#### Speaker

Stephanie Wehner, National University of Singapore, Singapore -- 17-10-2013

#### Abstract

A natural measure for the amount of quantum information that a physical system E holds about another system A = A_1,...,A_n is given by the min-entropy Hmin(A|E). Specifically, the min-entropy measures the amount of entanglement between E and A, and is the relevant measure when analyzing a wide variety of problems ranging from randomness extraction in quantum cryptography, decoupling used in channel coding to physical processes such as thermalization or the thermodynamic work cost (or gain) of erasing a quantum system. As such, it is a central question how the min-entropy changes after some process M transforms A to M(A). A simple example of such a process M is a random sampling of the subsystems where our question becomes: Given some initial entanglement between E and A, how entangled is E with a random subset of the systems A=A_1,...,A_n?

Here we introduce a powerful tool relating the min-entropy of the processed system M(A) to the original one that has numerous applications. For example, it enables us to construct quantum cryptographic protocols in the noisy-storage model with essentially optimal security parameters, as well as decoupling operations acting only on few qubits.

Joint work with Frederic Dupuis and Omar Fawzi.

(arXiv:1305.1316, cryptographic applications appeared as a short version in CRYPTO 2013).

#### Bio

Stephanie Wehner is an Associate Professor in the School of Computing at the National University Singapore and the Centre for Quantum Technologies. Prior to coming to Singapore in 2010, she spent two years as a Postdoctoral Fellow at the California Insitute of Technology, and three and half as a PhD student at the University of Amsterdam. Stephanie is one of the founders of QCRYPT, presently the largest conference in quantum cryptography, and was elected to the Steering Committee of QIP in 2013. Before entering academia, she worked in industry as a professional hacker.

Her research interests include quantum cryptography, quantum information theory, and the application of information-theoretic techniques to physics.

#### Slides