JPH07221614A - Josephson signal detection circuit and measuring device using the same - Google Patents

Abstract

PURPOSE:To provide a Josephson signal detection circuit capable of reducing the influence of current noise due to Josephson vibration, eliminating malfunction and performing highly accurate measurement. CONSTITUTION:In this circuit provided at least with a sensor 1 provided with at least one Josephson junction 31 and a comparator 2 provided with at least one Josephson junction 32 capable of identifying the size of the output voltage or the output current of the sensor 1, the frequency of the Josephson vibration generated by the Josephson junction 31 provided in the sensor 1 at the time of the operation of the sensor 1 is made higher than the frequency equivalent to the turn-on delay of the Josephson junction 32 provided in the comparator 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor including at least one Josephson junction and at least one Josephson capable of discriminating the magnitude of the output voltage or the output current of the sensor. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Josephson signal detection circuit including at least a comparator including a junction, and more particularly to a Josephson signal detection circuit that has stable operation and is easy to improve measurement accuracy, and a Josephson signal detection circuit. The present invention relates to a measuring device configured to include.

[0002]

2. Description of the Related Art A comparator formed by using a Josephson junction corresponds to whether the Josephson junction is in a superconducting state or in a normal conducting state depending on the presence or absence of an input signal. The comparator itself may be used as the sensor, but a sensor constituted by Josephson junction may be arranged in the preceding stage. As an example, SQU is provided in the front stage.
When the ID is arranged, there is an advantage that the analog voltage signal of the SQUID can be converted into a digital signal by the comparator, and the signal processing and the data transmission can be facilitated.
This is described in detail, for example, by Dr. Lang et al. In Cryogenics 1986, Vol. 26, pp. 623-627.

FIG. 15 shows a method of combining the SQUID 1 and the comparator 2 according to the prior art disclosed by Durang et al. The comparator 2 receives the signal from the SQUID 1 by the magnetic coupling 100 and detects the presence or absence of the input signal. The comparator 2 disclosed in the prior art includes two Josephson junctions 32.
And a superconducting wire that connects them to form a loop including an inductance 92, and an alternating current source 7. The superconducting critical current value of the Josephson junction 32 is 30μ.
The capacitance is 0.45 pF, and the value of the inductance 92 is 17 pH. Comparator is SQUI
The signal from D changes (switches) from a superconducting state of zero voltage to a finite voltage state. A signal current determined by the voltage generated in the comparator and the load resistance flows out as an output signal from the comparator.

[0004]

In the prior art in which the SQUID is arranged in front of the comparator, the comparator directly detects the output voltage generated by the Josephson junction included in the SQUID by converting it into an output current via a resistor. To do. FIG. 16 is a diagram schematically showing a change in characteristics when a magnetic flux signal is input to the SQUID. SQUID
The current-voltage characteristic of is continuously changed in the range from nΦ ₀ to (n + 0.5) Φ _{0 in} the figure. Therefore, if the bias current of the SQUID is selected as shown in FIG. 16, the operating voltage range of the SQUID is determined as shown in the figure.

At this time, an AC current due to the AC Josephson effect is superimposed on the output current of the SQUID. FIG. 17
Shows an example of the relationship between the magnitude of the input magnetic flux and the value obtained by converting the output voltage of the SQUID into a current by a resistor when the input magnetic flux signal of the SQUID increases in proportion to time. In FIG. 17, the solid line is the actual output current of the SQUID, on which the alternating current due to the alternating Josephson effect is superimposed. The dashed line is the SQU after passing the low-pass filter.
It is the value that the output voltage of the ID is converted into the current by the resistance. This is the SQU that is usually observed with an oscilloscope.
This is the output of the ID. The frequency of the alternating current due to the alternating Josephson effect is the output voltage of the SQUID
It is the value divided by ₀ (2/10 ¹⁵ Wb) and is usually 100M
It becomes a value of about 50 GHz from Hz. The peak value of this AC current is modulated at another frequency lower than the frequency of the AC Josephson effect, as shown by the solid line in FIG. 17, because of the electrostatic capacitance and the inductance included in the SQUID. It does not change monotonically with the output voltage of the SQUID.

SQUID observed with an oscilloscope or the like
The output of does not include the AC current due to such an AC Josephson effect. The AC current is due to the stray capacitance and inductance existing in the wiring from the SQUID placed at a cryogenic temperature to the oscilloscope placed at room temperature. This is because it is attenuated and the measurement band of the oscilloscope does not reach such a high frequency. However, SQUI
If a comparator using a Josephson junction is arranged near D, the AC current due to the AC Josephson effect reaches the comparator without being attenuated. Also, since the Josephson junction included in the comparator is capable of ultra-high-speed switching, if the comparator is manufactured without special consideration as in the prior art, the comparator will generate an AC current due to the AC Josephson effect. Respond,
Switch.

