For four decades semiconductor electronics has followed Moore's law: with each generation of integration the circuit features became smaller, more complex and faster. This development is now reaching a wall so that smaller is no longer any faster. The clock rate has saturated at about 3-5 GHz and the parallel processor approach will soon reach its limit. The prime reason for the limitation the semiconductor electronics experiences is not the switching speed of the individual transistor, but its power dissipation and thus heat. Digital superconductive electronics is a circuit- and device-technology that is inherently faster at much less power dissipation than semiconductor electronics. It makes use of superconductors and Josephson junctions as circuit elements, which can provide extremely fast digital devices in a frequency range - dependent on the material - of hundreds of GHz: for example a flip-flop has been demonstrated that operated at 750 GHz. This digital technique is scalable and follows similar design rules as semiconductor devices. Its very low power dissipation of only 0.1 mu W per gate at 100 GHz opens the possibility of three-dimensional integration. Circuits like microprocessors and analogue-to-digital converters for commercial and military applications have been demonstrated. In contrast to semiconductor circuits, the operation of superconducting circuits is based on naturally standardized digital pulses the area of which is exactly the flux quantum Phi(0). The flux quantum is also the natural quantization unit for digital-to-analogue and analogue-to-digital converters. The latter application is so precise, that it is being used as voltage standard and that the physical unit 'Volt' is defined by means of this standard. Apart from its outstanding features for digital electronics, superconductive electronics provides also the most sensitive sensor for magnetic fields: the Superconducting Quantum Interference Device (SQUID). Amongst many other applications SQUIDs are used as sensors for magnetic heart and brain signals in medical applications, as sensor for geological surveying and food-processing and for non-destructive testing. As amplifiers of electrical signals. SQUIDs can nearly reach the theoretical limit given by Quantum Mechanics. A further important field of application is the detection of very weak signals by 'transition-edge' bolo-meters, superconducting nanowire single-photon detectors, and superconductive tunnel junctions. Their application as radiation detectors in a wide frequency range, from microwaves to X-rays is now standard. The very low losses of superconductors have led to commercial microwave filter designs that are now widely used in the USA in base stations for cellular phones and in military communication applications. The number of demonstrated applications is continuously increasing and there is no area in professional electronics, in which superconductive electronics cannot be applied and surpasses the performance of classical devices. Superconductive electronics has to be cooled to very low temperatures. Whereas this was a bottleneck in the past, cooling techniques have made a huge step forward in recent years: very compact systems with high reliability and a wide range of cooling power are available commercially, from microcoolers of match-box size with milli-Watt cooling power to high-reliability coolers of many Watts of cooling power for satellite applications. Superconductive electronics will not replace semiconductor electronics and similar room-temperature techniques in standard applications, but for those applications which require very high speed, low-power consumption, extreme sensitivity or extremely high precision, superconductive electronics is superior to all other available techniques. To strengthen the European competitiveness in superconductor electronics research projects have to be set-up in the following field: - Ultra-sensitive sensing and imaging. - Quantum measurement instrumentation. - Advanced analogue-to-digital converters. - Superconductive electronics technology.

European roadmap on superconductive electronics – status and perspectives☆

Superconducting digital devices can be advantageously used in future supercomputers because they can greatly reduce the dissipation power and increase the speed of operation. Non-volatile quantized states are ideal for the realization of classical Boolean logics. A quantized Abrikosov vortex represents the most compact magnetic object in superconductors, which can be utilized for creation of high-density digital cryoelectronics. In this work we provide a proof of concept for Abrikosov-vortex-based random access memory cell, in which a single vortex is used as an information bit. We demonstrate high-endurance write operation and two different ways of read-out using a spin valve or a Josephson junction. These memory cells are characterized by an infinite magnetoresistance between 0 and 1 states, a short access time, a scalability to nm sizes and an extremely low write energy. Non-volatility and perfect reproducibility are inherent for such a device due to the quantized nature of the vortex.

/pdf/single-abrikosov-vortices-as-quantized-information-bits-4ecnp2p814.pdf

Single Abrikosov vortices as quantized information bits.

