Current undergraduate students

The puzzle of genuine multiparticle interference

Sascha Agne, IQC

Two recent experiments demonstrate access to a new realm of quantum phenomena called genuine multiparticle interference. For three photons this means that interference between all three photons is observed while, simultaneously, neither pairs nor single photons display interference.

Rigorous RG algorithms and area laws for low energy eigenstates in 1D

Thomas Vidick, California Institute of Technology

One of the central challenges in the study of quantum many-body systems is the complexity of simulating them on a classical computer. We give a new algorithm for finding low energy states for 1D systems, based on a rigorously justified RG type transformation.

Entropy measurement in quantum systems

Dr. Mohammad Ansari, Peter Grünberg Institute, and Jülich-Aachen Research Alliance Institute (JARA)

Entropy is an important information measure. A complete understanding of entropy flow will have applications in quantum thermodynamics and beyond; for example it may help to identify the sources of fidelity loss in quantum communications and methods to prevent or control them. Being nonlinear in density matrix, its evaluation for quantum systems requires simultaneous evolution of more-than-one density matrix.

Optical manipulation of polariton in semiconductor microstructures

Félix Marsault, French National Center for Scientific Research

Cavity polaritons are bosonic quasiparticles arising from the strong coupling between photons and excitons. They can massively occupy a single quantum state in the regime of polariton lasing [1], showing particular properties such as long coherence times [1], long range spatial coherence [1] and a linearly polarized emission [1,2,3]. Moreover, they possess strong excitonic nonlinearities and thus provide a new platform for elliptical photonic manipulation, with the demonstration of a polariton spin switch [4], polariton transistors [5] and the proposal of other proof-of-principle operations for elliptical integrated logic circuits [6].

Tip induced superconductivity at mesoscopic point contacts on topological semimetals

Leena Aggarwal, Indian Institute of Science Education and Research, Mohali

I will present the observation of a new phase of matter, tip-induced superconductivity (TISC), that emerges only under mesoscopic metallic point contacts on topologically non-trivial semimetals like a 3-D Dirac semimetal Cd3As2, and a Weyl semimetal, TaAs. From theoretical considerations, it is believed that such semimetals exist near topological phase boundaries.

The Power of Randomized and Quantum Computation

Shalev Ben-David, Massachusetts Institute of Technology

Randomized and quantum computing offer potential improvements over deterministic algorithms, and challenge our notion of what should be considered efficient computation. A fundamental question in complexity theory is to try to understand when these resources help; on which tasks do randomized or quantum algorithms outperform deterministic ones?

In this talk, I will describe some of my work investigating this question, primarily in the query complexity (blackbox) model.

Fabrication of Diamond Based Fabry-Perot Cavities: Boring is beautiful

Madelaine Liddy, IQC

Nitrogen-vacancy (NV) centers in diamond are promising candidates for acting as the nodes in a quantum network. Previous work has demonstrated the entanglement between two NV centers over a distance of 1.3km for the loophole-free bell test in 2015.

Quantum Entanglement, Sum-of-Squares and the Log-Rank Conjecture

Pravesh Kothari, Princeton University

This talk will be about a sub-exponential time algorithm for the Best Separable State (BSS) problem. For every constant \eps>0, we give an exp(\sqrt(n) \poly log(n))-time algorithm for the 1 vs 1-\eps BSS problem of distinguishing, given an n^2 x n^2 matrix M corresponding to a quantum measurement, between the case that there is a separable (i.e., non-entangled) state \rho that M accepts with probability 1, and the case that every separable state is accepted with probability at most 1-\eps.

Harnessing quantum systems with long-range interactions

Zhexuan Gong, University of Maryland, College Park

A distinctive feature of atomic, molecular, and optical systems is that interactions between particles are often long-ranged. Together with control techniques from quantum optics, these long-range interacting systems could be harnessed to achieve faster quantum information processing and to simulate novel quantum many-body phenomena. A

Harnessing quantum entanglement 

Laura Mancinska, University of Bristol 

The phenomenon of entanglement is one the key features of quantum mechanics. It can be used to attain functionality lying beyond the reach of classical technologies. In practice, however, finding the best way of harnessing entanglement for a given task is extremely challenging and one is often forced to resort to ad hoc methods. The mathematical structure of entanglement- enabled strategies is poorly understood and many basic questions remain open. This lack of understanding has prevented us from fully exploiting the advantages that entanglement can offer for operational tasks.