JPH11311663A - Superconducting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge timing margin of fluxoid quantum propagating at fast speed and non-destructively perform detection by detecting circuit change producing as the result of transmission, without detecting a fluxoid quantum signal transmitted to a Josephson transmission wire path. SOLUTION: Current which flowed from a constant current source 313 into a Josephson junction 311 is a circulating current 305 because it is in a voltage applied state, flows into an inductor 302, and flows into a Josephson junction 301. Since only the circulation current 305 flows to the Josephoson junction 301, the Josephson junction 301 remains in a superconducting state. Thus, the propagation of the fluxoid quantum stops here, and the circulating current 305 leaves in an inductor 302. At this time, since current does not flow in the Josephson junction 311, it turns into a current absent state. Thus, as a result, the current absent state is shifted to one division and the circulation current 305 flows. Since the value of a magnetic flux generated by the circulation current is a value near the fluxoid quantum, any magnetic flux junction element can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high-speed superconducting circuit, and more particularly to a digital circuit suitable for handling magnetic flux quanta as information.

[0002]

2. Description of the Related Art A flux quantum switching circuit using flux quantum (2.07 × 10 ⁻¹⁵ Wb) propagating on a Josephson transmission line in a superconducting state as an information carrier has attracted attention as an element of an ultra-high-speed computer.

[0003] The relationship between a Josephson transmission line and magnetic flux quanta propagating therethrough will be described with reference to FIG. The Josephson transmission line 100 has a configuration in which a Josephson junction 101, an inductor 102, and a constant current source 103 are formed as a single section, and a plurality of the sections are connected in series.

In the constant current source 103, a current of about 70% of the critical current of the Josephson junction 101 is set. If the product of the critical current of the Josephson junction 101 and the inductance value of the inductor 103 is set to be a flux quantum,
A signal in units of magnetic flux quantum 200 (SFQ) propagates through the Josephson transmission line. The magnetic flux quantum propagates on the Josephson transmission line as an impulse signal. The propagating magnetic flux quantum 200 has, for example, a half width of a pulse of 10 ps and a wave height of 0.2 mV.

The time required for this signal to pass through one section of the Josephson transmission line is as high as 10 to 30 ps. However, it is extremely difficult to detect such a signal. Only RSFQ (Rapid Single
Flux Quantum) circuit is used.

[0006] This RSFQ circuit is, for example, an IEEE Transactions on Applied Superconductivity (IEEE Trans. Appl. Supercond.),
vol.1, pp.3-28, March 1991. This RSFQ circuit has a configuration in which magnetic flux quanta are incorporated into a flip-flop circuit, and has the following drawbacks: 1) the timing margin of the flip-flop circuit is small;

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for non-destructively detecting the above-described magnetic flux quantum propagating at a very high speed with a large timing margin and a high speed and a large operating margin. It is to realize.

[0008]

For this purpose, the present invention does not detect the magnetic flux quantum signal itself transmitted to the Josephson transmission line, but detects a circuit change resulting from the transmission. I do. That is, a method of detecting the trace of the transmission of the quantum magnetic flux is employed.

[0009]

FIG. 1 shows a method of detecting magnetic flux quanta according to the present invention. Josephson transmission line 300 of FIG.
Has a configuration in which a Josephson junction 101, an inductor 102, and a constant current source 103 are formed as a single section, and a plurality of the sections are connected in series similarly to FIG. However, in the section including one Josephson junction 301 and the inductor 302, the constant current source is removed or the current of the constant current source is set to a small value.

In the Josephson transmission line 300, in the initial state when the power is turned on, the current of each constant current source flows through each directly connected Josephson junction. At this time, no current flows in the Josephson junction 301 to which the constant current source is not connected. This is referred to as a current vacant state (FIG. 1A). In this state, when the magnetic flux quantum 200 is applied as a signal from the left side of the Josephson transmission line 300, the magnetic flux quantum passes through the section and reaches the Josephson junction 301.

The circuit operation at this time is as follows. The current flowing from the constant current source 313 to the Josephson junction 311 becomes a circulating current 305 because the Josephson junction 311 is in a voltage state, flows into the inductor 302, and flows into the Josephson junction 301. Since only the circulating current 305 flows through the Josephson junction 301, the Josephson junction 301
Remains in the superconducting state.

Accordingly, the propagation of the flux quantum stops here,
A circulating current 305 remains in the inductor 302. At this time, since no current flows through the Josephson junction 311, the current is vacant (FIG. 1B). Therefore, as a result, the current vacant state shifts to the left by one section, and the circulating current 305 flows. This circulating current is a trace of the passage of the magnetic flux quantum 200 and operates statically.

Similarly, when another flux quantum 201 is applied to the Josephson transmission line 300 from the left, the current vacant state shifts to the left by one section as in FIG.
Move to section 21 (Fig. 1 (c)). Further, when another flux quantum 202 is applied to the Josephson transmission line 300 from the right, the current vacant state shifts to the right by one section and moves to the section of the Josephson junction 311 (FIG. 1D).

