Method, system, computer program and computer-readable storage medium for determining a loading state of a string of IONS of an ion trap of a quantum computer

Abstract

A method for determining a loading state of a string of ions of an ion trap (2) of a quantum computer is specified, comprising - providing a measurement information of the string of ions, - determining a number of ions of the string of ions dependent on the measurement information, - determining a health information dependent on the measurement information, wherein the health information is characteristic of a comparison of measurement properties of the string based on the measurement information and predetermined properties of the string being numerically calculated, and - determining the loading state of the string of ions dependent on the number of ions and the health information, wherein the loading state of the string is characteristic of a successful loading of the string or of an adjustment of the string. Further, a system (1), a computer program and a computer-readable storage medium are specified.

Description

[0001] Description

[0002] METHOD, SYSTEM, COMPUTER PROGRAM AND COMPUTER-READABLE STORAGE MEDIUM FOR DETERMINING A LOADING STATE OF A STRING OF IONS OF AN ION TRAP OF A QUANTUM COMPUTER

[0003] The present disclosure relates to a method, a system, a computer program and a computer-readable storage medium for determining a loading state of a string of ions of an ion trap of a quantum computer .

[0004] Typically, before a quantum computer comprising an ion trap can be started, a predetermined number of qubits each encoded by an ion must be generated . In particular, the ions arranged next to one another form a string of ions , which has to be healthy for any quantum computing process . This means that the string of ions should not contain any molecules , isotopes or ions populating any other than a desired state .

[0005] An obj ect to be achieved is to provide a method by which a string of ions is checked as to whether it can be used in particular for quantum computing processes , preferably automatically . Furthermore , a system, a computer program and a computer-readable storage medium for determining a loading state of a string of ions of an ion trap of a quantum computer are to be provided .

[0006] The method for determining a loading state of a string of ions of an ion trap of a quantum computer is described . The ion trap is particularly configured to trap a plurality of ions , forming the string of ions . The string of ions comprises , for example , at least 10 ions , at least 50 ions or at least 100 ions or at least 500 ions . The ion trap is , for example , part of a quantum computer which is configured to perform a predetermined quantum computing process by using at least some trapped ions of the string of ions . For the predetermined quantum computing process , in particular, the string of ions is predetermined accordingly . In other words , a predetermined string of ions is provided for performing the predetermined quantum computing process .

[0007] For example , the ion trap can be a Penning trap or a Paul trap, a linear ion trap, a surface ion trap and / or a multilayer ion trap . Exemplarily, the ion trap comprises a set of electrodes . For example , a radio frequency, RF, voltage is applied to the electrodes such that a time-varying electric field is provided, configured to trap, confine and / or modi fy at least some of the trapped ions , wherein the trapped ions form the string of ions .

[0008] For example , a magnetic gradient is provided to at least some of the trapped ions or all trapped ions , in particular to the string . Exemplarily, the magnetic gradient is provided by a permanent magnet arrangement . This means that at least some of the trapped ions are individually addressable due to the magnetic gradient .

[0009] A loading state of the string is for example characteristic of a condition of the string and / or a state of the ions of the string within the ion trap, in particular immediately after the ions are introduced and / or loaded into the ion trap .

[0010] According to at least one embodiment of the method, a measurement information of the string of ions is provided . The measurement information is , for example , characteristic of a position of each of the ions of the string and / or characteristic of a condition of each of the ions of the string . The measurement device comprises , for example , photomultipliers , single-photon avalanche diodes , SPADs , CMOS sensors , EMCCDs , or superconducting nanowire single-photon detectors , SNSPDs .

[0011] For example , the measurement information comprises a peak value or a geometric centre and / or a condition value for each ion of the string . Exemplarily, the measurement information comprises for each ion the position in lateral directions dependent on the corresponding peak value or the corresponding geometric centre in lateral directions of a corresponding imaged ion . Alternatively or additionally, the measurement information comprises for each ion the corresponding condition value dependent on a motion of the corresponding ion .

