Superconducting circuit system

Abstract

A superconducting circuit system (SCC) includes peripheral electronics and a superconducting device. The superconducting device includes a substrate and at least one superconducting film forming a ground plane. The superconducting device further includes at least one SCC formed near the ground plane and including a plurality of modules having elements connected to a plurality of pads providing an electrical interface between the superconducting device and the peripheral electronics. The superconducting device also includes a plurality of heating elements that, upon energization by the peripheral electronics, induce a non-uniform temperature distribution in at least the ground plane of the superconducting device. The heating elements are configured to establish a spatially varying temperature distribution within the superconducting device, thereby enabling controlled movement of regions transitioning between superconducting and normal states.

Description

SUPERCONDUCTING CIRCUIT SYSTEMCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U. S. Provisional Patent Application No. 63 / 749,812, filed on January 27, 2025, the contents of which are incorporated herein by reference in their entirety.BACKGROUND OF THE INVENTION1. Field of the Invention

[0002] The present invention generally relates to superconductive circuits (SCC), and more specifically, to a superconducting circuit system designed to manage and remove magnetic flux.2. Description of the Prior Art

[0003] One problem arising in superconductor digital electronic circuit applications is flux trapping (FT), i.e., the trapping of magnetic flux that can degrade superconducting circuit (SCC) device performance. The prior art has proposed various techniques for reducing magnetic flux in an SCC device. A common practice for reducing magnetic flux is thermal cycling, also referred to as thermal defluxing, in which the SCC is heated to a temperature above the critical temperature (Tc), for example by energizing an on-chip resistive heater, and then cooled to a temperature below Tc by de-energizing the heater. The random temperature fluctuation that occurs at the transition temperature of superconductors causes a modified distribution of magnetic fluxes By repeatedly heating and cooling the SCC, the likelihood of displacing trapped flux from critical regions of the SCC, or expelling such flux from the SCC, may be increased, and residual magnetic flux may be reduced. However, the magnetic field generated by current used to drive the heater can itself cause additional flux trapping, thereby limiting the effectiveness of such techniques. To reduce the possibility of trapping the flux accompanying the electric current, instead of a heater typically located on the chip, a heater located at the farthest possible point from the SCC device package is used and the heat is delivered to the device using a thermal link. Such heaters and thermal linksgenerally provide substantially uniform heating of the superconductor and, because flux trapping occurs in a largely stochastic manner, expulsion of trapped flux from the SCC is not assured.

[0004] Another technique for reducing flux trapping employs protective moats, such as elongated openings formed in ground planes and other superconducting films of an SCC device, which surround superconducting circuit elements and act as pinning sites for trapped flux, thereby maintaining the trapped flux at a distance from magneto-sensitive circuits. The density of such moats is preferably sufficiently high and may exceed an expected flux-trapping density, since flux trapped within a moat can repel additional flux of the same polarity and thereby reduce the effectiveness of the moat. Trapped flux can affect the SCC by penetrating Josephson junctions or coupling to magneto-sensitive gates. However, in typical design flows, the SCC circuitry is designed first, and the shapes and placement of moat patterns are defined afterward based on the space available around the circuitry. As a result, moats are generally formed surrounding Josephson junctions and magneto-sensitive gates.

[0005] Due to sophisticated magnetic shielding, the expected FT density can be reduced to a level at which moat density is sufficient to protect an SCC by trapping substantially all frozen flux. However, the distance between trapped fluxes should be compatible with, or less than, a typical circuitry cell size. To trap frozen fluxes at the Earth’s magnetic field, moat spacing should be narrowed to approximately 5 pm. However, such a scale of dimensions remains challenging for currently available superconductor technologies. Moreover, this technique does not provide protection if an SCC device is exposed to magnetic fields significantly stronger than those of the Earth.