As described above, the SQU is provided in the preceding stage of the comparator.
In the prior art in which the ID is arranged, a comparator is configured without special consideration for the influence of the AC current due to the AC Josephson effect on the measurement accuracy and the operation stability of the device, and the AC Josephson AC The signal including the alternating current due to the effect was read by the comparator. Therefore, in the conventional technique, there is a problem that the value of the output voltage of the SQUID read by the comparator does not correspond to the output voltage of the SQUID usually observed by an oscilloscope or the like.

More specifically, the following two points are problems. First, as explained in connection with FIG. 17,
The peak value or waveform of the alternating current is not steady and changes with time. Therefore, the SQ read by the comparator
There is a problem that the output of the UID greatly varies and the measurement accuracy decreases.

The amplitude of the AC current is not proportional to the DC component of the SQUID output voltage, and its magnitude may reach ten times or more the DC component of the SQUID output voltage. Therefore, there is a problem that the linearity between the output of the comparator and the input magnetic flux to the SQUID deteriorates, the measurement itself becomes difficult, and the operation of the circuit becomes unstable.

In this case, the SQUI is provided before the comparator.
Although the problem has been described with respect to the case where D is arranged, this problem is a problem common to all comparators in which a signal from a sensor including a Josephson junction is used as an input signal. As described above, in the prior art, there was no viewpoint to prevent the deterioration of the measurement accuracy of the comparator or the unstable operation of the device caused by the alternating current due to the alternating Josephson effect, or sufficient attention was not paid. It was

An object of the present invention includes a Josephson signal detection circuit which solves the above problems of the prior art, has high measurement accuracy, and is excellent in operation stability, and a Josephson signal detection circuit. It is to provide a configured measuring device.

[0012]

The above object is to provide a sensor including at least one Josephson junction and at least one output voltage or at least one output current of the sensor. In a circuit including at least a comparator including a Josephson junction, the frequency of the Josephson oscillation generated by the Josephson junction included in the sensor during operation of the sensor is included in the comparator. This can be achieved by configuring the Josephson signal detection circuit or the measuring device so that the frequency is higher than the frequency corresponding to the turn-on delay of the Josephson junction.

[0013]

According to the structure of the present invention, the comparator can be made to have a filtering effect on the alternating current due to the alternating Josephson effect. This is because the turn-on delay inherent in the Josephson junction is used to change the input current with a frequency higher than a certain frequency.
This is because the Josephson junctions that make up the comparator are set so that they do not respond.

The switch operation of the comparator will be described in more detail with reference to FIG. FIG. 18 shows a current-voltage characteristic of a Josephson junction or a Josephson quantum interferometer that constitutes a comparator. The comparator can be composed of a Josephson junction and a resistor, or a Josephson quantum interferometer, but the effect of turn-on delay can be explained in either case as well. In FIG. 18, Ib is a bias current, which is the sum of its value and the signal current input to the comparator, Ig.
However, when the maximum value Im of the superconducting current that can flow in the comparator in the superconducting state is exceeded for a certain period of time,
The comparator switches.

The inventors have noticed that Ig needs to exceed Im for a certain time or longer in order for the comparator to switch. This fixed time is usually called the turn-on delay (τ _D ) of the Josephson junction, and the capacitance C of the Josephson junction or, if there is another capacitance in parallel with the Josephson junction, those electrostatic capacitances. The total capacity C and Im can be expressed by the following equation.

[0016]

[Equation 5]

[0017] Therefore, when a frequency corresponding to the turn-on delay time of the comparator and f _1, Josephson junction constituting the comparator does not respond feel substantially reduce the high frequency of the input signal than f _1. That is, FIG.
As shown in, it is possible to obtain the same effect as providing a low pass filter in the comparator. If the frequency of noise due to the AC Josephson effect generated in the operating state of the Josephson junction of the sensor is f ₂ , and the frequency f ₁ corresponding to the turn-on delay time is set lower than this value, the AC Josephson effect received by the comparator causes The influence of noise can be reduced.

The frequency f ₂ of noise due to the AC Josephson effect corresponds to a value obtained by dividing the output voltage V of the Josephson junction of the sensor by the magnetic flux quantum Φ ₀ . Therefore, the frequency f ₂ depends on how much the output voltage V is used and the sensor is used. The smaller the output voltage V is, the lower the frequency f ₂ is.

