Cooling method of multi-ion crystal

Abstract

The invention provides a cooling method of a multi-ion crystal. The method comprises the following steps: selecting a preset number of ions at preset positions from the multi-ion crystal as auxiliary cooling ions; only the selected auxiliary cooling ion combination is cooled through cooling laser irradiation, and cooling of all ion crystals is completed. According to the technical scheme provided by the invention, the cooling effect which is high in cooling speed and close to the global cooling limit can be obtained by only using one beam or a few beams of cooling light and cooling ions which are less than 30% of the whole ionic crystal.

Description

Technical Field

[0001] This article involves but is not limited to ion cooling, ion cooperative cooling, ion quantum computing, involves but is not limited to a cooling method for multi-ion crystals, and in particular involves but is not limited to an optimization method based on the collective motion mode of ions to select the best ion combination for cooperative cooling. Background Art

[0002] With the development of ion quantum computing, the depth of quantum circuits is getting deeper and deeper, and the evolution time of quantum computing sequences is getting longer and longer. The ion crystals used for quantum computing will be affected by the heating rate caused by factors such as background gas, stray electromagnetic fields or background radiation during the calculation process. The ion crystals that were originally cooled to near the ground state or Doppler cooling limit will gradually thermalize, resulting in quantum bit decoherence and a significant decrease in the fidelity of quantum computing gate operations, which ultimately severely limits the scale of ion quantum computing.

[0003] To solve this problem, cooperative cooling in ion crystals is an effective method. Since direct cooling will destroy the quantum state of the quantum bits in the computing state, it is impossible to directly cool these bits during quantum computing. By performing direct cooling on specific auxiliary cooling ions, with the help of the interaction between ions, the entire ion crystal can be heated and cooled during the quantum computing operation. Therefore, cooperative cooling technology is of great value for large-scale ion trap quantum computing.

[0004] In the public technology, people have used different types of elements to cool one ion in a small-scale (2 to 4 ions) one-dimensional ion chain and verified its effectiveness. This technology only cools one ion and does not have universal significance in large-scale ion crystal cooling.

[0005] In a larger one-dimensional ion chain, people have proposed two methods of selecting auxiliary cooling ions, namely "edge cooling" and "periodic node cooling", from theoretical calculations, and have theoretically simulated them in an ion chain of 121 ions, see reference 1: Lin GD, Duan L M. Sympathetic cooling in a large ion crystal [J]. Quantum information processing, 2016, 15 (12): 5299-5313. However, the "edge cooling method" requires a large number of ions to be used as auxiliary ions for collaborative cooling (about half of the ions), while the "periodic node cooling method" requires multiple laser beams focused on a single ion (for a one-dimensional ion chain of 121 ions, 13 laser beams are required) to achieve a cooling effect close to that of global cooling that irradiates all ions. This does not have advantages in terms of ion quantum bit utilization and optical complexity and is difficult to implement.

[0006] The collaborative cooling scheme for long one-dimensional ion chains formed under axial secondary potential wells was verified theoretically and experimentally in Reference 2: Mao ZC, Xu YZ, Mei QX, et al. Experimental Realization of Multi-ion Sympathetic Cooling on a Trapped Ion Crystal [J]. Physical Review Letters, 2021, 127(14): 143201. However, there is no further discussion on this scheme for cases where the ions are more uniform, the axial potential well is more complex, and for two-dimensional and three-dimensional ionic crystals. This scheme proposed for the first time that there is a connection between collective vibration modes and the optimal ions for collaborative cooling. However, in the selection based on collective motion modes, this scheme only considers the relationship between the cooling limit and the coverage of the assisted cooled ions on the collective modes, without considering the correlation between the relaxation time and the collective modes. In actual operation, this scheme has a defect, that is, the ion pairs selected based on the coverage of the collective vibration modes do not have the optimal cooling limit.

