Josephson junction resistance tuning

Abstract

The invention is in the field of superconducting integrated circuits, in particular systems and methods for tuning superconducting integrated circuit elements such as Josephson junctions. A system (1) for simultaneously modifying the resistance of a plurality of Josephson junctions (112 i-112 iv) comprises an assembly (100) comprising a plurality of probes (102a-102h) configured to be brought into electrical connection with the plurality of Josephson junctions when the system is in use, measurement electronics (103a) for measuring a resistance of each of the plurality of Josephson junctions via the plurality of probes, and driving electronics (103b) for applying resistance change stimuli to the plurality of Josephson junctions in order to simultaneously modify the resistance of at least a subset of the plurality of Josephson junctions.

Description

[0001] JOSEPHSON JUNCTION RESISTANCE TUNING

[0002] Technical Field

[0003] The invention is in the field of superconducting integrated circuits, in particular systems and methods for tuning superconducting integrated circuit elements such as Josephson junctions.

[0004] Background

[0005] Superconducting qubits contain one or multiple Josephson junctions, also referred to as “superconducting tunnel junctions”. A Josephson junction comprises two superconducting regions, which may be referred to as electrodes, separated by a non-superconducting barrier, usually an electrical insulator.

[0006] The qubit frequency, i.e. the frequency difference between the ground state and first excited state, of a transmon qubit at cryogenic temperatures can be predicted from the normal state resistance of the Josephson junctions, i.e. their electrical resistance measured at room temperature. Consequently, the resistance of the Josephson junction(s) is carefully controlled in order to produce qubits with a desired qubit frequency.

[0007] Fine-grained control over qubit frequencies is required in order to scale up quantum computers, i.e. to increase the number of qubits in a single quantum processing unit. For example, frequency crowding makes it more difficult to address individual qubits as the number of qubits increases - a lack of precise control over qubit frequencies exacerbates the problem. However, even state of the art Josephson junction fabrication processes cannot produce Josephson junctions with the desired precision in their resistance values.

[0008] Prior art methods of modifying qubit frequencies include annealing Josephson junctions using a thermal source such as a laser to modify the resistance of the Josephson junction, for example as described in US 10,340,438 B2 and C. Granata et al, 2008 J. Phys.: Conf.

[0009] Ser. 97 012110. However, prior art methods for modifying qubit frequencies are generally only capable of annealing a single Josephson junction at a time and are therefore not suitable for large-scale production of Josephson junctions or superconducting qubits. Summary of the Invention

[0010] A first aspect of the invention relates to a system for simultaneously modifying the resistance of a plurality of Josephson junctions. The system comprises an assembly, which comprises a plurality of probes configured to be brought into electrical connection with the plurality of Josephson junctions when the system is in use; measurement electronics for measuring a resistance of each of the plurality of Josephson junctions via the plurality of probes; and driving electronics for applying resistance change stimuli to the plurality of Josephson junctions in order to simultaneously modify the resistance of at least a subset of the plurality of Josephson junctions. The system and assembly enable the efficient individual tuning of multiple Josephson junctions, e.g. those on the safe wafer or chip, in parallel.

[0011] The plurality of probes may comprise a plurality of pairs of probes. Each pair of probes of the plurality of pairs of probes may be configured to provide electrical connection with a different Josephson junction of the plurality of Josephson junctions such that a first probe of the pair of probes is electrically connected to a first electrode of the Josephson junction and a second probe of the pair of probes is electrically connected to a second electrode of the Josephson junction.

[0012] The system may further comprise at least one processor configured to measure the resistance of each Josephson junction of the plurality of Josephson junctions via the measurement electronics and to apply the resistance change stimuli to the plurality of Josephson junctions. The parameters of a resistance change stimulus applied to a given Josephson junction of the plurality of Josephson junctions depend on the measured resistance of the given Josephson junction and on a target resistance of the given Josephson junction. Measuring the resistance of each Josephson junction and comparing it to a target resistance allows for individual and independent tuning of the resistance of each Josephson junction.