The establishment at PTB of an AC Josephson voltage standard (Josephson Arbitrary Waveform Synthesizer- JAWS) based on pulse-driven Josephson arrays is focused on achieving an output voltage of at least 1 Vrms which is required for many metrology applications In this paper, we approached this goal by increasing the number of active junctions in two ways Firstly, we fabricated arrays containing triple-stacked SNS-type Josephson junctions with Nb
 x
Si
 1-x
 as barrier material We obtained current operation margins of about 02 mA with arrays of up to 9000 Josephson junctions at an rms voltage of 355 mV Secondly, we used a new 8-channel ternary pulse pattern generator (PPG) to bias up to 8 arrays connected in series An output voltage of V
 RMS
 = 1006 mV(V
 PP
 = 2845 V) was achieved by using 8 arrays (arranged on 4 separate chips) with 63000 junctions in total Higher harmonics are suppressed by at least -116 dBc The fabrication process and the experimental setup will be described, as well as experimental results that are leading towards our 1 V goal

Towards a 1 V Josephson Arbitrary Waveform Synthesizer

A quantum logic gate is formed from multiple qubits coupled to a common resonator, wherein quantum states in the qubits are transferred to the resonator by transitioning a classical control parameter between control points at a selected one of slow and fast transition speeds, relative to the characteristic energy of the coupling, whereby a slow transition speed exchanges energy states of a qubit and the resonator, and a fast transition speed preserves the energy states of a qubit and the resonator.

Arbitrary quantum operations with a common coupled resonator

In one embodiment, the disclosure relates to a method and apparatus for controlling the energy state of a qubit by bringing the qubit into and out of resonance by coupling the qubit to a flux quantum logic gate. The qubit can be in resonance with a pump signal, with another qubit or with some quantum logic gate. In another embodiment, the disclosure relates to a method for controlling a qubit with RSFQ logic or through the interface between RSFQ and the qubit.

Method and apparatus for controlling qubits with single flux quantum logic

A rapid single-flux-quantum RSFQ logic circuit includes a first circuit portion having a first end grounded and having in-series connected first and second Josephson junctions. A second circuit portion has a first end grounded and has in-series connected third and fourth Josephson junctions. A first inductance element connects a second end of the first circuit portion to a second end of the second circuit portion. A tap is provided in the first inductance element, an input current signal being supplied to the tap. A bias current source is connected to a first connection node between the first and second Josephson junctions. A second inductance element connects the first connection node to a second connection node between the third and fourth Josephson junctions. A superconducting quantum interference device has fifth and sixth Josephson junctions and is coupled to the second inductance element through a magnetic field.

Rapid single-flux-quantum logic circuit and rapid single-flux-quantum output conversion circuit

We have designed a 16 kbit superconducting latching/SFQ hybrid (SLASH) RAM, which enables high-frequency clock operation up to 10 GHz. The 16 kbit SLASH RAM consists of four 4 × 4 matrix arrays of 256 bit RAM blocks, block decoders, latching block drivers, latching block senses, impedance matched lines and the powering circuits. The 256 bit RAM block is composed of a 16 × 16 matrix array of vortex transitional memory cells, latching drivers, SFQ NOR decoders and latching sense circuits. We have also designed and implemented an SFQ NOR decoder that is composed of magnetically coupled multi-input OR gates and RSFQ inverters.

https://iopscience.iop.org/article/10.1088/0953-2048/12/11/371/pdf

Design of a 16 kbit superconducting latching/SFQ hybrid RAM

In order to establish a quantum ac voltage standard at NMIJ/AIST, we have developed a Josephson arbitrary waveform synthesizer based on overdamped Josephson junction arrays (JJAs) using optoelectronics and a liquid helium free compact cryocooler. We have succeeded in the generation of sine waves at 60 Hz and 152.6 kHz. To verify the performance of the system, two different types of JJAs with different characteristic frequencies have been developed. An application to a quantized voltage noise source for Johnson noise thermometry is also discussed, with experimental results.

https://iopscience.iop.org/article/10.1088/0953-2048/22/11/114012/pdf

Operation of a Josephson arbitrary waveform synthesizer with optical data input

PROBLEM TO BE SOLVED: To stabilize the operation of a single flux quantum logic circuit to improve the degree of freedom in circuit design. SOLUTION: A superconductor quantum interference element including a fifth and sixth Josephson junctions JL5 , JL6 is formed so as to make a second inductance magnetic field coupling to provide the element on an output circuit part in a single flux quantum logic circuit 10.

Hideo Suzuki

Papers

Rapid single-flux-quantum logic circuit and rapid single-flux-quantum output conversion circuit

Design of a 16 kbit superconducting latching/SFQ hybrid RAM

Operation of a Josephson arbitrary waveform synthesizer with optical data input

Single flux quantum logic circuit and single flux quantum output converter circuit