JPH02206184A - Fluxoid quantum element - Google Patents

Abstract

PURPOSE:To enable fluxoid quanta inputted into the first Josephson line to be propagated independently to the second or third Josephson line by constituting a superconducting loop of second and third Josephson lines, a Josephson junction and a superconductor and controlling the fluxoid quanta inputted into the fourth Josephson line. CONSTITUTION:A superconducting loop 8 is constituted of second and third Josephson lines 2 and 3, a Josephson junction 10 and a superconductor 7. The initial condition is set such that fluxoid quanta which have been propagated through a line 1 are propagated to the line 3 via a second resistor 6b but not propagated to the line 2. When the fluxoid quanta are propagated from the line 1 and enter the superconducting loop 8, the fluxoid quanta are propagated to an output 2 and not held in the loop 8 if a control signal is inputted into a line 4. If a control signal is inputted to the line 4, the fluxoid quanta are propagated to an output 1 and not held in the superconducting loop 8. Accordingly, the fluxoid quanta inputted into the first Josephson line 1 are propagated independently to the second or third Josephson line.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic flux quantum device that controls the propagation of magnetic flux quanta (referred to as Josephson vortex) in a Josephson line by other magnetic flux quanta, and particularly relates to a It relates to magnetic flux quantum devices used in circuits.

[Conventional technology]

Conventionally, as a method for controlling the propagation of magnetic flux quanta in a Josephson line using magnetic flux quanta, a magnetic flux quantum insertion game (FI gate) has been proposed (1961 Telecommunications Society Technical Report 5C88).
5-52).

FIG. 5 is a configuration diagram showing a magnetic flux quantum insertion gate. In the figure, 1 is the first Josephson line (hereinafter referred to as line 1), 2 is the second Josephson line (hereinafter referred to as line 2), and 3 is the third Josephson line (hereinafter referred to as line 3). , 4 is a fourth Josephson line (hereinafter referred to as line 4), and 5 is a superconductor. In addition, each Josephson line is composed of an upper electrode (■) and a lower electrode (■) formed to sandwich the tunnel barrier I, as shown in the line 4.
It has an input end and an output end.

The upper electrode of the line 2 and the lower electrode of the line 4 are arranged such that the input end of the line is common to the upper electrode of the line 4 - the tunnel barrier of the line 4 - the lower electrode of the line 4 - the upper electrode of the line 2 - the line Electrically, the line 2 and the line 4 are connected in series in the order of the lower electrode of the tunnel barrier line 2 of No. 2.

Further, at the input end where the two lines 2.4 are connected, the upper electrode of the line 4 and the upper electrode of the output end of the line 1 are connected by a superconductor 5, and the lower electrode of the line 2 and the upper electrode of the output end of the line 1 are connected. The lower electrode at the output end of the line 1 is connected with a superconductor 5a that does not include inductance, and an S branch is formed in which the line branches in a direction perpendicular to the tunnel barrier surface.

Further, at the branch part of the S branch, the upper electrodes of the line 2 and the line 3 are connected by a superconductor 5, and the lower electrodes are connected via a ground.

Next, the gate operation of the conventional magnetic flux quantum device will be explained. First, if there is a magnetic flux quantum input to input 2, line 3, line 1
Since the magnetic flux quantum is held in the T-branch (the line branches horizontally to the tunnel barrier) formed by the line 2 and the line 2, the magnetic flux quantum is propagated to the line 2.

On the other hand, when there is no magnetic flux quantum input to input 2, line 3,
Since magnetic flux quanta are not held in the T-branch formed by line 1 and line 2, the magnetic flux quantum is propagated to line 4.

In this way, in the conventional magnetic flux quantum element, by holding the magnetic flux quantum, the magnetic flux quantum propagating from the line 1 forming the S branch becomes 4'j! It is possible to control whether it propagates to 1 m2 or to the line 4.

[Problem to be solved by the invention]

However, in the conventional magnetic flux quantum device, as shown in the figure, line 2 and line 4 are electrically connected in series, so all the current supplied to line 4 is also supplied to line 2. Put it away. Therefore, even if the currents can be added to the line 2, there is a drawback that the bias current cannot be supplied completely independently.

Furthermore, even if this drawback were solved, in order to realize one S branch in a junction type, a so-called double junction, in which the junctions are stacked in two stages, would be required. requires multiple junctions with even more layers. For this reason, it has been difficult to form by thin film type bonding.