[0013] The at least one processor may be further configured to determine the parameters of the resistance change stimulus to be applied to a given Josephson junction based on the measured resistance of the given Josephson junction and on the target resistance of the given Josephson junction. The processor may be configured to iteratively measure the resistance of the plurality of Josephson junctions and apply a resistance change stimulus to a given Josephson junction until the difference between the measured resistance of the given Josephson junction and the target resistance of the given Josephson junction is lower than a threshold. In some embodiments, the iterative measurement and application of the resistance change stimulus is performed continuously.

[0014] The resistance change stimuli may be varying voltages, where the varying voltages are applied to the plurality of Josephson junctions via the plurality of pairs of probes, and where the parameters of a given resistance change stimulus include the length of time for which the varying voltage is applied to the Josephson junction to which the given resistance change stimulus is applied.

[0015] The assembly may further comprise a plurality of heating elements configured to be brought into proximity to the Josephson junctions. The resistance change stimuli may be heat applied to the plurality of Josephson junction via the heating elements, and the parameters of a given resistance change stimulus may include the length of time for which heat is applied to the Josephson junction to which the given resistance change stimulus is applied.

[0016] A second aspect of the invention relates to an assembly for simultaneously modifying the resistance of a plurality of Josephson junctions. The assembly comprises a plurality of probes configured to be brought into electrical connection with the plurality of Josephson junctions; and a plurality of heating elements configured to be brought into proximity to the Josephson junctions of the plurality of Josephson junctions.

[0017] A third aspect of the invention relates to a method of simultaneously modifying the resistance of a plurality of Josephson junctions using the systems and assemblies described above. The method comprises measuring a resistance of each Josephson junction of the plurality of Josephson junctions via the measurement electronics; and applying resistance change stimuli to the plurality of Josephson junctions via the driving electronics. The parameters of a resistance change stimulus applied to a given Josephson junction of the plurality of Josephson junctions depend on the measured resistance of the given Josephson junction and on a target resistance of the given of Josephson junction. The method may further comprise determining the parameters of the resistance change stimulus to be applied to a given Josephson junction based on the measured resistance of the given Josephson junction and on a target resistance of the given Josephson junction.

[0018] The method may further comprise iteratively measuring the resistance of a given Josephson junction of the plurality of Josephson junctions and applying a resistance change stimulus to the given Josephson junction until the difference between the measured resistance of the given Josephson junction and the target resistance of the given Josephson junction is lower than a threshold. In some embodiments, the iterative measurement and application of the resistance change stimulus is performed continuously.

[0019] The resistance change stimuli may be varying voltages, wherein the varying voltages are applied to the plurality of Josephson junctions via the plurality of pairs of probes of the assembly.

[0020] The parameters of a given resistance change stimulus may include the length of time for which the varying voltage is applied to the Josephson junction to which the given resistance change stimulus is applied or the number of cycles of the varying voltage applied to the Josephson junction.

[0021] When the assembly comprises a plurality of heating elements configured to be brought into proximity to the Josephson junctions, the resistance change stimuli may be heat applied to the plurality of Josephson junction via the heating elements.

[0022] The parameters of a given resistance change stimulus may include the temperature of the heated element and / or the length of time for which heat is applied to the Josephson junction to which the given resistance change stimulus is applied.

[0023] A fourth aspect of the invention relates to a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method described above.

[0024] A fifth aspect of the invention relates to a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method. Brief Description of the Drawings

[0025] Figure 1 shows a system for simultaneously modifying the normal state resistance of a plurality of Josephson junctions according to a first embodiment of the invention.

[0026] Figure 2 shows an assembly for simultaneously modifying the normal state resistance of a plurality of Josephson junctions according to the first embodiment of the invention.

[0027] Figure 3 shows an assembly for simultaneously modifying the normal state resistance of a plurality of Josephson junctions according to a second embodiment of the invention.

[0028] Figure 4 shows a flow chart of the method of simultaneously modifying the normal state resistance of a plurality of Josephson junctions according to the present invention.

[0029] Detailed Description of the Invention

[0030] The invention relates to assemblies, systems and methods for tuning superconducting integrated circuit elements such as Josephson junctions, in particular to assemblies, systems and method for tuning a large number of Josephson junctions simultaneously. The invention includes assemblies for applying a resistance change stimulus simultaneously to a plurality of Josephson junctions. In one embodiment, the resistance change stimulus is electrical, and in another embodiment the resistance change stimulus is thermal. The invention also includes systems including such assemblies and methods for modifying the normal state resistance of a plurality of Josephson junctions employing these assemblies and systems.

