Seminar

Quantum photonics provides a powerful toolbox with vast applications ranging from quantum simulation, photonic information processing, all optical universal quantum computation, secure quantum internet as well as quantum enhanced sensing.

It is sometimes said that 99% of a quantum programmer's task is constructing and manipulating circuits and only 1% is actually running them. In this talk, I will introduce and demonstrate Proto-Quipper-D, an experimental quantum circuit programming language. Like previous versions of Proto-Quipper, it uses linear types to enforce the no-cloning property. In addition, Proto-Quipper-D features the use of dependent types for describing families of circuits and for type-safe garbage qubit management.

The theories of optimization and machine learning answer foundational questions in computer science and lead to new algorithms for practical applications. While these topics have been extensively studied in the context of classical computing, their quantum counterparts are far from well-understood. In this thesis, we explore algorithms that bridge the gap between the fields of quantum computing and machine learning. First, we consider general optimization problems with only function evaluations.

The position states of the harmonic oscillator describe the location of a particle moving on the real line. Similarly, the phase difference between two superconductors on either side of a Josephson junction takes values in the configuration space of a particle on a circle. More generally, many physical systems can be described by a basis of "position states," describing a particle moving on a more general configuration or state space. Most of this space is usually ignored due to the energy cost required to pin a particle to a precise "position".

Resource theories have mushroomed in quantum information theory over the past decade. Resource theories are simple models for situations in which constraints limit the operations performable and the systems accessible. In a fixed-temperature environment, for instance, the first law of thermodynamics constrains operations to preserve energy, and thermal states can be prepared easily.  Scores of resource-theory theorems have been proved. Can they inform science beyond quantum information theory?

The AdS/CFT correspondence is a concrete instance of holographic duality, where a bulk theory of quantum gravity in d+1 dimensions can emerge from a conformal field theory (CFT) in d dimensions. In particular, we expect the semi-classical spacetime of d+1 dimensions to emerge from the entanglement patterns of certain quantum states in the CFT. Therefore, it is crucial to understand what kind of states encode such spacetime geometries and how to explicitly reconstruct these geometries from quantum entanglement.

"Mana" is a measure of the degree to which a state cannot be approximated the result of Clifford gates; consequently, it can measure both the difficulty of state preparation on a quantum computer, and the degree to which entanglement is non-Bell-pair. I will show numerical calculations of the mana of ground states of the one-dimensional Z3 Potts model, chosen for convenience, in which we find that the mana is extensive and peaked at the phase transition.

Demonstrating a superpolynomial quantum speedup using feasible schemes has become a key near-term goal in the field of quantum simulation and computation. The most prominent schemes for "quantum supremacy" such as boson sampling or random circuit sampling are based on the task of sampling from the output distribution of a certain randomly chosen unitary. But to convince a skeptic of a successful demonstration of quantum supremacy, one must verify that the sampling device produces the correct outcomes.

Daniel Gottesman is a faculty member at the Perimeter Institute in Waterloo, Ontario. He is also a Senior Scientist with the company Quantum Benchmark. He received his Ph.D. at Caltech in 1997, and did postdocs at Los Alamos National Lab and Microsoft Research, after which he served in the UC Berkeley CS department as a Long-Term CMI Prize Fellow with the Clay Mathematics Institute.

Quantum dots formed in silicon heterostructures have emerged as a promising candidate for creating qubits, the building blocks of quantum computing. Their small size, ease of control, and compatibility with modern semiconductor processes make them especially enticing. However, the intrinsic near-degeneracy (valley splitting) of the conduction band electrons that form these quantum dots poses a serious concern for the viability of these qubits, but may also hold the solution.