Abstract: The existence of many-body mobility edges in closed quantum systems has been the focus of intense debate after the emergence of the description of the many-body localization phenomenon. We propose that this issue can be settled in experiments by investigating the time evolution of local degrees of freedom, tailored for specific energies and initial states. An interacting model of spinless fermions, with exponentially long-ranged tunneling amplitudes and whose non-interacting version known to display single-particle mobility edges, is used as the starting point upon which nearest-neighbor interactions are included. We verify the manifestation of many-body mobility edges by using numerous probes, directly comparing it with the predictions of the Eigenstate Thermalization Hypothesis (ETH). Our results indicate the coexistence of regions, with finite measure when approaching the thermodynamic limit, where thermalization and localization are manifest, suggesting that one cannot explain their appearance as merely being a result of finite-size effects. We will further hint on how implementations using superconducting quantum processors allows one to experimentally verify these ideas, showing preliminary numerical results which emulates an existing quantum device.
Ref.: Phys. Rev. B 99, 165137 (2019)
Abstract: We live in an era where everyone is constantly connected via the internet. The way we work, play, socialise and perform transactions can no longer be dissociated with our smartphones. This is possible only because we could communicate securely over the virtual world, keeping our sensitive information away from prying eyes. However, quantum computers could break our current encryption scheme, completely disrupting our way of life in the current digital age. Fortunately, quantum theory also provides a means of encrypting unconditionally secure messages. In this talk, the art and science of quantum cryptography will be introduced. Our vision of connecting people securely via quantum links in the upcoming quantum internet will also be shared.
Speaker: Dr Goh Koon Tong, Research Fellow, Department of Electrical & Computer Engineering, National University of Singapore (NUS)
Speaker’s Profile: Dr Goh Koon Tong, Research Fellow, Department of Electrical & Computer Engineering, National University of Singapore (NUS) Dr Goh Koon Tong is a Research Fellow at the Department of Electrical & Computer Engineering, NUS and leads a theoretical team of scientists in the Quantum Communications Laboratory. His research interest is centred on quantum cryptography, focusing on the development of practical quantum protocols for the future Quantum Internet.
More info and registration: https://www.sginnovate.com/events/securing-communications-quantum-networks
CQT Talk by Shayan Mookherjea, University of California, San Diego
Title: Integrated photonics for high-performance quantum sources and detectors Date/Time: 14-Nov, 04:00PM Venue: CQT Level 3 Seminar Room, S15-03-15
Integrated photonics can greatly reduce the size, weight and power (SWaP) of optical assemblies, and also improve functionality and utility of quantum photonic sources and detectors, which may, in turn, benefit large-scale deployment and adoption of quantum technology.
We report on good performance in entangled photon-pair and heralded single-photon generation using spontaneous four-wave mixing (SFWM) in silicon photonic micro-resonators, and using spontaneous parametric down-conversion (SPDC) in periodically-poled thin-film lithium niobate waveguides. Using superconducting nanowire single-photon detectors, we demonstrated capture of ultra-high bandwidth (>100 GHz) optical modulated signals at ultra-low received average power (below -100 dBm), a new milestone in optical oscilloscopy.
Shayan Mookherjea received the BS degree with honors from Caltech, the SM degree from MIT, and the PhD from Caltech in Electrical Engineering with a minor in Physics. He is a Professor of Electrical and Computer Engineering at the University of California, San Diego. His awards include: Wilts Prize, Hellman Faculty Fellow, NSF CAREER grant, IEEE Senior Member, and OSA Fellow. He leads the Micro/Nano-Photonics Group at UCSD (http://mnp.ucsd.edu).
CQT PhD Thesis Defense by Seah Yi-Lin
Title: Detecting prior-data conflict in quantum state estimation Date/Time: 22-Oct, 03:00PM Venue: CQT Level 3 Conference Room, S15-03-17
Abstract: This work concerns the check for prior-data conflict in quantum experiments. A prior-data conflict occurs when the prior places most of its weight in regions of the parameter space that the data suggests are unfeasible. Such a conflict could indicate that the prior was poorly chosen, or that the experiment has not been behaving as expected. In quantum measurements, the permissible probability space is a subset of the entire probability simplex, often with boundaries that do not have closed-form expressions. This causes the marginal likelihood, an important quantity in checking for prior-data conflict, to be computationally difficult to evaluate. We developed tools for sampling from the quantum state space, a necessity for the rest of this work. We also investigated the feasibility of performing prior-data conflict checks on quantum problems using the marginal likelihood as a measure of typicality of the data. Subsequently, we explore other checking methods that may be more suited for quantum problems, considering sensitivity of the tests as well as computational tractability.