[0031] The invention is applicable to essentially any type of Josephson junction, e.g. those manufactured according to the “Manhattan” method described in Potts, A., Routley, P.R., Parker, G.J. et al., “Novel fabrication methods for submicrometer Josephson junction qubits” Journal of Materials Science: Materials in Electronics 12, 289-293 (2001), or the Dolan method described in G. J. Dolan, “Offset masks for lift-off photoprocessing”, Appl. Phys. Lett. 31, 337-339 (1977). A Josephson junction in general has a superconductor- insulator-superconductor structure. Some exemplary commonly used superconductors are aluminium, niobium, tantalum or titanium nitride or any combination thereof. The insulator layer is typically a very thin layer of oxide, e.g., aluminium oxide. The substrate may be silicon, sapphire, ceramic or any other material suitable for use as a substrate for superconducting integrated circuits. The Josephson junction may be formed as a component of a superconducting qubit, for example as a transmon qubit as described in Koch, J. et al. “Charge-insensitive qubit design derived from the Cooper pair box”, Phys. Rev. A, 76(4), 042319 (2007), or a unimon qubit as described in Hyyppa, E., Kundu, S., Chan, C.F. et al. Unimon qubit. Nat Commun 13, 6895 (2022).

[0032] When the Josephson junction is formed as part of a qubit, the Josephson junction’s normal state resistance accounts for almost the entire normal state resistance of the qubit. The qubit frequency, i.e. the transition frequency corresponding to the transition from the qubit ground state to the first excited state, which are typically used to represent computational basis states, varies based on the normal state resistance of the qubit. Therefore, by modifying the normal state resistance of the Josephson junction, the normal state resistance of the qubit can be modified, allowing fine tuning of the qubit frequency. In particular, modifying the qubit frequency may comprise increasing the normal state resistance of the Josephson junction thereby decreasing the qubit frequency. The modification of the normal resistance of the Josephson junction is done after fabrication of the Josephson junction and corresponds to a post-fabrication method of changing the qubit frequency.

[0033] According to a first embodiment of the invention, an assembly comprises a plurality of probes that are brought into electrical connection with the Josephson junctions when the assembly is in use, such that each Josephson junction is electrically connected to two probes, such that each probe of the two probes is electrically connected, e.g. via one or more intermediate components such as capacitor pads, to a different one for each electrode of the Josephson junction. This allows a normal state resistance across the barrier layer to be measured via the probes, e.g. by applying a first voltage across the barrier layer and measuring the resulting current, and for a resistance change stimulus in the form of a second voltage, e.g. a timevarying voltage of a certain shape and frequency, to be applied via the probes across the barrier layer in order to modify the normal state resistance of the Josephson junction. One exemplary way of modifying the resistance of a Josephson junction by applying a voltage across the barrier is described in Pappas, D.P., Field, M., Kopas, C.J. et al. “Alternating-bias assisted annealing of amorphous oxide tunnel junctions”, Commun Mater 5, 150 (2024), This way, according to the invention, the assembly can measure a normal state resistance of the Josephson junction as well as also apply a resistance change stimulus in order to modify the normal state resistance of the Josephson junction.

[0034] The first embodiment of the invention is shown in more detail in Figures 1 and 2. Figure 1 shows a system 1 for simultaneously modifying the resistance of a plurality of Josephson junctions 112i-112iv according to a first embodiment of the invention. The system 1 includes an assembly 100, which is made up of a support structure 101 and a plurality of probes 102a- h provided on the support structure 101. It will be appreciated that the assembly 100 may include an essentially arbitrary number of probes 102a-h.

[0035] The system 1 further comprises measurement electronics 103a and driving electronics 103b, which are connected to the probes 102a-h. The measurement electronics 103a measure a resistance of each of the plurality of Josephson junctions 112i-iv via the plurality of probes 102a-h of the assembly 100. The driving electronics 103b apply resistance change stimuli to the plurality of Josephson junctions. The system 1 may further include one or more processors for obtaining data from the measurement electronics, processing said data, and controlling the driving electronics. Measurement electronics 103a and driving electronics 103b may be provided by a single system or device capable of performing the functions attributed to the measurement electronics 103a and those attributed to the driving electronics 103b.

