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arXiv:0908.1955

Entanglement Metrology Using a Joint Readout of Superconducting Qubits

Jerry M. Chow, L. DiCarlo, Jay Gambetta, Andreas Nunnenkamp, Lev S. Bishop, Luigi Frunzio, Michel Devoret, S. M. Girvin, R. J. Schoelkopf

Published Aug 13, 2009• 10 citations

Abstract

Accurate and precise detection of multi-qubit entanglement is key for the experimental development of quantum computation. Traditionally, non-classical correlations between entangled qubits are measured by counting coincidences between single-shot readouts of individual qubits. We report entanglement metrology using a single detection channel with direct access to ensemble-averaged correlations between two superconducting qubits. Following validation and calibration of this joint readout, we demonstrate full quantum tomography on both separable and highly-entangled two-qubit states produced on demand. Using a subset of the measurements required for full tomography, we perform entanglement metrology with ~95% accuracy and ~98% precision despite ~10% fidelity of single measurements. For the highly entangled states, measured Clauser-Horne-Shimony-Holt operators reach a maximum value of 2.61+/-0.04 and entanglement witnesses give a lower bound of ~88% on concurrence. In its present form, this detector will be able to resolve future improvements in the production of two-qubit entanglement and is immediately extendable to 3 or 4 qubits.

DOI: 10.48550/arxiv.0908.1955

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