[0007] In summary, it is an unresolved problem to find a universal optimization method in large-scale ionic crystals, select a small number of ions, and use a simple optical path to achieve a collaborative cooling solution that is close to the global cooling rate and cooling limit. Summary of the invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] In order to implement efficient cooperative cooling in large-scale ionic crystals composed of the same or different ions from one to three dimensions, this paper provides a scheme for selecting auxiliary cooling ions based on the collective motion mode of ions. For an ionic crystal containing N ions, the collective motion mode in the x, y, and z coordinate directions in three-dimensional space can be calculated, by checking the coverage of all collective modes by the n auxiliary cooling ions in the ionic crystal in the direction to be cooled, and checking the cooling limit of the n auxiliary cooling ions on the entire ionic crystal. And select the best combination. In this way, a combination of auxiliary cooling ions with both excellent cooling speed and cooling limit is obtained.

[0010] A method for cooling a polyionic crystal, comprising:

[0011] Selecting a preset number of ions and preset positions in a multi-ion crystal as auxiliary cooling ions; cooling only the selected auxiliary cooling ion combination using cooling laser irradiation to achieve the effect of cooling the entire ion crystal;

[0012] Selecting a preset number and preset positions of ions as auxiliary cooling ions includes: based on the occupation number of ions in the multi-ion crystal in the collective motion mode, selecting an ion combination whose cooling rate and cooling limit meet certain standards; the calculation of the collective motion mode is based on the potential field of the multi-ion crystal, and the potential field can be the result of theoretical simulation or the result obtained by fitting the position of each ion.

[0013] The selection criteria of the cooling limit are: the ratio of the cooling limit of the auxiliary cooling ion combination to the global cooling limit is (1 to 10):1; in one embodiment provided in the present application, the ratio of the cooling limit of the auxiliary cooling ion combination to the global cooling limit is (1 to 2):1; the cooling limit ratio is the amplitude or temperature under the cooling limit, the lower the temperature, the better the cooling effect, and the closer the amplitude is to the amplitude under global cooling, the better.

[0014] The selection criteria of the cooling rate are as follows: the occupation number of the auxiliary cooling ion combination is normalized, and a set of auxiliary cooling ion combinations with characteristic index not less than 50% is selected, and the characteristic index is selected from any one of the minimum value, variance and standard deviation.

[0015] In one embodiment provided in the present application, the cooling method of the polyion crystal includes:

[0016] Firstly, an auxiliary cooling ion combination that meets the selection criteria of the cooling limit is selected, and then an auxiliary cooling ion combination that meets the selection criteria of the cooling rate is selected from the auxiliary cooling ion combinations that meet the selection criteria of the cooling limit;

[0017] Alternatively, an auxiliary cooling ion combination that meets the selection criteria of the cooling rate is first selected, and then an auxiliary cooling ion combination that meets the selection criteria of the cooling limit is selected from the auxiliary cooling ion combinations that meet the selection criteria of the cooling rate.

[0018] In one embodiment provided in the present application, the cooling method of the polyion crystal includes:

[0019] Selecting a preset number of ions and a preset position of ions in a multi-ion crystal as auxiliary cooling ions;

[0020] Set a set of auxiliary cooling ion combinations including n ions {S i,n}, where i represents the i-th selected auxiliary cooling ion combination.

[0021] Select a combination S from the set of auxiliary cooling ion combinations i,n , the occupation number set defined in reference 2: Mao ZC, Xu YZ, Mei QX, et al. Experimental Realization of Multi-ion Sympathetic Cooling on a Trapped Ion Crystal[J]. Physical Review Letters, 2021, 127(14): 143201 is calculated. Where m represents the mth collective vibration mode; select each occupation number set The minimum value in Standard Deviation or variance value Any one of the following is a characteristic indicator Traverse the set of auxiliary cooling ion combinations {S i,n}, get the feature index set The characteristic index set Perform linear normalization to obtain parameters with values ​​between 0 and 1 A collection of .

