Method for determining a magnetic field model and device

Abstract

A method for determining a magnetic field model of a magnetic field established by at least one magnet arrangement (2) is specified, with - providing a first information characteristic for magnetic field values in a predetermined region (4) spaced apart from the magnet arrangement (2), wherein the magnet arrangement (2) is in an environment with a first temperature, - providing a second information characteristic for magnetic field values in the predetermined region (4), wherein the magnet arrangement (2) is in an environment with a second temperature, and - determining the magnetic field model characteristic for a temperature dependent behaviour of the magnetic field of the at least one magnet arrangement (2) dependent on the first information and the second information. Additionally, a device (1) used for carrying out the method is specified.

Description

[0001] METHOD FOR DETERMINING A MAGNETIC FIELD MODEL AND DEVICE

[0002] The present disclosure relates to a method for determining a magnetic field model of a magnetic field established by at least one magnet arrangement and a device .

[0003] Typically, a magnetic field distribution of a magnet changes dependent on the temperature of the magnet . This is that the magnetic field distribution at room temperature is typically di f ferent to a magnetic field distribution under cryogenic conditions .

[0004] An obj ect to be solved is to provide a method, which has an improved magnetic field distribution . Furthermore , a device used for carrying out the method is to be provided .

[0005] The obj ect is solved by the subj ect matter of the independent claims . Advantageous embodiments , implementations and further developments are the subj ect matter of the respective dependent claims .

[0006] The method for determining a magnetic field model of a magnetic field established by at least one magnet arrangement and provided to an ion trap is described . Exemplarily, the at least one magnet arrangement comprises at least two magnets being spaced apart from one another . In particular, the at least one magnet arrangement is configured to establish the magnetic field, exemplarily, a gradient of magnitudes of the magnetic field, in a predetermined region . Exemplarily, the magnetic field of the magnet arrangement has magnitudes being di f ferent from one another for di f ferent positions in the predetermined region . Particularly, the gradient of magnitudes of the magnetic field being established by the magnet arrangement is at least 0 . 5 T / m or and at most 500 T / m . In particular, the gradient of magnitudes of the magnetic field in the predetermined region is at least 50 T / m and at most 250 T / m, exemplarily 150 T / m .

[0007] The at least one magnet arrangement can comprise at least one permanent magnet , in particular at least two permanent magnets , and / or at least one solenoid, in particular at least two solenoids . Exemplarily, the permanent magnet does not require an external magnetic field to maintain magnetic properties such as a magneti zation . Further, the permanent magnets are in particular configured to provide the magnetic field without being provided with an electrical current . Exemplarily, the solenoid is in particular configured to provide the magnetic field due to an electrical current applied to the solenoid .

[0008] According to at least one embodiment of the method, a first information is provided characteristic for magnetic field values in a predetermined region spaced apart from the magnet arrangement , wherein the magnet arrangement is in an environment with a first temperature . Exemplarily, the environment is a physical space , where the magnet arrangement is arranged . In particular, a temperature of the magnet arrangement in the environment with the first temperature is in a range of the first temperature plus minus at most 50 % of the first temperature .

[0009] The predetermined region has , for example , an extent in lateral directions and in vertical direction perpendicular to the lateral directions . This is that the predetermined region encloses a three dimensional region in space , which is particularly displaced from the magnet arrangement .

[0010] According to at least one embodiment of the method, a second information is provided characteristic for magnetic field values in the predetermined region, wherein the magnet arrangement is in an environment with a second temperature . In particular, a temperature of the magnet arrangement in the environment with the second temperature is in a range of the second temperature plus minus at most 50 % of the second temperature . Exemplarily, the second temperature is smaller than the first temperature .

[0011] The first information and the second information are , for example , each characteristic for a measurement of a magnetic field sensor device . Exemplarily, the magnetic field sensor device is spaced apart from the predetermined region . In particular, the magnetic field sensor device is used to provide the magnetic field established by the magnet arrangement in the predetermined region, which measured magnetic field is the first information when the magnet is in the environment with the first temperature and which measured magnetic field is the second information when the magnet is in the environment with the second temperature .

