JPS61132885A - Dc bias quantum interferometer - Google Patents

Abstract

PURPOSE:To improve the magnetic field sensitivity by constituting a magnetic field detecting part by connecting one or more of the third inductances in parallel to the first and the second inductances, in a loop of superconductive strip lines which have been arranged in a shape of a plane without being overlapped to each other. CONSTITUTION:The first and the second branches B1, B2 are connected in parallel to a bias current line, the respective connecting points of industances 3, 4 and Josephson junctions 1, 2 are connected to a control current line 6, and one or more of magnetic field detecting use inductance branches 8 are connected as the third inductance to the inductances 3, 4. Also, the branches 8 are arranged in a shape of a plane and without being overlapped to each other, and in one or more of planes surrounded by this branches 8 in a loop of a super conductive strip line, there is no ground surface in an inductance loop 7 constituted of the branches B1, B2, and a ground surface is provided on other circuit part. In this way, the sensitivity for measuring a magnetic field can be improved in proportion to the area sum of the planes surrounded by the branches 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a direct current bias quantum interferometer used for detecting minute magnetic fields. More particularly, the present invention relates to a DC-biased quantum interferometer that can be constructed using thin film technology used in the production of integrated circuits.

[Technical background of the invention and its problems]

This type of DC-biased quantum interferometer fabricated using conventional thin film technology consists of a first branch B1 in which a blind junction 1 and an inductance 3 are connected in series, as shown in Figure 2.
is configured, the second branch B2 is configured by connecting the I-Sefson junction 2 and the inductance 4 in series, and the I-th
and second branches Bl, B2 are connected in parallel,
It has a structure in which a control current line 6 is connected to the bias current line 5 and magnetically coupled to the inductances 3 and 4. H is the magnetic field to be measured. In the current control characteristics of the DC bias quantum interferometer, that is, the current versus control current characteristics, a particular quantum interference/arm turf appears as shown in FIG. This quantum interference pattern is
When the magnetic flux interlinks with the inductance loop 7 composed of the first branch B and the second branch B2 in FIG. 2, the flux changes along the control current axis. Since the amount of transition A is proportional to the amount of magnetic flux interlinked with the inductance through differential, the strength of the magnetic field interlinked with the inductance loop 7 can be determined from the area surrounded by the inductance through differential and the amount of transition A.

This conventional DC-biased quantum interferometer is also used as a logic r-) of a Ji1 Cefson integrated circuit. Therefore, the magnetic field a degree of this DC bias quantum interferometer is comparable to that of a logic gate used in an integrated circuit. Therefore, the magnetic field sensitivity of this DC bias quantum interferometer is insufficient to accurately measure a low magnetic field environment that will not cause malfunction of the integrated circuit.

In order to increase the magnetic field sensitivity, it is sufficient to increase the area of the inductance loop 7 where the magnetic flux interlinks.
In that case, the value of the loop inductance of loop 1 will also increase, so the modes of the quantum interference pattern shown in Figure 3 will overlap more, making it difficult to distinguish between modes, and the quantum interference/four-turn transition amount will also increase. The measurement sensitivity does not increase because it decreases in inverse proportion to the loop inductance. As described above, the conventional DC bias quantum interferometer has a serious drawback in that it cannot improve the magnetic field sensitivity by an order of magnitude compared to the magnetic field sensitivity of the logic f-).

[Purpose of the invention]

In order to solve this drawback, the present invention connects loop inductances in parallel to increase the area surrounded by the inductance loops interlinked with magnetic fields, and to reduce the effective loop inductance as a parallel composite value of the loop inductances. The magnetic field sensitivity has been improved by the following, and the drawings will be explained in detail below.

[Embodiments of the invention]

One embodiment of the present invention is as shown in FIG.
A Son junction 1 and a first inductance 3 composed of a superconducting strip wire are connected in series to form a first branch B.
1 is formed, a second di-neck Cefnon junction 2 and a second inductance 4 made of a superconducting strip wire are connected in series to form a second branch B2, and the first and second branches Bl , B2 are connected in parallel to the z4 current line 5 which supplies the bias current, and the inductance 3 and the Josephson junction, the &[ point of l, and the connection point of the inductance 4 and the Josephson junction 2 respectively. A control current line 6 for injecting current is connected, and an inductance branch 8 for magnetic field detection is connected as a third inductance.
are connected in parallel to inductance 3 and inductance 4.

The inductance branch 8 is composed of multiple superconducting conductors (17) arranged in a plane without overlapping with each other, and has a plurality of loops of f-rays, and the inductance branch 8 surrounds at least one of the first and second planes. There is no ground plane on the lower side of the part other than the part included in the inductance loop 7 composed of the second branch Bl and B2,
It has a structure in which a ground plane is provided below the other circuit parts.