[Means to solve the problem]

The present invention has been made to solve the above-mentioned drawbacks.
a first resistor connecting an upper electrode at the output end of the first Josephson line and an upper electrode at the input end of the second Josephson line; a second resistor connecting the upper electrode of the input end of the third Josephson line and the upper electrode of the input end of the second Josephson line; a Josephson junction and a superconductor connected in series, and a third connection point between the Josephson junction and the superconductor connected in series and the upper electrode at the output end of the fourth Josephson line. It is equipped with a resistor.

[For production]

A superconducting loop is formed through the second Josephson line, the third Josephson line, the Josephson junction, and the superconductor, and the magnetic flux quantum input to the fourth Josephson line causes the first Josephson The magnetic flux quantum input to the Son line is completely independently propagated to the second Josephson line or the third Josephson line.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of a magnetic flux quantum element showing one embodiment of the present invention. Here, it has a laminated structure in which a tunnel barrier is sandwiched between an upper electrode and a lower electrode made of a superconductor. A distributed constant type line configured to have a length will be explained.

In the figure, the same parts as in FIG. 5 are given the same reference numerals.

6a is the first resistor, 6b is the second resistor, and 6c is the third resistor.
The resistor 2.7 is an inductance corresponding to a superconductor, 8
is a superconducting loop capable of stopping and holding magnetic flux quanta, 9 is an auxiliary bias current supply line, 10 is a Josephson junction, Jl is a Josephson junction 10 and an inductance 7
It is the junction with Here, between the output end of the line 1 and the input end of the line 2, and between the output end of the line 1 and the input end of the line 3, a first resistor 6a and a second resistor 6b are provided, respectively. connected with. Furthermore, a Josephson junction 10 and an inductance 7 are connected in series between the input end of the line 3 and the input end of the line 2. For this reason, line 3
A superconducting loop 8 is formed by - Josephson junction 10 - inductance 7 - line 2 and can stop and hold a plurality of magnetic flux quanta. Furthermore, the output end of the line 4 is connected to the connection point 11 between the Josephson junction 10 and the inductance 7 via a third resistor 6C.

Next, the operation of the magnetic flux quantum element configured as described above will be explained. First, in order to set initial conditions, a current is supplied only to the input end of the line 3 via the auxiliary bias current supply line 9. Thereby, the magnetic flux quantum that has propagated through the line 1 is set to propagate to the line 3 through the second resistor 6b, but not to propagate to the line 2.

In this state, when a magnetic flux quantum is propagated from the line 1, the magnetic flux quantum enters the line 3 and also enters the superconducting loop 8 formed by the line 3, the Josephson junction 10, the inductance 7, and the line 2. Then, the magnetic flux quantum that has entered the line 3 propagates and reaches the output 2. but,
When a magnetic flux quantum enters this superconducting loop 8, the Josephson junction 10 undergoes a portex transition, and the magnetic flux quantum in the superconducting loop 8 is emitted outside the loop. Therefore, when a control signal is not input to the line 4, magnetic flux quanta propagate to the output 2, and the magnetic flux quanta are not retained in the superconducting loop.

On the other hand, when a control signal is input to the line 4, magnetic flux quanta propagate through the line 4 and are stopped and held in the superconducting loop 8.

In a state in which magnetic flux quanta are retained in the superconducting loop 8, a circulating current accompanying the magnetic flux quanta flows from the upper electrode to the lower electrode at the input end of the line 2 and acts as an auxiliary bias current. On the other hand, since the circulating current is supplied from the lower electrode to the upper electrode at the input end of the line 3,
The auxiliary bias current applied as an initial condition and the circulating current cancel each other out. As a result, magnetic flux quanta propagating from line 1 do not propagate to line 3, but only to line 2. The magnetic flux quantum that has entered the line 2 propagates to the output 1 and is annihilated with the magnetic flux quantum held in the superconducting loop 8. Therefore, when the control signal is input to line 4,
This shows an operation in which magnetic flux quanta propagate to output 1 and eventually are not retained in the superconducting loop.

FIGS. 2(a) to 2(d) are time charts showing the above-mentioned operation.

In this way, it is possible to control whether the magnetic flux quantum is propagated to output 1 or output 2 depending on the presence or absence of the control signal.

Further, FIGS. 3(a) and 3(b) are waveform diagrams showing the current flowing through the inductance 7 and the Josephson junction 10.

As is clear from the figure, it can be seen that the current flowing through the Josephson junction 10 has a substantially inverted waveform with respect to the current flowing through the inductance 7. Here, the symbol A is the circulating current associated with the stopping flux quantum.

Next, FIGS. 4<a> to 4(e) are waveform diagrams in which the operation in FIG. 1 was confirmed by simulation using a circuit analysis program. This is a plot of the phase of the junction at the input end and output end of each line, the time change in the phase of the Josephson junction, and the time change of the current flowing in the superconducting loop.