[0022] Select A collection of auxiliary cooling ion combinations; Optionally, select A collection of auxiliary cooling ion combinations; In one embodiment provided in the present application, select A collection of auxiliary cooling ion combinations;

[0023] Calculate the amplitude {δz of the cooling limit of each ion under global cooling i,Gc}, select the set of auxiliary cooling ion combinations in turn {S i,n}, the calculation is for each group of auxiliary cooling ions in the ionic crystal during cooperative cooling {δz i,SC}, and then use the ratio of the two {δz i，SC / δz i，GC The average amplitude ratio is obtained by averaging The calculation method is the method in reference 2: Mao ZC, Xu YZ, Mei QX, et al. Experimental Realization of Multi-ion Sympathetic Cooling on a Trapped Ion Crystal [J]. Physical Review Letters, 2021, 127(14): 143201.

[0024] Select the average amplitude ratio The auxiliary cooling ion combination closest to 1 or less than a certain threshold value is used for cooling only the selected auxiliary cooling ion combination by cooling laser irradiation to complete the cooling of the entire ion crystal; optionally, the auxiliary cooling ion combination is selected A collection of auxiliary cooling ion combinations; preferably, A collection of auxiliary cooling ion combinations; preferably, A collection of auxiliary cooling ion combinations

[0025] The cooling limit includes: the temperature of each ion, or the amplitude of each ion near the equilibrium position, or the average number of phonons of each ion.

[0026] In one embodiment provided in the present application, the average ratio is selected The auxiliary cooling ion combinations below a certain threshold are:

[0027] Select A collection of auxiliary cooling ion combinations;

[0028] Preferably, select A collection of auxiliary cooling ion combinations;

[0029] Preferably, choose A collection of auxiliary cooling ion combinations.

[0030] In one embodiment provided in the present application, the cooling laser is used to perform any one of Doppler cooling, electromagnetically induced transparent cooling, sideband cooling and polarization gradient cooling, or a combination thereof.

[0031] In one embodiment provided in the present application, the number n of ions in the auxiliary cooling ion combination is no greater than 30% of the total number of ions in the ion crystal.

[0032] In one embodiment provided in the present application, the multi-ion crystal includes any one of a one-dimensional, two-dimensional or three-dimensional ionic crystal; the potential field of the ionic crystal can be the result of theoretical simulation or can be fitted according to the position of each ion.

[0033] In one embodiment provided in the present application, the multi-ion crystal includes any one of a two-dimensional or three-dimensional ionic crystal.

[0034] In one embodiment provided in the present application, the multi-ion crystal is composed of ions of the same type.

[0035] In one embodiment provided in the present application, the multi-ion crystal is composed of different types of ions.

[0036] In one embodiment provided in the present application, the ion types of the multi-ion crystal include any one or a combination of ions of different element types, ions of different isotopes of the same element, molecular ions of the same type, or molecular ions of different types.

[0037] On the other hand, the present application provides an ion trap quantum computing device, which includes an ion cooling device, and the ion cooling device is configured to use the above-mentioned cooling method of the ion crystal for cooling.

[0038] The purpose of cooling the entire ion crystal or suppressing background heating can be achieved by using cooling lasers to cool these ion combinations cooperatively. By further optimizing the number and topological characteristics of the auxiliary cooling ion combinations n, a cooling effect with fast cooling speed and close to the global cooling limit can be obtained by cooling the auxiliary cooling ion combinations that are less than 30% of the entire ion crystal with only one or a few cooling beams of light.

[0039] For two-dimensional or three-dimensional crystals, the existing technology conventionally uses computational methods or extremely complex simulation dynamics. The method provided in this article can be used to quickly screen ionic crystal combinations that can achieve a cooling effect that is fast and close to the global cooling limit.

