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How fast can entanglement be spread between two distant points? It depends on the strength and range of the interaction. For short-range systems, the time to generate an entangled state between two points will be linear in the distance between them. For long-range interacting systems, we can usually do better, but how much better is an open question.

Understanding and engineering of quantum many-body systems is a big challenge in quantum physics and quantum information processing. Studies in artificial quantum many-body systems with well-controlled parameters should play a central role for that purpose. One of the promising platforms for realizing an artificial quantum many-body system is a Josephson junction array (JJA).

Information complexity (IC) was introduced around 2000 to study communication complexity (CC) and it turns out to be one of the most powerful methods. Many elegant message-compression algorithms have been discovered to compress protocols with low IC since then.

We study controllable friction in a system consisting of a dark soliton in a one-dimensional Bose gas and a non-interacting Fermi gas. The fermions act as impurity atoms, not part of the original condensate, that scatter off of the soliton. We investigate semiclassical dynamics of the dark soliton, a particle-like object with negative mass, and calculate its friction coefficient. Surprisingly, the amount of friction depends on the ratio of interspecies (impurity-condensate) to intraspecies (condensate-condensate) interaction strengths.

Superconductivity that spontaneously breaks time-reversal symmetry (TRS) has been found, so far, only in a handful of 3D crystals with bulk inversion symmetry. Here we report an observation of spontaneous TRS breaking in a 2D superconducting system without inversion symmetry: the epitaxial bilayer films of bismuth and nickel. The evidence comes from the onset of the polar Kerr effect at the superconducting transition in the absence of an external magnetic field, detected by the ultrasensitive loop-less fiber-optic Sagnac interferometer.

This talk will be about a sub-exponential time algorithm for the Best Separable State (BSS) problem. 

Lunch served at 12:00

We present a new scheme for quantum homomorphic encryption which is compact and allows for efficient evaluation of arbitrary polynomial-sized quantum circuits. Building on the framework of Broadbent and Jeffery [BJ15] and recent results in the area of instantaneous non-local quantum computation [Spe15], we show how to construct quantum gadgets that allow perfect correction of the errors which occur during the homomorphic evaluation of T gates on encrypted quantum data.

In this talk, I will unzip a recent progress on quantum interactive proofs---communications in quantum multi-prover interactive proofs can be exponentially compressed.

Recent years have witnessed a rapid development of quantum information technologies. In this talk, I will describe my personal strategies on how to contribute to this exciting field as a theorist and how my own research fits in the big picture.