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Robust Preparation of Wigner-Negative States with Optimized SNAP-Displacement Sequences

Marina Kudra, Mikael Kervinen, Ingrid Strandberg, Shahnawaz Ahmed, Marco Scigliuzzo, Amr Osman, Daniel Pérez Lozano, Mats O. Tholén, Riccardo Borgani, David B. Haviland, Giulia Ferrini, Jonas Bylander, Anton Frisk Kockum, Fernando Quijandría, Per Delsing, and Simone Gasparinetti
PRX Quantum 3, 030301 – Published 1 July 2022

Abstract

Hosting nonclassical states of light in three-dimensional microwave cavities has emerged as a promising paradigm for continuous-variable quantum information processing. Here we experimentally demonstrate high-fidelity generation of a range of Wigner-negative states useful for quantum computation, such as Schrödinger-cat states, binomial states, Gottesman-Kitaev-Preskill states, as well as cubic phase states. The latter states have been long sought after in quantum optics and have never been achieved experimentally before. We use a sequence of interleaved selective number-dependent arbitrary phase (SNAP) gates and displacements. We optimize the state preparation in two steps. First we use a gradient-descent algorithm to optimize the parameters of the SNAP and displacement gates. Then we optimize the envelope of the pulses implementing the SNAP gates. Our results show that this way of creating highly nonclassical states in a harmonic oscillator is robust to fluctuations of the system parameters such as the qubit frequency and the dispersive shift.

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  • Received 10 December 2021
  • Revised 19 April 2022
  • Accepted 8 June 2022

DOI:https://doi.org/10.1103/PRXQuantum.3.030301

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Quantum Information, Science & Technology

Authors & Affiliations

Marina Kudra1,*, Mikael Kervinen1, Ingrid Strandberg1, Shahnawaz Ahmed1, Marco Scigliuzzo1, Amr Osman1, Daniel Pérez Lozano1, Mats O. Tholén2, Riccardo Borgani2, David B. Haviland2, Giulia Ferrini1, Jonas Bylander1, Anton Frisk Kockum1, Fernando Quijandría1,§, Per Delsing1,†, and Simone Gasparinetti1,‡

  • 1Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg 412 96, Sweden
  • 2Nanostructure Physics, KTH Royal Institute of Technology, Stockholm 114 19, Sweden

  • *kudra@chalmers.se
  • per.delsing@chalmers.se
  • simoneg@chalmers.se
  • §Present address: Quantum Machines Unit, Okinawa Institute of Science and Technology Graduate University, Onna-son, Okinawa 904-0495, Japan.

Popular Summary

The ability to store and manipulate quantum states is one of the milestones on the road to building a quantum computer. However, the "quantumness" of quantum states, which is measured by a property called coherence, can be easily destroyed by interactions with the environment. A solution to this problem is to encode the quantum states redundantly and perform error correction. Generally, quantum error correction requires some hardware overhead, for example, many physical quantum bits are used to encode a logical bit of information. An alternative, promising way to implement error correction is to encode the quantum information in a superposition of the many states that a single resonator inherently offers. In this way we get a compact logical qubit that has only one dominant source of decoherence to correct for, namely, photon loss in the resonator.

In our work, we show a technique to create any non-trivial quantum state of microwave photons in a 3D-cavity by coupling it to a superconducting qubit. The states are created by applying a sequence of a few displacement pulses, sent to the cavity, and qubit pulses. The latter exploit the dispersive qubit-cavity interaction to realize arbitrary phase rotations of the cavity field, conditioned on the photon number in the cavity, which are known as "SNAP" gates. We optimize the parameters of the SNAP and displacement pulses, in a two-step optimization sequence. We leverage this approach to demonstrate fast and robust generation of GKP, cat, and binomial states that were previously used for quantum error correction. We also generate the cubic phase state, which has not previously been generated and is a valuable resource in continuous variable quantum computing.

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Vol. 3, Iss. 3 — July - September 2022

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It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

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