Quantum computation and quantum optics with circuit quantum electrodynamics
Quantum information is a new field of research that promises exponentially more powerful computers than those offered by current technology. To realize tasks that are impossible for their classical counterparts, quantum computers will harness effects that are fundamentally quantum mechanical. These effects (superposition of states, entanglement and interference) are at the heart of our understanding of quantum theory. As a result, a quantum computer would not only be a major technological advance, it would also represent a unique laboratory for the fundamental study of quantum mechanics. The realization of such a quantum information processor is however an extremely difficult task.
Josephson junction-based superconducting circuits are arguably amongst the most promising systems towards this goal. This research project will be focused on the physics of these mesoscopic devices, also known as superconducting qubits, and will be at the interface between mesoscopic physics, quantum information science and quantum optics. It will in particular focus on an architecture known as circuit quantum electrodynamics (circuit QED) where a superconducting qubit is strongly coupled to photons stored in a microwave resonator. In addition to being one of the most promising avenues for the realization of a full scale quantum computer, circuit QED opens the possibility to study the rich physics of quantum optics in the completely new parameter regime offered by a solid-state environment.
Depending on the student interest and background, this research project will be focused on one of the many outstanding challenges in the field of circuit QED:
a) High fidelity and rapid (~ 100 ns) qubit readout. The current state of the art relies on amplifying a weak microwave signal (~1 photon) going through the cQED setup using a superconducting amplifier, most commonly a Josephson junction parametric amplifier. While 95% single-shot readout fidelity has been achieved, this is not enough for full-scale quantum computation. The objective of this project is to understand what limits the fidelity of these devices, and suggest news quantum-limited amplifier designs reaching near ideal performances. Although theoretical, this work will be done in close collaboration with the experimental groups.
b) Quantum optics with circuit QED. The goal of this project is to find new ways to take advantage of the strong light-matter interaction and strong single photon nonlinearity that can be realized in circuit QED.
c) Quantum logical gates in circuit QED. While the fidelity of single-qubit quantum gates has increased over the last several years, this has not been the case of the two-qubit gates. These logical operations are however required to create entangled state and so for all quantum algorithms and protocols. The goal of this project will be to study a new type of two-qubit gate and to evaluate its potential performance.
For more information about circuit QED consult http://epiq.physique.usherbrooke.ca/data/files/publications/blais2011.pdf or http://www.youtube.com/watch?v=t5nxusm_Umk