As can be seen from the equation 5, in order to reduce the frequency f ₁ corresponding to the turn-on delay time, the capacitance C of the Josephson junction or the capacitance of the Josephson junction and the capacitance present in parallel with the Josephson junction are present. It suffices to change the total value C and Im of the capacitance to be used. Specifically, C may be increased and Im may be decreased. Actually, if Im is made small, the current output to the circuit at the next stage is decreased when the comparator is switched unless special measures are taken, so that the Josephson logic circuit connected to the comparator operates normally. There is a problem that it will not do. Therefore, it is not practical to change only the value of Im to increase the turn-on delay.

On the other hand, the capacitance of the Josephson junction is determined by the area of the junction and the dielectric constant of the material of the tunnel barrier layer. Since it is difficult to arbitrarily change the junction area, it is necessary to change the material of the tunnel barrier layer to a material with a large dielectric constant in order to increase the capacitance of the Josephson junction.

On the other hand, the capacitance existing in parallel with the Josephson junction can be easily changed because it is sufficient to provide the capacitance in parallel with the Josephson junction. Therefore, it can be seen that in order to increase the turn-on delay without changing the characteristics of the Josephson junction of the comparator, a new capacitor should be provided in parallel with the Josephson junction. At this time, if the two superconducting electrodes forming the Josephson junction are extended and the capacitor is provided by using that portion as an electrode, it is possible to prevent the circuit from becoming large due to the addition of the capacitor.

FIG. 20 shows the relationship between the capacitance value C and the turn-on delay. Here, the difference between the current flowing in the Josephson junction and the maximum superconducting current in the Josephson junction after switching, which corresponds to so-called overdrive, is shown. 1
μA. FIG. 20 shows the frequency f ₂ of noise due to the AC Josephson effect that can be filtered by each turn-on delay, and the corresponding SQUID voltage V. For each value of C, if the SQUID and comparator are used at a voltage higher than the voltage of SQUID shown in this figure, the effect of current noise due to the AC Josephson effect is reduced and more precise measurement is possible. become.

When the Josephson signal detection circuit according to the present invention is constructed, the capacitance of the Josephson junction included in the comparator and the total value C of the capacitances included in parallel with the capacitance, and the Josephson junction included in the sensor. Table 1 shows examples of recommended values for the operating voltage value V of
Shown in.

The configuration of the comparator may be a single Josephson junction or a circuit in which a Josephson junction and a resistor are combined. Further, it may be a Josephson quantum interference device including two or more Josephson junctions. When the comparator includes a plurality of Josephson junctions, among them, if the Josephson junction that first switches to the voltage state according to the input signal satisfies the conditions shown in Table 1, according to the concept of the present invention. The turn-on delay of the comparator can be increased.

As described above, according to the configuration of the present invention, the Josephson signal detection circuit which solves the problems of the prior art, has high measurement accuracy, and is excellent in operation stability, and , It is possible to realize a measuring device including a Josephson signal detection circuit.

[0026]

[Table 1]

[0027]

【Example】

(Embodiment 1) FIG. 1 is a circuit diagram showing a first embodiment according to the present invention. In this embodiment, SQ is used as the sensor.
UID1 is used. The comparator 2 is driven by using an alternating current source 7, and has an inductance 92 made of a superconductor and a resistor 5 provided in parallel with the inductance 92.
2, a Josephson junction 32 and a capacitor 42 provided in parallel with the Josephson junction 32. SQUID
1 is driven by a direct current source 6. The change in the output voltage caused by the input of the magnetic flux to the SQUID 1 by the magnetic flux input means 10 causes the shunt resistance 51 of the SQUID 1,
And, it is converted into a magnetic flux signal by the inductance 91 and input to the comparator 2 by the magnetic coupling 100. The input signal causes the comparator 2 to change from the superconducting state to the voltage state, thereby converting the SQUID analog signal into a digital signal.

In this embodiment, SQUID1 is n
When the bias current of SQUID is set so that the output voltage changes between about 10 μV and about 60 μV in response to the change of the input magnetic flux from Φ ₀ to (n + 0.5) Φ ₀ , 3Ω
The shunt resistor 51 causes the output signal current 11 of about 3 μA to 20 μA to flow in the inductance 91. About 70% of the signal is transmitted from the inductance 91 to the inductance 92 through the magnetic coupling 100.
A current of μA to 14 μA flows to the comparator 2.

