Variable superconducting phase shifter, diode element, and rectifier

Abstract

To provide a phase shifter which realizes an arbitrary phase shift regardless of an external magnetic field.SOLUTION: A variable superconducting phase shifter 110 is formed of a superconducting loop including: a π-junction 30; a first inductor 31; a second inductor 32; a current input part 33; and a current output part 34. The π-junction 30 includes: a first superconducting electrode; a second superconducting electrode; and a barrier layer composed of a ferromagnetic material interposed between the first superconducting electrode and the second superconducting electrode. When the superconducting loop is traced from the current input part 33 to the current output part 34, the first inductor 31 is located on the same side as the side where the π-junction 30 is located, and the second inductor 32 is located on the opposite side to the side where the π-junction 30 is located.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to variable superconducting phase shifters, diode elements and rectifiers. [Background technology]

[0002] A diode has been disclosed that is composed of a long Josephson junction that is made asymmetric by a current injection point or the like, and a magnetic field generating section, and that can operate in a voltage range of several mV (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2018-170329 Summary of the Invention [Problem to be solved by the invention]

[0004] Superconducting devices and circuits using superconducting loops containing Josephson junctions must satisfy the quantization condition (i.e., the phase of the superconducting macroscopic wave function, when integrated around the loop, must be an integer multiple of 2π). By inputting a current or applying a magnetic field to this superconducting loop, the phase can be changed to realize device and circuit operation.

[0005] The technology disclosed in Patent Document 1 magnetizes the element by applying an external magnetic field in order to create asymmetry in the critical current of the Josephson junction and realize its function as a diode. This requires a great deal of effort because magnetization must be applied just below the Curie temperature when the element becomes superconducting.

[0006] The present disclosure has been made in light of these circumstances, and its purpose is to provide a variable phase shifter that realizes an arbitrary phase shift without relying on an external magnetic field. [Means for solving the problem]

[0007] To solve the above problems, a variable superconducting phase shifter according to one embodiment of the present disclosure is composed of a superconducting loop including a π-junction, a first inductor, a second inductor, a current input section, and a current output section. The π-junction is composed of a first superconducting electrode, a second superconducting electrode, and a barrier layer made of a ferromagnetic material sandwiched between the first and second superconducting electrodes. When tracing the superconducting loop from the current input section to the current output section, the first inductor is on the same side as the π-junction, and the second inductor is on the opposite side from the π-junction.

[0008] In one embodiment, the inductance of the first inductor is L1, the inductance of the second inductor is L2, and the inductance of the π-junction is L jj And L total =L1+L2+L jj Let A=L2 / L total Then, the phase difference between the current input section and the current output section may be Aπ.

[0009] In one embodiment, the inductance of the first inductor L1 and the inductance of the second inductor L2 may be variable.

[0010] Another aspect of the present disclosure is a diode element. The element includes a variable superconducting phase shifter and a dc-SQUID element including the variable superconducting phase shifter. The dc-SQUID element includes a first 0-junction, a second 0-junction, a dc-SQUID current input, a first dc-SQUID inductor between the first 0-junction and the dc-SQUID current input, and a second dc-SQUID inductor between the second 0-junction and the dc-SQUID current input. The current input of the variable superconducting phase shifter is connected to the opposite side of the first dc-SQUID inductor of the first 0-junction to form a superconducting loop of the dc-SQUID element. The current output of the variable superconducting phase shifter is connected to the opposite side of the second 0-junction and the second dc-SQUID inductor.

[0011] Yet another aspect of the present disclosure is a diode element. This element is composed of the aforementioned diode element. The inductance value of the first dc-SQUID inductor is different from the inductance value of the second dc-SQUID inductor, or the critical current value of the first 0-junction is different from the critical current value of the second 0-junction.

[0012] Yet another aspect of the present disclosure is a rectifier including the above-described diode element.

[0013] Any combination of the above components, and conversion of the present disclosure into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present disclosure. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a variable phase shifter that realizes an arbitrary phase shift without depending on an external magnetic field. [Brief explanation of the drawings]

