Thus, the acousto-optic deflector 3 can realize the continuous movement of the laser focal spot in a one-dimensional or two-dimensional plane in the ion trap.

[0039] Preferably, the acousto-optic deflector 3 of the embodiment of the present invention uses the model ISOMET D55-T80S-2, and its scanning angle 36 is about 2.78 degrees when the central wavelength is 729 nm. In one or other embodiments of the present invention, other models of acousto-optic deflectors 3 can also be selected according to whether the central wavelength of the laser conforms to the working wavelength range of the acousto-optic deflector 3 and whether the scanning angle 36 of the acousto-optic deflector 3 meets the system requirements.

[0040] Exemplarily, the acousto-optic deflector 3 of the embodiment of the present invention supports continuous scanning in one direction. In one or other embodiments of the present invention, a biaxial acousto-optic deflector 3 (such as ISOMET DXY110-T50S-9) can be selected. The biaxial acousto-optic deflector 3 of the embodiment of the present invention supports continuous scanning in both perpendicular directions. By injecting a plurality of radio frequency signals symmetric with respect to the central frequency into the two acousto-optic channels respectively, independent addressing of about 20 individual ions in the ion chain of the ion trap can be achieved.

[0041] Exemplarily, the focusing and shaping unit of the embodiment of the present invention includes a lens group 19 and a focusing lens 10. The lens group 19 is used to achieve two-stage beam expansion and correct aberration, and the focusing lens 10 is used to focus the laser into the ion trap to form a focal spot. The beam expansion ratio of the lens group 19 to the laser is set to 2-7. Each lens in the lens group 19 is coaxially arranged with the focusing lens 10. As Figure 1 shown, the lens group 19 includes a primary beam expansion lens group, a secondary beam expansion lens group, and an aberration correction lens group. Among them, the primary beam expansion lens group is composed of a first achromatic lens 4 (Thorlabs AC254-050-AB, with a diameter of 1 inch, a focal length of 50 mm, and coated with an anti-reflection film for 400-1100 nm) and a second achromatic lens 5 (Thorlabs AC254-100-AB, with a diameter of 1 inch, a focal length of 100 mm, and coated with an anti-reflection film for 400-1100 nm), and is used to perform the first beam expansion on the laser output by the acousto-optic deflector 3. The secondary beam expansion lens group is composed of a first plano-concave lens 6 (Thorlabs LC1715-B, with a diameter of 1 inch, a focal length of -50 mm, and coated with an anti-reflection film for 650-1050 nm) and a third achromatic lens 7 (Thorlabs AC254-150-AB, with a diameter of 1 inch, a focal length of 150 mm, and coated with an anti-reflection film for 400-1100 nm), and is used to perform the second beam expansion on the laser. The aberration correction lens group is composed of a plano-convex lens 8 (Thorlabs LA1484-B, with a diameter of 1 inch, a focal length of 300 mm, and coated with an anti-reflection film for 400-1100 nm) and a second plano-concave lens 9 (Thorlabs LC1120-B, with a diameter of 1 inch, a focal length of -100 mm, and coated with an anti-reflection film for 650-1050 nm), and is used to correct the spherical aberration and coma of the laser.

[0042] Exemplarily, a plano-concave lens is selected in the secondary beam expansion lens group to compress the optical path length while achieving effective beam expansion, which is beneficial to the miniaturization of the system. The achromatic lens can not only correct chromatic aberration but also be preferentially selected because of its small spherical aberration. Exemplarily, the beam expansion ratio of the lens group 19 in the addressing system in the embodiment of the present invention is set to 6. In one or other embodiments of the present invention, if the laser waist spot size entering the focusing and shaping unit is large enough, the secondary beam expansion lens group can be omitted, and only the primary beam expansion lens group and the aberration correction lens group are retained. At this time, the beam expansion ratio can be set to 3. This can reduce the length of the optical system and improve the adaptability of the system to the environment. In addition, when selecting lenses, if there are lenses with similar performance, short-focus lenses are preferentially selected to further compress the system size.

