Master's defense: Love Pettersson

Exploring near-term quantum applications with graph states from quantum emitters

The heart of this thesis is comprised of a spin-photon interface which can deterministically generate graph states. With this interface we explore the class of graph states available up to eight photons. Further, we construct a realistic error model accounting for its infidelities, which are directly linked to experimental parameters. With the error model, we explore three different quantum algorithms and two error correction applications that can be implement on the available graph states.

 More in detail, we analyse Grover’s search and Deutsch’s algorithm implemented on four qubit graph states. Furthermore, we also describe a variational quantum eigensolver (VQE) which can be implement with the interface, and simulate its performance on a few-qubit experiment. Moreover, we study error-protected measurements of logical qubits, including both Pauli errors and photon loss. This error-protection is investigated in the context of two potentially near term applications: (1) Reading out the spin using graph codes, (2) a BB84 protocol using graph codes instead of single photons.

 From our analysis we identify that Grover’s and Deutsch’s algorithms show significant resilience to errors present in the system, while the VQE protocol appears more susceptible. We then also identify various quantum error-correcting states that can provide noise-suppression, both for losses and Pauli errors, for realistic noises in quantum emitters. These results provide a class of protocols that could enable interesting quantum experiments and applications in near-term spin-photon quantum hardware.