[0006] According to the technique disclosed in U. S. Pat. No. 5,173,620 (the “’620 Patent”), elimination of trapped flux is achieved by producing a non-uniform temperature distribution during thermal cycling. The temperature distribution is induced by a heating arrangement comprising a plurality of resistive heating elements mounted on a substrate of the SCC device. The resistive heating elements are connected to a plurality of drivers controlled by a microcontroller The temperature distribution is periodically changed over time such that regions of normal conduction, corresponding to areas heated to a temperature above Tc, are moved across the SCC.

[0007] According to the ’620 Patent, a non-uniform temperature distribution can also be induced by a heating arrangement that heats the SCC laterally In response to a decrease in temperature induced by a heating part located outside the SCC, a region of the superconducting state grows in a direction toward the heating part, thereby pushing trapped flux out of the SCC The described embodiment can be modified by providing a pair of heating parts on the chip substrate at opposite sides of the SCC. In this case, the separation between the heating parts is determined in consideration of the thermal conductivity and heat capacity of the substrate and the SCC such that a temperature profile formed in response to a decrease in temperature includes a valley between the heating parts.

[0008] The magnetic field induced by the resistive heating elements is attenuated by using elements that carry current in opposite directions and are arranged to form a magnetic dipole. However, because the device disclosed in the ’620 Patent includes multiple resistive heating elements located in the vicinity of the SCC, as well as multiple conductors used to connect the resistive heating elements to their drivers, the magnetic field produced by current flowing through these heating elements and conductors may cause new FT.

[0009] The ’620 Patent also discloses a system for eliminating magnetic flux from a superconductor used to form an SCC, in which a laser is used to heat the superconductor to a temperature above Tc by scanning over the superconductor from one end to another. The laser beam forms a region of normal conduction that moves in the scanning direction and collects and transfers flux quanta outside the superconductor. However, such a system requires a complex scanning mechanism. Furthermore, heating the superconductor using a scanning laser beam may be ineffective due to beam reflection.SUMMARY OF THE INVENTION

[0010] It is an object of the invention to provide a novel superconducting circuit (SCC) system for reducing flux trapping (FT) in a superconductor forming an SCC by heating the SCC to atemperature above Tc and subsequently cooling the SCC to a temperature below Tc, while avoiding the foregoing problems associated with prior-art techniques,[0011 J Another object of the present invention is to provide an SCC system in which reduction of FT in a superconductor forming an SCC is accomplished by providing a non-uniform temperature distribution in the superconductor upon energization of a heating unit, which preferably includes a plurality of heating plates. The heating plates provide the non-uniform temperature distribution while not inducing a magnetic field that could cause additional FT.

[0012] Another object of the present invention is to provide an SCC system for reducing FT in a superconductor forming an SCC, in which reduction of the flux trapping is achieved using a simple construction that employs existing SCC modules or elements as heating plates,

[0013] Another object of the present invention is to provide an SCC system for reducing FT in a superconductor forming an SCC, in which reduction of the flux trapping is achieved with a simple construction that employs bonding wires and pads of the SCC device, as well as contacts and traces of a printed circuit board (PCB) connector, as thermal links for delivering heat to the SCC.

[0014] Another object of the present invention is to provide an SCC system for reducing FT in a superconductor forming an SCC, in which reduction of the flux trapping is achieved by¬ directing magnetic flux motion toward moat patterns.

[0015] A SCC system includes peripheral electronics and a superconducting device. The superconducting device includes a substrate and at least one superconducting film forming a ground plane. The superconducting device further includes at least one SCC formed near the ground plane and including a plurality of modules having elements connected to a plurality of pads providing an electrical interface between the superconducting device and the peripheral electronics. The superconducting device also includes a plurality' of heating elements that, upon energization by the peripheral electronics, induce a non-uniform temperature distribution in at leastthe ground plane of the superconducting device In one embodiment, the plurality of heating elements is energized through thermal links connected to at least one heating fixture located outside the superconducting device. The heating elements are configured to establish a spatially varying temperature distribution within the superconducting device, thereby enabling controlled movement of regions transitioning between superconducting and normal states. Additionally, the heating elements may include heating plates embedded in the substrate of the superconducting device. In one embodiment, portions of the superconducting circuit modules, or elements thereof, are configured to function as heating elements.

