Date of Graduation

5-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Julio Gea-Banacloche

Committee Member

Reeta Vyas

Second Committee Member

Hugh Churchill

Third Committee Member

Salvador Barraza-Lopez

Keywords

CPHASE quantum gate; Gate fidelity; photons as qubits

Abstract

In the first part of this dissertation we study in detail the interaction of single-photon and two-photon wavepackets with a three-level V-type atom in a cavity without any control over the interaction time. We solve analytically for the spectrum of the outgoing wavepackets as a function of the incident wavepacket that is valid in all the cavity limits. We consider the potential performance of this system as a CPHASE gate by considering several special input pulses. We optimize for the gate fidelity and find values of the cavity, atomic and pulse parameters that yield a conditional phase shift of π, albeit with a relatively small overlap between the incoming and outgoing pulse forms. The small gate fidelity of this system motivated us to consider the simultaneous ”gated” interaction of two single-photon fields with a single atoms inside a cavity for the second part of this dissertation. We show that under the conditions to describe the fields by single temporal mode, such as using dynamical coupling technique to get the fields in and out of the cavity and using strong external fields to induce large detuning to start and stop the atom-field interaction, it is possible to produce a conditional phase gate with arbitrary high fidelity when a single three-level V-type atom is inside the cavity. We show how the performance of the phase gate degrades with using more atoms and finally the nonlinearity vanishes for very large number of atoms. We also show how spontaneous emission losses into modes other than the cavity mode decrease the gate fidelity. Finally, we will show the differences, similarities, advantages, and disadvantages of considering alternative atomic level schemes such as two-level atom and five-level atom in M-configuration.

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