CQT PhD QE II by Chai Jing Hao — 25 Nov, 03:30 PMCQT PhD QE II by Chai Jing Hao Title: Fault Tolerant Quantum Computing in the context of NonMarkovian noise from small baths Date/Time: 25 Nov, 03:30 PM Venue: CQT Level 3 Seminar Room, S150315 Abstract: Is accurate quantum computing possible with scalable resources? Previous studies have explored quantum error correction and fault tolerant design under the assumption of different types of noise. In particular, two general types of noise were studied: CPTP maps on the system that corresponded to noise without "memory", and joint systembath unitary evolution which describes noise that has "memory". However, the conclusions about the possibility of quantum computing under these two types of noise were quite different. In the former case, the target probability of error for quantum components to achieve was ~1e4. In the latter, the target probability of error was found instead to be ~1e8. To put these numbers into perspective, consider that the best experimental standards have only reached an average fidelity of ~1e3/1e4 currently. While some may claim that we have reached the threshold for a quantum computer, we are quite far away from building one if the true threshold is ~1e8. These two types of situations correspond respectively to one where noise has no "memory" and one where noise has full "memory" on an infinite time scale. One expects that the typical experimental situation to lie somewhere in between: the presence of a small bath that acts as a small memory, but itself may be situated in a larger dissipative bath that limits the memory time to some finite length scale. Such a situation can be described with a CPTP map on acting the joint systembath composite. This talk presents exploratory research in this direction. CQT Talk by Kadir Durak, CQT — 26 Nov, 04:00 PMCQT Talk by Kadir Durak, CQT Title: The thickcrystal regime in photon pair sources Date/Time: 26 Nov, 04:00 PM Venue: CQT Level 3 Seminar Room, S150315 Abstract: We present comprehensive measurement data on the pump and collection beam parameters necessary to achieve high collection efficiency (89%) together with high brightness when a single betaBarium Borate crystal is operated in the thickcrystal regime and pumped with a narrow linewidth laser source. Spectral analysis of the collinear, nondegenerate photons suggest that the effective interaction length within the crystal is dominated by the collection beam mode and the use of longer crystals with increased spatial walkoff does not necessarily lead to a reduced collection efficiency. This result is an important consideration for optical designers who seek to develop practical photon pair sources. CQT Talk by Luis L. SánchezSoto, Max Planck Institut für die Physik des Lichts, Erlangen, Germany and Facultad de Física, Universidad Complutense, Madrid, Spain — 27 Nov, 11:00 AMCQT Talk by Luis L. SánchezSoto, Max Planck Institut für die Physik des Lichts, Erlangen, Germany and Facultad de Física, Universidad Complutense, Madrid, Spain Title: The quest for the kings of quantumness Date/Time: 27 Nov, 11:00 AM Venue: CQT Level 3 Seminar Room, S150315 Abstract: The characterization of the polarization properties of a quantum state requires the knowledge of the joint probability distribution of the Stokes variables. This amounts to assessing all the moments of these variables, which are aptly encoded in a multipole expansion of the density matrix. The cumulative distribution of these multipoles encapsulates in a handy manner the polarization content of the state. We work out the extremal states for that distribution, finding that SU(2) coherent states are maximal to any order, so they are the most polarized allowed by quantum theory. The converse case of pure states minimizing that distribution, which can be seen as the most quantum ones, is investigated for a diverse range of number of photons. Exploiting the Majorana representation, the problem appears to be closely related to distributing a number of points uniformly over the surface of the PoincarÃ© sphere. Prospects for the experimental generation of these states and their potential applications will be also discussed. CQT Talk by Stanley Williams, Hewlett Packard Labs — 03 Dec, 04:00 PMCQT 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, S150315 Abstract: We are working on a project to explore the use of locallyactive memristors as the basis for extremely lowpower transistorless computation. We have analyzed the thermallyinduced phase transitions from a Mott insulator to a highly conducting state in a family of correlatedelectron transitionmetal oxides, such as VO2 and NbO2. The currentvoltage 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 selfheating if the ambient temperature is below the metalinsulator transition (MIT). We have derived simple analytical equations for the behavior these devices [1] 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 [2]. 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 PearsonAnson oscillators without inductors based on a parallel circuit of one locallyactive 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 [3] in 1960 without an experimental implementation, using two locally active memristors and two capacitors. The neuristor electronically emulates the HodgkinHuxley model of the axon action potential of a neuron, which has been recently shown by Chua et al. [4] 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 [5] that are believed to be the basis for computation and communication in biological systems.
1. Pickett, M. D. and Williams, R. S. Sub100 femtoJoule and subnanosecond thermallydriven threshold switching," Nanotechnology 23, art. #215202 (2012). 2. Chua, L. & Kang, S. Memristive devices and systems. Proceedings of the IEEE 64, 209223 (1976). 3. Crane, H. D. The Neuristor. IRE Transactions on Electronic Computers EC9, 370371 (1960). 4. Chua, L., Sbitnev, V. & Kim, H. HodgkinHuxley axon is made of memristors. International Journal of Bifurcation and Chaos 22, 148 (2012). 5. Pickett, M. D., MedeirosRibeiro, G. and Williams, R. S. A scalable neuristor built with Mott memristors, Nature Materials 12, 114117 (2013). CQT Annual Symposium 2015 — 07 Dec, 04:30 PMCQT 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.
PROGRAMME: 4.30pm "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. 5.30pm: break 6.00pm "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 processorcentric von Neumann paradigm that has dominated for the past seven decades to a memorydriven architecture based on a flat nonvolatile memory space, high bandwidth photonic interconnect and dispersed systemonchip 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 NanotechnologyInspired 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 More events