[0016] The at least one heating fixture and the superconducting device may be provided on a printed circuit board PCB having traces routed to pads on the superconducting device. The heating fixture may include resistive heating elements The peripheral electronics include drivers configured to energize the heating fixture by controlling current flowing through the resistive heating elements. The heating fixture may be thermally coupled to the traces of the PCB via thermal links.

[0017] In one embodiment, the superconducting device is mounted on a PCB having traces routed to pads of the superconducting device. The traces may be connected to heating elements and may include resistive elements used as heating fixtures.

[0018] In one embodiment, the SCC system further includes a laser directing a beam toward a heating fixture to induce localized heating. The heating fixture may include a box provided with an opening for the laser beam. The box may have an elliptical shape, and the laser beam may be directed toward one of the foci of the ellipse

[0019] In one embodiment, the SCC system includes an SCC device mounted on a substrate, the substrate including a ground plane and a heating part surrounding the SCC device. The SCC device may further include a plurality of connecting pads provided on the substrate outside a boundary of the SCC device. A plurality of heating elements may be provided outside the SCC substrate and electrically coupled to the plurality of connecting pads, wherein the plurality of heating elements, upon energization by an external power source, provide heat to the heating partof the substrate, thereby inducing a non-uniform temperature distribution in the ground plane to facilitate magnetic flux motion.

[0020] The heating pan may include a plurality of heating plates embedded in the substrate of the SCC device and coupled to the plurality of connecting pads The heating plates may be located on at least two opposing sides of the SCC device. The external power source may include a microcontroller and drivers electrically coupled to the heating elements. The heating elements may include a heating fixture having at least one resistive heating element mounted on a thermal pad. The ground plane may include a plurality of moats for accommodating magnetic flux.[0021 J These and other objects, advantages, and features of the present invention will become apparent from the following more particular description.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a schematic view of a first embodiment of an SCC system;

[0023] FIG. 2 is a schematic view of the SCC device of FIG. 1, illustrating a heating part in detail;

[0024] FIG. 3 is a diagram illustrating a non-uniform temperature distribution induced in the SCC using the heating part of FIG. 2;

[0025] FIG. 4 is a schematic view of an alternative embodiment of the SCC device of the system; of FIG 1;

[0026] FIG. 5 is a schematic view of a second embodiment of the SCC system;

[0027] FIG. 6 is an exploded perspective view illustrating an embodiment of a heating fixture adapted to be energized by electrical current;[0028J FIG, 7 is a schematic view of a third embodiment of the SCC system; and

[0029] FIG. 8 is a schematic view of an embodiment of a heating fixture adapted to be energized by a laserDETAILED DESCRIPTION

[0030] Those skilled in the art will appreciate that an electronic system comprising an SCC device may include a cryocooler thermally coupled to the SCC device by a thermal link, as wellas electrical connectors for coupling components of the electronic system to room-temperature electronic devices. The operating temperature of the SCC device is typically around 4 K. For connecting the SCC device to the room-temperature electronic devices, beryllium-copper wires are commonly used to reduce the thermal load on the cryocooler due to the relatively low thermal conductivity of beryllium-copper. The SCC device is typically installed on a printed circuit board (PCB) comprising top and bottom layers with traces routed to the SCC device. The bottom layer may also be used as a ground plane and may be thermally coupled to the cryocooler via a thermal link.