[0043] Exemplarily, the focusing lens 10 is used to focus the beam-expanded and shaped laser in the ion trap to form a focal spot, and to achieve precise addressing of a single target ion 11 in the one-dimensional ion chain. The working distance of the focusing lens 10 is set to 30 - 40 mm, and the focal length is set to 15 - 25 mm. To reduce spherical aberration, a short focal length lens with a long working distance and a numerical aperture (N.A.) greater than the N.A. value corresponding to the laser beam should be preferentially selected. In the embodiment of the present invention, the central wavelength of the laser is 729 nm. If it is necessary to focus to a focal spot within 2 or less, at least a focusing lens 10 with a numerical aperture of 0.233 should be selected. This configuration can not only achieve a smaller diffraction limit with a smaller incident pupil laser diameter, but also effectively reduce the spherical aberration of the system, thereby improving the beam quality. An infinity-corrected plan apochromatic objective lens is selected, so that its imaging surface is a plane and is consistent with the arrangement direction of the ion chain, effectively reducing the coma caused by the diffraction angle. The selected model of the focusing lens 10 is: LBTEK PLNAPO10X, its focal length is 20 mm, the working distance is 34 mm, and the working wavelength is 400 - 700 nm. Although the designed working wavelength is in the range of 400 - 700 nm, in experimental verification, it is still applicable to the laser with a central wavelength of 729 nm.

[0044] Exemplarily, the translation stage 20 is installed on the bottom breadboard and is used to fixedly install the fiber collimator 1, the acousto-optic deflector 3, and the focusing and shaping unit, so that the fiber collimator 1, the acousto-optic deflector 3, and the focusing and shaping unit are integrated into a whole. Regarding this whole as the optical system of the ion addressing system, due to the fixed installation of the optical system, the user can adjust the position of the focal spot without changing the optical path structure at all. In the embodiment of the present invention, a mirror post is used in cooperation with a pressing block and screws to achieve a fixed connection between the optical system and the translation stage 20. In one or other embodiments of the present invention, other connection methods that can achieve a stable integration between the optical system and the translation stage 20 are used, including but not limited to gluing, clamping, etc. Exemplarily, in the embodiment of the present invention, a translation stage 20 of model Newport 562-XYZ is adopted. Optionally, a tilt platform is added to the translation stage 20, and the model of the tilt platform can be Newport 562F-TILT or Newport 562F-TILT-LH. The tilt platform can adjust the swing angle of the optical system within a certain range, so that the optical axes of the lens group 19 and the focusing lens 10 are always perpendicular to the ion chain. Thus, the focal spot can be directly focused on the ion chain where the single target ion 11 is located, optimizing the focusing effect of the focal spot in the ion trap.

[0045] In the embodiments of the present invention, three actuators are used to achieve the movement of the translation stage 20 along at least three dimensions. Exemplarily, in the embodiments of the present invention, the first actuator 21, the second actuator 22, and the third actuator 23 are respectively used to control the translation stage 20 to translate along three different directions, and these three different directions are perpendicular to each other pairwise. In this way, the translation stage 20 can be freely moved to any spatial position within the stroke under the control of the actuators. The model of the actuator selected in the embodiments of the present invention is Newport TRB12CC, its driving force is 90N, and the minimum step size is 0.1 , and the typical value of the bidirectional repeatability accuracy is ±0.13 , and the guaranteed value of the bidirectional repeatability accuracy is ±0.75 . The model of the communicator between the actuator and the addressing control system is Newport SMC100CC.

[0046] Exemplarily, to achieve the automatic alignment of the focal spot with a single target ion 11, the ion addressing system in the embodiments of the present invention further includes an addressing control module. The addressing control module includes a detection unit and a control unit, which are used to detect the response signal of the ion trap to the focal spot, and control the acousto-optic deflector 3 and the translation stage 20 according to the response signal, so that the laser is focused on a single target ion 11. In the embodiments of the present invention, the detection process includes using a computer to control the acousto-optic deflector 3 and the translation stage 20 to scan the focal spot within a predetermined spatial range in the ion trap. When the resonance transition of the ion is detected by the response signal during the scan, the detection unit records the response signal and the coordinates of the corresponding focal spot. In the embodiments of the present invention, the response signal includes the Rabi frequency of a single target ion 11. The larger the Rabi frequency, the greater the laser intensity received by the single target ion 11, that is, the higher the spatial coincidence degree between the focal spot and the single target ion 11. After the scan is completed, the coordinates of the focal spot corresponding to the maximum Rabi frequency are selected as the confirmation coordinates for the coincidence of the focal spot and the single target ion 11. The control unit adjusts the propagation direction of the laser output by the acousto-optic deflector 3 and the position of the translation stage 20 controlled by the actuator according to the above-mentioned several confirmation coordinates, so that the focal spot is respectively positioned at the positions of different single target ions 11, realizing high-precision automatic addressing and providing a basis for subsequent quantum operations.