The critical current value (Im) of the comparator 2 is set to 3
50 μA, and considering the magnitude of the output signal current 11 from SQUID 1, the bias current (I
b) is 347 μA, when the output signal current 11 from the SQUID 1 is injected into the comparator 2, the total current (Ig) injected into the comparator 2 is 349.
The range is from μA to 361 μA. 350μ in total
When A or more, the comparator 2 switches to the voltage state. The Josephson junction 32 of the comparator 2 is about 0.6 pF, and the inductance 92 is 3 pH. In the case of the present embodiment, the current noise due to the Josephson oscillation generated by SQUID1 is removed by the turn-on delay, and the LC due to the inductance 92 of the comparator 2, the Josephson junction 32, and the capacitance of the capacitance 42. The resonance was designed so that it would not be lower than the frequency of Josephson vibration during SQUID operation.
As the operating voltage range of the SQUID, it suffices to avoid the voltage corresponding to the frequency of the LC resonance, that is, to set the range that satisfies the formulas 3 or 4. In addition, the voltage range shown in the following equation is more desirable.

[0030]

[Equation 6]

[0031]

[Equation 7]

This is because, when the LC resonance is damped by using the resistor, the influence of the resonance is almost eliminated at a voltage that is ½ or less of the resonance voltage or a voltage that is ≧ 2 times the resonance voltage. A voltage that is less than half the resonance voltage, and
The area of the voltage more than double is the operation area A in FIG.
Corresponds to B respectively.

In this embodiment, in order to operate in the range shown as the operating area A, the capacitance of the capacitor 42 is about 19.
It was 4 pF. In addition, the inductance 92 of the comparator 2, the Josephson junction 32, and the capacitance 4
A resistor 52 of 0.1Ω is provided to damp the LC resonance due to the capacitance of 2. In addition, because the resistor 52 shunts the current noise due to Josephson oscillation,
It also has the effect of reducing the effect of current noise on Josephson junction 32 due to Josephson oscillation.

As described above, according to the present invention, by selecting each parameter, the SQUID1 is obtained by the filter action by the turn-on delay of the Josephson junction 32 included in the comparator 2 and the capacitor 42 in parallel with it.
It was possible to reduce the influence of the current noise due to the Josephson vibration generated by the Josephson junction 31 of FIG. As a result, the malfunction of the comparator 2 can be prevented and the measurement accuracy of the Josephson signal detection circuit can be improved.

Further, in the present embodiment, the influence of the current noise due to Josephson vibration is very small, about 1/20, and the comparator 2 is operated at the frequency avoiding the LC resonance. Therefore, the minimum current required for the comparator 2 to transition from the superconducting state to the normal conducting state and the magnitude of the signal current from the SQUID 1, that is,
The signal magnitude relationship input to SQUID1 is proportional. Therefore, if a current source whose value changes stepwise as shown in FIG. 3 as the reference signal current is used as the bias current source of the comparator 2, the time when the comparator 2 changes to the voltage state. By obtaining the bias current flowing in the comparator 2 from (t1 in FIG. 3), the comparator 2 can be used as a successive approximation type analog-digital converter. In that case, as shown in FIG. 4, a wiring 61 for injecting a reference signal current may be provided in addition to the alternating current source 7. In FIG. 1, the comparator 2 is a magnetic coupling type in which the current flowing through the resistor 51 is switched by the magnetic flux generated by the inductance 91, but as shown in FIG. 4, it is switched by the current injected through the resistor 51. It is clear that the same effect can be obtained by using a current injection type comparator.

Further, the minimum current required for the comparator 2 to transit from the superconducting state to the normal conducting state, and SQU
The magnitude of the signal current from ID1, that is, SQUID
Since the magnitude of the signal input to 1 is proportional, a feedback method for controlling the operation of SQUID1 is FLL (Flux Locked Loop).
Circuits can be used.

Further, in the present embodiment, the operating point of the comparator 2 is used within the range shown as the operating area A in FIG. 2, but it is shown as the operating area B in FIG. 2 in order to avoid the influence of LC resonance. It is obvious that the same effect can be obtained by setting the range as the operating point of the comparator 2.

(Embodiment 2) FIG. 5 is a circuit diagram showing a second embodiment according to the present invention. In this embodiment, the SQUID is used as the sensor. The comparator 2 is driven by using the alternating current source 7, and the Josephson junction 32
It consists of The SQUID 1 is driven by the direct current source 6 and the SQUID is driven by the magnetic flux input means 10.
The change in output voltage caused by the input of magnetic flux to D1 is SQ
Output signal current 11 via shunt resistor 51 of UID1
Is directly input to the comparator 2. The comparator 2 switches to the voltage state when the total value of the output signal current 11 from the SQUID 1 and the current injected by the AC bias from the AC current source 7 is larger than the critical current value of the Josephson junction 32, and when it is smaller, The analog signal is converted into a digital signal by maintaining the superconducting state.

In this embodiment, the current noise due to the Josephson oscillation generated from the Josephson junction 31 during the operation of the SQUID 1 can be removed by the turn-on delay due to the capacitance of the Josephson junction 32 included in the comparator 2. According to the present invention, S
A QUID1 and a comparator 2 were constructed. SQUI
D1 corresponds to the change of the input magnetic flux from nΦ ₀ to (n + 0.5) Φ ₀ , and when the bias current is set so that the output voltage changes from about 10 μV to about 60 μV, the shunt resistance of 3Ω 51 Causes an output signal current 11 of about 3 μA to 20 μA to be injected into the comparator 2. When the critical current value (Im) of the comparator 2 is 350 μA, S
Considering the magnitude of the output signal current 11 from the QUID 1, the bias current (Ib) of the comparator 2 is set to 346 μ.
If the output signal current 11 from SQUID 1 is injected into the comparator 2, the total current (Ig) injected into the comparator 2 is 349 μA to 366 μA.
It becomes the range of. Therefore, under the above conditions, the capacitance of the Josephson junction 32 is set to 1 so that the current noise due to the Josephson oscillation can be removed by utilizing the turn-on delay due to the capacitance of the Josephson junction 32 of the comparator 2.
It was set to 5 pF. The Josephson junction 32 has a junction area of 10 μm square. As a result of making SQUID1 and comparator 2 using the above values, comparator 2
The effective magnitude of the current noise due to the Josephson oscillation generated by the Josephson junction 31 of the SQUID 1 sensed by the can be reduced to about 1/10 of the conventional one by the turn-on delay. As a result, minute changes in the output signal current 11 that could not be detected because they were buried in the current noise due to Josephson vibration in the past can be detected, the measurement accuracy is improved, and malfunction does not occur.

In this embodiment, since both the SQUID and the comparator are made of superconductor,
It was possible to fabricate them on the same chip by a usual integrated circuit process technology using Nb for the superconductor.

(Embodiment 3) FIG. 6 is a circuit diagram of another embodiment according to the present invention. In this embodiment, the SQUID is used as the sensor. The comparator 2 has a resistor 51
It is a current injection type that is switched by the current injected through the. In the present embodiment, the comparator 2 is composed of four pairs of parallel connection bodies of the Josephson junction 32 and the capacitor 42 and the resistor 53, and has an input / output separation type circuit configuration. Even after the transition to the voltage state, the current is prevented from flowing backward from the comparator 2 to the SQUID 1. Further, since the comparator 2 shown in this embodiment does not include an inductance as a constituent element, LC resonance does not occur. Therefore, SQUID1
The capacitance of the capacitance 42 included in the comparator 2 is selected so that the noise due to the Josephson vibration generated by the Josephson junction 31 during the operation of can be removed by the turn-on delay of the Josephson junction 32 and the capacitance 42 of the comparator 2. Thus, the malfunction of the comparator 2 can be prevented and the measurement accuracy can be improved.

In the present embodiment, the comparator 2 has four pairs of the Josephson junction 32 and the capacitor 42 connected in parallel,
Although the input / output separation circuit composed of the resistor 53 is used,
The structure of the input / output separation circuit is not limited to this. For example, as shown in FIG. 7, Josephson junction 32 and capacitance 4
JAWS consisting of 2 sets of 2 parallel connections and resistor 53
(Josephson Atto Weber Switch) type, or as shown in FIG.
DCL (Direct Coupl) consisting of a group and two resistors 53
It goes without saying that the ed Logic type may be used.

(Embodiment 4) FIG. 9 is a circuit diagram of another embodiment according to the present invention. In FIG. 9, SQUID1 and
A plurality of Josephson signal detection circuits combined with the comparator 2 are provided, and changes in the input magnetic flux at a plurality of locations can be measured at the same time. In this embodiment, the comparator 2 is a magnetic coupling type in which the current flowing through the resistor 51 is switched by the magnetic flux generated by the inductance 91, and the comparator 2 is provided in parallel with the inductance 92 and the inductance 92 formed of a superconductor. Resistor 52, Josephson junction 32, Josephson junction 3
2 and a capacitor 42 provided in parallel. With this configuration, as shown in the first and second embodiments, by selecting each parameter, the malfunction of the comparator 2 can be prevented and the measurement accuracy can be improved.

Further, in this embodiment, the SQUID
1, a resistor 54 is provided in parallel with an inductance 91 for inputting a signal to the comparator 2 by magnetic coupling. By providing the resistor 54, SQUID1
Josephson junction 31 capacitance and inductance 9
The LC resonance due to 1 can be damped. Further, since the current noise due to the Josephson vibration generated by the Josephson junction 31 is shunted to the resistor 54, the current noise magnetically coupled with the comparator 2 can be reduced. Therefore, in the configuration of the present embodiment, the current noise due to Josephson vibration can be further reduced, and the measurement accuracy can be improved.

(Embodiment 5) FIG. 10 is a top view showing the shapes of a Josephson junction 32 and a capacitor 42 provided in parallel with the Josephson junction 32 of a comparator 2 according to another embodiment of the present invention.
In the present embodiment, the capacitance 42 provided in parallel with the Josephson junction 32 has four capacitance portions 421, 422, 42.
3 and 424, and the two superconducting thin films forming the upper electrode 321, and the lower electrode 322 of the Josephson junction 32 are the electrodes of these capacitance portions 421 to 424.

In this embodiment, the Josephson junction 3
In No. 2, Nb is used for the upper electrode 321 and the lower electrode 322, and AlOx is used for the tunnel barrier layer 323. The electrode forming the capacitor 42 was also formed by using the same thin film as the electrode forming the Josephson junction 32. However, as the insulating film 324, Nb ₂ O ₅ instead of AlOx, or
When Ta ₂ O ₅ or Hf ₂ O ₅ is used to form the capacitor 42, these materials have a large relative permittivity as compared with AlOx, so that there is an advantage that the area of the capacitor portion can be reduced. is there.

When the capacitor 42 is divided into four capacitor portions 421, 422, 423, and 424 as in this embodiment, the upper electrode of the capacitor portion 424 is replaced by the upper electrode as shown in FIG. The capacitance of the capacitor 42 can be changed by cutting with a laser trimmer or the like. With such a configuration, it is possible to easily configure a filter with a turn-on delay that is optimal for the operation of the SQUID.

(Sixth Embodiment) FIG. 12 is a circuit diagram of another embodiment according to the present invention. In FIG. 12, the sensor 200
Is composed of a Josephson junction 31 and a resistor 51, and this Josephson junction 31 can detect X-rays, electromagnetic waves and the like. Further, the comparator 2 is composed of a Josephson junction 32 and a capacitor 42 provided in parallel with it. Unlike other embodiments, the sensor is SQUI
Although not D, by providing the capacitance 42 in parallel with the Josephson junction 32 forming the comparator, it is possible to reduce the influence of the current noise generated from the Josephson junction 31 included in the sensor 200, and to accurately measure X. Lines and electromagnetic waves can be detected.

In FIG. 12, the output signal current 11 from the Josephson junction 31 in the preceding stage of the comparator is injected into the comparator 2, but as shown in FIG. 13, as the sensor 200 and the constituent elements of the comparator 2,
A signal may be transmitted to the comparator 2 by the magnetic coupling 100 by adding an inductance 91 and an inductance 92, respectively. In FIG. 13, the comparator is composed of a Josephson quantum interferometer. Further, the sensor 200 has an array configuration in which two or more Josephson junctions are arranged in series. With such a configuration, when detecting a minute X-ray or an electromagnetic wave, there is an advantage that the detection area can be increased without increasing the capacitance of the detector. In the circuit configuration shown in FIG. 13, the current noise due to Josephson oscillation generated by the Josephson junction array 311 is removed by the turn-on delay, and the inductance 92 of the comparator 2, the Josephson junction 32, and the capacitance 42 are removed. The effect of the present invention can be obtained and the operation can be stabilized by configuring the LC resonance due to the capacitance of No. 1 so as not to be equal to the frequency of the Josephson oscillation generated when the Josephson junction array 311 transits to the voltage state. It was possible to realize a highly accurate comparator. In addition, the inductance 9 of the comparator 2
2, and Josephson junction 32, and capacitance 42
The resistor 52 provided for damping the LC resonance due to the electrostatic capacitance of is, in addition to the damping of the LC resonance, current noise due to Josephson oscillation is shunted to the resistor 52.
The effect of the current noise due to the Josephson vibration applied to the Josephson junction 32 is also reduced, and the accuracy of the comparator can be further improved by providing the resistor 52.

(Embodiment 7) FIG. 14 is a circuit diagram of another embodiment according to the present invention. In FIG. 14, a Josephson counter 300 is arranged at the next stage of the Josephson signal detection circuit having the configuration shown in FIG. By thus configuring the counting circuit with a circuit using the Josephson junction, the counting circuit can be installed in the low temperature tank together with the comparator 2 and the like, so that the measuring device can be downsized. In addition, since the measurement results such as X-rays and electromagnetic waves can be processed in the low temperature tank, it is possible to correspond to higher speed counting as compared with the case where the counting circuit is placed at room temperature, and also to prevent noise from mixing. Therefore, the measurement accuracy can be further improved.

[0051]

As described above in detail, a sensor including at least one Josephson junction and at least one Josephson capable of discriminating the magnitude of the output voltage or the output current of the sensor. In a circuit including at least a comparator including a junction, the frequency of the Josephson oscillation generated by the Josephson junction included in the sensor during operation of the sensor is the Josephson oscillation included in the comparator. By configuring the frequency to be higher than the frequency corresponding to the turn-on delay of the junction, it has high measurement accuracy,
Further, it is possible to provide a Josephson signal detection circuit having excellent operation stability.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing an operation area of a comparator.

FIG. 3 is an operation waveform when the comparator is used as a successive approximation type analog / digital converter.

FIG. 4 is a circuit diagram showing another embodiment of the present invention.

FIG. 5 is a circuit diagram showing another embodiment of the present invention.

FIG. 6 is a circuit diagram when an input / output separation circuit type comparator is used.

FIG. 7 is a circuit diagram when another input / output separation circuit type comparator is used.

FIG. 8 is a circuit diagram when another input / output separation circuit type comparator is used.

FIG. 9 is a circuit diagram when a plurality of SQUIDs and comparators are provided.

FIG. 10 is a top view showing a shape of a Josephson junction and a capacitor including a capacitor portion divided into four pieces.

FIG. 11 is a circuit diagram of a capacitance composed of four capacitance portions and a Josephson junction.

FIG. 12 is a circuit diagram showing an embodiment for detecting X-rays or electromagnetic waves.

FIG. 13 is a circuit diagram showing another embodiment for detecting X-rays or electromagnetic waves.

FIG. 14 is a circuit diagram showing an embodiment for detecting an X-ray or an electromagnetic wave having a Josephson counter.

FIG. 15 is a circuit diagram of a conventional digital SQUID.

FIG. 16 is an explanatory diagram of current-voltage characteristics of SQUID.

FIG. 17 is an SQUID output signal waveform including AC noise.

FIG. 18 is an explanatory diagram of current-voltage characteristics of a comparator.

FIG. 19 is an equivalent SQUID output signal waveform sensed by a comparator.

FIG. 20 is a diagram showing a relationship between capacitance and turn-on delay.

[Explanation of symbols]

1 ... SQUID, 2 ... Comparator, 31, 32 ... Josephson junction, 311 ... Josephson junction array, 32
DESCRIPTION OF SYMBOLS 1 ... Upper electrode, 322 ... Lower electrode, 323 ... Tunnel barrier layer, 324 ... Insulating film, 42 ... Capacitor provided in parallel with Josephson junction, 421, 422, 423, 424 ... Capacitance part, 51 ... Shunt resistance, 52 , 53, 54 ... Resistance,
6 ... DC current source, 61 ... Wiring, 7 ... AC current source, 8 ... Signal output terminal, 9, 91, 92 ... Inductance, 10 ...
Input means for magnetic flux, 11 ... Output signal current, 100 ... Magnetic coupling, 200 ... Sensor, 201 ... X-ray, 300 ... Josephson counter.

Claims (24)

[Claims] 1. A sensor including at least one Josephson junction and at least one Josephson junction capable of discriminating the magnitude of an output voltage or an output current of the sensor. And a comparator configured to include at least
The frequency of the Josephson vibration generated by the Josephson junction included in the sensor during the operation of the sensor is
A Josephson signal detection circuit configured to have a frequency higher than a frequency corresponding to a turn-on delay of a Josephson junction included in the comparator. 2. The comparator according to claim 1, wherein:
A Josephson signal detection circuit having a capacitance portion formed of at least one capacitance connected in parallel with the Josephson junction included therein. 3. The electrostatic capacitance C of the Josephson junction included in the comparator, or the electrostatic capacitance of the Josephson junction and the capacitive portion of the Josephson junction, if the capacitive portion is included. The total value C of the electrostatic capacitance is the current value Ig after the signal is input to the comparator, and the critical current value Im of the comparator,
And a Josephson signal detection circuit, which is selected so as to satisfy the relationship represented by the following formula by the output voltage V and the magnetic flux quantum Φ ₀ during the operation of the sensor. [Equation 1] 4. The Josephson signal detection circuit according to claim 2, wherein the capacitor portion is composed of two or more capacitors connected in parallel. 5. The capacitance of the capacitance portion according to claim 4, wherein the capacitance of the capacitance portion is cut by cutting a part or all of the wiring connecting the two or more capacitances forming the capacitance portion and connected in parallel to each other. A Josephson signal detection circuit that can be changed. 6. The capacitor according to claim 2, wherein the capacitor portion provided in parallel with the Josephson junction included in the comparator has a structure in which an insulator is sandwiched by metal electrodes, and The material of this insulator is Nb ₂ O ₅ ,
Alternatively, the Josephson signal detection circuit is Ta ₂ O ₅ or Hf ₂ O ₅ . 7. The method according to claim 1, wherein the comparator includes a Josephson quantum interferometer composed of at least an inductance composed of a superconductor, and a resistance connected in parallel to the inductance is provided. Josephson signal detection circuit characterized by. 8. The value R of the resistance according to claim 7, wherein the capacitance C of the Josephson junction included in the comparator, or the capacitance R of the Josephson junction when the capacitance portion is included, A Josephson signal detection circuit, wherein the total value C of the capacitance of the capacitance portion and the inductance L are values satisfying the following formula. [Equation 2] 9. The electrostatic capacitance C of the Josephson junction included in the comparator according to claim 7, or, if the capacitance portion is included, the electrostatic capacitance of the Josephson junction and the capacitance portion. The total value C of the electrostatic capacities should satisfy the relationship represented by the following equation by the inductance L included in the comparator, the output voltage V during the operation of the sensor, and the magnetic flux quantum Φ ₀ . , A Josephson signal detection circuit, wherein the capacitance of the Josephson junction and the capacitance of the capacitance portion are set. [Equation 3] 10. The capacitance C of the Josephson junction included in the comparator according to claim 7,
Alternatively, when the capacitance section is included, the total value C of the capacitance of the Josephson junction and the capacitance of the capacitance section is equal to the output of the inductance L included in the comparator and the output during operation of the sensor. According to the voltage V and the magnetic flux quantum Φ ₀ , the capacitance of the Josephson junction and the capacitance of the capacitance portion are set so as to satisfy the relationship expressed by the following equation. circuit. [Equation 4] 11. The comparator according to any one of claims 1 to 10, wherein the comparator has a reference signal current applying unit serving as a detection reference, and operates by gradually increasing the value of the reference signal current. Josephson signal detection circuit, characterized in that it constitutes a successive approximation type analog-digital converter. 12. The Josephson signal detection circuit according to claim 1, wherein the sensor includes an inductance formed of a superconductor. 13. The Josephson signal according to claim 1, wherein the comparator operates by directly injecting an output current of the sensor into the Josephson junction included in the comparator. Detection circuit. 14. The comparator according to claim 13, wherein the comparator includes a Josephson junction, and
The output signal from the sensor is applied to one of the two input terminals of this Josephson junction, and the other input terminal is included in a comparator connected to another Josephson junction or a resistor to prevent backflow. A Josephson signal detection circuit having means. 15. The Josephson signal detection circuit according to claim 1, wherein the comparator is magnetically coupled to the sensor. 16. The Josephson signal detection circuit according to claim 1, wherein the sensor has two or more Josephson junctions connected in series. 17. A Josephson signal detection circuit according to claim 1, wherein said sensor is provided with an X-ray or electromagnetic wave incident means. 18. The Josephson signal detection circuit according to claim 1, wherein the sensor is a superconducting quantum interference device. 19. The Josephson signal detection circuit according to claim 18, wherein the sensor is provided with a magnetic flux applying means. 20. A sensor including at least one Josephson junction and at least one Josephson junction capable of discriminating the magnitude of an output voltage or an output current of the sensor. And a comparator configured to include at least
The frequency of the Josephson vibration generated by the Josephson junction included in the sensor during the operation of the sensor is
A measuring apparatus comprising a plurality of Josephson signal detection circuits, wherein the frequency is higher than a frequency corresponding to a turn-on delay of a Josephson junction included in the comparator. 21. The sensor according to claim 20, wherein the sensor is 2
A measuring device characterized in that two or more Josephson junctions are connected in series. 22. The measuring device according to claim 20, wherein the sensor is provided with an X-ray or electromagnetic wave incident means. 23. The measuring device according to claim 20, wherein the sensor is a superconducting quantum interference device. 24. The measuring device according to claim 23, wherein the sensor is provided with a magnetic flux applying unit.