A superconducting optoelectronic neuron will produce a small current pulse upon reaching threshold. We present an amplifier chain that converts this small current pulse to a voltage pulse sufficient to produce light from a semiconductor diode. This light is the signal used to communicate between neurons in the network. The amplifier chain comprises a thresholding Josephson junction, a relaxation oscillator Josephson junction, a superconducting thin-film current-gated current amplifier, and a superconducting thin-film current-gated voltage amplifier. We analyze the performance of the elements in the amplifier chain in the time domain to calculate the energy consumption per photon created for several values of light-emitting diode capacitance and efficiency. The speed of the amplification sequence allows neuronal firing up to at least 20\,MHz with power density low enough to be cooled easily with standard $^4$He cryogenic systems operating at 4.2\,K.
A superconducting optoelectronic neuron will produce a small current pulse upon reaching threshold. We present an amplifier chain that converts this small current pulse to a voltage pulse sufficient to produce light from a semiconductor diode. This light is the signal used to communicate between neurons in the network. The amplifier chain comprises a thresholding Josephson junction, a relaxation oscillator Josephson junction, a superconducting thin-film current-gated current amplifier, and a superconducting thin-film current-gated voltage amplifier. We analyze the performance of the elements in the amplifier chain in the time domain to calculate the energy consumption per photon created for several values of light-emitting diode capacitance and efficiency. The speed of the amplification sequence allows neuronal firing up to at least 20,MHz with power density low enough to be cooled easily with standard 4He cryogenic systems operating at 4.2,K.
Superconducting circuits that operate by propagation of small voltage or current pulses, corresponding to propagation of single flux or charge quantum, are naturally suited for implementing spiking neuron circuits. Quantum phase-slip junctions (QPSJs) are 1-D superconducting nanowires that have been identified as exact duals to Josephson junctions, based on charge-flux duality in Maxwell’s equations. In this paper, a superconducting quantized-charge circuit element, formed using quantum phase-slip junctions, is investigated for use in high-speed, low-energy superconducting spiking neuron circuits. By means of a SPICE model developed for QPSJs, operation of this superconducting circuit to produce and transport quantized charge pulses, in the form of current pulses, is demonstrated. The resulting quantized-charge-based operation emulates spiking neuron circuits for brain-inspired neuromorphic applications. Additionally, to further demonstrate the operation of QPSJ-based neuron circuits, a QPSJ-based integrate and fire neuron circuit is introduced, along with simulation results using WRSPICE. Estimates for operating speed and power dissipation are provided and compared to Josephson junction and CMOS-based spiking neuron circuits. Current challenges are also briefly mentioned.
A number of current approaches to quantum and neuromorphic computing use superconductors as the basis of their platform or as a measurement component, and will need to operate at cryogenic temperatures. Semiconductor systems are typically proposed as a top-level control in these architectures, with low-temperature passive components and intermediary superconducting electronics acting as the direct interface to the lowest-temperature stages. The architectures, therefore, require a low-power superconductor-semiconductor interface, which is not currently available. Here we report a superconducting switch that is capable of translating low-voltage superconducting inputs directly into semiconductor-compatible (above 1,000 mV) outputs at kelvin-scale temperatures (1 K or 4 K). To illustrate the capabilities in interfacing superconductors and semiconductors, we use it to drive a light-emitting diode (LED) in a photonic integrated circuit, generating photons at 1 K from a low-voltage input and detecting them with an on-chip superconducting single-photon detector. We also characterize our device's timing response (less than 300 ps turn-on, 15 ns turn-off), output impedance (greater than 1 MΩ), and energy requirements (0.18 fJ/um^2, 3.24 mV/nW).
A novel superconducting neuron circuit and two types of variable synapses, which are based on superconducting quantum interferometer devices (SQUIDs), are presented. A neuron circuit with good input-output isolation and steep threshold characteristics is accomplished using a combination of a single-junction SQUID coupled to a double-junction SQUID. The quantum state of the single-junction SQUID represents the neuron state, and the output voltage of the double-junction SQUID, which is operated in a nonlatching mode with shunt resistors, is a sigmoid-shaped function of the input. Both variable synapse circuits are composed of multiple shunted double-junction SQUIDs. The first type changes its conductance value by using both superconducting and voltage states. The second variable synapse circuit changes its output current digitally by switching its bias currents. Besides numerical simulations of the circuit characteristics, we have fabricated superconducting neural chips in a Nb/AlO/sub x//Nb Josephson junction technology. The fundamental operation of each element and a 2-bit neural-based A/D converter have been successfully tested. A learning system with a variable synapse is also discussed.>
An optical input/output interface system for a Josephson junction integrated circuit is fabricated and tested. The system consists of a superconducting optical detector, a dc powered Josephson circuit, a dc powered Josephson high voltage circuit, a liquid-He-cooled semiconductor amplifier, and a liquid-He-cooled semiconductor laser. Features of the system are use of an ultrathin NbN film for the optical detector and adoption of the dc powered Josephson circuits for logic operation circuits. Correct optical output signal is detected by a liquid-He-cooled semiconductor photodiode. The optical input/output interface has the advantage of low heat penetration and low crosstalk compared to the interface using conventional coaxial lines. Moreover, dc powered Josephson circuits have an advantage of low crosstalk from power supply lines compared to conventional Josephson circuits, which are driven by ac supply current.>
Superconductive electronics offers a unique combination of high bandwidth and low power for mission critical hardware such as digital processors at 20 to 100 GHz, microwatt per bit analog to digital converters, large digital switches at multi-Gb/s data rates, and low noise parametric amplifiers. This cryogenic technology, typically operating at a few degrees or a few tens of degrees Kelvin, depends upon the unique physics of superconducting materials such as Nb, NbN, and YBaCuO, and the fundamental circuit element, the Josephson junction (JJ) to create unique architectures of unprecedented design efficiency and performance. These circuits are based on the single flux quantum (SFQ) logic family, a technology that has no parallel in semiconductor electronics. Digital data is transmitted by voltage pulses with amplitude less than 1 mV, but at extremely high speeds. Individual gates have been operated as high as 370 GHz. In this paper, we present a brief overview of superconductive digital technology, describe some recent circuits, and discuss how the challenges to superconductive technology are being met, including the use of multi-chip module (MCM) technology, and the potential use of III-V HBT and HEMT circuits to provide interface drivers and amplifiers, possibly operated cryogenically.
The optoelectronic coupling for a pulse-driven Josephson junction array (JJA) for use as a quantum voltage synthesizer has been designed. This system uses optoelectronic components to drive a group of JJAs in parallel. Since the drive system is electrically isolated from the JJAs, they can be connected in series, leading to a higher output voltage. A thin film circuit, including interdigitated capacitors to couple a photodiode to the JJAs has been designed and tested and shown to meet the design goals.