Demonstration of a CNOT gate using electromagnetically induced transparency

  • Katie McDonnell

Student thesis: Doctoral Thesis

Abstract

This thesis demonstrates a CNOT gate realised using electromagnetically induced transparency (EIT) which relies on the strong long-range interactions between Rydberg atoms. The CNOT gate is achieved on a microsecond time scale and robustly implements a conditional transfer between the two qubit states of a target atom that is solely dependent on the initial qubit state of a control atom. This method has the potential to be scaled to a target ensemble without typical√N scaling. The experiment presented is a cold atom system with two caesium atoms trapped in optical tweezers at a separation of 5μm. The hyperfine ground states of the caesium atoms are utilised as qubit states with optical pumping ensuring the atoms are prepared in the correct state jF = 4;mF = 0i. Coherent control between the hyperfine ground states is achieved using microwaves and excitation lasers, and excitation to the Rydberg state |81D5/2,mj=5/2> is achieved by two-photon excitation from lasers locked to a high-finesse ultra-low-expansion (ULE) cavity. This thesis details the optimisation steps taken in the experiment to demonstrate the CNOT gate, including experiment upgrades, and how the CNOT gate is used to prepare the maximally entangled Bell state |ϕ+>. We detail how the Bell state is probed using parity oscillations to verify the quantum nature of the CNOT gate. We achieve a loss corrected CNOT gate fidelity of FCNOT >0.82(2), measure the Bell state fidelity F|ɸ+>0:66(3) and finally present a number of technical improvements to advance this to a level required for fault-tolerant scaling.
Date of Award15 Oct 2021
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorJohn Jeffers (Supervisor) & Jonathan Pritchard (Supervisor)

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