Events

Measuring Entanglement Entropy in a Many-body System

K. Rajibul Islam, MIT-Harvard Center for Ultracold Atoms

Entanglement, perhaps the most counter-intuitive feature of quantum mechanics, describes non-local correlations between quantum objects. In recent years, entanglement has emerged as a central concept in our understanding of quantum many-body physics. It allows us to characterize phases of quantum matter that cannot be distinguished by broken symmetries, such as topological states.

Quantum Randomness Expansion - New Results

Carl Miller, University of Michigan

Is it possible to create a source of provable random numbers? An affirmative answer to this question would be highly useful in information security, where random numbers are needed to provide the keys for encryption algorithms. Bell inequality violation experiments offer hope for this problem, since the outputs of a Bell violation must be non-classical and therefore not fully predictable to an adversary. The challenge is to prove something stronger: that the outputs can be processed (extracted) to obtain uniformly random data. This leads to some complex and beautiful mathematics.

Quantum optics of strongly correlated many-body systems

Igor Mekhov, University of Oxford

We show that quantum backaction of weak measurement constitutes a novel source of competitions in many-body systems, thus leading to new phenomena. We consider a system of ultracold atoms in optical lattices trapped inside a high-Q cavity, which requires a fully quantum description of both light and matter waves. The QND measurements lead to the generation of genuinely multipartite entangled modes of the matter fields, which have analogies in quantum optics (e.g. two-mode squeezing), but are non-Gaussian.

Hybrid quantum systems using collective degrees of freedom in solids

Yasunobu Nakamura, The University of Tokyo

In the course of the development of superconducting qubits, we learned that we can fully control quantum states of selected collective degrees of freedom in superconducting circuits. Such collective modes, rigidly extending in a macroscopic scale, strongly couple to electromagnetic fields via their large dipole moments. Moreover, Josephson junctions bring large nonlinearity into the system without adding dissipation.

Quantum information processing with superconducting quantum circuits

Archana Kamal, Massachusetts Institute of Technology

The promise of quantum computers to solve problems intractable with their best classical counterparts has catapulted quantum information processing into a major research effort in recent years. In addition, rapidly evolving capabilities in manipulating quantum systems have provided us with new insights into the dynamics of nature at small scales. One of the primary challenges in developing any practical quantum information platform, however, is to harness quantum effects on macroscopic scales.

Bottom-up approaches for quantum many-body physics with cold trapped atoms

Crystal Senko, Harvard University

A major outstanding challenge in quantum science is the development and refinement of techniques to control interactions among quantum particles, which will be a key ingredient in quantum information processing and laboratory studies of quantum many-body physics. This talk will describe two atom-based platforms for studying artificial spin-spin interactions.

Finding non-signalling agents and subsystems in global theories

Lidia del Rio, University of Bristol

How can we find operational notions of local agents within a global theory? In this talk, I will present an operational way to model the effective state spaces of individual agents, as well as the range of their actions. I will then address the aspects of locality relevant to derive independence and non-signalling conditions between agents. This approach establishes an operational connection between local action and local observations, and gives a global interpretation to concepts like discarding a subsystem or composing local functions.

Tensor Rank and Entanglement Transformation between Multipartite Pure States

Cheng Guo, Tsinghua University & University of Technology, Sydney

The tensor rank of a symmetric tensor is equal to the polynomial rank of some homogeneous polynomial. I will introduce the isomorphism between symmetric states and homogeneous polynomials.

Multicolor quantum channels for nanowire-based photonic devices 

Wayne Cheng-Wei Huang, University of Nebraska-Lincoln 

Using a two-color laser field and tungsten nanotips, we showed that multicolor quantum channels led to a twofold increase in quantum efficiency. By gating quantum efficiency with pulse delay, optical control of electron photoemission was attained for fields with modest intensity. In this talk, I will discuss the observed effect and potential applications for nanowire-based photonics transistors and ultrafast spin-polarized electron sources. 

Yuval Sanders of the Department of Physics and Astronomy will be defending his thesis:

Characterizing Errors in Quantum Information Processors

Yuval is supervised by Professors Raymond Laflamme and Frank Wilhelm-Mauch.