[0031] FIG. 1 depicts an SCC system in which the technique of the present invention for reducing flux trapping may be implemented. The system 100 includes an SCC device 101 comprising a substrate 102, a heating part 103 embedded in the substrate 102, a ground plane (not shown), an SCC 104 formed near the ground plane, and a plurality of pads 105 connected by bond wires 106 to the SCC 104 or to the heating part 103. The SCC system further includes room¬ temperature peripheral electronic devices 107 located at a distance from the SCC 104. The roomtemperature peripheral electronic devices may include a microcontroller 108, drivers 109 coupled to the microcontroller 108, and control electronics 110. Heating fixtures 111 are energized by the drivers 109 and are thermally coupled to thermal pads 112 located on a top layer of a PCB. PCB traces 113 electrically connect the control electronics 110 to the SCC 104 and are located on the top layer of the PCB PCB traces 114 connect the thermal pads 112 to the heating part 103 and are also located on the top layer of the PCB. A PCB ground plane 115 is located on a bottom layer of the PCB below the traces 113. Electrical conductors 116 connect the room -temperature electronic devices 107 to the traces 113 and 114. The ground plane under the traces 113 may be removed.

[0032] A preferred configuration of the heating fixture 111 is illustrated in FIG. 6. The heating fixture 111 preferably includes a copper conductor 601 attached to a dielectric part 602 of the conductor 601, two leads 603 attached to the dielectric part 602, and a horizontal heat-conduction surface 604. The heating fixture I ll further includes resistive heating elements 605 connecting the conductor 601 to the leads 603. A high-thermal-conductivity dielectric 606 may be attached to the horizontal heat-conduction surface 604 using a screw 607 and a nut 608. The heat-conduction surface 604, the dielectric 606, the thermal pad 112, and the PCB 115 may be provided with alignedopenings for pressing the heating fixture 111 against the thermal pad 112 using the screw 607 and the nut 608. If the screw 607 is made of metal, a diameter of an opening in the thermal pad 112 may be greater than diameters of corresponding openings in the heat-conduction surface 604 and the dielectric 606. The thermal pad 112 is located near a footprint 609 used for soldering the leads 603 to the PCB 115. Traces 610 connect the heating fixture 111 to beryllium-copper wires 116, shown in FIGS. 1 and 5.

[0033] To minimize a magnetic field produced by driving current, the resistive heating elements 605 are arranged such that a magnetic dipole is formed, the magnetic field strength of which decreases with increasing distance. To reduce the possibility of flux trapping (FT) caused by the magnetic field produced by current flowing through the resistive heating elements 605, the thermal pads 112 are installed at a distance from the SCC device 101 sufficient to attenuate the magnetic field at the SCC device. In one embodiment, the thermal pads 112 are positioned outside an immediate vicinity of the SCC device. In a preferred embodiment, the thermal pads 112 are positioned remote from the SCC device.

[0034] As shown, for example, in FIG. 1, heat generated by the heating fixture 111 is coupled to thermal pads 112 and transferred to the heating part 103 through traces 114 and bond wires 106 serving as thermal links to heat the SCC 104. When the SCC system 100 is used for testing SCC devices 101, a separate connector may be inserted in the heat path. Use of a separate electrical connector for installing the SCC device 101 on the PCB should be considered carefully, because resilient conductors of such connectors are typically made of beryllium-copper and may exhibit relatively high thermal resistance, in which case a higher current may be required to drive the resistive heating elements 605 to heat the heating part 103. A connector disclosed in patent applications WO 2019 / 204686 and US 2021 / 0036446, the disclosures of which are incorporated herein by reference, may be used to reduce an increase in thermal resistance in the heat path to the heating part 103 when a separate connector is used to install an SCC device 101. Such a connector does not substantially increase thermal resistance, as it provides a direct thermal connection between the traces 114 and the pads 105.

[0035] FIG. 2 is a schematic view of an SCC device 101, in which the heating part 103 is shown in detail. The heating part 103 preferably includes a plurality of heating plates 201 embedded in the substrate 102 and connected to pads 105 of the SCC device 101 by bond wires 106 The number of heating plates 201 and their arrangement are selected in consideration of an actual size and construction of the SCC 104, as well as thermal conductivity and heat capacity of the substrate 102. Preferred patterns include heating plates located outside boundaries of the SCC 104, at least at two opposing sides thereof.