[0012] The magnetic field sensor device comprise , for example , at least one of a Hall sensor device , a flux gate sensor device and a superconducting quantum interference device .

[0013] According to at least one embodiment of the method, the magnetic field model is determined, the magnetic field model is characteristic for a temperature dependent behaviour of the magnetic field of the at least one magnet arrangement comprising the at least one permanent magnet dependent on the first information and the second information . The magnetic field model , exemplarily, comprises a plurality of components for di f ferent points in space in the predetermined region, such as at least one of a magnetic field strength, a magnetic field direction . In particular, the magnetic field strength is represented by a magnetic flux density or a magnetic field intensity .

[0014] In particular, the temperature dependent behaviour of the magnetic field in the predetermined region is characteristic for a change of the magnetic field in the predetermined region for temperatures in the range between the first temperature and the second temperature .

[0015] Typically, the magnetic field established by the magnet arrangement is dependent on the temperature of the magnet arrangement . When the temperatures are comparatively high, magnetic domains of the permanent magnet can become disordered, leading to a reduction in the magnitude of the magnetic field . When the temperatures are comparatively low, the magnetic domains of the permanent magnet can align more coherently, leading to an increase in the magnitude of the magnetic field . Particularly, the magnetic field established by the magnet arrangement comprising the solenoid is dependent on a fluctuation of the electrical current applied to the solenoid . The fluctuation of the electrical current is particularly dependent on the temperature of the solenoid .

[0016] It is therefore desirable to know as accurately as possible how the magnetic field acts in the predetermined region for di f ferent temperatures , e . g . at the first temperature after magneti zation of the permanent magnets and during operation at the second temperature of the permanent magnets , or e . g . at the first temperature while operating the solenoid with a first electrical current and during operation at the second temperature while operating the solenoid with the first electrical current .

[0017] It is an idea, inter alia, to determine a magnetic field model being characteristic for a temperature dependent behaviour of the magnetic field of the at least one magnet arrangement . In this way, devices with magnet arrangements having advantageously an accurately tailored magnetic field pattern in the predetermined region can be provided and / or produced . This is that also magnet arrangements can be reali zed advantageously on demand dependent on the magnetic field model , which allows for little or even no recalibration of the magnet arrangement when operated at the second temperature .

[0018] Exemplarily, the magnet arrangement can be produced dependent on the magnetic field model , as the change in the magnetic field in the predetermined region from the first temperature to the second temperature can be advantageously predicted with the the magnetic field model . Further, the permanent magnet can be magneti zed and / or re- magneti zed dependent on the magnetic field model , advantageously . Likewise , the solenoid can be operated dependent on the magnetic field model , advantageously . Thus , the magnet arrangement can be adapted dependent on the magnetic field model for achieving a predetermined magnetic field pattern in the predetermined region . The method described herein above is , exemplarily, performed in the order indicated . The method described herein is , exemplarily, a computer implemented method .

[0019] According to at least one embodiment of the method, the provision of the first information and the provision of the second information is repeated alternatingly . This is the magnetic field values are measured at the first temperature and at the second temperature followed by at least one further repetition of measuring the magnetic field values at the first temperature and the second temperature . Exemplarily, after every repetition from the first temperature to the second temperature , the magnetic field model is determined and updated .

[0020] The repetition of the method is advantageously used to obtain the components of the magnetic field model more precise , in order to predict the change from the first temperature to the second temperature more accurately .

[0021] According to at least one embodiment of the method at least one further information is provided characteristic for magnetic field values in the predetermined region, when the magnet arrangement is in an environment characterised by a further temperature between the first temperature and the second temperature . In particular, the magnetic field model is additionally determined dependent on the further information .