As apparent from the above operation, in the circuit of the present invention shown in FIG. 1, the current vacant state moves right and left by the magnetic flux quantum signal applied to the Josephson output transmission line.
Focusing on the position of the current unoccupied state, this circuit is nothing but the operation of an up / down counter for counting the input magnetic flux quantum. Further, the circulating current generated by this current vacant state operates statically (direct current), and the value of the magnetic flux generated by this circulating current is close to the value of the magnetic flux quantum, so that any magnetic flux coupling element can be detected. Further, the magnetic flux coupling element can be detected without changing the state of the Josephson transmission line 300. Therefore, the signal can be detected in a non-destructive manner by the method of the present invention.

FIG. 3 shows an embodiment in which the circulating current of the circuit of the present invention shown in FIG. 1 is detected by a magnetic flux coupling element. FIG.
In FIG. 1, the circulating current 305 flowing through the inductor 302 of the Josephson transmission line 300 shown in FIG.
The circuit configuration is to detect at 400. Quantum flux parametron 4
00 is the two Josephson junctions 401 and 402 and the transformer 405
The secondary winding 403 forms a superconducting closed circuit. Transformer 405
A load inductor 410 is connected to the middle point of the secondary winding 403. The primary winding of the transformer 405 is the inductor 302 so that the exciting current of the quantum flux parametron 400 becomes the circulating current 305.

In this circuit configuration, when the circulating current 305 is applied to the inductor 302, a magnetic flux links with the superconducting loop, and a current flows through the load inductor 410 due to a nonlinear negative inductance phenomenon. Magnetic flux is generated. The load inductor 410 models another quantum flux parametron or another Josephson transmission line, and it is clear that the quantum flux parametron 400 can drive other circuits.

The conventional technology of quantum flux parametron is based on IEEE Trans. Magnetics, vol. MAG-2.
3, pp. 3801-3807, Sept. 1987.

FIG. 4 shows an embodiment of the method for resetting the circuit shown in FIG. 1 of the present invention. As described above, in the circuit of FIG. 1, the position of the current vacant state moves due to the flux quanta entering from the left and right. The resetting returns the current vacant seat position to the initial state. The reset is performed by returning the circulating current 305 flowing through the Josephson junction 301 to the original Josephson junction 311 in the circuit of FIG.

FIG. 4A shows that the Josephson junction 301 is newly connected to a variable current source 503. The above variable current source 503
, The same up / down counter operation as in FIG. 1 is executed. To execute the reset, a current is flowed from the variable current source 503 to the Josephson junction 301, the Josephson junction 301 is temporarily transitioned to a voltage state, and the circulating current 305 is pushed back to the Josephson junction 311. .
Next, if the current of the variable current source 503 is returned to zero, the current of the Josephson junction 301 becomes zero, and the current vacant state is at this position. That is, a reset operation is performed.

FIG. 4B shows another method for resetting. 4B, the flux quantum 501 is applied as a reset signal to the Josephson junction 301 to temporarily transition the Josephson junction 301 to a voltage state, and the circulating current 305 is applied to the Josephson junction 311. Push back. After the flux quantum 501 has passed, the current vacant state becomes the above-mentioned Josephson junction 301, and the reset operation is executed. Fig. 4 (b)
In this configuration, the magnetic flux quantum 501 propagates through another Josephson transmission line 500.

[0021]

According to the present invention, a magnetic flux quantum for transmitting a signal at high speed in a Josephson transmission line is statically (directly),
It can be detected nondestructively. For this reason, the magnetic flux quantum can be used as a signal to increase the timing margin and to use the circuit configuration in a simple form. The effect of the present invention is extremely large because a super-high-speed computer and other digital systems can be realized by the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the operation of a superconducting circuit according to one embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional Josephson transmission line.

FIG. 3 is a circuit diagram of a superconducting circuit for detecting a circulating current according to one embodiment of the present invention.

FIG. 4 is an explanatory diagram of a method for resetting a superconducting circuit of the present invention to an initial state.

[Explanation of symbols]

100: Josephson transmission line, 101: Josephson junction,
102: inductor, 103: constant current source, 200, 201, 202: magnetic flux quantum, 300: Josephson transmission line, 301, 311, 321:
Josephson junction, 302: inductor, 305, 306: circulating current, 313: constant current source, 400: quantum flux parametron, 40
1, 402: Josephson junction, 405: transformer, 403: secondary winding, 410: load inductor, 500: Josephson transmission line, 501: magnetic flux quantum, 503: variable current source.

Claims (7)

[Claims] 1. A Josephson transmission line in which a Josephson junction, an inductor, and a constant current source are formed as a single section, and a plurality of the sections are connected in series, wherein at least one section of the constant current source is removed. Or the output current of the constant current source is maintained at a value close to zero for a certain period of time. 2. The superconducting circuit according to claim 1, further comprising a circuit for detecting a circulating current flowing through the inductor in the section. 3. The superconducting circuit according to claim 2, wherein said detecting circuit uses a flux-coupling type superconducting element. 4. The superconducting circuit according to claim 3, wherein a quantum flux parametron is used for said flux-coupling type superconducting element. 5. The superconducting circuit according to claim 1, wherein a circulating current flowing through the inductor in the section is pushed back to a Josephson junction in an adjacent section to reset the circuit to an initial state. . 6. A superconducting circuit according to claim 5, wherein said current source in said section is a variable current source, and a current is passed through said Josephson junction for a certain period of time to push back said circulating current. Superconducting circuit. 7. The superconducting circuit according to claim 5, wherein said circulating current is pushed back by applying a magnetic flux quantum signal to said Josephson junction.