High-fidelity controlled-σZ gate for resonator-based superconducting quantum computers

Joydip Ghosh, Andrei Galiautdinov, Zhongyuan Zhou, Alexander N. Korotkov, John M. Martinis, and Michael R. Geller
Phys. Rev. A 87, 022309 – Published 8 February 2013

Abstract

A possible building block for a scalable quantum computer has recently been demonstrated [Mariantoni et al., Science 334, 61 (2011)]. This architecture consists of superconducting qubits capacitively coupled both to individual memory resonators as well as a common bus. In this work we study a natural primitive entangling gate for this and related resonator-based architectures, which consists of a controlled-σz (cz) operation between a qubit and the bus. The cz gate is implemented with the aid of the noncomputational qubit |2 state [Strauch et al., Phys. Rev. Lett. 91, 167005 (2003)]. Assuming phase or transmon qubits with 300 MHz anharmonicity, we show that by using only low frequency qubit-bias control it is possible to implement the qubit-bus cz gate with 99.9% (99.99%) fidelity in about 17ns (23ns) with a realistic two-parameter pulse profile, plus two auxiliary z rotations. The fidelity measure we refer to here is a state-averaged intrinsic process fidelity, which does not include any effects of noise or decoherence. These results apply to a multiqubit device that includes strongly coupled memory resonators. We investigate the performance of the qubit-bus cz gate as a function of qubit anharmonicity, identify the dominant intrinsic error mechanism and derive an associated fidelity estimator, quantify the pulse shape sensitivity and precision requirements, simulate qubit-qubit cz gates that are mediated by the bus resonator, and also attempt a global optimization of system parameters including resonator frequencies and couplings. Our results are relevant for a wide range of superconducting hardware designs that incorporate resonators and suggest that it should be possible to demonstrate a 99.9% cz gate with existing transmon qubits, which would constitute an important step towards the development of an error-corrected superconducting quantum computer.

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  • Received 11 June 2012

DOI:https://doi.org/10.1103/PhysRevA.87.022309

©2013 American Physical Society

Authors & Affiliations

Joydip Ghosh1,*, Andrei Galiautdinov1,2, Zhongyuan Zhou1, Alexander N. Korotkov2, John M. Martinis3, and Michael R. Geller1,†

  • 1Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, USA
  • 2Department of Electrical Engineering, University of California, Riverside, California 92521, USA
  • 3Department of Physics, University of California, Santa Barbara, California 93106, USA

  • *joydip.ghosh@gmail.com
  • mgeller@uga.edu

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Vol. 87, Iss. 2 — February 2013

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