[0047] Since the ions trapped in the ion trap can only be uniformly arranged within a certain range centered on the ion trap, such as within the range of 10 ions. The spacing of the trapped ions beyond this range is in a non-uniform state, and these ions are usually referred to as edge ions. In the prior art, even when the laser focal spot is deflected to the position of the edge ions, usually due to the off-axis effect of the lens group 19, the laser focal spot shows varying degrees of dispersion and deformation, resulting in a decline in the focal spot quality, making it impossible to complete precise ion addressing and limiting the ion addressing range. Exemplarily, in the embodiments of the present invention, the translation stage 20 and the acousto-optic deflector 3 are combined to control the laser deflection and focusing. While improving the focal spot quality of the laser, the addressing range is increased, which can be used for ion chains with non-uniform spacing, significantly enhancing the applicability of the system.

[0048] Exemplarily, the ion addressing system in the embodiments of the present invention further includes a frequency calibration module, which is arranged between the fiber collimator 1 and the laser, and is mainly used to finely adjust the frequency of the laser to ensure that the laser frequencies focused on different target ions 11 are relatively stable, so that the qubits at different spatial positions in the ion trap can all achieve resonance transitions of the laser spectrum.

[0049] Exemplarily, the frequency calibration module includes: a polarization beam splitter prism 25 (PBS), an acousto-optic modulator 26 (AOM), a positive lens 27, a plurality of reflectors, and a beam collector 28. Specifically, the laser first passes through the PBS and enters the AOM, and the AOM divides the laser into diffracted light and 0th-order light. Among them, the 0th-order light is collected by the beam collector 28 to avoid leakage and cause dangerous accidents. The diffracted light exits the AOM and passes through a positive lens 27. The focal point of this positive lens 27 is near the center of the AOM, allowing for a slight deviation. After passing through this positive lens 27, the diffracted light is reflected by the third mirror 29. Since the focal point of this positive lens 27 is aligned with the center of the AOM, the reflected diffracted light returns along the original incident path. The returned beam is reflected by the PBS and the fourth mirror 30 and then enters the fiber coupler 31. In one or other embodiments of the present invention, to improve the efficiency of the fiber coupler 31, a half-wave plate can be arranged between the PBS and the AOM, which is used to continuously adjust the frequency of the laser while not changing the direction of the laser incident on the fiber collimator 1. Through the synergistic effect of the acousto-optic deflector 3 and the AOM, the dynamic adjustment of the laser focal spot frequency focused on a single target ion 11 can be achieved, thereby realizing the frequency matching and resonance excitation of the qubits at different spatial positions.

[0050] Please refer to the attached Figure 4 , Figure 4 which is the measured diagram of the focused light spots of the ion addressing system in the embodiments of the present invention at different deflection angles. Figure 4 Figure (a) shows the measured diagram of the laser focal spot in the ion trap magnified 20 times when the deflection angle is 0 degree. Figure 4(b) shows the measured image of the laser focal spot in the ion trap magnified 20 times when the maximum deflection angle is 1.39 degrees. When the deflection angle is 0, the transverse diameter of the focal spot is 56 , and the longitudinal diameter is 57 . When the deflection angle is 1.39 degrees, the transverse diameter of the focal spot is 55 , and the longitudinal diameter is 53 . Theoretically, Figure 4 (a) shows the measured image of the focal spot with the optimal focusing quality in the embodiment of the present invention, Figure 4 (b) shows the measured image of the focal spot with the worst focusing quality in the embodiment of the present invention. When the laser deflection angle reaches the maximum, the corresponding focal spot quality is the worst during the entire deflection process, and when the laser has no deflection, the corresponding focal spot quality is the best. From Figure 4 (a) and Figure 4 (b), it can be seen that even under the condition of the maximum deflection angle, the focal spot size only changes slightly, and the change range of the longitudinal diameter is slightly larger than that of the transverse diameter, and the overall focal spot quality remains good, thus ensuring the stability and reliability of the ion addressing system during wide-range deflection operations.