[0040] Other features and advantages of the present application will be described in the following description, and partly become apparent from the description, or be understood by implementing the present application. Other advantages of the present application can be invented and obtained by the schemes described in the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The accompanying drawings are used to provide an understanding of the technical solution of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present application and do not constitute a limitation on the technical solution of the present application.

[0042] Figure 1 A flowchart of the technical solution of this application;

[0043] Figure 2 is the normalized value when cooling n=2 auxiliary cooling ions at different positions in the one-dimensional ion chain under the condition of quadratic simple harmonic potential in Example 1 With normalization

[0044] Figure 3 The normalized values ​​of 53 ion combinations calculated in the two-dimensional ionic crystal in Example 2 are And among the 53 ion combinations {1 / μ a} min , calculate the cooling limits perpendicular to the ionic crystal plane for 53 ion combinations Statistical chart of .

[0045] Figure 4 This is a schematic diagram of the ion combination (60, 63, 69) of combination number 2 in Example 2.

[0046] Figure 5 This is a schematic diagram of the ion combination (41, 43, 50) of combination number 21 in Example 2.

[0047] Figure 6 This is a schematic diagram of the ion combination (40, 47, 49) of combination number 22 in Example 2.

[0048] Figure 7 This is a schematic diagram of the ion combination (21, 27, 30) of combination number 40 in Example 2. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the present application more clear, the embodiments of the present application are described in detail below. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other arbitrarily without conflict.

[0050] The present application provides a method for cooling a multi-ion crystal, and the method for cooling a multi-ion crystal includes:

[0051] Selecting a preset number of ions and preset positions in the multi-ion crystal as auxiliary cooling ions; cooling only the selected auxiliary cooling ion combination using cooling laser irradiation to complete the cooling of the entire ion crystal;

[0052] Selecting a preset number and preset positions of ions as auxiliary cooling ions includes: based on the occupation number of ions in the multi-ion crystal in the collective motion mode, selecting an ion combination whose cooling rate and cooling limit meet certain standards; the calculation of the collective motion mode is based on the potential field of the multi-ion crystal, and the potential field can be the result of theoretical simulation or the result obtained by fitting the position of each ion.

[0053] The selection criteria of the cooling limit are: the ratio of the cooling limit of the cooling ion combination to the global cooling limit is (1 to 10):1; exemplarily, the ratio of the cooling limit of the cooling ion combination to the global cooling limit is (1 to 2):1; the cooling limit ratio is the amplitude or temperature under the cooling limit, the lower the temperature, the better the cooling effect, and the closer the amplitude is to the amplitude under global cooling, the better.

[0054] The selection criterion of the cooling rate is: the occupation number of the cooling ion combination is combined with each occupation number in a linear normalization process, and a set of auxiliary cooling ion combinations not less than 0.5 is selected.

[0055] Exemplarily, the cooling ion combination can be any ion combination above a threshold value; it can also be an ion combination selected by further calculating the cooling limit of the entire ionic crystal for each of these cooling ion combinations; it can also be an ion combination with the best cooling limit tested through actual experiments.

[0056] The selection criteria of the cooling rate are as follows: the occupation number of the auxiliary cooling ion combination is normalized, and a set of auxiliary cooling ion combinations with characteristic index not less than 50% is selected, and the characteristic index is selected from any one of the minimum value, variance and standard deviation.

[0057] Exemplarily, the cooling method of the polyion crystal includes:

[0058] Firstly, an auxiliary cooling ion combination that meets the selection criteria of the cooling limit is selected, and then a cooling ion combination that meets the selection criteria of the cooling rate is selected from the auxiliary cooling ion combinations that meet the selection criteria of the cooling limit;

[0059] Alternatively, an auxiliary cooling ion combination that meets the selection criteria of the cooling rate is first selected, and then an auxiliary cooling ion combination that meets the selection criteria of the cooling limit is selected from the auxiliary cooling ion combinations that meet the selection criteria of the cooling rate.