[0015] [Figure 1] Figure 1(a) is a cross-sectional view of a 0-junction, and Figure 1(b) is a cross-sectional view of a π-junction. [Figure 2] FIG. 2 is a diagram showing the current-voltage characteristics of the 0-junction. [Figure 3] 1 is an equivalent circuit diagram of a variable superconducting phase shifter according to a first embodiment. [Figure 4] FIG. 10 is an equivalent circuit diagram of a diode element according to a second embodiment. [Figure 5] 10 is a graph showing the critical value of the sum of the current flowing through the first 0-junction and the current flowing through the second 0-junction of the diode element according to the second embodiment, and the phase changed by the magnetic field and current applied from the outside to the superconducting loop and the variable superconducting phase shifter. [Figure 6] FIG. 11 is a diagram showing current-voltage characteristics when the inductance value or critical current value of the dc-SQUID of the diode element according to the third embodiment is changed. [Figure 7] Fig. 7(a) is a schematic diagram of a rectifier according to a fourth embodiment, and Fig. 7(b) is a simplified schematic diagram corresponding to the rectifier of Fig. 7(a). [Figure 8] FIG. 7(a) shows the results (bottom) of full-wave rectification of a triangular wave (top). DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. Furthermore, the embodiments are merely examples and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0017] In addition, the dimensions (thickness, length, width, etc.) of each component shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of multiple components do not necessarily represent their relative sizes, and even if a component A is depicted as being thicker than another component B in the drawings, it is possible that component A is thinner than component B.

[0018] First, we will provide an overview. Conventionally, phase has been controlled only by current and magnetic field. In contrast, this disclosure provides a third method, which controls the π phase shift generated by a π junction to any value. In this sense, this disclosure realizes a "variable superconducting phase source."

[0019] A Josephson junction is a junction that consists of two superconducting electrodes sandwiched between a barrier layer. If the barrier layer is thin enough, a superconducting current will flow between the superconducting electrodes. Usually, Josephson junctions have barrier layers made of insulators or nonmetals. In this case, if the phase difference between the macroscopic wave functions of the two superconducting electrodes is θ, the junction characteristics are as follows: I=I c sinθ where I is the current flowing through the Josephson junction, and I c is the Josephson critical current. The ground state of this junction is θ=0 rad when I=0. For this reason, this type of Josephson junction is called a 0-junction (or 0-JJ). In this specification, a 0-junction Josephson junction is simply referred to as a 0-junction.

[0020] 1(a) is a cross-sectional view of a 0-junction 100. The 0-junction 100 includes a barrier layer 21 made of an insulator sandwiched between a first superconducting electrode 11 and a second superconducting electrode 12. FIG. 2 shows the current-voltage characteristics of the 0-junction 100.

[0021] On the other hand, if a ferromagnetic material or a laminated structure of a ferromagnetic material and an insulator is used for the barrier layer, the junction characteristics are as follows: I=I c sin(θ+π)=-I c sinθ This relationship holds. This is because a phase shift term of 0 rad or π rad appears in the wave function of the Cooper pair that leaks from the superconducting layer to the ferromagnetic layer due to the exchange interaction in the ferromagnetic material. A Josephson junction with a phase shift term of π rad is called a π-junction (or π-JJ) because in the ground state, its phase differs by π rad from that of a 0-junction. In this specification, a π-junction Josephson junction will be simply referred to as a π-junction.

[0022] By using a π-junction instead of a 0-junction, a phase difference of πrad can be generated in a superconducting loop containing a Josephson junction, which is expected to realize a phase shift of π that is not possible with a 0-junction. However, in this state, it is not possible to realize a phase shift of any amount other than π.

[0023] 1(b) is a cross-sectional view of the π-junction 101. The π-junction 101 includes a first superconducting electrode 13, a second superconducting electrode 14, and a barrier layer 22 made of a ferromagnetic material sandwiched between the first superconducting electrode 13 and the second superconducting electrode 14.

[0024] [First embodiment] 3 is an equivalent circuit diagram of variable superconducting phase shifter 110 according to the first embodiment. Variable superconducting phase shifter 110 is composed of a superconducting loop including a π-junction 30, a first inductor 31, a second inductor 32, a current input section 33, and a current output section 34. As shown in FIG. 3, when tracing the superconducting loop of variable superconducting phase shifter 110 from the current input section 33 to the current output section 34, the first inductor 31 is on the same side as the π-junction 30, and the second inductor 32 is on the opposite side from the π-junction 30. As described above, the π-junction 30 is composed of a first superconducting electrode 13, a second superconducting electrode 14, and a barrier layer 22 sandwiched between the first and second superconducting electrodes and made of a ferromagnetic material or a laminated structure of a ferromagnetic material and an insulator.

[0025] The first superconducting electrode 13 and the second superconducting electrode 14 may be made of a superconducting material such as niobium (Nb). The barrier layer 22 is a very thin (for example, on the order of 10 nm) ferromagnetic film, and may be made of a ferromagnetic metal or a ferromagnetic insulator.

[0026] The π-junction 101 is formed on a substrate such as silicon (Si). Although not essential, depending on the application, a metal ground plane may be formed on the silicon substrate, and an insulating layer such as silicon oxide (SiO2) may be formed on top of that.