[0051] In the embodiment of the present invention, the target ion 11 is calcium ion. In one or other embodiments of the present invention, the target ion 11 can also be any one of barium ion and ytterbium ion.

[0052] Exemplarily, in the embodiment of the present invention, by selecting a suitable fiber collimator 1, and cooperating with an acousto-optic deflector 3 with a large working wavelength range and a wide enough scanning angle 36, and still selecting the foregoing parameter configurations for each lens of the lens unit, high-quality and strong focusing of the laser with the central wavelength in the range of 400 nm to 700 nm can be achieved without changing the relative positions of the acousto-optic deflector 3 and the lens unit. In this wavelength range, the focal spot size is mainly affected by the laser wavelength. The longer the laser wavelength, the larger the focal spot size after focusing. Specifically, the laser with a wavelength of 405 nm can obtain a focal spot with a diameter of about 1 . The laser with a wavelength of 729 nm can obtain a focal spot with a diameter of about 2.3 .

[0053] Embodiment 2

[0054] On the basis of Embodiment 1 of the present invention, the ion addressing system of Embodiment 2 of the present invention further includes a cage coaxial device and a rigid housing 24. Please refer to the appendix Figure 5 , Figure 5It is a schematic structural diagram of other ion addressing system according to an embodiment of the present invention. As can be seen from the figure, the cage-type coaxial device includes a coaxial connecting rod 12, a coaxial holder 16 and a coaxial mounting plate 18, which are used to form a coaxial body by hard connection of the fiber collimator 1, the acousto-optic deflector 3 and the focusing and shaping unit, and mount the coaxial body on the translation stage 20. The coaxial holder 16 is used to fix the position of the acousto-optic deflector 3. One end of the four rigid coaxial connecting rods 12 of the coaxial holder 16 is connected to the 45-degree mounting and adjusting bracket 14 for mounting the mirror, and the other end is connected to the coaxial mounting plate 18 of the lens group 19. Exemplarily, in the embodiment of the present invention, the coaxial holder 16 of model LBTEK CRVP1 is adopted.

[0055] Exemplarily, the rigid housing 24 is used to cover the entire optical system and the translation stage 20 to reduce the temperature fluctuation caused by the air flow between the system and the outside. On the side close to the target ion 11, the rigid housing 24 is provided with an opening, the diameter of which is slightly larger than the aperture of the focusing lens 10, to allow the focusing lens 10 to extend out, facilitating the focusing lens 10 to enter the inverted view window of the ion trap platform vacuum chamber. Preferably, the inside of the rigid housing 24 can be covered with heat-insulating material and equipped with a temperature control module to keep the temperature of the system stable, further avoiding the shift of the focal spot position caused by the change of the system operating temperature, thereby improving the system stability. In the embodiment of the present invention, the lenses of the lens group 19 are fixed by using the rigid sleeve 17 in combination with the coaxial mounting plate 18. In one or other embodiments of the present invention, the lens is fixed in the rigid sleeve 17 by using optical adhesive.