[0022] Exemplarily, a plurality of further information are provided, wherein each of the further information is characteristic for magnetic field values in the predetermined region . In particular, to each further information one further temperature is associated, which is between the first temperature and the second temperature .

[0023] With having a plurality of further measuring steps when cooling the magnet arrangement from the first temperature to the second temperature , the magnetic field model more is advantageously determined particularly precise .

[0024] According to at least one embodiment of the method, the first temperature is higher than the second temperature . For example , the first temperature is at least four times higher than the second temperature . Exemplarily, the first temperature is at most 40 ° C or at most 25 ° C and / or at least 0 ° C or at least 10 ° C . The second temperature is at most 70 K, at most 30 K or at most 15 K and at least 0 . 3 K, at least 4 K .

[0025] In particular, the magnet arrangement is cooled down to the second temperature , e . g . by a cryostat .

[0026] According to at least one embodiment of the method, a target magnetisation and / or a target position of the at least one magnet arrangement is determined dependent on the magnetic field model . In particular, dependent on the magnetic field model , the target magnetisation and / or the target position of the magnet arrangement is determined such that the magnetic field at the second temperature corresponds to a desired magnetic field . In particular, the at least one magnet arrangement produced having the target magnetisation and / or the target position such that the magnetic field at the second temperature corresponds to a desired magnetic field . According to at least one embodiment of the method, the at least one magnet arrangement comprising the at least one permanent magnet is magnetised when the magnet arrangement is in the environment with the first temperature . Exemplarily, the target magnetisation and / or the target position can be determined for other devices with at least one permanent magnet , which are magnetised and / or positioned at the first temperature .

[0027] Typically, a permanent magnet is magneti zed by aligning magnetic domains within a material of the permanent magnet in a preferred direction with an external magnetic field . I f the magnetic moments are aligned up to a predetermined portion, the permanent magnet establishes the magnetic field . A strength of the magneti zation of the permanent magnet arrangement is dependent on a strength of the external magnetic field .

[0028] According to at least one embodiment of the method, a magnetisation of the at least one permanent magnet is monitored during the magnetisation .

[0029] According to at least one embodiment of the method, the at least one permanent magnet comprising the at least one permanent magnet is magnetised and / or positioned such that magnitudes of the magnetic field vanish at a predetermined point in the predetermined region, when the permanent magnet arrangement is in the environment with the second temperature .

[0030] In particular, the at least one permanent magnet is magnetised at the first temperature dependent on the magnetic field model . During magneti zation, the strength of the external magnetic field is adj usted dependent on the magnetic field model , such that the permanent magnet in the environment with the second temperature establishes the magnetic field with vanishing magnitudes at the predetermined point in the predetermined region . For this , the magneti zation is in particular monitored .

[0031] According to at least one embodiment of the method, the at least one permanent magnet comprising the at least one permanent magnet is magnetised and / or positioned such that a gradient of the magnitudes of the magnetic field is maximi zed in the predetermined region, when the permanent magnet is in the environment with the second temperature .

[0032] During magneti zation of the at least one permanent magnet , the strength of the external magnetic field is adj usted dependent on the magnetic field model , such that the permanent magnet in the environment with the second temperature establishes the maximised gradient of the magnitudes of the magnetic field in the predetermined region, e . g . along an axis . For this , the magneti zation is in particular monitored .

[0033] According to at least one embodiment of the method, the at least one magnet arrangement is part of the ion trap . The ion trap can be a Paul trap, a linear ion trap, a surface ion trap and / or a multi-layer ion trap . For example , a radio frequency, RF, voltage is applied to at least some electrodes of the ion trap such that a time-varying electric field is provided configured to confine and / or to manipulate an ion . In particular, the ion is located within a processing region being the predetermined region . In particular, the at least one magnet arrangement is configured to establish the gradient of magnitudes of the magnetic field of the magnet arrangement in the processing region, e . g . along a trapping axis . This is that the magnetic field of the magnet arrangement has magnitudes being di f ferent from one another for di f ferent positions in the processing region and in particular on the trapping axis . Advantageously, a resonance frequency of each of the ions at the processing region, on which the gradient of magnitudes of the magnetic field of the magnet arrangement acts , is unique for each ion in the processing region, i . e . each trapped ion .