[0036] The pattern of heating elements shown in FIG. 2 includes a plurality of heating plates 201 located outside boundaries of the SCC 104. Such a pattern may be used to induce a non-uniform temperature distribution across the SCC 104, with regions of elevated temperature located outside the boundary of the SCC 104.

[0037] FIG. 3 illustrates representative temperature distributions along a direction X across the SCC 104, as schematically shown for explanatory' purposes. The illustrated graph includes a temperature axis T and a spatial axis X, with positions along the axis X corresponding to locations across the SCC 104, including boundary' locations denoted by BL and BR. A reference temperature corresponding to the superconducting critical temperature Tc is also shown. A plurality of example temperature profiles Pl, P2, P3,... are illustrated to show different non-uniform temperature distributions that may occur in the SCC 104 as heat is transferred from heating plates 201 positioned outside the SCC 104. In the illustrated examples, regions of relatively higher temperature are located proximate to boundary regions of the SCC 104, while a region of relatively lower temperature is located in a central area of the SCC 104. Temperature differences indicated in the figure are shown for illustrative purposes only.

[0038] In FIG. 3, regions of the superconducting material at temperatures above the critical temperature Tc are indicated by the character “A,r,” corresponding to a normal conduction state, while regions at temperatures below Tc are indicated by the character “5,” corresponding to a superconducting state. As the superconducting material is cooled through the superconducting transition, FT may occur at a temperature slightly below Tc, sometimes referred to as a fluxfreezing temperature. Although superconducting materials generally expel magnetic flux uponentering the superconducting state, non-uniform cooling can result in localized regions that remain in the normal conduction state for a period of time, within which magnetic flux may persist. As cooling continues and such regions transition into the superconducting state, magnetic flux present in those regions may become trapped in the form of flux quanta. At temperatures at or below Tc, the trapped magnetic flux becomes effectively immobilized within the superconducting material.

[0039] The diagram in FIG. 3 schematically represents a FT reduction process. In one example, the SCC device 101 is cooled to a temperature near the superconducting critical temperature Tc. Heating fixtures 111 may then be energized to introduce heat that is thermally coupled to the SCC device 101 through thermal pads 112, traces 114, and bond wires 106, which serve as thermal links due to their relatively high thermal conductivity. As a result, heating plates 201 may be heated relative to other regions of the SCC device 101, producing a non-uniform temperature distribution across the SCC 104, as illustrated by profile Pl in FIG. 3. In this illustrative condition, the superconducting material of the SCC 104 is shown in a normal conduction state N.

[0040] As illustrated in FIG. 3, successive heating conditions applied to the heating plates 201 may result in changes in the non-uniform temperature distribution across the SCC 104 during cooling. In one example, a region of superconducting conduction state S may form between regions A of normal conduction located closer to boundary locations BL and BR of the SCC 104, as shown by profile P2. Magnetic flux F present in regions N may be displaced toward boundary -adjacent regions, as schematically indicated by arrows 130, as the superconducting state region expands during cooling.

[0041] With continued cooling, regi ons of normal conduction N eventually disappear, and the superconducting state S extends across substantially the entire SCC 104. Magnetic flux displaced toward boundary-adjacent regions of the SCC 104, such as those indicated near locations denoted by BL and BR, becomes pinned outside active regions of the SCC 104.

[0042] FIG. 4 illustrates a modified SCC device 401 relative to the SCC device 101 shown in FIG. 2. The SCC device 401 includes a substrate 102, heating plates 402 embedded in the substrate 102, a ground plane (not shown in FIG. 4) including a plurality of moats 403, an SCC 104 formed near the ground plane, and a plurality of pads 105 connected by bond wires 106 to the SCC 104 or to the heating plates 402. The heating plates 402 are arranged along boundary regions of the SCC 104 with varying orientation and spacing relative to one another.