[0036] Figure 1 also depicts a plurality of Josephson junctions 112i-iv, located on a substrate 110. Each Josephson junction 112i-iv of the plurality of Josephson junctions is connected to external components 111 a-h, such as capacitor pads. The Josephson junctions 112i-iv may be, for example, part of the same superconducting device, e.g. a quantum processing unit. While Figure 1 depicts multiple Josephson junction arranged regularly on a single substrate, it will be appreciated the present invention is not limited to this arrangement of Josephson junctions and may be used with essentially any layout of Josephson junctions by varying the arrangement of the probes 102a-h.

[0037] The probes 102a-h are arranged to be brought into electrical connection with the plurality of Josephson junctions 112i-iv that are to be tuned when the assembly 100 I system 1 is in use. Here, “electrical connection” means an electrical connection that can at least be used to measure the resistance of a Josephson junction. The electrical connection may be “direct” in that there are no other components with a significant electrical resistance between the probes and the Josephson junctions and in that the connection does not involve capacitive or inductive coupling of the probes to the Josephson junction. The electrical connection may be formed between the Josephson junction and the probes at capacitor pads 111 a-h or other electrically conductive components of a superconducting integrated circuit that the Josephson junction is part of. Measuring the normal state resistance of the Josephson junctions may be done according to any conventional means of measuring the resistance of an electrical component, e.g. according to Ohm’s law.

[0038] In the first embodiment of the invention, the same electrical connection provided by the probes 102a-h to measure the resistance of the Josephson junction 112i-iv is also used to apply a varying voltage to the Josephson junction 112i-iv for the purpose of modifying the resistance of the Josephson junction112i-iv. In this embodiment, the resistance change stimuli relate to a voltage. The system 1 therefore further includes driving electronics 103b for applying a voltage to each of the Josephson junctions 112i-iv to modify the resistance of the Josephson junctions112i-iv.

[0039] The driving electronics 103b and measurement electronics 103a may be provided by a single device capable of both measuring the resistance and applying the resistance change stimulus voltage. Therefore, the driving electronics 103b may also be used to apply a voltage to the Josephson junctions 112 i-i v to measure the resistance of the Josephson junctions 112i-iv.

[0040] Measurement of the resistance of a Josephson junction and modification of the resistance of a Josephson junction may be carried out sequentially or simultaneously. One benefit of the first embodiment of the invention is that it is not necessary to wait for the Josephson junction to return to a different state, e.g. to cool down, before measuring the resistance change due to the resistance change stimulus.

[0041] Figure 2 depicts a single Josephson junction 112i and single pair of probes 102a, 102b from an assembly 100 contacting capacitor pads 111a, 111 b in according with the first embodiment discussed above.

[0042] According a second embodiment of the invention, as illustrated in Figure 3, an assembly 200 includes a plurality of probes 102a-h that are brought into electrical connection with the Josephson junctions 112i-iv when the assembly 200 is in use such that each Josephson junction is electrically connected to two probes of a pair of probes, one for each superconducting electrode of the Josephson junction, as in the first embodiment. This allows a normal state resistance across the barrier layer to be measured via the probes 102a-h. The assembly 200 of the second embodiment also includes a plurality of heating elements 104, each of which is associated with a pair of probes and is arranged such that the heating element 104 is in proximity to Josephson junction when the probes 102a-h are electrically connected to the electrodes of the Josephson junction. By controlling the temperature of the heating element 104 and therefore controlling the temperature of the Josephson junction, the Josephson junction is thermally annealed, modifying its normal state resistance.

[0043] Measurement of the resistance of the Josephson junction in the second embodiment may be performed in essentially the same manner as in the first embodiment and as described above with respect to Figure 1. In particular, the system 1 for simultaneously modifying the resistance of a plurality of Josephson junctions 112i-112iv according to a second embodiment of the invention includes an assembly 200, which is made up of a support structure 101 and a plurality of probes 102a-h, and measurement electronics 103a, which is connected to the probes 102a-h. It will be appreciated that the assembly 200 may include an essentially arbitrary number of probes 102a-h.