[0060] Exemplarily, the cooling method of the polyion crystal includes:

[0061] Selecting a preset number of ions and a preset position of ions in a multi-ion crystal as auxiliary cooling ions;

[0062] Set a set of auxiliary cooling ion combinations including n ions {S i,n}, where i represents the i-th selected auxiliary cooling ion combination;

[0063] Select a combination S from the set of auxiliary cooling ion combinations i,n , calculated and obtained from reference 2: Mao ZC, Xu YZ, Mei QX, et al. Experimental Realization of Multi-ion Sympathetic Cooling on a Trapped Ion Crystal[J]. Physical Review Letters, 2021, or variance value Any one of the following is a characteristic indicator Traverse the set of auxiliary cooling ion combinations {S i，n}, get the feature index set The characteristic index set Perform linear normalization to obtain parameters with values ​​between 0 and 1 A collection of .

[0064] Select A collection of auxiliary cooling ion combinations; illustratively, selecting A collection of auxiliary cooling ion combinations; In one embodiment provided in the present application, select A collection of auxiliary cooling ion combinations;

[0065] Calculate the amplitude {δz of the cooling limit of each ion under global cooling i,Gc}, select the set of auxiliary cooling ion combinations in turn {S i,n}, which is the cooling limit {δz i,SC}, and then use the ratio of the two {δz i,SC / δz i,GC The average amplitude ratio is obtained by averaging The calculation method is the method in reference 2: Mao ZC, Xu YZ, Mei QX, et al. Experimental Realization of Multi-ion Sympathetic Cooling on a Trapped Ion Crystal [J]. Physical Review Letters, 2021, 127(14): 143201.

[0066] Select the average amplitude ratio The auxiliary cooling ion combination that is closest to 1 or less than a certain threshold value is cooled only by cooling laser irradiation to complete the cooling of all ion crystals;

[0067] The cooling limit includes: the temperature of each ion, or the amplitude of each ion near the equilibrium position, or the average number of phonons of each ion.

[0068] For example, the average ratio is selected The auxiliary cooling ion combinations below a certain threshold are:

[0069] Select A collection of auxiliary cooling ion combinations;

[0070] Preferably, select A collection of auxiliary cooling ion combinations;

[0071] Preferably, choose A collection of auxiliary cooling ion combinations;

[0072] Exemplarily, the cooling laser is a cooling laser used to perform any one of Doppler cooling, electromagnetically induced transparent cooling, sideband cooling and polarization gradient cooling, or a combination thereof.

[0073] Exemplarily, the number n of ions in the auxiliary cooling ion combination is no greater than 30% of the total number of ions in the ion crystal.

[0074] Exemplarily, the multi-ion crystal includes any one of a one-dimensional, two-dimensional or three-dimensional ion crystal; the potential field of the ion crystal may be a result of theoretical simulation or may be obtained by fitting according to the position of each ion.

[0075] Illustratively, the multi-ion crystal includes any one of a two-dimensional or three-dimensional ionic crystal.

[0076] Exemplarily, the multi-ion crystal is composed of ions of the same type.

[0077] Exemplarily, the multi-ion crystal is composed of different types of ions.

[0078] Exemplarily, the ion types of the multi-ion crystal include any one or a combination of ions of different element types, ions of different isotopes of the same element, molecular ions of the same type, or molecular ions of different types.

[0079] An ion trap quantum computing device is also provided in an embodiment of the present application. The ion trap quantum computing device includes an ion cooling device, and the ion cooling device is configured to use the above-mentioned ion crystal cooling method for cooling.

[0080] Example 1

[0081] This example selects 121 171 Yb + The one-dimensional ion chain composed of ions has a trap frequency {ω x ,ω y ,ω z}=2π×{5,5.5,0.05}MHz, and select two consecutive ions as auxiliary cooling ions, that is, n=2. Select the damping coefficient of cooling light γ 0 =13.425kNz, background heating coupling coefficient γ bg =0.167mHz, cooling limit T D =3mK, background temperature T bg =300K (the technical solution provided in this article can be used not only in this case, but any multi-ion crystal can use the collaborative cooling method provided in this article).