[0043] In the arrangement shown in FIG 4, the relative spacing, orientation, and branching of the heating plates 402 influence thermal conditions in regions of the SCC 104 located between portions of the heating plates 402. Regions located between closely spaced portions of heating plates 402, as well as regions proximate to angular portions thereof, may retain elevated temperatures during operation. During cooling of the SCC device 401, such regions may transition to the superconducting state later than surrounding regions, thereby influencing displacement of magnetic flux, as schematically indicated by arrows in FIG. 4.

[0044] A distinctive feature of the SCC device 401 shown in FIG. 4 is the use of heating-plate-oriented patterns that influence pathways of magnetic flux during the cooling process. Certain moats 403 are located around heating plates 402 in the vicinity thereof, while a plurality of moats 403 are located near boundary regions of the SCC 104, at a distance from flux-sensitive devices, in areas where magnetic flux tends to accumulate due to regions of elevated temperature. During initial cooling of the SCC 104, magnetic flux quanta may be trapped either in one of the moats 403 or directly in the ground plane and become immobilized therein. In an initial stage of a fluxreduction process, the SCC 104 may be heated to a condition corresponding to a temperature distribution represented by profile P1 of FIG. 3. Under this condition, the temperature of the ground plane is above the superconducting critical temperature Tc, such that the ground plane is in a normal conduction state A, allowing magnetic flux to move either in moats or in the ground plane.

[0045] Further, in the system 400 shown in FIG. 4, successive heating conditions of the heating plates 402 may result in changes in the non-uniform temperature distribution across the SCC 104 during cooling. In response to such changes, a superconducting state region S at a temperaturebelow the critical temperature Tc may appear between regions N of normal conduction and may be located closer to boundary regions of the SCC 104, as illustrated by profile P2. Magnetic fluxes F present in regions N may be displaced toward boundary-adjacent regions, as schematically indicated by arrows in FIG 3 and FIG. 4. As displaced magnetic flux encounters moats 403 that may already contain trapped magnetic flux of the same polarity, mutual repulsion between flux quanta makes further trapping in those moats energetically unfavorable. As a result, the displaced magnetic flux may be redirected toward other moats 403 located along its path toward boundary regions of the SCC 104, thereby promoting distribution of magnetic flux among multiple moats. With continued cooling, regions N may disappear and the superconducting state S may extend across substantially the entire SCC 104, while magnetic flux is displaced to regions outside active portions of the SCC 104, where some flux may become pinned in the ground plane and other flux may be trapped by moats 403 located proximate to boundary regions and heating plates 402.

[0046] Those skilled in the art will appreciate that the moats 403 may have different shapes and sizes. The heating plates 402, as well as the moats 403, may also be formed in other closely located superconducting films of the SCC device.

[0047] A schematic view of a second embodiment of the system is presented in FIG. 5. The SCC system 500 includes an SCC device 501 comprising a substrate 102, a ground plane 502 having a plurality of moats 503, at least one SCC 504 formed near the ground plane 502, and a plurality of pads 105 connected by bond wires 106 to the SCC 504. The SCC system 500 further includes room-temperature electronic devices 107. The room-temperature electronic devices 107 may include a microcontroller 108, drivers 109 coupled to the microcontroller 108, and control electronics 110. Heating fixtures 111 are energized by the drivers 109 and are thermally coupled to thermal pads 112. PCB traces 113 and 114 electrically connect the SCC 504 to the control electronics 110 through the pads 105. A PCB ground plane 115 is located below the traces 113. Electrical conductors 116 connect the room-temperature electronic devices 107 to the traces 113 and 114. The PCB traces 114 are provided with thermal pads 112, and the PCB ground plane 115 under the traces 114 is removed.