[0027] The operating principle of the variable superconducting phase shifter 110 will now be explained. In the absence of input of current I, the π-junction 30 generates a phase of θ+π (where θ is near 0 rad and varies depending on the value of the current flowing through the junction). The superconducting loop formed by the π-junction, the first inductor 31, and the second inductor 32 must satisfy the quantization condition. In addition, 2πI c When the condition (L1+L2)>Φ0 is satisfied, a current is spontaneously induced in the superconducting loop. The magnitude of this current is I c , L1, and L2, and a phase difference occurs between the current input section 33 and the current output section 34.

[0028] The inductance of the first inductor 31 is L1, the inductance of the second inductor 32 is L2, and the inductance of the π-junction 30 is L jj =Φ0 / 2πI c (Strictly speaking, L jj =Φ0 / 2πI c cosθ, where θ is 2πI c (It can be approximated to 0 if the condition (L1+L2)>Φ0 is fully satisfied), and L total =L1+L2+L jj Let A=L2 / L total Then, the phase difference between the current input section 33 and the current output section 34 is Aπ. However, Φ0 is given by Φ0=h / 2e=2.067851×10 -15 The magnetic flux quantum is defined as Wb (h is Planck's constant, and e is the charge of an electron). That is, by appropriately adjusting the inductance L1 of the first inductor 31 and the inductance L2 of the second inductor 32, any desired phase shift can be realized.

[0029] The inductance L1 of the first inductor 31 and the inductance L2 of the second inductor 32 may be variable. In this case, the amount of phase shift realized by the variable superconducting phase shifter 110 can be dynamically set.

[0030] As described above, according to this embodiment, by appropriately adjusting the inductance L1 of the first inductor 31 and the inductance L2 of the second inductor 32, it is possible to provide a variable phase shifter that realizes an arbitrary phase shift without depending on an external magnetic field.

[0031] [Second embodiment] 4 is an equivalent circuit diagram of a diode element 130 according to the second embodiment. In the diode element 130, a dc-SQUID element (direct current-superconducting quantum interference device) 120 is configured to include the variable superconducting phase shifter 110 described above. The dc-SQUID element 120 is configured as a superconducting loop including a first O-junction 41, a second O-junction 42, a dc-SQUID current input section 45, a first dc-SQUID inductor 43 between the first O-junction 41 and the dc-SQUID current input section 45, and a second dc-SQUID inductor 44 between the second O-junction 42 and the dc-SQUID current input section 45. In the superconducting loop of the dc-SQUID element 120, the first O-junction 41 is connected to the current input section 33 of the variable superconducting phase shifter 110 on the opposite side to the first dc-SQUID inductor 43. The second O-junction 42 is connected to the current output section 34 of the variable superconducting phase shifter 110 on the opposite side to the second dc-SQUID inductor 44.

[0032] 5 shows the critical value above which a voltage is generated when the sum of the current flowing through the first O-junction 41 of the diode element 130 and the current flowing through the second O-junction 42 of the diode element 130 exceeds the critical value, and the phase changed by the magnetic field and current applied to the superconducting loop from outside and the variable superconducting phase shifter. Here, however, the phase shifts of π / 3, π / 2, and 2π / 3 are realized by adjusting the inductances of the first inductor 31 and the second inductor 32 of the variable superconducting phase shifter 110, respectively.

[0033] As described above, according to this embodiment, by using the dc-SQUID element 120, the amount of phase shift caused by the variable superconducting phase shifter 110 can be observed.

[0034] [Third embodiment] The third embodiment is a diode element. This diode element is configured as the diode element 130 shown in Fig. 5. In this diode element, the inductance value L SQUID1 and the inductance value L of the second dc-SQUID inductor 44. SQUID2 or the critical current value Ic1 of the first O-junction 41 is different from the critical current value Ic2 of the second O-junction. In this way, by having an appropriate asymmetry in the inductance value or critical current value of the inductor of the dc-SQUID 120, the current flowing in the loop of the dc-SQUID 120 can be controlled to flow in only one direction, thereby realizing a diode element.

[0035] FIG. 6 shows the current-voltage characteristics when the phase is shifted by the variable superconducting phase shifter 110 of the dc-SQUID element 120.

[0036] [Fourth embodiment] 7(a) is a schematic diagram of a rectifier 160 according to the fourth embodiment. Rectifier 160 includes four diode elements according to the third embodiment, namely, diode element 140, diode element 141, diode element 150, and diode element 151, two resistors, namely, resistor 90 and resistor 91, current input unit 55, current output unit 56, voltage port 65, and voltage port 66. Diode element 140, diode element 141, diode element 150, and diode element 151 according to the third embodiment are configured to include variable superconducting phase shifter 111, variable superconducting phase shifter 112, variable superconducting phase shifter 113, and variable superconducting phase shifter 114 according to the first embodiment, respectively.

