## Location: Room L016, CWI, Science Park 123, Amsterdam

Date and time: 4 december, 2015, 10:00

**Four one-hour seminars on a variety of topics related to quantum physics, cryptography and information theory.**

**Program**

**10:00 – 11:00**: Mario Szegedy (Rutgers University)

**Title: The Many Faces of the Area Law in Quantum Physics**

Abstract: When asking experts what the area law of quantum physics is, one may get different answers. What are the currently known area laws of quantum physics, why are they interesting (or un-interesting), do they make ground state computation easy, and where lie the limitations to our knowledge? In this survey talk we investigate these questions.

**11:05 – 12:05**: Stacey Jeffery (Caltech)

**Title: Quantum homomorphic encryption for circuits of low T-gate complexity**

Joint work with Anne Broadbent (arXiv:1412.8766)

Abstract: A fully homomorphic encryption scheme is an encryption scheme with the property that any computation on the plaintext can be performed by a party having access to the ciphertext only. We give schemes for quantum homomorphic encryption, which is the encryption of quantum information such that quantum computations can be performed given the ciphertext only, in the setting of standard cryptographic security under computational assumptions. Our schemes allow for arbitrary Clifford group gates, but become inefficient for circuits with large complexity, measured in terms of the non-Clifford portion of the circuit (we use the “pi/8” non-Clifford group gate, which is also known as the T-gate).

**13:30 – 14:30:** Richard Jozsa (DAMTP, University of Cambridge)

**Title: Entropy, subentropy and symmetric polynomials**

Joint work with Graeme Mitchison

Abstract: The Shannon entropy function H is the most fundamental quantity in information theory. It is normally given as a function of probabilities (p_i’s) but we show that if H is viewed instead as a function of the associated elementary symmetric polynomials (e_k’s), then it acquires a series of remarkable properties. We will also introduce the subentropy function Q and briefly discuss its origins and significance in quantum information theory. We’ll show that viewing it too in terms of the e_k’s, reveals surprising new relationships between Q and H. Despite these results, an information-theoretic operational significance of the use of the e_k’s as variables remains a mystery.

**14:35 – 15:35:** Gilles Brassard (U. Montreal)

**Title: Parallel Lives: Why Quantum Mechanics is a Local Realistic Theory After All**

Joint work with Paul Raymond-Robichaud

Abstract: Most physicists take it for granted that the experimental violation of Bell’s inequality provides evidence that our universe is nonlocal. However, this is not the case! Indeed, I shall describe a toy universe (not meant to describe our world) in which Bell’s (CHSH) inequality is maximally violated, yet this world is purely local. Then, I shall present mathematical requirements for quantum mechanics itself to be local. It turns out that these requirements cannot be satisfied if we take the universal wavefunction as a complete representation of reality, even if we admit the existence of the multiverse. Nevertheless, I shall present a solution to this conundrum with a framework that provides a simple local-realistic description of quantum mechanics. In particular, one can recover the whole (even if entangled) from the description of the parts, in sharp contrast with the standard formalism of quantum mechanics.

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