[0044] As discussed above with respect to the first embodiment, Josephson junctions 112i-iv are located on a substrate 110. Each Josephson junction 112i-iv is connected to external components 111 a-h, such as capacitor pads. The Josephson junctions 112i-iv may be, for example, part of the same superconducting device, e.g. a quantum processing unit. While Figure 1 depicts multiple Josephson junction 112i-iv arranged regularly on a single substrate, it will be appreciated the present invention is not limited to this arrangement of Josephson junctions 112 i-i v and may be used with essentially any layout of Josephson junctions 112i-iv by varying the arrangement of the probes 102a-h.

[0045] The probes 102a-h are arranged to be brought into electrical connection with the plurality of Josephson junctions 112i-iv that are to be tuned. Here, “electrical connection” means an electrical connection that can at least be used to measure the resistance of a Josephson junction. The electrical connection may be “direct” in that there are no other components with a significant electrical resistance between the probes 102a-h and the Josephson junctions 112i-iv and in that the connection does not involve capacitive or inductive coupling of the probes to the Josephson junction. The electrical connection may be formed between the Josephson junction 112 i-i v and the probes 102a-h at capacitor pads 111 a-h or other electrically conductive components of a superconducting integrated circuit that the Josephson junction is part of. Measuring the normal state resistance of the Josephson junctions 112i-iv may be done according to any conventional means of measuring the resistance of an electrical component, e.g. according to Ohm’s law.

[0046] In the second embodiment of the invention, the assembly 200 further includes a plurality of heating elements 104 for providing a resistance change stimulus in the form of heat to the Josephson junctions 112i-iv. The heating elements 104 are arranged with respect to the probes 102a-h such that the heating elements 104 are brought into proximity to the Josephson junctions 112i-iv when the probes are brought into electrical connection with the Josephson junctions 112i-iv. The plurality of heating elements 104 and the plurality of probes 102a-h are provided on a supporting structure 101. A heating element 104 is associated with a pair of probes so that there is a repetitive arrangement of pair of probes with heating element 104 on the supporting structure 101 of the assembly 200. A single pair of probes 102a-b and heating element 104 are shown in more detail in Figure 3. It will be understood that the arrangement of probes 102a-b and heating element 104 is repeated multiple times across the assembly of the second embodiment in order to allow the simultaneous tuning of multiple Josephson junctions 112i-iv.

[0047] In the second embodiment, the system 2 may further include driving electronics 103b for applying a suitable voltage / current to each of the heating elements 104. The driving electronics 103b and measurement electronics 103a may be provided by a single device capable of both measuring the resistance and applying the resistance change stimulus voltage.

[0048] In all embodiments of the invention, the probes 102a-b are arranged such that they can quickly and easily simultaneously provide a connection with multiple Josephson junctions 112i-iv, e.g. multiple Josephson junctions in superconducting quantum processing unit (QPU), or multiple Josephson junctions on a single un-diced wafer. In the second embodiment of the invention, the heating elements 104 are also arranged such that they can be quickly and easily brought into proximity with multiple Josephson junctions 112i-iv, e.g. multiple Josephson junctions in superconducting quantum processing unit (QPU), or multiple Josephson junctions on a single un-diced wafer.

[0049] Figure 4 depicts a flow chart of a method according to the invention for simultaneously modifying the resistance of a plurality of Josephson junctions 112i-iv using the assembly 100, 200 or system 1 , 2 of either the first or second embodiment.

[0050] At 401 , the initial resistance of each Josephson junction 112i-iv is measured. The measured resistance is the normal state resistance, i.e. the resistance of the Josephson junction 112 i- i v at a non-superconducting temperature.

[0051] At 402, the initial measured resistance for each Josephson junction 112i-iv is compared to the target resistance for each Josephson junction 112i-iv, which may be the same for all Josephson junctions 112 i-i v or may differ for some or all of the Josephson junctions 112i-iv. The target resistance refers to a desired resistance for a given Josephson junction 112i-iv based on its intended use, e.g. in a qubit. As mentioned above, the frequency of a qubit at cryogenic temperatures can be predicted from the normal state resistance of the Josephson junctions, i.e. their electrical resistance measured at room temperature. Therefore, the target resistance of a Josephson junction 112i-iv may be determined according to a desired frequency of a qubit of which the Josephson junction will be a part. The target resistance may be the same for all Josephson junctions, or at least some Josephson junctions may have different target resistances. In particular, when applying the method to multiple Josephson junctions of the same quantum processing unit, it is likely to be necessary to have different target resistances for different Josephson junctions in order to produce qubits having different frequencies to avoid qubit frequency crowding.

