JQI

Abstract: 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.

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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract:  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. We show that a small amount of redundancy enables efficiency, presenting a second quantized fermion encoding using I + O( F ) qubits such that fermion operators can be implemented in depth O( log M ) and gate complexity O(I).

Abstract:  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.

Abstract: 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.

Dissertation Committee Chair: Jay Sau

Committee: 

Steven Anlage

Christopher Jarzynski

Johnpierre Paglione

Victor Yakovenko

Abstract: In many-body systems of cold atoms and their applications to quantum metrology and quantum computing, there are important questions around how large an entangled many-body state we can usefully and reliably prepare in the presence of decoherence. Information spreading and entanglement growth are typically limited by Lieb-Robinson bounds, so that the useful system size with short-range interactions will grow only linearly with the coherence time.