216 research outputs found
Cryogenic Neuromorphic Hardware
The revolution in artificial intelligence (AI) brings up an enormous storage
and data processing requirement. Large power consumption and hardware overhead
have become the main challenges for building next-generation AI hardware. To
mitigate this, Neuromorphic computing has drawn immense attention due to its
excellent capability for data processing with very low power consumption. While
relentless research has been underway for years to minimize the power
consumption in neuromorphic hardware, we are still a long way off from reaching
the energy efficiency of the human brain. Furthermore, design complexity and
process variation hinder the large-scale implementation of current neuromorphic
platforms. Recently, the concept of implementing neuromorphic computing systems
in cryogenic temperature has garnered intense interest thanks to their
excellent speed and power metric. Several cryogenic devices can be engineered
to work as neuromorphic primitives with ultra-low demand for power. Here we
comprehensively review the cryogenic neuromorphic hardware. We classify the
existing cryogenic neuromorphic hardware into several hierarchical categories
and sketch a comparative analysis based on key performance metrics. Our
analysis concisely describes the operation of the associated circuit topology
and outlines the advantages and challenges encountered by the state-of-the-art
technology platforms. Finally, we provide insights to circumvent these
challenges for the future progression of research
Controlling phonons and photons at the wavelength-scale: silicon photonics meets silicon phononics
Radio-frequency communication systems have long used bulk- and
surface-acoustic-wave devices supporting ultrasonic mechanical waves to
manipulate and sense signals. These devices have greatly improved our ability
to process microwaves by interfacing them to orders-of-magnitude slower and
lower loss mechanical fields. In parallel, long-distance communications have
been dominated by low-loss infrared optical photons. As electrical signal
processing and transmission approaches physical limits imposed by energy
dissipation, optical links are now being actively considered for mobile and
cloud technologies. Thus there is a strong driver for wavelength-scale
mechanical wave or "phononic" circuitry fabricated by scalable semiconductor
processes. With the advent of these circuits, new micro- and nanostructures
that combine electrical, optical and mechanical elements have emerged. In these
devices, such as optomechanical waveguides and resonators, optical photons and
gigahertz phonons are ideally matched to one another as both have wavelengths
on the order of micrometers. The development of phononic circuits has thus
emerged as a vibrant field of research pursued for optical signal processing
and sensing applications as well as emerging quantum technologies. In this
review, we discuss the key physics and figures of merit underpinning this
field. We also summarize the state of the art in nanoscale electro- and
optomechanical systems with a focus on scalable platforms such as silicon.
Finally, we give perspectives on what these new systems may bring and what
challenges they face in the coming years. In particular, we believe hybrid
electro- and optomechanical devices incorporating highly coherent and compact
mechanical elements on a chip have significant untapped potential for
electro-optic modulation, quantum microwave-to-optical photon conversion,
sensing and microwave signal processing.Comment: 26 pages, 5 figure
Programmable Superconducting Optoelectronic Single-Photon Synapses with Integrated Multi-State Memory
The co-location of memory and processing is a core principle of neuromorphic
computing. A local memory device for synaptic weight storage has long been
recognized as an enabling element for large-scale, high-performance
neuromorphic hardware. In this work, we demonstrate programmable
superconducting synapses with integrated memories for use in superconducting
optoelectronic neural systems. Superconducting nanowire single-photon detectors
and Josephson junctions are combined into programmable synaptic circuits that
exhibit single-photon sensitivity, memory cells with more than 400 internal
states, leaky integration of input spike events, and 0.4 fJ programming
energies (including cooling power). These results are attractive for
implementing a variety of supervised and unsupervised learning algorithms and
lay the foundation for a new hardware platform optimized for large-scale
spiking network accelerators.Comment: 16 pages, 11 figure
Addressable Superconductor Integrated Circuit Memory from Delay Lines
Recent advances in logic schemes and fabrication processes have renewed
interest in using superconductor electronics for energy-efficient computing and
quantum control processors. However, scalable superconducting memory still
poses a challenge. To address this issue, we present an alternative to
approaches that solely emphasize storage cell miniaturization by exploiting the
minimal attenuation and dispersion properties of superconducting passive
transmission lines to develop a delay-line memory system. This fully
superconducting design operates at speeds between 20 GHz and 100 GHz, with
24\% and 13\% bias margins, respectively, and demonstrates data
densities in the 10s of Mbit/cm with the MIT Lincoln Laboratory SC2
fabrication process. Additionally, the circulating nature of this design allows
for minimal control circuitry, eliminates the need for data splitting and
merging, and enables inexpensive implementations of sequential access and
content-addressable memories. Further advances in fabrication processes suggest
data densities of 100s of Mbit/cm and beyondComment: 13 pages, 8 figures, 1 table, under revie
Superconducting Nonlinear Kinetic Inductance Devices
We describe a novel class of devices based on the nonlinearity of the kinetic inductance of a superconducting thin film. By placing a current-dependent inductance in a microwave resonator, small currents can be measured through their effect on the resonator’s frequency. By using a high-resistivity material for the film and nanowires as kinetic inductors, we can achieve a large coefficient of nonlinearity to improve device sensitivity. We demonstrate a current sensitivity of 8 pA/√Hz, making this device useful for transition-edge sensor (TES) readout and other cutting-edge applications. An advantage of these devices is their natural ability to be multiplexed in the frequency domain, enabling large detector arrays for TES-based instruments. A traveling-wave version of the device, consisting of a thin-film microwave transmission line, is also sensitive to small currents as they change the phase length of the line due to their effect on its inductance. We demonstrate a current sensitivity of 5 pA/√Hz for this version of the device, making it also suitable for TES readout as well as other current-detection applications. It has the advantage of multi-gigahertz bandwidth and greater dynamic range, offering a different approach to the resonator version of the device. Finally, we also demonstrate a transmission-line resonator version of the device that combines some of the advantages of the nanowire resonator and the traveling-wave device. This version of the device has high dynamic range but can also be easily multiplexed in the frequency domain.