[0056] In the embodiment of the present invention, after the laser exits from the fiber collimator 1 and before entering the acousto-optic deflector 3, a mirror is provided to further reduce the system size. Exemplarily, the mirrors in the embodiment of the present invention include a first mirror 13 and a second mirror 15, which are used to deflect the propagation path of the laser to shorten the overall size of the system, and at the same time finely adjust the incident angle of the laser so that the laser reaches the Bragg angle 34 when entering the acousto-optic deflector 3, thereby improving the laser diffraction efficiency. In one or other embodiments of the present invention, the number of mirrors can be appropriately increased or decreased according to the design requirements of the ion addressing system. In the embodiment of the present invention, the central wavelength of the laser is 729 nm, and the coating of the mirror between the fiber collimator 1 and the acousto-optic deflector 3 is a 729 nm high-reflection film. In one or other embodiments of the present invention, when the central wavelength of the laser is other values within the range of 400 - 800 nm, the coating layer parameters of the mirror can be adjusted accordingly to match the central wavelength of the laser used. Preferably, in the embodiment of the present invention, both the first mirror 13 and the second mirror 15 are mounted on the 45-degree mounting and adjusting bracket 14, so that the laser light path remains basically parallel before and after passing through the two mirrors, but the emission directions are opposite.

[0057] Exemplarily, in the embodiment of the present invention, the distance from the acousto-optic deflector 3 to a single target ion 11 is approximately 30 cm, and the addressing range of the ion addressing system is approximately 232 , which is equivalent to the ion chain length containing 51 ions. In one or other embodiments of the present invention, by setting the beam expansion ratio of the lens group 19 for the laser to 3, the addressing range of the ion addressing system can be further extended to more than 300 .

[0058] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. An ion addressing system for ion trap quantum computing, used for addressing a single target ion in a one-dimensional ion chain in an ion trap, characterized in that: The ion addressing system comprises: A laser unit, including a laser and a fiber collimator, for outputting collimated laser light; an acousto-optic deflector for deflecting the laser according to a radio frequency signal; A focusing and shaping unit, used for expanding, shaping and focusing the laser output by the acousto-optic deflector, and outputting a focal spot to the ion trap; a translation stage, used for installing the fiber collimator, the acousto-optic deflector and the focus shaping unit, so that the fiber collimator, the acousto-optic deflector and the focus shaping unit are integrated into one; and An addressing control module is used to detect a response signal of the ion trap to the focal spot, and control the acousto-optic deflector and the translation stage according to the response signal, so as to focus the laser on the single target ion.

2. The ion addressing system according to claim 1, characterized in that: The translation stage is configured to move in at least three dimensions.

3. The ion addressing system according to claim 1, characterized in that: The acousto-optic deflector is provided with at least two deflection degrees in perpendicular directions.

4. The ion addressing system according to claim 1, characterized in that: The central wavelength of the laser output by the laser is 400-800nm; the optical fiber collimator is used to output a Gaussian beam, and the waist size of the Gaussian beam ranges from 300 -3.5mm.

5. The ion addressing system according to claim 1, characterized in that: The addressing control module includes a detection unit and a control unit; The detection unit is used to detect the response signal; The control unit is used to control the radio frequency signal of the acousto-optic deflector according to the response signal, so as to control the propagation direction of the laser output by the acousto-optic deflector.

6. The ion addressing system according to claim 1, characterized in that: The focus shaping unit comprises A lens group, used for performing two-stage beam expansion and aberration correction on the laser; and A focusing lens is used to focus the laser onto the ion trap to form the focal spot.

7. The ion addressing system according to claim 6, characterized in that: The lens group includes a primary beam expansion lens group, a secondary beam expansion lens group and an aberration correction lens group. The primary beam expansion lens group includes a first achromatic lens and a second achromatic lens; The secondary beam expansion lens group includes a first plano-concave lens and a third achromatic lens; The aberration correction lens group includes a plano-convex lens and a second plano-concave lens; The beam expansion ratio of the lens group to the laser is set to 2-7.

8. The ion addressing system according to claim 6, characterized in that: The focusing lens is a plan apochromatic objective lens, the working distance of the focusing lens is set to 30-40 mm, and the focal length of the focusing lens is set to 15-25 mm.

9. The ion addressing system according to claim 1, characterized in that: The ion addressing system further comprises a cage-type coaxial device for forming a coaxial body by hard-connecting the optical fiber collimator, the acousto-optic deflector and the focusing shaping unit, and the coaxial body is fixedly mounted on the translation stage.

10. The ion addressing system according to claim 1, characterized in that: The one-dimensional ion chain includes any one of calcium ions, barium ions and ytterbium ions.

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