[0012] According to at least one embodiment of the method, a number of ions of the string of ions is determined dependent on the measurement information . In particular, the number of ions is characteristic of a quantity of ions of the string trapped in the ion trap .

[0013] According to at least one embodiment of the method, a health information is determined dependent on the measurement information . Exemplarily, the health information is characteristic of that the string can be used for a predetermined quantum computing process . In particular, the health information is characteristic of that the string of ions solely comprises ions in a predetermined state , particularly used by the predetermined quantum computing process . According to at least one embodiment of the method, the health information is characteristic of a comparison of measurement properties of the string based on the measurement information and predetermined properties of the string being numerically calculated . Exemplarily, each measurement property is characteristic of a distance of a pair of directly neighbouring ions of the string determined dependent on the measurement information, and / or each measurement property is characteristic of a condition of each ion of the string determined dependent on the measurement information .

[0014] For example , each predetermined property is characteristic of a calculated distance of a pair of directly neighbouring ions of the string determined, and / or each predetermined property is characteristic of a calculated condition of each ion of the string determined . The predetermined property is , exemplarily, numerically calculated based on a predetermined theoretical model of the predetermined string used for the predetermined quantum computing process .

[0015] According to at least one embodiment of the method, the loading state of the string of ions is determined dependent on the number of ions and the health information .

[0016] According to at least one embodiment of the method, the loading state of the string is characteristic of a success ful loading of the string or of an adj ustment of the string . I f the loading state of the string is characteristic of the success ful loading, the loaded and trapped ions , i . e . the ions of the string, can be used for the predetermined quantum computing process . I f the loading state of the string is characteristic of the adj ustment of the string, ions of the string can be removed and / or inserted accordingly .

[0017] In particular, the method is carried out until the loading state of the string is characteristic of a success ful loading of the string .

[0018] The method described herein above is , exemplarily, performed in the order indicated . The method described herein above is , exemplarily, a computer implemented method . In particular, the method described herein is performed automatically .

[0019] An idea of the method described herein is , inter alia, that that the loading state of the string of ions is advantageously determined dependent on a combination of the determined number of ions and the health information, wherein the health information comprises a comparison of measured properties and predetermined - i . e . theoretically calculated - properties . Advantageously, the string can be adj usted or can be used dependent on the loading state - such that the predetermined string is obtained for carrying out the predetermined quantum computing process . This can advantageously be performed automatically .

[0020] According to at least one embodiment of the method, a predetermined maximum number of ions is provided . Exemplarily, the predetermined maximum number corresponds to the predetermined number of ions in the predetermined string plus a margin of at least 1 ion or at least 5 ions , or the predetermined maximum number equals the predetermined number of ions in the predetermined string . According to at least one embodiment of the method, after the determination of the number of ions , a first information is determined dependent on the number of ions and the predetermined maximum number of ions . Exemplarily, the first information is determined by a comparison of the determined number of ions and the predetermined maximum number of ions .

[0021] According to at least one embodiment of the method, i f the determined number of ions is higher than the predetermined maximum number of ions , the first information is determined, and the first information is characteristic of removing at least some of the ions from the sequence of ions . In particular, the first information is characteristic of the adj ustment of the string . Ions of the string can be selectively removed, e . g . by altering a trapping potential of the electrodes of the ion trap .

[0022] According to at least one embodiment of the method, the method comprises the step of providing a predetermined health information of the ions . The predetermined health information corresponds , in particular, to a predetermined health information of ions in the predetermined string . Exemplarily, the predetermined health information comprises the calculated distances and / or the calculated modes .

[0023] According to at least one embodiment of the method, after the determination of the health information, a second information is determined dependent on the health information and the predetermined health information . Exemplarily, the second information is determined by a comparison of the determined health information and the predetermined health information . According to at least one embodiment of the method, i f the determined health information is inadequate with respect to a predetermined health information, the second information is determined, and the second information is characteristic of removing at least some of the ions from the string of ions . In particular, the second information is characteristic of the adj ustment of the string .

