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AIP conference proceedings

Geometric Phase for Mixed States using Single-Photon Interferometry

Marie Ericsson

Published Jan 1, 2004• 0 citations
Publisher

Abstract

The inherent resistance of geometric phase to decoherence may enable fault‐tolerant quantum computation. However, as decoherence tends to affect many implementations, we must first understand the behavior of such phases for mixed states. Here we report an experimental measurement of geometric phase for polarization mixed states.
DOI
10.1063/1.1834456

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Examples of geometric phases abound in many areas of physics. They offer both fundamental insights into many physical phenomena and lead to interesting practical implementations. One of them, as indicated recently, might be an inherently fault-tolerant quantum computation. This, however, requires one to deal with geometric phases in the presence of noise and interactions between different physical subsystems. Despite the wealth of literature on the subject of geometric phases very little is known about this very important case. Here we report the first experimental study of geometric phases for mixed quantum states. We show how different they are from the well-understood, noiseless, pure-state case.
We calculate the geometric phase for an open system (spin-boson model) which interacts with an environment (ohmic or nonohmic) at arbitrary temperature. However there have been many assumptions about the time scale at which the geometric phase can be measured, there has been no reported observation of geometric phases for mixed states under nonunitary evolution yet. We study not only how they are corrected by the presence of the different type of environments but estimate the corresponding times at which decoherence becomes effective as well. These estimations should be taken into account when planning experimental setups to study the geometric phase in the nonunitary regime, particularly important for the application of fault-tolerant quantum computation.