Protected phase gate for the $0$-$π$ qubit using its internal modes

• URL: http://arxiv.org/abs/2503.14634v1
• Date: Tue, 18 Mar 2025 18:35:38 GMT
• Title: Protected phase gate for the $0$-$π$ qubit using its internal modes
• Authors: Xanda C Kolesnikow, Thomas B Smith, Felix Thomsen, Abhijeet A Alase, Andrew C Doherty,
• Abstract summary: We propose a protected phase gate for the $0$-$pi$ qubit.<n>The gate is achieved by varying the qubit-ancilla coupling via a tunable Josephson element.<n>We find that our scheme is compatible with the protected regime of the $0$-$pi$ qubit.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Protected superconducting qubits such as the $0$-$\pi$ qubit promise to substantially reduce physical error rates through a multi-mode encoding. This protection comes at the cost of controllability, as standard techniques for quantum gates are ineffective. We propose a protected phase gate for the $0$-$\pi$ qubit that utilises an internal mode of the circuit as an ancilla. The gate is achieved by varying the qubit-ancilla coupling via a tunable Josephson element. Our scheme is a modified version of a protected gate proposed by Brooks, Kitaev and Preskill that uses an external oscillator as an ancilla. We find that our scheme is compatible with the protected regime of the $0$-$\pi$ qubit, and does not suffer from spurious coupling to additional modes of the $0$-$\pi$ circuit. Through numerical simulations, we study how the gate error scales with the circuit parameters of the $0$-$\pi$ qubit and the tunable Josephson element that enacts the gate.

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