[0024] Exemplarily, the health information is represented by a value in particular determined based on the measurement information . For example , the predetermined health information is represented by a predetermined value in particular determined based on the calculation . The value can be compared to a predetermined value , e . g . being a threshold . I f the value is larger and / or smaller than the predetermined value , the determined health information is inadequate with respect to the predetermined health information .

[0025] According to at least one embodiment , the health information is characteristic of distances of directly neighbouring ions of the string and the predetermined health information is characteristic of predetermined distances of directly neighbouring ions . Exemplarily, for each pair of directly neighbouring ions of the string, a distance in lateral directions is determined based on the measurement information . Exemplarily, for each pair of directly neighbouring ions of the predetermined string, a distance in lateral directions is numerically calculated .

[0026] According to at least one embodiment , the health information is characteristic of a condition of each ion and the predetermined health information is characteristic of a predetermined condition of each ion . Exemplarily, for each ion of the string, a condition is determined based on the measurement information . Exemplarily, for each ion of the predetermined string, a condition in lateral directions is numerically calculated .

[0027] According to at least one embodiment , a further predetermined minimum number of ions is provided . Exemplarily, the further predetermined minimum number corresponds to the predetermined number of ions in the predetermined string minus a further margin of at least 1 ion or at least 5 ions , or the further predetermined minimum number equals the predetermined number of ions in the predetermined string .

[0028] According to at least one embodiment , after the determination of the number of ions and after the determination of the health information, a third information is determined dependent on the number of ions and the further predetermined minimum number of ions . In particular, the third information is characteristic of the loading state . Exemplarily, the third information is determined by a comparison of the determined number of ions and the further predetermined minimum number of ions .

[0029] According to at least one embodiment of the method, i f the determined number of ions is smaller than the further predetermined minimum number of ions , the third information is determined, and the third information is characteristic of inserting at least some ions into the string of ions . In particular, the third information is characteristic of the adj ustment of the string .

[0030] According to at least one embodiment of the method, a loading probability is determined dependent on the measurement information . Exemplarily, a loading apparatus comprises an ablation laser device and a cooling and ioni zing laser device . For example , prior to the start of the method, the laser devices are switched on and the ablation laser device is configured to execute an ablation pulse to a solid target comprising a material of the to-be-produced ions , with parameters being, for example , dependent on loading probability, for producing a plurality of atoms . In particular, subsequently, the produced atoms are ioni zed by the cooling and ioni zing laser device , being for example a resonant ioni zation laser device , and are cooled for a time interval . At least some of the produced ions are trapped in the ion trap, which forms the string of ions . In particular, the measurement information is provided based on the string . In particular, when adj usting the string by incorporating ions into the string, the ablation laser device is switched on and executes an ablation pulse dependent on the parameters . Subsequently, the cooling and ioni zing lasers ioni ze and cool the produced atoms dependent on the parameters to further ions . The produced further ions are trapped in the ion trap, which forms the adj usted string of ions . Exemplarily, for increasing iterations of the method, a dynamic waiting time increases for between ablation pulses . Exemplarily, cooling parameters , ioni zation parameters and / or trapping parameters of the cooling and ioni zing lasers can be dynamically adj usted for each iteration . Advantageously, a deterministic amount of ions can be loaded . Further, a chance of ion crystallisation can advantageously be maximised . In particular, during the ion loading process , the trapping potential and / or confinement potential or laser parameters can be altered, advantageously to allow the ions to cool and crystalli ze more quickly . The loading probability is , for example , dependent on the detected number of ions , in particular detected subsequently to the prior production of ions or subsequently to each adj ustment of the string . The loading probability is in particular characteristic of the number of ions detected after loading the ion trap with ions , e . g . when starting the method or after adj usting the string, exemplarily, dependent on the parameters of the ioni zing laser .

[0031] According to at least one embodiment of the method, at least one parameter of a loading apparatus is adj usted dependent on the loading probability . Advantageously, the number of inserted ions can be controlled due to the loading probability, in particular precisely . This means that the number of ions can advantageously be adj usted in a closed loop to maintain a stable ion loading probability over time .

