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Andrew C Doherty

Publications and source records attributed to Andrew C Doherty.

2 recordsLinked to original sources
arXiv2026

Protected measurements for protected superconducting qubits

Protected superconducting qubits such as the $0$-$\pi$ qubit promise to substantially suppress error rates, facilitating fault-tolerant quantum computing with fewer qubits. Measuring these qubits is challenging due to their protected nature, and thus far no concrete proposal exists for how to measure them without breaking their protection. Here we show how to perform protected measurements of the $0$-$\pi$ qubit in two orthogonal bases. The protection of these measurements is facilitated by their quantum non-demolition nature, allowing faults on ancillary measurement qubits to be tolerated. As experimental progress pushes protected qubits further into the low error-rate regime, our techniques will be crucial for fault-tolerant universal control.

quant-ph↗
arXiv2025

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

Protected superconducting qubits such as the $0$-$\pi$ qubit promise to substantially reduce physical error rates. However, a key challenge in the field is designing gates for these qubits that do not compromise their protection, or become infeasibly slow as the protection of the qubit is improved. In this work we propose a protected phase gate that is compatible with the protected regime of the $0$-$\pi$ qubit, and does not suffer from spurious coupling to additional circuit modes. Our gate utilises an internal mode of the circuit as an ancilla, and is achieved by varying the qubit-ancilla coupling via a tunable Josephson element. 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. Ultimately, we find that a protected gate with the $0$-$\pi$ qubit is possible with near-term circuit parameters. Our work opens up the possibility of performing protected gates on protected superconducting qubits, which may significantly reduce hardware overheads for quantum computation.

quant-ph↗