[0052] If the measured resistance for a given Josephson junction 112i-iv is not equal to or within a pre-determined margin of the target resistance for that Josephson junction, a resistance change stimulus is applied to that Josephson junctions at 403, to change the resistance of the Josephson junction 112i-iv. The resistance change stimulus can be a varying voltage applied via the probes and as described above with respect to the first embodiment. Such resistance change stimulus would result in current annealing of the Josephson junction. The resistance change stimulus may alternatively be heat applied to the Josephson junctions via the heating elements of the assembly, as described above with respect to the second embodiment. The heat may be produced by a varying electrical current applied to each heating element. In this case, the resistance change stimulus applied would result in thermal annealing of the Josephson junction, in particular to a local thermal annealing of the Josephson junction.

[0053] Steps 401-403 may be repeated iteratively for each Josephson junction until the target resistance is achieved. Steps 401-403 may be performed concurrently for all relevant Josephson junctions 112i-iv, i.e. those that have not already reached the target resistance.

[0054] In both embodiments, the iterative process may be applied to each Josephson junction individually, i.e. applying a resistance change stimulus to each Josephson junction having parameters, such as length of time of application, tailored to that individual Josephson junction. Alternatively, the same resistance change stimulus may be applied to all Josephson junctions and then repeated only for those Josephson junctions that have not yet reached the target resistance.

[0055] In the first embodiment of the invention, in which the resistance change stimulus is a voltage applied to the Josephson junctions, steps 401-403 may be performed continuously, since the resistance of a given Josephson junction may be measured at the same time as the resistance change stimulus is applied.

[0056] The method may further include a step between 402 and 403 of determining the parameters for the resistance change stimulus. In the first embodiment, the parameters may include: the length of time for which the varying voltage is applied, or the number of cycles of the varying voltage. In the second embodiment, the parameters may include: the temperature of the heated element and / or the length of time for the heated element to be turned on. Parameters may be determined on a per-Josephson junction basis in order to minimise the number of iterations of the method for each Josephson junction. Alternatively, parameters may be determined such that the same stimulus is applied to all Josephson junctions in each step. The parameters may be determined such that the expected resistance change as a result of the resistance change stimulus is less than the resistance change required to reach the target resistance, since the resistance change is generally only an increase in resistance, and it may not be possible to decrease the resistance of the Josephson junction if the target resistance is overshot. The method may include an optional step preceding step 401 of placing the entire quantum processing unit (or any other arrangement of Josephson junctions that are to have their resistances tuned) inside an annealer in order to cause global thermal annealing, which artificially expedites the oxide aging process. The purpose of this step is to make the oxide to become more stable so that the qubit resistance shows almost no further change for an extended period even when stored in ambient environment.

[0057] The method may be performed by a computer system configured to control the system of the first or second embodiments described above.

Claims

Claims1. A system (1 , 2) for simultaneously modifying the resistance of a plurality of Josephson junctions (112i-iv), the system comprising: an assembly (100, 200) comprising a plurality of probes (102a-h) configured to be brought into electrical connection with the plurality of Josephson junctions (112i- iv); measurement electronics (103a) for measuring a resistance of each of the plurality of Josephson junctions (112i-iv) via the plurality of probes (102a-h); and driving electronics (103b) for applying resistance change stimuli to the plurality of Josephson junctions (112i-iv) in order to simultaneously modify the resistance of at least a subset of the plurality of Josephson junctions (112i-iv).

2. The system (1 , 2) of claim 1 , wherein the plurality (102a-h) of probes comprises a plurality of pairs of probes (102a-h), and wherein each pair of probes (102a-h) of the plurality of pairs of probes (102a-h) is configured to provide electrical connection with a different Josephson junction of the plurality of Josephson junctions (112i-iv) such that a first probe of the pair of probes is electrically connected to a first electrode of the Josephson junction and a second probe of the pair of probes is electrically connected to a second electrode of the Josephson junction.