[0032] Furthermore , a system for determining a loading state of a string of ions of an ion trap of a quantum computer is described . The system is configured to perform the method described herein . Therefore , all features and embodiments disclosed in connection with the method are also disclosed in connection with the system and vice versa .

[0033] According to at least one embodiment , the system comprises a computing device , an ion trap and a loading apparatus . The method is in particular performed on the computing device , which is connected to the ion trap and the loading apparatus .

[0034] In addition, a computer program is speci fied, comprising instructions which, when the computer program is executed by a computer, cause the computer program to execute the method described herein . Further, a computer-readable storage medium is speci fied, on which the computer program described herein is stored .

[0035] In the following, the method and the system are explained in more detail with reference to exemplary embodiments and the associated Figures .

[0036] Figure 1 shows a flowchart of the method for determining a loading state of a string of ions of an ion trap of a quantum computer according to an exemplary embodiment .

[0037] Figure 2 shows a system which is configured to perform the method according to an exemplary embodiment .

[0038] 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 .

[0039] Method stage S I according to the exemplary embodiment of Figure 1 comprises that n ions are requested, e . g . by predetermining a string of ions which is configured to be used for a predetermined quantum computing process , e . g . being the ions trapped in an ion trap 2 . In particular, the predetermined string comprises a predetermined number of ions .

[0040] In particular, the requested ions are provided by a loading apparatus 3 , for example , dependent on a loading probability . The loading apparatus 3 comprises , for example , a laser ablation device which is configured to produce ions dependent on parameters . The produced ions are subsequently trapped by the ion trap 2 , forming the string of ions .

[0041] Subsequently, a measurement information of the string of ions is provided in method stage S2 . The measurement information is based, exemplarily, on a measurement of a measurement device , which is for example an imaging device such as a camera, e . g . a charged-coupled device , CCD, in particular an electron-multiplying CCD . In a next method step S3 , a number of ions of the string of ions is determined dependent on the measurement information .

[0042] Subsequently, in method stage S4 , a first information is determined dependent on the number of ions and the predetermined maximum number of ions . In particular, the number of ions and the predetermined maximum number of ions are compared . This means that it is determined whether the determined number is too high . I f the determined number is too high, the loading state is determined to be "not completed" .

[0043] I f the determined number of ions is higher than the predetermined maximum number of ions , the first information is determined, and in particular the ion trap 2 is partially or completely emptied, i . e . at least some or all of the ions are removed in method stage S5 . Subsequently, ions are loaded in the ion trap 2 again i f the ion trap 2 is completely emptied . Next , method stage S2 is carried out again .

[0044] I f the determined number of ions is not higher than the predetermined maximum number of ions , a health information is determined in method stage S 6 dependent on the measurement information, wherein the health information is characteristic of a comparison of measurement properties of the string based on the measurement information and predetermined properties of the string being numerically calculated .

[0045] In method stage S 6 , a predetermined health information of the ions is provided . Further, a second information is determined in method stage S 6 dependent on the health information and the predetermined health information . In particular, the health information and the predetermined health information are compared in stage S7 . I f the determined health information is not inadequate with respect to the predetermined health information, the loading state is determined to be "not completed" .

[0046] I f the determined health information is inadequate with respect to the predetermined health information, the second information is determined, and in particular the ion trap 2 is partially or completely emptied, i . e . at least some or all of the ions are removed in method stage S5 . Subsequently, further ions are loaded in the ion trap 2 and method stage S2 is carried out again .

[0047] I f the determined health information corresponds to , i . e . is adequate with respect to , the predetermined health information, a third information is determined in method stage S 8 dependent on the number of ions and a further predetermined minimum number of ions . For example , the further predetermined minimum number equals the predetermined number .

[0048] I f the determined number of ions is smaller than the further predetermined minimum number of ions , the third information is determined, and ions are inserted into the string in method stages S9, S10, Sil and S12. Subsequently, method stage S2 is carried out again.