[0048] An SCC device may comprise several modules formed on a common ground plane. Such modules may be electrically connected or electrically disconnected from one another on-chip. Electrically connected modules typically exhibit stronger thermal coupling to one another than modules that are electrically disconnected, although not every electrical connection necessarily provides effective thermal coupling. Accordingly, certain electrically connected modules may behave as thermally isolated from one another, while groups of modules that are thermally coupled may be considered thermally isolated from other modules. When heat is introduced to neighboring modules that are thermally isolated from one another, a non-uniform temperature distribution may form in regions between such modules after a characteristic thermal response period. Such non-uniform temperature distributions may influence displacement of magnetic flux toward moats, as described above. Thermal response characteristics may also differ among individual elements within an SCC module. Accordingly, SCC modules and their elements may be regarded as a system of thermally coupled and thermally isolated circuit elements and may be used by the system as heating elements

[0049] In practice, voltage and current characteristics of SCC devices fabricated in the same batch may vary due to imperfections in the fabrication process. In such cases, device performance may be influenced by operating temperature, and adjusting the temperature of an SCC device may allow operation closer to a desired operating condition. The ability to vary the temperature of a tested SCC device may therefore be advantageous.

[0050] FIG. 7 is a schematic view of a third embodiment of an SCC system 700 that enables adjustment of operating conditions of an SCC device. The system 700 includes an SCC device 501 comprising an SCC 504 including a plurality of module elements, and a plurality of pads 105 connected to the module elements by bond wires 106. The system 700 further includes room¬ temperature electronic devices 107, including control electronics 110. PCB traces 113 and PCB traces 114 electrically connect the control electronics 110 to the pads 105. A PCB ground plane 115 is located below the traces 113. Electrical conductors 116 connect the room-temperature electronic devices 107 to the pads 105 through the PCB traces 113 and 114, and resistive elements 701 are inserted into the PCB traces 114 The PCB ground plane 115 under the traces 114 may be removed. Heat generated by current flowing through the resistive elements 701 in the PCB traces114 is thermally coupled through the traces to the SCC 504 module elements. The resistive elements 701 may be selected in consideration of driving current levels and thermal characteristics of the SCC device.

[0051] To reduce additional thermal load on the cryocooler caused by heat generated by current flowing through resistive elements 701, the SCC system 700 may utilize such resistive elements as one option for providing heat to selected portions of the SCC device. As an alternative option, the SCC system 700 may utilize heat produced by other electronic components, such as resistors populating the PCB, that are not part of the SCC system. For this purpose, thermal coupling between a component producing such heat and a thermal pad 112 connected to a corresponding trace 114 may be adjusted by selecting a thermal link having an appropriate thermal resistance. The first and second system embodiments may be used not only during thermal cycling but also during operation of the system. Heating of selected SCC module elements may influence voltage and current characteristics of the SCC device during operation.

[0052] Another configuration of a heating fixture used to heat SCC 504 module elements is schematically shown in FIG. 8. The heating fixture 800 includes a copper box 801 soldered to a thermal pad 802 located on the PCB 115, and a thermal link 803 formed as a trace connecting the thermal pad 802 to the trace 114. The copper box 801 is provided with a hole 804 sized to pass a laser beam 805. An elliptical shape of the copper box 801 and orientation of the laser beam 805 toward one of the foci of the ellipse may be used, as an elliptically shaped box can reflect an incident laser beam along a major axis of the ellipse. Dimensions of the thermal link 803 may be selected to influence thermal coupling between the heating fixture 800 and SCC 504 module elements. The heating fixture 800 may be energized by a laser coupled to a beam splitter that produces multiple beams delivered through optical fibers (not shown) and directed to different copper boxes 801 soldered to respective thermal pads 802. Since the heating fixture 800 does not include elements that produce a magnetic field, thermal pads 802 associated with this heating fixture may be located in proximity to the SCC device 501.

[0053] The disclosed subject matter is not limited to the embodiments set forth above, but instead encompasses all variants, modifications, and combinations thereof that fall within the scope of the accompanying claims.