[0034] According to at least one embodiment of the method, the ion trap comprises at least one magnetic field sensor device or at least two magnetic field sensor devices configured to measure a magnetic field of the at least one magnet arrangement in the predetermined region .

[0035] According to at least one embodiment of the method, the at least one magnetic field sensor device or the at least two magnetic field sensor devices are spaced apart from the predetermined region in lateral directions and / or in vertical direction .

[0036] Exemplarily, the magnetic field sensor devices are configured to sense the magnetic field of the magnet arrangement at at least two speci fic locations each corresponding to a place where the magnetic field sensor devices are arranged in the ion trap . By combining the sensing of the at least two magnetic field sensor devices at the at least two speci fic locations , the magnetic field in the predetermined region can be determined and the first information and the second information can be provided . According to at least one embodiment of the method, the ion trap comprises at least two registers . Each register comprises a predetermined region, i . e . a processing region .

[0037] According to at least one embodiment of the method, at least one magnet arrangement is associated to each of the at least two registers . Additionally, at least one magnetic field sensor device and / or at least two least two magnetic field sensor devices are associated to each of the at least two registers .

[0038] According to at least one embodiment of the method, the magnetic field model is determined for each of the registers .

[0039] According to at least one embodiment of the method, a magnetisation and / or a position of each of the at least two magnet arrangements is determined independently from one another .

[0040] In this way, ion traps with an accurately tailored magnetic field pattern on demand can be generated that allow for little or even no recalibration when operated at the second temperature . This advantageously substantially simpli fies the operation for scalable architectures involving a large number of qubit registers and processing regions with each with a tailored magnetic field distribution . A combination of modelling and feed-back during magneti zation of the permanent magnet is advantageously implemented to yield the desired magnetic fields in the predetermined regions , i . e . processing regions . A combination of modelling and feed-back during operating the solenoid is advantageously implemented to yield the desired magnetic fields in the predetermined regions , i . e . processing regions .

[0041] Moreover, a device being preferably the ion trap, which is used for carrying out the method described herein above is speci fied . Thus , the features described in connection with the device are also applicable in connection with the method and vice versa . According to at least one embodiment , the device comprises at least one magnet arrangement configured to establish a magnetic field in a predetermined region, and at least one magnetic field sensor device spaced apart from the predetermined region . According to at least one embodiment of the device , the at least one magnetic field sensor device is arranged within the device , and the at least one magnetic field sensor device is configured to provide the magnetic field values in the predetermined region .

[0042] In the following, the ion trap and the method are explained in more detail with reference to exemplary embodiments and the associated Figures .

[0043] Figure 1 shows a flow diagram of the method according to an exemplary embodiment .

[0044] Figure 2 shows a device which is used for carrying out the method according to an exemplary embodiment .

[0045] Elements that are identical , similar or have the same ef fect are given the same reference signs in the Figures . The Figures and the proportions of the elements shown in the figures are not to be regarded as true to scale . Rather, individual elements may be shown exaggeratedly large for better representability and / or for better comprehensibility . In method stage S I of Figure 1 , a first information is provided characteristic for magnetic field values in a predetermined region 4 spaced apart from the magnet arrangement 2 , wherein the magnet arrangement 2 is in an environment with a first temperature .

[0046] In particular, the magnet arrangement 2 is part of an ion trap 6 . The magnet arrangement 2 exemplarily comprises at least two magnets being spaced apart from one another . The at least two magnets are in particular configured to establish a magnetic field in a processing region, being in particular the predetermined region 4 , of the ion trap 6 . In particular, the ion trap 6 with the magnet arrangement 2 are in the environment with the first temperature in method stage S I . The temperature of the ion trap 6 with the magnet 2 arrangement corresponds approximately to the first temperature in method stage S I .

