## Quantum capacities for nice channels

In this talk we will combine vNa and operator space tools to give estimates for the regularized and potential capacity of a channel. Joint with Gao and Laracurente

Seminar date and time:

2015-11-16 14:30

Affiliation:

University of Illinois at Urbana-Champaign, Department of Mathematics.

In this talk we will combine vNa and operator space tools to give estimates for the regularized and potential capacity of a channel. Joint with Gao and Laracurente

Location:

(To be announced on Monday)

Contact:

mariusjunge@gmail.com

Seminar date and time:

2015-11-12 14:30

Affiliation:

University of Bristol, Faculty of Engineering

*We'll discuss an entanglement verification protocol that allows any party in a network to check if a source is distributing a genuinely multipartite entangled state, even in the presence of distrustful parties and loss. The protocol remains secure against dishonest behavior of the source and other parties, including the use of system imperfections to their advantage. We demonstrate the verification protocol in a three- and four-party setting using polarization-entangled photons, thus highlighting its potential for realistic quantum communication and networking applications.*

Seminar date and time:

2015-11-04 14:30

Affiliation:

University of Geneva

The Bessis-Moussa-Villani conjecture states that the trace of exp(A-tB) is, as a function of the real variable t, the Laplace transform of a positive measure, where A and B are hermitian matrices. The long standing conjecture was recently proven by Stahl and streamlined by Eremenko. We report on that proof and recall the significance of the result when approximating the energy of perturbed quantum mechanical systems.

Seminar date and time:

2015-11-03 14:30

Affiliation:

University of Nottingham

Coherence, discord-type correlations, and entanglement are all fundamental manifestations of quantum theory and are all useful resources for certain quantum technological tasks. In this talk I show how these different signatures of quantumness can be converted into each other and interpreted under a common framework. I first review the rigorous mapping between discord-type measures and entanglement measures by means of premeasurement interactions, recently implemented experimentally.

Seminar date and time:

2015-10-27 14:30

Affiliation:

ULB

We analyze the conditions under which local operations and classical communication enable entanglement transformations between bipartite pure Gaussian states. A set of necessary and sufficient conditions had been found [G. Giedke et al., Quant. Inf. Comput. 3, 211 (2003)] for the interconversion between such states that is restricted to Gaussian local operations and classical communication. Here, we exploit majorization theory in order to derive more general (sufficient) conditions for the interconversion between bipartite pure Gaussian states that goes beyond Gaussian local operations.

Seminar date and time:

2015-10-20 15:15

Affiliation:

Oxford

Estimating the temperature of a cold quantum system is difficult. Usually, one measures a well-understood thermal state and uses that prior knowledge to infer its temperature. In contrast, we introduce a method of thermometry that assumes no knowledge of the state of a system and is potentially non-destructive. Our method uses a universal temperature-dependence of the non-equilibrium dynamics of an initially thermal system coupled to a qubit probe that follows from the Tasaki-Crooks theorem for non-equilibrium work distributions.

Location:

IFAE Seminar room

Seminar date and time:

2015-10-20 14:30

Today, theoretic analysis about quantum-scale heat engines is achieving a splendid success. They clarify that the average performance of these small-size heat engines obeys the second law of the macroscopic thermodynamics[1,2], and that the single-shot performance of the heat engines obeys different rules[3,4]. They also clarifies the thermodynamic laws for information processing [5,6].

Location:

IFAE Seminar room

Seminar date and time:

2015-09-29 14:30 to 15:30

Affiliation:

MPQ

Renormalization to low energies is widely used in condensed matter theory to reveal the low energy degrees of freedom of a system, or in high energy physics to cure divergence problems. Here we ask which states can be seen as the result of such a renormalization procedure, that is, which states can be “renormalized to high energies". Intuitively, the continuum limit is the limit of this "renormalization" procedure. We consider two definitions of continuum limit and characterise which states satisfy either one in the context of Matrix Product States. (Joint work with N. Schuch, D.

Location:

IFAE seminar room

Seminar date and time:

2015-09-22 14:30

Affiliation:

Bilbao

A striking result from nonrelativistic quantum mechanics is the

monogamy of entanglement, which states that a particle can be

maximally entangled only with one other party, not with several ones.

While there is the exact quantitative relation for three qubits and

also several inequalities describing monogamy properties it has not

been clear to what extent exact monogamy relations are a general feature

of quantum mechanics. We show that in all many-qubit systems

there exist strict monogamy laws for quantum correlations.

Location:

IFAE seminar room

Seminar date and time:

2015-09-17 14:30

The standard approach for describing and analysing macroscopic properties of physical systems is to consider a family of many-body quantum Hamiltonians defined on an increasing sequence of finite lattices, and then look for properties, like the groundstate degeneracy or the energy gap between the groundstate and the first excited states, that are satisfied uniformly for all system sizes large enough. This idea is at the core of the mathematical definition of thermodynamic limit, and is how most experiments (either numerical or in a lab) are carried over.