Claims

What is claimed is:

1. A superconducting circuit system comprising:peripheral electronics and a superconducting device comprising:a substrate;at least one superconducting film forming a ground plane;at least one superconducting circuit formed near the ground plane and including a plurality of modules having elements connected to a plurality of pads providing an electrical interface between the superconducting device and peripherals,a plurality of heating elements that upon energization, being powered by peripheral electronics, produce a non-uniform temperature distribution in at least the ground plane of the superconducting device;wherein the plurality of heating elements are energized through thermal links connected to at least one heating fixture located outside the superconducting device, and are configured to influence thermal conditions within selected regions the superconducting device.

2. A system as claimed in claim 1, wherein the heating elements include heating plates embedded in the substrate of the superconducting device.

3. A system as claimed in claim 1, wherein superconducting circuit modules having elements are used as heating elements.

4. A system as claimed in claim 2, wherein at least one heating fixture and the superconducting device are provided on a printed circuit board with traces routed to the pads on the superconducting device; wherein the heating fixture includes resistance heating elements; wherein the peripheral electronics includes drivers used to regulate current supplied to the resistance heating elements, and wherein the heating fixtures are connected to the traces of the printed circuit board by thermal links.

5. A system a claimed in claim 3, wherein at least one heating fixture and the superconducting device are provided on a printed circuit board with traces routed to thepads on the superconducting device: wherein the heating fixture includes resistance heating elements; wherein the peripheral electronics includes drivers used to regulate current supplied to the resistance heating elements; and wherein the heating fixtures are connected to the traces of the printed circuit board by thermal links.

6. A system as claimed in claim 4, wherein resistors serving as heating fixtures are inserted into interrupted traces connected to the heating elements, the resistors being energized by a peripheral electronic system configured to influence thermal behavior during thermocycling or to influence operating characteristics of the superconducting circuits.

7. A system as claimed in claim 5, wherein at least one heating fixture and the superconducting device are provided on a printed circuit board with traces routed to the pads on the superconducting device; wherein the heating fixture includes resistance heating elements; wherein the peripheral electronics includes drivers used to regulate current supplied to the resistance heating elements; and wherein the heating fixtures are connected to the traces of the printed circuit board by thermal links.

8. A system as claimed in claim 1, further comprising a laser functioning as a heater and directing its beam to at least one heating fixture to induce the temperature gradients, wherein the at least one heating fixture is provided on a printed circuit board with traces routed to the pads on the superconducting device.

9. A system as claimed in claim 8, wherein the heating fixture includes a box provided with a hole for the laser beam.

10. A system as claimed in claim 9, wherein the box has an elliptical shape, and the laser beam is directed to one of the ellipse’s focuses.

11. A superconductive circuit system comprising:a superconductive circuit device mounted on a substrate, the substrate including aground plane and a heating part, the superconductive circuit device further including a plurality of connecting pads provided on the substrate outside of a boundary of the superconductive device;a plurality of heating elements provided outside the superconductive circuit substrate and electrically coupled to the plurality of connecting pads, wherein the plurality of heating elements, upon energization by an external power source, provide heat to the heating part of the substrate thereby producing a non-uniform temperature distribution in the ground plane to trap magnetic flux.

12. The system as claimed in claim 11, wherein the heating part comprises a plurality of heating plates embedded in the substrate of the superconductive circuit devi ce and coupled to the plurality of connecting pads.

13. The system as claimed in claim 12, wherein heating plates are located on at least two opposing sides of the superconductive circuit device.

14. A system as claimed in claim 12, wherein the external power source comprises a microcontroller and drivers electrically coupled to the heating elements.

15. A system as claimed in claim 12, wherein the heating elements comprise a heating fixture including at least one resistance heating element mounted on a thermal pad.

16. A system as claimed in claim 12, wherein the ground plane includes a plurality of moats for trapping magnetic flux.

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