CQT Talk by Stanley Williams, Hewlett Packard Labs — 03 Dec, 04:00 PM|CQT Annual Symposium 2015 — 07 Dec, 04:30 PM
CQT Talk by Stanley Williams, Hewlett Packard Labs
Title: Toward Neuromimetic Computing: Locally Active Memristors, Spiking Neuristors
and an Electronic Action Potential at the Edge of Chaos
Date/Time: 03 Dec, 04:00 PM
Venue: CQT Level 3 Seminar Room, S15-03-15
Abstract: We are working on a project to explore the use of locally-active memristors as the basis for extremely low-power transistorless computation. We have analyzed the thermally-induced phase transitions from a Mott insulator to a highly conducting state in a family of correlated-electron transition-metal oxides, such as VO2 and NbO2. The current-voltage characteristic of a simple device that has a thin film of such an oxide sandwiched between two metal electrodes displays one or more regions of negative differential resistance (NDR) caused by Joule self-heating if the ambient temperature is below the metal-insulator transition (MIT). We have derived simple analytical equations for the behavior these devices  that quantitatively reproduce their experimentally measured electrical characteristics, and found that the resulting dynamical model was mathematically equivalent to the "memristive system" formulation of Leon Chua and Steve Kang . Moreover, these devices display the property of "local activity"; because of the NDR, they are capable of injecting energy into a circuit (converting DC to AC electrical power) over a specific biasing range. We have built and demonstrated a variety of Pearson-Anson oscillators without inductors based on a parallel circuit of one locally-active memristor and one capacitor, and were able to quantitatively reproduce the dynamical behavior of the circuit, including the subnanosecond and subpicoJoule memristor switching time and energy, as well as entrance into regimes of chaotic oscillations, using numerical circuit simulations. We then built a neuristor, an active subcircuit originally proposed by Hewitt Crane  in 1960 without an experimental implementation, using two locally active memristors and two capacitors. The neuristor electronically emulates the Hodgkin-Huxley model of the axon action potential of a neuron, which has been recently shown by Chua et al.  to be a circuit with two parallel ionic memristors, and we show experimental results that are quantitatively matched by simulations of the output signal bifurcation, signal gain and spiking behavior in our inorganic and electronic circuit  that are believed to be the basis for computation and communication in biological systems.
1. Pickett, M. D. and Williams, R. S. Sub-100 femtoJoule and sub-nanosecond thermally-driven threshold switching," Nanotechnology 23, art. #215202 (2012).
2. Chua, L. & Kang, S. Memristive devices and systems. Proceedings of the IEEE 64, 209-223 (1976).
3. Crane, H. D. The Neuristor. IRE Transactions on Electronic Computers EC-9, 370-371 (1960).
4. Chua, L., Sbitnev, V. & Kim, H. Hodgkin-Huxley axon is made of memristors. International Journal of
Bifurcation and Chaos 22, 1-48 (2012).
5. Pickett, M. D., Medeiros-Ribeiro, G. and Williams, R. S. A scalable neuristor built with Mott memristors, Nature Materials 12, 114-117 (2013).
CQT Talk by Alessandro Tosini, Università di Pavia — 08 Dec, 04:00 PM
CQT Annual Symposium 2015
Title: The famous, the bit and the quantum
Date/Time: 07 Dec, 04:30 PM
Venue: University Hall Auditorium, Lee Kong Chian Wing, Level 2, University Hall, NUS
Abstract: The CQT Annual Symposium is being held to celebrate the Centre's eighth birthday. Guests are invited to attend talks on topics at the forefront of research in quantum technologies.
"Certified Quantum Randomness"
Serge Massar, UniversitÃ© Libre de Bruxelles, Belgium
Abstract: Randomness is a physical phenomena which we are confronted with all the time. Will it rain today? At what time? Will the train be on time? But are such phenomena truly random? Good randomness is essential for many applications. Cryptography, the art of hiding information from malicious users, is only as good as the source of randomness that underlies it.
Quantum mechanics, the theory of microscopic phenomena, can only predict the probability of events: for instance quantum theory can only predict the probability that a radioactive nucleus will decay, not if the nucleus will decay. Does this mean that microscopic phenomena are truly random?
By studying systems of two entangled particles, it can be shown both theoretically and experimentally, that events at the microscopic scale are truly random, truly unpredictable. Beyond its philosophical implications, these works also have important potential applications. Indeed they imply that one can build random number generators that certify that they work correctly. That is, if the random number generator malfunctions in some way, if the numbers it produces cease to be random, this will automatically be detected. By extending this idea, one could also build quantum cryptographic systems and quantum computers that certify that they work correctly. We discuss the perspectives for practical implementations.
"Computing beyond the Age of Mooreâ€™s Law "
Stanley Williams, Hewlett Packard Labs, USA
Abstract: With the end of Mooreâ€™s Law within sight (really!), what opportunities exist to continue the exponential scaling of computer performance and efficiency into the future? The primary consumers of energy and time in computers today are not the processors, but rather the communication and storage systems in a data center. Even if it were possible to perform computation infinitely fast with zero energy consumption, there would be little change in the power and time required to perform a calculation on the types of â€˜big dataâ€™ sets that are beginning to dominate information technology. I will describe a path forward with two stages. The first is to change the fundamental structure of a computer from the processor-centric von Neumann paradigm that has dominated for the past seven decades to a memory-driven architecture based on a flat nonvolatile memory space, high bandwidth photonic interconnect and dispersed system-on-chip processors. This is the vision behind The Machine, a major research and development effort currently in progress in Hewlett Packard Enterprise. Once this transformation has been completed, a new era of hybrid computation can begin, which is the motivation behind a new Nanotechnology-Inspired Grand Challenge for Future Computing recently announced by the US White House. One of the drivers for this initiative is the thesis that although our present understanding of the brain is limited, we know enough now to design and build circuits that can accelerate certain computational tasks; and as we learn more about how brains communicate and process information, we will be able to harness that understanding to create a new exponential growth path for computing technology.
7.00pm: End of Symposium
CQT Talk by Alessandro Tosini, Università di Pavia
Title: The Fermionic quantum theory and the Fermionic Hubbard quantum walk
Date/Time: 08 Dec, 04:00 PM
Venue: CQT Level 3 Seminar Room, S15-03-15
The anticommutation of Fermionic fields raises the problem of simulating the evolution of Fermionic systems by means of commuting quantum systems, say qubits. We tackle this issue considering local Fermionic modes as the elementary systems of an operational probabilistic theory. We show that the locality of Fermionic operations, namely operations on systems that are not causally connected must commute, implies the parity superselection rule, which inhibits the superposition of states with an even and an odd number of excitations. Accordingly we derive the largest probabilistic theory compatible with the parity superselection constraint and show that it lacks two distinctive traits of quantum theory, the local tomography and the monogamy of the entanglement.
We generalize the notion of superselection rule to general probabilistic theories as sets of linear constraints on the convex set of states and prove a trade-off between the cardinality of the superselection rule and the degree of holism of the resulting theory. Within this scenario the Fermionic quantum theory, as well as the real quantum theory, can be regarded as superselected versions of the usual quantum theory.
In the last part of the talk I present an interacting Fermionic quantum walk that provides the quantum circuit counterpart of the Fermionic Hubbard model. The exact solution of the two-particle dynamics shows the existence of composite bound states.