26 research outputs found
Robustness of controlled Hamiltonian approaches to unitary quantum gates
We examine the effectiveness and resilience of achieving quantum gates
employing three approaches stemming from quantum control methods:
counterdiabatic driving, Floquet engineering, and inverse engineering. We
critically analyse their performance in terms of the gate infidelity, the
associated resource overhead based on energetic cost, the susceptibility to
time-keeping errors, and the degradation under environmental noise. Despite
significant differences in the dynamical path taken, we find a broadly
consistent behavior across the three approaches in terms of the efficacy of
implementing the target gate and the resource overhead. Furthermore, we
establish that the functional form of the control fields plays a crucial role
in determining how faithfully a gate operation is achieved. Our results are
demonstrated for single qubit gates, with particular focus on the Hadamard
gate, and we discuss the extension to -qubit operations.Comment: 9 pages, 3 figure
Commutativity and the emergence of classical objectivity
We examine how the ability of a system to redundantly proliferate relevant
information about its pointer states is affected when it is coupled to multiple
baths. To this end, we consider a system in contact with two baths: one --
termed the {\it accessible} environment -- which, on its own, induces a pure
dephasing mechanism on the state of the system and satisfies the conditions for
classical objectivity to be established. The second environment, which we dub
as {\it inaccessible}, affects the system in two physically relevant ways.
Firstly, we consider an interaction that commutes with the Hamiltonian
describing the interaction between system and accessible bath. It thus also
gives rise to dephasing of the system, albeit on different time scales.
Secondly, we consider a thermalising interaction, which does not commute with
the system-accessible environment Hamiltonian. While the former still allows
the system to redundantly encode its state into the accessible environment, the
latter degrades the correlations, eventually destroying them in the long-time
limit, and thus leads to a loss of the conditions necessary for classical
objectivity to be established. This sheds light on the role that commutativity
between the various system-bath interaction terms plays when establishing the
conditions for classical objectivity to be supported.Comment: 7 pages, 3 figure
Protecting public interest reporting: what is the future of journalistic privilege in Irish law?
In its opening statement, the Disclosure s Tribunal has drawn attention to several unanswered questions about the Irish law on journalistic privilege It is beyond the scope of a short note such as this to propose answers to the issues identified by the Tribunal ā not least because the facts pertaining to any assertion of privilege have not been established. The purpose of the note is rather to consider the conceptual framework in which these questions might be addressed. This is necessary given the relatively sparse authority on journalistic sources in Ireland