Subspace Confinement: How good is your qubit?

Abstract

The basic operating element of standard quantum computation is the qubit, an isolated two-level system that can be accurately controlled, initialized and measured. However, the majority of proposed physical architectures for quantum computation are built from systems that contain much more complicated Hilbert space structures. Hence, defining a qubit requires the identification of an appropriate controllable two-dimensional sub-system. This prompts the obvious question of how well a qubit, thus defined, is confined to this subspace, and whether we can experimentally quantify the potential leakage into to states outside the qubit subspace. In this paper we demonstrate that subspace leakage can be quantitatively characterized using minimal theoretical assumptions by examining the Fourier spectrum of the Rabi oscillation experiment.

13 pages, 11 figures, accepted for publication in New Journal of Physics

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• Coherent control of population transfer between vibrational states in an optical lattice via two-path quantum interference
• Quantum System Identification by Bayesian Analysis of Noisy Data: Beyond Hamiltonian Tomography
• Photon- and phonon-assisted tunneling in the three-dimensional charge stability diagram of a triple quantum dot array
• Physics-based mathematical models for quantum devices via experimental system identification
• Quantum system characterization with limited resources
• Quantum System Identification: Hamiltonian Estimation using Spectral and Bayesian Analysis
• Quantum computation mediated by ancillary qudits and spin coherent states
• Characterization and Control of Quantum Spin Chains and Rings
• Control-Induced Decoherence-Free Manifolds