QuICS seminar

The quantum steering ellipsoid formalism naturally extends the Bloch vector picture to provide a visualisation of two-qubit systems. If Alice and Bob share an entangled state then a local measurement by Bob steers Alice’s Bloch vector; given all possible measurements by Bob, the set of states to which Alice can be steered forms her steering ellipsoid inside the Bloch sphere. This gives us a novel geometric perspective on a number of quantum correlation measures such as entanglement, CHSH nonlocality and singlet fraction.

Is Brooklyn expanding?

Alan Turing was fascinated by the possible variation of natural laws in time. There is just a hint of this in his paper, "Computing Machinery and Intelligence," the source of the famous phrase "the imitation game." The subject, long at the intersection of science and philosophy, has recently started to become of practical interest.

Textbook conceptions of light-matter interactions have been challenged by two recent material

advances - the development of metamaterials and the introduction of parity-time (PT)-symmetric

media. Metamaterials allow considerable control over the electric and magnetic fields of light, so

that the permittivity, permeability, and refractive index can be tuned throughout positive, negative,

and near-zero values. Metamaterials have enabled negative refraction, optical lensing below the

Every time the release button of a digital camera is pressed, several megabytes of raw data are recorded. But the size of a typical jpeg output file is only 10% of that. What a waste! Can't we design a process which records only the relevant 10% of the data to begin with?

Considerable work has recently been directed toward developing resource theories of quantum coherence. In this talk I will review the general structure of such resource theories, and I will argue that all currently proposed basis-dependent approaches to quantum coherence fail to be physically consistent. That is, the “free” or “incoherent” operations defined within these frameworks ultimately require the consumption of quantum coherence to be physically implemented.

For the past twenty years, Tensor Network States (TNS) have been widely used to model the low energy sector of local Hamiltonians. Their success in doing so has led to the wide-held mantra that TNS of low bond dimension are the `only physical states' of natural condensed matter systems. However, given our experimental limitations to interact with such systems, it is not clear how this conjecture translates into any observable effect.

Gauge theories are the backbone of our current understanding of

fundamental interactions. While some of their aspects can be

understood using established perturbative techniques, the need for a

non-perturbative framework led to the lattice formulation of gauge

theories by Wilson in 1974. Since then, numerical simulations of

lattice gauge theories have celebrated success in a plethora of

equilibrium phenomena, such as the ab initio calculation of the

low-energy hadron spectrum. However, classical simulations of gauge

Is it possible to create a source of provable random numbers? If the answer to this question is "yes," it would be of importance in information security, where the safety of protocols such as RSA depends on the ability to generate random encryption keys. Bell inequality violations offer a potential solution: if a device exhibits a Bell inequality violation, then its outputs must have been computed by some quantum process and are therefore random.

The Boolean constraint satisfaction problem 3-SAT is arguably the canonical NP-complete problem. In contrast, 2-SAT can not only be decided in polynomial time, but in fact in deterministic linear time. In 2006, Bravyi proposed a physically motivated generalization of k-SAT to the quantum setting, defining the problem "quantum k-SAT".

In recent years, Bayesian methods have been proposed as a solution to a wide range of issues in quantum state and process tomography. In this talk, we make these methods practical by solving three distinct problems: numerical intractability, a lack of informative prior distributions, and an inability to track time-dependent processes. Our approach allows for practical computation of point and region estimators for quantum states and channels, and allows tracking of time-dependent states.