[0082] The occupation number set defined in reference 2: Mao ZC, Xu YZ, Mei QX, et al. Experimental Realization of Multi-ion Sympathetic Cooling on a Trapped Ion Crystal[J]. Physical Review Letters, 2021, 127(14): 143201. Select each set of occupancy numbers The minimum value in As a characteristic indicator, we get a characteristic indicator set And it is linearly normalized to obtain a parameter with a value between 0 and 1 A collection of .

[0083] The threshold is 0.8, that is The ion pairs are {(48, 49), (50, 51), (55, 56), (66, 67), (71, 72), (73, 74)}.

[0084] like Figure 2 As shown, The ion pairs {(48, 49), (50, 51), (55, 56), (66, 67), (71, 72), (73, 74)} were further screened. Figure 2It can be seen that there is a dotted line at 0.8, and the The six endpoints of the curve represent ion pairs (48, 49), (50, 51), (55, 56), (66, 67), (71, 72), and (73, 74) from left to right.

[0085] Calculate the amplitude {δz of the cooling limit of each ion under global cooling i,GC}, select the set of auxiliary cooling ion combinations in turn {S i,n}, wherein the calculation includes calculating the cooling limit amplitude {δz i,SC}, and then use the ratio of the two {δz i,SC / δz i,GC The average amplitude ratio is obtained by averaging The calculation method is detailed in reference 2: Mao ZC, Xu YZ, Mei QX, et al. Experimental Realization of Multi-ion Sympathetic Cooling on a Trapped Ion Crystal[J]. Physical Review Letters, 2021, 127(14): 143201.

[0086] Select the average amplitude ratio The auxiliary cooling ion combination closest to 1 is cooled only by cooling laser irradiation on the selected auxiliary cooling ion combination to complete the cooling of the entire ion crystal.

[0087] Figure 2 As shown, There are 6 groups with a value greater than 0.8. The cooling limit of the above combination is are not consistent, their average amplitude ratio (The closer to 1, the better the cooling limit effect) are approximately { 1.0599 , 1.0684, 1.1486, 1.1486, 1.0684, 1.0599 This indicates that the two groups of symmetrical sites (48, 49) and (73, 74) have cooling rates above a certain threshold and also have good cooling limits (i.e. Figure 2 Six of them are above the dotted line at 0.8 The six endpoints of the curve, the first and sixth points from left to right). This is different from simply choosing the best The combination of (55, 56) or (66, 67) values ​​is obtained, and its cooling limit effect is improved by about 7.72%.

[0088] verify:

[0089] Using formula S1 in reference 2: Mao ZC, Xu YZ, Mei QX, et al. Experimental Realization of Multi-ion Sympathetic Cooling on a Trapped Ion Crystal [J]. Physical Review Letters, 2021, 127(14): 143201, we get λα,

[0090] The λ α Written in plural form λ α =μ α +iw α , take the real part as μ α The inverse of μ is the μ of different auxiliary cooling ion combinations. α The set of reciprocals of is denoted as {1 / μ α}, select {1 / μ α The auxiliary cooling ion combination represented by the minimum value in} is used as the auxiliary cooling ion combination in the multi-ion crystal;

[0091] That is, after calculation, (48, 49) and (73, 74) are selected for cooling, and 121 171 Yb + The one-dimensional ion chain composed of ions is cooled as a whole. The conclusion is the same as that of Example 1.

