title: On readout of vibrational qubits using quantum beats.
abstract: Readout of the final states of qubits is a crucial step towards implementing quantum computation in experiment. Although not scalable to large numbers of qubits per molecule, computational studies show that molecular vibrations could provide a significant (factor 2-5 in the literature) increase in the number of qubits compared to two-level systems. In this theoretical work, we explore the process of readout from vibrational qubits in thiophosgene molecule, SCCl2, using quantum beat oscillations. The quantum beats are measured by first exciting the superposition of the qubit-encoding vibrational states to the electronically excited readout state with variable time-delay pulses. The resulting oscillation of population of the readout state is then detected as a function of time delay. In principle, fitting the quantum beat signal by an analytical expression should allow extracting the values of probability amplitudes and the relative phases of the vibrational qubit states. However, we found that if this procedure is implemented using the standard analytic expression for quantum beats, a non-negligible phase error is obtained. We discuss the origin and properties of this phase error, and propose a new analytical expression to correct the phase error. The corrected expression fits the quantum beat signal very accurately, which may permit reading out the final state of vibrational qubits in experiments by combining the analytic fitting expression with numerical modelling of the readout process. The new expression is also useful as a simple model for fitting any quantum beat experiments where more accurate phase information is desired.
authors.affiliation: Chemistry Department, Marquette University, Milwaukee, Wisconsin 53201, USA.
authors.forename: Dmytro
authors.initials: D
authors.lastname: Shyshlov
authors.affiliation: Department of Chemistry, Department of Physics and Center for Biophysics and Computational Biology, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Berrios
authors.affiliation: Department of Chemistry, Department of Physics and Center for Biophysics and Computational Biology, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Gruebele
authors.affiliation: Chemistry Department, Marquette University, Milwaukee, Wisconsin 53201, USA.
authors.forename: Dmitri
authors.initials: D
authors.lastname: Babikov
mesh_terms: D003198:Computer Simulation; D005453:Fluorescence; D008956:Models, Chemical; D010705:Phosgene / Q000031:analogs & derivatives* / Q000737:chemistry; D011789:Quantum Theory
chemical_list: C016145:thiophosgene; D010705:Phosgene