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arXiv:0903.0671 · Physical Review A

Two-qubit decoherence mechanisms revealed via quantum process tomography

Abraham G. Kofman, Alexander N. Korotkov

Published Oct 5, 2009• 36 citations
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Abstract

We analyze the quantum process tomography (QPT) in the presence of decoherence, focusing on distinguishing local and nonlocal decoherence mechanisms for a two-partite system from experimental QPT data. In particular, we consider the $\sqrt{i\text{SWAP}}$ gate realized with superconducting phase qubits and calculate the QPT matrix $\ensuremath{\chi}$ in the presence of several local and nonlocal decoherence processes. We determine specific patterns of these decoherence processes, which can be used for a fast identification of the main decoherence mechanisms from an experimental $\ensuremath{\chi}$ matrix.

DOI
10.1103/physreva.80.042103

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We describe experiments with photon pairs to evaluate, correct for, and avoid sources of error in optical quantum information processing. It is well known that a simple beamsplitter can non-deterministicially prepare or select entangled polarization states. We use quantum process tomography (QPT) to fully characterize this effect, including loss and decoherence. The QPT results identify errors and indicate how well they can be corrected. To evade decoherence in a noisy quantum channel, we identify decoherence-free subspaces using experimental channel characterization, without need for a priori knowledge of the decoherence mechanism or simplifying assumptions. Working with pairs of polarization-encoded photonic qubits, we use tomographic and adaptive techniques to identify 2- and 3-state decoherence-free subspaces for encoding decoherence-free qubits and qutrits within the noisy channel.
We describe experiments with photon pairs to evaluate, correct for, and avoid sources of error in optical quantum information processing. It is well known that a simple beamsplitter can non-deterministicially prepare or select entangled polarization states. We use quantum process tomography (QPT) to fully characterize this effect, including loss and decoherence. The QPT results identify errors and indicate how well they can be corrected. To evade decoherence in a noisy quantum channel, we identify decoherence-free subspaces using experimental channel characterization, without need for a priori knowledge of the decoherence mechanism or simplifying assumptions. Working with pairs of polarization-encoded photonic qubits, we use tomographic and adaptive techniques to identify 2- and 3-state decoherence-free subspaces for encoding decoherence-free qubits and qutrits within the noisy channel.