[0092] Figure 2 The calculation was performed under the condition of quadratic harmonic potential in the axial potential well of the ion chain, when cooling n = 2 auxiliary cooling ions at different positions, and the minimum value was normalized to obtain {1 / μ α} min (In order to more intuitively reflect {1 / μ α} min and The changing trend of {1 / μ α} min Normalization is performed or not, and {1 / μ α} min With normalization

[0093] Example 2

[0094] This embodiment selects a two-dimensional multi-ion crystal. Different from the one-dimensional case, for the convenience of discussion, it is assumed that the binding in the x direction is the strongest and the ion plane is in the yz plane, that is, the trap frequency ω x >ω y >ω z , in this case the motion in the x direction is independent of the y and z directions, but the motions in the y and z directions are coupled to each other. Assume that in an ionic crystal with 91 ions, (ω x ,ω y ,ω z )=(3,1,0.5)×2π×MHz.

[0095] At the same time, the cooperative cooling light is set to a narrow spot with a radius of 2μm that can illuminate three adjacent ions. After traversing all combinations, a total of 53 groups of ion combinations that can be illuminated by the spot can be obtained. That is, for all the combinations of 3 ions selected from 91 ions, C(91,3) = 121485 combinations, check one by one whether the three ions in each combination can be covered by the spot with a radius of 2μm. There are 53 groups of ion combinations that meet the requirements.

[0096] As in Example 1, the characteristic indices of 53 groups of ions were calculated respectively. Normalized result of the collection The smallest 1 / μ among 53 groups of ions α , that is {1 / μ a} min and each of the 53 groups of ions

[0097] like Figure 2 As shown, the threshold can be determined There are 4 ion pairs, from left to right, they are 2, 21, 22, 40. The cooling rates of the above four ion combinations meet the conditions. Due to complete symmetry, they have exactly the same cooling rate and cooling limit. The value closest to 1 is 1.0443. That is, the combination numbers 2, 21, 22, 40 (such as Figures 4 to 7 ) is the best ion combination for collaborative cooling. Combination No. 2 ( Figure 4 ) The corresponding selected ion combination is numbered {60,63,69}; combination number 21 ( Figure 5 ) The corresponding selected ion combination is numbered {41,43,50}; combination number 22 ( Figure 6 ) The corresponding selected ion combination is numbered {40,47,49}; combination number 40 ( Figure 7 )The corresponding selected ion combination is numbered {21,27,30}.

[0098] verify:

[0099] like Figure 3 As shown, we can also see that the normalized {1 / μ a}(Right now Figure 3 The dots in the It is completely similar to the one-dimensional solution of Example 1. It can be seen that It can effectively screen out ion combinations that meet the cooling rate, and then select based on the cooling limit The ion combination closest to 1, normalized {1 / μ a} also fully meets the requirements For the ion combination closest to 1, the two different methods reached the same conclusion.

[0100] Therefore, the applicant believes that the method provided in this application can effectively select auxiliary cooling ion combinations for cooperative cooling of ion crystals based on matrix motion modes, which is of great value for large-scale ion trap quantum computing.

Claims

1. A method for cooling a polyionic crystal, characterized in that: The cooling method of the multi-ion crystal comprises: Selecting a preset number of ions and preset positions in a multi-ion crystal as auxiliary cooling ions; cooling only the selected auxiliary cooling ion combination using cooling laser irradiation to achieve the effect of cooling the entire ion crystal; Selecting a preset number and a preset position of ions as auxiliary cooling ions includes: selecting an ion combination that meets certain standards of cooling speed and cooling limit based on the occupation number of ions in the collective motion mode in the multi-ion crystal; The selection criteria of the cooling limit are: the ratio of the cooling limit of the auxiliary cooling ion combination to the global cooling limit is (1 to 10):1; optionally, the ratio of the cooling limit of the auxiliary cooling ion combination to the global cooling limit is (1 to 2):1; The selection criteria of the cooling rate are as follows: the occupation number of the auxiliary cooling ion combination is normalized, and a set of auxiliary cooling ion combinations with characteristic index not less than 50% is selected, and the characteristic index is selected from any one of the minimum value, variance and standard deviation.