[0049] In method stage S9, an ionizing laser of the laser ablation device is switched on. Subsequently, in method stage S10, the ionizing laser is configured to execute an ablation pulse, with parameters being, for example, dependent on a loading probability. Next, in method stage Sil, the ions are cooled for with dynamic cooling parameters. Exemplarily, the cooling parameters, the ionization parameters and / or the trapping parameters are adjusted dependent on a number of iterations of method stages S9, S10, Sil and S12. Subsequently, the ionizing laser is switched off and method stage S2 is carried out again.

[0050] Finally, if the determined number of ions is not smaller than the further predetermined minimum number of ions, the loading state is determined to be "completed". Thus, the loading state validates that the loaded string is adequate with respect to the predetermined string such that, advantageously, the predetermined quantum computing process can be executed with the loaded string.

[0051] The system 1 according to Figure 2 comprises an ion trap 2, a measuring device 4 and a loading apparatus 3 comprising an ablation laser. The ion trap 2, the measuring device 4 and the loading apparatus 3 are connected via connections 5 to a computing device 6, e.g. a classical computer. Exemplarily, the computing device 6 is configured to perform the method of Figure 1. The invention is not limited to the exemplary embodiments by their description . Rather, the invention encompasses any new feature as well as any combination of features , which in particular includes any combination of features in the claims , even i f this feature or combination itsel f is not explicitly indicated in the claims or exemplary embodiments .

[0052] Reference signs

[0053] 1 system

[0054] 2 ion trap 3 loading apparatus

[0055] 4 measuring device

[0056] 5 connections

[0057] 6 computing device S 1...S4 method stages

Claims

Claims1 . Method for determining a loading state of a string of ions of an ion trap ( 2 ) of a quantum computer, comprising- providing a measurement information of the string of ions ,- determining a number of ions of the string of ions dependent on the measurement information,- determining a health information dependent on the measurement information, wherein the health information is characteristic of a comparison of measurement properties of the string based on the measurement information and predetermined properties of the string being numerically calculated, and- determining the loading state of the string of ions dependent on the number of ions and the health information, wherein the loading state of the string is characteristic of a success ful loading of the string or of an adj ustment of the string .2 . Method according to claim 1 , further comprising the step of- providing a predetermined maximum number of ions , wherein- after the determination of the number of ions , a first information is determined dependent on the number of ions and the predetermined maximum number of ions .3 . Method according to claim 2 , wherein- i f the determined number of ions is higher than the predetermined maximum number of ions , the first information is determined, and- the first information is characteristic of removing at least some of the ions from the sequence of ions .4 . Method according to one of claims 1 to 3 , further comprising the step of- providing a predetermined health information of the ions , wherein- after the determination of the health information, a second information is determined dependent on the health information and the predetermined health information .5 . Method according to claim 4 , wherein- i f the determined health information is inadequate with respect to the predetermined health information, the second information is determined, and- the second information is characteristic of removing at least some of the ions from the string of ions .6 . Method according to one of claims 4 or 5 , wherein- the health information is characteristic of distances of directly neighbouring ions of the string and the predetermined health information is characteristic of predetermined distances of directly neighbouring ions , and / or- the health information is characteristic of a condition of each ion and the predetermined health information is characteristic of a predetermined condition of each ion .7 . Method according to one of claims 2 to 6 , further comprising- providing a further predetermined minimum number of ions , and- after the determination of the number of ions and after the determination of the health information, a third information is determined dependent on the number of ions and the further predetermined minimum number of ions .

8. Method according to claim 7, wherein- if the determined number of ions is smaller than the further predetermined minimum number of ions, the third information is determined, and- the third information is characteristic of inserting at least some ions into the string of ions.

9. Method according to one of claims 1 to 8, additionally comprising the steps of- determining a loading probability dependent on the measurement information, and- adjusting at least one parameter of a loading apparatus (3) dependent on the loading probability.

10. System (1) for determining a loading state of a string of ions of an ion trap (2) of a quantum computer, wherein the system (1) is configured to perform the method according to one of the preceding claims.

11. Computer program comprising instructions which, when the computer program is executed by a computer, cause the computer program to execute the method according to one of claims 1 to 9.

12. Computer-readable storage medium, on which the computer program according to claim 11 is stored.

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