Further, the fact that a magnetic flux quantum has passed can be known by the fact that the phase changes by 2π.

Now, when a magnetic flux quantum propagates from line 1 without inputting a control input at time TI, the magnetic flux quantum enters only line 3 and propagates to output 2, which is the terminal end of line 3. It can be seen that the phase of the Josephson junction 10 rotates by 2π in the negative direction, and magnetic flux quanta are emitted from the inside of the superconducting loop 8 to the outside.

Furthermore, at time T2, when the magnetic flux quantum that is the control input is propagated from the line 4, the Josephson junction 100 phase changes by 2π in the positive direction, the magnetic flux quantum is taken into the superconducting loop 8, and this stopped magnetic flux quantum The accompanying circulating current is supplied to the superconducting loop 8.

Then, when the magnetic flux quantum propagates from the line 1 during time T3 when the circulating current is supplied, the magnetic flux quantum propagates only to the line 2, and the circulating current supplied to the superconducting loop 8 disappears due to pair annihilation. can be confirmed.

In this way, the magnetic flux quantum element in this embodiment has the ability to propagate input magnetic flux quanta to output 1 or output 2 depending on the presence or absence of a control signal.
It has a propagation direction control function that determines whether or not it will propagate. Then, if the input of line 1 is input l, the IK large input of line 4 is input 2, and the output 1 of line 2 is output, then when an input magnetic flux quantum enters both input I and input 2, a magnetic flux quantum propagates to the output. . An AND circuit can be realized.

On the other hand, if a clock signal is input to the input of line 1, the control input of line 4 is made human, and the output 2 of line 3 is made output, then the input magnetic flux quantum enters and the magnetic flux quantum no longer propagates to the output only when ) (NOT) circuit can be realized.

In the above embodiment, a distributed constant line has been described, but instead of the distributed constant line, a lumped constant line in which Josephson junctions are connected in a ladder-like manner through inductance may be used.

〔Effect of the invention〕

As explained above, the present invention forms a superconducting loop via the second Josephson line, the third Josephson line, the Josephson junction, and the superconductor, and the superconducting loop is input to the fourth Josephson line. The magnetic flux quanta input to the first Josephson line can be propagated completely independently to the second Josephson line or the third Josephson line by the magnetic flux quanta, which increases the degree of freedom in circuit configuration. can be increased.

Furthermore, since it does not require multiple junctions like the conventional F2 gate, it is easy to realize the process using a thin-film type Josephson junction.

Furthermore, in an element in which other magnetic flux quanta are controlled by magnetic flux quanta stopped during a superconducting loop, it is necessary to eliminate the magnetic flux quanta that are no longer needed when the elements are connected in multiple stages. In contrast, in the present invention, since the superconducting loop includes a Josephson junction, it is possible to easily release magnetic flux quanta to the outside of the superconducting loop using a reset signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a magnetic flux quantum element showing one embodiment of the present invention, FIGS. 2(a) to 2(d) are time charts showing the operation of FIG. 1, and FIG. 3(a). (b) shows inductance 7 and Josephson junction 10'
4(a) to 4(e) are waveform diagrams showing the operation in FIG. 1 through simulation using a circuit analysis program. FIG. 5 is a configuration showing the magnetic flux quantum insertion gate. It is a diagram. 1...First Josephson track, 2...Second Josephson track, 3...Third Josephson 3a road, 4
... Fourth Josephson line, 6a... First resistor, 6b... Second resistor, 6c... Third resistor, 7... Inductance, 8... superconducting loop, 9
... Auxiliary bias current supply line, 10... Josephson junction, 11... Junction point. Patent applicant: Nippon Telegraph and Telephone Corporation Agent: Masaki Yamakawa (and one other person)

Claims (1)

[Claims] In a Josephson line that is composed of an upper electrode and a lower electrode formed to sandwich a tunnel barrier and has an input end and an output end, the upper electrode at the output end of the first Josephson line and a first resistor connecting an upper electrode at the input end of the second Josephson line; and a third resistor connecting the upper electrode at the output end of the first Josephson line.
a second resistor connecting the upper electrode of the input end of the third Josephson line and the upper electrode of the input end of the second Josephson line; a third Josephson junction and a superconductor connected in series; a third connection point between the Josephson junction and the superconductor connected in series and an upper electrode at the output end of the fourth Josephson line; a resistor, forming a superconducting loop capable of stopping and holding magnetic flux quanta via the second Josephson line, the third Josephson line, the Josephson junction, and the superconductor. A magnetic flux quantum device characterized by: