© 2026 Aqora Quantum S.A.S.

Terms Privacy Legal Notice

IEEE Transactions on Magnetics

Single-fluxoid quantum four-junction-interferometer operated in the phase mode

Gin-ichiro Oya, Mamoru Yamashita, Yasuji Sawada

Published Mar 1, 1985• 6 citations

Abstract

We have theoratically and experimentally investigated the possibility of the phase mode operation of symmetrical four-junction Josephson interferometers (4J-loop), which are considered to play a key role as quantum logic devices for a Josephson switching system utilizing single-quanta as information bits, because of their excellent characters such as the kinetic momentum quantum effect and variety of the logic operations. The threshold characteristic, which is the most basic for Josephson interferometers to be operated in the phase mode and shows their fluxoid-quantum states, has experimentally been observed clearly for the first time for symmetrical 4J-loop's by using a novel radial-scanning, intensity-modulation technique, as predicted theoretically. It is characterized by a limited closed-shaped pattern. The number of the fluxoid-quantum states increases with LI0for the loops. Two different basic types of switching behaviors, a vortex-to-vortex and a vortex-to-voltage transition, have been confirmed, which have clearly been separated on the threshold characteristic, for the loops with LI0larger than\sim0.7\Phi_{0}The optimum LI0value for the phase mode operation of the loops has been found to be0.75\Phi_{0}\lsim LI_{0}\lsim 1.25\Phi_{0}. The desired performance of the phase mode operation of symmetrical 4J-loop has been confirmed by the shift motion of single fluxoids on the basis of the vortex-to-vortex transition of the loop. Finally, an application of such phase mode Josephson interferometers for pulse generators of Josephson sampling systems has been proposed.

DOI: 10.1109/tmag.1985.1063694

Related papers

Fluxoid motion in phase mode Josephson switching system

Kiyotaka Nakajima, Gin-ichiro Oya, Yasuji Sawada

We have investigated the possibility of the phase mode operation, i.e. the mode to transfer the fluxoid, not to transfer the voltage pulse, of Josephson switching system by fabricating a resistively coupled D.C. SQUID's array and 4J-loop which are expected to be advantageous in miniaturization by using its large kinetic momentum effect. The threshold characteristics of these superconducting loops and its LIcdependence agreed with the theoretical predictions. The phase mode logic actions were verified to operate really in a resistively coupled D.C.SQUID's and a coupled D.C. SQUID with a 4J-loop. A computer simulation showed that a resistively coupled SQUID's array acts both on phase mode and voltage mode by changing the circuit parameters, but that the two modes are clearly separated in a parameter space. Finally we have shown a total system configuration of the phase mode operation. For the power loss and the information processing speed, the phase mode was verified to have an advantage over the ordinary voltage mode by two orders of magnitude.

IEEE Transactions on Magnetics•May 1, 1983•22 citations

Josephson device with well-defined and low critical points

H. Beha

Two different basic types of switching behavior of Josephson interferometers are possible: a vortex-to-vortex and a vortex-to-voltage transition. Both transition types are separated by the so-called critical points on the threshold curve of the device. For critical points, in general, no analytic expression is available. Therefore, the position of the critical points can only be determined by numerical solutions. In the designs known, the critical points are very sensitlve with respect to parameter variations, which makes LSI design very difficult. In this paper, the design and the experimental results of an asymmetric Josephson interferometer with one well-defined and low critical point are described. This well-defined critical point corresponds to the tip point of the threshold characteristic, which is defined by an analytical expression. The practical consequence for the design of Josephson circuits will be indicated. The dynamic switching behavior of the asymmetric interferometer with respect to the critical points will be discussed extensively in the phase plane, together with the potential energy.

IEEE Transactions on Magnetics•May 1, 1983•1 citation

Dynamics of some single flux quantum devices: I. Parametric quantron

Konstantin K. Likharev

In this paper and the following one, the properties of two systems operating with single flux quanta are calculated. The first system is a quantron (a one-junction interferometer) with a Josephson gate as a junction. By a proper change of its critical current in time, the switching of quantron stable states can be controlled by a small external flux much less than Φo. This "Parametric Quantron" can be used as the basic cell of a Single Quantum Logic System. The most wonderful property of this device is that the energy dissipation during one logical step (PτT factor) can be much less than the thermal energy KBT and is limited by quantum effects only: Pτ2\simg102h.

IEEE Transactions on Magnetics•Jan 1, 1977•117 citations

Proposal of unilateral single-flux-quantum logic gate

Hidetaka MIYAKE, N. Fukaya, Yoji Okabe +1 more

A new type of single flux quantum logic gate is proposed, which can perform unilateral propagation of signal without using three-phase clock. This gate is designed to be built with bridge-type Josephson junctions. A basic logic gate consists of two one-junction interferometers coupled by superconducting interconnecting lines, and the logical states are represented by zero or one quantized fluxoid in one of one-junction interferometers. The bias current of the unequal magnitude to each of the two one-junction interferometers results in unilateral signal flow. By adjusting design parameters such as the ratio of the critical current of Josephson junctions and the inductances, circuits with the noise immunity of greater than 50% with respect to the bias current have been designed. Three cascaded gates were modeled and simulated on a computer, and the unilateral signal flow was confirmed. The simulation also shows that a switching delay about 2 picoseconds is feasible.

IEEE Transactions on Magnetics•Mar 1, 1985•4 citations

Experimental observation of the switching transients resulting from single flux quantum transitions in superconducting Josephson devices

Pierre Guéret

We have made what we believe is the first experimental observation of the switching transients resulting from single flux quantum transitions in superconducting devices. For that purpose, we used ``long'' Josephson junctions or interferometers which exhibit overlapping vortex modes. By applying a magnetic field to such devices, vortex-mode transitions are induced. The resulting transients are detected by a small Josephson junction located nearby. The experimental results show unambiguously that the points where a signal is detected by the sense junction correspond to the vortex-mode boundaries of the device. These results have important implications for memory applications.

Applied Physics Letters•Oct 1, 1974•33 citations

Phase mode Josephson computer system

Kiyotaka Nakajima, H. Mizusawa, H. Sugahara +1 more

A discussion is presented of one of the simplest models of Josephson computer systems (phase mode system), in which quantized vortices of magnetic flux (fluxoids) are employed as information bits and in which all logic functions are achieved by interactions between fluxoids. In a phase mode system, device operation depends on the existence of many stable states differing from each other by integer multiples of 2 pi in the phase plane. As an example, the authors propose a simple model of a complete phase mode computing system and discuss the basic computer elements and the instruction in this system. The total system is considered to be a prototype of quantum computer systems in which physical quantum states are employed as logic states for information processing.>

IEEE Transactions on Applied Superconductivity•Mar 1, 1991•75 citations

We have theoratically and experimentally investigated the possibility of the phase mode operation of symmetrical four-junction Josephson interferometers (4J-loop), which are considered to play a key role as quantum logic devices for a Josephson switching system utilizing single-quanta as information bits, because of their excellent characters such as the kinetic momentum quantum effect and variety of the logic operations. The threshold characteristic, which is the most basic for Josephson interferometers to be operated in the phase mode and shows their fluxoid-quantum states, has experimentally been observed clearly for the first time for symmetrical 4J-loop's by using a novel radial-scanning, intensity-modulation technique, as predicted theoretically. It is characterized by a limited closed-shaped pattern. The number of the fluxoid-quantum states increases with LI0for the loops. Two different basic types of switching behaviors, a vortex-to-vortex and a vortex-to-voltage transition, have been confirmed, which have clearly been separated on the threshold characteristic, for the loops with LI0larger than\sim0.7\Phi_{0}The optimum LI0value for the phase mode operation of the loops has been found to be0.75\Phi_{0}\lsim LI_{0}\lsim 1.25\Phi_{0}. The desired performance of the phase mode operation of symmetrical 4J-loop has been confirmed by the shift motion of single fluxoids on the basis of the vortex-to-vortex transition of the loop. Finally, an application of such phase mode Josephson interferometers for pulse generators of Josephson sampling systems has been proposed.

We have investigated the possibility of the phase mode operation, i.e. the mode to transfer the fluxoid, not to transfer the voltage pulse, of Josephson switching system by fabricating a resistively coupled D.C. SQUID's array and 4J-loop which are expected to be advantageous in miniaturization by using its large kinetic momentum effect. The threshold characteristics of these superconducting loops and its LIcdependence agreed with the theoretical predictions. The phase mode logic actions were verified to operate really in a resistively coupled D.C.SQUID's and a coupled D.C. SQUID with a 4J-loop. A computer simulation showed that a resistively coupled SQUID's array acts both on phase mode and voltage mode by changing the circuit parameters, but that the two modes are clearly separated in a parameter space. Finally we have shown a total system configuration of the phase mode operation. For the power loss and the information processing speed, the phase mode was verified to have an advantage over the ordinary voltage mode by two orders of magnitude.

Two different basic types of switching behavior of Josephson interferometers are possible: a vortex-to-vortex and a vortex-to-voltage transition. Both transition types are separated by the so-called critical points on the threshold curve of the device. For critical points, in general, no analytic expression is available. Therefore, the position of the critical points can only be determined by numerical solutions. In the designs known, the critical points are very sensitlve with respect to parameter variations, which makes LSI design very difficult. In this paper, the design and the experimental results of an asymmetric Josephson interferometer with one well-defined and low critical point are described. This well-defined critical point corresponds to the tip point of the threshold characteristic, which is defined by an analytical expression. The practical consequence for the design of Josephson circuits will be indicated. The dynamic switching behavior of the asymmetric interferometer with respect to the critical points will be discussed extensively in the phase plane, together with the potential energy.

In this paper and the following one, the properties of two systems operating with single flux quanta are calculated. The first system is a quantron (a one-junction interferometer) with a Josephson gate as a junction. By a proper change of its critical current in time, the switching of quantron stable states can be controlled by a small external flux much less than Φo. This "Parametric Quantron" can be used as the basic cell of a Single Quantum Logic System. The most wonderful property of this device is that the energy dissipation during one logical step (PτT factor) can be much less than the thermal energy KBT and is limited by quantum effects only: Pτ2\simg102h.

A new type of single flux quantum logic gate is proposed, which can perform unilateral propagation of signal without using three-phase clock. This gate is designed to be built with bridge-type Josephson junctions. A basic logic gate consists of two one-junction interferometers coupled by superconducting interconnecting lines, and the logical states are represented by zero or one quantized fluxoid in one of one-junction interferometers. The bias current of the unequal magnitude to each of the two one-junction interferometers results in unilateral signal flow. By adjusting design parameters such as the ratio of the critical current of Josephson junctions and the inductances, circuits with the noise immunity of greater than 50% with respect to the bias current have been designed. Three cascaded gates were modeled and simulated on a computer, and the unilateral signal flow was confirmed. The simulation also shows that a switching delay about 2 picoseconds is feasible.

We have made what we believe is the first experimental observation of the switching transients resulting from single flux quantum transitions in superconducting devices. For that purpose, we used ``long'' Josephson junctions or interferometers which exhibit overlapping vortex modes. By applying a magnetic field to such devices, vortex-mode transitions are induced. The resulting transients are detected by a small Josephson junction located nearby. The experimental results show unambiguously that the points where a signal is detected by the sense junction correspond to the vortex-mode boundaries of the device. These results have important implications for memory applications.

A discussion is presented of one of the simplest models of Josephson computer systems (phase mode system), in which quantized vortices of magnetic flux (fluxoids) are employed as information bits and in which all logic functions are achieved by interactions between fluxoids. In a phase mode system, device operation depends on the existence of many stable states differing from each other by integer multiples of 2 pi in the phase plane. As an example, the authors propose a simple model of a complete phase mode computing system and discuss the basic computer elements and the instruction in this system. The total system is considered to be a prototype of quantum computer systems in which physical quantum states are employed as logic states for information processing.>