3. The system (1 , 2) of claim 1 or 2, further comprises at least one processor configured to: measure the resistance of each Josephson junction of the plurality of Josephson junctions (112i-iv) via the measurement electronics (103a); and apply the resistance change stimuli to the plurality of Josephson junctions (112i- iv), wherein the parameters of a resistance change stimulus applied to a given Josephson junction of the plurality of Josephson junctions (112i-iv) depend on the measured resistance of the given Josephson junction (112i-iv) and on a target resistance of the given Josephson junction (112i-iv).

4. The system (1 , 2) of claim 3, wherein the at least one processor is further configured to determine the parameters of the resistance change stimulus to be applied to a givenJosephson junction (112i-iv) based on the measured resistance of the given Josephson junction and on the target resistance of the given Josephson junction (112i-iv).

5. The system (1 , 2) of claim 3 or 4, wherein the processor is configured to iteratively measure the resistance of the plurality of Josephson junctions (112i-iv) and apply a resistance change stimulus to a given Josephson junction (112i-iv) until the difference between the measured resistance of the given Josephson junction (112i-iv) and the target resistance of the given Josephson junction (112i-iv) is lower than a threshold.

6. The system (1) of any preceding claim, wherein the resistance change stimuli are varying voltages, wherein the varying voltages are applied to the plurality of Josephson junctions (112i-iv) via the plurality of pairs of probes, and wherein the parameters of a given resistance change stimulus include the length of time for which the varying voltage is applied to the Josephson junction (112i-iv) to which the given resistance change stimulus is applied.

7. The system (2) of any of claims 1 to 5, wherein the assembly (100, 200) further comprises a plurality of heating elements (104) configured to be brought into proximity to the Josephson junctions (112i-iv), wherein the resistance change stimuli are heat applied to the plurality of Josephson junction (112i-iv) via the heating elements (104), and wherein the parameters of a given resistance change stimulus include the length of time for which heat is applied to the Josephson junction (112 i-i v) to which the given resistance change stimulus is applied.

8. An assembly (200) for simultaneously modifying the resistance of a plurality of Josephson junctions (112i-iv), the assembly comprising: a plurality of probes (102a-h) configured to be brought into electrical connection with the plurality of Josephson junctions (112i-iv); and a plurality of heating elements (104) configured to be brought into proximity to the Josephson junctions (112i-iv) of the plurality of Josephson junctions (112i-iv).

9. A method of simultaneously modifying the resistance of a plurality of Josephson junctions using the system of any one of claims 1 to 7, the method comprising:measuring a resistance of each Josephson junction of the plurality of Josephson junctions via the measurement electronics; applying resistance change stimuli to the plurality of Josephson junctions via the driving electronics, wherein the parameters of a resistance change stimulus applied to a given Josephson junction of the plurality of Josephson junctions depend on the measured resistance of the given Josephson junction and on a target resistance of the given of Josephson junction.

10. The method of claim 9, wherein the method further comprises determining the parameters of the resistance change stimulus to be applied to a given Josephson junction based on the measured resistance of the given Josephson junction and on a target resistance of the given Josephson junction.

11. The method of claim 9 or 10, wherein the method comprises iteratively measuring the resistance of a given Josephson junction of the plurality of Josephson junctions and applying a resistance change stimulus to the given Josephson junction until the difference between the measured resistance of the given Josephson junction and the target resistance of the given Josephson junction is lower than a threshold.

12. The method of any of claims 9 to 11 , wherein the resistance change stimuli are varying voltages, wherein the varying voltages are applied to the plurality of Josephson junctions via the plurality of pairs of probes of the assembly.

13. The method of claim 12, wherein the parameters of a given resistance change stimulus include the number of cycles of the varying voltage or the length of time for which the vary voltage is applied to the Josephson junction to which the given resistance change stimulus is applied.

14. The method of any of claims 9 to 11 , wherein the assembly further comprises a plurality of heating elements configured to be brought into proximity to the Josephson junctions, wherein the resistance change stimuli are heat applied to the plurality of Josephson junction via the heating elements.

15. The method of claim 14, wherein the parameters of a given resistance change stimulus include the temperature of the heated element and / or the length of time for which heat is applied to the Josephson junction to which the given resistance change stimulus is applied.

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