[0037] 7(b) is a schematic diagram of a simplified rectifier 161 corresponding to rectifier 160. Rectifier 161 includes four diode elements according to the third embodiment, namely, diode element 142, diode element 143, diode element 152, and diode element 153, two resistors, namely, resistor 90 and resistor 91, current input unit 57, current output unit 58, and voltage port 67 and voltage port 68. Diode elements 142, 143, 152, and 153 according to the third embodiment are configured by sharing one variable superconducting phase shifter with variable superconducting phase shifter 115 and variable superconducting phase shifter 116 according to the first embodiment.

[0038] FIG. 8 shows the results (bottom diagram) of full-wave rectification of a triangular wave (top diagram) using rectifier 160.

[0039] The present invention has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the respective components and treatment processes, and that such modifications are also within the scope of the present invention.

[0040] The embodiments have been described above. When understanding the abstract technical ideas of the embodiments, the technical ideas should not be interpreted as being limited to the contents of the embodiments. The above-described embodiments and variations are merely illustrative examples, and many design changes, such as changes, additions, and deletions of components, are possible. In the embodiments, the contents in which such design changes are possible are emphasized by adding the notation "embodiment." However, design changes are also permitted even in contents not so notated. [Explanation of symbols]

[0041] 11··First superconducting electrode, 12··Second superconducting electrode, 13··First superconducting electrode, 14··Second superconducting electrode, 21··Barrier layer, 22··Barrier layer, 30··π-junction, 31··First inductor, 32··Second inductor, 33 Current input section, 34 Current output section, 41··First 0-junction, 42··Second 0-junction, 43··First dc-SQUID inductor, 44··Second dc-SQUID inductor, 45··dc-SQUID current input section, 55··Rectifier current input section, 56··Current output section of rectifier, 57··Rectifier current input section, 58··Current output section of rectifier; 65··Rectifier voltage port, 66··Rectifier voltage port, 67··Rectifier voltage port, 68··Rectifier voltage port, 90...Resistor, 91...Resistor, 92...Resistor, 93...Resistor, 100··0-junction, 101··π-junction, 110··Tunable superconducting phase shifter, 111··Tunable superconducting phase shifter, 112··Tunable superconducting phase shifter, 113··Tunable superconducting phase shifter, 114··Tunable superconducting phase shifter, 115··Tunable superconducting phase shifter, 116··Tunable superconducting phase shifter, 120··dc-SQUID, 130... Diode element, 140... Diode element, 141... Diode element, 142... Diode element, 143··Diode element, 150··Diode element, 151... Diode element, 152... Diode element, 153··Diode element, 160... Rectifier, 161... Rectifier.

Claims

1. a superconducting loop including a π-junction, a first inductor, a second inductor, a current input section, and a current output section; the π-junction is composed of a first superconducting electrode, a second superconducting electrode, and a barrier layer made of a ferromagnetic material sandwiched between the first superconducting electrode and the second superconducting electrode; When tracing the superconducting loop from the current input section to the current output section, the first inductor is on the same side as the π-junction, and the second inductor is on the opposite side to the π-junction.

2. The inductance of the first inductor is L １ , the inductance of the second inductor is L ２ , the inductance of the π-junction is L ｊｊ And L ｔｏｔａｌ =L １ +L ２ +L ｊｊ Toki, A=L ２ / L ｔｏｔａｌ 2. The variable superconducting phase shifter according to claim 1, wherein, when the phase difference between the current input section and the current output section is Aπ.

3. The inductance L of the first inductor １ and the inductance of the second inductor is L ２ 3. The variable superconducting phase shifter according to claim 2, wherein is variable.

4. A variable superconducting phase shifter according to any one of claims 1 to 3, and a dc-SQUID element including the variable superconducting phase shifter, the dc-SQUID device is comprised of a superconducting loop including a first 0-junction, a second 0-junction, a dc-SQUID current input, a first dc-SQUID inductor between the first 0-junction and the dc-SQUID current input, and a second dc-SQUID inductor between the second 0-junction and the dc-SQUID current input; the first 0-junction is connected to a current input of the variable superconducting phase shifter on an opposite side to the first dc-SQUID inductor; The second 0-junction is a diode element, the opposite side of which with respect to the second dc-SQUID inductor is connected to the current output portion of the variable superconducting phase shifter.

5. The inductance value of the first dc-SQUID inductor is different from the inductance value of the second dc-SQUID inductor, or 5. The diode element according to claim 4, wherein the critical current value of the first 0-junction is different from the critical current value of the second 0-junction.

6. A rectifier comprising the diode element according to claim 5.

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