[0047] The magnetic field values of the first information are , for example , provided by a magnetic field sensor . The magnetic field sensor device 3 is in particular spaced apart from the predetermined region 4 . In particular, the magnetic field sensor device 3 is used to provide the magnetic field established by the magnet arrangement 2 in the predetermined region 4 at the first temperature in method stage S I .

[0048] For example , the first temperature is characteristic for a typical room temperature .

[0049] Subsequently, in method stage S2 , a second information is provided characteristic for magnetic field values in the predetermined region 4 , wherein the magnet arrangement 2 is in an environment with a second temperature .

[0050] In particular, the ion trap 6 with the magnet arrangement 2 are in the environment with the second temperature in method stage S2 . The temperature of the ion trap 6 with the magnet arrangement 2 corresponds approximately to the second temperature in method stage S2 .

[0051] The magnetic field values of the second information are , for example , provided by the magnetic field sensor . In particular, the magnetic field sensor device 3 are used to provide the magnetic field established by the magnet arrangement 2 in the predetermined region 4 at the second temperature in method stage S2 .

[0052] The magnetic field sensor device 3 is configured to sense the magnetic field of the magnet arrangement 2 at a speci fic location corresponding to a place where the magnetic field sensor device 3 is arranged in the ion trap . By sensing the magnetic field of the magnet arrangement 2 at the speci fic location, the magnetic field in the predetermined region 4 can be determined and the first information and the second information can be provided .

[0053] For example , the second temperature is characteristic for a typical cryogenic temperature .

[0054] The magnetic field values at the first temperature and at the second temperature are , for example , provided, in particular measured, by the same magnetic field sensor of the ion trap 6 . Subsequently, in method stage S3 , a magnetic field model is determined characteristic for a temperature dependent behaviour of the magnetic field of the at least one magnet arrangement 2 dependent on the first information and the second information .

[0055] Exemplarily, the at least one magnet arrangement 2 comprising at least one permanent magnet , which is particularly mounted in the ion trap 6 , is magnetised, when the magnet arrangement 2 is in the environment with the first temperature . Dependent on the temperature dependent behaviour of the magnetic field of the permanent magnet 2 being a magneti zation behaviour, i . e . dependent on the magnetic field model , the permanent magnet is magneti zed such that magnitudes of the magnetic field vanish at a predetermined point in the predetermined region 4 , when the magnet arrangement 2 is in the environment with the second temperature , for example .

[0056] Additionally or alternatively, the at least one permanent magnet is magnetised at the first temperature dependent on the magnetic field model such that a gradient of the magnitudes of the magnetic field is maximi zed in the predetermined region 4 , when the permanent magnet arrangement 2 is in the environment with the second temperature .

[0057] The magneti zation of the permanent magnet can be monitored during magneti zation such that the magneti zation can be set particularly precise .

[0058] I f the ion trap 6 comprises at least two registers , a predetermined region 4 , i . e . a processing region, is assigned to each of the registers . Additionally, each of the registers is provided with at least two magnetic field sensor devices 3 . Advantageously, the magnetic field model is determined for each of the registers , in particular, independently from one another .

[0059] Advantageously, each of the magnet arrangements 2 assigned to one of the registers can be magneti zed individually dependent on the individual magnetic field model . This is that a desired magnetic field in the respective predetermined region 4 can be formed di f ferently for every register .

[0060] The device 1 according to Figure 2 comprises a magnet arrangement 2 configured to establish a magnetic field in a predetermined region 4 and a magnetic field sensor device 3 spaced apart from the predetermined region 4 . In particular, the magnet arrangement 2 is also spaced apart from the predetermined region 4 .

[0061] Preferably, the device 1 is an ion trap 6 .

