Semester Calendar Date

Graphene to gravity

Twisted bilayer graphene is a rich condensed matter system, which allows one to tune energy scales and electronic correlations. The low-energy physics of the resulting moiré structure can be mathematically described in terms of a diffeomorphism in a continuum formulation. Twisting is just one example of moiré diffeomorphisms.

Controlling light down to the single-photon level with integrated quantum photonic devices

Abstract: Light-matter interactions allow adding functionalities to photonic on-chip devices, thus enabling developments in classical and quantum light sources, energy harvesters and sensors. These advances have been facilitated by precise control in growth and fabrication techniques that have opened new pathways to the design and realization of semiconductor devices where light emission, trapping and guidance can be efficiently controlled at the nanoscale.

Optical pumping of electronic quantum Hall states with vortex light

A fundamental requirement for quantum technologies is the ability to coherently control the interaction between electrons and photons. However, in many scenarios involving the interaction between light and matter, the exchange of linear or angular momentum between electrons and photons is not feasible, a condition known as the dipole-approximation limit.

Unifying non-Markovian characterisation with an efficient and self-consistent framework

Noise on quantum devices is much more complex than it is commonly given credit. Far from usual models of decoherence, nearly all quantum devices are plagued both by a continuum of environments and temporal instabilities. These induce noisy quantum and classical correlations at the level of the circuit. The relevant spatiotemporal effects are difficult enough to understand, let alone combat. There is presently a lack of either scalable or complete methods to address the phenomena responsible for scrambling and loss of quantum information.

Novel tweezer-assisted sub-Doppler cooling of a 171Yb+ trapped ion crystal

We propose a new sub-Doppler cooling scheme in trapped ion crystals in Paul traps which utilizes a Sisyphus-like cooling mechanism to simultaneously cool all the motional modes of the crystal. We use a hollow tweezer, tuned near resonance with the transition from the qubit manifold to a short-lived excited manifold, to generate a state-dependent tweezer potential. This tweezer also introduces a position dependent quench rate for the qubit states.

Succinct Fermion Data Structures

Many applications of quantum simulation require qubit representations of a fixed number of fermions (F) in a larger number of possible modes (M). Representing such states is possible with I := ⌈log(M choose F)⌉ qubits, but existing constructions achieving this level of compactness result in fermion operators with gate complexity exponential in I.

Smooth and sharp complexity transitions in learning with bounded quantum memory

Learning properties of unknown quantum systems or processes is of fundamental importance to the development of quantum technologies. While many learning algorithms require access to external ancillary qubits (referred to as quantum memory), the statistical complexity and experimental costs for these algorithms vary considerably due to different sizes of quantum memory. Here, we investigate the transitions for statistical complexity required for learning quantum data with bounded quantum memory.

Some Unexpected Applications of Analog Quantum Computers

Demonstrations of quantum advantage for random circuit and boson sampling over the past few years have generated considerable excitement for the future of quantum computing and has further spurred the development of a wide range of gate-based digital quantum computers, which represent quantum programs as a sequence of quantum gates acting on one and two qubits.

Classical and quantum codes, 2d CFTs and holography

There is a rich connection between classical and quantum codes and holographic correspondence connecting 2d CFTs and abelian 3d Chern-Simons theories. In the 3d language the codes emerge as a way to parametrize condensable anyons. Upon condensation 3d topological field theory gives rise to 2d CFT at the boundary. This provides a way to construct 2d CFTs from codes - the so called "code CFTs." This construction of code CFT has a natural interpretation in terms of a CSS quantum code (defined in terms of the original classical code, defining the CFT).

The cost of solving linear differential equations on a quantum computer: fast-forwarding to explicit resource counts

I will discuss recent advances in improving and costing quantum algorithms for linear differential equations. I will introduce a stability-based analysis of Berry et al.’s 2017 algorithm that greatly extends its scope and leads to complexities sublinear in time in a broad range of settings – Hamiltonian simulation being a boundary case that prevents this kind of broad fast-forwarding. I illustrate these gains via toy examples such as the linearized Vlasov-Possion equation, networks of coupled, damped, forced harmonic oscillators and quadratic nonlinear systems of ODEs.