2. The cooling method according to claim 1, characterized in that: The cooling method of the multi-ion crystal comprises: Firstly, an auxiliary cooling ion combination that meets the selection criteria of the cooling limit is selected, and then an auxiliary cooling ion combination that meets the selection criteria of the cooling rate is selected from the auxiliary cooling ion combinations that meet the selection criteria of the cooling limit; Alternatively, an auxiliary cooling ion combination that meets the selection criteria of the cooling rate is first selected, and then an auxiliary cooling ion combination that meets the selection criteria of the cooling limit is selected from the auxiliary cooling ion combinations that meet the selection criteria of the cooling rate.

3. The cooling method of a polyionic crystal according to claim 1, characterized in that: The cooling method of the multi-ion crystal comprises: Selecting a preset number of ions and a preset position of ions in a multi-ion crystal as auxiliary cooling ions; Set a set of auxiliary cooling ion combinations including n ions {S i,n }, where i represents the i-th selected auxiliary cooling ion combination; Select a combination S from the set of auxiliary cooling ion combinations i,n , get the set of occupied numbers Where m represents the mth collective vibration mode; select each occupation number set The minimum value in Standard Deviation or variance value Any one of the following is a characteristic indicator Traverse the set of auxiliary cooling ion combinations {S i,n }, get the feature index set The characteristic index set Perform linear normalization to obtain parameters with values ​​between 0 and 1 A collection of; Select A collection of auxiliary cooling ion combinations; Optionally, select A collection of auxiliary cooling ion combinations; preferably, A collection of auxiliary cooling ion combinations; Calculate the cooling limit {δz for each ion under global cooling i,GC }, select the set of auxiliary cooling ion combinations in turn {S i,n }, the calculation is for each group of auxiliary cooling ions in the ionic crystal during cooperative cooling {δz i,SC }, and then use the ratio of the two {δz i,SC / δz i,GC The average value of} is the average ratio Select the average ratio The auxiliary cooling ion combination that is closest to 1 or less than a certain threshold value is cooled only by cooling laser irradiation to complete the cooling of all ion crystals; The cooling limit includes: the temperature of each ion, or the amplitude of each ion near the equilibrium position, or the average number of phonons of each ion.

4. The cooling method of an ionic crystal according to claim 3, characterized in that: Select the average ratio The auxiliary cooling ion combinations below a certain threshold are: Select A collection of auxiliary cooling ion combinations; Preferably, select A collection of auxiliary cooling ion combinations; Preferably, choose A collection of auxiliary cooling ion combinations.

5. The cooling method of an ionic crystal according to any one of claims 1 to 4, characterized in that: The cooling laser is used to perform any one of Doppler cooling, electromagnetically induced transparent cooling, sideband cooling and polarization gradient cooling, or a combination thereof.

6. The method for cooling an ionic crystal according to any one of claims 1 to 4, characterized in that: The number n of ions in the auxiliary cooling ion combination is no greater than 30% of the total number of ions in the ion crystal.

7. The cooling method of an ionic crystal according to any one of claims 1 to 4, characterized in that: The multi-ion crystal includes any one of a one-dimensional, two-dimensional or three-dimensional ion crystal; the potential field of the ion crystal can be the result of theoretical simulation or can be obtained by fitting according to the position of each ion.

8. The method for cooling an ionic crystal according to any one of claims 1 to 4, characterized in that: The multi-ion crystal is composed of ions of the same type; Optionally, the multi-ion crystal consists of different types of ions.

9. The cooling method of an ionic crystal according to claim 8, characterized in that: The ion types of the multi-ion crystal include any one or a combination of ions of different element types, ions of different isotopes of the same element, molecular ions of the same type or molecular ions of different types.

10. An ion trap quantum computing device, characterized in that: The ion trap quantum computing device comprises an ion cooling device configured to perform cooling using the cooling method for an ionic crystal according to any one of claims 1 to 9.

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