F is a region without a ground plane, such as a superconductor, and the reason for providing such a region F without a ground plane is as follows.

That is, if there is a ground plane such as a superconductor in region F, the magnetic field perpendicular to the ground plane to be detected will be disturbed by the ground plane, making it impossible to accurately detect the magnetic field. Also, the reason why a ground plane such as a superconductor is provided below the circuit parts other than area F is because if a magnetic field passes perpendicularly to this part, an error will occur when detecting the magnetic field. This is because a ground plane is provided below the circuit portion, and this ground plane prevents the magnetic field from passing in a direction perpendicular to the ground plane, thereby preventing errors from occurring when detecting the magnetic field.

The element structure of this example can be manufactured using the thin film technology used in the production of conventional integrated circuits. It has the great advantage of being able to be manufactured simultaneously with integrated circuits.

According to this embodiment, since the magnetic field to be measured is measured as the magnetic flux, which is the amount applied to the sum of the planes surrounded by a plurality of inductance branches 8, the magnetic field measurement sensitivity is proportional to the sum of the areas of the planes surrounded by the inductance branches 8. will improve. In this embodiment, the effective value of the loop inductance that determines the current control characteristics of the quantum interferometer is equal to the inductance of the inductance branches 8, so even if the number of inductance branches 8 is increased, The effective value of the loop inductance does not increase. Therefore, the number of overlapping modes in the current control characteristics will not increase, so the mode discrimination will not become K<, and the amount of transition of one-quantum interference no-turn will not become smaller. . Therefore, according to this embodiment, the magnetic field sensitivity of the DC Pipes quantum interferometer is -)! It is possible to improve the magnetic field sensitivity by an order of magnitude compared to that of the standard logic circuit.

Further, in this embodiment, the control current is directly injected from the control current line 6 to the inductance through f7 of the quantum interferometer via the first and second inductances, but this is because the control current line 6 and the inductance loop The magnetic coupling constant between the inductance 3.4 and the control current line 6 is effectively set to 11C to reduce the uncertainty and 9 ram in measurement, and the inductance 3.4 and the control current line 6 are magnetically connected as in the conventional example shown in Fig. 2. It goes without saying that a structure in which the control current is supplied by coupling is also possible.

〔Effect of the invention〕

As explained above, this embodiment has the advantage that the magnetic field measurement sensitivity of the DC bias quantum interferometer can be significantly improved. Since it is a highly sensitive magnetic field measuring element, this element can be easily installed within an integrated circuit chip.
If manufactured at the same time as a Sefson integrated circuit, it becomes possible to use it in ways unimaginable with conventional magnetic field measuring elements, such as being able to measure the magnetic field environment of the Sefson integrated circuit while it is operating.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a conventional DC bias quantum interferometer, and FIG. 3 is a Josephson current control characteristic diagram of the DC bias quantum interferometer. 1.2... Diverse Sefson junction, 3.4... Inductance, Bl, 82... First and second branches, respectively, 5... Bias current line, 6... Control current line, 7... Inductance loop, 8... Inductance branch for magnetic field detection.

Claims (2)

[Claims] (1) A first branch is formed by a first inductance composed of a first Josephson junction and a superconducting strip line, and a second inductance is composed of a second Josephson junction and a superconducting strip line. A second branch is formed in the first branch, the first and second branches are connected in parallel, a bias current is supplied from the bias current line, and the first
and a direct current bias quantum interferometer in which a control current is directly injected through a second inductance or supplied by magnetic coupling, in which superconducting strip lines are arranged in a plane without overlapping each other. A direct current bias quantum interferometer, characterized in that a magnetic field detection section is constructed by connecting at least one third inductance formed by a loop in parallel with the first or second inductance. (2) A first branch is formed by a first inductance composed of a first Josephson junction and a superconducting strip wire, and a second inductance is composed of a second Josephson junction and a superconducting strip wire. A second branch is formed in the first branch, the first and second branches are connected in parallel, a bias current is supplied from the bias current line, and the first
and a direct current bias quantum interferometer in which a control current is directly injected through a second inductance or supplied by magnetic coupling, in which superconducting strip lines are arranged in a plane without overlapping each other. At least one or more third inductances constituted by a loop are connected in parallel with the first or second inductance to constitute a magnetic field detection section, and at least one or more planes surrounded by this third inductance are connected in parallel with the first or second inductance. There is no ground plane below the portion of the circuit excluding the portion included in the inductance loop constituted by the first and second branches, and a ground plane is provided below the other circuit portions. DC bias quantum interferometer.