Ancilla Assisted Quantum Information Processing: General protocols and NMR implementations

TL;DR

This paper explores the use of ancillary qubits in quantum information processing, demonstrating their ability to efficiently characterize quantum states and dynamics, perform noninvasive measurements, and improve decoherence suppression in NMR systems.

Contribution

It introduces general protocols utilizing ancillary qubits for quantum state characterization, noninvasive measurements, and decoherence suppression, with experimental validation in NMR systems.

Findings

Ancillary qubits enable complete quantum state and dynamics characterization with a single measurement.

RUDD sequences outperform other dynamical decoupling sequences in suppressing decoherence.

Experimental demonstrations confirm the effectiveness of ancillary qubits in quantum information tasks.

Abstract

While a bit is the fundamental unit of binary classical information, a qubit is the fundamental unit of quantum information. In quantum information processing (QIP), it is customary to call the qubits under study as system qubits, and the additional qubits as ancillary qubits. In this thesis, I describe various schemes to exploit the ancillary qubits to efficiently perform many QIP tasks and their experimental demonstrations in nuclear magnetic resonance (NMR) systems. Particularly, we have showed that, in the presence of sufficient ancillary qubits, it is possible to completely characterize a general quantum state as well as a general quantum dynamics in a single measurement. In addition, it is also possible to exploit ancillary qubits for realizing noninvasive quantum measurements required for several experiments related to quantum physics. I will also illustrate some interesting applications of ancillary qubits in spectroscopy. At last, I describe an experimental study of the efficiency of various dynamical decoupling sequences for suppressing decoherence of single as well as multiple quantum coherences on large spin-clusters. The experiments reveal the superior performance of the recently introduced RUDD sequences in suppressing decoherence.