A lumped-element resonator similar to the first device can be placed in a loop configuration to make it sensitive to magnetic fields. We demonstrate an example of such a device whose sensitivity could ultimately reach levels similar to those of state-of-the-art DC SQUIDs, making it potentially useful for many magnetometry applications given its ease of multiplexing. Finally, a similar microwave resonator is shown to exhibit parametric gain of up to 29 dB in the presence of a strong pump tone. The noise performance of this parametric amplifier approaches the quantum limit, making it useful for applications in quantum information and metrology.</p
Single and entangled photon manipulation for photonic quantum technologies
Photonic quantum technologies that harness the fundamental laws of quantum physics open the possibility of developing quantum computing and communication that could show unprecedented computational power on specific problems and unconditional information security, respectively. However, the lack of high-efficiency single-photon sources and integrated photonic circuits that can generate, manipulate and analyse entanglement states are the major hurdles to demonstrate the quantum advantages. The potential solutions are clearly explained in this thesis. Chapter 1 provides a brief overview that explains the theme of each chapter. Chapter 2 emphasises the importance of a high-efficiency single-photon source and an integrated time-bin entanglement chip, after explaining the advantages of photonic quantum computing and communication over their classical counterparts. In Chapter 3, three different temporal multiplexing schemes are experimentally demonstrated as the potential solutions to build a high-efficiency single-photon source. Chapter 3 also identifies the potential limitations of temporal multiplexing with high repetition rate. In Chapter 4, the linear processing circuits and nonlinear photon source are separately demonstrated in a low-loss double-stripe silicon nitride waveguide. In the final section of Chapter 4, an integrated silicon nitride time-bin entanglement chip that combines linear processing circuits and nonlinear photon sources is demonstrated as a potential solution to build a robust, scalable and cost-efficient quantum network in the real world. After a succinct summarisation, the final chapter briefly discusses the promising strategies and platforms to build an integrated high-efficiency single-photon source and an integrated quantum node with broad bandwidth and long storage time
Advanced photon counting applications with superconducting detectors
Superconducting nanowire single photon detectors (SNSPDs) have emerged as mature detection technology that offers superior performance relative to competing infrared photon counting technologies. SNSPDs have the potential to revolutionize a range of advanced infrared photon counting applications, from quantum information science to remote sensing. The scale up to large area SNSPD arrays or cameras consisting of hundreds or thousands of pixels is limited by efficient readout schemes.
This thesis gives a full overview of current SNSPD technology, describing design, fabrication, testing and applications. Prototype 4-pixel SNSPD arrays (30 x 30 µm2 and 60 x 60 µm2) were fabricated, tested and time-division multiplexed via a power combiner. In addition, a photon-number resolved code-division multiplexed 4-pixel array was simulated. Finally, a 100 m calibration-free distributed fibre temperature testbed, based on Raman backscattered photons detected by a single pixel fibre-coupled SNSPD housed in a Gifford McMahon cryostat was experimentally demonstrated with a spatial resolution of approximately 83 cm. At present, it is the longest range distributed thermometer based on SNSPD sensing
A Nanocryotron Ripple Counter Integrated with a Superconducting Nanowire Single-Photon Detector for Megapixel Arrays
Decreasing the number of cables that bring heat into the cryocooler is a
critical issue for all cryoelectronic devices. Especially, arrays of
superconducting nanowire single-photon detectors (SNSPDs) could require more
than readout lines. Performing signal processing operations at low
temperatures could be a solution. Nanocryotrons, superconducting nanowire
three-terminal devices, are good candidates for integrating sensing and
electronics on the same technological platform as SNSPDs in photon-counting
applications. In this work, we demonstrated that it is possible to read out,
process, encode, and store the output of SNSPDs using exclusively
superconducting nanowires. In particular, we present the design and development
of a nanocryotron ripple counter that detects input voltage spikes and converts
the number of pulses to an -digit value. The counting base can be tuned from
2 to higher values, enabling higher maximum counts without enlarging the
circuit. As a proof-of-principle, we first experimentally demonstrated the
building block of the counter, an integer- frequency divider with
ranging from 2 to 5. Then, we demonstrated photon-counting operations at
405\,nm and 1550\,nm by coupling an SNSPD with a 2-digit nanocryotron counter
partially integrated on-chip. The 2-digit counter operated in either base 2 or
base 3 with a bit error rate lower than and a maximum count
rate of s. We simulated circuit architectures for
integrated readout of the counter state, and we evaluated the capabilities of
reading out an SNSPD megapixel array that would collect up to counts
per second. The results of this work, combined with our recent publications on
a nanocryotron shift register and logic gates, pave the way for the development
of nanocryotron processors, from which multiple superconducting platforms may
benefit
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