Qubits in Cavities for Quantum Optics and Computing

Jonathan Busch

This thesis concerns possible implementations of quantum computing schemes and tries to overcome some standard limitations. The central result is a technique we call reservoir engineering that is applied to optical cavity QED based quantum computing. The usual problem for quantum computing with atomic qubits in cavities is scalability as this requires either the coupling of photons leaking from cavities,using linear optics elements and measurements or shuttling of ions into and out of cavities. We propose an alternative that applies strong dissipative coupling to an environment as a control on fibre-coupled cavity systems. The control mechanism is effectively an overdamping of certain common cavity modes that restricts the time evolution of the qubit-cavity system onto a smaller subsystem consisting of only one common cavity modes. Within this subsystem, we then show that it is possible to implement quantum computing schemes that apply otherwise only to atomic qubits in the same cavity.

Alexandre Blais

Dean T. Clarke

Quantum technology has the potential to change the way we solve many problems in our daily lives. Perhaps the most ambitious quantum technology in development is quantum computers. In the past decade significant progress has been made in the number of qubits within a quantum computer, and this trend seems to be increasing. In this work we look at one particular architecture for quantum computing; the iontrap quantum computer. In this thesis we investigate the integration of this type of quantum computer with fibre tip optical cavities. We numerically analyse the effect of misalignment of these cavities and attempt to find the optimal cavity parameters for integration into the ion-trap quantum computer. This work should provide a useful framework for optimal integration of cavities, and the tolerances to misalignment. This should allow for future ion-trap quantum computer designs to be more efficient and help increase the number of qubits, paving the way to develop a useful universal quantum computer.

J. M. Raimond

Mohamed Barhoumi, Riccardo Bassoli, Frank H. P. Fitzek

Atom-cavity interconnected systems offer an outstanding possibility for experiments in quantum computing and quantum information. Investigating the interaction between different light fields and atoms in a cavity is a vital study area of quantum optics. In this paper, we investigate the interaction between an atom(qubit) and the cavity. The Jaynes-Cummings approach is used to determine the probability of the cavity and qubit into bad and good regimes. Moreover, we examine the Wigner-functions of the cavity depending on the coupling strength. It is possible to synchronize atoms to create extremely precise atomic clocks, which might revolutionize several sectors, including navigation, communications, and scientific study. We show that the synchronization of two qubits inside an optical lattice can be accomplished using the driven Tavis-Cummings Hamiltonian. In this framework, we employ sixteen photons and show that the best quantum synchronization can be achieved between two qubits 𝑞1 and 𝑞2 in a weak regime.

P. Tombesi V. Giovannetti