[0062] The magnetic field sensor device 3 is arranged within the device 1 and the magnetic field sensor device 3 is configured to provide the magnetic field values in the predetermined region 4 . The magnet arrangement 2 and the magnetic field sensor device 3 are arranged on a substrate 5 or carrier .

[0063] Reference signs

[0064] 1 device

[0065] 2 magnet arrangement

[0066] 3 magnetic field sensor device

[0067] 4 predetermined region

[0068] 5 substrate

[0069] 6 ion trap

[0070] S I . . S3 method stages

Claims

Claims1. Method for determining a magnetic field model of a magnetic field established by at least one magnet arrangement(2) and provided to an ion trap (6) , with- providing a first information characteristic for magnetic field values in a predetermined region (4) spaced apart from the magnet arrangement (2) , wherein the magnet arrangement (2) is in an environment with a first temperature,- providing a second information characteristic for magnetic field values in the predetermined region (4) , wherein the magnet arrangement (2) is in an environment with a second temperature, and- determining the magnetic field model characteristic for a temperature dependent behaviour of the magnetic field of the at least one magnet arrangement (2) dependent on the first information and the second information.

2. Method according to claim 1, wherein- the provision of the first information and the provision of the second information is repeated alternatingly .

3. Method according to one of the claims 1 or 2, wherein- at least one further information is provided characteristic for magnetic field values in the predetermined region (4) , when the magnet arrangement (2) is in an environment characterised by a further temperature between the first temperature and the second temperature.

4. Method according to at least one of the claims 1 to 3, wherein- the first temperature is higher than the second temperature .

5. Method according to one of the claims 1 to 4, wherein- a target magnetisation and / or a target position of the at least one magnet arrangement (2) is determined dependent on the magnetic field model.

6. Method according to one of the claims 1 to 5, wherein- the at least one magnet arrangement (2) comprising at least one permanent magnet is magnetised when the magnet arrangement (2) is in the environment with the first temperature .

7. Method according to claim 6, wherein- a magnetisation of the at least one magnet arrangement (2) is monitored during the magnetisation.

8. Method according to one of the claims 1 to 6, wherein- the at least one magnet arrangement (2) comprising at least one permanent magnet is magnetised and / or positioned such that magnitudes of the magnetic field vanish at a predetermined point in the predetermined region (4) , when the magnet arrangement (2) is in the environment with the second temperature .

9. Method according to one of the claims 1 to 8, wherein- the at least one magnet arrangement (2) comprising at least one permanent magnet is magnetised and / or positioned such that a gradient of the magnitudes of the magnetic field is maximized in the predetermined region (4) , when the magnet arrangement (2) is in the environment with the second temperature .

10. Method according to one of the claims 1 to 9, wherein- the at least one magnet arrangement (2) is part of the ion trap ( 6 ) , and- the ion trap (6) comprises at least one magnetic field sensor device or at least two magnetic field sensor devices (3) configured to measure a magnetic field of the at least one magnet arrangement (2) in the predetermined region (4) .

11. Method according to claim 10, wherein- the at least one magnetic field sensor device or the at least two magnetic field sensor devices (3) are spaced apart from the predetermined region (4) .

12. Method according to one of the claims 10 or 11, wherein- the ion trap (6) comprises at least two registers- at least one magnet arrangement (2) is associated to each of the at least two registers, and- the magnetic field model is determined for each of the registers .

13. Method according to claim 12, wherein- a magnetisation and / or a position of each of the at least two magnet arrangements (2) is determined independently from one another.

14. Device (1) used for carrying out the method according to one of the claims 1 to 13, with- at least one magnet arrangement (2) configured to establish a magnetic field in a predetermined region (4) , and- at least one magnetic field sensor device (3) spaced apart from the predetermined region (4) , wherein- the at least one magnetic field sensor device (3) is arranged within the device (1) , and- the at least one magnetic field sensor device (3) is configured to provide the magnetic field values in the predetermined region (4) .

Images